Nutrients and Phosphorus Release in Sediment in a Tropical Pumped Water Storage Reservoir

Abstract

Dajingshan Reservoir is a typical pumped-water storage reservoir, originally built for agricultural irrigation around Zhuhai City and for supplying drinking water to Macau. Because of its small catchment, river water began to be pumped into the reservoir for more water storage in the dry season from the only but polluted river in Zhuhai. After 30 years the accumulated nutrients in the sediments have become a major internal pollution factor in the eutrophication of the reservoir. In the present study, we measured the accumulation and release of nutrients from the sediments. The accumulated sediment reaches about 48,840 m³ in volume with a wet-weight of 54,027 t and drought-weight of about 36,137 t. Total inorganic phosphorus (TIP), total nitrogen (TN), and releasable phosphorus (Re-P) in the sediment were estimated at 21,886, 67,015, and 5,867 kg, respectively. TIP, TN, and Re-P were highest near the dam, reflecting the hydrodynamic characteristics of the reservoir. Because of the high Re-P content and anaerobic environment in the zone near the dam, this zone was the primary area releasing nutrients. Phosphorus release was measured through in situ experiments and was 4.09 mg·m⁻²·day⁻¹ in the zone near the dam. Total annual phosphorus release was about 109 kg, mainly contributed by release from the dam zone.