Do functional traits of chironomid assemblages respond more readily to eutrophication than taxonomic composition in Chinese floodplain lakes?

Functional trait-based measures can reflect local environmental conditions and are claimed as promising approaches for environmental monitoring and assessment programs. The chironomid larvae are a diverse and ecologically important group of benthic macroinvertebrates and have a set of functional traits that can be used to assess environmental quality of freshwater ecosystems. However, little is known regarding the relationships between chironomid functional structure and human disturbances, especially at a fine taxonomic resolution. Here, we compared the responses of functional traits and traditional taxonomic measures of chironomid assemblages to eutrophication in the Yangtze floodplain lakes. We found that functional composition showed higher sensitivity and robustness in discriminating the extents of eutrophication than taxonomic composition. Specifically, about half of functional categories examined significantly differed among the lake groups, while only two taxonomical measures (the abundance of Tanytarsini and Polypedilum) are suitable for assessing environmental quality of floodplain lakes. The macrophytic lakes showed higher abundance of scrapers, the small body size and oligotrphic individuals. Whereas the algal lakes were associated with high abundance of eutrophic/hypertrophic chironomids and those with haemoglobin. Chironomid assemblages showed significant differences among four lake groups for both trait-based and taxonomy-based variations, but with larger differences for trait-based groups. The distance-based redundancy analysis (dbRDA) indicated that taxonomic and functional assemblage structures were explained primarily by similar water quality variables (chlorophyll alpha, transparency and TN), but more functional variation (24.6%) was explained by environmental factors than taxonomic variation (10.9%) in chironomid assemblages. Our results indicated that chironomid trait-based approaches were more sensitive and robust to water quality gradients than taxonomy-based approaches. Therefore, we argued that the chironomid functional traits deserve considerations for biomonitoring programs in the lakes we studied and other freshwater lakes and aquatic ecosystems.

基于功能性状的测量方法能够反映当地环境条件，并被认为是环境监测和评估项目中有前景的方法。摇蚊幼虫是底栖大型无脊椎动物中一个多样且具有重要生态意义的类群，具有一系列可用于评估淡水生态系统环境质量的功能性状。然而，关于摇蚊功能结构与人类干扰之间的关系，尤其是在精细分类分辨率下的关系，人们知之甚少。在此，我们比较了摇蚊群落的功能性状和传统分类学方法对长江泛滥平原湖泊富营养化的响应。我们发现，在区分富营养化程度方面，功能组成比分类组成表现出更高的敏感性和稳健性。具体而言，在所检测的功能类别中，约有一半在不同湖泊组之间存在显著差异，而只有两种分类学方法（长跗摇蚊族和多足摇蚊属的丰度）适用于评估泛滥平原湖泊的环境质量。水生植物丰富的湖泊中刮食者、小型个体以及贫营养个体的丰度较高。而藻类湖泊则与富营养/超富营养摇蚊以及含血红蛋白的摇蚊丰度较高有关。基于性状和基于分类的摇蚊群落变化在四个湖泊组之间均存在显著差异，但基于性状的组间差异更大。基于距离的冗余分析（dbRDA）表明，分类和功能群落结构主要由相似的水质变量（叶绿素α、透明度和总氮）解释，但在摇蚊群落中，环境因素对功能变异的解释率（24.6%）高于对分类变异的解释率（10.9%）。我们的研究结果表明，基于摇蚊性状的方法比基于分类的方法对水质梯度更为敏感和稳健。因此，我们认为在我们所研究的湖泊以及其他淡水湖泊和水生生态系统的生物监测项目中，摇蚊的功能性状值得考虑。