Abstract
We estimated the net exchange of nitrogen and phosphorus species using core incubations under light and dark conditions in estuarine lakes that are the aquatic interface between the freshwater Everglades and marine Florida Bay. These lakes and adjacent shallow water Florida Bay environments are sites where the restoration of hydrological flows will likely have the largest impact on salinity. Sediment respiration, measured by oxygen uptake, averaged (±S.D.) −2400 ± 1300, −300 ± 1000, and 1900 ± 1400 μmol m−2 h−1 for dark incubations, light incubations, and gross photosynthesis estimates, respectively, with dark incubations consistent with oxygen uptake measured by microelectrode profiles. Although most fluxes of soluble reactive phosphorus, nitrate, and N2–N were low under both light and dark incubation conditions, we observed a number of very high efflux events of NH4+ during dark incubations. A significant decrease in NH4+flux was observed in the light. The largest differences between light and dark effluxes of NH4+ occurred in lakes during periods of low coverage of the aquatic macrophyte Chara hornemannii Wallman, with NH4+ effluxes > 200 μmol m−2 h−1. Increasing freshwater flow from the Everglades is expected to expand lower salinity environments suitable for Chara, and therefore, diminish the sediment NH4+ effluxes that may fuel algal blooms.
Highlights
The land–sea interface in coastal ecosystems faces numerous challenges including eutrophication, shoreline alteration due to development, sea-level rise-driven erosion of shorelines and wetlands, and changes in the hydrological connection between land and watersheds
The goal of this research was to determine whether changes in salinity and/or submerged aquatic vegetation (SAV) coverage changed the net exchange of N and P across the sediment–water interface
In Monroe Lake, the highest water column chlorophyll a concentration occurred during a period of increasing Chara cover, while an increase in water column chlorophyll a in Seven Palm Lake occurred during a period of decreasing Chara cover
Summary
The land–sea interface in coastal ecosystems faces numerous challenges including eutrophication, shoreline alteration due to development, sea-level rise-driven erosion of shorelines and wetlands, and changes in the hydrological connection between land and watersheds. Changes to the hydrology of coastal ecosystems alters water residence times, the timing and amount of nutrient input, rates of nutrient biogeochemical cycling, and the balance between benthic and water column primary production. Benthic biogeochemical processes respond to changes in salinity, temperature, pH, and organic matter loading [1,2,3,4], altering the rate, direction, and nature of nitrogen (N) and phosphorus (P) flux to the water column. The restoration of freshwater flows into the coastal ecosystem can have myriad beneficial effects such as improved habitat for submerged aquatic vegetation [5], though the deleterious effects of increased nutrient inputs are a concern to both freshwater and downstream estuarine environments [6,7,8]
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