Shift in the synchronisation of leaf decay processes in fragmented streams
Final Report Abstract
Field observations ascertained proposed alteration of the in-stream environmental conditions in fragmented streams of the temperate region. There were strong effects of these environmental conditions on leaf decaying macroinvertebrates (shredders), leaf associated microbial activity and decay rates that were found in both micro- and mesocosm experiments. Sudden flow reduction and oxygen concentrations within the hypoxic range reduce microbial and shredder mediated leaf decay. Moreover, high concentrations of solutes, presumably phenolic substances, leached from leaf litter slow down microbial mediated leaf decay and further reduce the leaf decay process in streams under the projected climate change scenario. In a field study, we measured physicochemical parameters, colonization of leaf decaying organisms, leaf associated microbial activity, and leaf decay rates and leaf litter standing stock during and after stream fragmentation in a lowland stream. We found that extreme hydrological drought events have the potential to slow down in-stream leaf decay processes during the drought and even several months after flow resumption. Consequently, leaf litter can accumulate in drought affected streams even in the post-drought period and still be present during seasons that are usually characterized by low litter supply. Moreover, the community structure of stream macroinvertebrates can be altered during and after the drought and drought sensitive aquatic species might be substituted by more drought tolerant species. From 13 drought sensitive stream reaches in the German lowlands data had been collected to detect indications for recent drought impacts. More than 60% of these reaches were recently fragmented into pools and more than 30% of inspected stream reaches indicated low oxygen levels. Moreover, around 50% of drought sensitive streams had reduced shredder abundance and, hence, low leaf decay due to reduced shredder contribution leading to partly high accumulation of leaf litter standing stock in the streams. The results from field observations, experimental research and modelling were in line and overall, they indicate that extreme hydrological drought events can have long-term effects on community structure and leaf decomposition in temperate lowland streams with implications for the providence of decay products within the impacted streams and their receiving systems. Our findings have significance for the transformation of organic carbon in lowland streams and should be considered in the management of these streams under climate change.
Publications
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2007: Response of aquatic leaf associated microbial communities to
elevated leachate DOC: A microcosm study. International Review of Hydrobiology, Vol. 92. 2007, Issue 2, pp. 146–155.
Schlief, J. & Mutz, M.
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2009. Grazing impact and phenology of the freshwater sponge Ephydatia muelleri and the bryozoans Plumatella emarginata and Fredericella sultana under experimental warming. Freshwater Biology, Vol. 54. 2009, Issue 5, pp. 1078–1092.
Vohmann, A., Mutz, M., Arndt, H., Weitere, M.
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Effect of sudden flow reduction on the decomposition of alder
leaves (Alnus glutinosa [L.] Gaertn.) in a temperate lowland stream: a mesocosm study. Hydrobiologia, Vol. 624. 2009, Issue 1, pp 205–217.
Schlief, J. & Mutz, M.
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2011. Leaf Decay Processes during and after a Supra-Seasonal Hydrological Drought in a Temperate Lowland Stream.
International Review of Hydrobiology, Vol. 96. 2011, Issue 6, pp. 633–655.
Schlief, J., Mutz, M.
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2012. Aquatic protists modulate the microbial activity associated with mineral surfaces and leaf litter. Aquatic Microbial Ecology, Vol. 66.2012, pp. 133-147.
Risse-Buhl, U., Karsubke, M., Schlief, J., Baschien, C., Weitere, M., Mutz, M.
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2012. Temperature dependent consumer-resource dynamics: a coupled structured model for Gammarus pulex (L.) and leaf litter.
Ecological Modelling, Vol. 247. 2012, pp. 157–167.
Kupisch, M., Moenickes, S., Schlief, J., Frassl, M., Richter, O.
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2012: Temporal patterns of populations in a warming world: a modelling framework. Marine Biology, Vol. 159. 2012, Issue 11, pp 2605–2620.
Moenickes, S., Frassl, M., Schlief, J., Kupisch, M., Mutz, M., Suhling, F., Richter, O.
