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The wetland status of 7,000 plants is determined upon information contained in a list compiled in the National Wetland Inventory undertaken by the U.S. Fish and Wildlife Service and developed in cooperation with a federal inter-agency review panel (Reed, 1988). The National List was compiled in 1988 with subsequent revisions in 1996 and 1998.
Plant community composition can change dramatically over a gradient of groundwater depth: plants that can only survive in wetland conditions can be replaced by plants that are tolerant of drier conditions as groundwater levels are reduced, causing habitat community shifts and in some cases complete loss of riparian species. [7]
Wetlands exist on every continent, except Antarctica. [3] The water in wetlands is either freshwater, brackish or saltwater. [2] The main types of wetland are defined based on the dominant plants and the source of the water. For example, marshes are wetlands dominated by emergent herbaceous vegetation such as reeds, cattails and sedges.
Watershed delineation is the process of identifying the boundary of a watershed, also referred to as a catchment, drainage basin, or river basin.It is an important step in many areas of environmental science, engineering, and management, for example to study flooding, aquatic habitat, or water pollution.
The plants found in hydric soils often have aerenchyma, internal spaces in stems and rhizomes, that allow atmospheric oxygen to be transported to the rooting zone. [2] Hence, many wetlands are dominated by plants with aerenchyma; [3] common examples include cattails, sedges and water-lilies.
The techniques used by NWI have recently been adopted by the Federal Geographic Data Committee as the federal wetland mapping standard (FGDC Wetlands Subcommittee 2009). This standard applies to all federal grants involving wetland mapping to insure the data can be added to the Wetlands Layer of the National Spatial Data Infrastructure.
Aerenchyma in stem cross section of a typical wetland plant. Aerenchyma or aeriferous parenchyma [1] or lacunae, is a modification of the parenchyma to form a spongy tissue that creates spaces or air channels in the leaves, stems and roots of some plants, which allows exchange of gases between the shoot and the root. [2]
An example of a modern-day chinampa As of 1998, chinampas are still present in San Gregorio, a small town east of Xochimilco , in addition to San Luis, Tlahuac , and Mixquic . [ 35 ] Although many of these gardens were constructed and thoroughly tended to from the Postclassic Period through the Spanish conquest , many of these plots of land ...