engleski

Seasonal and fine-scale spatial drift patterns in a tufa-depositing barrage hydrosystem

We examined seasonal patterns of drifting macroinvertebrates, and transported moss and (in)organic particulate matter at a fine spatial scale within the tufa-depositing barrage hydrosystem of Plitvice Lakes, Croatia. Samples were collected at six sites along a stream reach during autumn, winter, spring and summer. The sampling sites differed in flow velocity, depending on their position within the study reach and distance from tufa barriers and associated waterfalls. Seasonality was pronounced for most physico-chemical measurements. The highest concentrations of transported (in)organic particulate matter, being related to increased amounts of moss in transport, were observed in autumn. Drift densities were highest at tufa barriers that had higher flow velocities. Drift abundance partially followed the seasonal pattern in transported (in)organic matter. Autumn peaks in drift of Oligochaeta, Coleoptera as well as some Diptera and Trichoptera were related to increased moss and particulate matter quantities, while observed increases in drifting Nematoda, Cladocera, Copepoda, Ephemeroptera, Simuliidae and Chironomidae in spring and summer were probably due to distribution shifts of larvae or to higher seston levels originating from the upstream lake. Although we found that faster flowing stream sites generally had higher drift densities, there typically was no significant correlation between flow velocity and the amount of drift. Therefore, our expectation that fine-scale spatial drift patterns primarily depend on flow differences between lotic habitats was not supported for this system. The positive correlation between transported moss and other measured drift parameters, both at the seasonal and fine spatial scale, suggests that drift patterns were influenced by trapping/refuge efficiency of moss-covered tufa substrate and respective seasonal changes in instream vegetation (moss) as linked to hydrochemistry and water temperature.

macroinvertebrate drift; moss; tufa; small scale; flow velocity; seasonal; small spatial scale

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