Integrating High-Resolution Coastal Acidification Monitoring Data Across Seven United States Estuaries

Abstract

Beginning in 2015, the United States Environmental Protection Agency’s (EPA’s) National Estuary Program (NEP) started a collaboration with partners in seven estuaries along the East Coast (Barnegat Bay; Casco Bay), West Coast (Santa Monica Bay; San Francisco Bay; Tillamook Bay), and the Gulf of Mexico (GOM) Coast (Tampa Bay; Mission-Aransas Estuary) of the United States to expand the use of autonomous monitoring of partial pressure of carbon dioxide (pCO2) and pH. Analysis of high-frequency (hourly to sub-hourly) coastal acidification data including pCO2, pH, temperature, salinity, and dissolved oxygen (DO) indicate that the sensors effectively captured key parameter measurements under challenging environmental conditions, allowing for an initial characterization of daily to seasonal trends in carbonate chemistry across a range of estuarine settings. Multi-year monitoring showed that across all water bodies temperature and pCO2 covaried, suggesting that pCO2 variability was governed, in part, by seasonal temperature changes with average pCO2 being lower in cooler, winter months and higher in warmer, summer months. Furthermore, the timing of seasonal shifts towards increasing (or decreasing) pCO2 varied by location and appears to be related to regional climate conditions. Specifically, pCO2 increases began earlier in the year in warmer water, lower latitude water bodies in the GOM (Tampa Bay; Mission-Aransas Estuary) as compared with cooler water, higher latitude water bodies in the northeast (Barnegat Bay; Casco Bay), and upwelling-influenced West Coast water bodies (Tillamook Bay; Santa Monica Bay; San Francisco Bay). Results suggest that both thermal and non-thermal influences are important drivers of pCO2 in Tampa Bay and Mission-Aransas Estuary. Conversely, non-thermal processes, most notably the biogeochemical structure of coastal upwelling, appear to be largely responsible for the observed pCO2 values in West Coast water bodies. The co-occurrence of high salinity, high pCO2, low DO, and low temperature water in Santa Monica Bay and San Francisco Bay characterize the coastal upwelling paradigm that is also evident in Tillamook Bay when upwelling dominates freshwater runoff and local processes. These data demonstrate that high-quality carbonate chemistry observations can be recorded from estuarine environments using autonomous sensors originally designed for open-ocean settings.

Attributing Controlling Factors of Acidification and Hypoxia in a Deep, Nutrient-Enriched Estuarine Embayment

“…The effects of seasonal temperature change on pCO 2 in the deconvolution were like those seen in pCO 2 monitoring across several United States estuaries (Joesoef et al, 2015;Rosenau et al, 2021) who used similar analytical methods to separate the effects of temperature and aggregated metabolism/mixing on pCO 2 . Like those studies, we did not quantitatively separate the metabolic and mixing effects.…”

“…We observed the NE shelf region to have pCO 2 at near-equilibrium or slightly below atmospheric levels and pH close to 8.1, with little seasonal variability, but larger pCO 2 and pH variations were routinely observed further into the Hauraki Gulf, and especially toward the inner Firth. It was clear that carbonate conditions at the Firth were responding to more complex conditions than those for the open NE shelf, as described for other systems in proximity to the land-sea interface (Provoost et al, 2010;Joesoef et al, 2015;Rosenau et al, 2021). Among these conditions are freshwater effects (Carstensen and Duarte, 2019;Van Dam and Wang, 2019).…”

“…Biological metabolism (uptake, release) and physical mixing (horizontal, vertical and air-sea exchanges) affect pCO 2 , DIC and TA. Following the approaches of Joesoef et al (2015) and Rosenau et al (2021) we determined the combined effects of seasonal changes in biological metabolism and physical mixing on pCO 2 . We calculated the effect of inter-seasonal temperature change on surface layer pCO 2 , (pCO 2,thermal ), by holding DIC and TA at observed starting seasonal conditions and imposing the observed inter-seasonal temperature changes (Mehrbach et al, 1973;Dickson and Millero, 1987).…”

Effect of nutrient reductions on dissolved oxygen and pH: a case study of Narragansett bay

“…Studies have confirmed that the combination of physical and biological processes in coastal ecosystems causes strong diurnal variability in carbonate chemistry: the diurnal amplitudes for pCO 2 and pH in many shallow coastal areas are 10~100 times higher than that in the open ocean (Carstensen and Duarte, 2019;Rosenau et al, 2021;Torres et al, 2021). This high temporal variability creates significant challenges for detecting OA changes (Carter et al, 2019).…”

Ecosystem Metabolism Modulates the Dynamics of Hypoxia and Acidification Across Temperate Coastal Habitat Types

“…In addition, most studies of ecosystem metabolism in estuaries have focused either on high frequency O 2 measurements or less frequent, lower resolution pH or carbon measurements. There has been little focus on high frequency and high-resolution measurements of both O 2 and pH (Rosenau et al, 2021) coupled with measurements of carbonate chemistry. Studies that have focused on the monitoring of high frequency carbonate chemistry in coastal environments (Baumann et al, 2015;Saderne et al, 2015;Wang et al, 2015), have lacked simultaneous comparisons of distinct habitats.…”