Читать книгу Wetland Carbon and Environmental Management - Группа авторов - Страница 18

Wetlands are defined by having unique hydric soils, vegetation, and hydrology due to their topographic position. Wetlands can be saltwater, freshwater, or brackish, develop carbon rich histosol soils, and host diverse aquatic adapted flora and fauna. There are many ways that the soil, vegetation, and hydrology properties can intersect with one another and this has led to a large range of wetland types and an extensive and complex nomenclature that includes more familiar categories such as “swamps,” “bogs,” and “marshes” to less familiar categories including “morass,” “muskeg,” and “carr.” Here, we loosely follow the comprehensive wetland classification system established by Cowardin et al. (1979), used by many State and Federal agencies in the United States and by international treaties such as the Convention on Wetlands of International Importance (RAMSAR). The Cowardin system groups wetlands into five major systems: Marine, Estuarine, Riverine, Lacustrine, and Palustrine. In addition, the Cowardin system includes permafrost as wetlands, meaning that almost the entire Arctic region is treated as a wetland. Arguably, permafrost does not fulfil the criteria for the Cowardin wetland definition, i.e., hydrology or soil type or vegetation. Here, we distinguish between permafrost soils and high‐latitude wetlands (both organic soil and mineral) aligned more closely with the classification system developed by the Canadian National Wetlands Working Group (1997). We do not provide a detailed carbon stock section for submerged reef habitats or sea grasses, and, instead, the combined estimate of Duarte (2017) is used in our summary table. We also do not provide estimates of carbon stocks in the sediments of non‐vegetated, mainly Lacustrine, wetland subclasses that include rivers, lakes, and small ponds. Fig. 1.1 shows the global distribution of wetlands based on a combined remote sensing and inventory based integration, with key wetland complexes visible, such as the Hudson Bay Lowlands, the Western Siberian Lowlands, the Cuvette Central, Sudd wetlands, Okavango Delta in Africa, and the Pantanal wetlands and Amazonian lowlands in South America.