The Ecological Statusof The Keta Lagoon Using Physicochemical And Biological Indicators Of Water Quality

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University Of Ghana


The Keta Lagoon and its catchment areas are under the influence of intensive agriculture which depend heavily on agrochemical usage. It is necessary that, the quality of water in the lagoon is assessed to broaden our understanding of how the lagoon and its associated biota are responding to agro-related activities in its watershed. This study carried out a comprehensive assessment of the ecological status of the lagoon using physicochemical parameters (temperature, DO, turbidity, pH, nitrate, phosphate, silicate, ammonia), Trophic State Index and diversities of benthic macroinvertebrates and phytoplankton communities. The lagoon was partitioned into five zones (A to E) to depict the intensity of human impact as reflected through farming along the bank of the lagoon. Zone A is the area in close proximity to Anloga, Zone B, covers the mid-section of the lagoon and falls between Anloga and Woe, Zone C is main Woe area, Zone D represents the area between Woe and Afedome and finally Zone E which represents the area beyond Afedome extending towards Keta. The average physicochemical parameters reported during the study showed that Zones A and B recorded the highest levels of pH, 9.6  0.16 which was above the acceptable range levels by Ghana’s EPA and USEPA (6.0 to 9.0). The least pH level was recorded for Zone C at 8.5  0.03 which was within the acceptable range of pH. Dissolved oxygen levels measured was highest in Zone D (8.1  0.26 mg/l) and least in Zone A (6.5  0.13 mg/l), all within Ghana EPA and USEPA as well as the World Health Organization tolerable limits. Zones A recorded the higest nitrate values of 3.4  0.03mg/l and least in Zone E, 1.9  0.02 mg/l. All zones recorded nitrate levels that were above the Ghana and US EPA permissible ranges. Ammonia was highest in Zone A (0.12  0.02 mg/l) and least in Zone E (0.03  0.02 mg/l), and Phosphate levels was highest in Zone A (0.26  0.01mg/l) and least in Zone E (0.13  0.01 mg/l). Both phosphate and ammonia measured were within the permissible limits. The Trophic State Index based on Chlorophyll-a estimation indicated that the lagoon was hypereutrophic (61.3-64.9). However, Zone A recorded the highest TSI value (64.9) and the least TSI was recorded by Zone E (61.3). Zones A, B and C (4.9-6.5) were in poor ecological conditions. D (3.0-3.8) was in fair ecological conditions. Zone E was in good ecological conditions. The mean Plankton Index of Biotic Integrity (P-IBI) for the entire lagoon, however, was 3.96 and that shows a mesotrophic lagoon with diverse populations of phytoplankton.The total number of macrobenthic species counted in the Keta lagoon was 1018 which consisted of 83% mollusks and 17% polychaetes as the major taxa. Generally, Macrobenthic assemblage richness, evenness and diversity were 1.2, 0.8 and 1.7 respectively for the lagoon. The trends of physicochemical parameters (temperature, DO, turbidity, pH, nitrate, phosphate, silicate, ammonia), Trophic State Index, diversities of benthic macroinvertebrates and phytoplankton communities showed that the lagoon is in the state of deterioration with time.


MPhil. Marine Science


Ecological, Keta Lagoon, Physicochemical, Biological Indicators