Quantifying the effect of hydraulic disturbances on sediment phosphate release is a key issue in the water quality assessment of lakes, especially for the shallow lakes which are susceptible to winds and waves. Here, we sampled the original sediment columns from 12 positions in the eastern, central, and western areas of the Chaohu Lake, a representative shallow lake in China, and observed phosphate release under three levels of hydraulic disturbances in the laboratory. When the disturbance was weak and the surface sediment of bottom mud moved individually (the Individual Motion Mode), sediment phosphate release rate was insigni cant (0.24 mg/m 2 /d). When the disturbance was medium and only a small percentage (<16%) of surface sediment started to move (the Small Motion Mode), phosphate release rate sharply increased to 4.81 mg/m 2 /d. When the disturbance was further strengthened and most (≥16%) of the surface sediment moved (the General Motion Mode), phosphate release rate was more than doubled (10.23 mg/m 2 /d). With the increase of hydraulic disturbance intensity, the variation range of phosphate release also became wider. Spatial distribution showed that the release rate varies the most in the western area, followed by the eastern and the central areas. By extrapolating the experimental results to the real scale, we found the phosphate release uxes would probably fall within a wide range between 203.43 kg/d to 7311.01kg/d under different levels of hydrodynamic disturbances with considerably affects phosphate release from shallow lakes. This study also has implications for the pollutant management in other shallow lakes.
Stability of nitrogen cycle is a key indicator to aquatic health. In recent years, water and sediment inflows to the Three Gorges Reservoir (TGR) have changed significantly. To reveal the effects of such dramatic hydrological changes on aquatic nitrogen cycle, this paper at first analyzed the changing trends of water and suspended sediment discharges of TGR based on dynamic harmonic regression, and found that the intra‐year distribution of water flow was significantly homogenized between flood and dry seasons, with the seasonal variations narrowed by 43.5%–69.9% during 2007–2016, while sediment concentration sharply dropped (the non‐periodic term decreased by 1.48%–2.07%/month). Modified with the effects of sediment concentration variations on nitrification/denitrification rates, the proposed numerical model surprisingly showed that ammonia nitrogen and total nitrogen concentrations in TGR were insensitive to either water flow homogenization or sediment reduction, implying relative stability of microbial community related to nitrogen cycle, which is a positive sign for aquatic health. However, N
2
emission varied more violently. The variation range of nitrogen gas (N
2
) emitted from TGR enlarged by 30% with the homogenization of water inflow from 2010 to 2016, while the annual total N
2
emission decreased by 7% due to the reduction of sediment concentration, indicating quick response and strong adaption of the microbial N
2
producing process to the environmental changes of TGR, which is beneficial for maintaining ecological functions related to nitrogen cycling. This work helps understanding nitrogen cycle of reservoirs experiencing dramatic changes in water and sediment inflows.
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