The Multitrophic Effects of Climate Change and Glacier Retreat in Mountain Rivers

Abstract

Climate change is driving the thinning and retreat of many glaciers globally. Reductions of ice-melt inputs to mountain rivers are changing their physicochemical characteristics and, in turn, aquatic communities. Glacier-fed rivers can serve as model systems for investigations of climate-change effects on ecosystems because of their strong atmospheric–cryospheric links, high biodiversity of multiple taxonomic groups, and significant conservation interest concerning endemic species. From a synthesis of existing knowledge, we develop a new conceptual understanding of how reducing glacier cover affects organisms spanning multiple trophic groups. Although the response of macroinvertebrates to glacier retreat has been well described, we show that there remains a relative paucity of information for biofilm, microinvertebrate, and vertebrate taxa. Enhanced understanding of whole river food webs will improve the prediction of river-ecosystem responses to deglaciation while offering the potential to identify and protect a wider range of sensitive and threatened species.

Patterns in Microbial Assemblages Exported From the Meltwater of Arctic and Sub-Arctic Glaciers

“…One of the most conspicuous of the anticipated effects will be the altered production of meltwater (e.g., Milner et al, 2017;Huss and Hock, 2018), along with associated changes in hydrologic pathways (e.g., meltwater generated further inland and at greater elevations, intensifying connectivity between supra-and subglacial habitats), which ultimately have the greatest relevance for determining the quantity and character of solute and particulate fluxes. Yet, while the physical and chemical changes accompanying deglaciation may be comparatively straightforward to predict, the biological consequences for glacial ecosystems are far less intuitive (Fell et al, 2017;Hotaling et al, 2017a), and generalizations are inherently difficult to make due to differences in glacier size, elevation, bedrock, thermal regime, vegetation, and precipitation patterns (e.g., Carnahan et al, 2019). By studying microbial assemblages exported by glacier meltwater streams, it may be possible to investigate microbial processes taking place in the overall glacial system, and assess changes in structure and export over time.…”

Ecological Stoichiometry of the Mountain Cryosphere

“…In general, glacier-fed streams and lakes are characterized by considerable sediment input from upstream grinding of bedrock, cold temperatures (e.g., < 10 • even in summer), and dynamic water levels. Climate change is accelerating glacier retreat (Masiokas et al, 2008;Zemp et al, 2015) and will alter downstream ecosystems from biogeochemical cycling to elemental flow through food webs Slemmons and Saros, 2012;Fell et al, 2017 ; Figures 4, 5).…”

Ecosystem shifts in Alpine streams under glacier retreat and rock glacier thaw: A review

“…Macroinvertebrates represent the most studied biotic component of alpine streams worldwide (Fell et al, 2017). Originally, this research field developed following the review papers by Ward (1994) on alpine stream habitat classification, and by Milner and Petts (1994) on the characterisation of glacial rivers.…”

“…While McGregor et al (1995) focus on the effects of hydropower generation and glacier loss specifically in the Alps, most reviews have a global perspective as they focus on the relationship between habitat changes and biotic shifts associated to glacier shrinkage at high latitudes and altitudes. Some focus on single ecosystem drivers (i.e., the importance of the ice melt: Slemmons et al, 2013); others provide different frameworks of analysis (i.e., hydroecology: Milner et al, 2009; the "multitrophic" approach: Fell et al, 2017); or focus on the organism-based research by emphasizing methods and approaches (i.e., Hotaling et al, 2017). Milner et al (2017) provide a wider context by considering the implications of glacier loss to physical and chemical fluxes, biodiversity, and ecosystem services to lowland areas along the river continuum.…”