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Automated Seepage Meter for Groundwater Discharge
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Project Title: Development of an Automated Chemical Sampler/Analyzer for Submarine Groundwater
Discharge in Estuaries
Research Locations: Waquiot Bay (Cape Cod, MA)
Last Update: September 8, 2003
Groundwater can collect nutrients as it moves through soil and sediment, often carrying large amounts of pollutants directly to coastal waters. These pollutants, including excess nutrients such as nitrogen and phosphorous, can degrade water quality and damage coastal habitats, causing such problems as algal blooms and oxygen depletion. While recognized as an important source of environmental degradation, groundwater discharge has received little attention because it is difficult to measure. Unlike river water which follows a distinct flow path, the flow path of groundwater is not easily defined. Devices that measure groundwater flow, called seepage meters, have been in existence for several decades. However, obtaining data with traditional models is often time consuming and labor intensive. This project is developing and testing a new, automated seepage meter that is easy to maintain and can provide high-resolution time series data.
Design
The seepage meter functions in two steps using a dye-dilution technique employed either automatically or manually (other meters do not offer this choice). A water-soluble dye is injected into a "dye-mixing chamber" mounted adjacent to a separate seepage chamber. Then, a continuous series of timed measurements are taken on the absorbance rate of the dyed solution. Water flowing in and out of the seepage chamber dilutes the dyed solution. The rate at which the solution is diluted is directly proportional to the flow of water over the surface of the seepage chamber. Flow quantities can be measured in two directions - inflow and outflow.
Results
- Tests in both Waquoit Bay (Cape Cod,MA) and Shelter Island (Long Island, NY) yielded hydrologically consistent flow rates and revealed both major and subtle connections between tidal stage and the rate and direction of submarine groundwater.
- The addition of sensors to record changes in salinity inside and outside of the seepage chamber has provided valuable information on the sources of discharge to the coastal ocean.
- Results of this work have been published in Limnology and Oceanography: Methods. Go to http://www.aslo.org/lomethods/free/2003/0016.pdf
Measuring Nutrients Now and in the Future
Data on nutrient flow from groundwater, as well as the forces that
regulate that flow, such as tide, weather and season, can now be
obtained faster and more accurately, with much less difficulty.
Knowing when and by what forces discharge is at its highest may
help predict high nutrient events, thus preparing managers for
surges that could affect the ecology and recreational use of coastal
areas.
Application to Other Aquatic systems
Although testing focused on the coastal ocean, This method can be applied in all aquatic environments, including freshwater systems.
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Project Coordinator
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Matthew Charette (508) 289-3205
Edward R. Sholkovitz (508) 289-2346 |
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Start -End Date:
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01/09/2002 - 01/09/2004
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NERR Reserve(s):
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Waquiot Bay (Cape Cod, MA)
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For more information: |
Dolores Jalbert Leonard |