Effect of vegetation on alpha cellulose decomposition in littoral lake sediments

The effect of vegetation cover on the decomposition of organic matter (alpha cellulose) was studied at three sediment depths (5, 15 and 25 cm) in the littoral area of a small Lake Kiruvere (Estonia). The experiment was carried out in two adjacent sites, with and without vegetation, using the litter bag method. At all sediment depths decomposition was faster at the site covered with vegetation, and was highest at 5 cm sediment depth (decomposition rate k = 0.0037 day−1) and lower at 15 and 25 cm depths (k = 0.0014 day−1 and k = 0.0013 day−1). Higher decomposition rates coincided with higher root mass in the sediment. Decomposition rates were similar at all sediment depths in the site without a vegetation cover (k = 0.0007–0.0009 day−1). The presence of a vegetation cover also affected temperatures in sediments. Temperatures were several degrees higher at all sediment depths in the area with vegetation cover, than in the area without. Mean sediment temperature differences between the two experiment areas were 1.4 °C at 5 cm sediment depth, 2.5 °C at 15 cm depth and 3.1 °C at 25 cm depth. Higher decomposition rates in the site covered with vegetation can be explained by oxygen dispersion from young roots in the higher sediment layers and by higher sediment temperatures due to the internal gas flow enhancing the microbial activity in the lower sediment layers.