A Spatially Distributed Investigation of Stream Water Temperature in a Contemporary Mixed-Land-Use Watershed

Abstract

A Spatially Distributed Investigation of Stream Water Temperature in a Contemporary Mixed-Land-Use Watershed Jason Horne Stream water temperature is an important physical variable that influences many biological and abiotic water quality processes. The land-use/land-cover (LULC) types and corresponding variability in stream water temperature (Tw) processes in contemporary mixed-land-use watersheds necessitate research to advance management and policy decisions. Water temperature was analyzed from 21 gauging sites using a nested-scale experimental watershed study design. Results showed that forested land use was significantly negatively correlated (α = 0.05) with mean and maximum Tw. Agricultural land use was significantly positively correlated (α = 0.05) with maximum Tw except during the spring season. Mixed development and Tw were significantly correlated (α = 0.05) at quarterly and monthly timescales. Correlation trends in some reaches were reversed between the winter and summer seasons, contradicting previous research. During the winter season, mixed development showed a negative relationship with minimum Tw and mean Tw. During the summer season, higher minimum, maximum, and mean Tw correlations were observed relative to the winter season. Advanced understanding generated through this high-resolution investigation improves land managers' ability to improve conservation strategies in freshwater aquatic ecosystems of contemporary watersheds. iii The undersigned, appointed by the dean of the Graduate School, have examined the thesis entitled A Spatially Distributed Investigation of Stream Water Temperature in a Contemporary Mixed-Land-Use Watershed presented by Jason P. Horne, a candidate for the degree of Master of Science, and hereby certify that, in their opinion, it is worthy of acceptance.

Modeling Watershed‐Wide Bioretention Stormwater Retrofits to Achieve Thermal Pollution Mitigation Goals

“…Aquatic organism health, growth, birth, and survivability are heavily impacted by increasing average temperatures and their more extreme fluctuations (Coutant 1999; Steel et al 2017). Since many aquatic organisms such as benthic macroinvertebrates and trout are thermally sensitive, species diversity is also impacted (Steel et al 2017; Horne and Hubbart 2020). Additionally, water temperature affects dissolved oxygen content and other water quality properties, further jeopardizing the survivability of aquatic species in the altered environment (Webb 1996; Virginia Citizen Water Quality Monitoring Program 2007; Thompson et al 2008).…”

“…Impervious surfaces contribute significantly to stream warming by reducing infiltration (Nelson and Palmer 2007) and adding heat to stormwater as it flows across those surfaces (Janke et al 2009; Jones et al 2012). As land use becomes more intensive, those areas will have higher thermal pollution potential (Zeiger and Hubbart 2015; Martin et al 2019; Horne and Hubbart 2020), especially closer to outlet points since the directness of runoff entry into a stream increases surface flow’s impacts on the stream’s temperature (Somers et al 2013; Hathaway et al 2016; Watson and Chang 2017). Greater impervious cover also causes higher runoff volumes, which change stream morphology in ways that allow more energy exchange with the atmosphere (Klein 1979; LeBlanc et al 1997; Nelson and Palmer 2007).…”