Leaf Decay Processes during and after a Supra-Seasonal Hydrological Drought in a Temperate Lowland Stream

Climate change models for Central Europe predict hydrological drought with fragmentation into pools during periods of high litter input in numerous lowland streams, presumably affecting in-stream leaf decay processes. To investigate this assumption, we measured physicochemical parameters, macro-invertebrate colonization, microbial activity, and decay rates of exposed leaves during and after a supra-seasonal drought in a German lowland stream. Microbial activity, shredder colonization and leaf decay rates during fragmentation were low, presumably caused by drought-related environmental conditions. Microbial activity and temperature-corrected decay rates increased after the flow resumption but not leaf mass loss and shredder colonization. During both periods, exposed leaves appeared physically unaffected suggesting strongly reduced shredder-mediated leaf decay despite shredder presence. Our results indicate that hydrological drought can affect organisms and processes in temperate lowland streams even after flow resumption, and should be considered in climate change scenarios.