Estimation of Nutrient Limitation of Bacterial Activity in Temperate Alkaline Fen Sediments from Cedar Bog

Author Institution: Dept of Biology, University of DaytonCedar Bog Nature Preserve, located near Urbana, OH, encompasses several wetland types including an alkaline fen. In this fen, groundwater emerges in quicksand-like discharge zones consisting of porous Ca/Mg carbonates mixed with organic detritus. This study evaluates seasonal changes in the heterotrophic sediment microbial communities, their response to nutrient amendment, and in the groundwater chemistry from a fen discharge zone at Cedar Bog. The hypothesis that the microbial community in this fen upwelling is nutrient limited throughout the year, particularly by C and P, was tested. The activity of the heterotrophic bacterial community in the sediment compartment was measured. A series of single factor experiments were conducted to study organic and inorganic nutrient regulation of these communities and to determine what nutrients, if any, were limiting. Activities were based on 3H-thymidine incorporation into DNA by control and nutrient amended sediment slurries and verified with 14C-leucine incorporation into protein. Bacterial cell abundance was determined using Acridine Orange direct counts. Samples amended with carbon showed significant increases in activity in three of four seasons tested. Bog extract also stimulated activity above that of the control for the winter microcosm. The site bacterial activity also appears to be limited by inorganic nitrogen and possibly phosphorus in summer