Alder cover drives nitrogen availability and decomposition of grass litter in salmon-rearing headwater streams, Kenai Peninsula, Alaska.
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Shaftel, Rebecca S.
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Terrestrial sources of nitrogen (N), such as N fixed by alder, may be important for sustaining production in headwater streams that typically lack subsidies of nutrients from spawning salmon. High nutrient concentrations in streams increase litter decomposition and can offset the low nutrient quality of grass litter. Alder cover was compared to watershed physiographic variables as predictors of stream N and contrasted over the growing season among 25 headwater streams. Leaf packs of bluejoint grass were deployed for two months across a nutrient gradient of 6 headwater streams. Alder cover explained over 75 – 96% of the variance in stream N. Bluejoint breakdown rates were related to dissolved stream nutrient concentrations and litter quality. A diversity of macroinvertebrate consumers utilized bluejoint for habitat and food. Alder drives stream N concentrations and the breakdown rate of bluejoint, which is an important consumer resource during the summer months when deciduous litter inputs are low.