土地利用驱动下洱海流域入湖河流水质时空分布规律

为更好地保护湖泊流域水环境,以洱海流域三大主要入湖水系为研究对象,采用空间分析、统计分析与模型相结合的方法,对2014年入湖河流水质对洱海水质的影响及土地利用驱动下的水质变化特征进行分析。结果显示:2014年三大主要入湖水系COD、TN、TP、NH4+-N均超过Ⅱ类水功能要求,TN、TP是主要污染因子;入湖河流水质存在时空差异,整体水质雨季较差,氮磷重污染区域为波罗江水系,苍山十八溪水系次之,北三江水系氮磷浓度相对低,但季节性差异显著。入湖河流与湖泊水质时空关联密切,雨季两者关联更强;空间上除TN外,入湖河流与湖泊污染分布规律基本一致。全流域尺度下COD与植被面积百分比呈显著负相关(P<0.05);TN、TP与建设用地面积百分比极显著正相关(P<0.01),与其他用地面积百分比呈显著负相关(P<0.05)。而由于三大入湖水系COD、TP、NH4+-N存在显著的空间异质性,采用地理加权回归模型进一步分析发现,COD与植被面积百分比、TP与建设用地面积百分比的回归关系随着空间位置变化有较大差异,前者相关关系由正相关转为负相关,拟合程度由南向北递增,后者在整个流域均呈正相关,拟合程度在西部苍山十八溪水系和北部入湖区域较高。因此建议流域污染治理应以雨季面源污染控制为主,重点加强波罗江水系面源污染综合治理,以及苍山十八溪水系城镇地表径流管控,同时应优化北三江植被等生态用地对径流的截蓄净化功能。

Spatial-temporal variation of inflow river water quality under land use effect

This study analyzes the water quality variation of inflow rivers directly affecting lake. Focusing on the three major river systems of the Lake Erhai basin, the effects of inflow rivers on the water quality of Erhai Lake and its change trend under land-use changes in 2014 were studied with spatial analysis method, statistical analysis method and model. Results indicated that the chemical-oxygen demand(COD), total nitrogen(TN), total phosphorus(TP), and ammonia nitrogen of inflow rivers in 2014 exceeded class Ⅱ levels;the main pollutants were the TN and TP. Water quality indexes of inflow rivers showed significantly spatial-temporal variation among the three river systems. The overall river quality was poorer in the rainy season than in the dry season. The contamination of the TN and TP in the Boluojiang river system was the most serious, followed by the Cangshanshibaxi river system. In spite of the low concentrations of TN and TP, significant temporal variation occurred in the Beisanjiang river system. The spatiotemporal association of the river quality between the river and Erhai Lake was significant, especially in the rainy season. The pollutant concentration, excluding TN, in Erhai Lake was higher in the areas with the most polluted inflow rivers. The COD and vegetation area percentage had a significant negative correlation(P<0.05). Furthermore,the river TN and TP had significant positive correlations with the construction land area percentage(P<0.01)as well as a significant negative correlation with other land use in the basin scale(P<0.05). COD, TP and ammonia nitrogen of inflow rivers showed significant spatial autocorrelation. A geographical weighted regression(GWR)model showed that there were significant spatial variations in the regression relationship between the vegetation area proportion and COD. This changed to a negative relationship and the fitting degree increased from the south to the north. The regression relationship of the area proportion of construction land and TP also showed a spatial difference but remained positive throughout the entire basin. The highest fitting degree of the two occurred in the west Cangshanshibaxi basin and north inflowing area. Suggestions regarding pollution regulation in Erhai Lake basin were made to focus on nonpoint pollution control in the rainy season, strengthen the comprehensive treatment of nonpoint pollution in the Boluojiang river system, and control the construction land surface flow in the Cangshanshibaxi river system. Furthermore, more attention should be paid to optimize the ecological land functions of interception and purification on runoff in the Beisanjiang river system.