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

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.

Rhode Island and Landsat

“…A recent Brown University study used 582 Landsat scenes from 1982 through 2021 to measure the effect of thermal pollution (increased water temperatures) originating from Brayton Point Power Station and affecting Narragansett Bay. The study documented a cooling of the water's surface after the cessation of power station effluent discharge in 2011 (Benoit and Fox-Kemper, 2021).…”

A Decade of Time Series Sampling Reveals Thermal Variation and Shifts in Pseudo-nitzschia Species Composition That Contribute to Harmful Algal Blooms in an Eastern US Estuary

“…One example of this was in 2015 on the US West Coast, when a large bloom of P. australis led to record levels of DA, and an anomalously warm water mass was implicated in bloom formation (McCabe et al, 2016). Narragansett Bay has also been impacted by climate change, with surface water temperatures that increased by 0.23± 0.1°C per decade from 1984 -2020 and more pronounced winter warming than other seasons (Fulweiler et al, 2015;Benoit and Fox-Kemper, 2021). Additionally, this location has experienced climate-driven nutrient cycle changes as well as a reduction in nutrient inputs due to recent management changes of sewage treatment (Oviatt et al, 2017).…”

“…The importance of sea surface temperature to phytoplankton community composition may be partially attributed to the wide range of temperatures that Narragansett Bay experiences throughout the year (Figure 5). As sea surface temperatures in Narragansett Bay continue to increase over time due to climate change (Fulweiler et al, 2015;Benoit & Fox-Kemper, 2021), this driver of Pseudo-nitzschia assemblage composition may lead to further shifts in the prevalence of certain species. This could include continued increases in the frequency of P. australis, P. hasleana, P. galaxiae, and P. subpacifica, all of which became more prevalent in Narragansett Bay in closure and subsequent years.…”