Leaf litter decomposition on insular lentic systems: effects of macroinvertebrate presence, leaf species, and environmental conditions

Abstract

The decomposition of leaf litter of terrestrial origin is a fundamental process in aquatic ecosystems in forest contexts. Little is known about what drives leaf litter decomposition in oceanic islands. We examined the relative importance of leaf litter identity (Acacia melanoxylon, Pittosporum undulatum, Morella faya) and environmental conditions on litter decomposition in seven lakes in the oceanic archipelago of Azores for 28 and 56 days. Leaf litter was incubated in coarse and fine mesh bags for the assessment of the relative contribution of macroinvertebrates to leaf litter decomposition. Leaf litter mass loss generally did not differ between mesh sizes, suggesting that in these lakes macroinvertebrates generally have a negligible role on leaf decomposition. Leaf litter decomposition was in the order M. faya < A. melanoxylon < P. undulatum. A negative correlation was found between leaf litter mass loss and lignin concentration. Mass loss of P. undulatum was related to lake elevation and chlorophyll a (taken as surrogates for water temperature and dissolved nutrient availability, respectively), whereas mass loss of M. faya was related to chlorophyll a on day 56. These results suggest that changes in the composition of the leaf litter input and environmental conditions can affect leaf litter decomposition in Azorean lakes, with potential consequences for nutrient cycling.