Urban stream temperature patterns: Spatial and temporal heterogeneity in the Philadelphia region, Pennsylvania, USA

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.

Seasonal and longitudinal water quality dynamics in three effluent-dependent rivers in Arizona

“…3 ). This pattern demonstrates the strong influence of atmospheric and climatic conditions on water temperature despite the stable, warm temperature of effluent at its point of release ( Beganskas & Toran, 2021 ). Trends in dissolved oxygen levels across seasons were generally opposite to those of temperature, with the lowest values observed in summer; however, this pattern was only significant in three of the six reaches ( Table 2 ; Fig.…”

“…The effect of longitudinal distance from effluent outfalls on water quality varied widely among measured parameters. Effluent is generally warmer than natural baseflow temperatures, so heat exchange between the atmosphere and stream likely led to longitudinal cooling trends ( Boyle & Fraleigh, 2003 ), especially during winter ( Beganskas & Toran, 2021 ; also see “4.2 Seasonal effects” below). As temperatures cooled, dissolved oxygen levels rose.…”

“…Seasonal atmospheric and climatic factors, such as air temperature, solar radiation, relative humidity, cloud cover, and wind speed, work together to shape water temperatures through heat exchange between the atmosphere and the stream ( Sinokrot & Stefan, 1994 ; Beganskas & Toran, 2021 ). This effect is usually stronger in unregulated stream systems ( Bowles, Fread & Greeney, 1977 ) and relatively weak in effluent-dependent stream systems, especially near effluent outfalls ( Hamdhani, Eppehimer & Bogan, 2020 ).…”

The heat is on: Predicting urban stream temperature responses to summer storms

“…As observed in other studies, in many cases heat pulses are observed to be generated by contributions from storm sewers, as was observed by Somers et al (2013) and Hester and Bauman (2013). Alternatively, heat pulses may result from contributions of runoff or water ponded on near‐stream impervious surfaces (though most cities work to eliminate such areas) that has been heated by hot pavement (Omidvar et al, 2018), stormwater management ponds or detention basins (Sabouri et al, 2016), or wastewater treatment plants (e.g., Beganskas & Toran, 2021). It also remains unclear whether warmer water in the shallow subsurface that has been heated in the lead up to the event and entering the stream with the first flush of precipitation, could also contribute to these responses.…”

“…Past studies have shown that stream temperature in urban areas depends substantially on the near‐stream land cover. Riparian buffer zones may cool urban stream temperatures (Arora et al, 2018), whereas effluent from waste water treatment plants is known to raise stream temperatures (Beganskas & Toran, 2021). Furthermore, stormwater control measures can substantially influence stream temperature by impacting urban discharge (Fanelli et al, 2019) as well as the temperature of the added localized runoff (Ouellet et al, 2021; Timm et al, 2020).…”