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Hurricanes can alter the rates and trajectories of biogeochemical cycling in coastal wetlands. Defoliation and vegetation death can lead to increased soil temperatures, and storm surge can variously cause erosion or deposition of sediment leading to changes in soil bulk density, nutrient composition, and redox characteristics. The objective of this study was to compare the biogeochemistry of pre-storm soils and a carbonate-rich sediment layer deposited by Hurricane Irma that made landfall in southwest Florida as a category 3 storm in September 2017. We predicted that indicators of biogeochemical activity (e.g., potential soil respiration rates, microbial biomass (MBC), and extracellular enzyme activities) would be lower in the storm sediment layer because of its lower organic matter content relative to pre-storm soils. There were few differences between the storm sediment and pre-storm soils at two of the sites closest to the Gulf of Mexico (GOM). This suggests that marine deposition regularly influences soil formation at these sites and is not something that occurs only during hurricanes. At a third site, 8 km from the GOM, the pre-storm soils had much greater concentrations of organic matter, total N, total P, MBC, and higher potential respiration rates than the storm layer. At this same site, CO2 fluxes from intact soil cores containing a layer of storm sediment were 30% lower than those without it. This suggests that sediment deposition from storm surge has the potential to preserve historically sequestered carbon in coastal soils through reduced respiratory losses. [ABSTRACT FROM AUTHOR]

The Suwannee River Basin (SRB) has served as a natural laboratory to study the impact of groundwater-surface water interaction on water quality and ecosystem function. Here we summarize our evolving understanding of groundwater-surface water exchange, and its impact on water quality. The SRB is underlain by the karstic Upper Floridan aquifer (UFA). The UFA is confined in the upper SRB, where surface water is enriched in organic carbon and CO2 as it drains from wetlands overland and through the surficial aquifer system. Remineralization of organic carbon enriches downstream water in CO2. This CO2-rich water flows onto the unconfined UFA, sinks underground, dissolves carbonate minerals, and thereby reduces CO2 evasion from the river. Discharge from the UFA enriches river water in nitrate. Groundwater-surface water exchange depends on groundwater head and river stage, which are controlled by timing and distribution of precipitation. Tides force water in and out of the UFA nearly 40 km upstream of the coast. Little is known about the magnitude of in-stream reactions in the SRB, or the extent of exchange between groundwater and coastal saltwater at the Suwannee River mouth. Both in-stream reactions and exchange at the coast impact nutrient fluxes, highlighting the need to further explore and quantify the water quality impacts of groundwater-surface water exchange. [ABSTRACT FROM AUTHOR]