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Marine derived nutrients delivered by large runs of returning salmon are thought to subsidize the in situ food resources that support juvenile salmon. In the Pacific Northwest, USA, salmon have declined to <10% of their historical abundance, with subsequent declines of marine derived nutrients once provided by large salmon runs. We explored whether low densities (<0.001 spawners/m2) of naturally spawning Chinook Salmon (Oncorhynchus tshawytscha) can affect ecosystem metabolism. We measured gross primary production (GPP) and ecosystem respiration (ER) continuously before, during, and after salmon spawning. We compared downstream reaches with low densities of spawning salmon to upstream reaches with fewer or no spawners...
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Managers make decisions regarding if and how to remove dams in spite of uncertainty surrounding physical and ecological responses, and stakeholders often raise concerns about certain negative effects, regardless of whether or not these concerns are warranted at a particular site. We used a dam-removal science database supplemented with other information sources to explore seven frequently-raised concerns, herein Common Management Concerns (CMCs). We investigate the occurrence of these concerns and the contributing biophysical controls. The CMCs addressed are: degree and rate of reservoir sediment erosion, excessive channel incision upstream of reservoirs, downstream sediment aggradation, elevated downstream turbidity,...
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Salmon that spawn and rear in Southeast Alaska watersheds are critically important to the region’s economic vitality and cultural identity. An estimated 90% of rural households in Southeast Alaska use salmon. Environmental changes that compromise the ability of these streams to support salmon could have dramatic consequences for the region. In particular, there is concern that climate change could undermine the capacity of the region’s streams to support productive fisheries. As a result, regional stakeholders are interested in identifying some of the potential impacts of climate change on watersheds that support abundant salmon. These stakeholders include federal and state agencies (U.S. Fish and Wildlife Service,...
Categories: Project;
Types: Map Service,
OGC WFS Layer,
OGC WMS Layer,
OGC WMS Service;
Tags: 2019,
Alaska,
Alaska CASC,
CASC,
Fish, All tags...
Fish,
Projects by Region,
Rivers, Streams and Lakes,
Rivers, Streams and Lakes,
Water, Coasts and Ice,
Water, Coasts and Ice,
Wildlife and Plants,
Wildlife and Plants, Fewer tags
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One of the desired outcomes of dam decommissioning and removal is the recovery of aquatic and riparian ecosystems. To investigate this common objective, we synthesized information from empirical studies and ecological theory into conceptual models that depict key physical and biological links driving ecological responses to removing dams. We define models for three distinct spatial domains: upstream of the former reservoir, within the reservoir, and downstream of the removed dam. Emerging from these models are response trajectories that clarify potential pathways of ecological transitions in each domain. We illustrate that the responses are controlled by multiple causal pathways and feedback loops among physical...
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Abstract (from Global Change Biology): Mountain watersheds often contain a mosaic of glacier-, snow-, and rain-fed streams that have distinct hydrologic, temperature, and biogeochemical regimes. However, as glaciers diminish and precipitation shifts from snow to rain, the physical and chemical characteristics that make glacial or snowmelt streams distinct from rain-fed streams will fade. Among the unforeseen consequences of this hydrologic homogenization could be the loss of unique food webs that sustain aquatic consumers. To explore the impacts of a melting cryosphere on stream food webs, we parameterized an aquatic food web model with empirical physicochemical data from glacier-, snow-, and rain-fed streams in...
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