Effect of organic contamination upon microbial distributions and heterotrophic uptake in a Cape Cod, Mass., aquifer

Abstract

Bacterial abundance, distribution, and heterotrophic uptake in a freshwater aquifer contaminated by treated sewage were determined from analyses of groundwater and sediment-core samples. The number of free-living (unattached) bacteria in contaminated groundwater declined steadily with increasing distance from the source of sewage infiltration, from 1.94 (±0.20) x 106 ml-' at 0.21 km to 0.25 (±0.02) x 106 ml-' at 0.97 km. Bacterial abundance in groundwater sampled at 0.31 km correlated strongly with specific conductance and increased sharply from 4.0 (±0.3) x 104 ml-' at a depth of 6 m to 1.58 (±0.12) x 0l m-1 at 14 m, then declined at 20 and 31 m to 1.29 (+0.12) x 106 and 0.96 (±0.12) x 106 ml-', respectively. A majority of the bacteria in contaminated and uncontaminated zones of the aquifer were bound to the surfaces of particulates, <60 ,um in diameter. The glucose uptake rate, assayed at in situ and 5 ,uM concentrations, declined steadily in contaminated groundwater sampled along a transect. A preparative wet-sieving technique for use in processing core samples for bacterial enumeration is described and evaluated.

Microbial biodiversity in groundwater ecosystems

“…The ratio of suspended to attached microbes in aquifers depends largely on the availability of DOC and nutrients, the sediment grain-size distribution, and the mineralogy of the sediments (Bengtsson, 1989;Kölbel-Boelke & Hirsch, 1989;Griebler, Mindl & Slezak, 2001;Lehman et al, 2001). This ratio may span several orders of magnitude from 0.2 (Wolters & Schwartz, 1956;Harvey, Smith & George, 1984) to 10 )4 (Alfreider et al, 1997;Griebler et al, 2002). Only a handful of studies have addressed the difference in microbial diversity of suspended versus attached communities, although early works based on physiological and morphological characterisation of isolates already reported significant differences (Wilson et al, 1983;Kö lbel-Boelke & Hirsch, 1989;Hazen et al, 1991;Hirsch, 1992a;Kö lbel-Boelke & Nehrkorn, 1992).…”

Spatiotemporal distribution of microbial communities in a coastal, sandy aquifer system (Doñana, SW Spain)

“…This is not surprising because, although the presence of algae, protozoa and fungi could be important in some aquifer ecosystems, prokaryotes represent, by far, the most abundant and diverse microbial group in aquifers, at least in the phreatic zone (Balkwill, 1989;Sinclair & Ghiorse, 1989;Whitman et al, 1998). Short rod-shaped bacteria have some advantages over large rod-shaped and filamentous bacteria for transport through sandy sediments (Harvey et al, 1984). Data in this study confirm previous ones (Velasco et al, 2008;in press) and demonstrate that mean bacterial abundance observed in this aquifer system was, at least, one order of magnitude higher than that found in other sedimentary and relatively similar aquifer ecosystems (Harvey et al, 1984;Kölbel-Boelke et al, 1988;Marxsen, 1988;Hirsch & Rades-Rohkohl, 1990;Hazen et al, 1991;Alfreider et al, 1997;Griebler et al, 2002).…”

“…Short rod-shaped bacteria have some advantages over large rod-shaped and filamentous bacteria for transport through sandy sediments (Harvey et al, 1984). Data in this study confirm previous ones (Velasco et al, 2008;in press) and demonstrate that mean bacterial abundance observed in this aquifer system was, at least, one order of magnitude higher than that found in other sedimentary and relatively similar aquifer ecosystems (Harvey et al, 1984;Kölbel-Boelke et al, 1988;Marxsen, 1988;Hirsch & Rades-Rohkohl, 1990;Hazen et al, 1991;Alfreider et al, 1997;Griebler et al, 2002). Groundwater mean bacterial abundance found in this study was also higher than planktonic bacterial densities found in granite (Eydal & Pedersen, 2007) or rock aquifer systems (Lehman et al, 2004).…”

Bacterial community and groundwater quality changes in an anaerobic aquifer during groundwater recharge with aerobic recycled water

“…Obtaining a representative sample for microbiological analysis from an aquifer is also challenging because of sample contamination by drilling muds and overlying sediments (Fredrickson et al, 1989). Also, groundwater samples alone may not represent subsurface microbial communities because 95% of the bacterial population is found attached to particle surfaces (Harvey et al, 1984). Aseptically sampling the center of an intact core has been suggested effective to gain access to a least contaminated subsurface sample for microbiological analysis (West et al, 1985).…”