Glaciers, snow, and rain: Water source influences invertebrate community structure and secondary production across a hydrologically diverse subarctic landscape

The melting cryosphere adds heterogeneity to the abiotic and biotic characteristics of many high latitude and montane rivers. However, climate change threatens the cryosphere's persistence in many regions. While existing research has explored the impacts of cryospheric loss on the diversity and structure of freshwater communities, implications for functional traits of communities, such as production of aquatic invertebrates, remain unresolved. Here, we quantified aquatic invertebrate community structure and secondary production in southeast Alaska (USA) streams that represent a meltwater to non-meltwater gradient, including streams fed primarily by: (1) glacier-melt, (2) snowmelt, (3) rainfall, and (4) a combination of these sources. We found alpha diversity was highest in the snow-fed stream and lowest in the glacier-fed stream. Annual secondary production was also lowest in the glacier-fed stream (0.56 g ash-free dry mass m-2), but 2-5 times higher in the other stream types primarily due to greater production of shared taxa that were found in all streams. However, despite low invertebrate diversity and productivity, the glacier-fed stream hosted distinct species assemblages associated with unique cycles of stream flow, water temperature, turbidity, and nutrient concentrations, which contributed to higher beta diversity between streams. Our findings suggest that the loss of glacier-melt contributions to rivers may result in increased freshwater invertebrate production but reduced beta diversity, which could have implications for community stability and the capacity of landscapes to support higher-level consumers, including fishes.

Automated summary

The melting cryosphere contributes to the heterogeneity of high latitude and montane rivers, but climate change poses a threat to its persistence. This study explores the effects of cryospheric loss on the diversity, structure, and functional traits of aquatic invertebrate communities in southeast Alaska streams.