CICEET Progress Report for the period 8/01/00 through 1/31/01

Project Title:

Development of an Automated Chemical Sampler/Analyzer for Submarine Groundwater Discharge in Estuaries

Principal Investigator(s):

Dr. Matthew Charette, Woods Hole Oceanographic Institution, Woods Hole, MA 02543
Dr. Edward Sholkovitz, Woods Hole Oceanographic Institution, Woods Hole, MA 02543

I. Accomplishments

1. Scheduled Tasks

Our primary objective for the first half of proposal Year 1 was to acquire the components and combine them into a unified system. Major components (in order of priority) include a seepage meter chamber, an automated flow-meter, an in situ nitrate analyzer, a CTD probe, and a Radium extraction system. Also, we planned to collect samples for nitrate analyses from various locations in Waquoit Bay and its sub-estuaries.

1. Progress on Tasks

During the summer/fall 2000, we constructed a simple seepage meter chamber for the explicit purpose of testing a prototype flow-meter design. An initial flow-meter was deemed unacceptable for the task; we are currently evaluating a new design. A YSI 600 CTD was purchased and tested in Waquoit Bay. We evaluated two in situ nitrate analyzers and decided on a W.S. Ocean Systems NAS-2E. Our decision was based on the positive track record of the instrument, which spans nearly a decade. We have been bench-top testing its stability and are currently preparing for a field test this spring. We have begun to work with a WHOI engineer on the design of the instrument platform, as well as a novel method for estimating seepage meter flow rates.

1. Difficulties Encountered

   During the summer/fall 2000, we constructed a simple seepage meter chamber for the explicit purpose of testing a prototype flow-meter design. The flow-meter was adapted from an off-the-shelf McMillan design which had been fitted into a water-tight housing. An underlying source of concern throughout the flow-meter testing was the possibility that, when deployed on the seepage meter, it would have too restrictive an effect on the flow, forcing the groundwater to seek an alternate route other than through the outlet port of the seepage meter. Our concerns were realized during laboratory and field testing and therefore, the McMillian design flow-meter was abandoned. We have begun to research and test alternate flow-meter designs, primarily a spectrophotometric technique employing dyes. This method involves the injection of a dye into a mixing chamber attached to the seepage meter. By measuring the drop in absorbance from the initial known concentration of dye, the flow-rate can be calculated. This has shown promise in the lab and in limited field testing. Also, it may be possible to use the NAS-2E nitrate analyzer to make the absorbance measurements thereby avoiding the cost and complexity of a dedicated spectrophotometer

2. Anticipated Sucess in Meeting Project Objectives in Schedualed Project Period
   
   Even with the set back associated with the initial flow-meter design, we are on track to have a prototype automated seepage meter by the end of the next reporting period. This would allow for extensive Year 2 testing and field deployment and collection of time-series data.
   
   
3. Preliminary data
   

   We have recently completed the analysis of bi-weekly nutrient samples collected at seven stations throughout Waquoit Bay its sub-estuaries. This data will allow us to evaluate groundwater-derived nitrate fluxes relative to other sources of nitrogen to Waquoit Bay.
   
   

II. Tasks and activities for next reporting period

1. Tasks for the next reporting period
   
   Construction of the main infrastructure of the automated seepage meter including the seepage meter itself and a frame for attaching the instrumentation. Devise a mixing chamber for dye-based measurement of flow rate. Continued nutrient sampling at Waquoit Bay time-series sites.
   
   
2. Work plan to accomplish tasks
   
   Our engineering colleague is working on building a working prototype including the seepage meter, instrument platform, and mixing chamber, which should be completed for spring-time testing. The first in situ test of the NAS-2E will take place at the WHOI dock during. Finally, we plan a comprehensive field test of each component during spring/summer 2001 at the Waquoit Bay study site.
   
   
3. Concerns or difficulties
   
   None at this time.

III. Expenditures

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