Hurricane Harvey and salt marsh sediment carbon: Impacts of variable storm intensities across stable and dynamic marsh landscapes along the coast of Texas

Salt marshes store carbon in sediments as buried organic matter, but these reservoirs are vulnerable to disturbances, such as extratropical storms. However, major storms have poorly understood effects on existing marsh sediment carbon stocks. On August 25, 2017, Hurricane Harvey made landfall as a Category 4 storm at Rockport, TX, circled back to the Gulf of Mexico, and made a second landfall as a tropical storm east of Port Arthur, TX on August 30, 2017. These two major storm landfalls coincided with locations of salt marsh carbon burial studies performed in 2014 at the Aransas and Anahuac National Wildlife Refuges. The objective of this study was to identify extratropical storm impacts on marsh sediment carbon storage under variable storm intensities and marsh stabilities. Pre- and post-storm sediment cores (35 cm depth) were collected in June 2014 and January 2018 from both sites, respectively. Sediments were analyzed for total organic carbon, δ¹³C, and ²¹⁰Pb. Sediments from Aransas were also analyzed via ramped pyrolysis/oxidation coupled with Δ¹⁴C accelerator mass spectrometry to further understand alterations in sediment organic carbon quality and age post-hurricane. In-situ observations show the storm minimally impacted the more stable Anahuac marsh, but exacerbated ongoing changes in vegetation at the Aransas site. Storm sedimentation was not observed at either site, but about 2 cm of vertical accretion was measured between pre- and post-sampling periods at both sites. In Aransas sediments, Δ¹⁴C results suggest organic carbon sources are local and reflect the ¹⁴C atmospheric bomb curve. Thermal stability of sediment organic carbon decreased overall in the upper 5 cm between sampling periods, indicating an addition of more labile material. Understanding the response of salt marsh carbon quality and storage to the effects of climate change is crucial in the face of increasing intensity of extratropical storms, like Hurricane Harvey.