Fluxes and influencing factors of phosphorus release in sediments in northern lacustrine areas of Jiaxing City

In order to understand the effect of phosphorus release from sediment on water pollution, the diffusive gradients in thin-films technique (DGT) was introduced to clarify phosphorus fluxes and its influencing factors in sediments in Fen Lake, Liansidang Lake and Beiguandang Lake in northern lacustrine areas of Jiaxing City. The effect of phosphorus release from sediment on overlying water was evaluated. The results showed that concentrations of soluble available phosphorus (DGT-P)in sediment water interface (SWI) displayed various trend at three sampling sites and generally showed the following decreasing order: Liansidang Lake (0.735 mg∕L) > Beiguandang Lake (0.154 mg∕L) > Fen Lake (0.077 mg∕L). In terms of vertical distribution, the concentrations of DGT-P in the surface sediments of the three lakes were higher than that of overlying water. But the situation was different within the range of ±10 mm at the SWI; there was no obvious concentration gradient of DGT-P at the SWI of Fen Lake, indicating that the phosphorus release capacity of sediments to overlying water was weak, while that of Liansidang Lake presented an obvious concentration gradient and had a strong phosphorus release capacity, and that of Beiguandang Lake was between the two. From the perspective of the phosphorus release fluxes at the SWI, the phosphorus release flux of each lake sediment had a limited effect on the overlying water. Among them, the phosphorus release flux at the Liansidang Lake SWI was the highest (0.490 mg∕(m ²·d)), and its contribution to overlying water was also the highest (1.93%), which showed the source of phosphorus. The second was Beiguandang Lake, whose phosphorus release flux was 0.047 mg∕(m ²·d), and its contribution to overlying water was 0.24%. The phosphorus release flux at the SWI of Fen Lake was close to 0 and showed a phosphorus sink. Correlation analysis showed that the migration and transformation of phosphorus was significantly affected by the reduction and dissolution of iron oxides in SWI, meanwhile attention should also be paid to the influence of organic matter mineralization on phosphorus release in sediment.