哑铃湾网箱养殖对底层水环境的影响研究

Environmental Impact of Cage Culture on Bottom Water in Yaling Bay

采用现场调查的方法,于2002年4月—2003年1月对哑铃湾2个不同养殖年限的网箱养殖区、对照海区和网箱周围海区底层水化学进行了四季采样和结果分析。哑铃湾网箱养殖使底层海水中TO C、SS、有机污染物和溶解态氮磷营养盐都有不同程度的增加,春、夏、秋3季D O有不同程度的下降,SS、C O D M n、N H4+、D IN、D IP的增加相对更显著,而对pH值、盐度、水温和冬季D O的影响较小;在水质状况上,D O、B O D5受影响最大,其次是D IP;养殖期较长的网箱区底层海水在春、秋2季已达到富营养化水平。短期网箱养殖对底层海水的水质影响较小,长期养殖影响较明显。A N O V A分析结果显示养殖期较短的网箱邻近海区底层海水营养盐含量与对照点无明显的差异,网箱养殖对底层海水的影响范围主要局限于网箱下。养殖过程中应提高饵料的利用率、采取轮养或休养等措施,以利于海水网箱养殖业的可持续发展。

Yaling Bay is a main marine cage culture area in Guang Dong Province, China. Red tide has often been appearing in this region in recent years, due to eutrophication in the seawater. In order to find degree and extent of environmental impact on bottom water from cage culture in Yaling Bay, a field investigation was done from Apr. 2002 to Jan. 2003 in two different cage culture time stations, namely, (S3, more than five years, and S6, more than twenty years), one control (S7), and S3 cage neighbor area (S1, S2, S4, S5). Water depth at samplingsites was 6～8 m. We have found that concentrations of total organic carbon, suspend substance, organic pollutants, dissolved nitrogen and phosphorus in bottom water of cage culture area were increased, the concentrations <IMG SRC='IMAGE/05300000.JPG' HEIGHT=11 WIDTH=18>of dissolved oxygen were decreased in Spring, Summer and Autumn. The increases of suspend substance, chemical oxygen deplete, ,dissolved nitrogen and phosphorus were relatively significant, but the impacts on pH, dissolved oxygen in winter, water temperature and salinity were little. In comparison with the Marine Water Standard of China, chemical oxygen and biological oxygen demands were the main pollutants with regard to water quality impacted by cage culture, and dissolved phosphorus was the next. The bottom water under a long time cage in Yaling Bay was eutrophic in spring and autumn. The ANOVA results demonstrated that the difference of nutrients in bottom water was little between a short time cage neighbor area and the control. The impact of a short time cage culture on bottom water quality was little, while very markedly for a long time cage culture. The extent of environmental impact on bottom water was limited under the culture cage. Thus it was important for the cage culture to improve the using rate of feed, alternate culture and fallow to reduce the amounts of organic pollutants and nutrient substance into water.