engleski

Energy resources and feeding guild structure of macroinvertebrate assemblages in the hyporheic zone of calcite depositing lake outlets

We investigated the distribution of particulate organic matter (POM) and its relation to flow velocity andtufa deposition rates (TDR) in the 4– 10 cm deep zone at tufa barriers. We expected surface conditionsaffect the hyporheic zone, even in habitats with non-moving substrate in calcite depositing lake outletstreams. Additionally, we analyzed feeding guild structure of macroinvertebrate assemblages againstenvironmental conditions, food resources and predatory abundance. Overall, more POM was depositedin the hyporheic zone of slow flow and low TDR habitats. Mean energy stored in the hyporheic POMwas 163.4 kJ dm−3. While least abundant in mass, coarse POM represented the majority of organic matterenergy stock. Coarse particles accumulated more at fast flow habitats and finer particles accumulatedmore at slow flow habitats. We propose that fast flow partly flushes small particles and partly macroin- vertebrate fauna ingests and converts them to larger particles (fecal pellets) and transports them to thehyporheic zone. Collector gatherers dominated the assemblages (76%) and as passive filterers (4%) theythrived at fast flow sites. Grazers were the second dominant feeding guild (14%) and were more abundantat slow flow sites. Surface flow and predation pressure were the most important controls of hyporheicassemblage structuring. POM content was not as important. We propose that in the stable, non-movingtufa hyporheic zone food is plenty for the scarce fauna so macroinvertebrates are more reactive to pred- atory pressure. Moog’s functional feeding guild allocation system, while more complex, proved moresuitable for our analyses than classification system derived from Cummins’.

particulate organic matter; tufa; detritus; flow velocity; predatory pressure; stable substrate; karst

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