DEPOSITION, RESUSPENSION, AND DECOMPOSITION OF PARTICULATE ORGANIC-MATTER IN THE SEDIMENTS OF LAKE ITASCA, MINNESOTA, USA

Sediment traps were used to investigate the settling, resuspension, an d decomposition of particulate organic matter in Lake Itasca, MN (USA) . Traps were deployed in the epilimnion and hypolimnion of the deepest basin during June, 1988, sampled twice during stratified conditions ( August, September) and once after the lake had mixed (October). The do wnward flux of particulate material increased from summer to fall. The net sedimentation of organic matter ranged from 0.6 to 2.3 g m-2 d-1 at 4 m and increased to 2.1 to 3.2 g m-2 d-1 two meters above the bott om sediment indicating that resuspended sediment was at least 33% of t he settling mass during all periods. The C:N ratios of captured partic les (6.8-9.5) were between the ratios of plankton (5.8 to 6.8) and the sediments (9.9 to 10.2) but smaller than the ratios of terrestrial or ganic materials (13.5 to 222). The monosaccharide compositions of the entrapped particles were similar to plankton samples and different fro m the distinct composition of the sediments. Capture of rebound partic les similar to the primary flux and not decomposition may have been re sponsible for this similarity. Total monosaccharide concentrations wer e lower in the sediments than in entrapped particles. Individual sugar s exhibited different patterns of accumulation in the sediments. Gluco se was lowest in sediments when the relative concentrations were compa red to those in source materials and entrapped particles. In contrast, sediments had,the highest rhamnose and fucose concentrations. Bacteri al biomass could only account for small portions of these sugars in th e sediment. The distinct monosaccharide composition of resuspended sed iments was not strongly recorded in materials captured by the sediment traps even after the lake had mixed.