Release fluxes estimate of phosphorus in a urban shallow lake:Lake Xuanwu, Nanjing

Abstract

以南京玄武湖为研究对象,通过静态条件下5℃、10℃、15℃、25℃、35℃玄武湖底泥释磷室内实验计算玄武湖释磷速率,得出底泥释磷速率与上覆水温度的关系,进而算出玄武湖北湖每年磷释放量为0.815 t,东南湖每年磷释放量为 1.013t,西南湖每年磷释放量为0.266t.玄武湖每年底泥释磷总量为2.094 t.根据费克定理,建立了间隙水扩散模型,利用模型计算玄武湖北湖每年磷释放量为0.799 t,东南湖每年磷释放量为0.983 t,西南湖每年磷释放量为0.232 t.玄武湖每年底泥释磷总量为2.014t.在不考虑外源污染的情况下,由底泥磷释放造成的内源污染使玄武湖磷浓度年均维持在 0.101 mg/L,超过湖泊富营养化磷标准,因此,在切断外源污染的情况下应采取措施治理磷的内源污染.;The phycial and chemical characteristics of the surface sediment of Lake Xuanwu, Nanjing were investi-gated in April-September, 2004 and April-July, 2005. After simulating the phosphorus release in laboratory fromthe surface sediments samples under static conditions under 5, 10, 15,25,35℃, respectively, the release fluxes ofphosphorus across the water-sediment interface in different sub-lakes of Lake Xuanxu were calculated, i. e.0.815 t/a, 1.013 t/a and 0.266 t/a for northern, southeastern and southwestern sub-lakes, separately. The totalrelease flux for Lake Xuanwu could be 2. 094 t/a. Based on the Fick's Law, a pore water dispersion model wasbuild up, and the phosphorus release for the whole Lake Xuan could be calculated as 2. 014 t/a to the water, with0.799 t/a, 0. 983 t/a and 0. 232 t/a for northern, southeastern and southwestern sub-lakes. Such a net releasefrom lake sediment for phosphorus makes an appropriate 0, 101 m/L in lake water-a value exceeding threshold forlake eutrophication-on the year run when excluding the diffusion pollution to the lake. As a result, additional meas-ures should be taken to reduce internal phosphorus pollution even when external pollutants are under control.