Development of a benthic macroinvertebrate-based multimetric index to quantify riverbed substrate condition in Swedish streams

Human activities have degraded riverbed substrate structure via reduced heterogeneity of substrate particle sizes and increased fine sediment loadings. Despite increasing recognition of the importance of substrate quality in river ecosystems, our ability to assess substrate condition effects on biodiversity and functioning of river ecosystems is at present inadequate resulting in discrepancies between the needs of conservation, restoration, and mitigation of running waters, and water management practice. Several macroinvertebrate-based metrics are currently used to assess the impacts of degraded riverbed substrate structure. However, few metrics confer a direct relationship to the functions that substrates provide independent of interacting and potentially confounding factors (e.g. current velocity, excess nutrients and pesticides) or, based solely on presence-absence of taxa so that they may be implemented regardless of the identification method. Data on riverbed substrates and benthic macroinvertebrates was extracted from several databases. Using stream data on riverbed substrates and macroinvertebrates, we developed a macroinvertebrate-based multimetric index (MMI) for riverbed substrate condition (LISSA) to assess impacts of and recovery from substrate degradation using information on measures of traits. The dataset was explored for correlation between measures of traits to riverbed substrate condition. A substrate quality gradient (SQG) was constructed by combining four components of substrate quality in an index where decreasing substrate quality is defined as an increasing percentage of fine sediment and sand and decreasing substrate diversity and evenness. Significantly correlated candidate metrics were chosen using forward stepwise linear regression models against SQG. Five metrics were included in LISSA: one trait state of aquatic stages (egg), two trait states of reproduction (isolated eggs, cemented + clutches, cemented or fixed and clutches, free + asexual reproduction), one trait state of locomotion and substrate relation (crawler + temporarily attached) and the locomotion trait state (% burrowing/boring). LISSA is a promising metric for stream macroinvertebrate assessments of riverbed substrate condition and monitoring impacts and recovery across Sweden and potentially elsewhere.