Michał Ciepłucha’s research while affiliated with Medical University of Lodz and other places

The Warta River (795 km long) is the largest tributary of the Odra (Oder) River. This study presents results from one of the best-documented long-term monitoring projects in Poland, based on three periods of electrofishing: 1986–88 (T1), 1996–98 (T2) and 2011–12 (T3). After decades of severe point-source pollution, water quality has been improving since the early 1990s. However, the recovery of fish assemblages was recorded with a considerable delay, i.e. not in T2 but in T3. Species richness in T3 increased by ≥50% in relation to T2. The recovery process proceeded at a different pace in the upper (section X), middle (section Y) and lower (section Z) river courses. The good status recorded in X in T3 was qualitatively different from the good status observed in T1 as migratory and/or lithophilic species were less common. Section X, with relatively clean tributaries, was isolated from the rest of the Warta system by the Jeziorsko Reservoir constructed between X and Y in 1986 (without fish passage). Ichthyofauna in Y was not only in the poorest condition but was also recovering very slowly because of migration barriers and polluted tributaries, resulting in a severe shortage of sources of recolonizers. The quickest positive changes were recorded in Z because of the beneficial role played by certain less degraded tributaries and the direct connection to the recipient Odra River. Significant increases in biomass were recorded in Z for both limnophilic and rheophilic species; the former may be linked to zones of stagnant water existing between groynes and the latter to fast-flowing water near groyne heads.

The aim of the study was to assess whether ichthyofauna variability follows the natural downstream gradient or the degradation gradient, and to assess the bioindication potential of fish zonation. The study was conducted along the entire length (795 km) of the lowland Warta River, Poland, wherein the complexity of the ecotone zone and availability of hiding places for fish decreased downstream. The catchment of the middle course carried a heavy load of pollutants. In the lower course, groynes were common, the channel width exceeded 100 m and the mean discharge reached 210 m3/s. In 2011–2012, single-run electrocatches of fish and lampreys were performed at 73 sites, generally while wading along 100 m long reaches of both riverbanks (farthest upper course, depth ≤ 0.6 m) or drifting in a boat along a 500 m riverbank stretch (in the remaining river parts). An indicator species analysis allowed identification of species associated significantly with particular river sections: one (a rheophil) in the source fragment (S1), seven (all rheophilic) in the upper course (S2), three in the middle course (S3), and nine (including three rheophils) in the lower course (S4). On this basis, the S1 was classified as an impoverished grayling zone, S2 as a barbel zone, and S4 as the bream zone. Section S3 remained unclassified, as its ichthyofauna was in the worst condition due to: (i) the strong destabilizing upstream impact of the Jeziorsko dam reservoir, (ii) large amounts of wastewater discharged from towns located in the catchment area of this section and (iii) the lack of unpolluted tributaries that could serve as sources of recolonizers. In summary, in the human-modified Warta River, the variability of fish assemblages followed a degradation gradient, which was also reflected in the disturbed fish zonation. Consequently, this study confirms the usefulness of a fish fauna zonation analysis for the bioindication of large-scale human impacts in rivers.

The Warta River (795 km long) is the largest, right side tributary of the Odra (Oder) River. The study presents results from one of the best-documented long-term monitoring projects in Poland based on four terms of electrofishing: 1963–66, 1986–88, 1996–98 and 2011–12, conducted in the upper Warta. The Warta River underwent human-induced modifications typical for most European lowland rivers (damming, regulation, water pollution), of which the most destructive for fish was point-source water pollution. In the late 1980s, pollution reached its highest level and stopped increasing as the former political system collapsed and many industrial plants went bankrupt. Surprisingly, recovered fish assemblages were not recorded during the sampling in 1996–98, but in 2011–12. This is why we believe that in large degraded rivers, it takes about 10–20 years before a considerable improvement in fish fauna can be observed. Ichthyofauna recovered to a good status, but was qualitatively different compared to the good status observed in the 1960s. On the one hand, in 2011–12, high species richness and high assemblage diversity were observed, and many species, including seven rheophils, were more common than earlier. On the other hand, the populations of catadromous eel and anadromous vimba have not recovered, and these species were absent in the 2011–12 samples. Because water quality has improved, the most important factor seems to be the impact of the Jeziorsko dam reservoir which is located downstream of the study area and has no fish pass.