Nutrient release from inundated land of a tropical reservoir (nanhua reservoir, Taiwan)

Abstract

Nutrient release from land inundated by creation of a tropical reservoir (Nanhua Reservoir, Taiwan) is investigated. Both the magnitudes of nitrogen and phosphorus which might be released from inundated land are determined on the basis of measurements of biomass and nutrients content of terrestrial vegetation and the nutrients content of topsoil. The fresh biomass of the terrestrial vegetation was estimated at 48600 kg/ha, with an equivalent dry biomass of 15500 kg/ha. After complete decay following submergence, the terrestrial vegetation could potentially contribute 242 kg of nitrogen and 37 kg of phosphorus per hectare. The kinetics of nutrient release from topsoil is determined on a laboratory scale for 80 days, which showed that the phosphorus release rate is averaged at 5.25 mg TP/m2/day in anaerobic conditions and 1.34 mg TP/m2/day in aerobic conditions, also the nitrogen release rate is averaged at 78.31 mg TKN/m2/day in anaerobic condition and 35.71 mg TKN/m2/day in aerobic conditions. Based on the actual operation status of Nanhua Reservoir during the initial operation period of 21 months after construction (from August, 1993 to April, 19950 and nutrient release kinetics, the accumulated nutrient loads originating from the topsoil of the inundated land are about 81342 kg of nitrogen and 4701 kg of phosphorus.