Seasonal and tidal pH changes in a New England salt marsh: climate change implications for marsh functionality

Salt marshes and other blue carbon systems (mangroves, seagrasses) provide numerous ecosystem services such as preventing coastal erosion, protecting against sea level rise, and providing a home to biodiversity. Most importantly, salt marshes are natural sinks for atmospheric carbon dioxide (CO2) and mitigate against climate change. Human impacts (i.e., land use change, draining, pollution, construction) are deteriorating salt marshes and their ability to provide these ecosystem services. Ocean acidification from the burning of fossil fuels, release of CO2, and subsequent reaction of CO2 with water to form carbonic acid can also affect marsh function. Acidic conditions can negatively impact marsh organisms as decreasing pH results in decreased dissolved oxygen (DO), limiting respiration among other consequences. In this study, weekly in situ water samples were collected in the Neponset River Salt Marsh (June 2018- June 2019) in Boston, MA. Water pH, DO, temperature, and salinity were measured using Vernier (Beaverton, OR) instrumentation in two different marsh locations (freshwater and saltwater endmembers) to determine if any seasonal or tidal trends were present as well as variations between locations. All four variables showed a significant difference across season (p-value < 0.05). pH and DO were lowest in the summer and highest in the winter. Salinity was significantly different between the two endmembers only and both pH and DO were significantly different between high and low tide. Future considerations for marsh functionality will also be discussed.