Hurricanes are major ecological disturbances, which can have a tremendous impact on low-lying, coastal ecosystems. The storm surge, saltwater intrusion, wind, and extreme rainfall produced by hurricanes can knock down forests, induce peat collapse, deposit thick sediment layers, lead to erosion, and transform plant communities. Some hurricane effects can be positive; for example, the addition of valuable sediment and nutrient subsidies that increase elevation capital and promote plant growth. However, in extreme cases, hurricanes can lead to abrupt and irreversible ecological transformations. Along a southwestern section of Everglades National Park near Big Sable Creek, hurricanes are thought to have contributed to the conversion of mangrove forests to mudflats. For almost twenty years, USGS scientists have been measuring surface elevation change in mangrove forests and the adjacent mudflats using the SET-MH approach (i.e., surface elevation tables in combination with marker horizons). This period of data collection includes the impacts of Hurricane Wilma in 2005 and Hurricane Irma in 2017. Here, we examine the effects of these hurricanes as well as the impacts of mangrove forest conversion to mudflat upon surface elevation change processes that affect the ability of coastal wetlands to persist with hurricanes and rising sea levels.
Results/Conclusions
Inundation regimes play an extremely important role in coastal wetlands, producing potent abiotic gradients and affecting plant-meditated, biogeomorphic feedbacks that govern ecosystem stability. Hence, small changes in elevation can have large ecological consequences. Throughout the past twenty years, rates of elevation change in the mangrove forests and the adjacent unvegetated mudflats have been very different. Whereas the soil elevation in the mangrove forests has been relatively stable, the rate of elevation loss in the mudflat sites has been comparatively large. Hurricane Irma recently deposited a large layer of sediment in the mudflats; however, the tidal energy is strong at these sites and it is unclear how long those storm sediments will stay in place. Collectively, our two decades of data highlight the ability of mangrove plants to minimize erosion, reduce elevation loss through root production, and promote wetland stability. Our findings also indicate that the effects of mangrove conversion to mudflat are long-lasting.