Carbon cycling in a mangrove forest of the Florida Everglades

The objective of this presentation is to investigate the environmental and physiological controls on carbon sequestration in a mangrove forest of the Florida Everglades. Since 2004 we have investigated the net carbon ecosystem exchanges between a mangrove forest and the atmosphere. Sufficient information has emerged to quantify the edaphic and physiological conditions controlling the rates of carbon assimilation by the mangrove forest. In addition, the long-term studies include the influences of disturbances created by tropical storms and cold spells on ecosystem function. Despite their pan-tropical distribution, results indicate that the mangrove forests exhibit highly variable daytime net carbon ecosystem exchanges. Maximum daytime net ecosystem exchanges occur during the springtime (March to May) and range from -20 to -25 μmol (CO2) m-2 s-1. Respiration rates are relatively low (2.81±2.41 μmol (CO2) m-2 s-1) in response to reduced biomass decomposition in the soils. Tidal inundation can exert control on net carbon ecosystem exchanges in response to reduced respiration by as much 0.9 μmol (CO2) m-2 s-1 and 0.5 μmol (CO2) m-2 s-1 during day- and night-time conditions. Salinity is an important control on forest carbon assimilation. Elevated (>30 parts per thousand) salinity levels can lead to reductions in light-use efficiency of up to 45 %. Mangroves exhibit substantial variations in the seasonal patterns of net ecosystem production. The forest can be a large carbon sink, with an annual net ecosystem production of about 1,000g C m-2. Such unusually high net ecosystem production values can be attributed to year-round productivity, low ecosystem respiration, and lateral transport of dissolved organic and inorganic carbon into the adjacent estuary. Tropical storm and cold spell disturbances not only reduce the capacity of the ecosystem to assimilate carbon, but also modulate the carbon cycling process during the ecosystem recovery phase. One key conclusion derived from the field studies is that carbon balance in mangrove ecosystems can change in response to variable salinity and inundation patterns, possibly resulting from sea level rise and atmospheric warming. Disturbances can initially suppress the forest carbon assimilation capacity. However, during the recovery phase the ecosystem can gradually augment carbon assimilation capacity in response to new physiologically active biomass.