We examined the relationship between extreme events and carbon dioxide (CO2) exchange rates across major ecosystems in Everglades National Park, FL, USA. These pulse events are particularly important for understanding how freshwater marsh and mangrove dominated ecosystems will adapt to sea-level-rise (SLR) and climate change in this low elevation, subtropical wetland complex. Productivity across the Everglades peaks near the coast (mangroves) where the supply of P from seawater is balanced by freshwater supplies. Productivity is greatest in mangrove forests (1200 g C m-2 yr-1), compared to long- and short-hydroperiod freshwater marsh ecosystems that range from being a small sink to a small source of CO2 (-11– -110 g CO2 m-2 yr-1) annually. Although climate and hydrology are major drivers of ecosystem structure and function, disturbance regimes (i.e., drought, extreme flooding, hurricanes, low temperature events, and fire) interact with hydrology to modify populations, communities, and ecosystems across the coastal gradient. Recent El Niño Southern Oscillation cycles (ENSO; 2009-2013) and low temperature events (2009-2012) have provided important opportunities to explore variation in ecosystem sensitivity to disturbances and recovery trajectories in freshwater marsh and mangrove forests.
Results/Conclusions
In Florida, fluctuations in precipitation patterns occur with changes in the El Niño southern oscillation (ENSO) phases. While El Niño events co-occur with wetter than average conditions, La Niña phases are associated with drier than average conditions. Under normal conditions, short-hydroperiod freshwater marshes have higher productivity rates during the dry season while long-hydroperiod freshwater marshes exhibit greater productivity rates during the wet season. This site-specific seasonality in productivity is driven by changes in hydrology and as a result, ENSO phases either magnify or mute seasonal productivity rates. La Niña phases were concurrent with increased productivity in short-hydroperiod freshwater marshes compared to El Niño and neutral years. The exceptionally wet year associated with an El Niño phase led to greater productivity in the long-hydroperiod freshwater marsh. When it comes to low-temperature events (<5°C), both water levels and distance from the coast influenced ecosystem sensitivity. While the long-hydroperiod freshwater marsh gained 0.26 g CO2 m-2 more carbon during low-temperature events due to the higher light levels, mangrove forest had the greatest carbon lost (7.11 g CO2 m-2 low-temperature event-1). Across disturbance types, hydrology played a major role in determining the degree of exposure and therefore the sensitivity to disturbance.