Nature and Rates of Bacterial Metabolism in the Aquifers of SoutheasternLouisiana

摘要

High Na-HCO3 water in the stacked sand and clay aquifer system of SoutheasternLouisiana was found to be caused by a combination of baterial oxidation of organic matter, ion exchange, and calcite dissolution. Dissolution of feldspar had little impact on water chemistry. Na and alkalinity are highly correlated as a result of calcite dissolution and subsequent exchange by clays of 2 Na ions for each Ca ion. Na content is a good indicator of the amount of calcite dissolved. The contribution to the carbon budget by bacterially-mediated organic degradation is substantial and coequal to the contribution by calcite dissolution. Microbial activity is dominated by aerobic bacteria, and there is little or no contribution by either sulfate-reducers or methanogens. Bacterial activity is concentrated within the deeper aquifers, and is much less important in the shallow and intermediate sands. The average rate of CO2 production is estimated to be .0054 mmol/L/yr, while in high CO2 productivity areas, rates are more than ten times greater (.064 mmol/L/yr).