Bacteria in deep coastal plain sediments of Maryland: A possible source of CO₂ to groundwater

Abstract

Nineteen cores of unconsolidated Coastal Plain sediments obtained from depths of 14 to 182 m below land surface near Waldorf, Maryland, were collected and examined for metabolically active bacteria. The age of the sediments cored range from Miocene to Early Cretaceous. Acridine orange direct counts of total (viable and nonviable) bacteria in core subsamples ranged from 108 to 104 bacteria/g of dry sediment. Direct counts of viable bacteria ranged from 106 to 103 bacteria/g of dry sediment. Three cores contained viable methanogenic bacteria, and seven cores contained viable sulfate‐reducing bacteria. The observed presence of bacteria in these sediments suggest that heterotrophic bacterial metabolism, with lignitic organic material as the primary substrate, is a plausible source of CO2 to groundwater. However, the possibility that abiotic processes also produce CO2 cannot be ruled out. Estimated rates of CO2 production in the noncalcareous Magothy/Upper Patapsco and Lower Patapsco aquifers based on mass balance of dissolved inorganic carbon, groundwater flow rates, and flow path segment lengths are in the range 10−3 to 10−5 mmol L−1 yr−1. Isotope balance calculations suggest that aquifer‐generated CO2 is much heavier isotopically (∼—10 to + 5 per mil) than lignite (∼−24 per mil) present in these sediments. This may reflect isotopic fractionation during methanogenesis and possibly other bacterially mediated processes.

Microbial activities in deep subsurface environments

“…Although previous subsurface studies have reported the presence of microorganisms, it was only recently suggested that microorganisms may alter groundwater chemistry (Chapelle et al, 1987). Harvey et al (1987) demonstrated that microorganisms could be transported through subsurface materials, thus providing a source for inocula.…”

“…A major obstacle was overcome when sampling techniques were developed which allowed aseptic recovery of sediments (Wilson et al, 1983). Recent studies incorporating these techniques have established that aquifers and subsurface sediments contain substantial microbial populations (Wilson et al, 1983;White et al, 1983;Ghiorse and Balkwill, 1983;Chapelle et al, 1987;Fliermans, et al, in press). …”

“…have suggested that subsurface microorganisms may impact groundwater quality through the production of carbon dioxide. Chapelle et al, (1987) Microbiology of groundwaters and subsurface sediments have received increased attention due to severe groundwater contamination and impending loss of substantial portions of our subsurface potable water resources (Pye and Patrick, 1983;Westerick et al, 1984). Predominant contaminants include short-chained halogenated hydrocarbons associated with defense, dry cleaning and metal finishing industries.…”

Incorporation of CO2 and introduced organic compounds by bacterial populations in groundwater from the deep crystalline bedrock of the Stripa mine

“…for acetogenic bacteria (Fuchs, 1986;Wood & Ljungdahl, 1991), methanogenic bacteria Belyaev & Ivanov, 1983;Godsy, 1980) and several species of sulphate-reducing bacteria (SRB) (Fauque et al, 1991). Fermentative or respiratory utilization of geological deposits of organic material are other possible explanations as to why heterotrophic bacteria have been found in deep geological formations (Chapelle et al, 1987(Chapelle et al, , 1988Hicks & Fredrickson, 1989;Pedersen & Ekendahl, 1990).…”

Groundwater impacts on surface water quality and nutrient loads in lowland polder catchments: monitoring the greater Amsterdam area

“…The seepage of the alkalised groundwater increases the alkalinity of the surface water, which is indicated by the high correlation between groundwater and surface water HCO 3 , and with Ca in surface water (Table 1). Subsurface organic matter mineralisation by processes like sulfate reduction and methanogenesis (Chapelle et al, 1987;Griffioen et al, 2013) (Table 3, Reactions R5 and R6), is a probable major reason for enhanced surface water HCO 3 in polders with brackish groundwater, like the polders in the Zuider Zee margin and the upconing polders.…”