engleski

Flow velocity effect on leaf litter breakdown in tufa depositing system (Plitvice Lakes, Croatia)

Considerable amount of riparian leaf litter is annually supplied to a cascade lake system of Plitvice Lakes (Croatia). In order to examine leaf breakdown dynamics in different lotic conditions on tufa dams, a leaf bags experiment was carried out. Leaves of two species (non-woody butterbur, Petasites sp. and woody common beech, Fagus sylvatica L.) were immersed in four sites differing in current velocities (0.1 m/s - 1 m/s) and tufa deposition rates. Measurements of physico-chemical water characteristics showed stable oligotrophy. Bags were retrieved in monthly intervals during one year. Ash free dry mass loss was calculated, and the negative exponential decay model (Nt = N0e-kt) was used to determine breakdown rates (k). Beech leaf breakdown was nearly an order of magnitude slower than butterbur, with rates ranging from 0. 0020 to 0. 0088 day-1 while butterbur presented decaying rates from 0.0215 to 0. 0853 day-1. There was no significant difference in breakdown rates for both species at flow velocities of app. 0.1 m/s and 0.5 m/s. However, both beech and butterbur broke down significantly faster at flow velocity higher than 0.6 m/s and with high tufa deposition rate. Non-woody butterbur had also significantly different k values in two sites which can be attributed to environmental factors (tufa deposition and water chemistry), while beech leaves did not show significant difference on these sites. These results indicate that flow velocity higher than 0.6 m/s is a dominant breakdown factor for both species presumably due to physical fragmentation of leaves in synergy with high tufa deposition rate. In slower flow velocities (<0.6 m/s) physico-chemical properties of water and tufa deposition had a significant impact on breakdown, but only of fast decomposing leaves (butterbur).

Flow velocity; leaf litter; Croatia

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