River temperatures have long been an area of study, but until recently, the field has been hampered by technological constraints. Fine-scale measurements over large distances and long time periods have been difficult to collect, and research efforts have focused instead on average river temperatures, lethal extremes, and small-scale patterns. However, a suite of new technologies and methods, driven by inexpensive sensor technology, are enabling new insights, with significant implications for the future of river management.
Writing in BioScience , E. Ashley Steel of the USDA Forest Service and her colleagues detail the effects of these new data and describe the ways in which the new information will assist future management efforts. Key among data-enabled innovations is the incorporation of measurements over time and space to create a holistic view of river thermal regimes that the authors dub the "thermal landscape." In natural thermal landscapes, there are complex patterns in which temperatures fluctuate over time, in slightly different ways, at every location on a river network.
The authors argue that a greater understanding of thermal landscapes could guide new insight into humans' effects on river networks. "New data, models, and conceptual frameworks are providing insights into the biological implications of both temporal and spatial variability in water temperature patterns as well as illuminating ways in which humans have altered and are continuing to alter thermal landscapes," they report.
Specifically, fine-scale data may elucidate surprising effects of thermal variability, such as enzymatic reactions that respond to fluctuations in water temperature in ways that could not be predicted using blunt measurements. The study of thermal landscapes is still in its early phases but insights are already leading to restoration actions such as reconnecting side channels and cool-water tributaries to floodplain main channels that are aimed at restoring thermal complexity. More research is needed to untangle anthropogenic from natural effects and to uncover the complex ecological responses to thermal landscape variability. "Without this understanding," caution the authors, "we may unknowingly continue to degrade (or fail to restore) essential functions of riverine ecosystems."
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E. Ashley Steel et al, Envisioning, Quantifying, and Managing Thermal Regimes on River Networks, BioScience (2017). DOI: 10.1093/biosci/bix047