INTRODUCTION:

There have been repeated attempts to use biology in the assessment of water quality for several decades in developed countries (Resh and Jackson, 1993). In North America and Western Europe, several rapid assessment procedures have been formulated and some have been codified through legislation. Because rapid assessment, offers a cost-effective approach to water quality monitoring, the application of such an approach in developing countries is very much appealing (Resh, 1995).

Water quality assessment programmes in developing countries have generally been concerned with public health issues; safe drinking water has been the primary emphasis of these programmes. Interest in environmental monitoring in some countries has increased in recent years (e.g., for habitat conservation programmes).

ELEMENTS OF RAPID ASSESSMENT APPROACHES:

Resh and Jackson (1993) described the use of rapid assessment approaches in water quality monitoring as somewhat analogous to the use of thermometers in assessing human health; easily obtained values are compared to a threshold that is considered normal, and large deviations indicate that further examination is necessary. The application of the term "rapid assessment" to water quality is largely in vogue in North America but programmes in several European countries share common elements, many of which arose from saprobien system. Rapid assessments differ from both the saprobien system and quantitative studies in that they are usually characterized by involving more than one type of measurement, and summary of these measurements is used to compare them with predetermined thresholds rather than relying on statistical comparisons.

Rapid assessment involves sampling and analysis approaches that are designed to fulfill two objectives. First, effort (and cost) is reduced in assessing environmental conditions at a site, relative to that needed in quantitative approaches. A second objective of rapid assessment approaches is to summarize the results of site surveys in a way that can be understood by non-specialists such as managers, other decision-makers, and the concerned public. This is done by using analytical measures that express results as single scores, as well as by placing the scores obtained in categories of environmental quality based on regional background data (Resh and Jackson, 1993).

The success of any rapid assessment approach depends on the ability to detect impacted and non-impacted conditions. Therefore, efforts to reduce costs must not be carried to the point that information used in the analysis does not adequately represent the site examined. Likewise, the analysis and summary should not be so simplified that impact-related conditions are not detected.

FRESHWATER BENTHIC MACROINVERTEBRATES AS TOOLS IN WATER QUALITY MONITORING:

Several biological communities including plankton, periphyton, microphytobenthos, macrozoobenthos, aquatic macrophytes and fish have been considered in assessments of stream and river water quality. However, experience from North American, European and Australian programmes as well as extensive studies in Cauvery river system in India have demonstrated that the most useful biological assessment methods for routine monitoring of wadeable streams and rivers are those based on macroinvertebrates. Benthic macroinvertebrates are organisms that inhabit the bottom substances (sediments, debris, logs, macrophytes, filamentous algae etc.,) of freshwater habitats, for at least part of their life cycle. Aquatic flatworms, oligochaetes, insects and molluscs constitute the major taxa of benthic macroinvertebrates. They are retained by mesh sizes £ 200 to 500 mm. Rosenberg and Resh (1993) have examined the advantages and difficulties in using macroinvertebrates in water quality assessments (Table I).

COMPONENTS OF THE SUGGESTED RAPID BIOASSESSMENT PROTOCOL (RBP) MODULE (Modified from Barbour et al., 1999): HABITAT ASSESSMENT AND PHYSICOCHEMICAL PARAMETERS:

An evaluation of habitat quality is critical to any assessment of ecological integrity and should be performed at each site at the time of the biological sampling. In general, habitat and biological diversity in rivers are closely linked. In the present protocol, the definition of the "habitat" is restricted to the quality of the stream and riparian habitat that influence the structure and function of the aquatic community in a stream. The presence of an altered habitat structure is considered one of the major stresses on aquatic systems (Karr et al., 1986).

The habitat quality evaluation can be accomplished by characterizing selected physicochemical parameters in conjunction with a systematic assessment of physical structure (Data Sheet II). Through this approach, key features can be rated or scored to provide a useful assessment of habitat quality.

FIELD SAMPLING, LABORATORY PROCESSING AND APPLICATION OF BENTHIC METRICES: FIELD SAMPLING:

Sampling of a single habitat is usually recommended. Riffles or runs are preferred to standardize assessments among streams having such habitats. Macroinvertebrate diversity and abundance are usually highest in cobble substrate (riffle/run) habitats. One-meter kick net is used for sampling. At each sampling site, 3 samples are taken and the duration of each sampling is usually 5 minutes. For each sample, a 1m2 area should be marked off. While one person holds the kick-screen, the other person should systematically sample the area. Every large boulder or cobble in the area is picked up if it could be lifted and organisms vigorously washed by hand into the net. Finally, substrate with smaller boulders should be disturbed by kicking systematically across the area 3 times such that the invertebrates wash downstream into the net. The organisms are then carefully picked from the net surface and preserved immediately in 80% ethanol. These samples should be returned to the laboratory for processing. In case, where the cobble substrate represents less than 30% of the sampling reach in reference stream (i.e., those streams that are representative of the region), D-frame Dip Net should be used.

LABORATORY PROCESSING AND APPLICATION OF BENTHIC METRICES:

Specimens collected should be sorted and identified to operational taxonomic unit (at least to family level with the help of regional keys) in the laboratory under a dissecting microscope. After identification, the 3 samples for each site may be lumped together for calculation of the functional feeding group and make-up of the community according to taxonomic order. Classification of the functional feeding group may presently be based on Merritt and Cummins (1996) until regional functional feeding categorization is worked out. Benthic metrices that can be adopted and predicted direction of metric response to increasing perturbation are given in Table2 (Barbour et al., 1996) since results s previous extensive work in Cauvery basin (Sivaramakrishnan et al.,) support initiation of future studies based on a habitat assessment and the BMWP (Biological Monitoring Working Party) scrore as formulated by Armitage et al., 1983), BMWP and BMWP - ASPT (average score per taxon) scores, identification to family is sufficient. Family tolerance scores from Table3 (modified version of Armitage et al., 1983) should be used and the score for each family should be ascribed and added together to arrive at a site value (BMWP S t1, where t1 is the tolerance score for a family). Pollution intolerant families have high scores and pollution-tolerant families have low scores. The average score per taxon (BMWP - ASPT St1/number of families); a high ASPT value usually characterizes clean upland sites containing relatively large numbers of high scoring taxa. Lowland sites that do not support many high scoring taxa generally have lower ASPT values (Armitage et al., 1983). An advantage of using the ASPT scoring system is that the number of individuals collected does not affect the index. The BMWP and the BMWP-ASPT scores should be evaluated separately.

DATA INTEGRATION & REPORTING: DATA INTEGRATION:

Integration of information from physical characterization, water quality field data, habitat assessment, benthic metrices including the Biotic Index values should be done through graphical display (Bivariate scatter plots, Cluster dendrogram, Pie charts, Box-and wisker plots, Line graphs, Cumulative frequency diagram, Bar charts etc.) to reveal patterns of biological response to impaction.

REPORT FORMAT:

Barbour et al., (1999), recommend two basic formats for reporting ecological assessments. Each of these formats is intended to highlight the scientific process, focus on study objectives, and judge the condition of the assessed sites. The first format is a sort of eco-summary, targeted for use by managers in decision making regarding the resource. It has a simple style but conveys varied information including study results. An executive summary format is very appropriate. The second format for reporting is a scientific report, which is structured similarly to a peer-reviewed journal. The report should be peer-reviewed by non-agency scientists to validate its scientific credibility. An abstract should be included to highlight the essential findings.

CONCLUSION:

The ultimate objective should be to evolve an empirical (statistical) model, Ind RivAS (Indian Rivers Assessment System) similar to RIVPACS (River Invertebrate Prediction & Classification Scheme) of U.K. and its derivative AusRivAS (Australian Rivers Assessment System) of Australia (Norris, 1995) which would predict the aquatic macroinvertebrate fauna, expected to occur at a site in the absence of environmental stress.

REFERENCES:

Table 1. Advantages and Difficulties to consider in using Benthic Macroinvertebrates for Biological Monitoring. (after Resh, 1994)

Advantages

Difficulties to consider

Being ubiquitous, they are affected by perturbations in all types of waters and habitats. Large numbers of species offer a spectrum of responses to perturbations. Their sedentary nature allows spatial analysis of disturbance effects. Their long life cycles allows effects of regular or intermittent perturbations, variable concentrations, etc. to be examined temporally. Qualitative sampling and analysis are well developed, and can be done using simple, inexpensive equipment. Taxonomy of many groups is well known and identification keys are available. Many methods of data analysis for macro invertebrate communities have been developed. Responses of many common species to different types of pollution have been established. Macro invertebrates are well suited to experimental studies of perturbation Biochemical and physiological measures of individual -organism stress to perturbations are being developed.

Quantitative sampling requires large number of samples, which can be costly. Factors other than water quality can affect distribution and abundance of organisms. Seasonal variation may complicate interpretations of comparisons. Propensity of macro invertebrates to drift may offset advantages of being sedentary. Perhaps too many methods of analyses are available. Certain groups are not well known taxonomically. Benthic macro invertebrates are not sensitive to some perturbations, such as pathogens and trace amounts of some pollutants.

Table-2: Benthic Metrics and Predicted Direction Of Metric Response to Increasing Pertubation (after Barbour et al., 1999)

Table-3: Modified Biological Monitoring Working Party Score System (BMWP)