The variability of seawater carbonate chemistry in two Florida urban mangrove ecosystems

Anthropogenic carbon dioxide (CO2) emissions into the atmosphere are yielding serious impacts across the world’s ocean, including ocean acidification, sea level rise, and increasing seawater temperature. However, these changes are not occurring uniformly across all marine ecosystems. Coastal ecosystems, such as mangroves, already experience extreme and variable environmental conditions due to natural biogeochemical and physical processes. The goal of this study was to document small-scale variability in two urban mangrove ecosystems to gain insight into how ocean acidification will manifest within these systems. Using a stand-up paddleboard, a suite of sensors, and traditional bottle sampling techniques, we measured temperature, salinity, oxygen, and carbonate chemistry over short spatial distances (meters to kilometers) and timescales (minutes to days) in the surface waters of Whiskey Creek and West Lake (Fort Lauderdale, FL). While Whiskey Creek exhibited greater day-to-day variability in carbonate chemistry than spatial variability on any single day, the magnitude of spatial and temporal variability in West Lake was similar. Total alkalinity (TA) and dissolved inorganic carbon (DIC) were highly correlated in both systems, as is common for coastal ecosystems. Both sites showed a correlation between salinity and TA and DIC indicative of a freshwater source of both alkalinity and inorganic carbon. The ratio of TA:DIC changed from day-to-day in both systems based on mixing between fresh and salt water. Our results indicate that while a multitude of complex factors control the carbon chemistry of these two mangrove systems, buffering capacity (e.g., TA:DIC) is largely controlled by freshwater inputs. Further quantifying the drivers of seawater buffer capacity in coastal ecosystems could provide a way for managers and conservationists to locally manage the global trend of ocean acidification.

Rangel A. R., 2021. The variability of seawater carbonate chemistry in two Florida urban mangrove ecosystems. MSc thesis. Nova Southeastern University, 38 p. Thesis.

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