HR: 0800h
AN: H41F-0347    [Abstracts]
TI: Estimating Effective Vertical Diffusivity in Shallow Ponds by a Constrained Flux-Gradient Method
AU: * Bean, J R
EM: j.bean@uconn.edu
AF: University of Connecticut, Department of Marine Sciences, 1080 Shennecossett Road, Groton, CT 06340 United States
AU: Torgersen, T
EM: thomas.torgersen@uconn.edu
AF: University of Connecticut, Department of Marine Sciences, 1080 Shennecossett Road, Groton, CT 06340 United States
AB: Shallow ponds have been used to mitigate the deleterious effects of storm water run-off by acting as detention/retention basins that sequester run-off associated pollutants in sediments. Studies show that the retention efficiency of these systems can decrease over time as a result of the internal loading of nutrients/contaminants from the sediments back to the water column where they are available for export downstream. Quantifying the vertical transport of gases (down) and sediment derived materials (up) is vital to the modeling and understanding of the processes that contribute to the magnitude of internal loading. A critical parameter is the effective vertical diffusion coefficient: K$_{z}$=D$_{molecular}$ +D$_{eddy}$ (cm$^{2}$ sec$^{-1}$). The flux gradient method for estimating effective vertical thermal diffusivity has been applied with success in large lakes which undergo stratification cycles on seasonal or longer time scales. We offer a constrained version of the flux-gradient method that has been adapted for use in a shallow pond with a daily stratification cycle. The method employs heat as a tracer and assumes that transport in the face of a stable gradient is diffusive. By shrinking the spatial and temporal resolution of measurement to scales appropriate to the system of interest and carefully accounting for internal source and sink terms of heat (e.g solar radiation and sediment heat fluxes) we are able to calculate K$_{z}$ as a function of time and depth during periods of stable stratification, i.e when the pond is not vertically well-mixed. Results show the magnitude of K$_{z}$ varies from ca. 10$^{-3}$ to 10$^{-1}$ (cm$^{2}$ sec$^{-1}$) under stratified conditions depending primarily on the strength of stratification.
DE: 4227 Diurnal, seasonal, and annual cycles
DE: 4239 Limnology
DE: 4568 Turbulence, diffusion, and mixing processes
DE: 1857 Reservoirs (surface)
DE: 1871 Surface water quality
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting