CARBON REMINERALIZATION IN A NORTH FLORIDA SWAMP FOREST - EFFECTS OF WATER-LEVEL ON THE PATHWAYS AND RATES OF SOIL ORGANIC-MATTER DECOMPOSITION

Water level controlled gas emissions from North Florida swamp forests. Under flooded conditions, CO2 and CH4 were the principle carbon gases trasported to the atmosphere by bubble ebullition and molecular diffu sion. The respective emission rates were for CO2, 29.3 +/- 16.4 (13% b y means of ebullition, 87% by means of diffusion, error is +/- 1 stand ard deviation throughout) and for CH4, 2.16 +/- 2.24 (45% by means of ebullition, 55% by means of diffusion) mol m-2 yr-1. Methane emissions were significantly attenuated by CH4 oxidation which occurred primari ly at the sediment-water interface. Forty-six +/- 22% (n=19) of the be lowground CH4 diffusing to this interface was oxidized before it could escape to the atmosphere. Under dry conditions, CO2 was the principle carbon gas released and atmospheric CH4 was consumed by microbes in t he soil. The respective rates were 101.2 +/- 26.80 and -0.015 +/- 0.00 5 mol m-2 yr-1. A carbon budget for the degradation of soil organic ma tter was developed for a swamp forest site under flooded and dry condi tions. Assuming that live root respiration accounted for 67% (value de termined in a swamp forest and is at the upper range of literature val ues) of the total CO2 emissions (given above), we calculate that under flooded conditions carbon remineralization proceeded at a total rate of 11.9 mol C m-2 yr-1. Forty-nine percent of the remineralization was by means of nonmethanogenic processes which produce CO2; the balance was by means of methanogenic processes, which produce both CH4 and CO2 . Under dry conditions, remineralization was dominated by aerobic proc esses at a rate of 33.7 mol C m-2 yr-1. Carbon inputs to the soil occu rred by aboveground and belowground production. Aboveground litter pro duction contributed 25.6 mol C m-2 yr-1. If belowground production con tributed an equal amount, then over the course of this study organic c arbon accumulated in the soils at rates of 39.3 and 17.5 mol C m-2 yr- 1 under flooded and dry conditions, respectively. If root respiration accounted for only 6% (lowest value in literature) of the total CO2 em issions, organic carbon would accumulate in the ,;oil at a rate of 21. 6 mol C m-2 d-1 under flooded conditions and be lost from the soil at a rate of 43.8 mol C m-2 d-1 under dry conditions.