The tasks scheduled for completion in year 2 include: Continuously monitor nitrate, temperature, salinity, dissolved oxygen, etc. at two locations in Elkhorn Slough. Process and analyze data in a timely fashion. Adapt phosphate chemistry to analyzer. Make necessary changes to manifold (e.g., add heater) and electronics/software. Purchase parts and assemble four more analyzers. Test phosphate analyzers in Elkhorn slough. Begin deployments at other NERR sites. Present preliminary results at National meeting.

Dr. Thomas Chapin is continuing to work to optimize the Digi-Scanner design in the laboratory at the same time as it is being deployed in Elkhorn Slough. The first deployments began in October 1999 at the South Marsh YSI site. It has been deployed 7 times in the Slough, three at the South Marsh YSI site and four times at the Azevedo Pond site. There were some problems with the beginning deployments at South marsh, so there is only one dataset from South Marsh and 3 Azevedo Pond datasets. A YSI data sonde has been deployed next to the Digi-scanner during each deployment.

Dr Chapin presented the preliminary results from October, November and December in a poster at the Ocean Sciences Meeting January 24-28, 2000 in San Antonio, Texas. There was a significant interest in his poster, and several scientists were interested in developing future collaborations with him.

We anticipate that we will successfully meet our project objectives, although we will probably need a 6 month no cost extension of the contract.

Preliminary graphs from deployments in South Marsh and Azevedo Pond are included (Figures 1-3). Surprisingly, nitrate concentrations were much lower than we anticipated, particularly at the Azevedo Pond site during November and December. This is probably a result of the lack of rain and runoff before and during those deployments. During this period, nitrate concentrations varied between 0-10 µM at the South Marsh site (Figure 1) and 0-30 µM at the Azevedo Pond site (Figure 2). Nitrate concentrations showed a strong tidal signature, i.e. nitrate concentrations varied with salinity(and temperature) where the highest nitrate concentrations coincided with warm, low salinity water (Figure 2).

The latest deployment from January showed a strong response to rainfall, with concentrations exceeding 450 µM following 3.5 mm of rain in the area (Figure 3a and b). Concentrations gradually declined to 80 µM over the remaining 4 days of the deployment and slowly resumed the tidal signature pattern.

We will continue working on the tasks for year 2. As new Digi-Scanners are constructed, they will be tested in the laboratory and field. After the nitrate analyzers performance has been optimized, Dr. Chapin will begin working on adapting the Digi-Scanner to measure dissolved phosphate. We will continue the current YSI deployments and prepare for an additional deployment when the analyzers are ready for field testing.

We anticipate deploying Digi-Scanners in other National Estuarine Research Reserves with the funding for the third year of this project.

In the next 6 months we plan to continue to deploy the first Digi-Scanner in Azevedo Pond, build 2-3 new Digi-Scanners, evaluate results from initial slough deployment, perform lab evaluations for the new Digi-Scanners, begin laboratory work on the phosphate technique, and work on extending the duration of the Digi-Scanner.