The study assessed plant nutrient loads in water of a pond and irrigation dam in the Tolon District of Ghana. The pond is located downstream of croplands used mainly for rice and maize cultivation whilst the irrigation dam is located further downstream of the pond and used for irrigation of a developed area of 40 ha. Water samples were taken from each location and laboratory analysis determined the concentrations of NH3, NO3-, NO2-, PO43-, P and K. The results indicated that irrigation dam water recorded grand mean concentration of 0.877 mg/l, 0.284 mg/l, 0.020 mg/l, 0.379 mg/l, 0.139 mg/l and 4.620 mg/l for NH3, NO3-, NO2-, PO43-, P and K respectively. In the pond water however 1.290 mg/l, 0.033 mg/l, 0.167 mg/l, 0.404 mg/l, 0.063 mg/l and 4.757 mg/l were recorded for NH3, NO3-, NO2-, PO43-, P and K as grand mean concentration respectively. Farmers used mainly nitrogen and phosphorous based fertilizers and the wash-off effect is as exhibited in the laboratory results. The nutrient concentration of the irrigation dam and pond water resulted in it being oligotrophic and risk eutrophication with potential to reduce reservoir capacity. Nutrient concentration reduction methods will largely contribute to an increase lifespan of the water harvesting systems.
