Effect of Anthropogenic Activities and Seasons on Nutrients and Heavy Metal Loads of the Water and Sediments along Amala and Nyangores, Tributaries of River Mara Kenya

Abstract

The Mara River Basin accommodates natural forests at its source. The forests' encroachment for human settlement has led to extensive deforestation and farming activities which may cause pollution of the natural aquatic system resulting from soil erosion, farming inputs and household waste. Changing rainfall seasons cause variations in the amounts and rates of surface runoffs flowing downstream. The human settlements have caused changes in rainfall regimes in the Mara River Basin. It is not known how these human settlements and related anthropogenic activities have impacted on water quality at the tributaries of the River Mara that drains into Lake Victoria. The objective of this study was to establish if the nutrient loads and heavy metals in water and sediments and water quality physicochemical parameters along Rivers Amala and Nyangores, tributaries of the River Mara, have been influenced by the anthropogenic activities, and to determine their variations in different seasons. Samples were obtained in both dry and wet seasons in three replicates from 13 sites selected on the basis of varying human activities along each tributary; at streams feeding the tributary and on the main tributary. The nutrient levels and water quality parameters of springs closest to the forest, where land has not been disturbed, were used as control, to assess the effects of anthropogenic activities along the two tributaries. The pH and temperature of water were determined insitu and electrical conductivity in the laboratory. Water samples were collected in precleaned bottles and sediment samples in polythene bags and stored at 4°C. Spectrophotometric methods and atomic absorption spectrophotometer measured nutrient and heavy metals loads, respectively. ANOV A was done using a two factor completely randomized design with sites as main treatment and season as sub-treatment. The nutrient and heavy metals loads were significantly (pSO.OS) different among sites and with the control for both water and sediments implying the anthropogenic activities were influencing water quality. The River Amala registered relatively higher values of the dissolved nutrients and heavy metals than the River Nyangores. Most of the metals and nutrient loads registered a significant (PSO.OS) difference in different rainfall seasons. The nutrients and heavy metals levels obtained in this study, except for total phosphorous; were below the WHO water quality set limits. Control of the anthropogenic activities is recommended, as with time, they could seriously impact water quality of River Mara water negatively and by extension that of Lake Victoria.