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Abstract Emissions of methane (CH₄) and nitrous oxide (N₂O) from soils to the atmosphere can offset the benefits of carbon sequestration for climate change mitigation. While past study has suggested that both CH₄and N₂O emissions from tidal freshwater forested wetlands (TFFW) are generally low, the impacts of coastal droughts and drought‐induced saltwater intrusion on CH₄and N₂O emissions remain unclear. In this study, a process‐driven biogeochemistry model, Tidal Freshwater Wetland DeNitrification‐DeComposition (TFW‐DNDC), was applied to examine the responses of CH₄and N₂O emissions to episodic drought‐induced saltwater intrusion in TFFW along the Waccamaw River and Savannah River, USA. These sites encompass landscape gradients of both surface and porewater salinity as influenced by Atlantic Ocean tides superimposed on periodic droughts. Surprisingly, CH₄and N₂O emission responsiveness to coastal droughts and drought‐induced saltwater intrusion varied greatly between river systems and among local geomorphologic settings. This reflected the complexity of wetland CH₄and N₂O emissions and suggests that simple linkages to salinity may not always be relevant, as non‐linear relationships dominated our simulations. Along the Savannah River, N₂O emissions in the moderate‐oligohaline tidal forest site tended to increase dramatically under the drought condition, while CH₄emission decreased. For the Waccamaw River, emissions of both CH₄and N₂O in the moderate‐oligohaline tidal forest site tended to decrease under the drought condition, but the capacity of the moderate‐oligohaline tidal forest to serve as a carbon sink was substantially reduced due to significant declines in net primary productivity and soil organic carbon sequestration rates as salinity killed the dominant freshwater vegetation. These changes in fluxes of CH₄and N₂O reflect crucial synergistic effects of soil salinity and water level on C and N dynamics in TFFW due to drought‐induced seawater intrusion. 

Mangrove ecosystems in the Caribbean are frequently exposed to hurricanes, leading to structural and regenerative change that elicit calls for recovery action. For those mangroves unaffected by human modifications, recovery can occur naturally. Indeed, observable natural recovery after hurricanes is the genesis of the “disturbance adaptation” classification for mangroves; while structural legacies exist, unaltered stands often regenerate and persist. However, among the >7,000 islands, islets, and cays that make up the Caribbean archipelago, coastal alterations to support development affect mechanisms for regeneration, sediment distribution, tidal water conveyance, and intertidal mangrove transgression, imposing sometimes insurmountable barriers to natural post-hurricane recovery. We use a case study approach to suggest that actions to facilitate recovery of mangroves on Caribbean islands (and similar settings globally) may be more effective when focusing on ameliorating preexisting anthropogenic stressors. Actions to clean debris, collect mangrove propagules, and plant seedlings are noble endeavors, but can be costly and fall short of achieving recovery goals in isolation without careful consideration of pre-hurricane stress. We update a procedural framework that considers six steps to implementing “Ecological Mangrove Restoration” (EMR), and we apply them specifically to hurricane recovery. If followed, EMR may expedite actions by suggesting immediate damage assessment focused on hydrogeomorphic mangrove type, hydrology, and previous anthropogenic (or natural) influence. Application of EMR may help to improve mangrove recovery success following catastrophic storms, and reduce guesswork, delays, and monetary inefficiencies. Key words: ecological mangrove restoration, EMR, genetic considerations, hydrogeomorphic type, regeneration, resiliency bottlenecks, tropical cyclones 

Environmental observation networks, such as AmeriFlux, are foundational for monitoring ecosystem response to climate change, management practices, and natural disturbances; however, their effectiveness depends on their representativeness for the regions or continents. We proposed an empirical, time series approach to quantify the similarity of ecosystem fluxes across AmeriFlux sites. We extracted the diel and seasonal characteristics (i.e., amplitudes, phases) from carbon dioxide, water vapor, energy, and momentum fluxes, which reflect the effects of climate, plant phenology, and ecophysiology on the observations, and explored the potential aggregations of AmeriFlux sites through hierarchical clustering. While net radiation and temperature showed latitudinal clustering as expected, flux variables revealed a more uneven clustering with many small (number of sites < 5), unique groups and a few large (> 100) to intermediate (15–70) groups, highlighting the significant ecological regulations of ecosystem fluxes. Many identified unique groups were from under-sampled ecoregions and biome types of the International Geosphere-Biosphere Programme (IGBP), with distinct flux dynamics compared to the rest of the network. At the finer spatial scale, local topography, disturbance, management, edaphic, and hydrological regimes further enlarge the difference in flux dynamics within the groups. Nonetheless, our clustering approach is a data-driven method to interpret the AmeriFlux network, informing future cross-site syntheses, upscaling, and model-data benchmarking research. Finally, we highlighted the unique and underrepresented sites in the AmeriFlux network, which were found mainly in Hawaii and Latin America, mountains, and at under- sampled IGBP types (e.g., urban, open water), motivating the incorporation of new/unregistered sites from these groups. 

This dataset contains the result of simulated daily emissions of methane (CH4) and nitrous oxide (N2O) from the soils in Tidal Freshwater Forested Wetlands (TFFW) along the Waccamaw River (SC, USA) and the Savannah River (GA and SC, USA) under drought-induced saltwater intrusion using a process-driven biogeochemistry model. 

Comparing marsh elevation change across four continents provides an explanation for variable marsh responses to sea-level rise. 

Abstract Climate change is altering species’ range limits and transforming ecosystems. For example, warming temperatures are leading to the range expansion of tropical, cold-sensitive species at the expense of their cold-tolerant counterparts. In some temperate and subtropical coastal wetlands, warming winters are enabling mangrove forest encroachment into salt marsh, which is a major regime shift that has significant ecological and societal ramifications. Here, we synthesized existing data and expert knowledge to assess the distribution of mangroves near rapidly changing range limits in the southeastern USA. We used expert elicitation to identify data limitations and highlight knowledge gaps for advancing understanding of past, current, and future range dynamics. Mangroves near poleward range limits are often shorter, wider, and more shrublike compared to their tropical counterparts that grow as tall forests in freeze-free, resource-rich environments. The northern range limits of mangroves in the southeastern USA are particularly dynamic and climate sensitive due to abundance of suitable coastal wetland habitat and the exposure of mangroves to winter temperature extremes that are much colder than comparable range limits on other continents. Thus, there is need for methodological refinements and improved spatiotemporal data regarding changes in mangrove structure and abundance near northern range limits in the southeastern USA. Advancing understanding of rapidly changing range limits is critical for foundation plant species such as mangroves, as it provides a basis for anticipating and preparing for the cascading effects of climate-induced species redistribution on ecosystems and the human communities that depend on their ecosystem services. 

Abstract Wetland methane (CH 4 ) emissions ( $${F}_{{{CH}}_{4}}$$ F C H 4 ) are important in global carbon budgets and climate change assessments. Currently, $${F}_{{{CH}}_{4}}$$ F C H 4 projections rely on prescribed static temperature sensitivity that varies among biogeochemical models. Meta-analyses have proposed a consistent $${F}_{{{CH}}_{4}}$$ F C H 4 temperature dependence across spatial scales for use in models; however, site-level studies demonstrate that $${F}_{{{CH}}_{4}}$$ F C H 4 are often controlled by factors beyond temperature. Here, we evaluate the relationship between $${F}_{{{CH}}_{4}}$$ F C H 4 and temperature using observations from the FLUXNET-CH 4 database. Measurements collected across the globe show substantial seasonal hysteresis between $${F}_{{{CH}}_{4}}$$ F C H 4 and temperature, suggesting larger $${F}_{{{CH}}_{4}}$$ F C H 4 sensitivity to temperature later in the frost-free season (about 77% of site-years). Results derived from a machine-learning model and several regression models highlight the importance of representing the large spatial and temporal variability within site-years and ecosystem types. Mechanistic advancements in biogeochemical model parameterization and detailed measurements in factors modulating CH 4 production are thus needed to improve global CH 4 budget assessments. 

Abstract Wetlands cover a small portion of the world, but have disproportionate influence on global carbon (C) sequestration, carbon dioxide and methane emissions, and aquatic C fluxes. However, the underlying biogeochemical processes that affect wetland C pools and fluxes are complex and dynamic, making measurements of wetland C challenging. Over decades of research, many observational, experimental, and analytical approaches have been developed to understand and quantify pools and fluxes of wetland C. Sampling approaches range in their representation of wetland C from short to long timeframes and local to landscape spatial scales. This review summarizes common and cutting-edge methodological approaches for quantifying wetland C pools and fluxes. We firstdefineeach of the major C pools and fluxes and providerationalefor their importance to wetland C dynamics. For each approach, we clarifywhatcomponent of wetland C is measured and its spatial and temporal representativeness and constraints. We describe practical considerations for each approach, such aswhereandwhenan approach is typically used,whocan conduct the measurements (expertise, training requirements), andhowapproaches are conducted, including considerations on equipment complexity and costs. Finally, we reviewkey covariatesandancillary measurementsthat enhance the interpretation of findings and facilitate model development. The protocols that we describe to measure soil, water, vegetation, and gases are also relevant for related disciplines such as ecology. Improved quality and consistency of data collection and reporting across studies will help reduce global uncertainties and develop management strategies to use wetlands as nature-based climate solutions.