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1. Climate-driven tradeoffs between landscape connectivity and the maintenance of the coastal carbon sink

   https://doi.org/10.1038/s41467-023-36803-7  

   Valentine, Kendall; Herbert, Ellen R.; Walters, David C.; Chen, Yaping; Smith, Alexander J.; Kirwan, Matthew L. (March 2023, Nature Communications)

   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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2. Sediment Exchange Across Coastal Barrier Landscapes Alters Ecosystem Extents

   https://doi.org/10.1029/2023GL103680  

   Reeves, I_R_B; Moore, L_J; Valentine, K.; Fagherazzi, S.; Kirwan, M_L (July 2023, Geophysical Research Letters)

   Abstract Barrier coastlines and their associated ecosystems are rapidly changing. Barrier islands/spits, marshes, bays, and coastal forests are all thought to be intricately coupled, yet an understanding of how morphologic change in one part of the system affects the system altogether remains limited. Here we explore how sediment exchange controls the migration of different ecosystem boundaries and ecosystem extent over time using a new coupled model framework that connects components of the entire barrier landscape, from the ocean shoreface to mainland forest. In our experiments, landward barrier migration is the primary cause of back‐barrier marsh loss, while periods of barrier stability can allow for recovery of back‐barrier marsh extent. Although sea‐level rise exerts a dominant control on the extent of most ecosystems, we unexpectedly find that, for undeveloped barriers, bay extent is largely insensitive to sea‐level rise because increased landward barrier migration (bay narrowing) offsets increased marsh edge erosion (bay widening). 

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3. Effects of landscape setting on oyster reef structure and function largely persist more than a decade post‐restoration

   https://doi.org/10.1111/rec.12651  

   Ziegler, Shelby L.; Grabowski, Jonathan H.; Baillie, Christopher J.; Fodrie, F. J. (December 2017, Restoration Ecology)

   Long‐term monitoring is vital to understanding the efficacy of restoration approaches and how restoration may enhance ecosystem functions. We revisited restored oyster reefs 13 years post‐restoration and quantified the resident and transient fauna that utilize restored reefs in three differing landscape contexts: on mudflats isolated from vegetated habitat, along the edge of salt marsh, and in between seagrass and salt marsh habitat. Differences observed 1–2 years post‐restoration in reef development and associated fauna within reefs restored on mudflats versus adjacent to seagrass/salt marsh and salt marsh‐only habitats persisted more than 10 years post‐restoration. Reefs constructed on open mudflat habitats had the highest densities of oysters and resident invertebrates compared to those in other landscape contexts, although all restored reefs continued to enhance local densities of invertebrate taxa (e.g. bivalves, gastropods, decapods, polychaetes, etc.). Catch rates of juvenile fishes were enhanced on restored reefs relative to controls, but to a lesser extent than directly post‐restoration, potentially because the reefs have grown vertically within the intertidal and out of the preferred inundation regime of small juvenile fishes. Reef presence and landscape setting did not augment the catch rates of piscivorous fishes in passive gill nets, similar to initial findings; however, hook‐and‐line catch rates were greater on restored reefs than non‐reef controls. We conclude that ecosystem functions and associated services provided by restored habitats can vary both spatially and temporally; therefore, a better understanding of how service delivery varies among landscape setting and over time should enhance efforts to model these processes and restoration decision‐making. 

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4. Temperature optimum for marsh resilience and carbon accumulation revealed in a whole‐ecosystem warming experiment

   https://doi.org/10.1111/gcb.16149  

   Smith, Alexander J.; Noyce, Genevieve L.; Megonigal, James Patrick; Guntenspergen, Glenn R.; Kirwan, Matthew L. (March 2022, Global Change Biology)

   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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5. Modeling long‐term salt marsh response to sea level rise in the sediment‐deficient Plum Island Estuary, MA

   https://doi.org/10.1002/lno.11444  

   Langston, Amy K.; Durán Vinent, Orencio; Herbert, Ellen R.; Kirwan, Matthew L. (April 2020, Limnology and Oceanography)

   Abstract An accelerating global rate of sea level rise (SLR), coupled with direct human impacts to coastal watersheds and shorelines, threatens the continued survival of salt marshes. We developed a new landscape‐scale numerical model of salt marsh evolution and applied it to marshes in the Plum Island Estuary (Massachusetts, U.S.A.), a sediment‐deficient system bounded by steep uplands. To capture complexities of vertical accretion across the marsh platform, we employed a novel approach that incorporates spatially variable suspended sediment concentrations and biomass of multiple plant species as functions of elevation and distance from sediment sources. The model predicts a stable areal extent of Plum Island marshes for a variety of SLR scenarios through 2100, where limited marsh drowning is compensated by limited marsh migration into adjacent uplands. Nevertheless, the model predicts widespread conversion of high marsh vegetation to low marsh vegetation, and accretion deficits that indicate eventual marsh drowning. Although sediment‐deficient marshes bounded by steep uplands are considered extremely vulnerable to SLR, our results highlight that marshes with high elevation capital can maintain their areal extent for decades to centuries even under conditions in which they will inevitably drown. 

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