Stability and meromixis in a water-filled mine pit

Stevens, C. L., G. A. Lawrence

Limnol. Oceanogr., 43(5), 1998, 946-954 | DOI: 10.4319/lo.1998.43.5.0946

ABSTRACT: A field experiment examined stability and stratification in a disused mine Fit filled with 1.75 X 107 m3 of water. Vertical profiles of conductivity and temperature indicated that, due to substantial chemical stratification, spring and autumn overturn did not penetrate to the base of the pit. Although parameterization indicated that double diffusion should be expected, we found only circumstantial evidence of associated step structure. The available data suggest that groundwater inflow created a warm salty pool of water at the base of the water column, giving the appearance of a meromictic structure with a monimolimnion. However, this pool was not a consistent feature, suggesting both a variable inflow and significant diffusion rates. From the temperature data, estimates indicated that hypolimnetic vertical eddy diffusivity varied between 1 X 10-7 and 5 X 10-5 m2 s-l. The observations identify short-term relatively energetic internal wave events that may have a significant impact on this value. The present study is useful in two ways: first, it shows how pit-lakes form a natural laboratory for a range of processes, and second, it illustrates how these processes relate to diffusion paranieterization. It is clear that reliable parameterization is vital for long-term modeling required for prediction of water quality over decadal timescales.

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