After reading this article you will learn about the monitoring bio-monitoring of water quality.
Water Quality Monitoring:
There are two basic kinds of water monitoring—chemical analysis and biological assessment.
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Normally, surface water quality was monitored by both ways.
But the groundwater quality is monitored principally by chemical ways except a few bacteriological tests.
In India, river water quality was monitored regularly by joint efforts of Central Water Commission, State and Central Pollution Control Board. There are couple of stations of Global Environmental Monitoring Systems (GEMS) for monitoring of major river water quality.
In contrary, groundwater quality was monitored by Central Ground Water Board and also State Water Investigation Departments. The primary objective of these monitoring was to assess the groundwater quality and also to assess the chemical or biological contaminations that are harmful for mankind.
Though over decades the routine analysis were made for water quality assessment, but, in recent years, the utility of biological approaches to water quality assessment were also realised.
The principal biological approaches are described in Table 11.7:
Bio Monitoring of Water Quality:
In addition to conventional water quality monitoring, there are various biological systems of water quality monitoring. These systems are also very sensitive and useful. The biotic resources of water bodies are diverse, these include a variety of macrophytes, phytoplankton’s, zooplanktons, bacterial and other animal communities.
Some well-known biological representatives of lentic communities. Identically, some representative animals of the littoral zones of ponds and lakes of tropics is shown in Fig. 11.2. Among these biota, many forms are sensitive to pollutants of water or rather sensitive towards change in water quality.
However, there are couple of forms which appears to be tolerant and acting as ‘bio indicator’ species.
According to Liebmann (1962) there are three distinct categories of tolerant aquatic species which are considered to be good indicator of pollution load of water, viz. oligosaprobic organisms (indicators of scarcely polluted waters), mesosaprobic organisms (indicators of moderate to highly polluted water) and polysaprobic organisms (indicator of extremely polluted water).
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The detailed check list of indicator species of various saprobic categories are given in the Table 11.8:
Usually, for quantitative way of water assessment, species diversity indices of diverse water bodies were computed in recent years. These exercise provide valuable clues for water quality monitoring. The diversity indices are calculated from the abundance data of the organisms and serve as a very good indicator of pollution.
Some diversity indices are described:
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(a) The Shannon-Wiener Index:
Species richness may be compared between two communities or areas by simply counting the number of species either in the whole community—if that is practical—or in suitable samples. However, there is at least one more aspect of species diversity that should sometimes be considered—relative abundance or equitability.
Imagine two communities each made up of two species. In one community there are 99 individuals of species A and one individual of species B, whereas, in the second community, there are 50 individuals of each species. The second community is more diverse in this sense; almost every individual sample is predictable in the first community but not in the second.
One widely used measure of diversity that combines species richness with equitability is the Shannon- Wiener index. It is supposed to measure the uncertainty involved in predicting the identity of the next individual.
The formula for calculating the index H’ is:
where S = number of species and P, = proportion belonging to the i-th species. The logarithms used can be to any base. The base 2 is used by some because the answer H’ is then in bits; however, most people use base e because it is easy and not so far from 2.
Calculation of H’ may be illustrated using some fabricated numbers from tropical African Savanna:
In the formula we take the negative sum of Pi (log P,) for the practical reason of preferring to deal with positive numbers, H’ for this set of data is then 0.936, (If the index is needed in binary form, the value log Pi may be converted to log 2 Pi by dividing it by 0.6931. For example, -log 2 0.556 equals – 0.5870/0, 6931 equals – 0.8469).
One practical application of index has been in assessing stream pollution. For the bottom fauna an H’ greater then 3 (using log 2) usually indicates no, or very slight, pollution. Because some species decline or disappear while a few species increase, the index drops with pollution. An index of 2 to 3 indicates light pollution and an index below 1 indicates heavy pollution.
(b) Kothe’s Species Deficit Index (1962):
This index is based on the principle that in a flowing ecosystem the number of species decreases after they are exposed to some pollutant discharge.
In this method the number of species of either a particular group (algae or macro invertebrates) or of all the groups are counted at the polluted and non-polluted points and then index is calculated as:
Species deficit index = A 1 – A x/A1 x 100
where, A1 = Number of species at the unpolluted site
AX = Number of species at the polluted site (downstream)
It gives the data in a percentage linear scale and is very useful in indicating the consequences of point sources of waste water discharges.
(c) Odum’s Species Index (1971):
It is an excellent index to determine the level of pollution in both flowing and standing water bodies.
It is calculated as:
Index Value = Total number of species encountered in the sample/Total number of individuals of all the species x 1,000
(d) Simpson Diversity Index:
It is also an important index, used widely for water quality monitoring.
The formula used is:
D= N(N-1) /∑ n(n-1)
where D = Diversity index
N = Total number of individual plants
n = number of individuals per species
∑ = Sum
The value of ‘D’ indicate the level of water pollution.