Spatial and Temporal Changes in Nitrogen, Phosphorus and Potassium Concentration in Water in the Thirappane Tank Cascade in Dry Zone of Sri Lanka

This study was conducted to assess spatial and temporal changes of major plant nutrients; nitrogen (NO₃^--N), phosphorus (PO₄^3--P) and potassium (K⁺) in the Thirappane tank cascade system. Three tanks namely Meegasagama, Alistana and Thirappane and drain channel in two rice cultivated tracks in between three tanks were selected for water sampling. Sampling was done monthly intervals from nine locations. In all water samples, dissolved NO₃^--N, PO₄^3--P and K⁺ were determined using standard laboratory techniques. NO₃^--N, PO₄^3--P and K⁺ concentrations in water created significant spatial changes from upper tank to lower tank of cascade. All three plant nutrients showed a significant steady increase from upper tank Meegasagama to middle tank Alistana and then to lower tank Thirappane and waters of three sampling points of two paddy tracks. As temporal changes, it was found that NO₃^--N, PO₄^3--P and K⁺ concentrations of waters of these three tanks and sampling points showed a bimodal pattern which was coincided with the bimodal rainfall of the dry zone. Highest concentration of nutrients was observed in months of April and May in Yala compared to the Maha season. Low nutrients concentration in the Maha period could be due to dilution effect caused by comparatively high volume of tank water during Maha season.

DOI: http://dx.doi.org/10.4038/jepsl.v1i1.5143

Journal of Environmental Professionals Sri Lanka Vol.1(1) 2012 70-81