Influence of water source on alpine stream community structure: linking morphological and metabarcoding approaches

Alpine streams support unique biodiversity because of their isolation in the river network and harsh environmental conditions. Variation in water sources to alpine streams are an important driver of benthic community structure; however, studies with long-term data on stream abiotic characteristics and biological communities remain relatively rare. This is especially true for very high elevations where effects of climate change will be most pronounced. We used a combination of morphological and metabarcoding approaches to characterize benthic communities at nine locations within a high elevation catchment (~ 3200 to 3700 m) in the Southern Rocky Mountains, USA. Survey sites included ephemeral and permanent streams dominated by glacier meltwater, snowmelt, lake outflows, and mixed-source waters. Discharge, water temperature, conductivity, pH, total dissolved nitrogen, and total dissolved phosphorus differed between water source types. Environmental differences between source water types reflected their position in the catchment, the influence of subsurface ice meltwater on nitrogen and ions, and the biological activity and stabilizing effects of lakes. In total, we detected 130 macroinvertebrate taxa (52 via morphology and 99 via metabarcoding). Macroinvertebrate composition was more strongly correlated with stream permanence and conductivity than with water temperature or nutrient availability. Glacial and snowmelt-fed streams were dominated by Chironomidae (especially Diamesinae) and Oligochaeta, with increasing richness of Plecoptera, Ephemeroptera, and Trichoptera at the lake-outlet and mixed-source sites. Lake outlets showed the highest beta diversity, with unique communities dominated by various filter feeders (Simuliidae and Sphaeriidae). Alpha diversity was similar at the glacial, snowmelt, and lake outlet sites, but increased at the downstream mixed-source sites which had proportionally more non-dipteran taxa. Our results support the idea that distinct source waters have unique environmental conditions, leading to variation in their community structure. These results provide motivation for conservation efforts that protect a diversity of alpine stream types within and between catchments.