近10a廉州湾富营养化因子变化特征及其与赤潮演变的关系

The development of eutrophication and its impact on the evolution of red tide in the Lianzhou bay for recent ten years

利用2005~2015年广西廉州湾每年枯水期、丰水期和平水期共32个航次的监测数据,分析了营养盐等富营养化因子的变化特征,用富营养化指数评价该海域富营养化程度的演变,并探讨富营养化因子变化与浮游植物响应的关系。结果表明,近10a廉州湾的营养盐及COD最高浓度主要出现在丰水期,DIN和PO_4-P枯水期明显高于平水期,SiO_3-Si和COD在枯水期和平水期浓度相近。PO_4-P年际间变化幅度较大并呈较明显上升趋势,SiO_3-Si呈下降趋势,DIN和COD年均变化总体不大。在枯水期PO_4-P、DIN和COD均呈现出上升趋势。径流输入对海湾的DIN和COD变化起主导作用,生活排污、水产养殖对PO_4-P的分布和变化有重要的作用。年均富营养化指数范围为0.10~1.85,富营养化程度主要由DIN、PO_4-P决定。海湾营养盐结构总体处于P限制状态,近10aN/P和Si/P比例呈显著下降趋势,P限制在一定程度减轻。廉州湾在高DIN和高SiO_3-Si值的条件下,PO_4-P输入量的徒增及其导致营养盐比例的改变是诱发赤潮的最重要环境因素。近年来营养盐输入增加,富营养化程度有所加重,P限制得到一定的缓解,海湾赤潮的生态风险加大。

A total of 32 research cruises were set to monitor the water quality parameters in the Lianzhou bay in dry,wet,and normal season between 2005 and 2015.We analyzed the changes of factors related to the eutrophication,and applied an index to show the development of eutrophication in this important bay.Finally,the relationship between the eutrophication index and the response of phytoplankton was discussed.Our results indicated that the nutrients and the maximum concentration of COD generally occurred in the wet season.The DIN and PO_4-P concentrations were higher in dry season than normal season,while the SiO_3-Si and COD concentrations were comparable between dry and normal season.The PO_4-P concentrations varied significantly in different years and exhibited an obvious increasing pattern.In contrast,SiO_3-Si concentrations decreased and there were not much changes in DIN and COD concentrations.The PO_4-P、DIN and COD concentration generally increased in dry season.It was found that the input of runoff may have a major impact on the changes of DIN and COD levels,while the sewage discharge and aquaculture industry may remarkably affect the PO_4-P distribution.The annual average eutrophication index ranged between 0.10~1.85,which was mainly attributed to the changes of DIN、PO_4-P.Our results indicated that P was limited in the Lianzhou bay.The ratio of N/P and Si/P kept decreasing in the recent 10 years,indicating the abatement of P limitation.Under the high levels of DIN and SiO_3-Si,the sharp input of PO_4-P had changed the nutrient structure,which was the major factor triggering red tides.With increasing input of nutrients into the bay,the limitation of P keep relieving and the eutrophication is becoming serious,which will eventually lead to higher ecological risk.