Urban stream temperature patterns: Spatial and temporal heterogeneity in the Philadelphia region, Pennsylvania, USA. Issue 2 (23rd February 2021)

• Record Type: Journal Article
• Authors: Beganskas, Sarah; Toran, Laura
• Is Part Of: Hydrological processes. Volume 35:Issue 2(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-02-23
• Subjects: Cobbs Creek -- land cover -- stormwater runoff -- stream temperature -- thermal mitigation -- urbanization -- wastewater treatment plants -- Wissahickon Creek; Hydrology -- Periodicals; Hydrology -- Research -- Periodicals; Hydrologic models -- Periodicals; Hydrological forecasting -- Periodicals; 631.432
• DOI: 10.1002/hyp.14039
• Languages: English
• ISSNs: 0885-6087

Abstract

Abstract: Stream temperature is a critical water quality parameter that is not fully understood, particularly in urban areas. This study explores drivers contributing to stream temperature variability within an urban system, at 21 sites within the Philadelphia region, Pennsylvania, USA. A comprehensive set of temperature metrics were evaluated, including temperature sensitivity, daily maximum temperatures, time >20°C, and temperature surges during storms. Wastewater treatment plants (WWTPs) were the strongest driver of downstream temperature variability along 32 km in Wissahickon Creek. WWTP effluent temperature controlled local (1–3 km downstream) temperatures year‐round, but the impacts varied seasonally: during winter, local warming of 2–7°C was consistently observed, while local cooling up to 1°C occurred during summer. Summer cooling and winter warming were detected up to 12 km downstream of a WWTP. Comparing effects from different WWTPs provided guidelines for mitigating their thermal impact; WWTPs that discharged into larger streams, had cooler effluent, or had lower discharge had less effect on stream temperatures. Comparing thermal regimes in four urban headwater streams, sites with more local riparian canopy had cooler maximum temperatures by up to 1.5°C, had lower temperature sensitivity, and spent less time at high temperatures, although mean temperatures were unaffected. Watershed‐scale impervious area was associated with increased surge frequency and magnitude at headwater sites, but most storms did not result in a surge and most surges had a low magnitude. These results suggest that maintaining or restoring riparian canopy in urban settings will have a larger impact on stream temperatures than stormwater management that treats impervious area. Mitigation efforts may be most impactful at urban headwater sites, which are particularly vulnerable to stream temperature disruptions. It is vital that stream temperature impacts are considered when planning stormwater management or stream restoration projects, and the appropriate metrics need to be considered when assessing impacts. Abstract : Many factors drive urban stream temperature heterogeneity. In this study, wastewater treatment plants were the strongest driver of downstream temperature changes; treatment plants that discharged into larger streams, had cooler effluent, or had lower discharge had less impact. Urban headwater sites with more local riparian canopy had cooler maximum temperatures, while watershed‐scale impervious area was associated with greater surge frequency and magnitude during some storms. Restoring riparian canopy in urban settings may impact stream temperatures more than treating impervious area.