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  1. Free, publicly-accessible full text available June 1, 2024
  2. Coastal landscapes are naturally shifting mosaics of distinct ecosystems that are rapidly migratingwith sealevel rise. Previous work illustrates that transitions among individual ecosystems have disproportionate impacts on the global carbon cycle, but this cannot address nonlinear interactions between multiple ecosystems that potentially cascade across the coastal landscape. Here, we synthesize carbon stocks, accumulation rates, and regional land cover data over 36 years (1984 and 2020) for a variety of ecosystems across a large portion of the rapidly transgressing mid-Atlantic coast. The coastal landscape of the Virginia Eastern Shore consists of temperate forest, salt marsh, seagrass beds, barrier islands, and coastal lagoons. We found that rapid losses and gains within individual ecosystems largely offset each other, which resulted in relatively stable areas for the different ecosystems, and a 4% (196.9 Gg C) reduction in regional carbon storage. However, new metrics of carbon replacement times indicated that it would take only 7 years of carbon accumulation in surviving ecosystems to compensate this loss. Our findings reveal unique compensatory mechanisms at the scale of entire landscapes that quickly absorb losses and facilitate increased regional carbon storage in the face of historical and contemporary sea-level rise. However, the strength of these compensatory mechanisms may diminish as climate change exacerbates the magnitude of carbon losses. 
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    Free, publicly-accessible full text available September 15, 2024
  3. Abstract

    Ecosystem connectivity tends to increase the resilience and function of ecosystems responding to stressors. Coastal ecosystems sequester disproportionately large amounts of carbon, but rapid exchange of water, nutrients, and sediment makes them vulnerable to sea level rise and coastal erosion. Individual components of the coastal landscape (i.e., marsh, forest, bay) have contrasting responses to sea level rise, making it difficult to forecast the response of the integrated coastal carbon sink. Here we couple a spatially-explicit geomorphic model with a point-based carbon accumulation model, and show that landscape connectivity, in-situ carbon accumulation rates, and the size of the landscape-scale coastal carbon stock all peak at intermediate sea level rise rates despite divergent responses of individual components. Progressive loss of forest biomass under increasing sea level rise leads to a shift from a system dominated by forest biomass carbon towards one dominated by marsh soil carbon that is maintained by substantial recycling of organic carbon between marshes and bays. These results suggest that climate change strengthens connectivity between adjacent coastal ecosystems, but with tradeoffs that include a shift towards more labile carbon, smaller marsh and forest extents, and the accumulation of carbon in portions of the landscape more vulnerable to sea level rise and erosion.

     
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  6. Abstract

    Coastal marshes are globally important, carbon dense ecosystems simultaneously maintained and threatened by sea‐level rise. Warming temperatures may increase wetland plant productivity and organic matter accumulation, but temperature‐modulated feedbacks between productivity and decomposition make it difficult to assess how wetlands and their thick, organic‐rich soils will respond to climate warming. Here, we actively increased aboveground plant‐surface and belowground soil temperatures in two marsh plant communities, and found that a moderate amount of warming (1.7°C above ambient temperatures) consistently maximized root growth, marsh elevation gain, and belowground carbon accumulation. Marsh elevation loss observed at higher temperatures was associated with increased carbon mineralization and increased microtopographic heterogeneity, a potential early warning signal of marsh drowning. Maximized elevation and belowground carbon accumulation for moderate warming scenarios uniquely suggest linkages between metabolic theory of individuals and landscape‐scale ecosystem resilience and function, but our work indicates nonpermanent benefits as global temperatures continue to rise.

     
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