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Urban stormwater infrastructure: Understanding hydrologic and greenhouse gas fluxes in detention basins

You may have seen dark green buckets partially buried in detention basins around campus and wondered, "What's going on here?" The buckets you see are part of an experiment to determine whether detention basins are sources of greenhouse gases. This experiment is being conducted by the Soil and Water Lab in the Department of Biological and Environmental Engineering. Near several detention basins there are also small containers positioned (often on the edge of a parking lot) to collect samples of stormwater runoff entering and leaving the basins, providing us with data with which to judge the effectiveness of the detention basins.

   

Examples of the bucket chambers for gas sampling (left) and the containers used for water sampling (right) - Please do not disturb them.






What is a Detention Basin?    

A detention basin (pictured to the right) is a vegetated depression in the land that is designed to serve two main purposes: 1) it temporarily stores runoff from parking lots and other impervious surfaces, thus reducing the threat of flooding during rain events, and 2) it allows runoff to naturally filter through soil, which traps contaminants before the water enters the stormwater sewer system or a stream, thus improving water quality. The purpose of this study is to understand the hydrologic and greenhouse gas fluxes in the basins, in order to asses their effectiveness and their impact on the environment, and to inform the construction of future detention basins.


Below is a map of the detention basins on campus. The basins indicated by the blue markers are areas where stormwater runoff samples are being collected. The basin marked with purple is a new basin that was just completed in May of 2013 and is now being sampled regularly in order to track the performance of a basin over it's lifetime. Basins marked in red are being tested for greenhouse gas production, while basins marked in teal have been monitored for both stormwater runoff and greenhouse gases.

Previous research suggests that detention basins and other areas that are frequently inundated with water may serve as biogeochemical hotspots. Biogeochemical hotspots are areas where the rate of production of methane, nitrous oxide, and other gases exceeds the normal rates of production in comparatively dry areas.

Update: July 2013

Both stormwater and gas sampling are ongoing although the actual results will not be discussed at this time - please check back later for updates as both data collection and analysis continue. Greenhouse gas data is being compared to soil moisture and temperature trends in order to determine the drivers of methane and nitrous oxide emissions. Pollutant loads over the life-time of each basin are being estimated based on observed inflow values and stormflow records.

Detection of Synthetic Fibers:
Soil samples are also being collected at each of the detention basins, to be used for a variety of purposes, including the detection of synthetic fibers. Previous research has shown that synthetic fibers indicate the presence of municipal sludge, which could have been used as fill for the basins when they were first constructed. Synthetic fibers enter the waste-water system through laundry machines, but do not break down during the process and settle out into the waste sludge. Fibers can be detected in soil because they fluoresce under polarized light microscopy. If a significant number of fibers are found in these soil samples, it would indicate that municipal sludge was used to construct a basin, which in turn may better explain some of the water quality data and further inform the construction of future detention basins.


Soil Texture Analysis:
Soil samples are also being analyzed for texture to determine whether accumulated sediments are changing physical properties of the soil. Soil samples are being taken from three different locations within each basin: the inlet, the pool of the basin, and the edge as a control. Since larger particles settle out first, it is expected that the inlet will contain the highest percentage of sand, and the pool will contain a lower percentage of sand. A transect sample will be taken from each detention basin's pool area to see if changes in soil texture can be used to determine the water's path in the pool. The movement of water in the basins may be an indicator of how well the basins are functioning.
Both soil and water samples will also be tested for bacteria and E. coli to determine whether selective accumulation is occurring. If the basins are functioning properly, bacteria from storm water will be held in the soil, and the outlet water should contain lower amounts of bacteria.

More information as to the validity of these findings will be posted to this website as the experiment progresses. Please check back here for updates!



Staff: This project is led by Professor Todd Walter, and students working on this project include Lauren McPhillips (graduate student) and Andrea Fortman, Rachel Whiteheart, Christine Georgakakos and Breann Liebermann (undergraduate students)


Funding: This work is funded by the NYS Water Resources Institute Hudson Estuary Program and the Cornell Engineering Learning Initiatives Undergraduate Research Grant Program

If you have any questions about this project, please contact Lauren McPhillips.

Last updated July 2013