Distribution Characteristics and Fluxes of Nitrogen and Phosphorus at the Sediment-water Interface of Yuqiao Reservoir

Abstract

Yuqiao Reservoir is an important source of drinking water in Tianjin. In recent years, the eutrophication status is becoming more and more serious, but its internal loading and distribution characteristics of nitrogen and phosphorus is not clear. The profiles of nitrogen and phosphorus at the sediment-water interface were analyzed using the Peeper (pore water equilibrium) technique and the spatial distribution was investigated. The existing forms of the released nitrogen and phosphorus were investigated by the static intact sediment cores, and the fluxes of nitrogen and phosphorus at the sediment-water interface were estimated by static incubations with intact sediment cores. The results demonstrated the following. ① The contents of PO43--P, NH4+-N, NO3--N, and NO2--N in sediments were 0.5-6.5, 0.5-10.9, 2.2-16.2, and 0.05-0.6 mg ·kg-1, respectively. The contents of nutrient were lower as depth increased, and horizontal distribution characteristics indicated significant differences. ② The contents of PO43--P and NH4+-N in the interstitial water were much higher than in the overlying water, suggesting that the interstitial water had the potential to diffuse nutrients to the overlying water. The concentrations of PO43--P and NH4+-N in the interstitial water increased rapidly at 0-5 cm and then decreased gradually. ③ PO43--P and NH4+-N diffused from the sediment to the overlying water, and the fluxes of them were 1.1-13.3 mg ·(m2 ·d)-1 and 20.6-250.5 mg ·(m2 ·d)-1, respectively. The exchange fluxes of NO3--N and NO2--N ranged from -20.4 to 33.4 mg ·(m2 ·d)-1 and from -7.4 to 0.4 mg ·(m2 ·d)-1, respectively. PO43--P and NH4+-N were the main nutrients in the sediment released to the overlying water. The fluxes were high in the south and low in the north, and also high in the mouth of the Linhe River and downstream of the reservoir. Compared with similar studies, the fluxes at the sediment-water interface of Yuqiao Reservoir were relatively high, indicating that the sediment was an important source of nutrients for the overlying water in Yuqiao Reservoir.