Abstract
Glacier retreat is a worldwide phenomenon with important consequences for the hydrological cycle and downstream ecosystem structure and functioning. To determine the effects of glacier retreat on aquatic communities, we conducted a 4-year flow manipulation in a tropical glacier-fed stream. Compared with an adjacent reference stream, meltwater flow reduction induces significant changes in benthic fauna community composition in less than 2 weeks. Also, both algal and herbivore biomass significantly increase in the manipulated stream as a response to flow reduction. After the flow reduction ceased, the system requires 14–16 months to return to its pre-perturbation state. These results are supported by a multi-stream survey of sites varying in glacial influence, showing an abrupt increase in algal and herbivore biomass below 11% glacier cover in the catchment. This study shows that flow reduction strongly affects glacier-fed stream biota, prefiguring profound ecological effects of ongoing glacier retreat on aquatic systems.
Highlights
Glacier retreat is a worldwide phenomenon with important consequences for the hydrological cycle and downstream ecosystem structure and functioning
To determine whether our experimental results would be corroborated across a spatial gradient in glacial cover, we analyse the spatial variability in benthic algae and fauna across 33 stream sites, in the same study area
Corroboration could help predict future temporal ecological variability under reduction in glacial influence[13].We show that meltwater flow reduction induces changes in the benthic community, characterized by an increase in biomass of benthic algae and macroinvertebrate herbivores
Summary
Glacier retreat is a worldwide phenomenon with important consequences for the hydrological cycle and downstream ecosystem structure and functioning. A wholeecosystem manipulation of meltwater reduction, simulating the effect of glacier retreat on glacier-fed streams, in which both disturbance effects and return times to pre-disturbance conditions are determined, should provide insights into the ecological response to forthcoming glacial meltwater alteration Such an ecosystem manipulation has never been performed in alpine rivers. The stream manipulation consists of three time intervals: (1) establishment of baseline conditions under unaltered stream flow (B1 year); (2) diversion of water flow, inducing a water flow reduction in the downstream reach (B1 year; the upper reach was kept undisturbed); and (3) reset to initial flow conditions to evaluate post-drought recovery trajectories (B2 years) This experimental design allows us to assess the response of benthic algal and faunal communities to flow reduction, and evaluate the ecosystem resilience, defined as the capacity of the benthic communities to return to their initial configuration after flow disturbance cease[12]. We discuss the ecosystem capacity to recover from meltwater flow reduction and emphasize the importance of understanding how glacier retreat will affect whole alpine freshwater ecosystems in a rapidly changing world
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