HETEROTROPHIC MICROBIAL ACTIVITY IN SHALLOW AQUIFER SEDIMENTS OF LONG-ISLAND, NEW-YORK

Bacterial numbers and activities (as estimated by glucose uptake and t otal thymidine incorporation) were investigated at two sites in Long I sland, New York aquifer sediments. In general, bacterial activities we re higher in shallow (1.5-4.5 m below the water table or BWT), oxic se diments than in deep (10-18 m BWT), anoxic sediments. The average tota l 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) an d 0.03 +/- 0.03 pmol gdw(-1) h(-1) in shallow and deep sediments, resp ectively. Incorporation of glucose was highly efficient, as only about 10% of added label was recovered as CO,. Bacterial abundance (estimat ed from acridine orange direct counts) was 2.5 +/- 2.0 x 10(7) cells g dw(-1) and 2.0 +/- 1.3 x 10(7) cells gdw(-1) in shallow and deep sedim ents, respectively. These bacterial activity and abundance estimates a re similar to values found in other aquifer environments, but are 10- to 1000-fold lower than values in soil or surface sediment of marine a nd estuarine systems. In general, cell specific microbial activities w ere lower in sites from Connetquot Park, a relatively pristine site, w hen compared to activities found in sites from Jamesport, which has ha d a history of aldicarb (a pesticide) contamination. To our knowledge, this is the first report of bacterial activity measurements in the sh allow, sandy aquifers of Long Island, New York.