Testing the coherence of several macroinvertebrate indices and environmental factors in a large lowland river system (Volga River, Russia)
Introduction
Distinguishing between anthropogenic and natural influences and effects on ecosystems is a fundamental problem in environmental science. In bioassessment of flowing waters with macroinvertebrates, most of the currently applied biological indices depend on natural environmental factors. This is determined by the fact that running waters represent a complex mosaic of habitats characterised by variable physico-chemical conditions (e.g., temperature, current velocity) and inhabited by differing biological communities (Allan, 1995). Taking this into account, usually two major approaches are used in environmental assessment: (i) use of reference conditions with establishment of large and diverse ranges of reference sites (e.g., Bailey et al., 2004, Nijboer et al., 2004), and (ii) development of stressor-specific indices, poorly dependent on natural environmental factors, but strongly dependent on particular anthropogenic stressors (Beketov and Liess, 2008, Liess et al., 2008a). Besides, a number of analytical methods consider natural variability by mathematical techniques and therefore separate anthropogenic effects from natural variability. These are multivariate statistical methods (Lepš and Šmilauer, 2003) and artificial neural networks (Cereghino et al., 2003). All these approaches however do not exclude, but rather complement each other.
The reference conditions approach – comparison of a given site with an undisturbed reference site – is the most widely used method for the current bioassessment of anthropogenic impacts on freshwater ecosystems (e.g., Bailey et al., 2004, Hering et al., 2004, Nijboer et al., 2004, Wright et al., 2000). The use of reference sites is stipulated by legislative instruments, e.g., EU Water Framework Directive (European Commission, 2000). High natural variations within macroinvertebrate communities require large ranges of reference sites to cover all the main watercourses types (e.g., AQEM Consortium, 2002). However, this is problematic in densely populated areas, such as for example Central Europe, because undisturbed watercourses of certain types (mainly relatively large streams or rivers) may not exist any more (Nijboer et al., 2004). One possible approach to tackle this problem is to use reference conditions from other comparable geographical regions with low population density and respective low anthropogenic impacts (e.g., Eastern Europe, Nijboer et al., 2004, Birke and Lorenz, 2006). Thus, due to low population density, many areas in Eastern Europe have been shown to remain least contaminated (Birke and Lorenz, 2006, Schletterer, 2006). However, further investigations are necessary to describe pristine or near-natural situations appropriately and to define reference conditions of large Central European Rivers.
Stressor-specific indices are biological metrics responsive to particular stressors, but independent of other anthropogenic and natural influences. Establishment of such stressor-specific indices is highly challenging due to high natural variability and diversity of factors affecting biological communities (Beketov and Liess, 2008). The promising approach to find stressor-specific indices is to employ biological traits (ecological, physiological and behavioural traits; e.g., life cycle duration, respiration type) rather than taxonomic characteristics (Lamouroux et al., 2004, Statzner et al., 2005, Bonada et al., 2006). Thus, the SPEAR (SPEcies At Risk) bioindicator system based on biological traits was shown to be highly sensitive to particular groups of toxicants and relatively independent of confounding factors (Beketov and Liess, 2008, Liess et al., 2008a). Currently the SPEAR system includes two types of indicators designed for two different types of contaminants (particularly for two different organic toxicants): (i) SPEARpesticides designed for agricultural pesticides occurring in water in short-term pulses (Liess and von der Ohe, 2005, Schäfer et al., 2007, Beketov et al., 2009) and (ii) SPEARorganic that is specific for organic toxicants with a relatively constant exposure regime (e.g., synthetic surfactants, petrochemicals) (Beketov and Liess, 2008) (terminology according Beketov et al., 2009).
Validation of the index SPEARpesticides in small streams in Europe has shown it to be highly sensitive to pesticide contamination, relatively independent of abiotic environmental factors and applicable across different biogeographical regions (Liess and von der Ohe, 2005, Schäfer et al., 2007, Schriever et al., 2007, Liess et al., 2008a, Beketov et al., 2009). To include the SPEARpesticides index into monitoring programmes according to the EU Water Framework Directive (European Commission, 2000) the boundaries of ecological status classes for this index have been defined in small European streams (Beketov et al., 2009). However, in large-scale river systems (e.g., in medium-size and large rivers) sensitivity, independence of confounding factors and validity of the ecological status classes’ boundaries of this index remain to be checked.
The second index in the SPEAR system, SPEARorganic, was found to be highly dependent on organic toxicants such as synthetic surfactants and petrochemicals, and relatively independent on natural environmental factors along a large-scale river continuum (Beketov and Liess, 2008). Nevertheless, further studies focused on relations of this index with both the target stressor (i.e. organic toxicants) and natural environmental factors are necessary to prove its applicability in different river systems and regions.
In contrast to the recently created SPEAR system, the Saprobic system is the classical and perhaps oldest bioassessment system for running waters (Kolkwitz and Marsson, 1902, Pantle and Buck, 1955, Zelinka and Marvan, 1961). The Saprobic Index (SI) indicates oxygen deficiency caused by biologically decomposable organic pollution. Although SI was shown to be strongly dependent on natural environmental factors and poorly stressor-specific (Bonada et al., 2006 and references therein), it is known to provide reliable and sufficient information for monitoring of organic pollution, related oxygen depletion, and eutrophication when effects of natural factors are taken into account, and therefore, nowadays it is widely used in Central Europe (Moog, 2002, Rolauffs et al., 2004).
Understanding of relations between different bioassessment indices (e.g., SI and SPEAR) and natural environmental factors is necessary for evaluation of the indices’ independence from natural confounding factors and stressor-specificity. Investigations of such relations is particularly meaningful when a set of indices having different target stressors (e.g., SI and SPEAR indices) as well as conventional ecological and bioassessment metrics (e.g., taxa richness (TR), Shannon's diversity index, Shannon, 1948) are considered in a large and uncontaminated river system. However, due to pollution such investigations are impossible in densely populated areas.
The Volga River is the largest river in Europe. In contrast to most large rivers in Europe, which were severely contaminated during the 20th century, the headwaters of the Volga River remain uncontaminated due to low population density (Grigoreva and Komissarov, 2008). Many parts of the upper basin of this great river can be defined as reference sites. At the same time, the Volga River represents a typical lowland river right from its headwaters (Schletterer, 2006). Therefore, the Volga River basin is a unique platform to define reference status conditions for large and medium-size rivers in Europe, and to investigate relations of bioassessment indices with basic environmental factors over a large-scale river system.
The aim of the present study was to analyse relations between SI, SPEAR indices, and other macroinvertebrate community indices and basic environmental factors in the large and relatively uncontaminated lowland river system such as the upper Volga River. Particular objectives were: (i) to analyse interrelations between the different indices, including indices focused on different stressors (e.g., SI and SPEARpesticides), (ii) to investigate relations of the indices with basic environmental parameters and reference/non-reference status of the watercourses, (iii) to establish preliminary ecological status classification (according to the EU Water Framework Directive, European Commission, 2000) for SPEARpesticides and SI indices on the basis of the reference sites’ characteristics, and (iv) provide recommendations for the bioassessment.
Section snippets
Research area
Samples were collected in the headwater of the Volga River located in the Tver’ province, Russian Federation (Fig. 1). The Volga River drains to the Caspian Sea and represents the largest river system in Europe (Litvinov et al., 2009). Catchment analyses revealed that the investigated part of the basin of the Volga River (from the source in the Valdaian hills to the city of Tver’) amounts to 31,300 km2: about 41.5% (12,980 km2) are forested, 2.4% (760 km2) covered by mires, and 2.1% (668 km2) of
Results
The indices characterising the macroinvertebrate communities of the watercourses investigated are summarised in Table 1. Comparison of the indices’ values between the Volga River and its tributaries has revealed no significant differences for all the indices except E that was significantly higher in the tributaries (P < 0.05, n = 23 and 30, respectively). Coefficient of variation varied form 10% for SI to 76% for EPT.
The PCA showed that the environmental variables could explain up to 40% of the
Interrelations of the indices and environmental factors
The present study showed complex interrelations between the biological indices. Remarkably, the SPEAR indices and SI did not intercorrelate (Fig. 2, Fig. 3a). Such independence was shown previously for the indices SPEARpesticides and SI in small streams in Europe (Schriever et al., 2007, Von der Ohe et al., 2007, Liess et al., 2008a, Liess et al., 2008b), however it has never been investigated for large lowland rivers, such as the headwaters of the Volga River and the tributaries investigated
Acknowledgements
Thanks to M.L. Egorov, who funded the expedition, and to the whole team of the “Upper Volga Expedition 2005”, especially to I.I. Terentyev, A.V. Kurganov, and S.V. Kurganova for their help in collecting and presorting the samples. We would also like to acknowledge Dr. Sabine Sommaruga for comments on the manuscript. This research was financially supported by a scholarship (“Kurzfristige wissenschaftliche Arbeiten im Ausland”) of the University of Innsbruck. The last author was supported by the
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