Carbonate Chemistry of Galveston Bay Estuary: Impact of Hurricane Harvey and Implications for Oyster Reef Health

Tacey Lynn Hicks, Texas A&M University College Station, Oceanography, College Station, United States, Amy Baco-Taylor, Florida State University, Earth, Ocean, and Atmospheric Sciences, Tallahassee, United States, Christine Jensen, Texas Parks and Wildlife Department, TX, United States and Jessica N Fitzsimmons, Texas A&M University, Oceanography, College Station, TX, United States
Abstract:
Galveston Bay, an anthropogenic estuary on the Texas coast, contains oyster reefs that provide critical ecosystem services including water filtration, shoreline protection, and habitat for several valuable fisheries. Anthropogenic activities, including fossil fuel burning, freshwater diversion, and eutrophication, cause global and coastal ocean acidification that decreases pH and saturation state (Ω), thereby slowing production and increasing dissolution of calcium carbonate oyster shells. Therefore, characterizing acidification levels is an important part of assessing the health of the bay ecosystem. Here we describe the carbonate chemistry of Galveston Bay at 6 time points from June 2017–September 2018, including the effects of Hurricane Harvey. Average pH and aragonite Ω (Ωa) in Galveston Bay were 8.1±0.1 and 2.3±0.7, respectively. Spatially, pH tends to be lower near the coast (by ~0.1), whereas Ω follows the salinity gradient, with higher Ω near the mouth of the bay where salinity is high (Ωa~1.9–3.2), decreasing towards freshwater sources (Ωa~0.1–2.3). Temporal changes in pH are driven by seasonal changes in water temperature, while Ω responds more to seasonal changes in stream discharge. In August 2017, excessive rainfall and runoff from Hurricane Harvey led to significant and prolonged acidification and calcium carbonate undersaturation in the bay, with an average pH of 7.7±0.2 and average Ωa of 0.6±0.5. In addition, the entire bay was flushed with freshwater for up to 2 weeks, causing a large oyster freshwater die-off. While bay carbonate chemistry appears to have recovered by March 2018, recovery of the oyster reefs requires recruitment and growth of new larval oysters that are particularly sensitive to Ωa levels. This study provides a critical opportunity to assess the impacts of the increasing rainfall and runoff associated with hurricanes on the carbonate chemistry of coastal ocean systems.
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