Modelling nitrogen transformation and removal in Mara river basin wetlands

A model for nitrogen transformation and removal in Mara river basin wetlands was developed. Samples for model input were taken from water, plants and sediments for 45 days between months of April and July 2012. These samples were analyzed for pH, temperature and dissolved Oxygen (DO) in situ while chemical parameters such as NH3-N, Org-N, NO2-N, and NO3-N were analyzed in the laboratory in accordance with standard methods. For plants, the density, dominance, biomass productivity and total Nitrogen (TN) were determined while for sediments only TN was analyzed. It was observed that average plants density was 3.2 ± 0.3 plants/m2 with 20 plant species being dominant. Average biomass productivities were 4.3±0.79 kgDWm-2, 3.74±0.5 kgDWm-2 and 2.71±0.6 kgDWm-2 for Papyrus, Phragmites and Typha species, respectively, while plant nitrogen contents were 3.35±0.22 %DW, 3.63±0.7 %DW and 3.47±0.45 %DW for the same plant species. The average total for all plants’ nitrogen content determined was 67.88±15.53 gN/m2. The average nitrogen contents in the sediments found was 201.26±30.78 gN/m2. Inflow rate was determined using stage-discharge relationship and was found to be 734,400 m3/day and the average wetland volume was 1,113,500 m3. Data collected by this study were used for model calibration of nitrogen transformation and removal in the wetland using STELLA II v. 9.0®2006 while data from another wetland were used for model validation. It was found that the major pathways resulting into nitrogen removal in the wetland were sedimentation (26.59 %), plant uptake (6.55%) and de-nitrification (4.56%). About 37.7% of total nitrogen was removed by the wetland system.