Jane M. Matty

Early Diagenesis of Mercury in the Laurentian Great Lakes

Abstract The early diagenesis of mercury in deep lake environments was investigated by examining the distribution of mercury among waters and sediments from several depositional basins in the Laurentian Great Lakes. Partitioning of mercury among different sediment phases was examined by sequential chemical extraction (using procedures specifically designed for mercury). Mercury in porewaters and sediment extracts was analyzed by flow-injection/hydride-generation atomic absorption spectroscopy. Results indicate that mercury is affected by early diagenesis at all of the sites studied. Much of the mercury is enriched in the surface layer of sediments, where it is primarily associated with organic matter and iron oxides. The redox cycling of iron and manganese influences the behavior of mercury; concentration profiles suggest that as oxides begin to dissolve in reduced sediments, nearly all of the adsorbed mercury is released. Organic matter decay also appears to release significant amounts of mercury. Porewater profiles suggest that most of the dissolved mercury released from decaying organic matter or from dissolving iron oxides may be taken up by freshly deposited organic matter and iron oxides in the near-surface layers. Much of the mercury that reaches the sediment column is thus recycled near the sediment-water interface, increasing both the residence time and the concentrations of mercury in surface sediments of these deep lake basins.

Effect of multiple precipitation inhibitors on calcium carbonate nucleation

Abstract Understanding the factors which affect the precipitation of calcium carbonate is important to the study of most natural waters. The effect of blends of precipitation inhibitors on calcium carbonate nucleation is investigated via a new test apparatus. Results indicate that the behavior of mixed inhibitors at minimum concentration levels is strictly additive, as predicted theoretically. The potential existence of a “super effective” inhibitor in nature or in industry is therefore precluded; this may have significant consequences for water-processing industries. The possibility of extending the upper limit of inhibitor effectiveness, imposed by the solubility of the calcium-inhibitor salts, through the use of mixed inhibitors is discussed. It is also possible that the notion of additive effects of mixed inhibitors may be valid in other systems, such as geochemical environments, potable water treatment systems, and industrial waters in which naturally occurring calcium carbonate inhibitors exist.

Ground-water, large-lake interactions in Saginaw Bay, Lake Huron: A geochemical and isotopic approach

Delineating the nature and extent of ground-water inputs is necessary to understand the hydrochemistry of large lakes. Characterizing the interaction between ground water and large lakes (e.g., the Great Lakes) is facilitated by the use of geochemical and isotopic data. In this study, pore waters were extracted from sediment cores collected from Saginaw Bay and the surrounding Saginaw lowland area; the geochemistry and stable isotope signature of these pore waters were used to identify sources for the water and solutes. Cores from Saginaw Bay and the Saginaw lowland area yielded strong vertical gradients in chloride concentrations, suggesting that a high-chloride source is present at depth. The spatial distribution of cores with elevated chloride concentrations corresponds to the regional distribution of chloride in ground water. Most of the Saginaw lowland area cores contain water with significantly lower δ 18 O values than modern meteoric water, suggesting that the water had been recharged during a much cooler climate. The δ 18 O values measured in pore waters (from Saginaw Bay cores) containing high chloride concentrations are similar to modern meteoric water; however, values lighter than modern meteoric water are encountered at depth. Chloride:bromide ratios, used to distinguish between different chloride sources, identify formation brine as the likely source for chloride. Transport models indicate that a combination of advection and diffusion is responsible for the observed Saginaw lowland area pore-water profiles. Pore-water profiles in Saginaw Bay sediments are produced primarily by diffusion and require significantly less time to evolve. An upward flux of solutes derived from formation brine could occur elsewhere within the Great Lakes region and significantly affect the geochemical cycling of chloride and other contaminants (e.g., trace metals).