Factors affecting the summer maximum stream temperature of small streams in northern Japan
2010
Nagasaka, A., Hokkaido. Forestry Research Inst., Bibai (Japan) | Sugiyama, S.
Riparian forests influence aquatic ecosystems. Maintaining cool water by shading, in particular, is a key role for conserving habitat for juvenile masu salmon (Oncorhynchus masou). Empirical models were developed from using water temperature data obtained at 68 points of 12 watersheds in Hokkaido, for estimating summer maximum water temperature (SMTP). Generalized linear model (GLM) chose the following four variables to explain the variation in SMTP: open channel length (OCL), altitude-adjusted August maximum air temperature, presence or absence of forested tributary, and watershed geology. We examined the relationship between estimated SMTP and OCL by a simple regression model. Difference in geology was reflected in the intercept (SMTP in OCL= 0); the value of volcanic rock watersheds showed 2degC lower than that of sedimentary rock watersheds. On the other hand, sensitivity of fluctuation in SMTP by removal of riparian forests was reflected in the coefficient of regression; the value of volcanic rock watersheds showed larger than that of sedimentary rock watersheds. In both geological types, the coefficients of regression became smaller when forested tributaries join at the upstream of a given observed point. In this model, when OCL reaches 4km (without forested tributary) or 6km (with forested tributary), SMTP is estimated to be 24degC, which is the upper limit of thermal tolerance for active feeding and growth of juvenile masu salmon.
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