Presenter: Tacey Hicks (Texas A&M University)

Description:
Characterizing processes driving coastal acidification supports the protection and management of valuable ecosystems, particularly calcifying reefs. Here, we present evidence for intense, short-term coastal acidification in Galveston Bay driven by high-rainfall tropical cyclones Hurricane Harvey (Aug 26, 2017) and Tropical Storm Imelda (Sep 22, 2019). Galveston Bay, the largest Texas estuary, is home to oyster reefs that provide critical services, including water filtration, habitat, and fisheries, but are vulnerable to acidification. Long-term acidification has been documented in the bay, highlighting the importance of studying multi-stressor acidification in this region. During an analogous non-storm period (September 2018), average pH and aragonite saturation state (Ω_ar) in Galveston Bay were 8.0±0.1 and 2.4±0.4, respectively. Two weeks post-Harvey (September 2017), average pH was 7.6±0.2 and Ω_ar was 0.2±0.2, demonstrating significant storm-induced acidification. Three weeks post-Harvey there was indications of recovery, but undersaturation persisted throughout the bay (average Ω_ar=0.6±0.4). Hurricane Harvey is the wettest tropical storm on record in the US, with a maximum rainfall total of 152 cm. Floodwaters were manually released for 6+ weeks following Harvey to mitigate severe flooding. The extreme rainfall and extended floodwater release contributed to the intensity and duration of acidification in Galveston Bay. In comparison, less rainfall was associated with Imelda (112 cm, September 2019) and storm-induced acidification was less severe (average pH=8.0±0.2 and Ω_ar=1.2±0.8), six days post-Imelda. However, undersaturation was still measured in upper Galveston Bay, with negative implications for the bay ecosystem. As rainfall associated with tropical cyclones increases under climate change, coastal undersaturation events will likely become more frequent and prolonged, especially in regions already experiencing local coastal acidification.