Development and validation of a macroinvertebrate-based biomonitoring tool to assess fine sediment impact in small mountain streams

Abstract Increased fine sedimentdeposition is recognised as one of the major causes of biological impairment of rivers and streams influencing all components of aquatic communities. Notably, stream macroinvertebrates are affected showing changes in abundance and community composition. This makes macroinvertebrates an attractive choice for biomonitoring fine sedimentstress. However, there are substantial knowledge gaps regarding the quantification of deposited fine sedimentand the identification of taxa sensitive to fine sedimentdeposition, which could serve as indicators. In this study, we developed a stream type-specific index based on the taxon-specific response of macroinvertebrates to deposited fine sedimentin small, coarse substrate-dominated mountain streams. We sampled fine sedimentat 73 sampling sites in Western Germany (Europe) in spring 2014 and 2015 using a sedimentremobilization technique. Macroinvertebrate taxalists originating from WFD monitoring surveys were available for all sites. We applied Threshold Indicator Taxa ANalysis (TITAN) on the fine sedimentmass of the sampling sites and the corresponding macroinvertebrate taxalists to identify indicator taxa, which were then used for index development. In total, TITAN identified 95 reliable indicator taxa, of which some taxa tolerated large amounts of fine sediment(e.g., Gammarus roeseliiand Tubificidae Gen. sp.), while others were found to be highly sensitive to increased fine sedimentmass (e.g., Elodes sp. and Limnius perrisi ). The newly developed index was tested on an independent data set and performed well in detecting fine sedimentstress (Spearman's r  = 0.63). Furthermore, the index was better related to the deposited fine sedimentmass as compared to other fine sedimentindices and standard metrics used for monitoring purposes under the Water Framework Directive(WFD). The diagnostic index can be a cost-effective biomonitoringtool for stream managers and can be used as a proxy for the impact of deposited fine sedimenton the reach scale.