ABSTRACT: The HERMES model-predicted Hg concentrations and fluxes in Lake Ontario were based on twelve lake and drainage basin variables (i.e., water temperature, precipitation rate, air Hg, surface area, mean depth, water volume, water inflow rate, inflow water Hg, inflow and lake suspended particulate matter, air-water and water-air mass transfer coefficients, and sedimentation rate). The HERMES model-predicted Hg water and surface sediment concentrations were found to be significantly correlated (±20%) with measured values (r(2) = 0.94, p < 0.0001, n = 13) and mechanistic model predictions (LOTOX2-Hg, r(2) = 0.95, p < 0.0001, n = 10). The predictive capacity of HERMES was previously tested on smaller (≤1 km(2)) lakes in Nova Scotia and Ontario, Canada (i.e., water and sediment Hg concentrations were ±15% of measured data). Results suggest that HERMES could be applicable to a broad range of lake sizes. Uncertainty analyses on HERMES model input variables indicated a larger atmospheric Hg contribution for Lake Ontario when compared to previous predictions for smaller lakes.
Environmental pollution (Barking, Essex: 1987) 07/2011; 161:335-42. · 3.43 Impact Factor
ABSTRACT: Diffusive convection driven by the differential diffusion of density altering fluid properties may enhance the scavenging of particles from natural buoyant plumes. For single-phase (fluid–solute–heat) systems this phenomenon has been extensively studied because salt fingering generated at the oceanic thermocline is a major mechanism of salt transport in the oceans. However, the influence of this process on particle laden plumes, for example, fluvial plumes in lakes and estuaries volcanic clouds and seafloor hydrothermal plumes is largely unknown. In this paper, we present direct experimental measurements of the interfacial particle flux at the plume base which can be applied to predict particle scavenging from natural buoyant plumes. Particle flux is measured using a light attenuation technique employing a chain of photodiodes which average concentration over a large number of fingers. The results are in good general agreement with earlier studies based on finger velocity. Flux measurements cover a wide range of conditions from those where diffusive convection dominates to those where settling and diffusive convection are of a similar magnitude. For very small particles double diffusive (salt finger) theory is applicable to two component particulate systems as suggested by earlier studies [Green, T., 1987. The importance of double diffusion to the settling of suspended material. Sedimentology 34, 319–331]. Two component diffusive convection theory is extended to three components in order to predict particle scavenging from marine fluvial plumes which involve the diffusion of sediment, salt and heat. For larger particles which settle significantly the flux can be approximated by adding the double-diffusive and settling fluxes. A theory to predict particle transport through the lower layer and sedimentation at the bed is developed based on the observation of strong convection below the plume. Application of our theory and experimental results indicates that while double diffusion may significantly influence the longitudinal distribution and vertical sorting of deposits from lacustrine plumes, the diffusive convection process is generally insignificant in marine plumes. Observational evidence for lacustrine double diffusion based on water column measurements is presented.
Marine Geology - MAR GEOLOGY. 01/1999; 159(1):205-220.
ABSTRACT: We present results Irom an experimental study of suspended particle (4.5–36.5 μm silicon carbide powder deposition from surface
water to ‘clean’ equi-granular permeable beds in a small 12.5×12.5×15cm box and a re-circulating flume. Enhanced deposition
rates of up to 5 times the accepted sediment deposition model (e.g., Einstein,1968 are explained by filtration of particles in the bed. Compared to this model depotiion increases with increasing surface fluid
speed, decreasing suspended particle size and increasing bed particle size. These results can be explained by an increased
ability of particles to penetrate into the bed with the pore water which increases the effective filter thickness. The predominant
deposition mechanism within the bed pores appears to be settling. Enhanced deposition, evident in Einstein's (1968) experimental
data, was previously attributed to flocculation but may be explained better by filtration. These enhanced deposition rates
drop off to close to the accepted model predicted rate after a certain volume of sediment has entered the bed, which may be
due to the stumping of deposits from the top of bed elements. This reduction in deposition rate occurs long before the bed
is filled with fine sediment.
Water Air and Soil Pollution 04/1997; 99(1):157-171. · 1.63 Impact Factor