ORGANIC-MATTER MINERALIZATION IN AN ORGANIC-RICH SEDIMENT - EXPERIMENTAL STIMULATION OF SULFATE REDUCTION BY FISH FOOD PELLETS

The combined effects of organic matter additions and temperature on sh ort chain fatty acid (SCFA) turnover, sulfate reduction and nutrient a ccumulation were examined in an organic-rich fish farm sediment. Fish food pellets, which contribute significantly to the organic matter los s from fish farms, were added to surface sediment at three loadings (2 .8; 14.0; 28.0 mg ww g(-1) ww sediment; equivalent to organic matter l oadings measured during fish farming) and incubated for 30 days in ana erobic bags at 5 degrees C and 15 degrees C. SCFA accumulated to high levels (acetate up to 85 mM, propionate up to 17 mM, butyrate up to 25 mM) in sediments amended with food pellets, and sulfate reduction was stimulated up to 30 times relative to unamended sediments. Sulfate re ducers appeared saturated with substrates (SCFA) even in the lowest ad ditions. A low C/N ratio (0.4-1.8) of the major mineralization product s (TCO2 and NH4+) indicated preferential nitrogen mineralization in am ended sediment compared with the total particulate pool (C/N = 8.8-11. 9) and added food pellets (C/N = 8.4).