Impact of nutrients on phytoplanton productivity of the coastal marine waters of Mtwapa, Mida and Kilifi creeks, Kilifi county, Kenya
Pole, Tunje Mwamuye
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Major sources of coastal and marine pollution affecting coastal condition vary throughout the world, and there is an increasing body of research indicating that the nature and intensity of development activities, the state and type of industry and agriculture, and the size of human populations are significant contributing factors to each region’s unique problems. This study aimed at understanding the extend and impacts of coastal marine waters from land based pollution sources. The main objectives includes the determination of actual levels of three nutrients (PO4-, NO3- and NH3) and whether they are within acceptable limits, their relationship with ongoing human activities and their relationship with marine primary productivity. To achieve these objectives, marine water samples were sampled and analyzed from identified point and area pollution sources. A Quantitative one way ANOVA was used to determine the variations between treatments. Spearman correlation test between nutrients and carbon and nutrients and rainfall was also computed. The study revealed that the levels of nutrients kept on fluctuating throughout the entire study period along the entire three creeks and the sampling stations. The levels of nitrates were within the oligotrophic range in all the three creeks. Mtwapa creek recorded on average the highest levels of nitrates at α = 0.05 from June to November 2011. Phosphate levels in the three creek waters were not significantly different throughout the sampling period. Ammonia levels in Mtwapa were in the higher mesotrophic levels of upto 0.009mg/L while Kilifi and Mida, levels were within the oligotrophic levels. Along Mtwapa creek, there was a positive correlation coefficient between phosphate and carbon fixation (r = 0.869) in the outer creek while the correlation coefficient for nitrates and ammonia were negative (r= -0.624 and -0.295). All nutrients had a negative correlation coefficient with rainfall in outer creek of Mtwapa (r=.-0.76, -0.37 and -0.336 for nitrates, phosphates and ammonia respectively. In Kilifi there was positive correlation between carbon fixation and all the three nutrients in the inner creek There was positive correlation between nutrients and rainfall in all the sampling stations. Mida there was positive correlation between rainfall and phosphates in all the six stations (r = 0.78, 0.3, 0.22, 0.78, 0.23 respectively). In Mtwapa the high levels of nutrients in the outer creek stations and the negative correlation coefficient between the nutrients and rainfall suggests that runoff did not contribute to increased levels of nutrients but rather the waster roadside canal and sewage outfall from urban and tourist development contributed to increased levels. The higher levels nutrients in the inner creek waters of Kilifi can be attributed to destruction of vegetation close to the creek for farming upstream of the creek. Mida creek had the lowest recorded levels of nutrient apart from phosphates in all the sampling stations. These phosphates levels most likely were contributed by waste water from some of the tourist establishment especially at the Temple point hotel which encroaches to the shore waters. To reduce the impacts of land based human activities, it is recommended that analysis of existing land-based activities which impact negatively on coastal marine ecosystems and livelihoods be carried out in order to design mitigation measures.