An important but often overlooked consequence of saltwater intrusion is the potential increase of groundwater soluble reactive phosphorus concentrations. The phosphorus sorption dynamics of two limestone rocks of different composition were investigated by simulating seawater intrusion over a wide range of mixing ratios between freshwater and saltwater. Both rocks exhibited a

The balance of fresh and marine water sources in coastal mixing zones can affect phosphorus (P) availability, one of the important drivers of primary productivity. This study focuses on an abiotic portion of the P cycle in the mangrove ecotone of Taylor Slough, coastal Everglades, Florida. We investigated the P sorption properties of sediment with three distinct water sources in this region: 1) fresh groundwater from the inland Everglades, 2) bicarbonate enriched groundwater from the mangrove ecotone, and 3) surface saltwater from Florida Bay. Ecotone groundwater caused soluble reactive P (SRP) to exhibit markedly low sorption efficiency (K d =0.2 L g-1) compared to fresh groundwater and Florida Bay water (11.3 L g-1 and 3.4 L g-1 , respectively). The low SRP buffering capacity of the sediment in ecotone groundwater would maintain higher ambient water SRP concentration in ecotone groundwater than in the other two waters, and would trigger desorption if the sediment changed from one of them to ecotone groundwater. The relative sorption efficiency is consistent with the measured zero equilibrium SRP concentration being highest in ecotone groundwater (0.094 ± 0.003 M) and lower in fresh groundwater and Florida Bay surface water (0.075 ± 0.005 M and 0.058 ± 0.004 M respectively). The temporal variability of SRP concentration in groundwater at the ecotone field station is greater than the range of zero equilibrium SRP concentration for all three waters, so very low SRP concentration in the ambient water would induce desorption from the sediment. Soluble reactive P would be expected to begin desorbing from the sediments at a higher ambient SRP concentration in ecotone groundwater than the other two water types. Our results suggest that ecotone groundwater would release more SRP from mangrove sediments compared to the upstream and downstream waters, due to both its lower P sorption efficiency and its higher zero equilibrium SRP concentration.

In this paper, we provide screening-level analysis of plausible Everglades ecosystem response by 2060 to sea level rise (0.50 m) interacting with macroclimate change (1.5 °C warming, 7% increase in evapotranspiration, and rainfall that either increases or decreases by 10%). We used these climate scenarios as input to the Ecological Landscape Model to simulate changes to seven interactive hydro-ecological metrics. Mangrove forest and other marine influences migrated up to 15 km inland in both scenarios, delineated by the saltwater front. Freshwater habitat area decreased by 25-30% under our two climate change scenarios and was largely replaced by mangroves and, in the increased rainfall scenario, open water as well. Significant mangroves drowned along northern Florida Bay in both climate change scenarios due to sea level rise. Increased rainfall of 10% provided significant benefits to the spatial and temporal salinity regime within the marine-influenced zone, providing a more gradual and natural adjustment for at-risk flora and fauna. However, increased rainfall also increased the risk of open water, due to water depths that inhibited mangrove establishment and reduced peat accumulation rates. We infer that ecological effects related to sea level rise may occur in the extreme front-edge of saltwater intrusion, that topography will control the incursion of this zone as sea level rises, and that differences in freshwater availability will have ecologically significant effects on ecosystem resilience through the temporal and spatial pattern of salinity changes.

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