Continuous monitoring in the benthic boundary layer off

Continuous monitoring in the benthic boundary layer off the Northwestern Florida shelf. William M. Landing, Stephanie Fahrny, Kevin Speer, Markus Huettel Department of Oceanography, Florida State University, Tallahassee, FL Continuous, high-frequency records of biogeochemical parameters (such as dissolved oxygen, chlorophyll, p. H, and nutrients) are imperative for understanding and quantifying biogeochemical cycles in dynamic coastal environments. Such data records also serve to constrain coupled physical/biogeochemical models in these environments. Instrument arrays containing a YSI 6600 multisensorprobe that collects pressure, temperature, conductivity, p. H, PAR-light, turbidity, chlorophyll, and dissolved oxygen data at 15 min. intervals and an upward-looking ADCP were established at two sites along a transect in the Northeastern Gulf of Mexico. After two weeks of deployment, the sensor package at station A failed due to serious biofouling despite wipers and anti-fouling treatment. However, data show interesting trends and here we show the first few weeks of data retrieved recently from Station A. Nitrate is a required (and often growth-limiting) nutrient for phytoplankton and sea grasses, and exhibits significant concentration changes in dynamic coastal environments due to variable input (stormwater, submarine groundwater discharge, tidal flushing, water-mass mixing and long-shore transport) and removal (photosynthetic growth/uptake, water-mass mixing and long-shore transport) processes. A robust optical sensor for measuring dissolved nitrate at concentrations as low as 0. 5 micromolar (0. 7 ppb-N; the ISUS-V 3 from Satlantic) is now available and has been integrated into the bottom (20 m) instrument array at the “K-Tower” site off the coast from the FSU Marine Laboratory. First data are expected in June 2008 Monitoring stations established in the Northeastern Gulf of Mexico. Stations A and K-Tower have been equiped with YSI multisensor probes and ADCPs. Station B will follow during summer After only 4 weeks deployment, the YSI sensor package showed a high degree of biofouling. Growth on the PAR sensor wiper locked the wiper causing a major increase in current consumption that affected the readings of the other optical sensors. Only data not affected by this fouling are shown here. PAR data are reported without units because we are still in the process assessing the reliability of the data collected. Plotting salinity versus temperature shows a correlation with salinity decreasing with increasing temperature suggesting effects of warmer nearshore water moving offshore where it mixes with colder more saline Gulf water. During the recording period, water temperature in the bottom layer increased from about 17 C to 23 C and then rapidly dropped again after 4/11/08 to about 20 C at the end of the measuring period (4/16/08). K-Tower ADCP data showing the current directions at different water depth Salinity showed strong initial variations (25 -33 ppt) but in general remained high at about 32 ppt. After 3/30/08, salinity steadily dropped from 32 to 26 ppt reached at the end of the measuring period. Chlorophyll a values ranged between 0 and 8. 1 µg/l, turbidity between 1 and 71 turbidity units. Both chlorophyll and turbidity indicate two phases with increased phytoplankton in the water during the first two weeks of measurements. PAR showed increasing values during the first half of the measuring period and erratic data after 4/1/08. Oxygen concentrations started at about 100% saturation at the beginning of the measuring period and then concentrations build up in the water column reaching 108% on 3/30/08. During this period, clear day/night oscillations of the oxygen are visible in the signal and there seems to be a correlation between PAR and oxygen concentration. The p. H values dropped from initially 7. 9 to 7. 76 reached on 4/1/08. During this period there are phases where p. H seems to be correlated to oxygen content. After this period p. H suddenly dropped to 7. 5 probably due to a malfunction in the PAR sensor