Assessment of the hydromorphological quality of streams in the Venta River Basin District, Latvia

Abstract

INTRODUCTION According to the EU Water Framework Directive (WFD), surface waters in Europe must achieve good ecological quality by 2015 (European Commission, 2000). The WFD requires ecological quality assessment of running waters based on various biotic (phytoplankton, macrophytes, phytobenthos, benthic invertebrates, and fish fauna), chemical, and hydromorphological elements (European Commission, 2000). When evaluating the quality status of water bodies, the predominant role used to be given to the assessment of biotic elements (Logan and Furse, 2002), with the support of hydromorphology and physico-chemical assessment (European Commission, 2000). Previous monitoring focused on chemical parameters and assessment of benthic invertebrates in running waters (O'Hare et al., 2006), but the new legislation of the WFD states that it is necessary to include hydromorphology in the assessment of ecological status. Assessment of river hydromorphology is needed not only for the implementation of the WFD but also for nature conservation purposes, such as the monitoring of the condition of Special Areas of Conservation under the EC Habitats Directive and helping the management and restoration of rivers (Boon et al., 2010). Rivers have important functions in ecosystems, such as natural flood control, ecological refuge development, production, and species conservation. However, aquatic ecosystems are among the most severely affected habitats (Sala et al., 2000). Streams and their floodplains have been modified as a result of land drainage, floodplain urbanization, and flood defence (Sparks, 1995; Kronvang et al., 2007). More recently, physical disturbances such as damming, channelization, separation of channel and floodplain, and destruction of riparian vegetation have become more relevant in Europe and have therefore been included into the assessment methods (Feld, 2004; Lorenz et al., 2004; Timm et al., 2011). The morphology, longitudinal and lateral connectivity, as well as the discharge regime of running waters are severely disturbed in Central Europe. Only 10% of the river reaches in the alpine region can be classified as near natural (Muhar et al., 2000). In Latvia there are still streams with sites corresponding to 'conditions that are representative of a group of minimally disturbed sites, i.e. reference site, described by selected physical, chemical and biological characteristics' (Springe et al., 2010). There is a long history of biological assessments in Europe but systems for the assessment of hydromorphological quality are far less developed (Erba et al., 2006). Various methods and indices (Muhar et al., 2000; Friberg et al., 2005; Kamp et al., 2007) are used in different countries to characterize hydromorphological quality. Characterization of the physical structure and assessment of the habitat quality of rivers are gaining importance in the context of environmental planning, appraisal, and impact assessment. Hydromorphological quality assessment plays a crucial role in the WFD because it is used to determine 'undisturbed' and 'heavily modified' conditions of rivers (Raven et al., 2002). In order to fulfil the demands of the WFD, stream and river assessment must be changed fundamentally from a single index system to a more holistic approach (Feld, 2004). Numerous researchers emphasize that the stream quality assessment requires knowledge about the hydrological regime, geological formation, and geomorphological processes of the stream, as well as about impacts of natural and anthropogenic origin both in the past and present (Riis and Biggs, 2003; Tremp, 2007). Several European countries have developed methodologies to identify the morphological character of rivers (Muhar and Jungwirth, 1998; Raven et al., 2000; Buffagni and Kemp, 2002; Rinaldi et al., 2013). The reason for the wide application of these methods is that they rely on well-established monitoring activities and simple classification criteria (Bizzi and Lerner, 2012). …