Evaluation of temporal water quality change(2008-2014) and the cause analysis in the upper-reach lakes of Lake Nansi, Shandong Province

基于南四湖上级湖6个监测点2008-2014年42个奇数月份的水质资料,选取溶解氧、化学需氧量(COD)、高锰酸盐指数(COD_Mn)、五日生化需氧量(BOD₅)、氨氮、总磷和氟化物作为水质评价的指标.对水质指标的归一化方法进行了改进,采用主成分分析法对6个监测点的水质综合状况进行评价,根据得出的各月综合得分序列分析水质变化趋势.与2000-2007年南四湖上级湖的水质综合状况进行比较,2008-2014年水质明显变好.评价结果表明,同一监测点的水质在不同时间点上有明显变化,同一时间序列不同监测点的水质状况也有不同变化.此外,分析得出南四湖上级湖的主要水质影响指标为COD、COD_Mn和BOD₅.结合评价结果,分析水质变化原因,入湖河流水质状况和湖区底泥是其重要影响因素.;Based on water quality information from 6 stations in the upper-reach lakes of Lake Nansi which was sampled from a total of 42 odd months during 2008 and 2014, choosing dissolved oxygen, COD, COD_Mn, BOD₅, ammonia nitrogen, total phosphorus and fluoride as the indexes of water quality evaluation. The water quality index normalization was used to improve the method, and the principal component analysis was used to evaluate water quality comprehensively for the data from the six monitoring stations. According to the obtained comprehensive score of the monthly sequence, the trend of water quality status was analyzed. Compared with the general condition of water quality during 2000 and 2007, it is found that water quality was significantly better during 2008 and 2014. The evaluation results showed that the water quality at any monitoring station had obvious changes at different time, and had different changes at any time sequence on different water quality monitoring stations. Besides, the main influenced indicators of water quality in the upper-reach lakes of Lake Nansi were COD, COD_Mn and BOD₅. According to the evaluation results and the analyzed changes in the water quality, we found that the river quality into the lake and lake sediments were the two important factors influencing on the water quality.