Search for: All records

Abstract Saltmarshes provide vital ecosystem services, including coastal protection and habitat for fisheries. While feedbacks influencing vertical sediment accretion in marshes are well‐documented, including those between relative sea level and primary production, relationships among nutrient cycles, flooding, and primary production remain less explored. This study presents a unique 30‐year data set from the North Inlet estuary, South Carolina, tracking monthly growth of the dominant macrophyte,Spartina alterniflora, and porewater concentrations of sulfide, ammonium, and phosphate. Our findings reveal correlated seasonal and decadal patterns of sulfides, nutrients, and plant growth, with periodicities linked to seasonal climate and decadal tidal cycles.S.alterniflorathrives in anaerobic sediments where sulfides are toxic byproducts of sulfate‐reducing bacteria (SRB) produced through the oxidation of organic acids. Dissolved organic compounds fluctuated seasonally in tandem with plant growth. Organic acids utilized by SRB are released as root exudates and produced via cellulosic biomass fermentation. SRB fix nitrogen and produce sulfides that solubilize phosphate, compensating for nutrients lost in drainage and rafting of aboveground biomass. By directly and indirectly producing the substrates,Spartinaeffectively regulates SRB activity, thereby orchestrating biogeochemical cycles and accumulating sulfides that inhibit competing species. Our results challenge the traditional view of sulfides as mere phytotoxins and saltmarshes as passive nutrient transformers. Instead, we propose a model whereinS.alterniflorasustains its growth and supports estuarine productivity by regulating its nitrogen and phosphorus supplies through a mutualistic relationship with SRB. 

Wetlands are major carbon sinks because waterlogged sediments suppress decomposition, but the depth at which organic matter becomes effectively preserved remains poorly constrained. We quantified depth-dependent decomposition of labile and refractory organic matter using birch dowels deployed for 7 years in fertilized and control plots across salt and freshwater tidal marshes in South Carolina and Massachusetts. A surface-limited decay model revealed a consistent three-zone profile across contrasting climates, salinities, and nutrient regimes: rapid decomposition at the sediment surface, declining decomposition through an active rooting zone (~0–20 cm), and slow, nearly depth-invariant decomposition below ~20 cm. Labile material continued to decay after burial, whereas lignin degradation was largely restricted to the surface and strongly suppressed in deeper, reducing sediments. Fertilization accelerated surface loss of labile material but had little effect at depth, indicating that nutrient availability did not overcome the constraints imposed by burial depth. Estimated persistence increased from decades near the surface to a century or more at depth. These results identify the active rooting zone as a decomposition filter through which plant production must pass before entering deeper sediments where decay is greatly reduced. Consequently, long-term carbon burial depends not only on the amount of organic matter produced, but also on the balance between decomposition and the rate at which accretion transfers that material through the active zone. Depth-dependent decomposition thus provides a mechanistic link among plant production, carbon preservation, vertical accretion, and marsh resilience to relative sea-level rise. 

Different CO₂exchange pathways were monitored for a year in short- and tall-formSpartina alternifloragrasses in a southeastern USA salt marsh at North Inlet, South Carolina. The tall form of grass growing close to a creek under favorable conditions reached a higher standing biomass than the short form of grass growing in the interior marsh. However, the photosynthetic parameters of both forms of grass were equivalent. The tall canopy had greater net canopy production, 973 versus 571 g C m⁻²year⁻¹, canopy growth, 700 versus 131 g C m⁻²year⁻¹, and canopy respiration, 792 versus 225 g C m⁻²year⁻¹, but lower sediment respiration, 251 versus 392 g C m⁻²year⁻¹. In a single growing season, tall-canopy biomass increased to intercept all the available solar radiation, which limits gross photosynthesis. Total respiration increased during the growing season in proportion to live biomass to a level that limited net production. Theoretically, the difference between net canopy production and canopy growth is carbon allocated to belowground growth and respiration. However, the computation of belowground production by this method was unrealistically low. This is important because carbon sequestration is proportional to belowground production and accounts for most of the vertical elevation gain of the marsh surface. Based on the allometry of standing live biomass, alternative estimates of belowground production were 927 and 193 g C m⁻²year⁻¹in creekbank and interior marshes, which would yield gains in surface elevation of 0.2 and 0.04 cm/year, respectively. 

Aboveground biomass and plant density were measured non-destructively as a component of a long-term project seeking to understand how salt marsh primary production and sediment chemistry respond to anthropogenic (e.g. eutrophication) and natural (e.g. sea-level rise) environmental change. Feedbacks between plants, sediments, nutrients and flooding were investigated with particular attention to mechanisms that keep marshes in equilibrium with sea level. Biomass was calculated from plant height measurements using allometric equations. Annual productivity was calculated from approximately-monthly biomass estimates. In addition to plant height measurements, observations of snails in sample plots were recorded. Other data collected as part of the project include marsh surface elevation and porewater nutrient concentrations. These data have been used to develop the Marsh Equilibrium Model, an important tool for coastal resource managers. Sampling occurred at Spartina alterniflora-dominated salt marsh sites in North Inlet, a relatively pristine estuary near Georgetown, SC on the SE coast of the United States. North Inlet is a tidally-dominated, bar-built estuary, with a semi-diurnal mixed tide and a tidal range of 1.4m. The 25-km2 estuary is comprised of about 20.5 km2 of intertidal salt marsh and mudflats, and 4.5 km2 of open water. Sampling began at one location in 1984, and at three additional locations in 1986. Sampling occurred approximately monthly through 2023. The study is on-going. There are four sampling locations at two sites. Two locations are in the low marsh; two locations are in the high marsh. One high marsh location had control sampling plots in addition to plots fertilized with nitrogen and phosphorus. 

Porewater nutrient concentrations were measured as a component of a long-term project seeking to understand how salt marsh primary production and sediment chemistry respond to anthropogenic (e.g. eutrophication) and natural (e.g. sea-level rise) environmental change. Feedbacks between plants, sediments, nutrients and flooding were investigated with particular attention to mechanisms that keep marshes in equilibrium with sea level. Other data collected as part of the project include aboveground macrophyte biomass, plant density, marsh surface elevation and annual above ground primary productivity. These data have been used to develop the Marsh Equilibrium Model, an important tool for coastal resource managers. Sampling occurred at Spartina alterniflora-dominated salt marsh sites in North Inlet, a relatively pristine estuary near Georgetown, SC on the SE coast of the United States. North Inlet is a tidally-dominated, bar-built estuary, with a semi-diurnal mixed tide and a tidal range of 1.4m. The 25-km2 estuary is comprised of about 20.5 km2 of intertidal salt marsh and mudflats, and 4.5 km2 of open water. Sampling began at two locations in December 1993, and at three additional locations in January 1994. Sampling occurred approximately monthly at these 5 locations through 2023. Sampling occurred at a sixth location from 2006 to 2010. The site was a dieback site that had recovered by 2010. At the other sites, the study is on-going. Porewater was collected at multiple depths from diffusion samplers and was analyzed for sulfide, salinity, ammonium, phosphate, and iron concentrations. There are five sampling locations at three sites. Two locations are in the low marsh; three locations are in the high marsh. One high marsh location had control sampling plots in addition to plots fertilized with nitrogen and phosphorus. 

No description provided.