Carbon Balance in Salt Marsh and Mangrove Ecosystems: A Global Synthesis

Alongi, Daniel M.

doi:10.20944/preprints202009.0236.v1

Cited by 23 publications

(21 citation statements)

References 27 publications

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“…Groundwater‐derived CH 4 fluxes in salt marshes were quantified only on three occasions and range from 0.2 to 1.2 mmol m −2 d −1 (Porubsky et al., 2014; Santos et al., 2019; Schutte et al., 2020). These values are comparable to the global average of 0.24 mmol m −2 d −1 emitted from salt marsh surface water (Alongi, 2020).…”

Section: Impact Of Surface Water and Groundwater Interaction On Coast...supporting

confidence: 83%

“…Salt marshes are primary production hotspots that accumulate sediment and carbon at high rates (Alongi, 2020; D. Wang et al., 2021). Part of the carbon accumulated in salt marsh sediments can be flushed out via shallow porewater exchange and deep groundwater flow, eventually reaching the coastal sea (Figure 13).…”

Section: Impact Of Surface Water and Groundwater Interaction On Coast...mentioning

confidence: 99%

“…The average global CH 4 water‐air flux in salt marshes is 0.24 mmol m −2 d −1 (Alongi, 2020) and can range from −0.09 to 94.4 mmol m −2 d −1 when including both water and sediment fluxes (Rosentreter et al., 2021). Methane is generated during microbial decomposition of organic matter usually under anaerobic conditions.…”

Section: Impact Of Surface Water and Groundwater Interaction On Coast...mentioning

confidence: 99%

“…The hydrological background was modified from Santos, Chen, et al. (2021), carbon fluxes upscaled to global salt marshes in units of Tg C y −1 are obtained from Alongi (2020), and simplified biogeochemical reactions are obtained from Burdige (2007). Globally, the gross primary production of salt marshes is 97 Tg C y −1 .…”

Section: Impact Of Surface Water and Groundwater Interaction On Coast...mentioning

confidence: 99%

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Surface Water and Groundwater Interactions in Salt Marshes and Their Impact on Plant Ecology and Coastal Biogeochemistry

Xin

Wilson

Shen

et al. 2022

Reviews of Geophysics

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Salt marshes are highly productive intertidal wetlands providing important ecological services for maintaining coastal biodiversity, buffering against oceanic storms, and acting as efficient carbon sinks. However, about half of these wetlands have been lost globally due to human activities and climate change. Inundated periodically by tidal water, salt marshes are subjected to strong surface water and groundwater interactions, which affect marsh plant growth and biogeochemical exchange with coastal water. This paper reviews the state of knowledge and current approaches to quantifying marsh surface water and groundwater interactions with a focus on porewater flow and associated soil conditions in connection with plant zonation as well as carbon, nutrients, and greenhouse gas fluxes. Porewater flow and solute transport in salt marshes are primarily driven by tides with moderate regulation by rainfall, evapotranspiration and sea level rise. Tidal fluctuations play a key role in plant zonation through alteration of soil aeration and salt transport, and drive the export of significant fluxes of carbon and nutrients to coastal water. Despite recent progress, major knowledge gaps remain. Previous studies focused on flows in creek‐perpendicular marsh sections and overlooked multi‐scale 3D behaviors. Understanding of marsh ecological‐hydrological links under combined influences of different forcing factors and boundary disturbances is lacking. Variations of surface water and groundwater temperatures affect porewater flow, soil conditions and biogeochemical exchanges, but the extent and underlying mechanisms remain unknown. We need to fill these knowledge gaps to advance understanding of salt marshes and thus enhance our ability to protect and restore them.

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Section: Impact Of Surface Water and Groundwater Interaction On Coast...supporting

confidence: 83%

Section: Impact Of Surface Water and Groundwater Interaction On Coast...mentioning

confidence: 99%

Section: Impact Of Surface Water and Groundwater Interaction On Coast...mentioning

confidence: 99%

Section: Impact Of Surface Water and Groundwater Interaction On Coast...mentioning

confidence: 99%

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Surface Water and Groundwater Interactions in Salt Marshes and Their Impact on Plant Ecology and Coastal Biogeochemistry

Xin

Wilson

Shen

et al. 2022

Reviews of Geophysics

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“…These ecosystems have high rates of C accumulation and burial, slow decomposition rates, and a relatively high fraction of biomass belowground. Autotrophic R (a large proportion of which is leaf R ) is a major component of the coastal wetland C cycle, accounting for an estimated ~50% of GPP in marsh and mangrove ecosystems (Alongi, 2020). However, direct measures of leaf R or its temperature sensitivity over space and time are relatively rare for marsh and mangrove species.…”

Section: Introductionmentioning

confidence: 99%

Temperature acclimation of leaf respiration differs between marsh and mangrove vegetation in a coastal wetland ecotone

Sturchio

Chieppa

Chapman

et al. 2021

Global Change Biology

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Temperature acclimation of leaf respiration (R) is an important determinant of ecosystem responses to temperature and the magnitude of temperature‐CO2 feedbacks as climate warms. Yet, the extent to which temperature acclimation of R exhibits a common pattern across different growth conditions, ecosystems, and plant functional types remains unclear. Here, we measured the short‐term temperature response of R at six time points over a 10‐month period in two coastal wetland species (Avicennia germinans [C3 mangrove] and Spartina alterniflora [C4 marsh grass]) growing under ambient and experimentally warmed temperatures at two sites in a marsh–mangrove ecotone. Leaf nitrogen (N) was determined on a subsample of leaves to explore potential coupling of R and N. We hypothesized that both species would reduce R at 25°C (R25) and the short‐term temperature sensitivity of R (Q10) as air temperature (Tair) increased across seasons, but the decline would be stronger in Avicennia than in Spartina. For each species, we hypothesized that seasonal temperature acclimation of R would be equivalent in plants grown under ambient and warmed temperatures, demonstrating convergent acclimation. Surprisingly, Avicennia generally increased R25 with increasing growth temperature, although the Q10 declined as seasonal temperatures increased and did so consistently across sites and treatments. Weak temperature acclimation resulted in reduced homeostasis of R in Avicennia. Spartina reduced R25 and the Q10 as seasonal temperatures increased. In Spartina, seasonal temperature acclimation was largely consistent across sites and treatments resulting in greater respiratory homeostasis. We conclude that co‐occurring coastal wetland species may show contrasting patterns of respiratory temperature acclimation. Nonetheless, leaf N scaled positively with R25 in both species, highlighting the importance of leaf N in predicting respiratory capacity across a range of growth temperatures. The patterns of respiratory temperature acclimation shown here may improve the predictions of temperature controls of CO2 fluxes in coastal wetlands.

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Modeling net ecosystem carbon balance and loss in coastal wetlands exposed to sea‐level rise and saltwater intrusion

Ishtiaq

Troxler

Lamb-Wotton

et al. 2022

Ecological Applications

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Coastal wetlands are globally important stores of carbon (C). However, accelerated sea‐level rise (SLR), increased saltwater intrusion, and modified freshwater discharge can contribute to the collapse of peat marshes, converting coastal peatlands into open water. Applying results from multiple experiments from sawgrass (Cladium jamaicense)‐dominated freshwater and brackish water marshes in the Florida Coastal Everglades, we developed a system‐level mechanistic peat elevation model (EvPEM). We applied the model to simulate net ecosystem C balance (NECB) and peat elevation in response to elevated salinity under inundation and drought exposure. Using a mass C balance approach, we estimated net gain in C and corresponding export of aquatic fluxes (FAQ$$ {F}_{\mathrm{AQ}} $$) in the freshwater marsh under ambient conditions (NECB = 1119 ± 229 gC m−2 year−1; FAQ = 317 ± 186 gC m−2 year−1). In contrast, the brackish water marsh exhibited substantial peat loss and aquatic C export with ambient (NECB = −366 ± 15 gC m−2 year−1; FAQ = 311 ± 30 gC m−2 year−1) and elevated salinity (NECB = −594 ± 94 gC m−2 year−1; FAQ = 729 ± 142 gC m−2 year−1) under extended exposed conditions. Further, mass balance suggests a considerable decline in soil C and corresponding elevation loss with elevated salinity and seasonal dry‐down. Applying EvPEM, we developed critical marsh net primary productivity (NPP) thresholds as a function of salinity to simulate accumulating, steady‐state, and collapsing peat elevations. The optimization showed that ~150–1070 gC m−2 year−1 NPP could support a stable peat elevation (elevation change ≈ SLR), with the corresponding salinity ranging from 1 to 20 ppt under increasing inundation levels. The C budgeting and modeling illustrate the impacts of saltwater intrusion, inundation, and seasonal dry‐down and reduce uncertainties in understanding the fate of coastal peat wetlands with SLR and freshwater restoration. The modeling results provide management targets for hydrologic restoration based on the ecological conditions needed to reduce the vulnerability of the Everglades' peat marshes to collapse. The approach can be extended to other coastal peatlands to quantify C loss and improve understanding of the influence of the biological controls on wetland C storage changes for coastal management.

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Carbon Balance in Salt Marsh and Mangrove Ecosystems: A Global Synthesis

Cited by 23 publications

References 27 publications

Surface Water and Groundwater Interactions in Salt Marshes and Their Impact on Plant Ecology and Coastal Biogeochemistry

Surface Water and Groundwater Interactions in Salt Marshes and Their Impact on Plant Ecology and Coastal Biogeochemistry

Temperature acclimation of leaf respiration differs between marsh and mangrove vegetation in a coastal wetland ecotone

Modeling net ecosystem carbon balance and loss in coastal wetlands exposed to sea‐level rise and saltwater intrusion

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