Hydroecological response of river systems to shrinking glaciers

Abstract

Abstract: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 offchannel 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.

Alpine aquatic ecosystem conservation policy in a changing climate

“…More specifically, the loss of a number of endemic, glacier stream specialists is likely to occur , particularly in basins fed by small glaciers such as the Taillon and the Mutt. This will lead to a reduction in basin and regional scale diversity (Jacobsen et al, 2012) despite a predicted increase in alpha (site) diversity as water source contributions change (Milner et al, 2009). This highlights the need for careful consideration regarding how biodiversity is measured and interpreted in the context of conservation, particularly in alpine environments where between site diversity and range restricted, endemic taxa are important components of regional biodiversity.…”

“…As benthic assemblages in high headwater alpine streams appear strongly deterministic, especially in highly glacial reaches where environmental filtering is particularly strong (Castella et al, 2001), habitat template changes can be used to predict how biodiversity and ecosystem functioning will respond (Fig.4). Changes in glacier cover/meltwater contribution can be used as a surrogate for the suite of environmental parameters which dictate macroinvertebrate community structure (Milner et al, 2009). …”

“…A similar, dense monitoring network exist for glaciers and has been utilised for identifying climate signals (Haeberli et al, 2007). However, while alpine river networks have been proposed as ideal indicators of hydroecological responses to climate change (Milner et al, 2009), an integrated network of monitoring sites with common protocols has yet to be established. In autumn 2013, this will be addressed by a European Science Foundation initiative entitled GLACier-fed rivers and climate change; current knowledge and future NETwork of monitoring sites (GLAC-HYDROECO-NET).…”

Altitudinal patterns of diversity and functional traits of metabolically active microorganisms in stream biofilms

“…DOC encompasses a large pool of molecules, which depending on their source (i.e., autochthonous versus allochthonous), can vary in chemical composition and bioavailability (e.g., Sun et al, 1997;Jaffé et al, 2012). Allochthonous constituents typically dominate the DOC pool, with the exception of alpine and arid catchments devoid of major terrestrial vegetation (e.g., Milner et al, 2009). In alpine streams, autochthonous deliveries from algal production (and mosses) characterise DOC in streams above the treeline, whereas terrestrial deliveries increasingly add to the carbon pool further downstream (Battin et al, 2004;Milner et al, 2009;Zah and Uehlinger, 2001).…”

“…Allochthonous constituents typically dominate the DOC pool, with the exception of alpine and arid catchments devoid of major terrestrial vegetation (e.g., Milner et al, 2009). In alpine streams, autochthonous deliveries from algal production (and mosses) characterise DOC in streams above the treeline, whereas terrestrial deliveries increasingly add to the carbon pool further downstream (Battin et al, 2004;Milner et al, 2009;Zah and Uehlinger, 2001). Several studies have reported DOC source and composition as potential drivers of microbial community structure and functioning in streams (e.g., Kaplan and Bott, 1989;Sun et al, 1997;Peter et al, 2011) and in lakes (e.g., Crump et al, 2003;Judd et al, 2006).…”