Tulane University GIS Team Uses Software to Query and Visualize Disparate Data Sets

Assessing the Mighty Mississippi's Water with ArcView GIS

More than 2,350 miles long, the Mississippi River is the world's second largest drainage basin. It ranks eighth in the world in terms of water volume discharged and provides habitat for nearly 300 fish and mussel species. The river sustains over five million acres of forested wetlands and provides the Gulf of Mexico with 90 percent of its freshwater, critical to the viability of the marine resources of that body. The river is vital to the basin's human inhabitants as well, supplying drinking water for 70 cities and towns—more than 18 million people.

Flowing through America's heartland, the Mississippi is one of the world's busiest commercial and recreational waterways. It is no wonder that Old Man River is richly woven through American history, literature, and folklore.

More than a Muddy Mississippi

If only the Mississippi's forecast was as rosy. For all its glory, the Mississippi also suffers.

Communities up and down the river discharge a variety of industrial, municipal, and agricultural pollutants into the water, which have the greatest potential impact on water quality. Extensive river travel and dredging are potential sources of water quality contamination.

All this "stuff" forms a nutrient-rich soup in the waters of the Mississippi. Nutrient-rich waters from the river have been linked to harmful algal blooms in the Gulf of Mexico. These blooms can lead to bioavailable oxygen depletion—hypoxia. Oxygen depletion occurs through overproduction of algae and its subsequent decay after it sinks to the bottom. Since 1992, the "dead zones" caused by the algal blooms have increased in size and duration in the Gulf of Mexico.

Joining Forces

In 1995, the Energy Spatial Analysis Research Laboratory of Tulane University Medical Center/School of Public Health and Tropical Medicine became an active participant in a research project that involves data collected from the public and private sectors. The project involves the identification and collection of ambient water quality parameter data of the lower Mississippi River and integrating it with desktop ArcView GIS. Though two phases of the research are complete, this is a long-term project.

The research started with the following objectives: to acquire existing water quality data; to screen the data to assure quality; to develop a database structure; to incorporate existing Louisiana and federal water quality criteria; to develop mapping and graphics capabilities; and to provide access to these capabilities.

The Tulane team first identified more than 34 sources of water quality monitoring data. Types of information for the database include numerical data, descriptive information, and government reference criteria concerning water quality. "For some parameters, we discovered there was an awful lot of sporadic data available, but putting together enough to analyze for specific time ranges or places presented a challenge," says Christopher Swalm, senior cartographic engineer at Tulane University Medical Center. The parametric database now has more than three million records containing data on approximately 799 compounds.

Important issues in the database design were security, expandability, longevity, and ease of maintenance. Along with ambient water quality data, issues related to land use, point source discharges, hydrodynamics, epidemiology, geology, and satellite imagery were significant. Interrelationships between different types of data came under consideration, and extending the study area could dramatically affect the size of the database. This made creating a format with adequate data storage capacity and efficient data search capabilities a priority. Given the magnitude of records and system requirements, Swalm says the team chose the Oracle relational database management system to manage and store queries from the project's research partners.

Parametric data sources include national water quality databases maintained by the U.S. Geological Survey, Environmental Protection Agency, state agencies, and commercial and industrial complexes. Major classes of compounds, such as organics and pesticides, are subject to quality control/quality assurance protocols and then are added to the parametric tables of the relational database.

The GIS basemap information consists of roads, railroads, political boundaries, and hydrography. All geographic data layers were georeferenced to the Universal Transverse Mercator (UTM) projection, Zone 15. Because of the number of reporting agencies, the building of the actual point coverages involved reformatting, reprojection, and transformations. "Each of those agencies was handled on a separate processing track. Some of the data came in one projection, some in another. We had to do whatever was required to get the data into UTM," explains Swalm.

"We have incorporated more of the actual map production work into ArcView GIS 3.2 because of its expanded capabilities," Swalm continues.

Expanding the Work

From 1995 to 1997, researchers selected specific parametric contaminants for evaluation including herbicides, ammonia, phosphates, nitrates and nitrites, lead, and mercury. Swalm's team produced summary maps by season and decade to illustrate contaminant values against established state and federal drinking water standards.

They developed three mapping strategies. The "snapshot" format maps the values of a contaminant at 10-mile intervals along the length of the river from data collected during a time span of just a few days. Each point represents a single water sample. The snapshot identifies the localized geographic variability in the concentrations of a parameter at a given point in time.

The "sampling station" format summarizes test results by specific river-mile locations using data collected from many years. This is useful for identifying sites with persistent high (or low) concentrations of a compound.

The "segment summary" format compiles test results by river segment. It is useful for evaluating changes in the river as it moves through the State.

From 1997 to 1998, the parametric and geographic databases expanded with additional sources of station monitoring data. The geographic database coverage now extends northward to include Cairo, Illinois, and includes partial region layers such as land use, soils, elevation, and multispectral satellite imagery.

Congress Takes Action

In response to research on algal blooms throughout coastal waters of the United States, Congress, in November 1998, enacted the "Harmful Algal Bloom and Hypoxia Research and Control Act of 1998," which authorizes appropriations for activities to control harmful algal blooms in the northern Gulf of Mexico.

Phase II of the project addressed nutrient data as a response to some of the issues that motivated Congress to enact its legislation. The team integrated this data with the geographic data sets to demonstrate the usefulness of the querying and visualization approach to identifying possible relationships between contaminant data of the tabular database and geographically based environmental, cultural, and imagery data.

Swalm says that GIS has enhanced the project's public and professional appeal. "One of the major benefits of this work is that it's presentable," he says. "We wanted to be able to make presentations to public gatherings as well as to people in the agricultural Business. Another major goal for the project is to make the research world aware of the database," says Swalm. The database will provide information that decision makers need to evaluate water quality.

Swalm's group will focus on expanding the database both parametrically and geographically. "A lot of additional issues have come up," he says. "We realized that weather conditions such as rainfall and wind need to be addressed." Future phases will also address developing Web-based access for researchers.

For more information, contact Christopher Swalm (e-mail: swalm@esarl.tulane.edu).

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