Hydrochemistry of a dolomite karst: the Bruce Peninsula of Ontario

Abstract

Surface and subsurface waters on the Bruce Peninsula, Ontario, were sampled and analysed for Ca2+, Mg2+, pH, HCO3−; partial pressure of CO2(PCO2), and saturation states with respect to calcite (SIc) and dolomite (SId) were calculated. A total of 250 samples representing six hydrochemical environments were collected. These environments are (1) Georgian Bay and Lake Huron, (2) inland lakes, (3) rivers and streams, (4) wetlands, (5) conduit-flow springs, and (6) diffuse-flow springs. The seasonal behaviour and chemical separation of these waters are examined.Except for Georgian Bay and Lake Huron the waters of the peninsula are very hard, ranging from 180–320 ppm Ca2+ plus Mg2+ (as CaCO3), and display increasing hardness as the summer season progresses. Surface recharge and conduit-flow springs are generally saturated with respect to calcite and dolomite. Only diffuse-flow springs, which are among the hardest of waters, are commonly undersaturated. These waters are also the easiest to distinguish chemically and results of a linear discriminant function analysis suggest other waters of the peninsula to be of one class.

Controls on the spatial and temporal variability of vadose dripwater geochemistry: Edwards aquifer, central Texas

“…Similarly, important controls on Mg/Ca ratios have since been demonstrated in carbonate groundwater systems with much shorter residence times (Langmuir, 1971;Cowell and Ford, 1980;Trudgill et al, 1980;Fairchild and Killawee, 1995;Fairchild et al, 1996). Proposed mechanisms for observed increases in groundwater Mg/Ca ratios with increasing residence time include progressive waterrock interaction processes such as the incongruent dissolution of dolomite, and calcite recrystallization (Wigley, 1973;Plummer, 1977;Lohmann, 1988).…”

Seasonal trace-element and stable-isotope variations in a Chinese speleothem: The potential for high-resolution paleomonsoon reconstruction

“…We have performed an ultra-high-resolution study of the stable-isotope (δ 18 O and δ 13 C) and traceelement (Mg/Ca, Sr/Ca, Ba/Ca, U/Ca) composition across 16 annual growth bands to investigate the nature of these geochemical cycles. Based on the comparison of the observed annual cycles with modern calcite, drip water, climatic data, and a simple model, we suggest that annual trace-element (Mg/Ca, Sr/Ca, Ba/Ca, and U/Ca) and stable-isotope (δ 13 C and δ 18 O) cycles record past hydrologic changes which directly reflect past variations in summer monsoon rainfall.…”

“…Four possible mechanisms have been proposed to explain annual Mg cycles in cave drip waters [6]: (1) Calcite dissolves at a faster rate than dolomite [13,14], therefore, increased residence time during drier periods may allow for more dissolution of dolomite, leading to higher Mg/Ca ratios in cave drip waters. (2) Prior calcite precipitation due to CO 2 degassing in the epikarst or on the roof of caves will lead to an increase in Mg/Ca of cave drip waters, because D Mg ≪ 1 [15].…”

Millennial-scale variations in western Sierra Nevada precipitation during the last glacial cycle MIS 4/3 transition

“…2010). Slower weathering of dolomite than calcite has been documented within karst systems in the field (Cowell and Ford, 1980;Atkinson, 1983) and experimentally (Chou et al, 1989). Seepage waters tend to reach supersaturation with respect to calcite before they reach dolomite saturation (Roberts et al, 1998), and changes in seepage-water flow rate can cause variations in the amount of dolomite dissolved and seepage-water Mg-content (Fairchild et al, 2000;Hellstrom and McCulloch, 2000).…”