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Salt marshes provide valuable ecosystem services but are vulnerable to drowning with accelerated sea-level rise (SLR). Marsh belowground biomass (BGB) production helps avoid drowning by building marsh surface elevation. Reductions in BGB can serve as an early warning sign of marsh deterioration, as they often precede decreases in aboveground biomass (AGB). However, landscape-scale BGB assessments to predict broad trends in marsh deterioration have not been previously available. We applied the Belowground Ecosystem Resiliency Model (BERM) to assess standing stocks and trends in both BGB and AGB over the past decade (2014–2023) across US Georgia coastSpartina alternifloramarshes (691 km2). Over this time period, BGB and AGB averaged 841 ± 323 and 221 ± 14 g m−2, respectively, but showed opposite trends. BGB decreased on average by 0.94% per year and over most of the marsh area (72%), while AGB increased on average by 0.66% per year and showed a net increase across most of the marsh area (88%). This disconnect suggests that AGB is not a good indicator of marsh resilience, and we highlight two areas with similar AGB but different BGB. Inundation intensity, an important predictor of BGB, rose through time and was negatively related to BGB. SLR trends suggest continuing increases in inundation, which will result in further declines in BGB followed by widespread marsh drowning. Landscape BGB assessments are a valuable tool to identify ecosystem vulnerability and proactively manage salt marshes and the services they provide under rising sea levels.
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Microtopographic Variation as a Potential Early Indicator of Ecosystem State Change and Vulnerability in Salt Marshes
Abstract As global climate change alters the magnitude and rates of environmental stressors, predicting the extent of ecosystem degradation driven by these rapidly changing conditions becomes increasingly urgent. At the landscape scale, disturbances and stressors can increase spatial variability and heterogeneity — indicators that can serve as potential early warnings of declining ecosystem resilience. Increased spatial variability in salt marshes at the landscape scale has been used to quantify the propagation of ponding in salt marsh interiors, but ponding at the landscape scale follows a state change rather than predicts it. Here, we suggest a novel application of commonly collected surface elevation table (SET) data and explore millimeter-scale marsh surface microtopography as a potential early indicator of ecosystem transition. We find an increase in spatial variability using multiple metrics of microtopographic heterogeneity in vulnerable salt marsh communities across the North American Atlantic seaboard. Increasing microtopographic heterogeneity in vulnerable salt marshes mirrored increasing trends in variance when a tipping point is approached in other alternative stable state systems — indicating that early warning signals of marsh drowning and ecosystem transition are observable at small-spatial scales prior to runaway ecosystem degradation. Congruence between traditional and novel metrics of marsh vulnerability suggests that microtopographic metrics can be used to identify hidden vulnerability before widespread marsh degradation. This novel analysis can be easily applied to existing SET records expanding the traditional focus on vertical change to additionally encapsulate lateral processes.
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- PAR ID:
- 10516330
- Publisher / Repository:
- Springer
- Date Published:
- Journal Name:
- Estuaries and Coasts
- ISSN:
- 1559-2723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1007/s12237-024-01368-1
