Heterotrophic microbial activity in shallow aquifer sediments of Long Island, New York

Abstract

Bacterial numbers and activities (as estimated by glucose uptake and total thymidine incorporation) were investigated at two sites in Long Island, New York aquifer sediments. In general, bacterial activities were higher in shallow (1.5–4.5 m below the water table or BWT), oxic sediments than in deep (10–18 m BWT), anoxic sediments. The average total glucose uptake rates were 0.18 ± 0.10 ng gdw⁻¹ h⁻¹ in shallow sediments and 0.09 ± 0.11 ng gdw⁻¹ h⁻¹ in deep sediments; total thymidine incorporation rates were 0.10 ± 0.13 pmol gdw⁻¹ h⁻¹ and 0.03 ± 0.03 pmol gdw⁻¹ h⁻¹ in shallow and deep sediments, respectively. Incorporation of glucose was highly efficient, as only about 10% of added label was recovered as CO₂. Bacterial abundance (estimated from acridine orange direct counts) was 2.5 ± 2.0 × 10⁷ cells gdw⁻¹ and 2.0 ± 1.3 × 10⁷ cells gdw⁻¹ in shallow and deep sediments, respectively. These bacterial activity and abundance estimates are similar to values found in other aquifer environments, but are 10- to 1000-fold lower than values in soil or surface sediment of marine and estuarine systems. In general, cell specific microbial activities were lower in sites from Connetquot Park, a relatively pristine site, when compared to activities found in sites from Jamesport, which has had a history of aldicarb (a pesticide) contamination. To our knowledge, this is the first report of bacterial activity measurements in the shallow, sandy aquifers of Long Island, New York.