Phosphorus Levels And In-Situ Processing Coefficients Of Selected Allochthonous Forage Detritus In River Nyangores, Bomet County, Kenya

ABSTRACT

River Nyangores experiences an all year round forage detrital input with previously unknown breakdown fate. Determination of in-situ processing coefficients of forage allochthonous detritus is important as it provides critical indication on: the level of biochemical oxygen demand, the rate at which food nutrients are distributed downstream, monitoring ecological changes in the aquatic ecosystem and as a climate change mitigation response for riparian forage agriculture. The study was done for a period of 9 months (between July 2013 to April 2014). The aim of the study was to determine the aquatic processing coefficients and its correlation with forage detrital phosphorus level, in addition to determining land use/cover spatio-temporal change along the riparian zone of River Nyangores. The three grass species investigated were; Pennisetum purpereum (Pp), Panicum coloratum (Pc) and Chloris gayana (Cg). These grasses are commonly cultivated in the riparian land of River Nyangores for erosion control and source of livestock feeds. Grass litter was collected from forage farms on the riparian zone and composite samples made. Leaf packs were deployed in the river with a withdrawal interval of 2 weeks. Ash-free dry mass was determined per withdrawal. The decay model was log-transformed for regression coefficients. Total phosphorus was analyzed using the molybdate-calorimetric procedure with Jeenway® spectrophotometer. Data was analyzed in XLSTAT computer program. ArcGIS®, Erdas Imagine® and GPS were used for riparian zone and adjacent landscape change detection procedures. The mean processing coefficients for Cg, Pp and Pc were 8.73 x10-4dd-1, 7.51 x10-4dd-1 and 7.81 x10-4dd-1 respectively. The decay rates were higher at downstream than upstream. There was a significant difference among the decay rates for the three species at 95% CI with ANCOVA (p= 0.0001). Pearson correlation (p=0.787, r =0.143) showed insignificant positive correlation between leaf P content and processing coefficient at 95% CI. Change detection analysis indicated 30.6 % forest cover loss and an increase of 189.9 % grass land cover within 41 years (1972 – 2013) in the riparian zone and adjacent landscape of River Nyangores. The study concluded that all the grass species studied are all slow processors with different phosphorus immobilization trends while the riparian areas have experienced increased grass cover development. The study was significant in understanding ecological relationships between aquatic and bordering agro-terrestrial ecosystems. From the study findings, it is recommended that for agro-ecologically sustainable agriculture on the riparian areas and adjacent landscapes, forage farmers should grow the three species in the following preferential order; Cg, Pc and Pp. Farmers should ensure minimal contact between grass hay and River water particularly for Pp that is most recalcitrant in decay process. It is also recommended that an environmental monitoring system should be created for River Nyangores to track ecological changes in the river. Afforestation is required for conservation of the river immediate landscape to protect the riparian areas.