南苕溪支流锦溪水质时空变化特征分析

Analysis of the spatial-temporal variation of water quality in Jinxi River, a tributary of Southern Tiaoxi River

综合运用灰色聚类法、综合污染指数法、等级聚类法就南苕溪支流锦溪近年水质时空变化特征进行分析。结果表明,锦溪入青山水库断面水质2005—2009年逐年改善,2007年后达到灰色聚类等级Ⅲ类水质要求;2009年秋季至2010年夏季期间秋、冬两季的污染程度高于春、夏季节;枯水期综合污染指数最高,但TN、TP污染分指数在丰水期最高,表明污染源中面源污染已占相当比例。空间变化方面从玲珑桥到江桥锦溪水质的综合污染指数不断提升,到江桥时达到极值13.25,锦溪末端三眼桥断面水质较江桥断面有所改善;SPSS空间聚类分析可分为轻污染区(从玲珑桥到冬韵桥)、重污染区(从群利桥到江桥)和中度污染区(从江桥到三眼桥)。锦溪上游农业区对河水中的COD、TN和TP的贡献率分别为66%、54%和49%,农业面源污染已成为制约锦溪水质改善的主要因素。

Grey clustering,comprehensive pollution index（CPI） and hierarchical clustering methods were employed to investigate the recent spatial-temporal variation of water quality in Jinxi River,a tributary of Southern Tiaoxi River.The results show that the water quality at the estuary section,where Jinxi River flows into Qingshan Reservoir,was gradually improved from 2005 to 2009 and could reach the Grade Ⅲ of the water standards since 2007 in the grey clustering analysis.The CPIs in autumn and winter were higher than those in spring and summer during the studied period from the autumn of 2009 to the summer of 2010.The highest CPI was observed in dry season while the highest sub-indexes of TN and TP appeared in the wet season,implying that non-point source pollution had already accounted for a significant portion of the overall pollution.In terms of spatial variation the CPI of Jinxi River aggravated gradually from Linglong Bridge to Jiang Bridge where it reached a maximal value of 13.25,and then mitigated to some extent till Sanyan Bridge.According to the hierarchical clustering analysis,Jinxi River could be divided into three segments,i.e.,the light-pollution（from Linglong Bridge to Dongyun Bridge）,heavy-pollution（from Qunli Bridge to Jiang Bridge） and moderate-pollution segment（from Jiang Bridge to Sanyan Bridge）.The COD,TN and TP from the upstream of Jinxi River contributed to 65%,54% and 49% of their total loadings,respectively.Therefore,the agricultural non-point source has become the restrictive factor for water quality improvement in Jinxi River.