长三角城郊樟溪流域水体氮磷分布特征及其影响因素

快速城镇化和人类活动导致城郊流域水体营养盐污染和富营养化问题加重,识别氮、磷污染对流域水质的管控具有重要的意义。本研究选取长三角典型城郊地区宁波樟溪流域,在流域内根据土地利用类型、地形特征等布设样点,于2016年连续4个季度进行水样采集,研究樟溪流域河流水体氮、磷的含量及形态,及氮、磷在该流域的时空分布特征,并对其来源和影响因素进行分析。研究结果表明,流域内氮、磷分布具有较大的空间差异性,其中NH+4-N(n.d.~1.375 mg·L~(-1))、TN-N(0.570~11.363 mg·L~(-1))、DIP(n.d.~0.169 mg·L~(-1))、TP(0.010~1.908 mg·L~(-1))。在子流域空间分布上,人类活动频度越高的区域氮、磷的浓度越高,各采样点水体不同形态氮含量和磷含量具有明显的季节变化规律:春季和秋季的含量要高于夏季和冬季。本研究选取采样点距城镇距离、距源头距离以及土地利用类型所占采样点缓冲区的比例来表征人类活动的影响,结果表明,TN和TP含量与距城镇距离呈显著负相关关系,表明城镇化水平对流域氮、磷污染的重要影响。另外,典型城郊流域河流水体氮、磷污染主要受土地利用类型的影响,其含量与农业和城镇用地呈显著正相关关系(P0.01),其含量随人类活动频度的增加而升高。

Distribution of Nitrogen and Phosphorus and Its Influencing Factors in Zhangxi Watershed of a Peri-urban Area in the Yangtze River Delta

Rapid urbanization combined with intensified human activities lead to serious eutrophication due to extra nitrogen and phosphorus loss in peri-urban areas. Thus, identifying nitrogen and phosphorus distribution is significant for controlling and managing water quality in those areas. In this study, the spatial and temporal distribution of nitrogen and phosphorus as well as the influencing factors were determined for Zhangxi watershed which located at a typical peri-urban area of Ningbo in the Yangtze River Delta. Water samples for nitrogen and phosphorus were collected in four consecutive quarters in 2016 based on land use and topographic features. The results showed that the concentration of nitrogen and phosphorus varied at large ranges, NH₄⁺-N (0.001-1.375 mg L^-1), TN-N (0.570-11.363 mg L^-1), DIP (0.008-0.169 mg L^-1) and TP (0.010-1.908 mg L^-1), across the watershed. Nitrogen and phosphorus also varied across different seasons. The concentrations are higher in spring and autumn than in summer and winter. Impact of human activities on water quality distribution were quantified with three indices, including distance to town, distance to source and land use. The results showed that the concentration of TN and TP was negatively correlated with the distance from town, indicating that urbanization level was important for nitrogen and phosphorus loss in the watershed. In addition, the concentration of nitrogen and phosphorus in peri-urban areas was positively correlated with agricultural and urban land-use (P <0.01). This indicated that the concentrations of nitrogen and phosphorus in watershed were also strongly influenced by human activities.