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Abstract Climate change is accelerating sea‐level rise and saltwater intrusion in coastal regions world‐wide and interacting with large‐scale changes in species composition in coastal wetlands. Quantifying macrophyte litter breakdown along freshwater‐to‐marine coastal gradients is needed to predict how carbon stores will respond to shifts in both macrophyte communities and water chemistry under changing environmental conditions.To test the interactive drivers of changing species identity and water chemistry, we performed a reciprocal transplant of four macrophyte litter species in seven sites along freshwater‐to‐marine gradients in the Florida Coastal Everglades. We measured surface water chemistry (dissolved organic carbon, total nitrogen and total phosphorus), litter chemistry (% nitrogen, % phosphorus, change in N:P molar ratio, % cellulose and % lignin as proxies for recalcitrance) and litter breakdown rates (k/degree‐day).Direct effects of salinity and surface water nutrients were the strongest drivers ofk, but unexpectedly, litter chemistry did not correlate with litterk. However, salinity strongly correlated with changes in litter chemistry, whereby litter incubated in brackish and marine wetlands was more labile and gained more phosphorus compared with litter in freshwater marshes. Our results suggest that litterkin coastal wetlands is explained by species‐specific interactions among water and litter chemistries. Water nutrient availability was an important predictor of breakdown rates across species, but breakdown rates were only explained by the carbon recalcitrance of litter in the species with the slowest breakdown (Cladium jamaicense), indicating the importance of carbon structure, and species identity on breakdown rates.Synthesis. In oligotrophic ecosystems, nutrients are often the primary driver of organic matter breakdown. However, we found that variation in macrophyte breakdown rates in oligotrophic coastal wetlands was also explained by salinity and associated seawater chemistry, emphasising the need to understand how saltwater intrusion will alter organic matter processing in wetlands. Our results suggest that marine subsidies associated with sea‐level rise have the potential to accelerate leaf litter breakdown. The increase in breakdown rates could either be buffered or increase further as sea‐level rise also shifts macrophyte community composition to more or less recalcitrant species.
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This content will become publicly available on February 20, 2026
Carbonate sediment production in coastal wetlands: Periphyton contributions and diatom indicators
Coastal ecosystems rapidly transform as sea levels rise faster than ecosystems can build elevation through biological processes that accrete organic matter and inorganic sediment. Benthic microbial communities (periphyton) are a crucial driver of sediment accretion in coastal wetlands by forming, trapping, and stabilizing sediments. Inorganic sediments can be either generated in situ by mineral-accreting organisms (e.g., calcium carbonates by periphyton), or materials can be transported from a different origin when sediments become resuspended and displaced, such as during high-wind weather events. In situ-generated sedimentary materials may contribute significantly to elevation gains. This study examines the drivers of coastal periphyton mineral production and whether periphytic diatoms may be used to characterize gradients in these drivers. Periphyton mineral production rates and diatom assemblage composition were measured along three coastal gradients of surface water salinity, conductivity, pH, and periphyton nutrient content in the Biscayne Bay Coastal Wetlands of South Florida. Periphyton mineral production rates ranged from 0.20-0.53 g/m2/d and were greatest at sites with the highest periphyton total carbon and mineral content while lowest at sites with the highest periphyton organic content and total nitrogen and soil depth. Diatom assemblages that sorted consistently along the coastal salinity gradient were reliable indicators of periphyton mineral production, with seven taxa indicating high rates and seven indicating low rates. Diatoms can provide a helpful link between biotic and abiotic processes, indicating where periphyton-driven mineral production contributes most to inorganic carbon cycling and mineral-driven elevation recovery and, hence, to resiliency to sea level rise.
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- PAR ID:
- 10643695
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Ecological indicators
- ISSN:
- 1872-7034
- Subject(s) / Keyword(s):
- Bio-indicators Carbon cycling Coastal wetlands Ecological monitoring Microalgae Saltwater intrusion Florida USA
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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