Archived: July 29, 2004

Over the past year, the Center for Space Research has begun the multi-temporal and multi-resolution mapping of wetland environments using remotely sensed imagery. Wetland classification results may vary because the biophysical properties vary in a continuous manner, making systematic boundary delinitation difficult. CSR has adopted a wetland classification scheme similar to that used by Dr. Bill White at the Bureau of Economic Geology at the University of Texas at Austin.

The Bureau of Economic Geology classifies the wetlands into several environments. These environments are differentiated primarily upon physical characteristics such as;

Typically, wetland areas such as marshes and flats have very mild topography with elevations ranging as little as five feet from submerged areas to upland areas. Because of this low surface relief, slight variations in the local elevation can drastically change the vegetation. Low marshes, inundated almost daily, will typically have taller vegetation, than high marshes, which are inundated less frequently.

Shallow Subaqueous Flats
Shallow subaqueous flats are delineated where water depths indicate that the flats are more frequently submerged than not. However, some of these are shallow enough to become occasionally emerged.

Mud and Sand flats
Mud and Sand flats lie slightly higher in elevation than shallow subaqueous flats and are generally characterized by moist or wet surfaces or blue-green algae mats, or both. Wind tidal flats are typically barren due to intermittent salt-water flooding, ponding, and evaporation. This process inhibts the growth of most plants. These flats may have sparse salt marsh vegetation along tidal channels.

Salt Water Marshes
Salt water marshes are defined on the basis of vegetation, proximity to open bay-lagoon-estuary waters, and soil and surface moisture. These marshes are broken up into three categories; proximal, distal, and proximal/open water.

Proximal marshes are defined as low marshes that are frequently flooded due to the lower elevation and proximity to open waters. Proximal vegetation commonly includes the following species: Spartina alterniflora, Batis maritima, Salicornia virginica, Salicornia bigelovii, Distichlis spicata, Borrichia frutescens, Suaeda, Mononthochloe littoralis, Juncus roemerianus, Lycium carolinianum, Iva frutescens, and Aster. Many species can grow in both proximal and distal marshes, but Spartina alterniflora usually grows only in the proximal marshes.

Distal marshes are flooded less frequently because of higher elevations and are located farther away from the bay-lagoon-estuary waters. Vegetations include; Borrichia frutescens, Mononthochloe littoralis, Distichlis spicata, Suaeda, and Aster. Species such as Spartina spartinae and Spartina patens are also found here as well as in brackish marshes.

Brackish Marshes
Brackish marshes are transitional marshes between salt and fresh marshes. These areas area typically affected by both flooding from bay-lagoon-estuaries and freshwater inundation from rivers and precipitation. The zones separating salt to brackish to fresh marshes are usually gradual. Brackish marshes can have salinities ranges from near fresh to near saline. For this reason, there are many different vegetation species can be found there. Brackish marshes can also be broken up into two categories, low and high marshes.

Low marshes are characterized by frequent flooding, vegetation types, soil moisture and standing surface water. Low marsh plants include, Scirpus spp., Typha spp., Eleocharis spp., and Bacopa monnieri.

Higher marshes are typically less frequently flooded and have a drier wetland plant assemblage and less soil and surface moisture. High marsh vegetation types include Spartina spartinae and Spartina patens.

Fresh Water Marshes
Fresh Water Marshes occur inland along river or fluvial systems or in basins or depressions on mainlands. Fresh water marshes also occur locally along swales. These environments are typically beyond the extent of salt water flooding. Freshwater low marsh vegetation consists of Typha, Scirpus americanus, Scirpus californicus, Phragmites australis, Eleocharis, Cyperus, Bacopa monnieri, Juncus, Ludwigia, Sagittaria and Paspalum lividum. High marsh vegetation consists of Spartina spartinae, Panicum, Borrichia frutescens, Rhynchospora macrostachya, Fimbristylis, Aster spinosus, Spartina patens, and scattered Scirpus.

Spartina spartinae can exist in a broad range of elevations and moisture levels, so it will be found in both low and high marshes.

Transitional Areas
Transitional Areas are defined as areas that lie between wetland and upland areas. They are occasionally inundated but not as frequently as marshes. They contain a mixture of upland prairie grasses and shrubs, and wetland vegetation. Wetland species in these transitional areas are those of higher marshes.

Swamps are defined as woodlands or forested areas that contain saturated soils or are inundated during much of the year.

Links to Related Sites
Dept. of Interior Wetlands Fact Sheet


Sunday, 01-Aug-2004 00:24:38 CDT