Rethinking the longitudinal stream temperature paradigm: region-wide comparison of thermal infrared imagery reveals unexpected complexity of river temperatures

Abstract

Prevailing theory suggests that stream temperature warms asymptotically in a downstream direction, beginning at the temperature of the source in the headwaters and levelling off downstream as it converges to match meteorological conditions. However, there have been few empirical examples of longitudinal patterns of temperature in large rivers due to a paucity of data. We constructed longitudinal thermal profiles (temperature vs distance) for 53 rivers in the Pacific Northwest (USA) using an extensive data set of remotely sensed summertime river temperatures and classified each profile into one of five patterns of downstream warming: asymptotic (increasing then flattening), linear (increasing steadily), uniform (not changing), parabolic (increasing then decreasing), or complex (not fitting other classes). We evaluated (1) how frequently profiles warmed asymptotically downstream as expected, and (2) whether relationships between river temperature and common hydroclimatic variables differed by profile class. We found considerable diversity in profile shape, with 47% of rivers warming asymptotically and 53% having alternative profile shapes. Water temperature did not warm substantially over the course of the river for coastal parabolic and uniform profiles, and for some linear and complex profiles. Profile classes showed no clear geographical trends. The degree of correlation between river temperature and hydroclimatic variables differed among profile classes, but there was overlap among classes. Water temperature in rivers with asymptotic or parabolic profiles was positively correlated with August air temperature, tributary temperature and velocity, and negatively correlated with elevation, August precipitation, gradient and distance upstream. Conversely, associations were less apparent in rivers with linear, uniform or complex profiles. Factors contributing to the unique shape of parabolic profiles differed for coastal and inland rivers, where downstream cooling was influenced locally by climate or cool water inputs, respectively. Potential drivers of shape for complex profiles were specific to each river. These thermal patterns indicate diverse thermal habitats that may promote resilience of aquatic biota to climate change. Without this spatial context, climate change models may incorrectly estimate loss of thermally suitable habitat. Copyright © 2015 John Wiley & Sons, Ltd.

Quantification of the contribution of the Beauce groundwater aquifer to the discharge of the Loire River using thermal infrared satellite imaging

“…Taking into account the uncertainties, the groundwater discharge calculated through the heat budget always remained positive between river kilometers 636 and 645. This river section corresponds to a known discharge area of the Beauce aquifer and the Val d'Orléans hydrosystem (Desprez and Martin, 1976;Gonzalez, 1991;Binet et al, 2011), which is also identified by groundwater modeling (calculated discharge was between 0.6 and 0.9 m 3 s −1 km −1 ). Schomburgk et al (2012) calculated a slightly lower but still significant groundwater discharge of 0.5 m 3 s −1 km −1 .…”

“…Until now, these images of watercourses have mainly been used (i) to identify cold refuges for fish in the summer (Belknap and Naiman, 1998;Torgersen et al, 1999;Tonolla et al, 2010;Monk et al, 2013); (ii) to study the thermal variability of rivers or alluvial floodplains and locate areas of similar thermal characteristics (Smikrud et al, 2008;Tonolla et al, 2010;Wawrzyniak et al, 2012, Fullerton et al, 2015; and (iii) to validate river temperature models (Boyd and Kasper, 2003;Cristea and Burges, 2009).…”

Human Impact on Spatial Water Temperature Variability in Lowland Rivers: a Case Study from Central Poland

“…For example, airborne thermal imagery has revealed the need to reconsider the dominant paradigm of longitudinal stream water temperature profi les because the mean temperature does not always rise asymptotically with river length [13]. Despite the signifi cant benefi ts of remote sensing, it must be emphasized that such techniques are expensive and hard to apply in the case of small rivers covered by riparian shade [14].…”

Crossing boundaries: Shigeru Nakano's enduring legacy for ecology

“…Although originally counterintuitive, salmonids are often found to be more strongly related to physical features that emerge at riverscape scales than to factors measured at local scales (e.g., Fausch et al 2002b;Isaak et al 2007;Flitcroft et al 2012;Falke et al 2013). Ongoing research in this arena, including advances in methods for measuring and modeling habitats across the entire spatial hierarchy (Peterson et al 2013;Fullerton et al 2015), will continue to yield insights and improve management of salmonids in riverscapes.…”