磷在农田溪流中的动态变化

Spatial Phosphorus Retention in an Agricultural Headwater Stream

磷是水体富营养化的限制因子 ,河流系统是农业非点源污染物的主要运移通道 ,污染物在河流中的持留控制着污染物向受纳水体的输出 .本次研究对象是巢湖流域一个长约 1 8km的农田源头溪流六岔河 ,河流由 4个渠道型、1个水塘型和 3个河口型断面构成 ,长度分别为 1 3km、0 1 5km和 0 36km .在河流上设置 9个监测点研究总磷、磷酸盐和悬浮物在六岔河中的持留空间特征 ,评价人为严重干扰下的农田溪流在农业非点源污染物运移中的生态功能 .结果表明 :总磷、磷酸盐、悬浮物在溪流中的持留和释放受溪流的渠道型、水塘型和河口型断面控制 ,水塘型和河口型断面是污染物持留的主要区域 ,总磷、磷酸盐和悬浮物在水塘型、河口型断面内的持留量分别占溪流持留量的 5 8%、77%和 5 8% ;污染物在降雨 径流过程中的持留是溪流持留的主要部分 ,总磷、磷酸盐和悬浮物的持留分别占溪流持留量的 96 %、98%和 93% ;渠道型断面是溪流最主要的内在污染源 ,总磷、磷酸盐和悬浮物的释放分别占溪流释放量的 93%、99%和 94 % ;养分和悬浮物在渠道型断面中具有不同的持留特性 ,而位于水塘前的渠道型断面在基流和降雨 径流过程中均能有效地持留污染物 .

The spatial dynamics of phosphorus and suspended solids were investigated for two years in a 1.8 km agricultural headwater stream, located by Chaohu Lake, southeastern China. The stream form was greatly modified by human activities. The stream could be divided into 4 channelized reaches (1.3 km), a pond reach (0.15 km) and 3 estuary reaches (0.36 km). It was found that the retention of total phosphorus (TP), phosphate and total suspended solids (TSS) predominantly occurred in the pond reach and estuary reaches. TP, phosphate and TSS retained in the pond and estuary reaches accounted for more than 50% of those retained in whole stream. The retention mostly happened in the precipitation-runoff events and it was 10 to 27 times than that in baseflow. The results showed that channelized reaches were the most important source for pollutant release under either runoff or baseflow conditions, and it accounted for more than 90% of whole stream release. There was a high spatial variation of nutrient dynamics in different channelized reaches. The channelized reach directly discharging into the pond did always retain nutrients and TSS under base flow and runoff, whereas the other channelized reaches performed differently in different hydrological conditions. Stream forms, hydrological conditions, and nutrients characteristics controlled the high spatial variation of the nutrients and TSS in the stream, while the human practices would accelerate these spatial patterns.