CICEET Progress Report for the period 8/1/02 through 1/31/03
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 have just submitted a paper to the new electronic journal being published by the American Society of Limnology and Oceanography (ASLO), called "Limnology and Oceanography, Methods". Our paper is entitled, Sholkovitz E. R., Herbold C. and Charette M. A. (submitted) An Automated Dye-Dilution Based Seepage Meter for the Time-Series Measurement of Submarine Groundwater Discharge. Limnol. Oceangr. Methods. A hard copy of this paper is being sent to the CICEET office at the University of New Hampshire. In addition, we presented a paper at the recent ASLO Aquatic Sciences conference (Salt Lake City, UT) in a special session organized by the PI Charette entitled "Groundwater-Surface Water Interactions".
Progress on Tasks
Our recently submitted paper contains a complete description of our automated seepage meter along with the results of a laboratory calibration and field deployment at Shelter Island and Waquoit Bay. The abstract and conclusion sections of this paper are given next.
Abstract: We have designed, built and tested an automated seepage meter that can detect and quantify both groundwater outflow and seawater infiltration. Based on a dye-dilution technique, this instrument can provide high-resolution time-series data for submarine groundwater discharge to the coastal zone. The dye-dilution method involves two repeatable steps - (1) the timed-injection of a water-soluble dye into a "dye-mixing chamber" mounted in series with a seepage chamber and (2) the subsequent timed-measurements of the absorbance of the dyed solution. The rate at which the dyed solution is diluted by the inflowing or out flowing water is directly proportional to the flow rate moving through the surface area of the seepage housing. In addition to describing the instrument's components and the operating principle, we provide examples of laboratory flow calibrations and field deployments. As indicated by three sets of time-series studies, this instrument has performed reliably in field tests at Waquoit Bay (Cape Cod, MA, USA) and Shelter Island (Long Island, NY, USA). The instrument has yielded hydrologically consistent flow rates and has revealed major and subtle connections between tidal stage and the rate and direction of submarine groundwater discharge.
In conclusion, the time-series data from Shelter Island and Waquoit Bay are very encouraging with respect to the capabilities of our new automated seepage meter. The dye-dilution method is versatile in being able to measure a wide range of flow rates in two directions. The instrument has yielded hydrologically consistent flow rates and has revealed major and subtle connections between tidal stage and the rate and direction of submarine groundwater discharge. The magnitude of the outflow at both sites is inversely correlated with the tidal height. In Waquoit Bay, the flow direction switches from outflow to inflow at the transition low to high tide. The addition of sensors to record changes in salinity inside and outside of the seepage housing provides valuable information on the sources of submarine groundwater discharge to the coastal ocean (freshwater and brackish water to the inshore and offshore sites at Shelter Island and predominately recirculated seawater to the Waquoit Bay site).
Difficulties Encountered
We have no concerns at this time.
Anticipated Success in Meeting Project Objectives in Scheduled Project Period
The project is on track as scheduled.
Preliminary Data
Our submitted paper provides the community with a detailed description of a new type of seepage meter and highlights its advantages over other automated seepage meters. The dye-dilution method operated in a reliable manner and yielded consistent data on the seepage flow rates. For example, the Waquoit Bay field experiment yielded hourly flow data for a period of three weeks. The data from this experiment revealed that there is tidally controlled seepage of seawater into and out of the sediments at the head of the Bay. This observation has important implications for the interpretation of the groundwater flux of nutrients into the Bay.
Unlike other automated seepage meters, the dye-dilution method can also be operated in a manual mode. In practice, this requires the recirculating pump, its battery pack and the dye-mixing chamber but not the automated dye injector and in situ spectrometer. The operator would hand inject dye into the mixing chamber and hand-remove aliquots of water from the mixing chamber on a timed basis. The absorbances of these aliquots could be measured with an inexpensive spectrophotometer and used to determine the flow rates in the field. This method is less labor intensive than the bag-method, and has the major advantage of detecting and accurately quantifying reverse flow. The equipment needed to turn a seepage housing into a manually operated dye-dilution based flow instrument would cost less than $1500
Tasks and activities for next reporting period
Tasks for the next reporting period
We will be carrying out a large field program in Waquoit Bay from April to July 2003. The plan is to use a suite of instruments and sampling techniques to simultaneously measure the seepage rate of water into and out of the sediments and the nutrient concentrations of the Bay water and surface pore waters. Our automated seepage meter will be deployed, and our new CICEET-funded ECOLAB instrument will be used to gather time-series data on the concentrations of nitrate and ammonia. We will also hand-collect surface water and pore water for analyses in the laboratory. The nutrient concentrations will be measured in the Bay water adjacent to the flow meter and in the pore waters of the upper (5- 10 cm depth) sediments adjacent to the flow meter.
The automated measurement of the pore water composition and the seepage flow will represent a significant technological advance in coastal oceanography. Our major scientific objective is to quantify how seepage of water into and out of sediments affects the flux of nutrients into the head of Waquoit Bay.
Expenditures
Expenditures were in the range anticipated for the work accomplished to date.