The impact of irrigated agriculture on water quality of Kongoni and Sirimon rivers, Ewaso Ng'iro North Basic
Mutisya, David Kioko
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Water is the most important resource issue in the 21St Century, given the current conflicts over the use of the resource both by human and wildlife. There is therefore need for better methods of conservation and management of water resources to increase not only the quantity of available water but also to ensure good quality. This study was carried out in Sirimon Sub-catchment of the Ewaso Ng'iro Basin, Nanyuki area, Northwest of Mt. Kenya. It was aimed at establishing the extent of irrigation within the sub-catchment and to determine the quality of river water for both River Sirimon and River Kongoni. The study aimed also to establish whether there is any pollution of the river water due to increased irrigation activities in the study area. Questionnaires were administered to 115 households selected at random for generation of information regarding the study area. Water sampling stations were mapped after a reconnaissance survey in the field using Geographical Positioning System devices. Surface water samples were collected in 1 litre amber glass bottles and half litre plastic bottles at all the sampling sites and transported to the lab inside a cooler box. Water quality determination was done for a period of five months between November 2005 and February 2006. The sampling was done once a week for two weeks in both wet season in November and dry season in February and early March 2006. The following parameters were determined on site: pH, water temperature, dissolved oxygen, salinity, turbidity and total dissolved solids by using portable paqualab equipment. The samples in plastic bottles were taken to Nanyuki CETRAD offices for the testing of ammonia, nitrate, nitrite, iron, manganese, phosphates and sulphate. Portable palintest equipment was used for the chemical analysis of these elements. This study established that 41 % of the interviewed farmers practice irrigation using sprinklers and furrows with a minority using drip method. Most of the homesteads use domestic water from river Sirimon. It was established further that, although peasant farmers owning on average 2.8 acres of land were using commercial fertilizers, they were not affecting the water quality of the rivers as was the case with the irrigated large horticultural farms i.e. over 9 ha within the study area. The study established that there were sulphates and phosphates mean concentrations of 22mgL-1 and 1.3mgL"1 respectively in the Kongoni River waters associated with the use of commercial fertilizers as compared to mean values of 7mgL"1 and 0.15mgL-1 respectively along Sirimon River. Like wise, mean salinity concentrations of 3mgL-1, were recorded at Kongoni River as compared to relatively lower mean value of 0.47mgL-1 along Sirimon River. On average, mean nitrates concentrations of 1.7mgL"1 were recorded for Kongoni River, higher than those recorded for Sirimon River (0.033mgL-'). These concentration levels were however within the standard levels set by WHO. Most of the significant ions' mean concentrations between upper and lower Kongoni had significant differences while there were no significant differences for corresponding sites along Sirimon River. It is recommended that continuous monitoring of the seasonal and periodic changes in the water quality of these rivers should be done. River Sirimon contains relatively low concentrations of pollutants as compared to River Kongoni. This is because River Kongoni has two major horticultural farms across it i.e. Homegrown and Kongom Farms hence these irrigated farms were polluting the rivers during the time of this study. After water samples were subjected to Gas Chromatography for pesticide residue analysis it was established that all the water samples were not polluted with any pesticide residues.