To assess how eutrophication affects leaf-litter decomposition and the associated biota
in streams, we examined i) the structure of invertebrate and fungal communities and ii)
leaf mass loss of different plant species. Leaves of alder, chestnut, eucalyptus, plane tree
and oak were placed in coarse-mesh bags and immersed in 6 low-order streams along an
eutrophication gradient during 38 days. Additional benthic invertebrate samples were
collected with a hand-net. The values of the IBMWP biotic index applied to benthic
invertebrates increased from low to intermediate levels of eutrophication and then
dropped sharply at high and very high levels of eutrophication. Cluster analysis applied
to leaf-associated invertebrate and fungal communities separated the streams according
to the eutrophication level. The % of shredders on leaves decreased, whereas the % of
oligochaetes increased along the eutrophication gradient. Invertebrate biomass and
density, as well as fungal biomass and reproduction increased along the eutrophication
gradient, but decreased in the most eutrophic stream. Alder leaves decomposed faster
than other leaf species. A hump-shaped relationship was established between leaf mass
loss and the eutrophication gradient for all leaf species, suggesting that leaf
decomposition is a valuable tool to assess changes in stream water quality. Results
suggested that both structural and functional measures of invertebrate and fungal
communities are good predictors of stream eutrophication when assessing the ecological
integrity of streams.FEDER-POFC-COMPETE and FCT supported this study (PEst-C/BIA/UI4050/2011
and PTDC/AAC-AMB/117068/2010) and IF (SFRH/BD/42215/2007)Fundação para a Ciência e a Tecnologia (FCT) - PEst-C/BIA/UI4050/2011, PTDC/AAC-AMB/117068/2010, SFRH/BD/42215/200
