Changes in the benthic fauna composition in the Upper Vistula over the last 50 years – the consequences of the water pollution reduction and alien species invasion

The composition of the benthic fauna in the biggest Polish rivers, such as the Vistula and the Oder, clearly changes due to the invasion of alien species from various groups e.g. crustaceans (Konopacka 1998; Jażdżewski et al. 2004; Konopacka 2004; Bącela et al. 2008; Grabowski et al. 2007; 2009), oligochaetous clitellates (formerly Oligochaeta) (Dumnicka 2016; Jabłońska et al. 2015) or mollusks (Piechocki, Szlauer-Łukaszewska 2016), as well as due to the water quality improvement (Absalon, Matysik 2007; Pająk 2016; Schöll 2003). These biological changes have not been documented in the Upper Vistula – the stretch of the Vistula between the mouth of the Przemsza River (95 km of the water course) and the San River mouth (368 km). For many years, this river section has been heavily polluted, mainly by sewage from the Upper Silesian Industrial Region and saline waters from coal mines. Water chemistry of the Upper Vistula has been studied many times (see Kasza, Galas 2002), especially within the shorter stretch between the Przemsza River (95 km) and Kraków (165 km), over a distance of ca. 70 km, and has regularly been monitored by the Regional Inspectorate for Environmental Protection. Research on the composition of benthic invertebrates was performed only twice, between 96 km and 158 km by Zięba & Zaćwilichowska (1966) and between 128 km and 153 km of the river course by Dumnicka & Kownacki (1988). In addition, the composition of oligochaete fauna throughout the Upper Vistula was discussed by Dumnicka (2002). According to Kownacki (1999), the smaller number of species recorded from the Upper Vistula was caused by a high level of pollution, but also by insufficient knowledge about its benthic fauna. Based on the published data and available manuscripts, the author compiled a checklist of taxa found in particular sections of the Vistula, from the sources to the estuary.

The objective of this work was to summarize changes in the composition of benthic invertebrates in the Upper Vistula during the last 50 years. An attempt was also made to determine the rate and directions of these changes.

Research on water chemistry and benthic fauna composition was carried out twice (14 July and 16 December 2014) at 187 km of the Upper Vistula between the town of Oświęcim (96 km) and the town of Szczucin (283 km) (Fig. 1). On the same days, samples were collected from the Gostynka River (heavily polluted by saline mine waters), 100 m upstream from the place where it flows into the Vistula, at 93 km of its course. Moreover, on 2 August 2017, mollusks were collected in the mouth of the Skawinka River (150 km of the Vistula). Water temperature and conductivity were measured in situ using a portable instrument Hi 98312 (Hanna Instr. Inc. Woonsocket-RI-USA). The content of inorganic ions (Cl⁻, SO₄²⁻, HCO₃⁻, NO₃⁻, PO₄⁻, NH₄⁺, Na⁺, K⁺, Ca²⁺, Mg²⁺) was analyzed using the ion chromatography (DIONEX ICS 1000 and IC DX 320). The remaining parameters of water were determined by classic methods according to APHA (1992).

Figure 1

Qualitative samples of benthic fauna were collected from all habitats using a bottom scraper (20 cm × 20 cm) with 0.3 mm mesh net. In the laboratory, specimens were isolated from the sediments and identified under a stereoscopic microscope to the family level. Selected groups were identified to the species level using the following identification keys depending on the group: Amphipoda (Konopacka 2004), oligochaetous clitellates (Timm 2009), Mollusca (Piechocki, Wawrzyniak-Wydrowska 2016).

In the mid-20th century, the benthic fauna of the Upper Vistula was exposed to strong stress, especially due to high water pollution and high salinity, which substantially affected its composition, especially in the stretch downstream of the Przemsza River and the city of Kraków (Zięba, Zaćwilichowska 1966). Since then, the water quality has gradually improved, which was followed by an increase in the richness of fauna in the 1980s. The absence of caddisflies and mayflies, sensitive to salinity levels (Piscart et al. 2006), shows that chloride concentrations, still high in the Upper Vistula at that time, may be a factor limiting their presence.

During our study in 2014, families characteristic of moderately polluted (Kownacki, Soszka 2004) and slightly saline or non-saline waters (Wolf et al. 2009) occurred, such as Baetidae, Hydropsychidae and Caenidae, while taxa characteristic of strongly polluted waters were not found. In the course of our current study, the number of identified families was similar or a slightly smaller than that reported in the 1980s (Dumnicka, Kownacki 1988), probably due to the clearly smaller number of samples collected during only two field campaigns. In 2014, Chironomidae were more numerous than Oligochaeta, which confirmed the improvement of water quality (Starmach et al. 1976).

Despite the still high water salinity level, only three benthic species typical of brackish waters (Gammarus tigrinus, Paranais frici and P. litoralis) were found in the Upper Vistula. Taxa considered to be euryhaline or halophilous (Piscart et al. 2006; Wolf et al. 2009) were more numerous. They were represented by two alien amphipod crustaceans, the majority of non-indigenous oligochaete species as well as Corbicula fluminea. In Polish rivers, the salinity-related distribution of alien crustacean species was confirmed by Grabowski et al. (2009). This regularity also seems to apply to non-indigenous species of oligochaetes (Dumnicka 2016). Apart from the effect of salinity, the construction of six weirs on the Upper Vistula (in 1949–2002) affected the composition of benthic fauna due to changes in hydrological conditions. The reduced water current in the river bed above the weirs allowed the deposition of fine sediments, which created the conditions preferred by such mollusks as Physa acuta or Corbicula fluminea and oligochaetes from the genera Psammoryctides and Potamothrix. The above-mentioned alien species were not found in localities where the river maintained its submontane character, with the stone-gravel bottom and fast current.

The ways of migration and the rates of dispersion of various alien species in the Upper Vistula have not been thoroughly explored and sometimes they are difficult to define. The invasion of alien amphipods is considered to be relatively fast and they continue to spread in Polish waters (Bącela et al. 2008; Grabowski et al. 2007; 2009). Gammarus tigrinus, an oligohaline North American species, was introduced in Western Europe in the 1950s and expanded its range in thirty years from west to east, most likely via the Baltic See coast, but possibly also through the German Mittelland-Canal (Jażdżewski et al. 2002). At the turn of the 21st century, Gammarus tigrinus was reported from most of the Oder reaches (from the estuary to the town of Kędzierzyn Koźle), also in a few localities along the Baltic Sea coast and in the deltaic system of the Vistula (Grabowski et al. 2007). Furthermore, it was recorded in a small tributary of the Upper Oder (Spyra et al. 2015). In the last decade, we found G. tigrinus in the Upper Vistula drainage system. It can be assumed that this species was transported from the Oder system to new localities by man (or by birds), or during long-lasting floods. Natural migration from the Vistula mouth is unlikely. Due to the invasion of alien species, the amphipod fauna in the Upper Vistula has changed completely. The native European freshwater gammarid species, G. fossarum, almost completely retreated in the 1960s due to the water pollution. At present, the North American G. tigrinus and the more recent invader, Dikerogammarus haemobaphes, represent the gammarid fauna. The Ponto-Caspian species, D. haemobaphes, entered the Vistula through the Pripyat-Bug canal connecting the Black Sea and the Baltic Sea basins (Konopacka 1998; 2004). Among oligochaetes and mollusks in the Upper Vistula, alien species account for about 20% of the total number of species. It is likely that their presence has not eliminated native species, which was also reported from the Oder by Piechocki and Szlauer-Łukaszewska (2016) for mollusks and by Jabłońska et al. (2015) for oligochaetes.

The distribution of alien species belonging to the above-mentioned groups has changed over time. The gastropod Physa acuta, reported from the Upper Vistula in the 1960s (Zięba, Zaćwilichowska 1966; Aleksandrowicz 1986; Dumnicka, Kownacki 1988), has not been found by Maćkiewicz (2013) in recent years. Over the last years, a new alien species – Corbicula fluminea was found in the Vistula, first in Kraków (Maćkiewicz 2013) and recently in the mouth of the Skawinka River. Such findings show that populations of some alien species are not stable in the studied stretch of the Upper Vistula, which was also observed for non-native oligochaete species (Table 4). This process was also observed for other alien species (Najberek, Solarz 2016).

For many years, the composition of benthic fauna communities in the Upper Vistula has been affected by some stress factors such as pollution, salinity, invasion of alien species and hydrotechnical constructions. Nevertheless, the gradual improvement of water quality has led to an increase in the number of species, while the impact of alien species has only been observed with regard to the species composition of the gammarid fauna.

Rare species such as Chaetogaster setosus and Gianius aquaedulcis (Timm 2009) colonized the Upper Vistula River as a convenient habitat. So far, Ch. setosus has not been found in Poland, the Czech Republic or Slovakia (Fauna Europaea), whereas G. aquaedulcis was known from only one locality in Poland – springs located close to the Warta River (near Częstochowa) (Dumnicka 2009).

The composition of benthic fauna as well as other communities in the Upper Vistula should be monitored, as in other big rivers (Fruget et al. 2015), in order to determine further directions and the rate of changes taking place.