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

Chapter 2 Review of River Assessment Methods (continued)

2.3 HABSCORE (USEPA Rapid Bioassessment Protocols)

• 2.3.1 How did HABSCORE come about?
• 2.3.2 How does HABSCORE work?
• 2.3.3 How does HABSCORE assess stream condition?
• 2.3.4 How does HABSCORE link physical and chemical features with the biota?

The United States Environmental Protection Agency (USEPA) has developed Rapid Bioassessment Protocols (RBP) that use fish, macroinvertebrates or periphyton to assess stream condition. Metrics representing structural, functional and process elements of the biotic community are calculated for each site, and aggregated into an index. This multimetric index represents the biological condition of a site (Barbour et al., 1999). Physical and chemical data are also measured at each site, and are used to aid the interpretation and calibration of the index, and also to define the reference condition. It is beyond the scope of this document to consider the process of biological metric calculation and calibration. Rather, the focus will be on the suite of physical and chemical measurements that are collected alongside the biota. In particular, the RBP includes a rapid habitat assessment method that uses a scoring system to rate habitat condition, and which will henceforth be referred to as HABSCORE. HABSCORE has utility outside the Rapid Bioassessment Protocols and has been used as a measure of habitat condition in the AusRivAS predictive models (see Section 2.2) and in the Habitat Predictive Modelling approach (see Section 2.7). HABSCORE was originally adopted by Plafkin et al. (1989) from work conducted on fish habitat, but has subsequently been updated and modified slightly by Barbour et al. (1999). The following discussion refers to the updated version of HABSCORE.

2.3.1 How did HABSCORE come about?

The USEPA Rapid Bioassessment Protocols were developed in response to a need for cost effective survey techniques to assess stream condition (Barbour et al., 1999). The principal requirements underpinning the protocols were:

• cost effective, yet scientifically valid, procedures for biological surveys;
• provisions for multiple site investigations in a field season;
• quick turn around of results for management decisions;
• scientific reports easily translated to management and the public; and,
• environmentally benign procedures (Barbour et al., 1999).

The HABSCORE component of the Rapid Bioassessment Protocols is commensurate with these requirements.

2.3.2 How does HABSCORE work?

HABSCORE is a visually based habitat assessment that evaluates 'the structure of the surrounding physical habitat that influences the quality of the water resource and the condition of the resident aquatic community' (Barbour et al., 1999, p5-5). It includes factors that characterise stream habitat on a micro-scale (e.g. embeddedness) and a macro-scale (e.g. channel morphology), as well as factors such as riparian and bank structure which influence the micro and macro-scale features (Barbour, 1991; Barbour et al., 1999). HABSCORE is composed of ten habitat parameters (Figure 2.3.1). To reflect the difference in habitat types between upland and lowland streams, separate assessments have been developed for high and low gradient conditions (Barbour et al., 1999). At each site, individual parameters are assessed and rated according to a continuum of scores that represent optimal, sub-optimal, marginal or poor condition (Figure 2.3.1). A total score is obtained for each site, and is subsequently used to determine the percent comparability to reference conditions (Plafkin et al., 1989). However, the individual parameter scores and the total assessment score also provide an overall assessment of habitat condition at the sampling site.

TOTAL HABITAT SCORE _________________

Figure 2.3.1 Habitat assessment data sheet for high gradient streams, showing habitat parameters assessed for HABSCORE. Each parameter is scored on a continuum of conditions representing optimal, sub-optimal, marginal and poor conditions. The score is totalled and to form the overall assessment of habitat quality. After Barbour et al. (1999).

In addition to the HABSCORE assessment of site condition, a suite of variables that represent factors integrated within HABSCORE are also collected at each site. These factors characterise stream type, watershed features, riparian vegetation, instream features, large woody debris, aquatic vegetation, water quality, inorganic substrate and organic substrate (Table 2.3.1). These factors can be included in determinations of reference condition, but are mostly used as an interpretative aid to the assessments of stream condition, made using the multimetric indices. These variables are also collected in AusRivAS (see Section 2.2) but are used mainly to aid interpretation of site condition, rather than as predictor variables.

2.3.3 How does HABSCORE assess stream condition?

As a stand-alone method, HABSCORE provides an ability to assess the quality of instream and riparian habitat at a sampling site. However, a more important function of HABSCORE is that it is used to determine the ability of the habitat to support the optimal biological condition of the region (Barbour et al., 1999). Assuming that reference sites represent optimal condition, the comparability of the habitat and the biota to this reference state can be plotted to determine the ability of the habitat to support the biological community (Figure 2.3.2). There are three important aspects of Figure 2.3.2:

• the upper right hand corner represents a situation with good habitat quality and good biological condition;
• the mid-section of the curve represents a situation where habitat quality decreases and the biological community responds with a concomitant decrease; and,
• the lower left hand corner represents a situation where habitat quality is poor and unable to support the biological community (Barbour, 1991).

Apart from the three situations outlined above, comparison of the condition of the biota with the condition of the habitat can also highlight situations of potential water quality degradation, where habitat quality is high but biological condition is poor (Barbour et al., 1999).

Habitat quality is the initial focus of the Rapid Bioassessment Protocols. Habitat quality at the reference sites is compared against habitat quality at the test site and if equivalent, then a direct comparison of the biological condition can be made using the biological metrics (Plafkin et al., 1989). This ensures that assessments of biological condition indicate impairment, rather than inherent natural differences in stream habitat. If habitat quality is lower at a test site than at the reference sites, then the ability of the habitat to support biota is investigated as a first step, before a determination of biological condition is made (Plafkin et al., 1989).

2.3.4 How does HABSCORE link physical and chemical features with the biota?

HABSCORE was designed to complement assessments of biological condition made using the rapid biological assessment protocols. This compatibility is based on the assumption that the quality and quantity of available physical habitat has a direct influence on biotic communities (Maddock 1999; Rankin, 1995). The parameters measured in HABSCORE (Figure 2.3.1) represent aspects of the habitat that are related to aquatic life use and which are a potential source of limitation to the aquatic biota (Barbour, 1991; Barbour et al., 1999). Thus, the empirical links between habitat and the biota are reflected in this relationship. The process used to determine the ability of the habitat to support an optimal biological community (see Section 2.3.3) also captures these empirical links by considering habitat quality to be a templet that influences the types of biotic communities that can potentially be attained under certain conditions.

Figure 2.3.2 The relationship between habitat and biological condition. Re-drawn from Barbour (1991).