Ecological Health via Satellite Photography

FAYETTEVILLE, Ark. — Engineering researchers at the University of Arkansas have developed an innovative system for obtaining important water-quality information on a near real-time basis and at much less expense than current methods. Using photographic images from a satellite and hand-held multispectral camera, researchers in the College of Engineering’s department of biological and agricultural engineering have built mathematical models that accurately predict sediment loads and nutrient content in Beaver Lake, the source of drinking water for more than 280,000 people in Northwest Arkansas.

“Remote sensing technology provides several advantages for any group responsible for the ecological health of a body of water,” says Indrajeet Chaubey, UA associate professor of biological and agricultural engineering. “Now we can monitor the entire lake, not just one area where you take a water sample. We can do this with much less expense because we don’t have to process hundreds of thousands of water samples through the traditional lab process. Until now, we’ve had very limited capability to monitor what is happening on a real-time or near real-time basis.”

Chaubey leads a team of UA ecological-engineering researchers and students who for many years have traveled to remote locations on the lake to gather water samples, which must be taken to a laboratory for analyses of pollutant concentrations. Results of those analyses are often not available until a week after the sample is taken. As Chaubey said, the new technology should help researchers gather information without physically taking water samples from every nook and cranny of a river, reservoir or lake.  

Reading the content of the photographs is tricky, but the process works because certain constituents -- sediment, chlorophyll and organic carbon in the water -- interact with light. The photos reveal nitrogen and phosphorous levels within sediment. Nitrogen and phosphorous are essential plant nutrients that in excess can accelerate eutrophication, which reduces oxygen in water and harms plant and animal life. Also, high concentrations of chlorophyll mean a source of energy of energy must be present, which again indicates the presence of nitrogen and phosphorous.

“If you see high concentrations of chlorophyll,” Chaubey said, “chances are there are high amounts of nitrogen and phosphorous. If there weren’t, algae would not be growing.”

Chaubey knew algae were present because his researchers continued to draw water samples at the exact locations captured in the photographs. They compared lab results from the samples to predictions based on the photographs. So far, their predictions of the concentration of nutrient levels at various locations on Beaver Lake, based on images provided by satellite and multispectral camera photography, have been 98 percent accurate.

Beaver Water District, the public entity charged with treating water from the lake and providing it to most Northwest Arkansans, will be able to use this technology to overlay snapshots that will help them identify water-quality trends in the lake over time.

The models of nutrient content in the lake based on satellite photographs are an important component of a broader, multi-year examination of Beaver Lake and its watershed. In the 1960s, the Army Corps of Engineers dammed the White River near Eureka Springs, and Beaver Lake was born. In addition to providing drinking water for more than a quarter of a million people in a four-county area, Beaver Lake generates millions of dollars annually in tourism revenue for the state of Arkansas and produces electricity for the nation’s power grid.

Because of the geology and topography of Northwest Arkansas, Beaver Lake has had a reputation of being one of the cleanest man-made reservoirs in the Midwest. It is still clean, said Chaubey, but environmental consequences of rapid growth are threatening the reservoir’s water quality. Widespread development and agricultural operations within the lake’s watershed have caused erosion in streams and rivers and increased transport of sediment and nutrients into the lake. The situation has caught the attention of many stakeholders because the lake is so vital to the health of the local economy.

These problems caused the Arkansas Natural Resources Commission (formerly the Arkansas Soil and Water Conservation Commission) to seek help from the university to develop a plan to protect Beaver Lake. Chaubey took on the project, and for the past five years, he has led a team of ecological engineering researchers and students who monitor the lake’s water quality and evaluate the impact of land-use changes in upland areas within lake’s watershed. The result of their work is Beaver Lake Watershed Decision Support System, a comprehensive, geographic-information-systems-based program for the management of Beaver Lake’s watershed.

The project initially required gathering a mountain of historical data from many water-quality reports and projects sponsored by various governmental agencies and environmental organizations. After collecting this information -- some of which had been discreet, in paper format or otherwise unavailable to the general public -- the researchers synthesized it into a single database, which helped them accurately assess water quality and identify knowledge gaps. The researchers also gathered water-quality samples from virtually every nook and cranny on the lake to fill in those gaps.

When combined, the historical information, water-quality samples and GIS-based information about the watershed allowed researchers to develop mathematical models that describe environmental processes in upland areas, streams and rivers, and the lake itself. The models show how the land is changing and how that change contributes sediment, nutrients, pesticides and other water-quality constituents into Beaver Lake.

Chaubey said publication of the database via the Internet will ensure that watershed water-quality information is easily accessible and free to the general public.