SEASONALITY OF SULFATE REDUCTION AND PORE-WATER SOLUTES IN A MARINE FISH FARM SEDIMENT - THE IMPORTANCE OF TEMPERATURE AND SEDIMENTARY ORGANIC-MATTER

Sulfate reduction and pore water solutes related to sulfur cycling and anaerobic processes (short chain fatty acids (SCFA), SO42-, TCO2, NH4 + dissolved sulfides (Sigma H2S) and CH4) were examined during one yea r at a marine fish farm. Mineralization of fish farm waste products wa s rapid in this non-bioturbated, organic rich sediment. Stimulation of sulfate reduction rates (SRR) occurred primarily in the surface layer s where the organic matter was deposited. Acetate was the most importa nt (>99%) of the measured SCFA attaining high concentrations during su mmer months (up to 4.7 mM). The acetate profiles exhibited distinct se asonal cycles, where periods with high concentrations in the pore wate rs were found coincident with a high pool of particulate organic matte r in the surface sediments and a low activity of the sulfate reducing bacteria (early spring and late summer). Periods with low acetate pool s occurred when sulfate reduction rates were high in early summer and in winter were pools of particulate organic matter were decreasing. Me thane production was observed concurrent with sulfate reduction in the microbial active surface layers in late summer. Subsurface peaks of S O42-, TCO2, NH4+ and Sigma H2S were evident in July and August due to rapid mineralization in these surface layers, With decreasing autumn w ater temperatures mineralization rates declined and subsurface peaks o f these solutes disappeared. A strong relationship was found between p ore water TCO2 and NH4+. Ratios between TCO2 and NH4+ were low compare d to a control site, attaining minimum values in mid-summer. This indi cated rapid nitrogen mineralization of nitrogen rich labile substrates in the fish farm sediment during the entire season.