LIU Kun1,2, WANG Shilu1, TAN Di1,2, GUO Mingwei1,2, HAN Xiangfeng1,2
（1.State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang , 550002, China;
2.University of Chinese Academy of Sciences, Beijing 100049, China；）
Abstract：In order to reveal the impact of river cascade development on the transport of biogenic elements nitrogen and phosphorus, water profile and sediment column samples were collected in August 2020 from three reservoirs of Puding, Wujiangdu and Silin in the Wujiang River Basin representing the upper, middle and lower cascade reservoir, respectively. The content of nitrogen and phosphorus in these samples were determined, and the SMT method was used to extract the sediment phosphorus species. The results indicate that the TN concentration in the Wujiangdu Reservoir was the highest, at 3.92 ± 0.50 mg/L, due to the anthropogenic pollution input in the middle and lower reaches, the TP concentration rose sharply from the front of the dam to the downstream, reaching 0.04 - 0.06 mg/L, which was 2 - 3 folds of that in the upstream; the sediment in front of the dam contains a large amount of Fe-Al active phosphorus (1310.3 ± 1003.3 mg/kg) with high release risk, which may become a potential source of downstream pollution. The higher biomass in the middle and lower reservoirs accelerated the activation rate of nitrogen and phosphorus, increased the concentration of active phosphorus, but reduced the biological interception efficiency of sediment organic phosphorus. Except for Wujiangdu Reservoir, the sediments of other reservoirs are dominated by calcium-bound phosphorus (accounting for more than 60% of inorganic phosphorus). After the construction of the cascade reservoirs, the sediment content is greatly reduced, which may be the main factor for the decrease of the calcium-bound phosphorus concentration in the sediments of the downstream reservoirs. In general, the cumulative effect of cascade reservoirs increases the ‘activation’ efficiency of reservoirs on biogenic elements and weakens the ‘intercept’ effect, which leads to an increase in the concentration of dissolved phosphorus in downstream water bodies and increases the risk of eutrophication.
Key words：Wujiang River Basin; cascade reservoir; nitrogen and phosphorus forms; nitrogen and phosphorus activation; interception effect
EARTH AND ENVIRONMENT Vol.50, No.6, Tot No.350, 2022, Page 821
