Page | i MORPHOMETRIC AND PHYSICO-CHEMICAL CHARACTERIZATION OF THE WEIJA RESERVOIR: IMPLICATIONS FOR WATER RESOURCE MANAGEMENT AT THE CATCHMENT SCALE BY ACQUAH-HARRISON CALEB ELI (10469522) THIS THESIS IS SUBMITTED TO THE UNIVERSITY OF GHANA, LEGON IN PARTIAL FULFILMENT OF THE REQUIREMENT FOR THE AWARD OF MPHIL IN ENVIRONMENTAL SCIENCE DEGREE INSTITUTE FOR ENVIRONMENT AND SANITATION STUDIES UNIVERSITY OF GHANA, LEGON FEBRUARY 2023 University of Ghana http://ugspace.ug.edu.gh Page | ii DECLARATION I hereby declare that; this thesis is a result of an original research work done under the supervision of Dr. Daniel Nukpezah and Dr. Philip-Neri Jayson-Quashigah with the exception of references to the work of other people which have been duly cited and that this work has neither in whole nor in part been presented for the award of another degree in this University or elsewhere. 23/10/2023 …………………………… ………………………... Acquah-Harrison Caleb Eli Date (Student) …………………………… ………………………….. Dr. Daniel Nukpezah Dr. Philip-Neri Jayson-Quashigah (Supervisor) (Supervisor) University of Ghana http://ugspace.ug.edu.gh Page | iii DEDICATION Firstly, I dedicate this thesis to the Lord God Almighty for His abundant love and mercies and to my mother, Madam Mabel Kpanga for her immense support throughout my education. University of Ghana http://ugspace.ug.edu.gh Page | iv ACKNOWLEDGEMENT My sincerest gratitude goes to the Almighty God for His unchanging and unending Grace and guidance throughout the course of my post-graduate education and also in my research work. I also appreciate my parents and the rest of my family for their continuous support towards my education. I am greatly indebted to my supervisors, Dr. Daniel Nukpezah and Dr. Philip-Neri Jayson- Quashigah who in spite of their busy schedule spent a lot of time instructing and guiding me to make this thesis possible. Thank you so much for your continuous support, advice and tolerance throughout this difficult and demanding period. I owe you much gratitude. My deepest gratitude to Dr. S. S. Koranteng and Dr. Opoku Pabi for their financial support towards this research work. Special thanks to Mr. Joseph Ansah and Mr. Nii Amartei Amartefio for their advice and contribution towards this research work. My heartfelt appreciation goes to all the lecturers, laboratory technicians, workers and colleagues who made my stay at the Institute for Environment and Sanitation Studies a fruitful and peaceful one. University of Ghana http://ugspace.ug.edu.gh Page | v TABLE OF CONTENTS 1.0 INTRODUCTION................................................................................................................... 1 1.1 Background ........................................................................................................................... 1 1.2 Problem Statement ................................................................................................................ 4 1.3 Significance of Study ............................................................................................................ 6 1.4 Research Questions ............................................................................................................... 7 1.5 Objectives .............................................................................................................................. 7 2.0 LITERATURE REVIEW ...................................................................................................... 9 2.1 Status of Fresh Water in Ghana............................................................................................. 9 2.2 Fresh Water Pollution of Lakes and Reservoirs in Ghana .................................................. 12 2.2.1 Point and Non-Point Sources of Fresh Water Pollution in Ghana ............................... 13 2.2.2 Major Sources of Fresh Water Pollution in the Regions of Ghana .............................. 13 2.2.3 Effects of Fresh Water Pollution in Ghana ................................................................... 15 2.3 Limnology of Reservoirs ..................................................................................................... 19 2.3.1 Some Factors Affecting the Limnology of Reservoirs ................................................. 19 2.4 Eutrophication ..................................................................................................................... 32 2.4.1 Eutrophication Process and its Causes ......................................................................... 33 2.4.2 Conceptual Model of Eutrophication ........................................................................... 34 2.4.3 External Nutrient Loading ............................................................................................ 36 2.4.4 Internal Nutrient Loading ............................................................................................. 36 University of Ghana http://ugspace.ug.edu.gh Page | vi 2.4.5 Models for Assessing Nutrient Enrichment in Waterbodies ........................................ 37 2.4.6 Effects of Eutrophication .............................................................................................. 40 2.4.7 Eutrophication Management......................................................................................... 41 2.5 Stratification and Stratification Effects ............................................................................... 45 3.0 METHODOLOGY ............................................................................................................... 51 3.1 Study Area ........................................................................................................................... 51 3.2 Reconnaissance Visit and Selection of sampling sites ........................................................ 51 3.3 Determination of Morphometric Parameters....................................................................... 52 3.4 Determination of Physico-Chemical Parameters ................................................................ 54 3.4.1 Water Samples .............................................................................................................. 55 3.4.2 Sediment Samples......................................................................................................... 57 3.5 Measurement of Trophic State Indices (TSI) ...................................................................... 60 3.6 Estimation of Nutrient Level during the sample period (Av. Nutrient over sampling period per Reservoir volume) ............................................................................................................... 62 3.7 Algal Species Composition ................................................................................................. 63 3.8 Data Analysis ...................................................................................................................... 64 4.0 RESULTS .............................................................................................................................. 66 4.1 Morphometric Characterization .......................................................................................... 66 4.1.1 Digital Elevation Model (DEM) ................................................................................... 66 4.1.2 Depth, Volume and Other Morphometric Parameters .................................................. 67 University of Ghana http://ugspace.ug.edu.gh Page | vii 4.2 Physico-Chemical Characterization .................................................................................... 68 4.2.1 Water Samples (Mixed Layer) ..................................................................................... 68 4.2.2 Water Samples (Depth Profile) ..................................................................................... 74 4.2.3 Distribution and variation of Key Physico-Chemical Parameters along a depth profile ............................................................................................................................................... 95 4.2.4 Sediment Characterization .......................................................................................... 102 4.3 Trophic State Indices (TSI) of Weija Reservoir ................................................................ 111 4.4 Estimated Nutrient Levels in the Weija Reservoir ............................................................ 117 4.5 Algae Species Composition .............................................................................................. 118 4.6.1 Class Bacillariophyceae .............................................................................................. 123 4.6.2 Class Chlorophyceae .................................................................................................. 123 4.6.3 Class Cyanophyceae ................................................................................................... 123 4.6.4 Class Dinophyceae ..................................................................................................... 123 4.6.5 Class Euglenophyceae ................................................................................................ 123 5.0 DISCUSSION ...................................................................................................................... 124 5.1 Morphometry ..................................................................................................................... 124 5.2 Physico-Chemical Characterization .................................................................................. 126 5.3 Sediment Characterization ................................................................................................ 130 5.4 Trophic State Index of Weija Reservoir ............................................................................ 131 5.5 Algae Species Composition .............................................................................................. 133 University of Ghana http://ugspace.ug.edu.gh Page | viii CONCLUSION AND RECOMMENDATIONS .................................................................... 135 6.1 Conclusion ......................................................................................................................... 135 6.2 Summary of Key Findings Relative to the Study Objectives............................................ 136 6.3 Recommendations ............................................................................................................. 137 REFERENCES .......................................................................................................................... 139 APPENDICES ........................................................................................................................... 156 University of Ghana http://ugspace.ug.edu.gh Page | ix LIST OF FIGURES Figure 2.1 Conceptual Model of Eutrophication .......................................................................... 35 Figure 2.2 Temperature profile in Reservoirs showing epilimnion, metalimnion, hypolimnion and the thermocline ....................................................................................................................... 48 Figure 3.1 Map of Sample Sites in Study Area ............................................................................ 52 Figure 4.1 Digital Elevation Model of Weija Reservoir ............................................................... 66 Figure 4.2 Temperature Variation in the Mixed Layer over the 6-Month Study Period .............. 68 Figure 4.3 DO Variation in the Mixed Layer over the 6-Month Study Period ............................. 69 Figure 4.4 E.C Variation in the Mixed Layer over the 6-Month Study Period ............................ 70 Figure 4.5 Salinity Variation in the Mixed Layer over the 6-Month Study Period ...................... 70 Figure 4.6 pH Variation in the Mixed Layer over the 6-Month Study Period.............................. 71 Figure 4.7 Total Dissolved Solids (TDS) Variation in the Mixed Layer over the 6-Month Study Period ............................................................................................................................................ 72 Figure 4.8 Turbidity Variation in the Mixed Layer over the 6-Month Study Period ................... 72 Figure 4.9 Orthophosphate Variation in the Mixed Layer over the 6-Month Study Period ......... 73 Figure 4.10 Nitrate Variation in the Mixed Layer over the 6-Month Study Period ..................... 73 Figure 4.11 Temperature Variation in Upper Weija Point A (UWa) ........................................... 74 Figure 4.12 Temperature Variation in Upper Weija Point B (UWb) ........................................... 75 Figure 4.13 Temperature Variation in Machigani Point A (Ma) .................................................. 76 Figure 4.14 Temperature Variation in Machigani Point B (Mb) .................................................. 77 University of Ghana http://ugspace.ug.edu.gh Page | x Figure 4.15 Temperature Variation in Kalabule Dam Point A (Ka) ............................................. 78 Figure 4.16 Temperature Variation in Kalabule Dam Point B (Kb)............................................. 79 Figure 4.17 DO Variation in Upper Weija Point A (UWa) .......................................................... 80 Figure 4.18 DO Variation in Upper Weija Point B (UWb) .......................................................... 81 Figure 4.19 DO Variation in Machigani Point A (Ma) ................................................................. 82 Figure 4.20 DO Variation in Machigani Point B (Mb) ................................................................. 83 Figure 4.21 DO Variation in Kalabule Dam Point A (Ka) ........................................................... 84 Figure 4.22 DO Variation in Kalabule Dam Point B (Kb) ........................................................... 85 Figure 4.23 Comparison of Average Temperature and Average DO over the 6-Month Period ... 86 Figure 4.24 Average Temperature Variation over the 6-month Study Period .............................. 95 Figure 4.25 Average DO Variation over the 6-month Study Period ............................................ 96 Figure 4.26 Average Orthophosphate Distribution over the 6-month Study Period .................... 97 Figure 4.27 Average Nitrate Distribution over the 6-month Study Period ................................... 98 Figure 4.28 Comparison of Average Orthophosphate and Average Nitrate Distribution over the 6-Month Period ........................................................................................................................... 100 Figure 4.29 Organic matter content in Sediment ........................................................................ 103 Figure 4.30 Total Nitrogen content in Sediment ........................................................................ 104 Figure 4.31 Total Phosphorus Content in Sediment ................................................................... 105 Figure 4.32 pH Variation in Sediment ........................................................................................ 106 Figure 4.33 E.C Variation in Sediment ....................................................................................... 107 University of Ghana http://ugspace.ug.edu.gh Page | xi Figure 4.34 Trophic State Index of Weija Reservoir from June to October ............................... 117 Figure 4.35 Percentage Contribution of the Various Algae Classes to the Reservoir ................ 119 University of Ghana http://ugspace.ug.edu.gh Page | xii LIST OF TABLES Table 2.1 The Trophic State Indices And Their Corresponding Attributes. ................................. 40 Table 3.1 Coordinates (C) of the Sampling Sites ......................................................................... 52 Table 4.1 pH Variations along the Depth Profile of Sample Points A & B of Upper Weija over the 6-month Study Period ............................................................................................................. 91 Table 4.2 pH Variations along the Depth Profile of Sample Points A & B of Machigani over the 6-month Study Period ................................................................................................................... 92 Table 4.3 pH Variations along the Depth Profile of Sample Points A & B of Kalabule Dam over the 6-month Study Period ............................................................................................................. 94 Table 4.4 Statistical ANOVA Table for Organic Matter ............................................................ 108 Table 4.5 Statistical ANOVA Table for Total Nitrogen ............................................................. 109 Table 4.6 Statistical ANOVA Table for Total Phosphorus ........................................................ 110 Table 4.7 Secchi Depth in Meters (m) from June to November ................................................. 112 Table 4.8 Trophic State Index (Secchi Depth) from June to November .................................... 112 Table 4.9 Chlorophyll a in microgram per liter (µg/L) from June to November ....................... 113 Table 4.10 Trophic State Index (Chlorophyll a) from June to November .................................. 114 Table 4.11 Total Phosphorus in microgram per liter (µg/L) from June to November ............... 115 Table 4.12 Trophic State Index (Total Phosphorus) from June to November ............................ 115 Table 4.13 Trophic State Index of the Weija Reservoir from June to November ...................... 116 Table 4.14 Composition of Various Algal Classes within the Weija Reservoir. ........................ 118 University of Ghana http://ugspace.ug.edu.gh Page | xiii Table 4.15 List of Algae in the Weija Reservoir in June and October, 2022 ............................. 120 Table 6.1 Summary of Key Findings Relative to the Study Objectives ..................................... 136 University of Ghana http://ugspace.ug.edu.gh Page | xiv ABSTRACT The Weija Reservoir, one of Ghana's water resources has been increasingly threatened by pollution in recent years as a result of fast population changes that have coincided with the formation of human settlements. In recent years, activities like as irrigation, nutrient pollution, sand mining, and encroachment on the Reservoir and along its boundary have had major impacts on the Reservoir, causing shortage in water supply. The aim of the study was to combine GIS and measurements of physico-chemical variables along a depth profile to map out the bathymetry and to model nutrient level in the Reservoir. Per that, a 3D (DEM) model of the Reservoir was constructed. Measurements were taken at a total of twenty-five thousand, two hundred and eleven data points with their corresponding coordinates and depths were recorded and processed using ArcGIS to obtain the current surface area and water holding capacity of the Reservoir of 19,330,988.38m2 (19.33km2) and 96,900,899.14m3 respectively. In order to assess the temperature variation and dissolved oxygen (DO) distribution along a depth profile, water and sediment samples for physicochemical analysis were obtained from the six sampling points. An echo sounder was then used to determine the depths at which the samples were taken and with a water depth sampler, the samples were taken along the depth profile at 1m intervals till the bottom of the Reservoir was reached. Measurements were taken along the depth profile in order to have a proper representation of the Reservoir. The physico-chemical parameters and nutrient in the samples were determined. A steady decrease in temperature was observed with increasing depth but analysis of variance (ANOVA) indicated that there was no significance in temperature with respect to depth. There was decrease in DO level along the depth profile and ANOVA showed that there was significant difference in DO distribution along the depth profile. University of Ghana http://ugspace.ug.edu.gh Page | xv This indicated that, the least change in temperature along the depth profile can cause a drastic change in DO which will lead to the thermocline effect. Total phosphorus, chlorophyll a content and Secchi depth were measured from the Reservoir and with the use of Carlson’s Trophic State Index, the TSI for total phosphorus, chlorophyll a and Secchi depth was calculated. Average TSI (TP) was 79.33 making the Reservoir eutrophic. It was also observed that TSI (TP) = TSI (SD) > TSI (CHL) with TSI (SD) having an average value of 68.61 over the study period and TSI (CHL) having an average value of 38.29. This relationship indicates that, the Reservoir is eutrophic as result of heavy siltation rather than phytoplankton abundance. The Utermöhl method for analysis was adopted in this study for analyzing the phytoplankton samples collected. Five (5) Classes were identified and the order of dominance was; Chlorophyceae (green algae) > Bacillariophyceae (diatoms) > Cyanophyceae (blue-green algae) > Euglenophyceae (euglenoids) > Dinophyceae (dinoflagellates). The Chlorophyceae were the most prevalent class (40.38%). Bacillariophyceae (30.77%), Cyanophyceae (23.08%), Euglenophyceae (3.85%), and Dinophyceae (1.92%) followed in declining order of abundance. These findings provide insight on the extent of anthropogenic contamination in the Reservoir and how it affects the distribution and treatment of water as the Reservoir provides water to the populace. Keywords: Digital Elevation Model, Thermocline Effect, Trophic State Index, Phytoplankton, Eutrophication, Depth Profile, Pollution University of Ghana http://ugspace.ug.edu.gh Page | 1 1.0 INTRODUCTION 1.1 Background Reservoirs, or man-made lakes, are crucial aquatic ecosystems that offer critical environmental and economic functions (Asante, Quarcoopome & Amevenku, 2008). They store water for use in power generation, agriculture, industry, and residential use. Most Reservoirs contribute considerably to national food and nutritional security levels, as well as the lives of populations along their coasts, in the tropics (Karikari, Akpabey & Abban, 2013). Many Reservoirs, including Volta, Vea, Barekese, Kpong, and Weija, have been built in Ghana during the previous four to five decades by damming rivers (Asante et. al., 2008). In Ghana, the requirement for comprehensive and integrated water resource management is much greater, necessitating immediate attention to the condition of our water bodies. This dilemma has emerged as a result of Ghana's growing population and the upstream nations that share the Volta River with Ghana. As a result, several sectors of the economy are now experiencing severe water shortages. Pollution and land degradation are also putting a strain on an already stressed resource base. According to reports, 44 percent of the country's water requirements are for residential consumption, 54 percent for agriculture, and 3 percent for industry (Nee-Whang, 1999). The Weija Reservoir, one of Ghana's water resources has been increasingly threatened by pollution in recent years as a result of fast population changes that have coincided with the formation of human settlements lacking adequate sanitary facilities (Anim, Odame, Duodu, Ahialey, & Serfor- Armah, 2011). The Weija Reservoir was built in 1977 by an Italian firm, Messrs Tahi to replace an older Reservoir that had been swept out by Ghana Water Company Limited (GWCL) damming River Densu in 1968, primarily to meet the need for potable water supply. It is the country's second largest water Reservoir after the Volta Reservoir. The Weija Reservoir covers an area of about University of Ghana http://ugspace.ug.edu.gh Page | 2 9,000 square hectares and serves over 2.5 million people in Accra East and West. The effective storage capacity the Weija Reservoir is around 133 million m3, computed as Reservoir volume at the maximum design level of 143 million m3 and therefore serves as a main source of water supply for millions of inhabitants in Accra East and West (Anonymous, 2007; Anonymous, 2015). Over the years, human activities along the banks and within the Reservoir have had an impact on the quality of water. In recent years, activities like as irrigation, nutrient pollution, sand mining, and encroachment on the Reservoir and along its boundary have had major impacts on the Reservoir, causing shortage in water supply. A number of environmental issues have been highlighted as a result of this (Tagoe & Mantey, 2017). Nutrient enrichment is one of such issues and can come from both point and non-point sources. Water treatment plants are examples of point sources; non- point sources include diffuse inputs from the atmosphere and agriculture, such as land runoff and animal waste. Excess phosphate and nitrate accelerate algal and plant development in natural environments, contributing to eutrophication and lowering oxygen levels. Algal blooms resulting from eutrophication reduce light penetration, affecting plant growth and die-offs in littoral zones, as well as diminishing the success of predators that require light to pursue and trap food. Furthermore, during the day, high rates of photosynthesis associated with eutrophication can deplete dissolved inorganic carbon and elevate pH to severe levels. Elevated pH can thus 'blind' organisms that rely on dissolved chemical signals for life by compromising their chemosensory capacities. When these dense algal blooms die, microbial breakdown substantially depletes dissolved oxygen, resulting in a hypoxic or anoxic 'dead zone' devoid of enough oxygen to support most life (Lehtiniemi, 2005). Warmer temperatures as a result of climate change have also led to the occurrence harmful algal blooms (HABs) in tropical waters. Generally, toxigenic cyanobacteria such as Anabaena, University of Ghana http://ugspace.ug.edu.gh Page | 3 Cylindrospermopsis, Microcystis, and Oscillatoria (Planktothrix) tend to dominate nutrient-rich freshwater systems due to their superior competitive abilities in conditions of high nutrient concentrations, low nitrogen-to-phosphorus ratios, low light levels, reduced mixing, and high temperatures (Downing et al., 2001; Paerl & Huisman, 2009; Paerl & Paul, 2012). Cylindrospermopsis raciborskii is particularly known for its invasiveness and ability to endure a wide range of temperature and light regimes and to employ a variety of feeding methods. It has been said to have benefited massively from the climate change phenomenon with regards to its ability to invade temperate areas (Antunes, Leão, & Vasconcelos, 2015). The Reservoir is typically susceptible to different types of deterioration as a result of pollution caused by anthropogenic activities such as, dumping of residential waste, industrial effluents, and agricultural runoffs which cause the nutrient enrichment and heavy metal pollution (Ansah, Nukpezah, & Hogarh, 2018; Asante et. al., 2008). The presence of these pollutants poses serious health risks to the citizenry and therefore affected water needs to be treated before use which in turn leads to an increase in the cost of treatment of water. Water consumption is limited by the quantity and quality of accessible water, both of which are impacted by many types of pollution, whether chemical, biological, or physical (Ayisi, Quarshie & Cobbina, 2013). Good quality water, available in sufficient amounts, supports cleanliness and public health, and hence social development. This necessitates the treatment of water from natural sources to fulfill the needed quality requirements prior to consumption in order to avoid any potential health and environmental hazards. Based on that the government spends thousands of Ghana cedis to treat polluted sources of water and make them accessible for household, industrial, and agricultural use (Ayisi, Quarshie & Cobbina, 2013). University of Ghana http://ugspace.ug.edu.gh Page | 4 1.2 Problem Statement Water supply Reservoirs such as the Weija Reservoir in numerous locations of Ghana guarantee an adequate and sustainable source of raw water throughout the year for treatment to deliver potable water to major cities and towns. The fresh water collected straight from these Reservoirs to meet the requirements of rapidly increasing metropolitan populations, however, varies in quality due to pollution (DFID, 1999). As a result of population growth and urbanization, portions of the Reservoir have been encroached upon, reclaimed, and used for residential and agricultural purposes, influencing the Reservoir with various activities such as the release of waste effluent from homes, farms and industries, which releases nutrients and other pollutants into the Reservoir. These human activities in the catchment of the Reservoir have a high potential to have a major influence on its physicochemical properties (Ameko, Achio, Okai–Armah & Afful, 2012) The major causes of water pollution include indiscriminate dumping of domestic, industrial, and municipal solid and liquid wastes, inefficient land use, bad agricultural practices, and environmental deterioration which cause eutrophication of the Reservoir, leading to high algal content which has been a persistent water quality problem in the Reservoir for a long time (Darko & Ansa-Asare, 2009). According to research by Bosque-Hamilton et al. (2004), the Reservoir contained a lot of aquatic weeds as demonstrated by nutrient dominance. These situations drastically increase the cost of water treatment. In a study conducted by Boah, Twum & Pelig-Ba (2016), they indicated that, in 2014, the total cost of water treatment from the Reservoir was GHC 29,240,832.52. Over the years, the water quality of the Reservoir has worsened, and 80% of the phytoplankton detected in the Weija Reservoir are bloom-forming blue-green algae. Algal blooms, low clarity, and fast volume loss in the Reservoir have all been recorded as symptoms of water quality issues. University of Ghana http://ugspace.ug.edu.gh Page | 5 The eutrophication of the Weija Reservoir has ramifications for the cost of potable water treatment (Oduro-Koranteng, 2003; Akuffo, 1989). Research indicates that eutrophication caused by excessive amounts of nutrient input into the Weija Reservoir has resulted in high water treatment costs as well as a drop in daily production capacity from 70 to 42 million gallons. Aside from the usual expense of water treatment, an additional $200,000 is paid each month to guarantee that the water being provided meets water quality requirements (Nukpezah, 2012). The assessment of water quality in the Weija Reservoir is critical since it is one of the primary sources of water for consumption and agriculture in Ghana. A lot of research has been conducted in order to enhance the quality of water in the Weija Reservoir (Ansa-Asare, 2001; Ameka et al., 2000; Ansa-Asare & Asante, 1998; Biney, 1987, 1982; Amuzu, 1975; Ansah, Nukpezah, & Hogarh, 2018) which involved the use of conventional approaches in the estimation of the per capita nutrient input of the Reservoir such as taking samples mainly from the mixed layer and using the results obtained to estimate the entire per capita nutrient input of the Reservoir. The issue with these approaches is that they not based on studies in Ghana and therefore do not accurately represent the actual situation on the ground. Based on this, a new methodological approach for assessing Reservoir volume and depths, as well as estimating nutrient input into the Reservoir at different depths of the Reservoir, is provided. This would offer the evidentiary foundation for targeted intervention to address the problem of pollution and nutrient input in the Reservoir by utilizing an ad hoc approach in problem identification. Earlier studies during the creation of the Reservoir in 1977 have established some of the morphometric parameters. However, in the face of climate change, land use change, encroachment of the Reservoir leading to heavy siltation, etc. some of these parameters such as surface area and volume might have changed. It is important to establish the key current morphometric parameters University of Ghana http://ugspace.ug.edu.gh Page | 6 as this influence water quality. Also, although past studies have suggested the Reservoir to be eutrophic, a quantitative measure of Trophic State Index (TSI) such as Carlson’s TSI would provide a baseline that enables comparison with future state of the Reservoir and help track changes in water quality and make appropriate policy interventions for improvement This study will help in developing a contextual understanding of cause-and-effect relationships, identifying key gaps in understanding in order to prioritize research and monitoring, identifying key pressures and drivers that if addressed would provide the greatest conservation benefit and aid the government of Ghana in attaining its national vision for the water and sanitation sector which is ‘sustainable basic water and sanitation service for all by 2025’ which ties into the United Nations broader vision of ‘ensuring availability and Sustainable Management of Water and Sanitation for all by 2030’, the sixth sustainable development goal of the organization. 1.3 Significance of Study The issue of water quality and sustainable development in Ghana cannot be fully addressed unless the problem of pollution and water quality of one of its major sources of potable drinking water, the Weija Reservoir is addressed. This is due to the fact that the development of a country is dependent on the health of its people, which is in turn dependent on the quality of water available. An understanding of the water quality state of the Reservoir will aid in the improvement of its quality management techniques. This study will help critically assess the current state of water quality in the Reservoir and its implications on cost of treatment and water supply. It will also help ascertain the pollution problems that may confront the Reservoir and provide a scientific basis for findings which will aid authorities in determining the most appropriate responses and remedies to the situation and mitigate its inherent impacts on the populations that rely on the Reservoir as well University of Ghana http://ugspace.ug.edu.gh Page | 7 reduce the cost of treatment of the water. The results and recommendations are also expected to enhance the sustainable management of natural resources in the Weija Reservoir. This approach to diagnostic study of our major Reservoirs will contribute to effective water resources management. 1.4 Research Questions 1. What is the contribution of internal loading to the state of the Weija Reservoir? 2. What is the relationship between temperature and DO along a depth profile? 3. What is the current nutrient status of the Reservoir? 4. What is the current water holding capacity of the Reservoir? 1.5 Objectives The overall objective of the study was to combine GIS and measurements of physico-chemical variables along a depth profile to map out the bathymetry and to model nutrient level in the Reservoir. The specific objectives will be to: 1. Construct a 3D (DEM) model of the Reservoir to determine the current water holding capacity. 2. Determine the temperature variation along a depth profile. 3. Determine the dissolved oxygen (DO) distribution in the Reservoir along a depth profile University of Ghana http://ugspace.ug.edu.gh Page | 8 4. Determine the nutrient distribution in the Reservoir along a depth profile 5. Determine the Trophic State Index (TSI) of the Reservoir 6. Identify algal species of the Reservoir. University of Ghana http://ugspace.ug.edu.gh Page | 9 2.0 LITERATURE REVIEW 2.1 Status of Fresh Water in Ghana Fresh surface water resources in Ghana include the Volta River System, the South-Western River System, and the Coastal River System (Ministry of Water Resources, Works and Housing, 2007). As stated by Ministry of Water Resources, Works and Housing (2007) in the Ghana National Water Policy (2007), surface water resources in Ghana are mostly derived from three river mainstem releases, including the Coastal River, the South-Western, and the Volta systems. The Volta River systems include the Red, Black, and White Volta rivers, as well as the Oti River. The South- Western River systems are made up of the Bia Tano, Ankobra, and Pra rivers. Coastal river systems include the Tordzie/Aka, Densu, Ayensu, Ochi-Nakwa, and Ochi-Amissah. These river systems account for 70%, 22%, and 8% respectively of the total land area of about 240,000 km2. Lake Bosumtwi is also Ghana's only natural freshwater lake. This is a forest-zone meteoritic Crater Lake with a surface size of 50 km2 and a maximum depth of 78 m (WRC, 2012). Groundwater resources on the other hand are composed of three geological formations, with the basement complex (metamorphic rocks and crystalline igneous), the consolidated sedimentary formations, and the Cenozoic and Mesozoic sedimentary rocks accounting for 54%, 45% and 1%, respectively (Ministry of Water Resources, Works and Housing, 2007). Aquifer depths typically varied from 10 to 60m, with yields seldom reaching 6m3 per hour. The Cenozoic and Mesozoic formations that are common in Ghana's extreme south eastern and western regions are also limestone aquifers with depths ranging from 120 to 300 meters. The limestone aquifers provide an output of roughly 184 cubic metres per hour on average (Ministry of Water Resources, Works and Housing, 2007; WRC Ghana 2007). University of Ghana http://ugspace.ug.edu.gh Page | 10 Reservoirs, dams, and impoundments were built for water supply, irrigation, hydroelectric power generation, and ecological support (Yeleliere, Cobbina & Duwiejuah, 2018). One of the world's largest man-made lakes is the Akosombo dam, which covers an area of around 8500 km2 and has a water volume capacity of 148 km3 (Mensah 2010; WRC Ghana 2015). Approximately 20 kilometres downstream of Akosombo, a comparably smaller impoundment with a covering area of roughly 40 km2 has been built at Kpong (WRC 2012; WRC Ghana 2015). Another impoundment developed for the sake of generating energy was the Bui hydroelectric project in the Black Volta, which has a capacity of 400 MW. Other large impoundments in Ghana are the Barekese and Owabi supplies (consumptive water for Kumasi Metropolis), the Weija (supply water for Accra), and the Nawuni (supply water in and out of Tamale Metropolis) on the rivers Densu, Volta, and Offin (WRC 2012; WRC Ghana 2015). Ex situ (withdrawal use) and in situ or in-stream use are the two primary kinds of freshwater resource consumption, which can also be referred to as consumptive and non-consumptive use, respectively as stated by Yeleliere et. al. (2018). In Ghana, municipal usage (water supply) accounts for 37% of total consumption, agricultural use (livestock watering and irrigation) accounts for 48%, and industrial use accounts for 15%. Consumptive water demand for surface water resources alone is expected to exceed 5 billion m3 by 2020, accounting for 12% of total surface water resources (WRC, 2005). The statement provides information on the water usage pattern in Ghana, indicating that there is a high demand for surface water in various sectors of the country. Per the consumptive water demand for surface water resources at the time, it was predicted the demand will exceed 5 billion cubic meters by 2020, which was estimated to account for 12% of total surface water resources. There is an increase in the population, year on year and as the population increases, the demand for water also increases so therefore it can be inferred that, University of Ghana http://ugspace.ug.edu.gh Page | 11 if the consumptive demand for water was pegged at over 5 billion cubic meters in 2020, then currently, in 2023, the demand will be higher and this will be a recurring pattern for years to come. This highlights the need for efficient water management and sustainable water resource usage practices in the country. Conversely, water transport, inland fisheries, hydropower generation, tourism, and ecosystem support services are among the principal non-consumptive uses of water. Growing populations and our persistent exploitation of this valuable resource to suit our basic requirements have jeopardized and corrupted the potential usage of freshwater resources (Yeleliere et. al., 2018). According to Nsubuga, Namutebi and Nsubuga-Ssenfuma (2014), climate change, as well as fiscal factors, combined with environmental pollution from waste (both municipal and industrial waste), leaching of toxic chemicals from fertilizers and pesticides used in agriculture, have exacerbated concerns about the potential use of this freshwater resource for our needs. A direct rise in pollution reduces the amount of operational water. Until the recent problem of localized pollution caused by the discharge of sewage into water bodies from industrial and domestic activities, leaching of fertilizers and pesticides used in agriculture, with the most recent and alarming canker being illegal artisanal mining denoted 'galamsey,' the quality of naturally occurring surface waters and groundwater was generally good (Yeleliere et. al., 2018). Furthermore, the use of chemicals in fishing, along with increasing population increase, has rendered our water supplies completely uncontrollable. Untreated sewage discharged from municipal garbage has resulted in major water contamination in most metropolitan areas. Lagoons and rivers near industrial regions are slowly dying as a result of the discharge of untreated municipal waste from household and industrial wastewater, which generates odor and nutrient enrichment, resulting in algal bloom (Nsubuga, Namutebi & Nsubuga-Ssenfuma, 2014) of which University of Ghana http://ugspace.ug.edu.gh Page | 12 the Korle Lagoon situated in Accra is a prime example of contaminated waterbodies in Ghana (WRC, 2015) 2.2 Fresh Water Pollution of Lakes and Reservoirs in Ghana Bawakyillenuo (2020) states that freshwater pollution in Ghana has an influence on livelihoods, health, transportation services, and drinkable water for home use. Population growth, urbanization, a negative attitude toward the environment, unsustainable traditional agricultural practices, and industrial activity are the main causes of freshwater contamination in Ghana (Ampomah, 2017; Bawakyillenuo, 2020). Despite the known benefits and uses of freshwater, these resources are becoming increasingly polluted at an alarming rate, for example, high nutrient levels, high faecal coliform numbers, low levels of dissolved oxygen, organic and inorganic waste elements in water resources, jeopardizing their life-supporting qualities (Bawakyillenuo, 2020). Approximately 60% of Ghana's water bodies are contaminated, with the majority of them in catastrophic condition (Ampomah, 2017). There are several issues regarding fresh water pollution of lakes and Reservoirs in Ghana, including: improper disposal of sewage and industrial waste is a major contributor to fresh water pollution, leading to the contamination of lakes and Reservoirs, excessive use of chemicals such as pesticides and fertilizers in agriculture contributes to fresh water pollution, as these chemicals run off into nearby water bodies during heavy rainfall, mining activities that have resulted in heavy metal contamination of fresh water sources, improper disposal of solid waste, including plastics and other non-biodegradable materials, which has become a common issue in Ghana that contributes to fresh water pollution and lastly, climate change and its resulting changes in precipitation patterns which have led to changes in the quality and quantity of fresh water University of Ghana http://ugspace.ug.edu.gh Page | 13 resources. These are issues need to be addressed and can be done through effective waste management practices, increased public awareness, and better regulation and enforcement of environmental protection laws in the country. 2.2.1 Point and Non-Point Sources of Fresh Water Pollution in Ghana There are two major methods for surface water to become polluted. Because surface water percolates through the soil and becomes groundwater, every pollutant in the surface water finds up in the groundwater and vice versa. There are two types of sources: point sources and non-point sources (Boateng, 2018). Pollutants that enter water bodies from a single recognized source are referred to as point sources because the source of pollution is easily known, the types of pollutants are easily determined, for example, mine tailings discharge or industry discharge while non-point source pollution refers to water contaminants that originate from several sources rather than a single discharge point (Boateng, 2018). These contaminants cannot be anticipated until experiments are carried out to determine their presence. For instance, urban runoff water or landfill leachate (Boateng, 2018). It is therefore an undeniable reality that Ghana's fresh water resources are under serious jeopardy, since water resources are running dry and becoming increasingly limited by the day. 2.2.2 Major Sources of Fresh Water Pollution in the Regions of Ghana According to Mantey (2017), illegal mining operations have contaminated fresh water sources in Ghana. The principal water bodies in the Western Region, the rivers Pra, Daboase, and Ankobra, have become contaminated. Birim, the principal water body in the Eastern Region, has been contaminated. As a result, water treatment plants in Kyebi were forced to close owing to river contamination that was beyond remediation. This difficulty has pushed the Ghana Water Company to build boreholes that would serve smaller populations (Mantey, 2017). Also, Fresh water bodies University of Ghana http://ugspace.ug.edu.gh Page | 14 around the settlements of New Juaben and Koforidua have become contaminated as a result of fishing activity. In addition to the above, the Densu River in the Greater Accra Region, which gets its water from Western Accra surrounding the Weija dam, has become contaminated as a result of industrial waste and farming activities. Some water bodies in the Central Region, notably around Cape Coast, have been contaminated as a result of galamsey activities. The situation is similar, if not worse, in Brong Ahafo, where citizens have been obstructing the path of the river at regular intervals, preventing water from flowing into some regions of the Region (Mantey, 2017). The scarcity of water in Sunyani, as at the time the study was done, was caused by farming operations, in which locals obstructed the river channel to irrigate farmland. The Ashanti Region is also plagued by pollution. According to Mantey (2017), illegal mining operations have contaminated the Enu River, which supplies Konogo inhabitants in the Ashanti Region. Sand winning is the most common activity that pollutes water bodies in the Northern Region, although galamsey activities pollute water bodies in some areas. The Nawuni River in Ghana's northern area has been subjected to significant sand winning activities, which have permanently changed the river's hue (Mantey, 2017). It is very disturbing to see that the pollution of our Reservoirs has reached epic levels such that treatment plants have been forced to close down because the water sources have been viewed as beyond remediation. As a nation we need to come to the realization that our mismanagement of our freshwater resources will have significant and long-lasting effects on the environment and the communities that depend on these water sources. Some of which include; loss of potable water, in the sense that when freshwater bodies become contaminated to the point of being beyond remediation, they may no longer be safe for human consumption or for other uses, such as agriculture and industry, there will be severe health impacts upon consumption, leading to increased rates of waterborne illnesses and diseases, death and displacement of organisms that are University of Ghana http://ugspace.ug.edu.gh Page | 15 adapted to specific water conditions, thereby altering the balance of the ecosystem and in the long run, ecosystem degradation. These impacts highlight the importance of preventing freshwater pollution and managing water resources in a sustainable manner. 2.2.3 Effects of Fresh Water Pollution in Ghana 2.2.3.1 Illegal Mining According to Ackah (2019), the practice of galamsey activities in the country, with their crude and inefficient techniques, poses one of the most serious threats to public health. It incorporates water usage methods and alluvial mining processes that pollute rivers, streams, and lakes. Toxic substances, such as mercury, are discharged into these bodies of water, with long-term health consequences for populations for centuries. The use of these heavy metals to contaminate surface and subsurface water has serious health consequences that will become apparent in the near future (Ackah, 2019). Galamsey practices expose Ghanaians to gaseous mercury, which is absorbed into the bloodstream by drinking and breathing. Once in the vascular system, it can cross the blood- brain barrier and build up in the brain, causing damage to the central nervous system. Millions of Ghanaians live along the banks of these rivers and collect raw water, which is extensively polluted with pollutants such as mercury and arsenic, for domestic use (Ackah, 2019). The use of mercury has increased dramatically as exploration has moved from alluvial to surface mining. Waste mercury is typically allowed to wash off into surrounding rivers or local soils, with a particularly negative impact on the ecosystem. An analysis of the health effects of mercury uses in a galamsey village discovered that 90% of villagers (galamsey and non-galamsey) registered a faint metallic taste and salivation issues. Twenty percent also have physical tremors, and 65 percent have trouble sleeping. Mercury levels in biological samples revealed that between 86 and 91 percent of the population had been exposed to mercury (Rambaud, Casellas, Sackey, Ankrah, University of Ghana http://ugspace.ug.edu.gh Page | 16 Potin-Gautier, Tellier, Bannerman & Babut, 1999). A second related analysis in a separate region of Ghana that looked at the impact of mercury usage on total river systems discovered that: river sediments were greatly polluted and were brought so far downstream that some coastal areas were almost as contaminated as inland areas; fish are also strongly impaired, so that in the specific area studied, ingestion of a mere 45g of fish per day was enough to surpass the World Health Organization's (WHO) weekly tolerance of 300 g and consumption of specific types of vegetables could exceed the weekly mercury intake set by the WHO/Food and Agriculture Organization's expert committee (Babut, Sekyi, Potin-Gautier, Tellier, Bannerman, Casellas, & Rambaud, 2001). The Tano River, which supplies water to more than 60% of the Brong Ahafo region's population, is being harmed by illegal miners. Communities such as Dormaa Akwamu, Kenyase, and Nkaseim face similar dangers. 2.2.3.2 Agricultural Activities Agricultural activities have an impact on water quality because they release nutrients (as a result of soil management and fertilizer application) and other chemicals (e.g., pesticides) into the water environment, cause biological contamination (e.g., from microbiological organisms in manure), and cause soil to erode and wash away from farmland. The major effect of agriculture on fresh water bodies will be the excessive use of agrochemicals such as fertilizers and pesticides. Pesticides such as 1,1,1-trichloro-2,2-bis (4-chlorophenyl) ethane (DDT) and 1,2,3,4,5,6- hexachlorocyclohexane (HCH), which are environmentally persistent and banned in developed countries (Fianko, Donkor, Lowor & Yeboah, 2011). Fianko et, al. (2011) state that since most farms have grown in size and are now commercialized, the difficulties of maintaining crops free of damage have grown. Hand-tilling weeds, for example, has been inefficient. As a result, the planet has seen a steady increase in the amount and quantity of agrochemicals used. The use of University of Ghana http://ugspace.ug.edu.gh Page | 17 agrochemicals has been crucial in the agricultural crop yield. Water samples from rivers in Ghana's Ashanti and Eastern Regions were found to contain the pesticides, lindane and endosulfan, similarly, mean pesticide concentrations in water samples for lindane and endosulfan in Ghana's Oda, Kowire, and Atwetwe rivers were 19.4 and 12.4 g/L (Oda), 16.4 and 17.9 g/L (Kowire), and 20.5 and 21.4 g/L (Atwetwe), respectively (Acquaah, 1997). Ntow, (2005) also observed the Volta Lake to be slightly polluted with lindane, DDT, DDE, and endosulfan. Pesticides can leach from the root zone or be washed off the land's surface by rain or irrigation water, ultimately ending up in nearby fresh waterbodioes as well as groundwater sources (Gooddy, Chilton & Harrison, 2002) 2.2.3.3 Domestic Waste It is a well-known truth that practically all water contaminants are harmful to humans as well as other creatures. For example, sodium is known to promote cardiovascular illness, but nitrates are linked to blood issues. Some pollutants are cancers, while others, such as DDT, are known to be hazardous to people and can potentially disrupt chromosomes. Others, such as PCBs, cause liver and nerve damage, skin eruptions, vomiting, fever, diarrhea, and prenatal anomalies. This is all as a result of improper disposal and treatment of domestic waste located at landfills and dumpsites as well open defecation and indiscriminate waste disposal by residents. A study conducted by Nartey, Hayford & Ametsi, (2012), on water samples that were collected from four water bodies, namely; Densu, Lafa, Bale Rivers and the Gbegbe lagoon (Glefe) that run through certain waste dump sites in Ghana's Accra metropolitan region indicated that Helminth egg counts, coliform and faecal coliforms were all high in water samples, indicating that the bodies of water were contaminated with bacteria and diseases. Organic waste, as well as coliform bacteria produced from these waste dumps, were found to be the predominant contributors of contaminants in the water bodies. Because of the high amounts of microbes, the water bodies are dangerous for both primary and University of Ghana http://ugspace.ug.edu.gh Page | 18 secondary interactions. The presence of these coliforms could be responsible for the transmission of infectious diseases which include typhoid fever, dysentery, salmonellosis, cholera and gastroenteritis (EPA, 2002). 2.2.3.4 Industrial Waste Waste discharges are a result of fast population increase, industrialization, and the associated technology, and the pace at which these pollutants are dumped into surface waterways is significantly larger than the carrying capabilities of the water bodies. Shivayogimath, Kalburgi, Deshannavar & Virupakshaiah, 2012). In Ghana, one of the primary sources of stream pollution is the discharge of industrial effluents, which causes water-borne illnesses such as cholera (Abdalla, Oppong-Kyekyeku, Donkor & Adiyiah, 2016). The tremendous rate at which industrial wastewaters are discharged into lakes and Reservoirs is such that the water bodies into which these wastewaters are discharged may no longer function as excellent quality water sources due to natural self-purification. High nutrient levels often cause dissolved oxygen depletion and the release of hazardous compounds such as heavy metals, which can bio-accumulate in microorganisms in the water are consequences (Morrison, Fatoki, Persson, & Ekberg, 2001). Microorganisms in fresh water bodies have the ability to collect persistent organic pollutants such as heavy metals, Polycyclic Aromatic Hydrocarbons (PAH), and Polychlorinated Biphenyl (PCB) in the environment (POPs) (Abdalla et, al., 2016). When these pollutants enter the body, they may not only affect the procreative capacity of these bacteria, but they may also have an influence on human health (Wagtech, 2015). University of Ghana http://ugspace.ug.edu.gh Page | 19 2.3 Limnology of Reservoirs Limnology is the study of inland water bodies, including their physical structure, water cycle, chemical structure, biological structure, nutrient cycling and material budget, pollution, and deterioration. The physical structure of a lake is concerned with basin morphometry, water cycle and hydrodynamics, turbidity and light penetration, thermal stratification, and sediment deposition (Balasubramanian, 2015). 2.3.1 Some Factors Affecting the Limnology of Reservoirs 2.3.1.1 Morphometry A lake's morphometry covers the basin's topography, bathymetry, area of water spread, and shoreline arrangement. The morphometric features of a lake influence sediment-water interactions (mixing, re-suspension, nutrient availability, littoral zone extent), productivity (amount of biomass created), and lake species. The following are the morphometric parameters: (1) Surface area (2) Mean depth (3) Volume (4) Maximum length (5) Mean width (6) Shoreline Length (7) Shoreline Development (8) Fetch (Balasubramanian, 2015). Lake morphometry can play a significant role in shaping the mixing patterns in a Reservoir, and can impact the physical, chemical, and biological characteristics of the Reservoir. Factors like mean and maximum depth affect mixing in terms of the amount of light penetration, water temperature, and water circulation. Deeper lakes tend to have less mixing and stratification compared to shallower lakes. The depth can also impact resuspension by affecting the water velocity and the amount of turbulence in the water column. Deeper lakes tend to have lower water velocities and less turbulence, which can reduce resuspension thus the deeper the lake, the lower the lower the rate of resuspension. The presence of developed shorelines thus shorelines with developments deviating from one and not having a circular shape can increase erosion and sedimentation in a lake, as well as alter water flow patterns University of Ghana http://ugspace.ug.edu.gh Page | 20 and water quality. The surface area of a lake can has a significant impact on the ecology, physical processes and water balance. A larger surface area can increase the amount of evaporation, which can affect the water balance and water temperature of the lake. Again, a larger surface area can increase the exposure of the lake to pollutants from the surrounding environment, such as fertilizers, sewage, and industrial waste. This can impact the water quality of the lake, including reducing its oxygen levels and increasing its nutrient levels, which can lead to the proliferation of harmful algae and bacteria. Fetch is the distance over which wind blows across a water body, and it can have a significant impact on a lake in several ways. The fetch of a lake determines the size of the waves that can be generated by the wind. Larger fetch can result in higher, more persistent waves, which can erode shorelines and impact water quality by mixing and resuspending bottom sediments. It can also affect water circulation patterns, including the distribution of temperature and dissolved substances thus longer fetch can result in more uniform water circulation and temperature, while shorter fetch can result in more localized circulation patterns. It can again influence the amount of light that penetrates into the water, which affects the growth and distribution of aquatic plants and animals. Longer fetch can result in lower light penetration, which can limit the growth of aquatic plants and reduce the productivity of the lake. Lastly, it can impact water quality by influencing the rate of water exchange with the surrounding environment, which can affect the balance of nutrients, pollutants, and dissolved oxygen in the water. The size of a lake is measured in surface area, which is usually represented in acres or squared meters. Lake surface area can be used to forecast the effects of wind on a lake. During windy circumstances, lakes with a larger surface area are vulnerable to bigger waves (UF/IFAS, 2001). This is crucial because stronger waves may mix water at higher depths, reaching all the way to the lake's bottom in some cases. The capacity to induce mixing at the lake's bottom is critical because University of Ghana http://ugspace.ug.edu.gh Page | 21 it can result in silt re-suspension and/or disturbance of submerged aquatic vegetation. As a result, other lake properties, such as water clarity and nutrient availability, may be impacted. The surface area of a lake also determines its diluting capacity (UF/IFAS, 2001). Dilution capacity refers to a lake's ability to dilute materials, whether they are naturally occurring from the watershed or caused by a human-caused spill. Lakes with a larger surface area have a better potential for dilution than lakes with a smaller surface area. A lake with a higher dilution capacity is less likely to be influenced by fertilizers or other elements introduced by human activities thus changes in Reservoir surface area may reflect changes in diluting capacity and hence water quality. A lake's mean depth is its average water depth. Due to early studies of algae, aquatic invertebrates, and fish populations revealed that shallow lakes are usually more productive than deep lakes, mean depth is crucial. This is because light can easily penetrate and reach the bottom for photosynthetic purposes. The ability for waves to alter bottom sediments is also heavily influenced by mean depth (Jeppesen, Søndergaard, Jensen, Havens, Anneville, Carvalho, Coveney, Deneke, Dokulil, Foy & Gerdeaux, 2005). This indicates that lakes with larger mean depths typically do not have as much bottom sediment mixing because wave action is less likely to reach the bottom. Maximum depth (Zmax) is the location where water is deepest and is measured in feet (ft) or meters (m). It influences stratification and the proportion of water in which algae can grow (Jeppesen et, al., 2005). Most water in shallow lakes may have enough light or algae to grow, but in deeper lakes, much of the deep water does not have enough light for algae. The deeper the lake the lower the rate of light penetration. The entire amount of water in a lake basin is known as volume, and it is commonly represented in acre-feet or cubic meters. Lake volume is an essential factor in lake management since it affects a lake's diluting capacity (UF/IFAS, 2001). Lakes with bigger water volumes have a better potential University of Ghana http://ugspace.ug.edu.gh Page | 22 to dilute items entering the lake basin. Lake volume is also important to consider when assessing nutrient loads since it might affect algal populations in a lake (Algesten, Sobek, Bergström, Ågren, Tranvik & Jansson, 2004). The loss of volume reduces the dilution capacity and increases the potential for eutrophication due to increased nutrient concentration. Fetch is the longest uninterrupted distance over which the wind blows across the lake. The fetch is significant because it influences the depth at which waves can mix water and/or bottom sediments in a lake (Von Einem & Grane´li, 2010). The longer the maximum length, the stronger the waves, and the greater the possibility of bottom sediment mixing or disturbance therefore, he longer the fetch and stronger the wind speed, the higher the rate of mixing. Hydraulic Residence Time (HRT), is the amount of time that water remains in a lake. Longer hydraulic residence periods result in greater carbon: phosphorus (C:P) ratios, which means that they are more nutrient-limited than shorter hydraulic residence times lakes. This is because less water from the watershed enters lakes with a high residence period, the phosphorus in the water is used up and not restored as rapidly (Dewey, 2018). Based on this, it can be deduced that Hydraulic Residence Time can therefore regulate primary production since it affects nutrient availability. Shoreline length is the linear measurement of a water body’s complete circumference. This distance denotes the whole area of lake front available for activities such as home construction and lake edge impacts. Shoreline length is significant because it quantifies the amount of interaction between a body of water and the surrounding land (UF/IFAS, 2001). Based on this, it can be inferred that the longer the shoreline length, the more the lake is exposed to shoreline erosion by virtue of the human activities occurring on the shore. Shoreline length can be determined by tracing around the water body on a map using a piece of string. The length of string will be compared with the map’s scale to convert the measurement to the actual shoreline length. University of Ghana http://ugspace.ug.edu.gh Page | 23 The length of a lake's shoreline in relation to a circle of the same area is referred to as shoreline development. In other words, lakes with longer, irregularly shaped shorelines have greater shoreline development, whereas circular lakes have less shoreline development (UF/IFAS, 2001). The shoreline development value of a complete circle is 1.0. The number rises as the morphology of the shoreline gets more uneven. Shoreline development values in irregularly shaped Reservoirs with several embayment (coves) can surpass 3. Lakes with very uneven shorelines contain more near shore shallows for rooted plant development, as well as more shoreline for buildings and shoreline erosion, both of which may boost lake productivity (Rosenberger, Hampton, Fradkin & Kennedy, 2008). This is to say, the more the shoreline development deviates from 1, the greater the exposure to erosion which will in tend lead to an increase in productivity in the lake. Again, increased shoreline development can lead to an increase in water temperature by means of a decrease in vegetation which can lead to a decrease in water quantity as a result of evaporation. The formula for calculating (LD) = L/2 √ π A0, where L = Shoreline length & A0 = surface area of the lake. 2.3.1.2 Physico-Chemical Parameters The temperature of lake water affects (a) biological activity and growth, (b) the types of organisms that may exist, (c) water chemistry, (d) chemical processes, and (e) water balance computations (Balasubramanian, 2015). Temperature changes in lake water are caused by seasonal and daily variations in air temperature, water intake and outflow from catchments, and artificially generated thermal pollution (Balasubramanian, 2015). In lakes, three types of strata are defined based on temperature distribution. Epilimnion refers to the upper layer of water in a lake that is consistently warm and well-mixed. The bottom layer of water in a lake that is consistently cold and mostly undisturbed is referred to as Hypolimnion. Metalimnion is the intermediate layer of water that University of Ghana http://ugspace.ug.edu.gh Page | 24 marks the transition between the top and bottom layers and where temperature fluctuates significantly with depth. The temperature of lake water determines the kind of organisms that may dwell in it. At increasing temperatures, the rate of chemical reactions normally rises, which has an effect on biological activity. (Balasubramanian, 2015). Lakes create strata called Thermoclines due to the odd relationship between water temperature and density. These are strata with radically different temperatures in relation to depth. Due to the fact that water has a very high specific heat capacity, a lake helps to regulate the temperature and climate of the surrounding region. During the day, a lake may cool the area next to it with local breezes, resulting in a cool breeze. Temperature-depth relationships in tropical and temperate water bodies vary based on several factors such as water column stability, mixing, solar radiation, and seasonality. In tropical water bodies, temperatures tend to be more stable and exhibit little vertical mixing, with a strong thermocline separating warm surface waters from colder deep waters. As a result, solar radiation warms the surface waters, creating a thermocline that stratifies the water column and limits the mixing of warm and cold waters (De Crop & Verschuren, 2019). This stability results in a relatively constant temperature with depth in the surface layer, with a more rapid drop in temperature in the thermocline. Temperate water bodies, on the other hand, exhibit more pronounced seasonal and vertical temperature variations. During the warmer months, the surface waters are heated, leading to vertical mixing that brings warmer surface waters into contact with colder deep waters. This mixing helps to distribute the heat throughout the water column and maintain a relatively homogeneous temperature profile with depth. During the colder months, the surface waters cool and the mixing decreases, leading to a more stratified water column (De Crop & Verschuren, 2019). University of Ghana http://ugspace.ug.edu.gh Page | 25 In general, the temperature-depth relationships in tropical and temperate water bodies are influenced by a complex interplay of physical, biological, and chemical factors, and are important for understanding the functioning and productivity of these water bodies. Dissolved oxygen refers to oxygen molecules that are dissolved in water and is an important indication of water quality. The existence of aquatic life is dependent on a suitable supply of oxygen dissolved in water. When it falls below the levels required to maintain aquatic life, it causes a major water quality degradation. DO concentrations in 100% saturated fresh water range from 7.56 mg/L (or 7.56 parts oxygen in 1,000,000 parts water) at 30°C to 14.62 mg/L at 0°C (MPCA, 2009). The primary reason of low dissolved oxygen (DO) is excessive algal growth driven by phosphorus. Another component that might aid in algal development is nitrogen. The process of algal death and decomposition uses dissolved oxygen. As a result, there may be inadequate dissolved oxygen available for fish and other aquatic organisms (MPCA, 2009). Higher water temperatures cause more molecular vibrations, which reduces the amount of space available between water molecules (Wilson, 2010). As salinity rises, so does the inability of water to contain DO (Wilson, 2010). Due to their ionic charges, the salts compete more effectively for intermolecular spaces. The quantity of DO in water is also affected by altitude owing to the different densities of O2 available for dissolution. DO concentrations will be lower at higher elevations because atmospheric O2 is less dense than at sea level because atmospheric O2 is denser (Wilson, 2010). In tropical water bodies, the strong thermocline that separates warm surface waters from colder deep waters creates a stable water column that limits vertical mixing. This stability leads to a well- defined oxygen-depletion layer, where the surface waters are rich in DO, while the deep waters are oxygen-deficient. The warmer surface waters and the lower solubility of oxygen at higher University of Ghana http://ugspace.ug.edu.gh Page | 26 temperatures also result in lower DO concentrations in the surface layer. One the other hand, in temperate water bodies, the more pronounced seasonal and vertical temperature variations result in more vigorous mixing and vertical exchange of water masses. This mixing helps to distribute DO throughout the water column, leading to relatively uniform DO concentrations with depth. During the warmer months, the increased respiration rates of aquatic organisms and decomposition of organic matter can lead to DO depletion in the surface waters, particularly in shallow and eutrophic (nutrient-rich) water bodies. Phosphorus (P) is a nutrient that is required by all living creatures. Phosphorus, for example, is contained in DNA (the genetic material of living things), is used to construct cell membranes, and is used to generate energy at the cell level (as ATP, adenosine triphosphate) (Walker, Younos & Zipper, 2007). Phosphorus enters lakes and Reservoirs through a variety of sources, including point-source discharges, terrestrial runoff, decomposing organisms, and phosphorus-containing rocks. Natural supplies of phosphorus to lakes and Reservoirs include waste products from aquatic creatures and wildlife, as well as decomposing plant and animal tissues (Wetzel 2001, Brönmark & Hansson 2005). Phosphorus can be found in the water column, within the bodies of aquatic species, or adhering to particles (such as silt) in the water. Organic phosphorus absorbed in plant and animal tissues can be converted into soluble inorganic phosphates by bacteria and used by primary producers. Similarly, particulate-bound phosphates (phosphates bound to particles) can be utilized by primary producers if the phosphorus dissociates from the particle and becomes soluble in the water column (Walker et, al, 2007). Phosphorus can sink to the bottom sediment as a component of fecal waste, a dead organism, or as a sinking particle connected to another sinking particle. Phosphorus may become buried and inaccessible to the system once it reaches the bottom of a lake or Reservoir. Rooted plants may transfer phosphorus from the sediment into their tissues, University of Ghana http://ugspace.ug.edu.gh Page | 27 where it can be released back into the water after death (Horne & Goldman, 1994). Phosphorus in sediment can be released back into the system by chemical processes; for example, with pH levels over 8, phosphate can dissociate from its particle and become soluble in water (Walker et, al., 2007). Bottom-feeding fish and species that live in bottom sediments, such as worms and other aquatic invertebrates, can disrupt the sediment and release phosphorus back into the water column (Brönmark & Hansson, 2005). Nitrogen in lakes and Reservoirs can come from natural sources such as plant and animal decomposition, waste products from aquatic life in the water, urine and feces of wildlife in the catchment, or (in typically tiny amounts) mineral dissolution of rocks. Nitrogen entering lakes and Reservoirs is frequently of direct human origin, such as sewage treatment plant discharges or leachate from septic systems, as well as fertilizer runoff (Walker et, al., 2007). Nitrogen may be found in a variety of forms in fresh water. Most algae and other primary producers may use inorganic nitrogen forms such as nitrates (NO3 -), nitrites (NO2 -), ammonia (NH3), and ammonium ions (NH4+). Nitrate level above 0.2 mg/L NO3-N in lakes likely to boost algal development and signal probable eutrophic conditions (Anku, 2001). Nitrate concentrations more than 10 mg/L pose a potentially major public health risk. Concentrations ranging from 11 to 40 mg/L have been linked to methaemoglobinemia (blue babies) in infants under the age of six months. Ammonium is found in low amounts in natural waterways and is a prevalent contaminant in sewage and industrial effluents (Anku, 2001). pH refers to a substance's alkalinity or acidity, which is measured on a scale ranging from 1.0 to 14.0 (Spellman and Drinan, 2000). The concentration of hydrogen ions [H+] in water is measured by the pH. As [H+] grows, pH lowers, and the solution becomes more acidic; conversely, as [H+] declines, pH rises, and the solution becomes more alkaline (Spellman and Drinan, 2000). As pH University of Ghana http://ugspace.ug.edu.gh Page | 28 levels move away from the optimum, animal systems are stressed, and hatching and survival rates are reduced. The higher the death rates, the further a number is from the optimal pH range. The more sensitive a species is to pH fluctuations, the more impacted it is. Aside from biological consequences, high pH levels generally enhance the solubility of elements and compounds, making harmful substances more mobile and elevating the danger of absorption by aquatic life (Fondriest Environmental Inc., 2013). Minor pH shifts can have long-term consequences. A little adjustment in water pH can improve the solubility of phosphorus and other nutrients, making them more available for plant development (Fondriest Environmental Inc., 2013). Aquatic plants and algae grow with more readily available nutrients, increasing the need for dissolved oxygen. This results in a eutrophic lake that is rich in nutrients and plant life but deficient in dissolved oxygen concentrations. The entire quantity of material dissolved in a water sample is often quantified as total dissolved solids (TDS). TDS is the total amount of organic and inorganic dissolved material that has been ionized and unionized in a water sample. TDS in freshwater systems is commonly composed of inorganic salts, trace quantities of organic matter, and dissolved minerals (Anku, 2001). TDS is a key indication of water quality. The mobility and transformation of metals and ionisable compounds are affected by dissolved solids, which affects ionic strength. TDS is also a significant indication of whether water is suitable for drinking, irrigation, or industrial usage. Excess dissolved solids in drinking water are unpleasant due to potential physiological impacts, unattractive mineral tastes, and increased expenses due to pipe corrosion and the need for extra treatment. The concentration of total dissolved solids influences the water balance in aquatic organisms' cells. This, in turn, inhibits the organism's capacity to maintain correct cell density, making it difficult to maintain its position in the water column. Excess dissolved minerals, gases, and organic University of Ghana http://ugspace.ug.edu.gh Page | 29 elements should be removed since they can induce physiological consequences and generate aesthetically unappealing color, taste, and odors (Anku, 2001; Spellman & Drinan, 2000). 2.3.1.3 Self-Purification Processes Lakes naturally purify themselves through self-purification processes, which assist to preserve water quality and enhance water conditions. Through physical, chemical, and biological phenomena as mixing, sedimentation, oxidation-reduction reactions, and the actions of lower and higher species, these processes take place (Gu, 1985). Pollutants and organic materials in the water are dispersed and diffused by physical processes including mixing and turbulence. Adsorption and oxidation-reduction reactions are two examples of chemical processes that remove or change organic materials and contaminants. Decomposition of organic matter and pollution removal are both carried out by biological processes, including those of microbes and higher species (Tian, Wang & Shang, 2011). The kind and quantity of pollutants, the physical and chemical characteristics of the water, the existence of pollution-degrading microbes and higher species, and other variables all affect how well self-purification processes work in lakes. Settling of solids is a crucial step in the lake's self-purification process. It happens when silt and organic debris from the water column settle to the lake's bottom where microorganisms may decompose them. This procedure aids in lowering the level of organic matter in the water, which can lead to eutrophication, a reduction in oxygen levels, and other issues in the lake. Pollutants that are affixed to or dissolved in the particles can be eliminated with the aid of settling (Chapman, 1992). The size, density, and water velocity of the particles, as well as the existence of turbulence and mixing, as well as other elements that may affect particle movement, all influence the pace of settling. Reducing the sediment intake can help facilitate effective settling. University of Ghana http://ugspace.ug.edu.gh Page | 30 Mixing is an important process in lake self-purification as it helps to distribute dissolved oxygen and nutrients throughout the water column and maintain a stable thermal structure in the lake. Mixing occurs when wind and other physical forces create turbulence in the water, causing different water masses to mix with one another. This process helps to remove pollutants that are attached to or dissolved in the water, as well as reducing the concentration of harmful substances, such as excess nutrients, that can contribute to eutrophication and oxygen depletion in the lake (Magee & Wu, 2017). The rate of mixing in a lake depends on a variety of factors, including the lake's size and shape, the intensity of wind and other physical forces, and the presence of physical barriers, such as bottom sediment, that can reduce mixing. Effective mixing can be promoted by increasing the input of oxygen and nutrients into the lake, reducing the concentration of pollutants, and promoting physical mixing in the water column. The natural purification process is sped up by a quick mixing of the entering waste material and the receiving water. Any natural body of water undergoes a wide range of biological activities, which eventually result in the purification of the water. Feeding on solid matter by microscopic organisms, particularly bacteria, transform more complex molecules into simpler ones. This process eventually reaches a stage where the complex material transforms into minerals, water, and carbon dioxide (complete mineralization of harmful substances into innocuous form). Some of the larger solid material particles are also consumed by huge creatures. Additionally, larger species consume the bacteria that break down waste. Additionally, these bigger creatures will consume smaller ones. It is obvious that any body of water's natural food cycle plays a crucial role in the process of self- purification. It is also necessary to underline the significance of photosynthesis in the process of self-purification. Under the influence of sunshine, algae and other green plants create oxygen and consume carbon dioxide. As a result, the technique tends to increase the amount of oxygen in University of Ghana http://ugspace.ug.edu.gh Page | 31 contaminated waterways. Additionally, any extra carbon dioxide that is dissolved in the water as a result of the purification process will be used by green plants' photosynthetic processes. River and lake characteristics vary, which has an impact on how each of them handles pollution. Three zones make up the purification process: the zone of degradation/decomposition, the septic zone, and the recovery zone. The impact of the wind direction causes rivers to flow turbulently whereas lakes move slowly. The rate of mixing of contaminants in rivers is pronounced near the point of waste deposition, also known as the decomposition zone, due to significant turbulence. Pollutants are transported farther downstream depending on the flow velocity before sedimentation, hence river turbidity rises as pollutants are suspended in the river for a longer period of time. Aquatic plants eventually perish as a result of diminished sun light penetration and reduced photosynthetic capacity. As a result, the amount of dissolved carbon dioxide (CO2) that would normally be used by aquatic plants in the river starts to increase. However, because lakes have slow water flow, contaminants (such as sludge, dead algae, organic debris, etc.) accumulate in vast amounts at the bottom of the lake, where microbial organisms start to decompose them (Whitehead & Lack, 1982). The amounts of dissolved oxygen rapidly decrease as the Biochemical Oxygen Demand (BOD) increases. As water in a lake's pelagic zone exchanges with the profundal zone's low-DO water, overturns aid in the purifying process. Water from the profundal zone that rises as a result of the overturn exchanges gases with the atmosphere at the top through a process called aeration, and the cycle repeats itself from time to time. This is significant because it aids in reducing stratification in lakes, which in turn reduces the thickness of the impermeable thermocline layer and allows dissolved oxygen to permeate deeper into the water. The turbulence and flow velocity are relatively important factors in the aeration process in rivers. The contaminants are entirely deposited at the bottoms of both rivers and lakes in the septic zone, making the water University of Ghana http://ugspace.ug.edu.gh Page | 32 cleaner and aerating it more effectively. The rate of decomposition is accelerated, and the lakes' concentration of dissolved oxygen reaches its lowest. Organic compounds continue to be broken down by anaerobic bacteria as they accumulate. In addition, sunlight can now reach the water, which causes algae to proliferate and BOD levels to drop. The recovery zone is the last stage, where algae proliferate and aquatic plants start to thrive, using dissolved CO2 while releasing oxygen into the water. The concentration of the DO increases when it exceeds the BOD due to the BOD and DO's inverse connection that started in the septic zone (McGhee & Steel, 1991). Similar mechanisms for self-purification exist in rivers and lakes alike, although rivers and lakes differ substantially in the way their waters travel. While lakes flow is languid and dependent on wind direction, rivers flow is turbulent because of their increased velocity. Lakes also undergo overturns, which is a significant method for self-purification. In essence, aeration in lakes happens as a result of overturns, allowing poor-quality (low oxygen content) profundal zone water to rise and exchange gases with the atmosphere, whereas aeration in rivers happens as a result of flow velocity and turbulence. 2.4 Eutrophication Lake eutrophication is produced by an excess of nutrients, primarily phosphorus. Excess phosphorus inputs to lakes are typically caused by sewage, industrial wastes, and runoff from agricultural, construction, and urban areas. Municipal and industrial discharges are examples of point sources of nutrients, whereas nonpoint sources of nutrients, such as runoff from agricultural or urban lands, are examples of nonpoint sources of nutrients and are the drivers of eutrophication. Excessive fertilizer or manure application, which promotes phosphorus accumulation in soils, is a significant driver of nonpoint nutrient intake. Phosphorus-rich soils wash into lakes, where part of University of Ghana http://ugspace.ug.edu.gh Page | 33 it dissolves and supports the growth of phytoplankton and aquatic plants. Erosion of soil particles into streams and lakes is a major cause of eutrophication in areas with high soil phosphorus concentrations (Carpenter, 2005; Bennett, Carpenter, & Caraco, 2001). Algal blooms are a typical observable result of eutrophication. Algal blooms may be either a nuisance to individuals who wish to utilize the water body or they can become dangerous algal blooms that cause significant ecological deterioration in water bodies. After the algae is degraded by microbes, the water body may become depleted of oxygen (Glibert & Burford, 2017; Schindler & Vallentyne, 2004). 2.4.1 Eutrophication Process and its Causes Increased nutrient concentrations promote the development of aquatic plants, including both macrophytes and phytoplankton. As more plant material becomes accessible as a food source, the number of invertebrates and fish species grows. As the process progresses, the biomass of the water body grows and biological diversity declines. With more severe eutrophication, bacterial decomposition of surplus biomass leads in oxygen consumption, which can lead to hypoxia, which begins at the bottom sediment and moves deeper into the water. In the summer, hypoxic zones are widespread in deep water lakes owing to stratification into the cold oxygen-poor hypolimnion and the warm oxygen-rich epilimnion (Schindler & Vallentyne, 2008; Smith, Tilman & Nekola, 1999). Phosphorus is a required nutrient for plants, and it is the limiting element for plant development in the majority of freshwater habitats. Because phosphorus binds to soil particles strongly, it is mostly transferred via erosion and runoff. The extraction of phosphate into water is sluggish once it has been translocated to lakes, which contributes to the difficulty of reversing the consequences of eutrophication (Schindler, 2012; Khan & Mohammad, 2014). When macrophytes and algae die in productive eutrophic lakes, rivers, and streams, they disintegrate, and the nutrients in that organic matter are transformed into inorganic form by microbes. Because the breakdown process uses University of Ghana http://ugspace.ug.edu.gh Page | 34 oxygen, the concentration of dissolved oxygen decreases (Jeppesen et, al, 2005). Depleted oxygen levels, in turn, may result in fish deaths and a variety of other impacts that reduce biodiversity. Nutrients may get concentrated in an anoxic zone, generally in deeper waters walled off by stratification of the water column, and may be made available again only during fall turn-over in temperate climates or under turbulent flow conditions. Increased development of aquatic vegetation, phytoplankton, and algal blooms disturbs the ecosystem's regular functioning, generating a range of difficulties such as a shortage of oxygen, which is required for fish and shellfish survival (Bartram, Wayne, Ingrid, Gary & Olav, 1999). Dense algae development in surface waters can obscure deeper water and impair the survival of benthic shelter plants, affecting the whole ecosystem. Eutrophication also reduces the value of rivers, lakes, and recreational opportunities. When eutrophic conditions interfere with drinking water treatment, health concerns might arise. Phosphorus levels in water are well correlated with algal concentrations and lake trophic status. Studies in Ontario's Experimental Lakes Area have revealed a link between phosphorus input and the rate of eutrophication. Later phases of eutrophication result in blooms of nitrogen-fixing cyanobacteria that are only restricted by the phosphorus concentration (Higgins, Paterson, Hecky, Schindler, Venkiteswaran & Findlay, 2017) 2.4.2 Conceptual Model of Eutrophication The introduction of extra nutrients into aquatic environments begins the eutrophication conceptual paradigm. Agricultural runoff, sewage discharge and industrial effluents are all common sources (Howarth et, al., 1996). These anthropogenic contributions considerably contribute to water body nutrient enrichment. The stage of nutrient enrichment begins when nutrients accumulate in the water. Increased nutrient levels increase primary production, resulting in rapid growth of aquatic plants and algae, especially phytoplankton (Paerl et, al., 2016). This phase leads to the formation University of Ghana http://ugspace.ug.edu.gh Page | 35 of algal blooms, which is a sign of eutrophication. Blooms are composed of intense concentrations of algae, which frequently form surface scums or mats (Huisman et, al., 2018). The ensuing decomposition of dead algae consumes dissolved oxygen in the water as algal biomass builds. This causes oxygen depletion, which can lead to hypoxia or anoxia, both of which are harmful to aquatic life (Diaz & Rosenberg, 2008). Water quality deteriorates further, as shown by decreased clarity, unpleasant odors, and, in certain cases, the buildup of hazardous algal toxins (Paerl & Otten, 2013). Rapid algal growth. and consequent depletion of oxygen affect aquatic species such as fish, invertebrates, and other wildlife (Smith & Schindler, 2009). Native species often get outcompeted by invasive species, resulting in biodiversity loss. The final component of the conceptual model emphasizes the relevance of eutrophication mitigation and management measures. These techniques seek to minimize nutrient inputs by implementing improved agricultural practices, updating sewage treatment systems, and regulating runoff. Ecological restoration strategies like as biomanipulation and nutrient removal technology can also assist minimize the effects of eutrophication. Figure 2.1 Conceptual Model of Eutrophication Adopted from (Nukpezah, 2020) University of Ghana http://ugspace.ug.edu.gh Page | 36 2.4.3 External Nutrient Loading External nutrient loading is the process through which nutrients, such as nitrogen and phosphorus, are added to a water body from sources that are external to the water body. Examples of such sources include agricultural runoff, sewage discharge, and atmospheric deposition. Increased nutrient levels can result in eutrophication, which is an overabundance of nutrients in the water body and can alter the aquatic ecology by increasing algae growth and decreasing oxygen levels (US Environmental Protection Agency, 2020; Howarth, Sharpley & Walker, 1996). This process takes place when nutrients from the land are not effectively absorbed or handled by the land and reach the water body, causing an increase in the development of algae and other aquatic plants that might result in eutrophication. Water quality might suffer, oxygen levels can drop, and aquatic life may be harmed as a result of eutrophication (Sharpley, 1994; Howarth & Marino, 2006). The land use and human activities in the immediate region, together with climatic and hydrological conditions, can all have a significant impact on the pace and volume of external nutrient loading. 2.4.4 Internal Nutrient Loading Internal phosphorus (P) loading refers to the flow and recycling of P between sediment in a lake and the water column. Phosphorus and nitrogen are delivered into a lake environment via a variety of point and non-point sources, where they accumulate in the sediment (Dubey & Dutta, 2020; Liang, Liu, Zhen & He, 2015; Wongaree, 2019; Yang, Wei, Xu, Zhang, Li & Wan, 2019). Various factors affect this process, including chemical processes such as redox potential and pH, biological processes like mobilization and mineralization, as well as physical processes such as diffusion and sediment mixing. (Kowalczewska-Madura et al., 2019; Yang et al., 2013). In other words, internal loading is obtained from ancient external loading that sinks in sediments (Nürnberg, LaZerte, Loh & Molot, 2013). Phosphate (PO4 3-) is adsorbed or precipitated with ferric (Fe3+) iron University of Ghana http://ugspace.ug.edu.gh Page | 37 oxyhydroxides (FeOOHP) in the surface sediment under aerobic and oxygenated conditions. Initially, freshly precipitated Fe-OOH is a very low molecular weight colloid particle composed of iron and hydroxyl ions that polymerize (form chains). When PO4 3- is coupled with Fe-OOH, it is mainly eliminated from recycling routes and in a form that algae cannot take up. As hypolimnetic dissolved oxygen depletes, anaerobic bacteria can create energy from organic detritus by using Fe- OOH as an alternative electron acceptor (James, 2016). The bacterially driven reduction of Fe- OOH to soluble Fe2+ breaks the connection between Fe-OOH and PO4 3-, leading in the diffusion of Fe2+ and PO4 3- into the sediment pore water and, subsequently, into the anoxic hypolimnion. As the summer advances, the slow process of diffusion at the sediment-water interface can cause significant soluble PO4 3- and Fe2+ buildup in the anoxic hypolimnion. By the conclusion of the summer stratification, soluble P concentrations above the sediment surface may surpass 1mg/L, with concentration gradients extending up into the metalimnion (James, 2016). 2.4.5 Models for Assessing Nutrient Enrichment in Waterbodies Assessing nutrient enrichment in waterbodies involves evaluating the level of nutrient inputs (e.g., nitrogen and phosphorus) relative to the natural background concentration. This can be done using a variety of models and methods. These include; Total Maximum Daily Load (TMDL) model: This model evaluates the total amount of a pollutant that a waterbody can receive without exceeding water quality standards. Water Quality Index (WQI) model: This model uses multiple water quality parameters to provide a single value that summarizes the overall water quality of a waterbody (Apostol & Christaki, 2002). University of Ghana http://ugspace.ug.edu.gh Page | 38 Trophic state indices: These indices, such as the Carlson Trophic State Index (TSI) and the Total Phosphorus Index (TPI), provide a relative measure of water quality based on the concentration of nutrients and other water quality parameters (Carpenter, Caraco, Correll, Howarth, Sharpley & Smith, 1998). Nutrient