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Rinella D.J.,University of Alaska Fairbanks | Rinella D.J.,University of Alaska Anchorage | Rinella D.J.,University of Alaska Anchorage | Wipfli M.S.,University of Alaska Fairbanks | And 3 more authors.

Spawning salmon deliver annual pulses of marine-derived nutrients (MDN) to riverine ecosystems around the Pacific Rim, leading to increased growth and condition in aquatic and riparian biota. The influence of pulsed resources may last for extended periods of time when recipient food webs have effective storage mechanisms, yet few studies have tracked the seasonal persistence of MDN. With this as our goal, we sampled stream water chemistry and selected stream and riparian biota spring through fall at 18 stations (in six watersheds) that vary widely in spawner abundance and at nine stations (in three watersheds) where salmon runs were blocked by waterfalls. We then developed regression models that related dissolved nutrient concentrations and biochemical measures of MDN assimilation to localized spawner density across these 27 stations. Stream water ammonium-N and orthophosphate-P concentrations increased with spawner density during the summer salmon runs, but responses did not persist into the following fall. The effect of spawner density on δ15N in generalist macroinvertebrates and three independent MDN metrics (δ15N, δ34S, and ω3:ω6 fatty acids) in juvenile Dolly Varden (Salvelinus malma) was positive and similar during each season, indicating that MDN levels in biota increased with spawner abundance and were maintained for at least nine months after inputs. Delta 15N in a riparian plant, horsetail (Equisetum fluviatile), and scraper macroinvertebrates did not vary with spawner density in any season, suggesting a lack of MDN assimilation by these lower trophic levels. Our results demonstrate the ready assimilation of MDN by generalist consumers and the persistence of this pulsed subsidy in these organisms through the winter and into the next growing season. © 2013 Rinella et al. Source

Callahan M.K.,University of South Florida | Rains M.C.,University of South Florida | Bellino J.C.,University of South Florida | Bellino J.C.,U.S. Geological Survey | And 4 more authors.
Journal of the American Water Resources Association

Headwater streams are the most numerous in terms of both number and length in the conterminous United States and play important roles as spawning and rearing grounds for numerous species of anadromous fish. Stream temperature is a controlling variable for many physical, chemical, and biological processes and plays a critical role in the overall health and integrity of a stream. We investigated the controls on stream temperature in salmon-bearing headwater streams in two common hydrogeologic settings on the Kenai Peninsula, Alaska: (1) drainage-ways, which are low-gradient streams that flow through broad valleys; and (2) discharge-slopes, which are high gradient streams that flow through narrow valleys. We hypothesize local geomorphology strongly influences surface-water and groundwater interactions, which control streamflow at the network scale and stream temperatures at the reach scale. The results of this study showed significant differences in stream temperatures between the two hydrogeologic settings. Observed stream temperatures were higher in drainage-way sites than in discharge-slope sites, and showed strong correlations as a continuous function with the calculated topographic metric flow-weighted slope. Additionally, modeling results indicated the potential for groundwater discharge to moderate stream temperature is not equal between the two hydrogeologic settings, with groundwater having a greater moderating effect on stream temperature at the drainage-way sites. © 2014 American Water Resources Association. Source

Walker C.M.,Kachemak Bay National Estuarine Research Reserve | King R.S.,Baylor University | Whigham D.F.,Smithsonian Environmental Research Center | Baird S.J.,Kachemak Bay National Estuarine Research Reserve

Headwater streams are typically closely connected with the surrounding watershed landscape, making them sensitive to local watershed conditions. Headwater streams of the Kenai Lowlands in Alaska provide important rearing habitat for juvenile salmon and other biota, and understanding the connections between surrounding landscapes and stream conditions will improve management capabilities. We conducted field evaluations of 30 headwater stream sites on the Kenai Lowlands of Alaska, stratified across watersheds and wetland types, and combined these results with GIS analysis of 12 landscape metrics. Flow-weighted slope (FWS), which is an indicator of the combined influence of percentage cover and topographic position of wetlands, was the best predictor of stream chemistry. Our results revealed distinct differences in water chemistry among headwaters that are largely driven by topography and the amount of wetland in the upstream drainage area. Streams with a high FWS (higher gradient, low wetness) had higher dissolved oxygen and dissolved inorganic nitrogen (mostly nitrate-N), and lower temperatures. Lower FWS streams (low gradient, high wetness) had higher dissolved organic carbon, temperatures, and ammonium and lower dissolved oxygen, all of which were consistent with strong connections between wetlands in watershed and headwater streams. The flow-weighted slope metric is a landscape feature that can be easily derived from GIS, and can be used as a spatially explicit approach for predicting landscape connections to headwater streams on the Kenai Lowlands. © Society of Wetland Scientists 2012. Source

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