Tropical rivers across the world are experiencing rapid degradation and loss of fish species due to flow regulation, pollution, and other anthropogenic pressures. Knowledge of how flow alterations at different scales affect tropical fish diversity remains limited, especially in terms of how resulting changes in water chemistry affect fish communities. We investigated fish guild composition and responses of guild richness to water chemistry in 120 river segments with and without local‐scale water removals and pollution. This included two regulated subbasins (with flow regulation by barrages and large‐scale water diversions) and two nonregulated subbasins (flows not regulated by these barriers) in India's Western Ghats. Using multivariate ordination and regression models, we identified covariates related to water chemistry and environmental characteristics that explained differences in fish species composition and species richness of three water column position‐based fish guilds in the study area. At the subbasin scale, effects of water chemistry were stronger for individual river segments. At the segment scale, no differences in water chemistry were found between segments with and without water removals or pollution in both regulated and nonregulated subbasins. Guild‐wise species richness, especially of surface‐dwelling fishes, was positively correlated with water temperature and total dissolved solids across regulated and nonregulated subbasins. In regulated subbasins, total alkalinity was positively correlated with species richness of bottom‐dwelling and mid‐column‐dwelling fishes. Landscape‐scale flow alterations and degree of flow regulation by river barriers significantly influenced fish composition and species richness over and above local water withdrawal or pollution. River restoration at both the local (segment) and landscape (basin) scales is crucial for fish conservation. To sustain fish guild diversity, maintenance of ecological flow regimes downstream of barriers needs to receive priority over mitigating local disturbances in regulated river catchments of the Western Ghats.

中文翻译：

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水化学对印度西高止山脉调节河与非调节河鱼类协会物种丰富度影响的多尺度研究：恢复的意义

由于流量调节，污染和其他人为压力，世界各地的热带河流正经历鱼类的快速退化和丧失。关于不同尺度的流量变化如何影响热带鱼类多样性的知识仍然很有限，特别是在水化学结果变化如何影响鱼类群落方面。我们调查了120个有或没有局部水去除和污染的河段的鱼类行会组成和行会丰富度对水化学的响应。其中包括印度西高止山脉的两个受调节的子流域（通过拦河坝和大规模引水进行流量调节）和两个非受调节的子流域（不受这些屏障调节的流量）。使用多元排序和回归模型，我们确定了与水化学和环境特征相关的协变量，这些协变量解释了研究区域中三个以水柱位置为基础的鱼行会的鱼类物种组成和物种丰富度的差异。在子流域范围内，水化学作用对单个河段的影响更大。在分段规模上，在调节和不调节子流域中，无论有无除水或污染的节段之间，在水化学上均未发现差异。在规范和非规范子盆地中，行会物种的丰富度，尤其是表层鱼类的丰富度与水温和总溶解固体呈正相关。在受监管的亚流域中，总碱度与底栖鱼类和中栖鱼类的物种丰富度呈正相关。除了局部取水或污染外，景观尺度的流量变化和河流屏障对流量的调节程度对鱼类的组成和物种丰富度也有很大影响。无论是在当地（区域）还是在景观（流域）尺度上的河流修复对于鱼类的保护都是至关重要的。为了维持鱼类协会的多样性，必须优先于维持屏障下游的生态流动状况，而不是减轻西高止山脉受管制河流集水区的局部干扰。