To assess the effect of water depth on the decomposition process, I measured the losses in dry mass of the above- and belowground materials of Carex utriculata and Nuphar luteum ssp. polysepalum as well as cellulose (Whatman filter paper) in the top 10 cm of sediment/soil in a subalpine marsh. Samples were examined by the litter bag technique at three flooding levels (0 to 5, 60, and 100 cm water depth). Over a 374-d period, the % mass losses of cellulose, Carex leaves and roots, and Nuphar leaves and rhizomes ranged from 98.5 to 99.0, 74.8 to 81.8, 36.3 to 44.9, 95.8 to 97.7, and 78.4 to 91.5%, respectively, Rates for cellulose decay in this study were much higher than for samples from other wetlands; this difference resulted from the location of the litter bag (in the top 10 cm of soil vs in the water column). Water depth significantly affected the decomposition of Carex roots and Nuphar rhizomes. The rate of loss for K was highest in all tissues of Carex and Nuphar, followed by Na in Carex and P in Nuphar. N and Ca loss rates generally were low. The C/N ratio tended to converge to a common value over the long term. This convergence has an important implication in the paleoecological interpretation of the C/N ratio change in sediment ; i.e., this ratio shift in the sediment tore results from a change in the environment, rather than the source material.