The deployed YSI instruments produce the first continuous data on key parameters in the boundary layer in the coastal Gulf of Mexico. These data provide detailed information on the magnitude and variablitity of e.g. oxygen concentrations and give insights in the temporal dynamics as well as the interplay between e.g. light and oxygen. In Fig. 6a, we show examples for the records produced by the instrument deployed at K-tower which also demonstrate the effects of biofouling. The latter is a major problem for long term measurements in the coastal zone, especially in warm waters. The funds requested for year 3 include funds for continuation of these measurements including materials for advanced biofouling treatment.
Our research investigating benthic primary production along a transect in the Northern Gulf of Mexico started with first measurements of photosynthesis-irradiance curves (P-I curves) of microalgal communities inhabiting the sandy sediment and with the purchasing of four YSI 6600 instrument packages that will permit the monitoring of chlorophyll, oxygen, light, turbidity, pH, conductivity, and temperature. Three of these instrument packages have been installed along a transect with stations at 5, 10, and 20 m depth. We also purchased a small multicorer system, funded through another funding source, that we will use to retrieve intact sediment cores from all stations. These cores will be analyzed for chlorophyll content and algal production. The ensuing production values will be compared to production measured in the water column in order to assess the relative importance of the benthic community for the production in the study area.
The first test measurements of sediments retrieved from the northern Gulf near our shallowest station indicate an adaptation of the macrobenthic community to high light levels. The first measurement resulted in an almost linear response of the production to light intensity even at high light intensities reaching up to 600 µ E m-2 s-1 (Fig. 6a) and response of the algal community even at very low light levels. The measurement in a second core from a nearby site indicated a similar behavior at high light intensities (Fig. 6b), however, activity was somewhat lower at reduced light levels. These first results suggest high primary productivity of the benthic community facilitated by an adaptation to the variable light environment in the nearshore zone. The second core confirmed this result but showed reduced production at the lower light levels. We propose to continue these measurement in year 3 and expand the investigations to all stations. Mike Santema, one of the students working on this project, analyzes the time series and will base his thesis on the links between the environmental parameters measured at the study site and the productivity at the stations.
Initial development of shallow surface drifters (funded separately) was begun in Year 1 to study the dispersion characteristics in the Big Bend coastal zone, the region of the FSU NGI observing system, where fresh water outflow from rivers and general seepage constitutes a large signal and influences the physical and biological characteristics of the water column (Fig. 7). Modeling activities carried out under NGI will be very important for prediction, but these models require testing and comparisons with observations to provide the best estimates of the transport of tracers, particulates, salinity, effluent etc., in the coastal environment. Our fixed sites (Fig. 12) are the backbone of this observing system.
Significant inputs of dissolved organic matter from the coastal zone into the northern Gulf shelf were observed (Fig. 8). Most nitrogen (>90%) on the shelf was associated with this organic matter flux. DOC and DON concentrations correlate significantly with salinity, indicating a mid-salinity source of these components. It is likely that not only rivers, but also brackish waters at the land-sea interface contribute significant amounts of organic carbon and nitrogen to the shelf waters. In particular submarine groundwater discharge or tidal pumping from salt marshes are likely mechanisms that provide DOC and DON to the shelf waters. Since most nitrogen in the system is present in organic form it is likely that most primary production, including the development of red tides, on the northern Gulf shelf is driven by organic matter inputs from the coastal zone. A significant source of nitrogen that was not associated with coastal organic matter inputs was observed in June 2007 (Fig. 8). The continuous monitoring of CDOM at K-tower will provide us with the necessary information to identify the sources of DOC and DON on the shelf and to identify the effects of extreme events. For this purpose, Wetlabs CDOM sensor is mounted at K-tower. The data produced by this sensor show clear fluctuations that are dominated by tides but also other long term fluctuations that depend on the large scale current dynamics. Modeling of the regional current patterns may explain the origin of these fluctuations that likely are influenced by river outflows and run off from coastal marshes and land. For year three, we propose to continue the probe measurements and associated water analysis in order to generate a time series that allows interpretation of the DOC dynamics in this region.
It is anticipated that the success in obtaining additional federal funding will strongly be increased through the proposed NGI activities. Additional funds have already been requested and granted by NSF for more detailed molecular work on dissolved organic matter in the northern Gulf of Mexico. This molecular work directly links to the central scientific and educational goals of NGI.