Continuing with the BES Seminar Series, Dr. M. Todd Walter spoke last Friday about his work in bio-geochemical hydrology, the movement of nutrients and water through a region.
When phosphorus and nitrogen leech into the environment, they can wreak havoc on the natural ecosystem. The extra nutrients supercharge organisms that use photosynthesis as a food source, creating a number of problems such as oxygen depletion zones in the water and toxic algae blooms that can harm both marine and terrestrial animals, including humans.
Dr. M. Todd Walter, a biogeochemical hydrologist from Cornell University, has always been interested in periodic “wet zones” and how pollutants find their way in into watersheds. His field of study focuses on the movement of water and the pollution it picks up along the way.
While working in the watershed surrounding New York City, Walter and his team started to identify how the water runoff was traveling in comparison to where pollution was being generated.
“If we could tell where these wet areas were, and we also knew where the potential polluting activities were,” Walter said, “Instead of worrying about a whole landscape, you could focus all of your attention just on this critical area where those things overlap.”
What Walter set out was to do with his team was to create models that show where water was moving through the landscape to help avoid placing pollution where it would be carried into water sources. The final product is a program that can be found on his website and can be used to see if, where and how likely it is that water runoff will be generated. Waste producers such as farmers and chemical companies can visualize on a map where they should not be dumping waste.
Instead of focusing on where streams discharged, his group focuses on the sources of these streams. Dr. Josephine Archibald looked at shallow well data and used it to see historically where wet spots are. The resulting graphs and models showed that wells 10 centimeters or less from the surface were usually where runoff was generated in a specific area.
The scientists saw from their measurements that in the winter that the amount of runoff in both forested and agricultural areas was being overestimated, Walter said. After reviewing the data again and adjusting for temperature, they saw that the model fit the observations much better.
With no real leads as to why phosphorus levels would peak in the summer and bottom out in the winter, the scientists began to look for answers. Walter and his team started investigating the polyphosphate accumulating organisms (PAO) that lived in the streams, the same type of microbes have been studied extensively in waster water treatment plants. The organism is used to biologically remove phosphorus from the water before it is returned to the environment.
Walter’s interest was sparked when a masters student needed hydrological help determining where fish were in the Adirondack Mountains of Upstate New York in the summer, when the water was warmer. The theory was that groundwater around portions of the lake would be more abundant in some areas than others. This groundwater keeps those areas colder and this is where the fish will be.
Walter realized that he could map where more water can be found and determine the rate that nitrogen is being converted to gas there. The process involves gathering soil at various levels of water saturation and adding a heavier nitrogen isotope so that it can be distinguished from the ambient nitrogen in the soil and atmosphere. After adding the nitrogen to the sample, it is allowed to incubate for approximately 4 hours. Measurements of how much of the nitrogen isotope is left in the sample are taken, with the difference being the rate of nitrogen converting to gas. This rate can be used across large regions to accurately calculate the amount and movement of nitrogen pollution in an area.
The lecture series continues this Friday in the Pharmacy Â Building Room 170 at 3 p.m. The topic is, “Communication and sustainability science: lessons learned about team design within large-scale collaboration networks in New England.”