Heterogeneity in leaf litter decomposition in a temporary Mediterranean stream during flow fragmentation

• Published in: The Science of the total environment 2016-05, Vol.553, p.330-339
• Main Authors: Abril, Meritxell, Muñoz, Isabel, Menéndez, Margarita
• Format: Article
• Language: English
• Subjects: Bacteria; Biodegradació; Biodegradation; Biodegradation, Environmental; Black poplar; DOC release; Drought; Ecologia fluvial; Ecosystem; Environmental Monitoring; Flow fragmentation; Fulles; Fungi; Habitat heterogeneity; Leaves; Microbial biomass; Nitrogen; Plant Leaves; Populus nigra; Rivers - microbiology; Seasons; Stream ecology; Water Movements
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2016.02.082

In temporary Mediterranean streams, flow fragmentation during summer droughts originates an ephemeral mosaic of terrestrial and aquatic habitat types. The heterogeneity of habitat types implies a particular ecosystem functioning in temporary streams that is still poorly understood. We assessed the initial phases of leaf litter decomposition in selected habitat types: running waters, isolated pools and moist and dry streambed sediments. We used coarse-mesh litter bags containing Populus nigra leaves to examine decomposition rates, microbial biomass, macroinvertebrate abundance and dissolved organic carbon (DOC) release rates in each habitat type over an 11-day period in late summer. We detected faster decomposition rates in aquatic (running waters and isolated pools) than in terrestrial habitats (moist and dry streambed sediments). Under aquatic conditions, decomposition was characterized by intense leaching and early microbial colonization, which swiftly started to decompose litter. Microbial colonization in isolated pools was primarily dominated by bacteria, whereas in running waters fungal biomass predominated. Under terrestrial conditions, leaves were most often affected by abiotic processes that resulted in small mass losses. We found a substantial decrease in DOC release rates in both aquatic habitats within the first days of the study, whereas DOC release rates remained relatively stable in the moist and dry sediments. This suggests that leaves play different roles as a DOC source during and after flow fragmentation. Overall, our results revealed that leaf decomposition is heterogeneous during flow fragmentation, which has implications related to DOC utilization that should be considered in future regional carbon budgets. [Display omitted] •Temporary Mediterranean streams are characterized by high spatial and temporal hydrological variability.•Flow fragmentation during the summer drought gives rise to a mosaic of aquatic and terrestrial habitat types.•We assessed leaf litter decomposition in running waters, isolated pools, moist sediments and dry sediments.•We found heterogeneous decomposition throughout the sites with implications to DOC utilization.•Addressing environmental heterogeneity is crucial to improving our understanding of temporary streams.