STREAM TEMPERATURE INCREASES AND LAND USE IN A FORESTED OREGON WATERSHED¹

Abstract

The Salmon Creek Watershed drains 325 km2 of forested terrain in the Cascade Mountains of western Oregon. Over a 30–year period (from 1955 to 1984) average daily maximum and minimum stream temperatures, calculated from the 10 warmest days of each year, have risen 6°C and 2°C, respectively. In contrast, a small decrease in maximum air temperatures was found over the same period. Regression analysis indicated a highly significant (p < 0.01) relationship between a cumulative index of forest harvesting and maximum stream temperatures. Maximum temperatures also tended to increase for several years following major peak flow events. The interaction between harvest activity (logging and road construction), changing forest and riparian management practices and the occurrence of natural hydrologic events (peak flows and associated mass soil movements) tend to obscure specific cause‐and‐effect relationships regarding long‐term changes in maximum stream temperature.

Effects of riparian grazing and channelisation on streams in Southland, New Zealand. 2. Benthic invertebrates

“…The higher daily maximum water temperatures during summer and the greater diurnal temperature variability observed in the more open, grazed or channelised reaches (Fig. 2), are consistent with other observations of the effects of shade removal (e.g., Graynoth 1979;Skovlin 1984;Beschta & Taylor 1988). The autumn temperature measurements at RP and RU2 (Fig.…”

“…• have a major influence on the amount and type of energy input to the stream (Fisher & Likens 1973;Minshall 1978;Cummins 1974Cummins ,1986); • reduce temperature fluctuations by providing shade (Graynoth 1979;Skovlin 1984;Beschta & Taylor 1988); • promote stream bank and channel stability (Smith 1976;Elmore & Beschta 1987); • maintain water quality by reducing nutrient and sediment inputs (Cooke & Cooper 1988;Smith 1989); and • provide habitat for birds, adult stages of aquatic insects, and cover for fish (McDowall 1980;Wescheetal. 1987).…”

The influence of riparian woodland on the spatial and temporal variability of stream water temperatures in an upland salmon stream

“…8 provides a conceptual model of the main controls on spatial temperature variability operating at the catchment and reach-scale, together with a brief description of their influences on stream temperature. Catchment topography, channel incision, channel orientation (Webb and Zhang, 1997;Arscott et al, 2001;Poole and Berman, 2001) and riparian vegetation (Beschta and Taylor, 1988;Sinokrot and Stefan, 1993;Stott and Marks, 2000;Isaak and Hubert, 2001) all affect stream surface shading. This shading moderates high stream temperatures by reducing incident short-wave radiation.…”

What causes cooling water temperature gradients in a forested stream reach?

“…The density of the semi-natural riparian forest canopy was a second-order control on net energy flux. On days with clear skies, net energy gain was greatest where trees were absent or the canopy was sparse and least where the canopy was densest (Leach and Moore, 2010), owing to the canopy providing shading from solar radiation (Beschta and Taylor, 1988;Macdonald et al, 2003;Malcolm et al, 2004;Moore et al, 2005;Imholt et al, 2010Imholt et al, , 2012. Contrasting meteorological conditions, and thus net energy gain conditions, within the study period drove differences in the timing and magnitude of water temperature dynamics and gradients observed within the reach.…”