The influence of in-stream structures on summer water temperatures via induced hyporheic exchange

Abstract

Temperature is an important controlling factor for ecological functions. In-stream geomorphic structures affect stream thermal regimes by facilitating hyporheic exchange of water and heat between stream channels and underlying sediments. We varied the height of an experimental weir (representing debris dams, log dams, and boulder weirs) in a small stream during the summer and monitored the hydraulic and thermal response of surface and subsurface water using a three-dimensional sensor array. The presence of the structure altered stream temperature patterns, increasing thermal heterogeneity in surface water and shallow sediments by up to ,1.0uC. We estimated heat conduction and weir-induced hyporheic heat advection across the streambed, and evaluated their response to key parameters. Conduction and advection were of similar magnitude and oscillated over the stream's diel temperature cycle. Weir-induced hyporheic heat advection caused slight cooling of the surface stream (up to ,0.01uC), and increased with weir height, but was considerably less important to the overall heat budget of the stream than was atmospheric heat exchange. Streambed hydraulic conductivity appears to be the overriding factor determining the magnitude of weir-induced hyporheic influence on surface water temperatures. We conclude that weir-type structures will induce ecologically significant surface and subsurface thermal heterogeneity in many stream settings, but that weir-induced hyporheic heat advection will have ecologically significant thermal effects on surface water only in coarse streambeds. Because these structures are common in natural streams and stream restoration projects, such thermal effects may be important on a landscape level.

Winter stream temperature in the rain-on-snow zone of the Pacific Northwest: influences of hillslope runoff and transient snow cover

“…Although previous studies have quantified the energy flux associated with hyporheic exchange across the streambed during summer (Story et al, 2003;Moore et al, 2005;Hester et al, 2009;Neilson et al, 2009), no previous studies have estimated this flux for winter periods. Our spot estimates of reach-average hyporheic energy exchange suggest that the magnitude of this term could be up to around 50 W m −2 for lower flows, which makes it comparable in magnitude to net radiation.…”

Urbanization Effects on Watershed Hydrology and In-Stream Processes in the Southern United States

“…The hyporheic zone is the subsurface area directly beneath and lateral to the wetted stream where surface water and groundwater mix. Researchers have demonstrated that streams with hyporheic zones have higher rates of nutrient retention [141,142] and metabolism [143,144] and that hyporheic zones modulate surface water temperatures [89,145]. Urbanization can have a diversity of impacts on the hyporheic zone and subsequently the surface stream.…”

A numerical investigation of the potential impact of stream restoration on in-stream N removal

“…In this study, we assumed the Field of Dreams hypothesis (Sudduth et al, 2011) (that if desirable habitat is available, organisms will occupy the space) holds true, which is not always the case for restoration projects. However, there have been many examples of the positive effects that restoration projects have on nutrient cycling, specifically in the hyporheic zone (Gordon et al, 2013;Hester et al, 2009). We found that the size of the hyporheic zone (A HTS ), where we assumed denitrification was occurring exclusively, was the single most sensitive model parameter that can significantly be affected by restoration projects to the amount of N removed.…”

“…Stream restoration structures, especially those targeting an increase in the hyporheic zone, have been shown to increase stream water residence time and contact with the benthos (Boulton, 2007;Hester et al, 2009), both important factors for removing N (Gomez et al, 2012). In-stream structures can also increase ammonium uptake 143-fold and transient storage size by as much as 227% in agricultural streams (Ensign and Doyle, 2005).…”