Phase 2 – Current Research

Intensive Monitoring to Quantify Nutrient Dynamics

Tidal Flow

The research team began collecting continuous water quality and flow data in March 2011. The dynamics of tidal flow are interesting to observe as the flow direction and water level vary so quickly. On a day trip to the site, we can witness a change in water level of over 0.8 m (2.6 ft). One thing to note about the data shown in all of the figures on this page is that it is preliminary data. There is a lot of calibration required to collect accurate continuous data. No matter how expensive the instrument is, they alll require calibration. The data will be adjusted throughout the project. One part of the data that we need to investigate is the noise in the flow data. This is caused by noise in the velocity data (not shown here). What we see as noise could actually be occurring in the stream or it could be the influence of wind or instrument error. We hope to learn more about the cause of the noise through measuring the flow using other instruments during site visits.

Figure 1 (left). A graph showing the variations in stage (water level) at the flume closest to the North River during one week in early March 2011. Figure 2 (right). This graph shows preliminary flow data at the downstream flume for one week at the beginning of data collection. When flow is positive, the water is flowing from the salt marsh to the North River.

Continuous Water Quality Results

The first continuous water quality data was collected from the tidal stream in March 2011. The water quality parameters were measured every 15 minutes and the results are shown in Figures 3 and 4. This data is also not calibrated. Calibrations will continue as we collect samples from the site and have them analyzed using lab equipment. The one week’s worth of data shown here, clearly demonstrates the need for high frequency sampling in tidal streams. Using methods that have traditionally been accepted as adequate for water quality monitoring, one water quality sample would have been collected during the week. One sample is not nearly enough to accurately describe the changes in concentration in a tidal marsh.

A few observations about the water quality in the marsh can be made from this first bit of data. When water is flowing from the marsh to the North River (flow is positive) the dissolved organic carbon (DOC) and nitrate concentrations are the highest. This means that water flowing through the marsh is a source of carbon and nitrate to the North River and its estuary. Negative flow values mean that water is flowing from the North River into the salt marsh. The low concentrations on the incoming tide (negative flow) indicate that the estuary is not a source of nitrate or DOC for the marsh.

Figure 3 (left). Continuous nitrate concentrations and flow at the downstream flume for one week in March 2011. Figure 4 (right). Continuous dissolved organic carbon (DOC) concentrations and flow at the downstream flume.