太湖底泥—水界面总溶解态磷的Fick扩散释放通量研究

Fick diffusion release flux study of dissolved total phosphorus at the sediment-water interface of Lake Taihu

太湖蓝藻暴发与水体中总溶解态磷(TDP)密切相关,而底泥是否向水中释放TDP是一个重要的科学问题。由于太湖底泥间隙水与上覆水的TDP之间存在3~5倍的浓度差,因此会存在TDP的Fick扩散过程。针对Fick扩散计算仍然未能精确地考虑含有机磷时的扩散系数等问题,本文在考虑有机磷的影响、孔隙率、温度等变化的条件下进行了监测和计算。基于全湖30个采样点的现场调查数据,使用只有无机磷扩散系数20%左右的扩散系数计算太湖TDP年Fick扩散量约为127.8 t;磷的Fick扩散量与上覆水磷浓度相同,具有西北高、东南低的特点。敏感性分析表明:相对于温度变化,有机磷的占比和孔隙率的取值对于Fick扩散量的计算值有更大的影响。

Algal blooms in Lake Taihu are intricately linked to total dissolved phosphorus(TDP),and the critical question of whether sediment releases TDP into the water column demands attention.Given the 3-5 times concentration disparity between TDP in the sediment and the overlying water of Lake Taihu,Fick diffusion emerges as a recurrent TDP release process.Notably,the calculation of Fick release has hitherto struggled to precisely account for the diffusion coefficient when organic phosphorus is present.This paper addressed this limitation by conducting monitoring and calculations,considering the influence of organic phosphorus,porosity,temperature,and other variables.Based on field investigation data from 30 sampling sites across the entire lake,the annual Fick diffusion of TDP in Lake Taihu was estimated,and it was approximately 127.8 tons per year.This calculation employed a diffusion coefficient only about 20%of that for inorganic phosphorus.The Fick release of phosphorus exhibited spatial characteristics,mirroring the phosphorus concentration in the overlaying water,with higher concentrations in the northwest and lower concentrations in the southeast.Sensitivity analysis underscored the greater impact of organic phosphorus percentage and porosity values on the calculated Fick diffusion compared to temperature changes.