HR: 16:00h
AN: OS52F-07    [PDF]
TI: Observations of exchange mechanisms within shallow, subtidal habitats --- effects of submerged aquatic vegetation
AU: * Sereno, D M
EM: sereno@uclink.berkeley.edu
AF: University of California, Berkeley, 631 Davis, Berkeley, CA 94720 United States
AU: Stacey, M T
EM: mstacey@socrates.berkeley.edu
AF: University of California, Berkeley, 631 Davis, Berkeley, CA 94720 United States
AB: Hydrodynamics and water quality in shallow, subtidal systems can be greatly influenced by the presence of submerged aquatic vegetation (SAV). Patches of SAV locally alter nutrient levels, light attenuation, suspended particle concentrations, current velocity, turbulent mixing, and bed sediment size distribution and organic content. If a patch of SAV is sufficiently dense, water quality parameters can vary significantly between the vegetation filled water column and the adjacent open water. Thus, the concentration of constituents, such as nutrients, in the open water depends on the exchange with waters within the SAV. The results of field observations are presented to evaluate different exchange mechanisms between SAV and the adjacent open water in Franks Tract, a shallow, subtidal habitat in Northern California. Hydrodynamic and water quality measurements, including temperature, conductivity, suspended sediment concentrations, and chlorophyll-a, were collected in spring 2003 both within the SAV and in the adjacent open water. Additionally, synoptic surveys of the flow field were conducted to examine the lateral transfer of momentum into the vegetation. Turbulence measurements reveal enhanced mixing at the vertical interface between the vegetation and open water. Concurrent measurements at different heights within the vegetation allow for an estimation of the depth of this mixing layer. Additionally, tidal asymmetries in both velocity and suspended particle concentrations indicate a net transport of sediment into the vegetation, suggesting a possible sink in the system. The synoptic surveys revealed that large, intermittent eddies generated at the edge of a jet entering the habitat were able to penetrate the lateral interface between the SAV and open water. Preliminary results indicate these vortices may be a significant process for lateral momentum transfer from the mean flow to the vegetation. The synoptic surveys also revealed that the net exchange between the shallow habitat and exterior waters due to the classical ``tidal pumping'' asymmetry is altered by the presence of SAV.
DE: 1845 Limnology
DE: 4558 Sediment transport
DE: 4568 Turbulence, diffusion, and mixing processes
DE: 4594 Instruments and techniques
DE: 4815 Ecosystems, structure and dynamics
SC: Ocean Sciences [OS]
MN: 2004 Ocean Sciences Meeting