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F. Reach and channel unit: habitat quality assessment

River habitats, as structured by instream and surrounding topographic features, are major determinants of aquatic community potential. The matrix used to assess habitat quality is based on the key physical characteristics of the waterbody, particularly those within the sub-catchments tributary to the sites under investigation. These physical characteristics and water quality parameters are pertinent to an overall characterisation of stream habitat. All of the habitat parameters evaluated are related to the overall aquatic community, and many act as limiting factors. The analysis of this information will provide insight as to the ability of the stream system to support an healthy aquatic community. It will also indicate the presence of chemical and non-chemical stressors affecting the stream ecosystem. As a result, an evaluation of these environmental data is particularly important in defining assessment techniques and interpreting biosurvey results (Figure 9.3).

The core of the European standard methods (CEN 2000) is based on the hydromorphological survey system, currently operating in Austria (Muhar et al. 1993), France (AFN 1998), Germany, and the United Kingdom (Raven et al. 1998). This methodology utilises the same information to assess habitat quality as is standard to most other assessment protocols (e.g., that used in the United States) (U.S. Environmental Protection Agency 1999).

Habitat features are recorded within three zones defined within riverine environments; namely, the:

• channel, defined by a bed and banks having a width and depth (e.g., channel geometry), epifaunal substrate and available cover, channel vegetation, organic debris, sediment regime (e.g., erosional/depositional character), flow regimes (e.g., flow patterns and velocities), and longitudinal continuity as affected by artificial structures;
• river bank or riparian zone, defined by the bank structure and modifications, vegetation type, and constructions on the banks and within the riparian zone;
• floodplain and adjacent lands, which are comprised of land uses and terrestrial habitats, open water habitats, ephemeral habitats (as assessed by duration, frequency and extent of flooding), and degree of lateral connectivity with, and potential for, channel mobility across and within the floodplain.

G. River channel unit: biological assessment

Under the European Union Water Framework Directive and the U.S. Clean Water Act, the assessment of the 'ecological status' of rivers is inherently based on biological indicators. Biological monitoring approaches are essential to achieving the goals of ecological sustainability, which espouse protection of biodiversity and the maintenance of essential ecological processes and life support systems. Aquatic macroinvertebrates have been extensively used as an indicator group in monitoring studies for many years. More than one hundred different bioassessment methods exist in Europe, two thirds of which are based on macroinvertebrates (see Rosenberg and Resh 1993, Verdonschot 1990, 2000). In compliance with the requirements of the European Union Directive, and WFD assessment approaches, recently developed biomonitoring studies have established an ecoregional river classification and typology in Europe, which serves as a base for generating type-specific benthic invertebrate reference communities across large-scale geographic areas. The essential elements of these systems are summarised below.

Saprobic, diversity, and biotic indices

Nowadays, there are three principal approaches to biological assessments that utilise taxonomic and pollution tolerance data:

• Saprobic indices, which focus on species presence in relation to organic pollution. The tolerance of an organism is described by the parameters of indicator (on a scale of 1 to 5), weighting (within tolerance ranges), and species abundance. Examples include the Saprobienindex (DEV 1992) and the Saprobic Water Quality Assessment (BMLF 1999);
• Diversity indices, which focus on the decrease in species diversity observed under increasing disturbance or stress. The number of observed species (richness) is related to the number of individuals (abundance). The most widely used indices of this type are the Shannon-Weaver, Simpson, and Margalef indices (see the review by Boyle 1990). Some diversity indices provide additional insight into the biotic community by calculating the uniformity of the distribution (evenness) of the number of individuals of the counted species;
• Biotic indices and scores, which focus on both the saprobic and diversity index approaches to evaluate taxa richness and pollution tolerance (mostly organic) using a scoring system. Examples of these systems include the Average Score Per Taxon BMWP-ASPT and BMWP Scores (Armitage et al. 1983), the Belgian Biotic Index (De Pauw et al. 1992), and the Indice Biologique Globale Normalisé (AFN 1985).

Multivariate analysis techniques applied to assemblages and community assessments

Multivariate approaches are able to detect subtle differences across taxa in space and time. These statistical techniques allow detection of patterns of variability within groups of taxa and/or between groups of taxa and environmental variables. Since the 1980s, ecologists have explored integrative relationships between taxa and their associated environmental parameters using multivariate analysis techniques. Wright et al. (1993) used multivariate analysis techniques to classify unpolluted running waters, and to predict community types from environmental data. The results were used in the River Invertebrate Prediction and Classification System (RIVPACS). This model calculates the probability of occurrence of an expected taxon from the weighted reference site group. The RIVPACS approach to predictive modelling consists of three basic steps:

• Determination of community types (based upon aquatic macroinvertebrate communities) using statistical classification methodologies (i.e., cluster analysis and/or ordination techniques, such as TWISPAN or UPGMA clustering),
• Determination of explanatory environmental variables (physical and chemical), and
• Prediction of the probability of taxa occurrence.

Comparing the observed fauna (at the species or family level) with the expected or "target" predicted fauna, yields a measure of site quality.

The System for Evaluating Rivers for Conservation (SERCON) is another broad-based and consistent technique for stream evaluation that provides a simple way of communicating technical information to decision-makers (Boon et al. 1997). SERCON uses catchment characteristics, physical and chemical descriptors, channel and floodplain characteristics, biotic structure, and aquatic impacts to evaluate a sub-catchment.

Multimetric and rapid assessment techniques

The use of rapid assessment techniques and multimetric techniques to evaluate instream biological impairment has become an essential assessment approach to river management in the United States. The approach was first developed by Karr (1991) for fish communities (the Index of Biological Integrity, or IBI) and refined for wider applications (e.g., based upon macroinvertebrate assemblages, in the Invertebrate Community Index or ICI) (Kerans and Karr 1994). These techniques use a number of single metrics to assess environmental degradation.

Barbour et al. (1992) presented the conceptual basis for a multimetric approach, in which community health is composed of community structure, community balance, and functional feeding groups. These indicators, in combination with habitat quality, provide an integrated assessment of community health. Multimetric methods remain based upon the ecological attributes of biological communities.

The following groupings indicate the metrics commonly used in multimetric and rapid assessment techniques:

• Richness/composition measures (e.g., the total number of taxa, number of EPT³ taxa, number of Chironomidae taxa, number of individuals, percent of dominant taxa, percent of sediment tolerant taxa, etc.) used to detect organic pollution.
• Tolerance/intolerance measures (e.g., presence of pollution is indicated by the ratio of intolerant to tolerant taxa), which rely on an assignment of (in-)tolerance values to taxa.
• Diversity measures (e.g., the Shannon-Wiener Index, or sequential comparison index).
• Biotic indices (e.g., the Hilsenhoff family biotic index, or BMWP, score, and the ASPT score), which use both the assignment of (in-)tolerance values to taxa and richness and/or diversity measures.
• Similarity/loss measures (e.g., the community loss index, Bray-Curtis Index, etc.), which are based upon comparisons between sites (reference vs. disturbed conditions) - these are often calculated, but rarely used in multimetric analyses; and,
• Functional measures (e.g., percentages of functional feeding groups and life cycle measures), which reflect the alteration of feeding styles and life spans in response to different types of disturbances.

H. Perspectives for biomonitoring at large spatial scales: biological and ecological traits of benthic macroinvertebrates

The biological assessment of water quality, using strict taxonomic-based metrics, does not provide insight into the causal mechanisms resulting in stream impairment. Thus, to support the current European Union environmental policy and legal requirements, biomonitoring tools must be not only based upon sound theoretical concepts in lotic ecology (Statzner et al. 1994, 2001), but also be aimed toward:

• a generalised geographical application across ecoregions,
• a robust indication of the degree of different types of human impacts on a given ecosystem,
• a specific indication of increasing and decreasing trends in human impacts.

³ EPT: Ephemeroptera, Plecoptera, Trichoptera.

Figure. 9.3.
A monitoring and assessment procedure, applied to water quality management, with special emphasis on (1) stream typology, based on landscape properties, (2) established reference conditions, (3) data acquisition and management, and (4) development of ecological integrated assessment, including hydrochemical, habitat, and biological assessments

As a result, indices that focus on biological traits (e.g., body size, descendants per cycle, numbers of reproductive cycles per year, life expectancy of adults, general mobility, regeneration potential, intensity of attachment to substrate, body flexibility, occurrence of resistant or resting stages, intensity of respiration, and active/passive food/feeding characteristics), and based upon the functional diversity of biocommunities, have been proposed by Statzner et al. (1994) and Townsend and Hildrew (1994). Such indices are advantageous indicators of the ecological integrity of freshwater ecosystems at a European scale.

Such indices provide a biomonitoring approach and technique for defining the mechanisms that control stream community assemblages. The predictive power of this approach reflects the coupling of large-scale environmental conditions and the set of evolutionary adaptations among taxa that ultimately result in the formation of a discernible biocommunity. In consequence, this holistic or ecosystem-based approach offers a unique dimension in assessing the natural and anthropogenic disturbances to freshwater ecosystems across large geographical units.

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