Measuring groundwater transport through lake sediments by advection and diffusion

Abstract

Environmental Research Branch, Chalk River Nuclear Laboratories, Chalk River, OntarioA method for estimating low rates of groundwater inflow and outflow through the bottom sediments of surface waters was developed and tested. A one-dimensional advection-diffusion model was fitted to measured pore water profiles of two nonreactive solutes, tritiated water and chloride, and the advection rate was calculated by a nonlinear least squares technique. Using 3H profiles measured 0-0.5 m below the sediment-water interface, rates of groundwater advection into a lake through interbedded sands and gyttja were estimated to be about 1.0 m/year. In midlake locations underlain by soft organic gyttja, rates of advection were much lower (<0.1 m/year). Knowledge of the rate and direction of groundwater flow substantially altered the interpretation of pore water profiles within the sediments and the fluxes of solutes. This technique can be used to estimate flow rates less than 2 m/annum with minimal disturbance, without enclosing the sediments in a container, in a diversity of systems.

Characterization of lake water and ground water movement in the littoral zone of Williams Lake, a closed‐basin lake in north central Minnesota

“…Values from site I lie along the gradient between ground water and lake water, with many values closer to the average value of υ 18 O and υ 2 H in ground water than the values found in lake water, reflecting the input of ground water at site I. The gradient of υ 18 O at the inflow site is indicative of advective flow and similar to gradients that result from advective flow observed in the sediments of other inflow lakes (Berner, 1980;Cornett et al, 1989;Mortimer et al, 1999). Measurement of water levels and hydraulic conductivity in wells in the areas of inflow of ground water to the lake between April 1991 and June 1992 indicate that ground water contributed approximately 390 000 m 3 /year, equivalent to a 990 mm rise in lake stage.…”

“…The advective-diffusive equations described in Berner (1980) show that uniform concentrations with depth are indicative of a system dominated by diffusive transport and the slope of the profile is related to the degree of diffusivity. However, as noted by Cornett et al (1989), a uniform profile with depth should occur where water is flowing out of the lake through the sediments; hence, at steady state the sediment profile cannot be used to recognize whether diffusive or advective processes are occurring. This profile is consistent with water-table gradients measured in wells in this part of the lake shore (Rosenberry, 1985), indicating it is an area of outflow.…”

“…The use of stable isotope profiles to estimate ground-water flow velocities has been suggested by others (Cornett et al, 1989). Here, the υ 2 H profiles of the littoral sediments of Williams Lake were used in an advection-diffusion model to calculate linear interstitial velocity (LIV).…”

Pathways of Acid Mine Drainage to Clear Lake: Implications for Mercury Cycling

“…It would be expected that a groundwater-lake system would have high discharge areas near the shoreline dominated by the advective transport of solutes, but that there would be a transition to diffusive transport of solutes where little or no groundwater is discharged (Cornett et al 1989). The shapes of the boron, sulfate, and iron profiles (Figs.…”

Use of a high‐resolution pore‐water gel profiler to measure groundwater fluxes at an underwater saline seepage site in Lake Kinneret, Israel

“…The flux of saline water from seepage into a lake can be estimated from detailed pore-water chemical profiles using an advection-diffusion model (Munk 1966;Berner 1972;Lee et al 1980;Cornett et al 1989). A requirement of such studies is that it is possible to determine a pore-water profile of sufficient resolution to resolve different solutions of the model.…”