The Use of GIS in Wetlands Health Assessment






Table of Contents





Introduction

Wetland conservation has recently become a major concern of the environmetalist population. The many benefits derived from wetland ecosystems coupled with the steady loss of wetland acreage throughout the past century provide the main reasoning behind this concern. Identifying, classifying, and evaluating wetland regions are becoming crucial tasks in assessing the current problem and possible remediation strategies. Recent Federal attempts to regulate wetland destruction and mitigate the effects of development call for an effective means of analyzing wetlands data. For this reason, this project is an investigation into the use of GIS as a tool in wetlands evaluation.





Background


Wetland Types

According to the US Army Corps of Engineers and the US Environmental Protection Agency, wetlands are defined as:

Those areas that are inundated or saturated by surface or ground water at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands generally include swamps, marshes, bogs, and similar areas.
(Taken from "Recognizing Wetlands: An Informational Pamphlet")


To simplify a rather complex definition, a wetland is an area of land that is saturated or covered with water during the growing season. Unfortunately, problems occur when classifying an area as a wetland due to changing land conditions and water cover over time. There is no definitive line between wet and dry environments, as any area will fluctuate from one to the other in many cases due to seasonal weather changes. Recent governmental regulation of wetlands has necessitated the derivation of a method for defining wetland boundaries.

Recent governmental regulation of wetlands has necessitated the derivation of a method for defining wetland boundaries. The US Fish and Wildlife Service, in response to this need, created a manual for classifying wetlands, titled "Classification of Wetlands and Deepwater Habitats of the United States." In this classification system, wetlands are defined and grouped into categories by a number of factors including substrate material, frequency of flooding, and vegetation. A general schematic of the classification system is given here:


Wetlands Classification Hierarchy

The first level of the classification hierarchy is the wetland system, divided into five sections: Marine, Estuarine, Riverine, Lacustrine, and Palustrine. Wetlands in the same system have similar hydrologic, geomorphologic, chemical, and biological characteristics. Each System is then divided into subsystems, which are dependent on the given system.


Marine     The Marine system consists of wetlands along the coastline. These environments are exposed to the open ocean, so they are strongly influenced by ocean waves and currents and have high salinities, generally above 30%. The most important factor in this system is the effect of the tidal waves on the natural habitat and on the water flow regime. This system is divided into Subtidal and Intertidal subsystems.

Estuarine     Wetlands in the Estuarine system include those associated with both estuaries and lagoons. Estuarine wetlands are open to the ocean, but are generally semienclosed by land. Because of this, the marine water is somewhat diluted by freshwater from land runoff or other adjacent freshwater sources, causing salinities to be lower than those typically found in the Marine system. Estuarine habitats are still influenced by ocean tides, but to a lesser degree. As in the Marine system, this system is divided into Subtidal and Intertidal subsystems.

Riverine     The Riverine system classification consists of wetlands and deepwater habitats contained within a channel. Water is generally flowing in this system due to the presence of the channel. Riverine wetlands are restricted to freshwater flows, so salinities usually stay below 0.5%. This system is divided into four subsystems: Tidal, Lower Perennial, Upper Perennial, and Intermittent.

Lacustrine     Lacustrine system wetlands are usually located in a topographic depression or a dammed river valley. This system includes permanently flooded lakes and reservoirs, intermittent lakes, and tidal lakes. Lacustrine wetlands generally contain large areas of deep water and are influenced by wave action. As in the Riverine system, water salinities remain below 0.5%. This system is divided into Littoral and Limnetic subsystems.

Palustrine     Wetlands in the Palustrine system are dominated by trees, shrubs, emergents, mosses, or lichens. These habitats are generally nontidal, but can also be tidal as long as salinities are below 0.5%. In general terms, the Palustrine system includes ponds, marshes, swamps, bogs, and prairies. Wetlands in this system are only weakly influenced by the movement of wind and water. This system contains no subsystems.


These five main systems of wetlands are further divided into classes, subclasses, and dominance types. Classes and subclasses are determined by the type of material in the substrate and the general flooding regime or by the type of vegetation present. The dominance type refers to the dominant plant or animal forms in the given area. This classification system also utilizes modifiers which denote the water flooding regime, general water chemistry, or soil type. More details (about 50 pages worth!) on these subsections as well as the entire classification hierarchy can be found in the manual. (See " Classification of Wetlands and Deepwater Habitats of the United States.")






Benefits of Wetlands

The primary reasons for recent attempts to protect natural wetlands are the numerous benefits these habitats incur. Now beyond past decades of draining and clearing wetland areas, their influences on the natural environment are being more carefully scrutinized as the impacts of "the four Dís" ("Dike it, dam it, divert it, and drain it!") are being felt. In their natural state, wetlands provide benefits to the natural environment as well as society, and unfortunately these are not easily derived from replacements.

Ecological

Wetlands are the natural habitats of thousands of species of fish and wildlife, including approximately one-third of the nationís endangered or threatened species. The richness and diversity of wetland ecosystems have been compared to those of the tropical rain forests, as they are both considered among the most biologically productive environments in the world.(EPA) Many more animal species are dependent on the wetlands for seasonal shelter, since these areas provide ample sources of food and water when other regionsí resources are scarce.

Another important ecological benefit of wetlands is their ability to act as water flow regulators. Wetland surfaces tend to act like sponges, absorbing water during flood periods and then releasing it slowly during dry times. Because of this, groundwater and surface waters are gradually replenished and the effects of drought are lessened. Wetlands also diminish flood effects by slowing water flow and retaining runoff during periods of high flow. Overall, wetland environments act as buffering systems, moderating the results of severe weather and climate conditions.(OEPC)

Water quality is also positively affected by the presence of wetlands. Runoff water filtering through a wetland will be naturally treated for nutrients and sediment, as the plant cover retains the nutrients, processes the organic wastes, and traps the sediments in the water. In fact, artificial wetlands are now being created solely to treat various types of wastewater.(OEPC)

Economical

In addition to the vital part wetlands play in their natural ecosystems, these areas also provide important economic benefits. Commercial fishing in the US is painfully dependent on wetland environments, as between 60 and 90% of commercial fisheries use coastal wetlands as growth habitats.(OEPC)

In total, fishery processing and sales in the US in 1991 accounted for $26.8 billion in economic activity.(EPA) Commercial fur is another important industry dependent on the nationís wetlands for harvesting grounds.

Wetlands also provide recreational activities including sport fishing, hunting, bird watching, and photography. Combined, these activities accounted for $59.5 million in economic activity in 1991.(EPA)






Reasons for Protection

Since the 1700ís, over half of the nationís wetlands have been lost or destroyed, reducing the total area from 221 million acres to only 104 million in 1985. The figure below describes the amount of wetlands acreage lost in each state through the 1980ís. Seven states have lost more than 80% of their original wetlands coverage.(EPA)


Percentage of Wetlands Acreage Lost

Agricultural development accounts for the majority of wetland conversions, but a growing percentage is being lost to urban development and commercial activities. As cities and industries expand, wetland regions provide inexpensive land for development. Since the majority (74%) of wetlands are privately owned, and few owners of wetlands actually enjoy direct benefits from them, the wetlands are sold or privately developed.(OEPC)

Some of the results of the loss of wetlands are obvious from the previously mentioned benefits. Increased flooding and increased severity of flood damage are two important effects. Another notable effect is the extinction of plant and animal species resulting from the loss of habitats. Also, as is obvious in many regions around the country, destruction of wetlands results in the degradation of water quality. Nutrient loadings increase, augmenting the growth of undesirable weeds and algae. Algae blooms deplete the dissolved oxygen in the water, depriving fish and other organisms of their natural source of oxygen. Beyond the effects on the ecosystem, drinking water supplies can become contaminated by increased urban runoff pollutants, normally controlled by the natural wetlands filtration system.(EPA)

Both the Federal and State governments are taking steps to slow the wetlands degradation process and prevent the worsening of these adverse effects. This is carried out through land acquisition, regulation, and mitigation. While land acquisition has been a major staple in preservation efforts, it remains costly due to the high percentage of wetlands which are privately owned. Regulation is a more cost effective means, but it remains limited by the lack of universally agreed-upon terms and definitions, as well as the inevitable bureaucratic delays. Mitigation calls for the restoration or creation of wetland areas to offset the effects of development. While this seems to be an ideal way to control wetland losses, problems arise in determining the success of mitigation efforts and the effectiveness of newly created wetlands. Overall, while the government is working towards wetland preservation, effective procedures for defining wetland areas and assessing their health still need to be developed.





Data and Data Sources


NWI Data

The US Fish and Wildlife Service department known as the National Wetlands Inventory (NWI) is in the process of compiling data on wetland types and areas for the entire United States. This data set includes location and classification of the wetlands, based on the classification system derived by the US Fish and Wildlife Service previously discussed. When completed, NWI hopes to provide coverages for the entire contiguous United States, Hawaii, Alaska, and the US protectorates in the Pacific and Caribbean.

The predominant source of data for the creation of these coverages and descriptions is aerial photography, taken in conjunction with the US Geological Survey, the US Department of Agriculture, and the National Aeronautics and Space Administration. The photographic sources range in date from February 1971 to December 1992. The maps were created by manually interpreting the aerial photography supplemented by soil surveys and field checks. The delineated wetland boundaries were then manually transferred to USGS topographic maps and labeled. This processing occurred between 1979 and 1992. Digital wetland data is manually digitized or scanned into topographically correct data files using the Wetlands Analytical Mapping System. Completed files include planimetric ground coordinates and wetland classification attributes. This process has been ongoing since October 1981.

The final results are digital line graph coverages divided into individual 7.5 minute quadrangles. The grid coordinate system is in the Universal Transverse Mercator (UTM) projection, in zones ranging from 4 to 20 depending on the location. The horizontal datum referenced is the North American Datum of 1927. A complete listing of an example coverage description is given below.


Description of Sample NWI Wetlands Coverage

While fairly detailed wetland coverages are completed for many areas, huge gaps in the entire nationís coverage exist. A listing of the status of the NWI digital mapping process across the United States is shown below. Completed coverages are shown in red.


Status of NWI Coverages

Another problem is the potential error associated with such detailed coverages. Since aerial photography was the primary source of wetland delineation, the final processed data is only as accurate as the photography. Many areas have tremendous amounts vegetation, inhibiting the complete and accurate description of the ground cover, especially the water cover, by photography. Also, some of the original photography was taken as early as 1971, and land cover can change fairly drastically in only a few years. Some of this earlier data may not accurately describe the areas as they exist today. In the future, satellite images may provide the most accurate and detailed data for specific wetland areas.






Other Related Data Sources

For this project, USGS digital elevation data as well as land use/land cover data were also used. Digital elevation model (DEM) data are given in 1 degree by 1 degree blocks (1:250,000 scale). The primary data sources are cartographic and photographic. This raw topographic data is digitized and then processed into the final coverages. These include elevations in meters relative to the National Geodetic Vertical Datum of 1929 and geographic coordinates in the World Geodetic System of 1972. Complete elevation data is available for all of the contiguous United States, Hawaii, and most of Alaska.

Land Use/Land Cover (LULC) data from the USGS were also used in this analysis. This coverage describes the vegetation, water, and natural surface for a given land area. The primary source of data is aerial photography, taken from NASA high altitude missions and other related sources. As in the case of the DEM coverage, the data is digitized and then processed into a final coverage. The LULC data are similarly in a standard map scale of 1:250,000. The completed coverages are in the Universal Transverse Mercator projection system. LULC data are available for most of the contiguous United States and Hawaii.





Study Area

The most important data in this analysis is the NWI wetlands classification coverage. This was also the most limiting data source, since the project is still in the processing stages in many areas and so complete data is not currently available. The Eastern Texas shoreline was one region of fairly comprehensive coverage. In relation to other studies currently being conducted, the Corpus Christi Bay area provided an ideal study area as far as data availability, size, and application to other research.

While more data is available for the surrounding areas, and a more comprehensive region study may be more applicable to the objectives of this research, size constraints kept the study area to a minimum. All of the data utilized here can be found in the NWI database. The data is divided into directories of 1:250,000 scale map units, labeled with the titles given to the same regions in the USGS topographic and other coverages. In this case, the directory was appropriately labeled "corpus_christi." Each directory contains the 7.5 minute quads for the given region.

Though just one region was chosen for this study, the processing steps are valid for any region where NWI wetlands classification data is available. Any size regionís data may be downloaded and analyzed, but memory may prove to be a major constraint. For the Corpus Christi study area, individual quad coverages ranged in size from as little as 5 Kb to as large as 821 Kb in their compressed states.





GIS Analysis


Objectives

The intention of this research project is first and foremost to utilize the NWI wetlands classification data in a GIS program. In this case, the GIS programs used are Arc/Info and the associated ArcView. Two of the main components of this project are converting the original NWI coverages into an Arc/Info coverage and manipulating this new coverage within the system.

Beyond this initial process, researchers and conservationists are often concerned with the status of specific wetland types, since each type has unique characteristics and, therefore, unique benefits and limitations. Different wetland types, for example, are better at filtering out pollutants, while others may provide more valuable wildlife habitats. The sensitivities of wetland areas are also dependent on the type of wetland present. Because of this need to identify regions by wetland type, another goal is to isolate different wetland classifications into individual coverages.

In order to assess the relative health of a wetland environment, pertinent data such as elevation, land cover, soil type, and precipitation are also needed, especially in a historical sequence. These data sources depict changes in the wetland characteristics over time. For this reason, a third objective of this research is to find a relatively easy method of editing related data coverages by wetland class. The combination of these steps should facilitate the assessment of the status of a specific wetland type in a given region.






Creating an Arc/Info Region Coverage from NWI Data


Step 1: Obtaining NWI Data

NWI wetlands classification data can be obtained in digital line graph format from the NWI web site (ftp://www.nwi.fws.gov/dlgdata/). Only the name of the USGS 1:250,000 scale map unit needs to be known initially, as this is the directory name where the individual coverages are found. The text file in each directory contains a listing of the 7.5 minute quads in that region. Once the correct directory and files are found, the files can be saved directly into a chosen directory by simply clicking on the file name. These files can also be accessed directly through FTP. For more information, see the README in the original /dlg/ directory.

The files will appear as filename.tgz. Each consists of two separate files that are "tar"ed together and compressed using the gzip utility. Both tar and gzip can be obtained directly from the NWI site (ftp://www.nwi.fws.gov/software/). The files first need to be unzipped by typing the command:

                    gunzip filename.tgz


This step results in a file titled filename.tar. The uncompressed file can be un"tar"ed by typing:

                    tar xvf filename.tar


The final result is two files labeled filename.dlg (the digital line graph data) and filename.att (the wetlands attribute data).


Step 2: Converting to an Arc/Info Coverage

In order to more easily convert these two files into an Arc/Info coverage, NWI provides a series of AMLís (Arc Macro Language files). These can be downloaded directly from the NWI site (ftp://www.nwi.fws/software/amls). There are six files in total that need to be downloaded:

                   dlg2arc.aml
                   dlg2arc.menu
                   dlglaunch.aml
                   dlgconvert.aml
                   dlgmajor.aml
                   dlgbuild.aml



These files must be in the same directory as the data files. All files and directories used should be in lower case lettering to prevent errors when using the Arc/Info program. Also, the AML file names need to be listed exactly as they appear here, despite the titles that appear when they are downloaded.

Once the files are properly copied and in the same directory a convertlist file must be created. This file should simply contain a single column containing the data filenames (prefixes only). There can be no extraneous spaces after the filenames, as the AMLís look for files with the precise prefix typed in the convertlist file. After the list is completed, "end" should be typed at the bottom of the list. This signals to the programs that the list is completed. A sample convertlist file is given here:



Sample Convertlist file


Once this file is saved (also in the same directory) the primary AML can be run within Arc/Info. Arc/Info should be opened by typing arc at the prompt, then the AML can be run by typing at the Arc prompt:

                    &r dlg2arc.aml


The program will open with a menu (dlg2arc.menu) and, to begin, option 1 should be chosen (dlg2arc.aml). For this project, the ATP files, which are specific versions of the attribute files, that are mentioned at the next prompt are not used. The program will then run, outputting the interface for each converted file into an error file called dlg.errors. After the program has completed its conversions, this error file should be checked to make sure there were no problems. A primary source of error here are a lack of exact filename matches between the desired files as listed in the convertlist file and actual file names. Another possible error may occur if capital letters are used in the directory or file names. If errors are encountered, the above steps need to be retaken until the AML has properly completed its conversions.

Once all of the desired files have been processed, each original data file should now have two associated directories:

                   filenamenwic
                   filenamenwip



These are the line and point coverages, respectively. The AML now needs to be rerun, this time choosing option 2 (dlgbuild.aml). This finishes the processing by building the polygon coverage for each file name, deleting the point coverage directory, and leaving a final directory called filenamenwic for each coverage. These can be brought up individually in ArcView or altogether, but each 7.5 minute quad coverage remains an individual theme. The results of the above processing on the Corpus Christi region data are shown here as an ArcView layout:



Converted NWI Digital Line Graph Data






Joining Arc/Info Coverages


By examining the converted polygon coverages in ArcView, it can be seen that the individual coverages need to be combined into one comprehensive coverage to successfully analyze a region. As the coverages now exist, each quad can be depicted by wetland type, but the depiction in ArcView differs for each quad since they are currently separate themes. In other words, Marine wetlands may show up as one color in one quad and another color in a different quad. This creates problems when trying to analyze a larger region consisting of multiple quads. For this reason, the individual coverages need to be joined into one coverage. This can be accomplished in Arc/Info by using the mapjoin command.

While mapjoin can in some cases be used successfully on coverages as they appear directly after conversion, problems may be encountered if quads are adjacent and border segments do not exactly match. For this reason, the coverages should be cleaned before using mapjoin. This intersects points and lines, reassembles the polygons, and rebuilds the attribute tables. Once in the Arc/Info Program (type arc), the following command should be typed:

                    clean incover outcover


After each of the polygon coverages has been cleaned, mapjoin can be run by typing:

                    mapjoin outputfile


The program will then prompt the user for the names of the coverages to be joined. A blank line is entered when all of the coverages have been inputted, as this signals the program that the file list is complete. Up to 500 different coverages can be joined at once, but memory tends to exceed easily in this program. If a memory error is encountered, the number of coverages joined at once should be reduced.

If the mapjoin process is successfully completed, the final dialog statement should be "Creating PAT..." and the program should return to the Arc prompt. If the program begins to create the PAT (polygon attribute table) but encounters an error and outputs the error message

                   COULD NOT DEFINE OUTPUT FAT
                   UNABLE TO CREATE FAT FILE



then the program will abort and no output coverage will be created. This is most likely due to errors in the output coverage name or in the input coverage names. No numbers or capital letters should be used in either. If these problems are corrected and the error message still appears, the name of the output file should be varied until the program successfully completes.

Another possible error may occur if there are problems in the input coverages. If the program reaches a point where it is "Assembling polygons..." but encounters an error and outputs the error message

                   FATAL ERROR
                   Mismatch of border segments (NODPOL)



then the borders of adjacent coverages are not meeting. The input coverages should be cleaned to remedy this before attempting to use mapjoin.

Once mapjoin has been successfully completed, the section borders can be dissolved to create one comprehensive coverage. This is done by typing:

                    dissolve incover outcover attribute poly


This dissolves the input coverage by the attribute characteristic to create the output coverage. A sample Arc/Info dialog is for the entire procedure is listed here:



Sample Arc/Info Dialog for Joining Coverages


Once these steps have been completed, the final comprehensive coverage can be opened and viewed in ArcView. The resulting coverage of the eastern half of the Corpus Christi study area is shown in an ArcView layout:



Joined NWI Wetland Coverages






Isolating Wetland Types in Arc/Info


After successfully creating a complete region coverage, the next step is to isolate specific wetland types in Arc/Info. This can most easily be done by first working with the coverage in ArcView. The ArcView program should be opened (type arcview) and the coverage should be added as a theme in a new view. The theme will appear as a single color with various lines overlaid. The legend for this theme should be altered so that Unique Value is shown attached to the value field Attribute. An array of colors should now appear in the theme, each one associated with a specific type of wetland, listed as a series of letters and numbers that can be interpreted based on the Wetlands Classification Hierarchy. To isolate a certain type of wetland, the Query option should be chosen under Theme/Properties on the menu bar. The theme should be queried in the form of the following statement:

                    (Attribute = AAAAA) or (Attribute = ABBBB) or ...


where AAAAA and ABBBB are the chosen wetland classification abbreviations. Once the query is completed the revised theme should display only those wetland types chosen. Additional queries can be made on the revised theme, if needed. Once the desired wetland types have been properly isolated, the resulting theme should be converted to a shapefile by choosing Theme/Convert to Shapefile from the menu bar.

After the shapefile is created, Arc should be opened and the shapefile should be converted into an Arc coverage by typing the following command at the Arc prompt:

                    shapearc incover outcover


The isolated wetland types now stand as their own separate coverage. To make sure segments and polygons are properly joined, the new coverage should be cleaned by typing:

                    clean incover outcover


This new coverage can now be used to view in more detail the specific wetland types in a given region. Also, the shapefile created in the process, basically an outline of the area covered by that wetland type, can be used to edit other data coverages. A sample dialog of the above steps is given here:



Sample Arc/Info Dialog for Isolating Wetland Types


For this and all remaining parts of the project, the study area, previously the entire Corpus Christi 1:250,000 cell block, is reduced to a single 7.5 minute quad, the Port Aransas quad. This is done for memory purposes and to enable more detail to be viewed. The above steps were performed on the Port Aransas quad, isolating only the Estuarine wetlands. The results are shown here in an ArcView layout:



Isolated Estuarine Wetlands of Port Aransas






Editing Related Data Coverages by Wetland Type


Land Use/Land Cover Data

Land Use/Land Cover data for a given area can be quickly downloaded from the USGS web site (http://sun1.cr.usgs.gov/doc/edchome/ndcdb/ndcdb.html). The data must then be converted into an Arc/Info coverage. For steps in this process, see Dr. Maidmentís Home Page.

For the desired wetland type previously isolated, related data can be clipped to the same covered area. This enables the wetland coverage and the related coverage to be readily compared by displaying only the data for those areas covered by the specific wetland type. This process is done rather easily with the USGS Land Use/Land Cover data. Since this data is already in UTM projection coordinates it needs only to be clipped with the desired wetland coverage. This is accomplished by typing the following command at the Arc prompt:

                    clip incover clipcover outcover poly


This clips the input coverage with the clip coverage to create an output coverage. The final coverage can be cleaned if necessary and displayed in ArcView. It should have the same shape as the coverage obtained in the previous section. This newly created land use map can now be studied to determine the relationship between land cover and the particular wetland type. Results of these steps when applied to the Port Aransas Estuarine Wetland Region are given here as an ArcView layout:



Land Use/Land Cover Data for Port Aransas Estuarine Wetlands


Digital Elevation Models

Digital Elevation Models can be downloaded from the same USGS web site (http://sun1.cr.usgs.gov/doc/edchome/ndcdb/ndcdb.html). The data must then be converted into an Arc/Info coverage. For steps in this process, see Dr. Maidmentís Home Page.

DEMís provide slightly more of a challenge since they are not in UTM projection coordinates. This means the DEM must be projected into these coordinates within the Arc/Info program. This is accomplished in Arc by typing the following command at the Arc prompt:

                    project grid ingrid outgrid projectionfile


This step projects the input grid into the coordinate system specified by the projection file and creates an output grid. The projection file must specify the coordinate system of the original DEM as well as the coordinate system of the desired projection. If the coordinate system for the DEM is unknown, it can be determined by describing the grid as is done by typing:

                    describe gridname


The projection file used to project the USGS DEM into UTM coordinates is listed here:



UTM Projection File


Once the projection has been successfully completed, the grid must be clipped to contain only those areas of the desired wetland type cover. This is a similar process to the clipping procedure used on the Land Use/Land Cover data. Instead of clip gridclip is used in the Grid system. At the Arc prompt, grid should be typed to open the Grid system. Then the DEM can be clipped by using the gridclip function, accessed by typing the following command at the Grid prompt:

                    gridclip ingrid outgrid cover clipcover


This statement instructs the program to clip the input grid with a coverage, the clip coverage, to create an output grid. Once this step is accomplished, the final clipped grid can be viewed in ArcView. As with the land use data, the final grid should cover the same area as the original wetland type coverage.

The Arc/Info dialog for clipping both the Land Use/Land Cover data and the DEM is listed here:



Arc/Info Dialog for Clipping Coverages




Conclusions

The intentions of this research project were to effectively utilize the National Wetlands Inventory wetlands classification data in a GIS program and to show some of its potential applications. The NWI data provides detailed if not comprehensive coverages of wetland types for certain sections of the United States. Though the database is not complete, it has the potential to become a source of valuable data for wetlands research and conservation studies.

One of the main reasons for bringing this data into a GIS program such as Arc/Info is to be able to readily manipulate and display the data, but another application is to link the wetlands data to other sources and be able to successfully compare the two. This process is crucial in attempting to asses the general state of the wetland region as a whole or the relative health of specific wetland types in the region. In this Arc/Info procedure, the basic steps for beginning a GIS analysis of regional wetlands data for the purpose of assessing health are outlined. These steps successfully created a comprehensive Arc/Info coverage, isolated specific wetland types in the coverage, and edited other related data sources for the chosen wetland types. The results were shown in maps that can be readily analyzed and compared.

Though the GIS portion of this project was successful, more work needs to be done before an accurate assessment of wetland health can be conducted. Other parameters such as historical land cover and water quality would augment this study by providing more detailed descriptions of the wetland regions. These data types could potentially be processed the same way the Land Use/Land Cover data and DEMís were processed, resulting in easily comparable coverages for the study region.

Though this analysis was applied only to a small region, the Corpus Christi Bay area, the potential exists for use on a much larger scale. Once the NWI classification data is in its completed digital form for the entire Untied States, the GIS applications and their effects on the movement towards wetlands conservation and mitigation will be tremendous. GIS will provide not only a means of assessing the health of natural wetlands, but also the results of current attempts to create new wetlands and their impacts on the ecosystem as a whole.





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