PARENT SESSION
Poster Session 3: Aquatic Ecology
Monday, August 8, 5:00 PM - 6:30 PM, Exhibit Hall 210 D, Level 2, Palais des congrès de Montréal
Influence of organic-matter standing stock on leaf-litter decomposition in streams.
Tiegs, Scott*,1, Robinson, Chris2, Peter, Fabian1, Uehlinger, Urs2, Gessner, Mark1, 1 Department of Limnology, Kastanienbaum, Switzerland2 Department of Limnology, Duebendorf, Switzerland
ABSTRACT- Autumn-shed leaves are a vital component of stream ecosystems in forested watersheds and differences in rates of leaf input and retention yield in-stream standing stocks of organic matter that are highly variable at local scales. We tested if organic matter availability influenced the key ecosystem-level process of leaf decomposition. Specifically, we suspected that greater amounts of local organic matter 1) slow decomposition by detritivorous macroinvertebrates because animals disperse among a larger number of resource units and 2) increase microbial decomposition since larger amounts of litter increase inoculum potential. We tested these hypotheses with a randomized block design in three streams of the Black Forest (Germany). In each stream we identified three morphologically similar reaches and randomly assigned each a treatment that consisted of 1) an enhanced standing stock of organic matter via the installation of leaf litter traps, 2) a manually depleted standing stock of organic matter or 3) a control that was not manipulated. We quantified decomposition with a leaf-bag approach that utilized coarse- and fine-mesh bags intended to either allow or deter access by macroinvertebrates. As anticipated, standing stocks of organic matter responded significantly to the treatments. Decomposition was significantly faster in coarse-mesh bags than in fine mesh. Contrary to expectations, decomposition rates did not differ between treatments, nor did the number of detritivorous invertebrates that colonized experimental leaf packs. These results suggest that local variability in organic-matter standing stocks does not, in the short-term, alter either microbial or invertebrate decomposition as components of stream ecosystem functioning.
Key words: leaf decomposition, stream functioning, litter retention