Introduction

The water bodies were to be the cheapest and convenient refuse disposal systems. This tendency has resulted in indiscriminate and excessive loading of waste matter into the aquatic systems, beyond their capacity of self purification. Normally over any short time interval in a water body not subject to human influence there is a balance, more or less between nutrient inflow and nutrient outflow.

In recent times, mismanagement of surrounding areas of a water body has resulted into unprecedented nutrient enrichment of water bodies causing cultural eutrophication, which is manifested by raised tropic status, increased rate of sedimentation, loss of water storage capacity, lowered retention period and deteriorated water quality.

The physico-chemical characteristics of any aquatic ecosystem and the nature and distribution of its biota are directly related to and influenced by each other and controlled by a multiplicity of natural regulatory mechanisms. However, because of man’s exploitation of the water resources, the normal dynamic balance in the aquatic ecosystem is continuously disturbed, and often results in each dramatic responses as depletion of fauna and flora, fish kill, change in physico-chemical character etc. Artificial changes which lead to such ecological responses are referred to as pollution and pollution stage may reach a stage when these valuable aquatic resources are no longer safe for human use.

Objective

The Deghi and ponds are important surface water resources which facilitate harvesting and storage of rain water from their catchment areas and replenishment of the ground water. Due to increasing urbanization along the catchment area within past few years, the quality of the water of these water bodies is deteriorating fast creating social, economical and technological problems.

The present study has been undertaken with a view to assessing the pollution load of a Deghi on the north of Agiye Chala Sangha, Melarmath, Agartala,West Tripura.

Problems

The Deghi is situated at the heart of Agartala town on the north of Agiye Chala Sangha. The Deghi is surrounded by roads with residents, shops, office complex and temple. Local people use the water of this Deghi for bathing, washing and other activities. Presently all kinds of waste materials generated by surrounding shops and residences are dumped into the Deghi. As a result the water quality of this Deghi has deteriorated.

In order to assess the deterioration in water quality of the said Deghi, a Scientific team of Tripura State Pollution Control Board collected water samples and biological samples from the Deghi on 2nd March 2005. Collected samples were analysed in the laboratory of the Tripura State Pollution Control Board.

Methodology

Environmental pollutants from anthropogenic sources affect the aquatic ecosystem in a synergistic manner, which cannot be detected comprehensively by determination of selected physico-chemical parameters alone. Whereas, biological system can integrate all environmental variables over a long period of times in terms of effects which can be easily measured and quantified.

  1. Physico-Chemical Assessment

The physico-chemical parameters of water quality were analysed using standard methods given in APHA (American Public Health Association).

  1. Biological Water Quality Assessment

Biological water quality assessment was done using the standard method developed by Central Pollution Control Board.

Central Pollution Control Board during the development and validation of Bio-monitoring methodology, established the fact that among all the biological components of the aquatic ecosystem, benthic macro- invertebrates are best suitable for evaluation of water quality. Most of these macro-invertebrates particularly insect larvae, which are aquatic, share their biological life in fresh water, while their adults fly over for miles together in search of suitable fresh water environment for reproduction, breeding and laying eggs in suitable habitats and establish biological communities.

Two methods for biological water quality evaluation have been adopted :

i)Sequential comparison for Diversity score.

Number of Runs

Diversity score = ------

Number of Organisms

ii)BMWP (Biological – Monitoring Working Party) for Saprobic score.

Grand Total Multiplied Score

Saprobic Score = ------

Grand Total Number of Families Encountered

Table-1Biological Water Quality Criteria (BWQC)

Sl.No / Taxonomic groups / Range of saprobic score
(BMWP) / Range
of
diversity
score / Water
quality charac-teristic / Water quality class / Indicator colour
1 / Ephemeroptera, Plecoptera, Trichoptera, Hemiptera, Diptera / 7 and more / 0.2 -1 / Clean / A / Blue
2 / Ephemeroptera, Plecoptera, Trichoptera, Hemiptera, Odonata, Diptera / 6 -7 / 0.5 -1 / Slight pollution / B / Light Blue
3 / Ephemeroptera, Plecoptera, Trichoptera, Hemiptera, Odonata, Crustacea, Mollusca, Polychaeta, Coleoptera, Diptera, Hirudinea, Oligochaeta / 3 -6 / 0.3 – 0.9 / Moderate pollution / C / Green
4 / Mollusca, Hemiptera, Coleoptera, Diptera, Oligochaeta / 2 -5 / 0.4 and less / Heavy pollution / D / Orange
5 / Diptera, Oligochaeta or No macro-invertebrates / 0 -2 / 0. -0.2 / Severe pollution / E / Red

Table-2PHYSICO-CHEMICAL RESULTS OF WATER SAMPLES OF THE DEGHI, ON THE NORTH OF AGIYE CHALA SANGHA, MELARMATH, AGARTALA, WEST TRIPURA.

Sl.
No / Parameters / S1 / S2 / S3 / S4 / Standard
(SW)*
Date of collection / 2.03.05 / 2.03.05 / 2.03.05 / 2.03.05 / -
Temperatures (0C) / 30 / 30 / 31 / 30 / -
PH / 7.83 / 7.66 / 8.1 / 7.75 / 6.5-8.5
Colour 1/m / 19.4 / 21.2 / 13.6 / 16.5 / 10
Turbidity (NTU) / 108 / 120 / 82 / 96 / -
Conductivity (
Mho/cm) / 330 / 340 / 340 / 350 / -
Phenolphthalein Alkalinity (mg/l) / 65.93 / 5.96 / 4.12 / 10.17 / -
Total Alkalinity (mg/l) / 136.22 / 66.62 / 61.23 / 71.25 / -
DO (mg/l) / 5.46 / 4.49 / 4.89 / 5.66 / 6
BOD (mg/l) / 7.02 / 6.39 / 7.56 / 7.33 / 3
COD (mg/l) / 29 / 43 / 15 / 32 / -
Sulfate (mg/l) / 14.32 / 11.95 / 12.81 / 11.36 / 400
Hardness (mg/l)) / 219.52 / 104.22 / 96.36 / 189.74 / 300
Calcium (mg/l) / 25.14 / 27.6 / 21.85 / 24.3 / 80.10
Magnesium (mg/l) / 38.10 / 8.59 / 10.17 / 31.38 / 24.28
Phosphate (mg/l) / 0.017 / 0.015 / 0.011 / 0.021 / -
Chloride(mg/l) / 67.25 / 59.13 / 55.42 / 61.88 / 250

*SW : Surface water

Locations :

S1 : East side of the deghi (bathing ghat), Melarmath, Agartala.

S2 : North side of the deghi , Melarmath, Agartala.

S3 : South side of the deghi, Melarmath, Agartala.

S4 : West side of the deghi (bathing ghat), Melarmath, Agartala.

Table-3 BIO-MONITORING OF THE DEGHI ON THE NORTH OF

AGIYE CHALA SANGHA, MELARMATH, AGARTALA

Surface water source / Location / Temperature OC / Saprobic Score / Diversity Score / Biological water quality class / Biological water quality / Indicator colour
Air / Water
Deghi / Melarmath, on the north of Agiye Chala Sangha / 33 / 30 / 5.15 / 0.61 / C / Moderate pollution / Green

OBSERVATION

A.Physico-chemical Parameters

The observation and graphical representations of physico-chemical characteristics of collected water samples are given in table-2 & figs 1-4.

From the table-2 a significant observation comes out in respect of Dissolved Oxygen (DO) and Biochemical Oxygen Demand (BOD) of the water samples. It was found that the DO values were below the standard limit (BIS: 6 mg/l) and the BOD values were higher than the standard limit (BIS: 3 mg/l).

From the table-2 it was observed that the magnesium value of two water samples (S1 & S4) were slightly higher than the standard limit (BIS: 24.28 mg/l)

From the table-2 it was also observed that the values of colour were higher than the prescribed standard limit (BIS : 10 1/m).

Rest of the parameters like temperature, pH, turbidity, conductivity, alkalinity, sulphate, hardness, calcium, magnecium, phosphate, chloride etc. were found below the permissible limit of the surface water.

Note:

  • If DO is above standard value (6 mg/l) the water quality is good.
  • If BOD is more than 3 mg/l the water quality is bad.
  • If COD is high then the water quality is bad.

B.Biological Parameters :

Results of Bio-Monitoring were shown in table-3. From the table it was observed that the Saprobic Score and Diversity Score are 5.15 & 0.61 respectively. This indicate that the water quality of the Deghi is moderately polluted.

Conclusion

From the Observation of Physico-chemical Parameters and Biological Parameters it is concluded that the water quality of the Deghi is not suitable for drinking and bathing puroposes due to high Biological Oxygen Demand and less Dissolved Oxygen content.

Tripura State Pollution Control Board 1