M. Parsons, M. Thomas, R. Norris
Cooperative Research Centre for Freshwater Ecology
Monitoring River Health Initiative Technical Report Number 21
Environment Australia, 2002
ISSN 1447 1280
ISBN 0 642 54887 0
The Australian River Assessment System (AusRivAS) is a nationally standardised approach to biological assessment of stream condition using macroinvertebrates (Coysh et al., 2000). It was developed under the auspices of the National River Health Program (NRHP). Within the AusRivAS component of the NRHP, a suite of 'toolbox' projects have been commissioned with the aim of either refining the existing assessment techniques, or developing additional aspects of river health assessment that are complementary to those made by the AusRivAS macroinvertebrate predictive models (O'Connor, 1999). One of these projects is the development of a physical and chemical assessment module.
One of the main aims of the physical and chemical assessment module is to develop a standardised protocol for the physical and chemical assessment of stream condition, that will complement the biological assessments of stream condition made using AusRivAS. Disregarding the chemical component for now, development of such a protocol requires simultaneous consideration of stream condition from a biological and a physical perspective. While there would seem to be obvious interdependencies between the physical and biological components of streams, merging the two components is, in reality, a complex task because of the different paradigms that exist within the disciplines of stream ecology and fluvial geomorphology. The physical and chemical assessment module represents a first step in bringing together biological and physical or geomorphological approaches to the assessment of stream condition. However, in developing a standardised protocol for physical assessment of stream condition, that is directly relevant to biological assessment of stream condition, several questions become apparent:
The common link between assessment of stream condition from a biological and a geomorphological perspective is the expression of stream habitat, or physical structure, as a templet for biological communities. From a biological perspective, the physical habitat is considered as a templet upon which the ecological organisation and dynamics of ecosystems are observed (Townsend and Hildrew, 1994; Montgomery, 1999; Norris and Thoms, 1999). Thus, measurement of biological habitat tends to include the factors that directly influence biotic communities, at scales relevant to the organism of interest (Weins, 1989; Cooper et al., 1998; Sale, 1998) or the disturbance of interest (Rankin, 1995). From a geomorphological perspective, the expression of physical habitat is related to a set of predictable geomorphic processes (Harper and Everard, 1998; Muhar and Jungwirth, 1998; Brierley et al., 1999; Montgomery, 1999). The pattern of stream habitat that forms as a result of these processes provides the templet for biotic communities. Thus, measurement of geomorphological habitat tends to consider fluvial processes as they relate to channel structure, at scales that reflect the hierarchical organisation of stream systems (Schumm; 1977; Frissell et al., 1986; Maddock, 1999). Regardless of how each perspective views habitat, the common ground between geomorphology and biology is that both disciplines consider that a 'healthy' habitat is vital for a 'healthy' biotic community and indeed, for a 'healthy' stream ecosystem (Maddock, 1999; Norris and Thoms, 1999).
Biological monitoring programs are used worldwide to assess stream condition. The use of biota to assess stream condition has numerous advantages, the most prominent being that biotic communities are affected by a multitude of chemical and physical influences (Rosenberg and Resh, 1993). Thus, condition of the biota is a reflection of the overall condition of the stream ecosystem (Reice and Wohlenberg, 1993). However, there are numerous methods that have been developed to assess the physical or geomorphological condition of streams and which have the potential to enhance the interpretation of biological assessments of stream condition, or to provide information on stream condition that is not directly apparent within biological assessment. Any attempt to merge aspects of biological assessment with aspects of physical condition must identify the physical features that are of importance to the biota (Harper et al., 1995; Maddock, 1999), while retaining aspects that may be important to the physical formation of stream habitat.
The aim of this document is to review methods for the assessment of stream condition that are potential candidates for inclusion in a nationally standardised physical and chemical assessment protocol. It is not the aim of this document to make final recommendations for the format of the protocol. Rather, this review forms an initial information base and will be used in conjunction with a habitat assessment workshop to make final recommendations for a physical (and chemical) stream assessment protocol. The focus of this review is on assessment of the physical and geomorphological aspects of stream condition, with consideration of the potential for each method to link physical condition with ecological condition. It will answer four questions about each method:
The final section of the review will summarise the advantages and disadvantages of each physical assessment method and evaluate the potential for each method to encompass the physical aspects of river condition that are relevant to stream biota.