Search

Upper reaches of temperate streams and oligotrophic lakes depend trophically on the organic matter coming from the surrounding watershed. These aquatic ecosystems accumulate particulate and dissolved organic matter, and chemical compounds liberated from decomposing leaves or from the leachates of leaf litter. These materials supply a wide range of chemical compounds, which may serve as food, but also cause ecotoxicological effects on aquatic organisms. However, this ecotoxicological risk has been amply ignored, especially for freshwater invertebrates. The aims of our study are: (1) to assess the direct toxicity of aqueous extracts of leaf litter from two native (Populus alba, Fraxinus angustifolia) and two tree species exotic to Europe (Robinia pseudoacacia, Ailanthus altissima) on a pelagic and a benthic species of model aquatic invertebrates: Daphnia magna (Cladocera) and Potamopyrgus antipodarum (Mollusca) and (2) to estimate the ecotoxicological risk of the leaf litter extracts to lacustrine ecosystems using different simulated scenarios of shallow lakes. For both invertebrate species, we assessed the effective concentration of leaf extract causing an effect on 50% of the population (EC50) by means of laboratory bioassays. Our results show that the extracts of leaf litter from all the tested trees have a potential ecotoxicological risk in some scenarios, which is independent from the geographic origin of the tree species. [ABSTRACT FROM AUTHOR]

Aims: To assess the impacts of Ailanthus altissima and Robinia pseudoacacia on the whole litterfall process and on soil properties of riparian ecosystems of Central Spain by comparing invaded and non-invaded forests. Methods: We selected 3-4 plots of four different types of forests: invaded by A. altissima or R. pseudoacacia, or dominated by the native Fraxinus angustifolia or Populus alba. In each plot we collected the litter monthly over 2 years and separated the litter from different plant organs. We calculated annual inputs of litter, nitrogen (N) and phosphorus (P) to soil. We also analyzed soil pH, organic matter (OM), N and P. Results: Most litter fractions from the two invasive trees contained over twice as much N as those from the native P. alba. Although not significantly different, the annual inputs of N in invaded forests were 1.7-2.2 times higher than in native forests. In the invaded forests, extra litterfall peaks were found in summer and/or late-spring (June), corresponding to reproductive and/or leaf litter fractions. The percentage of annual litter represented by these peaks was over twice those in native forests. Soil OM, N and P were higher in invaded than in P. alba forests. In addition, forests invaded by R. pseudoacacia had higher soil OM and N than F. angustifolia forests. Conclusions: This study showed the capability of A. altissima and R. pseudoacacia to alter soil properties and litterfall dynamics in riparian ecosystems. [ABSTRACT FROM AUTHOR]