Transport of calcium, magnesium and SO 4 in the Floridan aquifer, west-central Florida: implications to cementation rates

Abstract

Prior hydrogeochemical studies have documented a down-gradient increase in dissolved calcium, magnesium and SO 4 in the confined, upper Floridan aquifer and have attributed the changes to dissolution of gypsum and dolomite and precipitation of calcite. In this study, hydrochemical data (mol l −1) are coupled with calculated discharges (1 year −1) to calculate the down-gradient changes in ion fluxes (mol year −1) along two predevelopment stream tubes in west-central Florida. Evaluation of ion inflows (including leakage from above) and outflows to and from well-to-well sectors of the stream tubes enables isolation of the changes in ion fluxes due to the previously identified reactions and, hence, quantification of the geological work done by those reactions in the sectors. Over about half of the stream tubes, the amount of calcite precipitation is small to non-existent (0 ±0.25% of the bulk volume per million years), which is consistent with geological evidence. Significant cementation rates are calculated for areas influenced by upward flow, such as at the end of the stream tubes and along the Peace River. Half of these significantly large values are impossibly large, apparently reflecting an inherited signal from a flow history below the depth of the upper Floridan wells. Similarly, mass-balance results that suggest significant dissolution of dolomite and gypsum probably reflect upwelling, not diagenesis at the depths of the sampled wells.