Journal
ECOLOGY
Volume 100, Issue 5, Pages -Publisher
WILEY
DOI: 10.1002/ecy.2672
Keywords
carbon cycling; coastal marsh; Florida Everglades; peat collapse; phosphorus; sea level rise
Categories
Funding
- National Science Foundation's Florida Coastal Everglades Long Term Ecological Research Program [DEB-1237517]
- Everglades Section of the South Florida Water Management District [R/C-S-56]
- Everglades Foundation
- Everglades National Park
- State of Florida Department of Transportation Region
- Florida International University (FIU) Teaching Assistantship
- FIU Dissertation Year Fellowship [899]
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Saltwater intrusion and salinization of coastal wetlands around the world are becoming a pressing issue due to sea level rise. Here, we assessed how a freshwater coastal wetland ecosystem responds to saltwater intrusion. In wetland mesocosms, we continuously exposed Cladium jamaicense Crantz (sawgrass) plants and their peat soil collected from a freshwater marsh to two factors associated with saltwater intrusion in karstic ecosystems: elevated loading of salinity and phosphorus (P) inputs. We took repeated measures using a 2 9 2 factorial experimental design (n = 6) with treatments composed of elevated salinity (similar to 9 ppt), P loading (14.66 mu mol P/d), or a combination of both. We measured changes in water physicochemistry, ecosystem productivity, and plant biomass change over two years to assess monthly and two-year responses to saltwater intrusion. In the short-term, plants exhibited positive growth responses with simulated saltwater intrusion (salinity + P), driven by increased P availability. Despite relatively high salinity levels for a freshwater marsh (similar to 9 ppt), gross ecosystem productivity (GEP), net ecosystem productivity (NEP), and aboveground biomass were significantly higher in the elevated salinity + P treated monoliths compared to the freshwater controls. Salinity stress became evident after extended exposure. Although still higher than freshwater controls, GEP and NEP were significantly lower in the elevated salinity + P treatment than the + P treatment after two years. However, elevated salinity decreased live root biomass regardless of whether P was added. Our results suggest that saltwater intrusion into karstic freshwater wetlands may initially act as a subsidy by stimulating aboveground primary productivity of marsh plants. However, chronic exposure to elevated salinity results in plant stress, negatively impacting belowground peat soil structure and stability through a reduction in plant roots.
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