Abstract
We developed an integrated hydrologic model of the upper Nushagak and Kvichak watersheds in the Bristol Bay region of southwestern Alaska, a region under substantial development pressure from large-scale copper mining. We incorporated climate change scenarios into this model to evaluate how hydrologic regimes and stream temperatures might change in a future climate, and to summarize indicators of hydrologic alteration that are relevant to salmon habitat ecology and life history. Model simulations project substantial changes in mean winter flow, peak flow dates, and water temperature by 2100. In particular, we find that annual hydrographs will no longer be dominated by a single spring thaw event, but will instead be characterized by numerous high flow events throughout the winter. Stream temperatures increase in all future scenarios, although these temperature increases are moderated relative to air temperatures by cool baseflow inputs during the summer months. Projected changes to flow and stream temperature could influence salmon through alterations in the suitability of spawning gravels, changes in the duration of incubation, increased growth during juvenile stages, and increased exposure to chronic and acute temperature stress. These climate-modulated changes represent a shifting baseline in salmon habitat quality and quantity in the future, and an important consideration to adequately assess the types and magnitude of risks associated with proposed large-scale mining in the region.
Highlights
The Bristol Bay region of southwestern Alaska supports one of the world’s largest wild salmon fisheries, supplying over 50% of wild sockeye salmon catches worldwide [1]
Ongoing debate about the future of this region has focused on the potential impacts of mining on the fishery, recently culminating in a draft ruling by the U.S Environmental Protection Agency that would limit mining in the Bristol Bay region [3]
The integration of hydrologic modeling results with the Indicators of Hydrologic Alteration (IHA) approach provides a framework for understanding climate change impacts on habitat quality that is both quantitative and spatially explicit, and can help to inform risks from other stressors including mining. While this model was developed for the Bristol Bay region, the modeling framework we describe could be applied in other settings where climate-modulated changes in habitat quality need to be quantified
Summary
The Bristol Bay region of southwestern Alaska supports one of the world’s largest wild salmon fisheries, supplying over 50% of wild sockeye salmon catches worldwide [1]. The relatively low relief and complex glacial deposits have created a hydrologic system in which groundwater and surface water are closely linked: precipitation and stream water infiltrate into the coarse gravel in the upper reaches of the watershed, returning to the rivers at points downstream [3,15]. This groundwater input moderates stream temperatures throughout the year, provides a steady baseflow to the rivers through the relatively dry winter and summer months, and maintains open water reaches in winter when the majority of the landscape is frozen [3,15]
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