Glacier shrinkage driving global changes in downstream systems

Abstract

Glaciers cover ∼10% of the Earth's land surface, but they are shrinking rapidly across most parts of the world, leading to cascading impacts on downstream systems. Glaciers impart unique footprints on river flow at times when other water sources are low. Changes in river hydrology and morphology caused by climate-induced glacier loss are projected to be the greatest of any hydrological system, with major implications for riverine and near-shore marine environments. Here, we synthesize current evidence of how glacier shrinkage will alter hydrological regimes, sediment transport, and biogeochemical and contaminant fluxes from rivers to oceans. This will profoundly influence the natural environment, including many facets of biodiversity, and the ecosystem services that glacier-fed rivers provide to humans, particularly provision of water for agriculture, hydropower, and consumption. We conclude that human society must plan adaptation and mitigation measures for the full breadth of impacts in all affected regions caused by glacier shrinkage.

Alpine Glacier Shrinkage Drives Shift in Dissolved Organic Carbon Export From Quasi‐Chemostasis to Transport Limitation

“…DOC yield during autumn and winter contributed on average 8 ± 5% and 9 ± 8% to the annual DOC yield from glacierized and non‐glacierized catchments. We suggest that this is attributable to the DOC poor groundwater predominantly feeding high‐alpine streams during these periods (e.g., Milner et al, ).…”

When the going gets tough, the tough get going: The enigma of survival strategies in harsh glacial stream environments

“…Alpine headwaters are of importance for downstream aquatic networks by providing multiple ecosystem services, including water, nutrients, organic matter or invertebrate prey for higher trophic levels (Milner et al., ). The heterogeneity of alpine streams is also vital for the biodiversity of invertebrates (Finn, Bonada, Múrria, & Hughes, ) and bacteria (Besemer et al., ).…”

“…The heterogeneity of alpine streams is also vital for the biodiversity of invertebrates (Finn, Bonada, Múrria, & Hughes, ) and bacteria (Besemer et al., ). However, glaciers continue to retreat in alpine environments almost worldwide as a consequence of human‐induced warming (IPCC, ), leading to alterations of the physical conditions in alpine glacier‐fed stream ecosystems (e.g., altered water temperature, suspended sediment concentration and electrical conductivity) (Milner, Brown, & Hannah, ; Milner et al., ). These modification of freshwater habitats seem to occur accelerated and more obvious in the alpine life zone compared to lower altitudes and will increase over time as glaciers retreat (Zemp, Hoelzle, & Haeberli, ).…”

Incision and aggradation in proglacial rivers: Post‐Little Ice Age long‐profile adjustments of Southern Iceland outwash plains

“…The primary hydrological impact of glaciers on downstream river systems is to modulate the timing and seasonality of hydrological fluxes (Röthlisberger & Lang, ). A shift to deglacial conditions leads to marked changes in the seasonality of river flow (e.g., a shift of the hydrograph to an earlier peak flow in spring months) and the amount of annual glacier run‐off (Bliss, Hock, & Radić, ; Milner et al, ). Current trends in annual glacial run‐off differ among world regions and glacier hypsometry, but there is a consensus on the typical sequence of meltwalter changes during catchment deglaciation (Bliss et al, ): At the beginning of deglaciation, when the glacier is still sufficiently voluminous, the glacial meltwater tends to increase for a period lasting several decades, before decreasing when the ice stock runs out (Braun, Weber, & Shulz, ; Huss, Farinotti, Bauder, & Funk, ; Jansson, Hock, & Schneider, ; Marren, ).…”