象山港水体的磷酸盐及其对赤潮的潜在影响

The behavior of phosphate in the Xiangshan Bay and its potential impact on harmful algal blooms

根据2012年5月和2017年10月在象山港海域的调查结果,研究了象山港磷酸盐的来源、分布和消耗。磷酸盐浓度在两次的调查中均呈现由港顶向湾口逐渐降低的趋势,说明港顶区有较高浓度磷酸盐的输入,可能主要来自生活污水和海水养殖。磷酸盐、硝酸盐和盐度在象山港外湾的分布特征说明长江和钱塘江是外湾水体磷酸盐的一个重要来源;此外,磷酸盐、硝酸盐和盐度在牛鼻山水道和佛渡水道的差异分布说明,陆地径流可能经由佛渡水道向象山港贡献了一部分的磷酸盐。内湾水体的磷酸盐分布受控于内外湾水体混合和浮游植物的同化作用,磷酸盐在水体停留时间较长的内湾发生了明显的消耗,相比于保守混合模型的估算值,磷酸盐在象山港内湾中的净消耗比例在2012年5月和2017年10月分别约为20%和9%。2017年秋季观测到的磷酸盐浓度[(1.88±0.31)μmol/L]与2002-2005年在同季节观测到的结果相比增加超过了50%,N/P值下降明显,这一变化可能会导致象山港内引发藻华的藻类种群发生变化,同时也可能会引发更为严重的赤潮。

The estuarine distributions of salinity and nutrients(ammonium,nitrite,nitrate,and phosphate)measured in May 2012 and October 2017 were used to study the sources and assimilation of phosphate and the processes that control phosphate distributions within the Xiangshan Bay.In the upper bay,the highest phosphate concentrations observed during both surveys indicates a significant source of phosphate in this area,which was likely from the domestic sewage or/and mariculture.In the lower bay,the distributions of salinity,nitrate and phosphate suggest that phosphate in this area was likely from the Changjiang River and Qiantangjiang River.In addition,the different distribution patterns of nitrate and phosphate in the Fodu and Niubishan channels indicate a local input of phosphate.In the upper bay,phosphate distributions were controlled mainly by the mixing of waters from the upper bay and the lower bay and phytoplankton assimilation.Significant phosphate consumption was observed in the upper bay.In May 2012 and October 2017,phosphate was removed by^20%and^9%,respectively,in the upper bay compared to the calculated mixing line.The phosphate concentration has been found to increase by more than 50%compared to that in the same season of 2002 to 2005,and N/P ratio decreased significantly,which would result in variation of algal bloom species and occurrence of more serious harmful algal bloom.