Contextualizing Thermal Effluent Impacts in Narragansett Bay Using Landsat-Derived Surface Temperature

Jonathan Benoit,Baylor Fox-Kemper

doi:10.3389/fmars.2021.705204

Abstract

This work utilizes remotely sensed thermal data to understand how the release of thermal pollution from the Brayton Point Power Station (BPPS) affected the temperature behavior of Narragansett Bay. Building upon previous work with Landsat 5, a multi-satellite analysis is conducted that incorporates 582 scenes from Landsat 5, Landsat 7, and Landsat 8 over 1984–2021 to explain seasonal variability in effluent impacts, contrast data after the effluent ceased in 2011, identify patterns in temperature before and after effluent ceased using unsupervised learning, and track how recent warming trends compare to the BPPS impact. Stopping the thermal effluent corresponds to an immediate cooling of 0.26 ± 0.1°C in the surface temperature of Mt. Hope Bay with respect to the rest of Narragansett Bay with greater cooling of 0.62 ± 0.2°C found near Brayton Point; though, cooling since the period of maximal impact (1993–2000) totals 0.53 ± 0.2°C in Mt. Hope Bay and 1.04 ± 0.2°C at Brayton Point. During seasons with lower solar radiation (winter) and lower mean river input (autumn and late summer), the BPPS effluent impact is more prominent. The seasonal differences between the high impact and low impact periods indicate that river input played an important role in the heat balance when emissions were lower, but surface fluxes dominated when emissions were higher. Putting the BPPS effluent in context, Landsat data indicates that Narragansett Bay warmed 0.5–1.2°C over the period of measurement at an average rate of 0.23 ± 0.1°C/decade and that net warming in Mt. Hope Bay is near zero. This trend implies that Narragansett Bay has experienced climatic warming over the past four decades on the scale of the temperature anomaly in Mt. Hope Bay caused by the BBPS effluent.

Highlights

Using forcing data from the Ocean State Ocean Model (OSOM: Sane et al, 2020)—an application of the Regional Ocean Modeling System (ROMS) to Narragansett Bay and Rhode Island Sound—to facilitate this comparison, one billion gallons corresponds to 0.3–3.1% of the upper Taunton River input
Hope Bay and Brayton Point from the mean temperature of Narragansett Bay by season laid over the corresponding changes in map view
Maximum cooling at Brayton Point reveals that the greatest heat anomaly was at the location of the Brayton Point Power Station (BPPS) (Figure 6), pointing to the thermal effluent as the cause of the transient heat anomaly

Summary

Introduction

The Brayton Point Power Station (BPPS) was a coal-fueled power station in Massachusetts that operated from 1963 to 2017 This power station was New England’s largest fossil-fuel burning power station as well as a source of thermal pollution into Mt. Hope Bay, a northeastern embayment of Narragansett Bay (see Figure 1). The BPPS released nearly one billion gallons of water daily—enough to replace the entire volume of Mt. Hope Bay 3.5 times over a year—and released 44 petajoules (12 TWh) of heat annually into Mt. Hope Bay (United States Environmental Protection Agency, 2003). Comparing the heat released to the energy of incoming solar and longwave radiation and the effluent volume flux to the volume of river input contextualizes the scale of this impact. Hope Bay’s surface, is equivalent to 7–16% of the incoming shortwave plus longwave radiation from the sun and atmosphere (the range reflects seasonal solar variability)

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Conclusion