Accelerating sea-level rise and the fate of mangrove plant communities in South Florida, U.S.A.

Abstract

Analysis of four South Florida tide gauges, with records ranging from 27 to 116 yrs., indicate the average rate of sea-level rise has accelerated from 3.9 mm yr−1 (1900–2021) to 6.5 mm yr−1 (2000−2021), and 9.4 mm yr−1 over the past decade. Future rates are forecast to accelerate over the duration of this century. A predictive conceptual framework (model) was developed in which the resilience of South Florida mangrove plant communities is solely a function of the rate of sea-level rise and vertical sediment accumulation. The model was verified using historical (e.g., 1900–2021) and recent (e.g., 2000–2021) sediment accumulation rate data derived using three different methodological approaches. Results indicate by 2040–2050 South Florida mangrove plant communities, already subjected to the destabilizing effects of accelerating sea-level rise for decades, will begin a widespread conversion to estuarine conditions. This will initially trigger the formation and expansion of inundation ponds, as is already occurring in the study area. By the end of this century, most mangrove forested areas will be submerged. The loss of other coastal wetlands (e.g., brackish marsh) is also likely because their rates of sediment accumulation are lower than mangrove. The findings of this study are consistent with other resilience projections that have been conducted in South Florida and at the global scale. Several knowledge gaps were identified which must be filled to improve confidence in subsequent forecasts and the outcome of mitigation efforts undertaken to enhance resilience. These include the lack of (1) sediment accumulation data representative of transitional and freshwater wetlands, (2) a robust understanding of post-depositional processes (e.g., compaction) that can compromise resilience through shallow (~1 m) subsidence, and (3) recent sediment accumulation data necessary to determine how South Florida coastal wetlands have responded to a sustained acceleration in the rate of sea-level rise over the last decade.