Researchers developed tools to document long-term changes in the size and location of the estuarine ecotones in response to sea level rise, hurricanes, increased freshwater inflows, and fire. They expected that, over intermediate time scales (years to decades), the sea level rise and hurricanes will force the estuarine boundary of the ecotone landward, while increased fresh water inflows and fire will either force the fresh water boundary seaward or hold it near its current location. In the long term, though (decades to a century), scientists expected marine forces to prevail and the entire ecotone region to shift landward. Researchers found that the accumulation of peat due to the expansion of mangroves, which build this soil, was equal to the amount of sea level rise. However, the short-term sediment deposition associated with storm surge events was found to be much higher. For example, the storm surge from Hurricane Wilma (October, 2005) deposited over 3 cm of carbonate mud in the mangrove forests near the Gulf of Mexico.
Effects of restored fresh water to the Everglades eventually will be experienced on a template of high natural variability in water supply, so FCE research has been focused on the temporal dynamics of water delivery to the ecotone and its impact on ecosystem processes. Temporal variability in water delivery is both periodic (e.g., tides, subtropical seasonal weather patterns, and ocean-atmospheric teleconnections) and pulsed (e.g., cyclones and associated storm surge). The pulses punctuate the directional pressure of saltwater encroachment driven by SLR and the continued diversion of fresh water away from the Everglades drainages.
Legacies of Hurricane Wilma (Oct 2005)
The storm reduced net ecosystem production(NEP) (top right panel) calculated by eddy covariance (green bars) and leaf litter carbon (C) (blue bars) (Barr et al. 2012), while P from the storm deposit slowly leached from the wetland into the river water column (bottom panel), exemplifying the "upside-down" estuary concept of Childers et al. (2006).
To characterize the variation in water source, we developed the first water balance for the two Everglades drainages, finding that while precipitation and evapo-transpiration control the annual water budget in both sloughs, 20-30% of inputs come from groundwater, and <20% from upstream fresh water sources. Landward discharge of brackish groundwater causes a dry-season increase in salinity in both transects, and the position of this groundwater mixing zone is moving inland. Highly variable water residence times reflect seasonal precipitation patterns, which are partly driven by long-term cycles that regulate winter rainfall in South Florida. Cyclical patterns in water delivery to the upstream watershed appear to correlate with trends in the paleosalinity in Florida Bay, suggesting that local climate patterns control, to some degree, the high sensitivity of southeastern Florida coastal marshes to past and ongoing management.
The FCE study area is still experiencing the legacy of Hurricane Wilma (Oct 2005) that blew down our eddy covariance tower, defoliated the mangrove forest, and deposited 3-4 cm of P-enriched Gulf of Mexico sediment into the SRS ecotone. The storm reduced net ecosystem production of the mangrove forest (calculated by eddy covariance and leaf litter carbon), while P from the storm deposit slowly leached from the wetland into the river water column, exemplifying the "upside-down" estuary concept.
In 11+ years of FCE research, we have shown pronounced and persistent sensitivity of the flat South Florida landscape to SLR and storms, exacerbated by continued diversion of fresh water delivery away from the Everglades ecosystem. Land use change assessments are beginning to quantify connections between land and water use and restoration activities. In FCE II, we quantified the spatial patterns of land use in (sub) urbanizing southern Miami-Dade Co. using satellite imagery to resolve land cover to the parcel scale, and connected land cover to neighborhood social composition at the census block group scale.