Ecological Quality of Muni Lagoon and Its Tributaries in Effutu Municipality of Central Region, Ghana

Abstract

Muni Lagoon, located in Winneba in the Effutu Municipality, has two main tributaries, which are Pratu and Ntakofa Rivers. The Muni Lagoon catchment area provides a lot of benefits to residents in the area, including hunting, farming, fishing, and gathering of wood fuel. The lagoon area is the habitat of most plants and animals and serves as birds feeding spot. However, anthropogenic activities such as agricultural and industrial activities are deteriorating the quality of Muni Lagoon and its two tributaries. The study evaluated the heavy metal, physicochemical, and pesticide residual quality of Muni Lagoon and its tributaries. It also looked at how anthropogenic activities affected the provision of ecosystem services in the catchment area of the Muni Lagoon. The mixed method approach was employed to gather and evaluate both qualitative and quantitative data. In the study, 36 water samples each were collected from Muni Lagoon, River Pratu, and River Ntakofa for physicochemical analysis. Also, 36 samples each of sediments and water were collected from the three water bodies for heavy metal analysis, and 36 samples each of water and sediment were collected for pesticide analysis. Furthermore, 240 fish samples (black chin tilapia (Sarotherodon melanotheron) and Tilapia guineensis) were collected for heavy metal (120 fish) and pesticide (120 fish) analyses. These fish types are mostly consumed by people in the study area and hence sampled for the study. The collected samples were labelled and placed in a cold box before sending them to the laboratory for analysis. In addition, 384 respondents from four communities in the study area were conveniently sampled to respond to a questionnaire on provisioning ecosystem services in the Muni Lagoon catchment area. The four communities involved in the study were purposively selected because most people depend on the lagoon and its tributaries for their livelihood. The physicochemical parameters were analysed using the analytical procedure described by the American Public Health Association (1998). The water, sediment, and fish samples used for heavy metal analysis were acid digested and analysed using Nexion 2000 ICP-MS. Again, sample preparation, extraction, cleanup, and analysis of pesticide samples were done using the QuEChERS method. Gas chromatography GC-2010 equipped with 63Ni electron capture detector (GC-ECD) was used to analyse the extract for organochlorines and pyrethroid residues, while Gas chromatographic- flame photometric detector (GC-FPD) was used to determine organophosphate pesticides at their various operating condition. From the obtained data, the weighted arithmetic Water Quality Index (WQI) model was used to estimate the quality of surface water. The heavy metal pollution index and Geo-Accumulation Index (Igeo) were used to evaluate the various heavy metal accumulations in water and sediment samples, respectively. The Pesticides Quality Index (PQI) was used to assess pesticide quality in water and soil samples. Bioaccumulation Factor (BAF) was used to evaluate the degree of fish contamination by heavy metals and pesticides in the studied fish samples. The USEPA risk assessment model was used to determine daily exposure intake, non-carcinogenic and carcinogenic risks. Data from all samples were analysed using SPSS (version 25) for both descriptive (like mean and standard deviation) and inferential statistics. The variations in physicochemical, heavy metal, and pesticide residual levels in water, sediments, and fish at a 95% confidence level were established through inferential statistics like principal component analysis (PCA), linear regression, one-way analysis of variance (ANOVA), and Pearson correlation coefficient. The results revealed that most of the physicochemical parameters were above the WHO (2018) and GSA (2017) permissible values in Muni Lagoon and its tributaries. The WQI of the Pratu River was 249.98, and it suggests that the water from the river is unfit for drinking and irrigation purposes. Muni Lagoon and Ntakofa River had water quality indices of 71.612 and 66.05, respectively, and were within the class, which indicates poor water quality. Heavy metals were detected in Muni Lagoon and its tributaries. The Pratu river and Muni lagoon recorded As values greater than the WHO (2018) permissible value of 0.01 mg/L, while concentrations of Cd, Cr, Ni, and Pb in water samples of Muni lagoon and Ntakofa river at the time of the study were below their respective WHO values. On the other hand, the Pratu River recorded higher values of Cr, Ni, and Pb, which were above their recommended values. The Heavy metal pollution index (HPI) for the Ntakofa river was 6.899, while that of Muni lagoon was noted to be 51.85. These two values were below the critical value of 100, suggesting that the Ntakofa River and Muni lagoon have low levels of heavy metals. Contrarily, the HPI value of the Pratu River was more than 100, indicating that the river is unsuitable for consumption. Arsenic (As) and Cadmium (Cd) concentrations in sediment samples were higher in the Pratu River than those recorded in Muni Lagoon and Ntakofa River. Some of the heavy metals were below their accepted levels, and they include Co, Cu, Ni, and Se. The concentrations of Ba, Cr, Mn, and Zn in sediment samples from Pratu River were higher as compared to those recorded in Ntakofa River and Muni Lagoon. The mean Igeo value of heavy metals pollution in sediment samples from Pratu River was within the index class of 5 (4 ≤ Igeo ≤ 5), indicating heavily to extremely contaminated or polluted. The mean Igeo value of heavy metals in sediment samples from Ntakofa River was within index class 4 (3 ≤ Igeo ≤ 4), indicating heavily contaminated or polluted. Again, the mean Igeo value of heavy metals in sediment samples from Muni Lagoon was within the index class 2 (1 ≤ Igeo ≤ 2), indicating moderately contaminated sediment samples. In the principal component analysis (PCA), forty-four (44) components were extracted, and out of these, the first six (6) components cumulatively explained 93.89% of the total variations among physiochemical and heavy metal parameters. These six components were therefore retained in the model. The high loadings and high correlation values of heavy metals suggest a common source of origin. In this study, the source of pollution in water bodies was linked to anthropogenic activities such as industrial and agricultural activities, as well as domestic waste discharges into water bodies. The negative and positive loadings reflect the mixed sources of pollution from anthropogenic and natural sources. Organochlorine and pyrethroid pesticides were not detected in water and sediment samples from Muni Lagoon, Pratu, and Ntakofa Rivers were not detected. In addition, pesticides were not detected in fish samples. Apart from the detection of chlorpyrifos (an organophosphorus) in Ntakofa sediment samples, no organophosphorus was detected in either water or sediment samples from Pratu River, Muni Lagoon, or Ntakofa River. Human health risk assessments revealed that heavy metals in fish are likely to cause non-carcinogenic effects in children since their HI value exceeded 1 and was greatly influenced by As and Co. However, the HI for the adult population was less than 1 and which indicates no adverse non-carcinogenic health risk to the adult population through the consumption of fish from Muni Lagoon. In cancer risk assessment among the adult population, only As was likely to pose carcinogenic effects, while As and Cr were noted to pose carcinogenic effects in the children population since their CRI values exceeded 10-4. The respondents involved in the social survey revealed that ecosystem services have been negatively impacted in the Muni catchment area due to human activities. From the regression analysis, encroachment/Building, firewood collection, and agricultural activities have significantly deteriorated ecosystem services in the study area. To ensure the sustainable use of water bodies in the Muni catchment area, it is recommended that the EPA and, Water Resource Commission should periodically monitor all industrial activities taking place close to the Muni catchment area to ensure that their waste effluents do not pose health hazards to the public and the environment.