CARBON AND NITROGEN STABLE-ISOTOPE FRACTIONATION IN THE SEDIMENT OF LAKE-BLED (SLOVENIA)

Stable isotope composition of carbon and nitrogen in the sediment and pore water of a eutrophic freshwater lake was studied. Based on change s in the delta(13)C and delta(15)N values of dissolved components and sediment fraction, possible processes involved in the decomposition of sedimentary organic matter are outlined. The relative importance of a cetate fermentation and CO2 reduction was estimated using known mathem atical models, and ammonia assimilation by methanogenic bacteria is hy pothesised to be the main process governing the isotope fractionation of dissolved nitrogen in pore water.