溪流生态系统次生盐化的生态学研究进展

溪流次生盐化是人类活动干扰导致可溶性盐向水体迁移从而造成盐浓度异常增高的现象,由于干扰类型(如农业生产、河岸带植被破坏、采矿废水与污水排放等)的不同,溪流次生盐化呈现出溶解性无机离子组成复杂、盐浓度间歇性波动等特点. 已有研究发现:①溪流次生盐化会造成藻类、底栖动物和鱼类的群落结构产生变化,主要包括物种丰度、生物量、生物多样性、功能摄食类群等方面；②高盐环境对非耐盐物种产生胁迫从而降低其出现频率,敏感底栖动物会增加漂移行为以选择低盐环境,而敏感鱼类则消失；③耐盐物种应对高盐胁迫有不同策略,如卵胎生的产卵方式以减少在高盐环境中的时间,或拥有较强的渗透调节能力维持体内渗透平衡. 主要问题:①影响水生生物的可能是单一离子又或是离子组合,不同盐化水体所增加的离子类型及浓度都有很大差别,而要逐一探明单一离子及离子组合的影响需要巨大的工作量；②野外研究常以电导率或ρ(TDS)(TDS为总溶解性固体)表征盐化程度,而电导率或ρ(TDS)会改变有机污染物、重金属的生物毒性,也会与营养盐、悬浮物等因子产生交互作用,难以确定盐化对水生生物的独立影响. 因此,今后需关注全球变暖背景下次生盐化与营养盐、重金属的耦合作用,注重我国本土水生生物的耐受性及其适应调节机制,并重视基于野外调查与室内试验两类不同数据所获得水生生物适盐范围的对比验证；同时为满足水生生物健康保护,应加强对溪流次生盐化有指示作用的水质监测指标的开发及阈值的制订. 

A Brief Review of Ecological Studies on Secondary Salinization in Stream Ecosystems

Secondary salinization in streams is defined as increasing salinity due to the migration and accumulation of exogenous soluble ions. It is generally caused by anthropogenic disturbances, such as agricultural cultivation, degradation of vegetation in a riparian zone, discharge of mining and sewage wastewater. Secondary salinization in streams can be characterized by complexity of ionic composition and the intermittent fluctuation of salt ions. Previous studies have found that secondary salinization in streams affects algae, macroinvertebrate and fish communities structure, i.e. species richness, biomass, diversity and functional feeding groups. Intolerant species stressed by a hyper-salinity environment always have a lower occurrence frequency, e.g., sensitive macroinvertebrates transfer to a hypo-salinity environment through frequent drift behaviors. Similarly, sensitive fishes disappear from the salt-stressed environments. Tolerant species live in hyper-salinity environments by means of their different strategies, such as the spawning ritual of ovoviviparous which helps to shorten the time in salt-stressed environments, as well the stronger ability of osmotic adjustment which helps to maintain the inner osmotic balance. Current studies have to face some challenges. First, the single ion or mixture of ions shows different effects on aquatic life. Meanwhile, the dominant ion types and concentrations vary with different salinization water bodies; verifying the effects of a single ion or mixture of ions, one by one, is a huge workload. Second, conductivity and ρ(TDS) are used to estimate the degree of salinization in general, and the influence on biological toxicity of organic contaminants or heavy metals and interactions with nutrients or suspended solids, which makes it difficult to determine the independent effect of salinization. Therefore, more efforts should be devoted to illustrating the combined effects of secondary salinization with nutrients and metals against the background of global warming, focusing on the tolerance characteristics of native aquatic organisms and their osmoregulation mechanisms, and validating the optimum salinity ranges of aquatic life obtained from field investigation with those obtained from laboratory tests. In order to protect the health of aquatic organisms, we should develop monitoring parameters which sensitively indicate stream salinization and derive their thresholds.