Impact of the riverbed morphology on the source of organic material and the trophic structure of fish community along the upper reaches of the Nevėžis River, Lithuania

Abstract

Čivas L., Kesminas V., Barisevičiūtė R. 2016. Impact of the riverbed morphology on the source of organic material and the trophic structure of fish community along the upper reaches of the Nevėžis River, Lithuania. Acta Ichthyol. Piscat. 46 (4): 303-312.Background. The catchment of the Nevėžis River, the sixth longest river in Lithuania, is among the most affected by agricultural activities. Although seriously disturbed by land reclamation and agricultural pollution, the Nevėžis River still has natural, anthropogenically unaffected stretches. Fish species were studied at two sites of the upper part of the river with different hydrological regime, exhibiting clear differences in the trophic status of fish. The combined effect of hydrogeomorphic and water-chemistry variability on the stable isotope composition of fish assemblages in Lithuania has not been investigated. The presently reported study was intended to explore the possible effects of the riverbed morphology and agricultural activities on the chemistry and stable isotope composition of the three main fish species. Materials and methods. This study covered three species of freshwater fishes: the European perch, Perca fluviatilis Linnaeus, 1758; the roach, Rutilus rutilus (Linnaeus, 1758); and the northern pike, Esox lucius Linnaeus, 1758. The sampling was performed in both natural and regulated river stretches using backpack electrofishing equipment. Stable isotope composition of the samples was revealed by applying stable isotope analyses (SIA) with an elemental analyser connected to an isotope ratio mass spectrometer. To obtain more information about environmental variability and variation of stable isotopes δ 13 C and δ 15 N in fish, the entire data matrix was analysed using Principal Component Analysis (PCA). Results. In the study sites on the Nevėžis River, algal carbon isotope ratios were more 13 C-depleted than those from terrestrial sources. The fishes were clearly dependent on terrestrial carbon sources in natural locations. However, the fishes collected from regulated sites had carbon isotope signatures more similar to algal than to terrestrial sources. Mean values of δ 15 N of the fishes from the natural sites were lower than those from the regulated ones. Conclusion. The presently reported study revealed impact of abiotic habitat variables indicating the importance of physicochemical and morphological characteristics on δ 13 C and δ 15N isotopic values variance of fish at natural and regulated river sites. Our findings would help to evaluate and predict changes on river food webs that occur due to hydromorphological alterations determined by human activity and climate change. The results could be useful for fisheries, i.e., impact of environmental factors on fish nutrition and growth.

A technical guide to develop a statistically valid fish-based index in compliance with the water framework directive: an evaluation for Turkish freshwaters

“…of rivers supply limited information on the immanent characteristics of those water bodies (Meybeck et al 1996;Hunting et al 2017). Several researchers have shown that the hydromorphological variables such as distance from the source, slope and stream order also have an effect on fish assemblages (Olaya-Marin et al 2012;Civas et al 2016;Wolter et al 2016). Datasets for abiotic parameters are also useful to detect the behavior and fate of contaminants which may assist in developing management strategies.…”