Hydroecological response of river systems to shrinking glaciers

Aquatic ecosystems in high latitude and altitude environments are strongly influenced by cryospheric and hydrological processes due to links between atmospheric forcing, snowpack/glacier mass-balance, river discharge, physico-chemistry and biota. In the current phase of global climate warming, many glaciers are shrinking. Loss of snow and ice-masses will alter spatial and temporal dynamics in bulk basin runoff with important changes in the relative contributions of snowmelt, glaciermelt and groundwater to stream flow. Accordingly, altered water source contributions will be accompanied by changes to fluvial, solute, sediment and thermal regimes and, thus, channel stability and habitat. The projected reduction in sediment load, warmer water temperature and increased channel stability will drive significant shifts in the floral and faunal composition of glacier-fed rivers. This paper hypothesizes a general increase in the richness and production of micro-organisms, algae, macroinvertebrates and fish as glacier hydrological influence shrinks under a warmer climate. With reduced glacial influence, macroinvertebrate species trait diversity will increase with more organisms possessing larger body size, less specialized body shape and lower adult mobility. In larger river systems, potential reduction of meltwater inputs will have a significant influence on off-channel habitats (e.g. side-channels and sloughs) that depend on glacial runoff to sustain habitat availability and connectivity, particularly for fish. Some species such as cold stenothermic taxa (including some endemic macroinvertebrates) may be vulnerable to extinction and therefore gamma (regional) diversity will be reduced. These sensitive macroinvertebrate taxa may be important biological indicators of environmental change in glacierized river basins. Moreover, high climatic sensitivity and low human perturbation make glacially influenced river basins early indicator systems for identifying hydrological and ecological responses to climate change/variability. It is concluded that glacier shrinkage and associated changes in runoff amount and timing, water source contributions and physico-chemical habitat will be a major driver of the future biodiversity of stream communities in cold environments. Research imperatives and future directions are proposed for investigation of glacier-fed river hydroecology. Copyright © 2008 John Wiley & Sons, Ltd.