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Active Learning and Research
Active Learning and Research
Environmental analyst Gil Pontius and his students use computers and geographic software to simulate and make predictions about the environmental impact of land use change.

Meet the researchers: The impact of land use on water quality

Interview with Steve Aldrich
Steve Aldrich '02 is a senior geography major with a concentration in environment and society. He's been participating in research since the summer after his sophomore year.

How did you get involved in research while still an undergraduate?

Spring semester of my freshman year I took Computer and Quantitative Methods in Geography (Geography 110) with Gil Pontius. Toward the end of my sophomore year I got an email from him suggesting that I apply to be a Marsh Summer Fellow. That would enable me to get funding to work with him as a summer research assistant. I was really pleased that he thought of me. I got the position and I think it worked well for both of us. I helped out with several of his projects-whatever he needed me to do. I worked on some modeling methods and also on the Ipswich River (Watershed) project, inputting GIS data and helping to prepare the poster we submitted for a conference GIS and Environmental Modeling held in Canada.

Then in spring of my junior year I was able to work with Gil again thanks to a stipend made available through a Culpepper grant. I was taking Quantitative Modeling (Geography 260) with him at the time, and we worked on something called the "Sioux Falls data shoot-out" sponsored by Keith Clarke at the University of California at Santa Barbara. Dr. Clarke challenged researchers across the country to put their models for predicting urban growth to the test, and offered a set of data for everyone to work with. Gil thought the models being developed here at Clark would provide some real competition.

I understand you completed a Research Experience for Undergraduates (REU) fellowship this summer.

Yes. The National Science Foundation REU fellowship was administered through the Marine Biological Laboratory (MBL) at Wood's Hole, Massachusetts. It allowed me to spend this past summer doing more research on nitrate contamination in the Ipswich River watershed in collaboration with Gil. I just gave a presentation on this work at an MBL meeting that was attended by other scientists and REU students.

What's the Ipswich Project about?

The project examines how levels of nitrates in rivers, streams, and ground water are influenced by changing land use. Nitrates are plant nutrients: some in the water are good, but too much cause an ecological imbalance. Using Idrisi GIS software developed here at Clark and maps showing elevation, we can determine, for any location, where the water flowing to that location comes from and where that water will flow to next. The result is what we call a "runoff" map. We can also plot nitrate levels taken from water samples. This information, combined with land use maps, helps us understand why nitrate levels may be low in some areas, and high in others. For example, some areas may not have much water flowing through them, and in that case the type of land use won't really have much effect on raising or lowering nitrate levels. Other areas may have a lot of runoff, and here the type of land use can make a big difference in nitrate levels.

This summer I helped develop a procedure and write the Visual Basic code that makes it easy to analyze differences in nitrate levels in the Ipswich River watershed. What's particularly exciting is that this procedure can be used to determine the variability of any nutrient that can be measured in the water, not just nitrates, and for any watershed, not just the Ipswich one. The user can plug in maps and sample data for his or her region of interest and very quickly get information on the affect of a particular land use on the nutrient being investigated.

One of the surprising results of our research concerned the relationship between forests and high nitrate levels in the water. We expected that water that had flowed through or under a forested area would have lower levels of nitrates because the trees would extract them for food. But instead, we found just the opposite-the nitrate levels remained high. When I presented this information at the MBL conference, the other scientists were really surprised. Some possible explanations were offered; for example, perhaps the ground water was so far underground that tree roots couldn't reach it. A scientist from the University of New Hampshire is doing a similar investigation with the nearby Parker River watershed, and we want to compare our results with his.

Are you interested in continuing with this research topic?

Yes. For my senior honors thesis I'll be looking at what contributes to high levels of nitrates in the water. One of the possible sources we're getting interested in is septic tanks, because the sewage they contain is a source of nitrates. We want to map what areas still use septic tanks, and what areas have switched to a municipal sewer system. And even in towns that have switched to municipal sewer systems, old septic tanks haven't been removed might still be leaking into the ground water. Knowing where septic tanks are located can be a clue as to the source of nitrate contamination.


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Steve Aldrich
Steve Aldrich

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