Project Title: Development of an Automated Chemical Sampler/Analyzer for Submarine Groundwater Discharge in Estuaries
Principal Investigator(s): Matthew Charette, Edward Sholkovitz

Accomplishments
Scheduled Tasks:
We continued field-testing of our prototype seepage meter leading up to a submarine groundwater discharge (SGD) intercomparison experiment on Long Island, NY in May 2002 (Figure 1). There, we showcased our CICEET-funded instrument against other (heat-pulse and ultrasonic) automated seepage meter technologies. Below, we present a report on our participation in the SGD intercomparison; included are excerpts from a report to the SCOR working group prepared by Bill Burnett (FSU).

Progress on Tasks
This report presents our preliminary data from the SGD intercomparison experiment held on Shelter Island, New York May 17-24, 2002. Shelter Island (~28 km) is located in the Peconic Bay between the north and south forks of Long Island. The island is sparsely populated and only a small section in the northwestern area of the island has a storm drainage system. Therefore, precipitation evaporates, transpires, or recharges the freshwater aquifer. There are no major streams or creeks on the island and therefore, groundwater that enters the aquifer primarily discharges through the coastline into the surrounding waters. The island is composed of upper Pleistocene glaciofluvial deposits (Soren, 1978), consisting of outwash sands and drift that form high hills. Freshwater on Shelter Island is restricted to the unconfined Upper Glacial aquifer. Below the Upper Glacial are two distinct clay units: a marine gray-green clay ranging in thickness of 15 to 27 m; and a reddish brown non-marine clay having a thickness of 37 m.

Numerical modeling of groundwater flow based on a series of monitoring wells indicates that groundwater flow discharges at high velocities ranging from 60 to 240 cm/day in the West Neck Bay area. An inverse correlation between measured flow and tidal stage has been observed and measured discharge rates are within the range of those calculated from the model.

Difficulties Encountered
We have no concerns at this time.

Anticipated Success in Meeting Project Objectives in Scheduled Project Period
The initial two-year project was completed as scheduled. With an additional year of funding, we will work to integrate nitrate/ammonium analyses with flow measurements to yield time-series SGD-derived nutrient fluxes in Waquoit Bay.

Preliminary Results
The dye-dilution method was tested at the Shelter of May 2002. Our instrument was deployed at two locations: (1) the first deployment (18-21 May 2002) was at a site close to the beach where the seepage flow is higher (Figure 2), (2) the second deployment (21-23 May 2002) was in deeper water where the seepage flow is significantly lower.

The main observations and conclusions from the Shelter Island results are:

1. High-resolution data for seepage flow rates were obtained over a period of six days at flow rates ranging from 2 to 30 cm/day. The error on the flow rates is approximately 15-20 %.
2. The flow rates are tidally dependent with maximum flow at low tide.
3. There was significantly less flow at the second site, located further off the beach.
4. The YSI salinity data from inside of the first seepage meter show a large salinity decrease over three days as freshwater seepage slowly replaces the salt water initially in the seepage meter. The changes in the slope of salinity vs. time reflect periods of low and high flow. Note that the volume inside the seepage meter is large (20-30 L) and is not mixed to allow for rapid homogenization of the signal.
5. The slow decrease in salinity inside the second seepage meter reflects a much slower input of SGD that is not entirely freshwater.

In summary, the dye-dilution method operated in a reliable manner and yielded consistent data on the seepage flow rates. No comparison of our data with the flow data of other investigators has taken place yet. We came to Shelter Island expecting much higher flow rates. Hence, a large dye-mixing chamber was used. If a smaller dye-mixing chamber was used, precision would have been even better.

Tasks and activities for next reporting period

Tasks for the next reporting period
Not Applicable. Final reporting period.

Expenditures
Expenditures were in the range anticipated for the work accomplished to date.