Ganga

Background Information

Evaluating the water quality of any water body or waterway requires the development of a sampling strategy that reflects both the probably sources of pollution in the system and the ultimate uses of the waters. Activity WQ1 provides a means of identifying likely pollutants given good background knowledge of land covers and sources of pollution which occur in the drainage basin. A second approach involves sampling for a broad spectrum of indicator pollutants, characteristic of general classes of pollutants.

Many pollutants are quite easy to measure and can provide much information about the health of a system. Table 1 lists a set of pollutants and some of the possible sources of pollution than can affect the parameter's values

Table 1. Selected indicator pollutants and frequent sources within a watershed
Parameter	Possible sources
pH	Industrial discharges; lime (lawns and industry); acid precipitation
Conductivity	Salts from highways; erosion from agricultural practices; industrial discharges
Nitrate	Fertilizers; industrial discharges
Phosphate	Fertilizers; industrial discharges
Iron	Industrial discharges; erosion
Copper	Industrial discharges; wastewater treatment
Coliform bacteria	Sewage; wastewater treatment; agriculture
Fecal coliform bacteria	Sewage; wastewater treatment; agriculture

This approach is frequently supplemented by the use of bioassessment, or using the life of the ecosystem as a means of determining water quality. Polluted systems tend to be less diverse than clean ones, and certain organisms are far less tolerant of pollutants than others. The use of bioassessment is spreading and much work is being done to further our understanding of the pollution tolerance of different taxa.

Water quality testing can be done using any number of systems. Two of the most comprehensive are have been developed by Lamotte and Hach. Both offer a variety of methods for testing water quality at a range of prices and precisions. Both also provide extensive resources on their web sites that assist in the development of site-specific protocols and with the interpretation of results. The United States Environmental Protection Agency also provides information that is suitable for use internationally.

The following links provide useful information about bioassessment practices:

United States Environmental Protection Agency http://www.epa.gov/bioindicators/html/benthosid.html

Stround Water Research Center
http://www.stroudcenter.org/index.htm

A search of the internet using the region name and the word "bioassessment" will frequently provide specific information for a given locale. Particularly good information can be found at the “Missouri Stream Team” home page, which although regionally-biased provides links to many activities and much useful information.

Procedure

1. Identification of sampling sites
This can either be done using the techniques described in Activity WQ1 or by the instructor prior to a visit to the site. In all cases it is important to obtain permission from the landowner before proceeding, making public lands especially attractive for this type of work. Boat launches and docks are frequently convenient locations, however chemical pollution and repeated physical disturbance of the beds can create bias in the results.

2. Collection of water samples
Proper collection of water samples is critical to the success of the laboratory. In most cases this should be done immediately upon arrival at the sampling site to reduce the effects of students stirring up the sediments which will bias samples. For streams and rivers students must collect samples upstream from where they are standing, and must be adequately spaced to prevent contamination of the samples from upstream sources (primarily other groups disturbing the substrate).

Upon entering the water, students should rinse the sample container at least twice to remove any traces of nutrients and minerals left from the cleaning efforts. While one liter of sample water is sufficient to carry out all the tests described above, collection of a backup sample is advisable given the multiple opportunities for spillage and contamination between the waters and the testing site.

3. Testing of water samples
Conductivity, pH and turbidity data should be collected on site; other samples can be stored for 24 hours (depending on the testing procedures being used) and analyzed in the classroom.

4. Collection of organisms for bioassessment
Many techniques have been developed to sample aquatic macroinvertebrates for analysis. The three presented below are all likely to provide large numbers of organisms, and when used together allow for a defensible assessment of water quality. Selection of a technique depends on budget, number of times a site can be visited and regulations governing the collection of insects and other invertebrates.

i. Dipnetting
Far and away the easiest method of collecting aquatic insects, dipnetting allows for many organisms to be collected during a single visit given adequate training of the students. Collection can be affected by weather conditions, and animals inactive during the day may be under-sampled.

ii. Minnow or other funnel traps
Traps allow for the collection of animals over longer periods of time, reducing the bias associated with differing periods of activity which affects results from single period sampling. Minnow traps can be obtained commercially from a variety of sources, or funnel traps can be constructed from two liter soda bottles with the top removed and inverted into the body of the bottle (Figure 1)

Care must be taken in the placement of the traps, especially if there is the potential for fish, amphibians or reptiles to be collected. If this is likely, traps should be placed so that a portion of the trap is above water to allow for animals to breath (Figure 2)

iii. Leaf pack systems
Developed by the Stroud Water Research Center , Leaf Packs have emerged as a viable technique for the biological assessment of water quality in different aquatic ecosystems.

5. Calculation of biotic indices for evaluation of bioassessment results

Most biotic indices are based on tolerance values determined from past studies that describe the probability of a species being found in a polluted system and on the diversity of a system. The indices assume that effluents and other stresses on the aquatic environment decrease aquatic life diversity, which is an "indicator" of a healthy aquatic ecosystem. Thus, when a pollutant is discharged into a stream, the numbers of species decline, with an increase in the populations of those organisms that tolerate such stresses.

Tolerance indices can take many forms, but all are based on categories similar to those given below:

Class I Organisms (Sensitive or Intolerant)
Organisms that are unlikely to be found in a polluted system because of their inability to survive or reproduce in polluted systems. This is frequently attributable to reduced oxygen concentrations associated with eutrophic conditions, but may also be the result of senstivity to salts or other toxic materials.

Class II Organisms (Facultative)
Facultative organisms can be found in both polluted and non-polluted systems, but have exhibited reduced population densities in degraded or polluted systems.

Class III Organisins (Tolerant)
Organisms found in all systems, apparently able to survive conditions with low oxygen or high levels of toxins.

Organisms collected are identified to the highest level of classification as possible, although a determination of order is generally adequate for this type of analysis. Once the organisms have been sorted and identified, they are grouped and the number of taxa (not individuals) is recorded. The calculation below is for Beck's biotic index, which doubles the importance of sensitive organisms in the calculation of the index.

2*(number of Class I Taxa) + (number of Class II Taxa) = Biotic Index

The presence of only Class III organisms would yield a value of zero in this calculation. This provides a good opportunity for discussion: pollution does not necessarily lead to the absence of life, but to a change in the community.

6. Evaluation of Results

This laboratory work brings together many of the most important aspects of the study of water pollution in an AP Environmental Science curriculum. Looking at both the pollutants themselves and their direct effects on the ecosystem forces provides a greater understanding of the issues associated with the regulation of waste water discharges.

The large number of analyses possible with the data collected forces students to refine hypotheses and think through the logical relationships between dependent and independent variables. High levels of copper may not correlate to Biotic Index values if the organisms are not affected by the pollutants in the stream, while the unmeasured BOD, perhaps reflects in nutrient levels may correlate well with a drop in the Index values.