永定河怀来段水体富营养化评价

Evaluation of eutrophication of water body in Huailai section of Yongding River

为了解海河水系水污染防治重点区域永定河怀来段污染特征,于2016年11月—2017年10月进行了为期一年的监测。选择6个采样点的6项监测指标,阐述河流氮、磷的时空变化特征,并采用氮磷比和对数型幂函数普适指数公式法分析水体氮、磷营养盐结构时空变化规律,评估水体富营养化程度,解析富营养化风险。结果表明:永定河怀来段水体污染较为严重,其中TN浓度超过《国家环境保护标准"十三五"发展规划》中地表水环境功能区划分Ⅲ类水体浓度限值的13.25倍,有机氨(ON)和NO-3-N为TN的主要存在形式;TP浓度均值为0.64 mg/L;各指标具备农业面源污染特征。水体中氮、磷时空分布特征明显:在时间尺度上,水体中氮、磷浓度呈现季节性变化规律;在空间尺度上,水体中氮、磷分布特征相似。永定河怀来段氮磷比年均值为32.78,水体浮游植物总体处于磷限制状态。平水期表现出磷为限制性营养元素,枯水期、丰水期氮磷比适合藻类大量的生长繁殖。永定河怀来段水体时空变化大多处在富营养化阶段,水体富营养化评价综合指数(EI)枯水期最大,为228.11;丰水期最小,为213.06;平水期居中,为218.30。永定河怀来段河流动力学过程良好,河流流态具有连续性,河流干流流速为0.43~1.45 m/s,远大于水华爆发的临界流量,干流大面积蓝藻水华现象的风险较低。

In order to understand the pollution characteristics of the Huailai section of the Yongding River, which is the key water pollution prevention and control area of the Haihe river system, the water quality monitoring was performed for a period of 1 years from November 2016 to October 2017. Six sampling points with 6 monitoring indicators were selected to expound the temporal and spatial variation characteristics of nitrogen and phosphorus in the river. The N/P ratio and the universal index formula using logarithmic power function were used to analyze the temporal and spatial variations of nutrient structure of nitrogen and phosphorus in water, assess the degree of eutrophication, and analyze the eutrophication risk. The results show that the water pollution in the Huailai section of the Yongding River is comparatively serious. TN is 13. 25 times over the Class Ⅲ concentration limit of the surface water environment function area. The ON and NO-3-N are the main forms of TN. The mean value of TP is 0. 64 mg/L, and each index has the characteristics of agricultural non-point source pollution. The temporal and spatial distribution of nitrogen and phosphorus in the water body is obvious. On the time scale, the concentration of nitrogen and phosphorus in the water body shows seasonal variation, and on the spatial scale, the distribution of nitrogen and phosphorus in the water body is similar. The average N/P ratio of the river section is 32. 78, and thephytoplankton is overall in the state of phosphorus limitation. During the average water period, phosphorus is the limiting nutrient element, and the N/P ratio in the dry and flood periods is suitable for the growth and reproduction of algae. The temporal and spatial variation of water body in the Huailai section of the Yongding River is mostly in the  eutrophication＇ stage. The maximum EI value is 228. 11 in dry season and the lowest is 213. 06 in flood season, while that in average water period is 218. 30. The fluvial process of the river section is good, and the flow pattern is continuous. The flow velocity of the main stream is 0. 43 ～ 1. 45 m/s, which is much larger than that for the algal bloom. Therefore, the risk of cyanobacteria blooms in the main stream is low.