Australian River Assessment System: Review of Physical River Assessment Methods — A Biological Perspective

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

3. Summary and Evaluation of River Assessment Methods

• 3.1 Summary of river assessment methods
  • 3.1.1 AusRivAS
  • 3.1.2 HABSCORE
  • 3.1.3 Index of Stream Condition
  • 3.1.4 Geomorphic River Styles
  • 3.1.5 State of the Rivers Survey
  • 3.1.6 Habitat Predictive Modelling
  • 3.1.7 River Habitat Survey
• 3.2 Evaluation of river assessment methods
• 3.3 Future directions - habitat assessment workshop

3.1 Summary of river assessment methods

The following provides a summary of the advantages and disadvantages of each of the seven river assessment methods examined in detail in the previous section. Each method was developed for a different purpose and thus, the use of the term 'advantages' and 'disadvantages' are not judgements about the relative value of each method as an individual tool for river assessment. Rather, examination of advantages and disadvantages is framed in light of the potential for each method, or components of each method, to fit the requirements of a standardised physical and chemical assessment protocol, within an AusRivAS style framework.

3.1.1 AusRivAS

Advantages

• Nationally standardised biomonitoring approach
• Uses biota as the endpoint to represent environmental condition
• Comparisons to reference condition establish level of biological impairment
• Capability to predict taxon occurrence at sites
• Incorporates established empirical links between the biota and some of the physical and chemical variables used as predictor variables (e.g. substratum, riparian vegetation, altitude)
• Outputs easily understood by managers, scientists and community groups

Potential disadvantages

• Limited ability to link causal factors (water quality degradation, habitat quality degradation or both) to biological condition
• Assumes that all the major physical, chemical and habitat factors with an empirical link to macroinvertebrate community structure and which can provide an independent way of matching test sites with reference site groups, were included in constructing the predictive models
• Limited ability to predict macroinvertebrate community structure in large river systems

Sampling and data collection issues

• Requires collection of an extensive reference site database to develop models
• Rapid sampling philosophy - approximately 1 hour field work and 1-3 hours laboratory work per site
• Small deviations in methods can limit model capabilities (e.g. live pick and laboratory sort data are not interchangeable)

3.1.2 HABSCORE

Advantages

• Integrates habitat parameters into a score that represents a continuum of conditions for biota. Reference conditions are considered optimal.
• Can be used without modification in other monitoring programs (e.g. AusRivAS)
• Habitat parameters are used to determine the ability of the habitat to support biota
• Habitat parameters represent aspects of the habitat that are related to aquatic life use
• Additional site observations aid interpretation of biological condition at a site

Potential disadvantages

• Most criticism is of the multimetric approach to biomonitoring, rather than of the HABSCORE method
• Subject to operator differences in interpretation and scoring of the habitat parameters (Hannaford and Resh, 1995)

Sampling and data collection issues

• Rapid sampling philosophy - approximately 15min per site to assess habitat parameters

3.1.3 Index of Stream Condition

Advantages

• Used for long term assessments of whole stream reaches
• Integrates several key components of stream condition (hydrology, physical form, streamside zone, water quality and aquatic life)
• Management orientated, with a scientific basis. Also useful as a tool for monitoring management interventions
• Indices can be weighted according to their perceived importance, or according to data availability
• The reference state ratings are based on knowledge of levels of stress that cause biological community degradation (e.g. pH, riparian vegetation cover)

Potential disadvantages

• Designed to be repeated every five years, so it has limited suitability for routine monitoring programs
• Reach scale and long term assessment focus means that it may not be detailed or sensitive enough to pick up all perturbations
• Information on the link between a change in index value and a corresponding change in environmental condition is limited
• Determination of reference condition is subjective

Sampling and data collection issues

• Field assessment takes approximately 2 hours at a site. Desk based data collection is also required

3.1.4 Geomorphic River Styles

Advantages

• Foundation in geomorphological theory
• Measures habitats, or physical structure at different scales
• Ability to predict future river character and responses to disturbance, based on geomorphological process theory
• Habitat based links between geomorphology and biota
• Set within a hierarchical framework

Potential disadvantages

• Assumes that the habitat units considered are relevant to biota
• Requires a high level of geomorphological expertise, particularly for interpretation and prediction
• Establishment of the benchmark reference condition is subjective and requires a high level of geomorphological expertise to determine
• Indirect, rather than direct links to river ecology
• Limited testing of the links between geomorphological parameters and biota. For example, is the distribution of geomorphological process zones related to the distribution of the biota?

Sampling and data collection issues

• Air-photos may not be available for some areas, to delineate stream reaches
• Specialised equipment may be required for surveying

3.1.5 State of the Rivers Survey

Advantages

• Comprehensive coverage of stream sections within a catchment
• Assessment of at many levels - whole catchment, individual sections or individual tributaries, using data components individually or together
• Use of homogeneous stream sections allows extrapolation from the sampling scale to larger areas
• Physical measurements indirectly represent geomorphological processes
• Some empirical links between the parameters measured and stream biota (e.g. substratum, riparian vegetation)

Potential disadvantages

• Comparisons to reference condition are subjective
• Links between some measured parameters (e.g. bank condition, bar shape) and biota are not well established
• Links between structure and process are weak

Sampling and data collection issues

• Rapid sampling philosophy - 3/4 to 1 hour per site in the field
• Some desk based data collection also required

3.1.6 Habitat Predictive Modelling

Advantages

• Ability to predict the occurrence of stream habitat features
• Ability to incorporate variables that are directly relevant to biota, as well as variables that are based on geomorphological processes
• Comparisons to reference condition establish habitat impairment
• Use of a method identical to AusRivAS may facilitate direct comparison of macroinvertebrate and habitat observed:expected scores
• Set within a hierarchical framework

Potential disadvantages

• Choice of variables may affect predictive ability. Emphasis on biological variables may facilitate links to AusRivAS outputs, however, geomorphological process variables may also be important for predicting habitat features
• Currently subject to some analytical limitations (e.g. prediction of categories rather than continuous data)

Sampling and data collection issues

• Can make use of data collected for the existing AusRivAS program
• Depending on the choice of variables, rapid sampling philosophies can potentially be applied to data collection

3.1.7 River Habitat Survey

Advantages

• Geomorphological theory underlies many of the variables collected
• Uses the functional habitat and biotope philosophies to link physical habitat with the biota
• Several mechanisms available to determine habitat quality and identify benchmark sites
• Nationally standardised approach
• Potential for linkage with the RIVPACS biological assessment program

Disadvantages

• Links between biota some of the habitat components measured are not well established
• Counts of classes the only feasible data form for most measurements. Thus, the mixture of qualitative and quantitative data, with nominal, ordinal and interval types makes statistical tests difficult

Sampling and data collection issues

• Requires collection of an extensive database to determine initial stream types
• Problems were identified with operator differences - this necessitated the use of occurrence rather than quantitative data, which subsequently reduced the ability for statistical analysis
• Rapid sampling philosophy - approximately 1 hour per site in the field

3.2 Evaluation of river assessment methods

Each of the river assessment methods considered in this review was developed for a specific purpose and thus, the methods reflect a range of management goals and scientific approaches. However, development of a standardised protocol for the physical and chemical assessment of river condition requires consideration of the following specific qualities:

• scale of focus that is commensurate with the AusRivAS biological monitoring protocol;
• capacity to measure stream condition against a desirable reference state;
• incorporation of parameters that are relevant to the biota, especially macroinvertebrates;
• representation of important geomorphological processes that influence the formation of stream habitat;
• conformity with a rapid philosophy of data collection and analysis;
• potential for use by non-experts;
• scientific outputs presented in a form that is easily interpreted by managers;
• adaptability and applicability to a wide range of river types across Australia; and,
• ability to predict physical stream characteristics.

The representation of each of these qualities within the seven river assessment methods examined in this review is summarised in Table 3.2.1. Overall, the methods generally use rapid data collection and analysis methods, they have the potential for use by non-experts and their scientific outputs are presented in a form that is easily interpreted by managers (Table 3.2.1). Each of the methods also has some capacity to assess stream condition against a reference state, however, the degree to which this function is utilised in determining site condition varies among the methods. Similarly, the methods vary widely in predictive ability, applicability to a wide range of river types across Australia and scale of focus (Table 3.2.1). Differences between the dominant paradigms of stream ecology and geomorphology are reflected by two criteria: the incorporation of parameters relevant to biota and the representation of important geomorphological processes (Table 3.2.1). Geomorphic River Styles, State of the Rivers Survey and River Habitat Survey were each designed to assess physical or geomorphological aspects of streams and thus, they attempt to incorporate empirical relationships between physical parameters and biota indirectly. Conversely, AusRivAS, HABSCORE and Index of Stream Condition have a strong biological component and thus, they fail to fully consider geomorphological processes. Finding common ground between biologically and geomorphologically relevant parameters would provide a more holistic perspective on the assessment of stream condition.

3.3 Future directions - habitat assessment workshop

As discussed in Section 1.1, development of a protocol for the physical assessment of stream condition that is complementary to AusRivAS requires simultaneous consideration of biological and geomorphological methods and approaches. This review is a first step towards merging the two approaches to stream assessment, and provides an information base that that will be built upon at the habitat assessment workshop, scheduled for 2-3 May, 2000. The habitat assessment workshop will bring together geomorphologists, hydrologists and ecologists and will involve the authors of several of the methods covered in this review. The aim of the workshop is to develop a framework for a standardised physical and chemical assessment protocol. One of the main challenges of the workshop will be to determine the physical variables that are relevant to biota, and to determine the most suitable methods for measuring these variables in a cost effective manner, and within a rapid sampling philosophy. Specifically, it is hoped that the questions posed in Section 1.1 will be answered in detail during the course of the workshop to form the basis for a standardised physical and chemical assessment protocol. The outcomes and recommendations from the habitat assessment workshop will be reported in a future document.