Abstract
The influence of groynes in large rivers on caddisflies has been poorly studied in the literature. Therefore, we carried out an investigation on the 420-km stretch of the River Oder equipped with groynes. At 29 stations, we caught caddisflies in four habitats: current sites, groyne fields, riverine control sites without groynes and in the river’s oxbows. We found that groyne construction increased species richness, diversity, evenness, and altered the structure of functional groups into more diversified and sustainable ones compared to the control sites. The groyne field fauna is similar to that of natural lentic habitats, but its composition is largely governed by the presence of potential colonists in the nearby oxbows. We distinguished three of the river’s caddisfly assemblages. The distribution of Trichoptera was governed inter alia by the plant cover and the amount of detritus, and consequently, the food resources. Oxygen, nitrates, phosphates and electrolytic conductivity were important as well. Groynes have had positive effects for caddisflies—not only those in the river itself, but also those in its valley. They can therefore be of significance in river restoration (although originally they served other purposes), especially with respect to the radically transformed ecosystems of large rivers.
Highlights
Large rivers are aquatic ecosystems that have been heavily modified by humans and over many centuries
This study examines the following hypotheses: (1) the fauna and functional groups of Trichoptera resemble those of natural habitats of a similar character, (2) groyne constructions secondarily increase the biodiversity of the river and its valley by introducing habitat complexity, (3) both physical and chemical and structural factors are key to the distribution of caddisfly species in a river subjected to human pressure
The taxonomic richness of the oxbows and groyne fields was identical with 31 taxa each; 12 taxa were from the control sites and 7 from the current (Table 2)
Summary
Large rivers are aquatic ecosystems that have been heavily modified by humans and over many centuries. May have unintentionally reversed the negative effects of regulation. (Fig. 1) which are hard hydraulic structures built at right angles to a river bank. They are made from a wide variety of materials: in recent years, rock and concrete have been most often used. This, in turn, deepens the water in the channel, thereby prolonging the period for which the river is navigable. Structures of this kind have long been used in many countries. The Oder, the object of our study, has the largest number of groynes: they were built at regular intervals over a very long distance (Rast et al, 2000), creating the largest uniform stretch of river in Poland (40% of the river’s length) with altered habitat conditions
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