阳澄湖网围养殖区水体营养盐的时空变化与水质评价

2008年5月至2009年5月在阳澄湖中湖网围养殖区采集上、下层水样进行水质检测，并采用营养状态指数法对养殖区营养状况进行综合评价。结果显示，（1）养殖区营养盐的分布存在明显的时空变化，除了硝酸盐以外，所测指标均表现为养殖季节高于非养殖季节，高密度养殖区高于低密度养殖区，底层水高于表层水，说明高密度养殖造成氮磷的大量沉积。（2）高密度养殖区呈重度富营养状态，低密度养殖区也达到中度富营养。（3）2008年5月与2009年5月同期的水质监测数据显示，单季养殖的湖泊水质变化不明显。本研究表明，短期养殖对水质影响较小，但长期养殖则影响明显。网围养殖区富营养化日趋严重，目前已接近重度富营养状态，且磷污染较氮污染严重。

The spatial and temporal changes of nutrients of net-pen aquaculture area in Yangcheng Lake and its water quality evaluation

Beginning in May 2006 and ending in May 2009, surface and bottom water samples were collected in net-pen culture area in the middle of Yangcheng Lake, and were analyzed for water quality. The trophic state index (TSI) values were calculated and adopted to comprehensively evaluate the trophic levels in the net-pen culture area. The results showed that 1) the nutrient concentrations in net-pen culture area exhibited obvious spatial and temporal variations, all the measured parameters, except for the concentration of NO3--N, were higher in culture period than in other periods, meanwhile, they were also higher in high-density culture area than in low-density area, and in bottom water than in surface water, which might reflect that massive nitrogen and phosphorus sediment formed due to high-density culture; 2) the trophic status increased to a high level in high-density culture area, and also increased to a moderate level in low-density area; and 3) water-quality monitoring data from the same period in May 2008 and in May 2009 indicated that no obvious change of water-quality in the lake was found in the single culture period. It suggested that short-term aquaculture had less effect on the water quality, while long-term aquaculture could bring up obvious effects. The eutrophication in net-pen culture area had become more and more serious, and the culture area was currently considered to attend nearly-severe eutrophic level, and phosphorus pollution posed more threat to the lake than nitrogen pollution did.