Factors influencing stream temperatures in small streams: substrate effects and a shading experiment

Abstract

The temperature of stream water is an important control of many in-stream processes. To better understand the processes and consequences of solar energy inputs to streams, stream temperature dynamics were examined before, during, and after experimental shading of a 150-m reach of a second-order stream in the Oregon Cascade Range. Maximum water temperatures declined significantly in the shaded reach, but minimum and mean temperatures were not modified. Heat budget calculations before shading show the dominance of solar energy as an influence of stream temperature. The influence of substrate type on stream temperature was examined separately where the water flowed first over bedrock and then through alluvial substrates. Maximum temperatures in the upstream bedrock reach were up to 8.6°C higher and 3.4°C lower than downstream in the alluvial reach. Better understanding of factors that influence not only maximum but minimum temperatures as well as diurnal temperature variation will highlight types of reaches in which stream temperature would be most responsive to changes in shading. Many apparent discrepancies in stream temperature literature can be explained by considering variation in the relative importance of different stream temperature drivers within and among streams and over time.Résumé : Dans les cours d'eau, la température de l'eau est un important facteur de contrôle de plusieurs processus internes. Afin de mieux comprendre les processus reliés à l'apport d'énergie solaire dans les cours d'eau et d'en éva-luer les conséquences, nous avons examiné la dynamique thermique avant, pendant et après une expérience dans laquelle nous avons ombragé expérimentalement une section de 150 m d'un ruisseau d'ordre deux dans la chaîne des monts Cascades en Oregon. Les températures maximales de l'eau ont décru significativement dans la section ombragée, mais les températures minimales et moyennes sont restées inchangées. Les calculs de bilans thermiques avant l'expérience ont montré que l'énergie solaire a une influence dominante sur la température du cours d'eau. L'effet du type de substrat sur la température du cours d'eau a pu être examiné séparément là où l'eau coule d'abord sur la roche-mère pour ensuite traverser des substrats alluviaux. Les températures maximales dans la section de roche-mère d'amont sont jusqu'à 8,6°C supérieures et 3,4°C inférieures à celles de la section alluviale d'aval. Une meilleure compréhension des facteurs qui influencent non seulement les températures maximales et minimales, mais aussi la variation journalière de la température, permettra d'identifier les sections dans lesquelles la température du cours d'eau est plus susceptible d'être affectée par les changements d'ombrage. Plusieurs contradictions apparentes dans la littéra-ture scientifique concernant la température des cours d'eau peuvent s'expliquer en considérant les variations dans le temps, ainsi que dans un même cours d'eau et d'un cours d'eau à un autre, de l'importance relative des différents facteurs qui régissent la températu...

Buffered, lagged, or cooled? Disentangling hyporheic influences on temperature cycles in stream channels

“…On the contrary, hyporheic exchange enhances temperature diversity in surface and subsurface habitats [Malard et al, 2001;Johnson, 2004;Schmidt et al, 2006], moderates both diel and annual temperature cycles, and therefore induces responses from biota including fish [Baxter and Hauer, 2000;Geist et al, 2002;Hanrahan, 2007] and aquatic macroinvertebrate communities [Olsen and Townsend, 2003;Brown et al, 2005]. We highlight the distinction between cooler cycles and buffered and lagged cycles simply to promote a more critical evaluation of the underlying dynamics driving hyporheic influences on channel water temperatures.…”

“…[5] Where the magnitude of hyporheic exchange is sufficient, channel water temperatures are both influenced by and affect hyporheic water temperatures [e.g., White et al, 1987;Evans et al, 1995;Constantz and Thomas, 1997;Evans and Petts, 1997;Arscott et al, 2001;Malard et al, 2001;Johnson, 2004;Fernald et al, 2006;Loheide and Gorelick, 2006]. In small streams, hyporheic discharge commonly affects channel temperature across the entire channel [Storey et al, 2003;Johnson, 2004;Loheide and Gorelick, 2006], while in larger streams and rivers, hyporheic discharge has been shown to create thermal heterogeneity [Arscott et al, 2001;Fernald et al, 2006].…”

“…In small streams, hyporheic discharge commonly affects channel temperature across the entire channel [Storey et al, 2003;Johnson, 2004;Loheide and Gorelick, 2006], while in larger streams and rivers, hyporheic discharge has been shown to create thermal heterogeneity [Arscott et al, 2001;Fernald et al, 2006].…”

“…Thus hyporheic discharge is commonly cooler than channel water in spring and summer, and warmer than channel water in the winter and fall [Evans et al, 1995;Poole et al, 2008]. Similarly, hyporheic discharge commonly reduces the diel range in channel water temperature [Johnson, 2004;Loheide and Gorelick, 2006]. Along short hyporheic flow paths (e.g., ones to tens of meters in coarse-grained alluvial aquifers) the channel's diel temperature cycle can penetrate into the hyporheic zone via advection and/or conduction, though the timing of maximum and minimum temperatures in hyporheic discharge if often lagged relative to channel temperature cycles [Malard et al, 2001].…”

The influence of riparian vegetation shading on water temperature during low flow conditions in a medium sized river

“…Solar radiation reaching the stream is influenced by different topographic factors, including the prevailing riparian vegetation buffer, which can decrease incoming energy by up to 95% (Rutherford et al, 1997;Moore et al, 2005;DeWalle, 2010). During summer heatwave periods in particular, solar energy plays a key role in influencing stream energy heat budget, and consequently stream water temperature (Johnson, 2004;Leach and Moore, 2010;Groom et al, 2011). Hence shading through riparian vegetation, primarily in small to medium sized and slowly flowing lowland rivers, is often most relevant to avoid excessive heating in order to mitigate adverse effects on the ecosystem (Ghermandi et al, 2009;He et al, 2011;Holzapfel et al, 2013).…”