Chemical Evolution of Groundwater Near a Sinkhole Lake, Northern Florida: 2. Chemical Patterns, Mass Transfer Modeling, and Rates of Mass Transfer Reactions

Abstract

Chemical patterns along evolutionary groundwater flow paths in silicate and carbonate aquifers were interpreted using solute tracers, carbon and sulfur isotopes, and mass balance reaction modeling for a complex hydrologic system involving groundwater inflow to and outflow from a sinkhole lake in northern Florida. Rates of dominant reactions along defined flow paths were estimated from modeled mass transfer and ages obtained from CFC-modeled recharge dates. Groundwater upgradient from Lake Barco remains oxic as it moves downward, reacting with silicate minerals in a system open to carbon dioxide (CO2), producing only small increases in dissolved species. Beneath and downgradient of Lake Barco the oxic groundwater mixes with lake water leakage in a highly reducing, silicate-carbonate mineral environment. A mixing model, developed for anoxic groundwater downgradient from the lake, accounted for the observed chemical and isotopic composition by combining different proportions of lake water leakage and infiltrating meteoric water. The evolution of major ion chemistry and the •3C isotopic composition of dissolved carbon species in groundwater downgradient from the lake can be explained by the aerobic oxidation of organic matter in the lake, anaerobic microbial oxidation of organic carbon, and incongruent dissolution of smectite minerals to kaolinite. The dominant process for the generation of methane was by the CO2 reduction pathway based on the isotopic composition of hydrogen (•2H(CH4) = -186 to -234%0) and carbon (•13C(CH4) ---65.7 to -72.3%0). Rates of microbial metabolism of organic matter, estimated from the mass transfer reaction models, ranged from 0.0047 to 0.039 mmol L -• yr -• for groundwater downgradient from the lake. 1565 1566 KATZ ET AL.: CHEMICAL EVOLUTION OF GROUNDWATER, 2 adequately tested for sensitivity to uncertainties in hydrochemical data because of the lack of information on environmental isotopes and mineralogy of aquifer material. Furthermore, rates of chemical evolution were not determined because flow paths were poorly defined, the age of groundwater was not estimated, and sources of water were not identified.The Lake Barco study area represents an ideal site to study the hydrochemical interaction between groundwater and lake water leakage and recharge to the UFA. Groundwater flow paths and gradients are relatively stable in the overlying surficial aquifei' and intermediate confining unit [Sacks et al., 1992; Katz et al., this issue]. Recharge to the UFA in this area is representative of hydrologic conditions along upland, highlands, and ridge areas of peninsular Florida [Aucott, 1988].Furthermore, this dilute groundwater system is typical of many poorly confined shallow aquifers whose principal source of recharge is rainfall that reacts with minerals in overlying unconsolidated silicate aquifers [Fritz and Fontes, 1980, 1986]. Groundwater that contains low concentrations of dissolved minerals represents a challenge in assessing material transfer because the concentrations of major ions and ...

Sulfur in the South Florida Ecosystem: Distribution, Sources, Biogeochemistry, Impacts, and Management for Restoration

“…Rainwater from the northern Everglades has sulfate concentrations ranging from <1 to 2.5 mg l −1 (Bates et al, 2002;McCormick and Harvey, 2011), and rainwater from ENP has an annual volume-weighted mean of 0.5-0.7 mg l −1 sulfate (National Atmospheric Deposition Program, 2008). Also, sulfate in rainfall has sulfur isotopic (δ 34 S) compositions of +2 to +6 compared to +15 to +23 for sulfate in canal water (Bates et al, 2002;Katz et al, 1995). Rainwater may be an important source of sulfate to unenriched areas, but cannot account for the high sulfate levels in canals or sulfate-enriched marshes ( Figure 4).…”

Using groundwater age and hydrochemistry to understand sources and dynamics of nutrient contamination through the catchment into Lake Rotorua, New Zealand

“…Water age provides important information on vulnerability to contamination and can therefore be used to assess the security of drinking water supplies, particularly from groundwater bores Morris et al, 2005;New Zealand Ministry of Health, 2008). Water age measurements can also be used to quantify rates of hydrochemical evolution resulting from water-rock interaction (Katz et al, 1995;Burns et al, 2003;Glynn and Plummer, 2005;Daughney et al, 2010;Beyer et al, 2014). These applications of water dating cover the spectrum from applied water resource management to fundamental scientific research.…”

Frontiers of Karst Research: Proceedings and recommendations of the workshop held in San Antonio, Texas on 3-5 May 2007. Karst Waters Institute Special Publication 13

“…The vulnerability of karst aquifers to contamination is exacerbated by recharge of surface water into underlying aquifers (Katz et al, 1995). These processes can result in groundwaterquality problems, such as high concentrations of iron and hydrogen sulfide, and undesirable bacteria, protozoa, and fungi (Krause, 1979;McConnell and Hacke, 1993;Katz et al, 1995;Plummer et al, 1998).…”

“…These processes can result in groundwaterquality problems, such as high concentrations of iron and hydrogen sulfide, and undesirable bacteria, protozoa, and fungi (Krause, 1979;McConnell and Hacke, 1993;Katz et al, 1995;Plummer et al, 1998). The combined use of various geochemical tracers, including radiogenic and stable isotopes, tannic acid, chloride, and silica have been effective in calculating the proportion of river water that mixed with groundwater (Katz et al, , 1998.…”