Wetland Carbon and Environmental Management. Группа авторов

United States Geological Survey

      PREFACE

      The idea for this book, including its organization and contents, has its origin in the latest environmental and climate policy requirements in the United States, as well as science advances. In 2007, the U.S. Congress passed the Energy Independence and Security Act (EISA), from which Section 712 required U.S. Federal agencies to provide a better understanding of carbon and greenhouse gas fluxes across the United States. As a result, large‐scale and coordinated efforts were launched to assess carbon storage, carbon fluxes, and greenhouse gas fluxes – including CO₂, CH₄, and N₂O – from all major terrestrial and freshwater aquatic ecosystems, including forest, grassland/shrub, agricultural lands, wetlands, and rivers, streams, lakes, and impoundments. The EISA assessment produced major results (Selmants et al., 2017; Zhu, 2011; Zhu & McGuire, 2016; Zhu & Reed, 2012, 2014), but recognized that wetlands remained a significant source of uncertainty, especially for those wetlands that were being actively managed. The more recent Second State of the Carbon Cycle Report by the U.S. Global Change Research Program (USGCRP), which devoted two separate chapters to inland and coastal wetlands, respectively, noted that large knowledge gaps still remain, ranging from inadequate analysis of restored and managed wetlands, and consequences of management decisions, to future wetland responses to climate change (USGCRP, 2018). In recent literature, wetland management is suggested as a potential natural solution to mitigate climate change (Fargione et al., 2018, Kroeger et al., 2017) and help offset direct losses of wetlands from sea‐level rise, subsidence, and coastal erosion (Wang et al., 2017). The recognition that a synthesis of wetland carbon management was urgently needed was the genesis of Wetland Carbon and Environmental Management; discerning the relationships between wetland management and carbon flux (loss or gain) is an international goal.

      The management of wetlands to improve carbon storage, or to prevent carbon loss, is inherent to wetland stewardship. Wetland ecosystem health and sustainability, and persistence and loss, are linked to the same processes that promote carbon sequestration. Indeed, wetlands store more carbon per unit area than most other ecosystems on the planet (Nahlik & Fennessy, 2016). Wetland plant primary productivity facilitates the uptake of CO₂ from the atmosphere, and that carbon captured is committed to plant biomass both aboveground and belowground. While aboveground carbon biomass experiences different fates dependent on disturbance regime (e.g., cyclones, fire, etc.), carbon produced and stored belowground can accumulate and persist for millennia because of the presence of water, which facilitates reduced oxygen diffusion into the soil for part or most of the growing season in wetlands and decreases decomposition of organic matter. Belowground carbon is a mix of inputs from root growth and litter from senesced aboveground structures (often termed autochthonous) and that carbon combines with both inorganic and organic carbon deposited on the surface of wetlands from off‐site sources (often termed allochthonous). The last few decades of dedicated research on carbon and wetlands have identified a number of links between environmental management strategies and their impacts on the biogeochemical processes such as carbon sequestration, burial, emissions, and export, and ultimately the balance of carbon in the wetland ecosystem. The management of water offers a primary tool.

      Where major changes to the hydrology of wetlands have been instituted (e.g., tile draining of prairie potholes in the northern US and Canada, channeling or extracting seasonal sheet flow to drain the Everglades wetland ecosystem in Florida, leveeing large wetland areas in Europe, etc.), carbon armored by years of low oxygen diffusion into the soil is released. In addition, soil surface elevations are reduced and the naturally established long‐term ecosystem balance among plant primary productivity, carbon, nutrient, and water cycling is affected permanently. More persistent flooding and reduced mineralization of nutrients further leads to reduced primary productivity, perpetuating degradation. Causes of global environmental change are less important to debate than the net effect of those changes, and locally imposed changes (e.g., cutting off tides, dumping nutrients, etc.), on preventing the wetland ecosystem from responding as it naturally would. Coastal and inland wetlands, as well as herbaceous and forested wetlands, are affected by environmental change, which also means that environmental management, if implemented properly, can potentially mitigate the additional CO₂ or CH₄ released during the degradative process.

This book synthesizes just a few wetland research studies conducted from around the world that link environmental management actions to carbon, including carbon storage, regulation of atmospheric carbon fluxes, lateral carbon transport, enhanced carbon sequestration, and improved ecosystem service value. This book is intended to explain the role that environmental management of wetlands can have in influencing carbon fluxes.Part I presents introductory chapters that describe carbon storage on the landscape in places like the conterminous United States, detail how wetlands are involved biogeochemically, and provide an overview of some wetland management practices. This book then presents chapter‐level summaries of how management influences carbon storage or loss in specific tidal wetlands (Part II) and specific non‐tidal and inland wetlands (Part III). The case studies sections highlight the wide variation in how scientists assess wetland carbon processes, ranging from long‐term geological studies to shorter‐term flux studies, and over multiple spatial scales. All of these techniques have different applications, and while this book does not provide a comprehensive global assessment of all carbon studies underway, it provides representative accounts from multiple countries for quick reference. This book concludes with synthesis chapters (Part IV) that provide primers on the topics of carbon markets and ecosystem services, and summary results from the Second State of the Carbon Cycle Report delivered to the U.S. Congress in 2019 that identifies the role of inland and tidal wetlands in large‐scale efforts to sequester carbon from increased atmospheric CO₂ concentrations while limiting emissions of CH₄ under certain conditions. The final chapter represents a summary of the book and identifies pathways forward.

       Ken W. KraussZhiliang ZhuCamille L. Stagg United States Geological Survey

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