After reading this article you will learn about the impact of effluents from a chemical factory on the water quality. Also learn about its restoration.
Water is one of the foremost essential requirements for human beings. It is essentially required by all living organisms. The total water stock is fortunately most plentiful but the fresh waters on which man and other terrestrial organisms depend are only about 2.5% of the total water stock.
In different places and different seasons the quantity of water changes from abundant to scarce levels.
Expanding human populations, industrial and agricultural growth, higher living standards have affected water resource in two main ways:
(i) Over consumption of water, and
(ii) Release of impure waste water causing wide spread pollution of lakes, rivers, ground water etc.
Fresh water of a reasonable cleanliness standard is required to meet the needs of drinking and domestic consumption while for irrigation, fisheries and industrial needs the cleanliness standards are much lower. Municipal sewage and industrial effluents are the two most important sources of toxic chemicals of degrading the water quality and turning the elixir of life into a harmful source of toxic chemicals and numerous disease causing organisms. Therefore, it is very important to check this menace of pollution.
The present paper mainly concerns the deterioration of water quality, phytoplankton diversity, primary production and nutrient accumulation in Rihand reservoir under the impact of a chemical factory effluents. The restorative strategies have also been evolved based on the harvesting capacity of the nutrients and heavy metals by the phytoplankton and amphibious vegetation.
The research work has been carried out on the corridor of Rihand reservoir in Renukoot region, Sonbhadra district of Uttar Pradesh in North India (22° 45′-24° 38′ N lat. and 82° 30′-83° 32′ E long). The River Rihand, a subtributory of River Ganga, originates in the hilly tracts in the south of the Madhya Pradesh State and flows towards north in the State of Uttar Pradesh (Fig. 1). At Renukoot in U.P., the Rihand reservoir has been created through the river damming, for water storage, irrigation, fish culture and hydroelectric power generation. The river further flows down and joins river Son which in turn joins river Ganga.
Three sampling points:
(i) Stream water (effluent free zone),
(ii) Effluent water itself,
(iii) Confluence of reservoir water and stream water, and
(iv) Effluent diluted downstream, 1 km away from the confluence zone, were selected to assess the impact of chemical effluents on the hydrobiology of River Reservoir.
The physicochemical properties of water and sediment of the Rihand river was studied at monthly intervals from January to December, 1988. The analyses of different physicochemical properties was made using the methods described in Standard Methods. Analysis of heavy metal was performed with the help of Atomic Absorption Spectrophotometer.
Phytoplankton density, diversity and primary production were estimated by number counts, Shannon Weiner index and light and dark bottle methods, respectively. Nutrient accumulation (N, P, K) in plants was analysed using the methods as described by Jackson Statistical analyses of the data were made using statistical programmes.
Results and Discussion:
The temperature variation was between 18.2°C to 31.5°C and the trend was similar at all the sites. Effluent temperature was always higher in the range 0.5°C to 1.5°C than that of the receiving water. The highest temperature was observed in the summer followed by the rainy season and least in the winter season (Fig. 2). The variation of temperature was significant (p < 0.005) between sites and months.
The pH was near neutral (6.8-7.6) at the stream site, slightly alkaline (7.2-8.3) at the affected site and more alkaline (7.2-9.0) in the effluent itself. In the summer season, the pH was towards alkaline than in the other two seasons which may be due to the reduced water level in the reservoir, whereas the mount of effluent discharged remain the same.
It varied significantly (p < 0.005) between sites and months. Electrical conductance did not show the constant trend, however, effluent water contained relatively higher (200-400 M-S cm-1) electrical conductance than in the river water (95-125 (µS cm-1). Total solids were higher in the effluent water (400-1000 mgl-1) in which greater contribution was due to the presence of more than 60% of suspended solids.
The transparency of the affected site water was lower than that of the stream site due to the high amount of suspended and dissolved materials. Seasonally, it was lower in the rainy season due to the increased input as surface runoff. Higher amount of total solids reduced the transparency and growth of primary producers in the affected water.
The dissolved oxygen, NO3—N and PO4—P were always higher at the stream site followed by the affected water, confluence water and least in the effluent water (Fig. 3). Downstream and confluence site waters have much lower oxygen concentration which was mainly attributed with maximum dissolution of organic matter.
Effluent water had quite high (1500-2800 mgl-1) chloride concentration due to the fact that the factory manufacturing hydrochloric acid, caustic soda, BHC and bleaching powder, consequently the concentration of chloride got increased significantly (p < 0.05) in the confluence and affected waters (Table. 1).
Heavy metal concentration was within the permissible limit (Table. 2). However, Fe concentration was slightly higher than the other elements studied and Cu was found below the detection limit. These elements were in the order of Cd > Cr > Ni > Pb > Fe.
The trend of variation in the pH was similar to that of water quality, having higher values at the upstream site. Electrical conductance in the effluent sediment was 2 to 3 times higher than in the upstream sediment (Fig. 4) and consequently increased the cation anion exchange in effluent affected sediments.
The peak value at the stream site was noticed in the summer at the upstream site, while in the effluent water it was higher in the rainy season and lower in the summer, which was mainly associated with the dilution effect of the rains. Total nitrogen and available phosphorus concentrations were significantly (p < 0.005) higher at the upstream site.
Effluent affected sediments has caused depletion in the nutrient elements. Seasonally, the values were higher in the rainy season at the stream site however; at the downstream site it was higher in summer (Fig. 5). Higher nutrient availability is responsible for a better plant growth and primary production.
The concentration of heavy metals was relatively higher in sediment than that of in water, however, iron was found to be exceptionally high in the effluent (2565 µg/g) followed by the confluence (1754 µg/g) and downstream (1348.7 µg/g). The presence of such a high concentration of Fe in the effluent and in downstream sediment was mainly due to the discharge of iron rich ash slurry (6-8%) through the rusted and poor/degraded quality of iron pipes.
Phytoplankton genera belonging to chlorophyta, Bacillariophyta and Cyanophyta at the stream site were recorded. These were totally absent in the effluent and confluence waters while some of them reappear at the far away affected site. At the Stream site, Chlorophyta dominated with Chlorococdum and Spirogyra while Bacillariophyta dominated with Navicula and Pinnularia at the downstream site.
The effluent appears to be enough toxic to allow any phytoplankton growth, but at the affected site some of them reappear due to the dilution of the effluent. Total phytoplankton density at the stream site was 2650 Unit 1-1, from which the contribution of Chlorophyta was 1200 Unit 1-1, Bacillariophyta 800 Unit 1-1 and Cyanophyta 400 (Fig. 6).
However, at the affected site, total phytoplankton density was (1885 Unit 1_1) among which maximum of 1000 Unit 1-1 contribution was due to the member of Bacillariophyta followed by Chlorophyta (600 Unit l-1) and minimum by Cyanophyta (250 Unit 1 -1).
Seasonally, the density at the upstream site was summer > rainy > winter, while at the diluted site it was rainy > winter > summer (Fig. 6). This inverse relationship was obviously due to the dilution of the effluent at the affected site. Higher density of the phytoplankton was associated with higher dissolved oxygen and nutrient concentration in the water.
In contrast, lower phytoplankton density in rainy and early winter season was due to the increase in water level, higher suspended materials, lower light penetration and high water current. Stepwise multiple regression equation showed that at the stream site phosphate-P explained 29% variability (p < 0.05) in the Chlorophyta density and chloride showed for a 27% (p < 0.05) change in Bacillariophyta density. At the diluted site, pH explained 36% (p < 0.05) change in the density of Chlorophyta and total phytoplankton (Table. 3).
The Shannon index (H’) varied from 2.94 to 3.77 with the mean of 3.45 at the stream site and from 2.52 to 3.34 (mean 3.02) at the diluted site (Table 4). Seasonally, the values were higher in summer followed by the winter and least in rainy seasons. A higher diversity index with a narrow range shows greater stability and capability to resist the adversities of the environment in a better way. Patrick have also reported a lower diversity in the polluted condition and higher diversity in unpolluted condition.
The index of dominance was inversely related to the Shannon index, it varied from 0.07 to 0.16 with a mean of 0.09 at the stream site and 0.09 to 0.18 (mean 0.14) at the diluted site. Species richness was directly proportional to the Shannon index which was higher at the stream site (4.44 to 5.18) than at the diluted site (2.39 to 4.65).
Primary productivity of the fresh water ecosystems gives quantitative information about the nutritional relationship to the successive trophic level organisms. At the stream site, the gross and net primary productivity were high (35 to 125 mg cm– hr-1 for GPP and 25 to 85 mg cm-3 hr-1 for NPP), however at the downstream site, it varied from 30 to 60 mg cm hr-1 for GPP and 15 to 45 mg cm-3 hr-1 for NPP/Fig. 7).
Higher production at the stream site was largely due to the higher concentration of NO3—N and PO4P of the water and sediment. Statistically, it was found that NO3—N and PO4—P and CI individually as well as in combination, significantly (p < 0.05) influence the gross (GPP) and net (NPP) primary productivity (Table. 3).
Marginal Wetland Vegetation:
Standing crop biomass and the relative share of component species and rate of production are of prime importance in structural and functional characterization of any ecosystem. Biomass and energy per unit area was highest in rainy season followed by winter and least in summer obviously due to higher soil moisture and nutrient availability to the marginal wetlands (Fig. 8). Hot temperature and low soil moisture contents prevailing during summer have retarded the growth of the species. Singh and Singh have observed similar findings in grassland and riparian communities, respectively.
During rainy season, peak of the community aboveground biomass reached earlier (August) in comparison to below ground (September) in both the upstream and downstream study stands. The difference in the peak biomass periodicity is mainly due to time lag in the production of photosynthetic in aboveground parts and their translocation to below ground parts.
The vegetation in the marginal wetland community normally has a greater nutrient concentration than the submerged and free floating macrophytes. They have probably higher nutrients retention capacity from the soil water. It was estimated that in the upstream marginal community the accumulation of N, P and Ca were relatively higher in upstream than in the downstream, however K and Na showed the reverse trend (Fig. 9).
It was probably due to a high potassium and sodium concentration in the downstream sediments. Dykyjova has reported the similar trends of observations of Reed Swamp in Czechoslovakia. The potassium concentration decreased gradually up to maturity stage which may be due to translocation to the belowground parts.
The chemical composition of the plant species is also affected by the nutrient content which varies from species to species. It is because of varying genetic set up of the species which require different amount of chemical constituent for metabolic activities. Boyd also confirmed that elemental composition of individual wetland species may vary greatly between site to site.
The marginal species especially Polygonum amphibium and Ammannia baccifera accumulated quite high iron content (>1000 ppm) from the stream bed, however Bacopa monnieri and Alternanthera sessilis uptake other metal elements in moderate concentration. It has also been observed that Cu has some suppressive influence on the Fe uptake rate. Similar observations have also been reported. Such interactions are more common between nutrients and of similar size, charge and electronic configuration. It has been well realised that Cu toxicity had antagonistic influence to the Fe concentration.
The impact of effluent discharged on the receiving water body significantly (p < 0.05) altered the physicochemical properties of water and sediments, and distinct reduction in phytoplankton density, diversity and primary productivity at the effluent affected zone were clearly indicated. Among the marginal species Ammannia baccifera L., and Polygonum amphibium L. accumulated quite high Fe (>1000 ppm) into their component parts and thus purify the river water by harvesting the excess pollutants from the river bed to a certain extent.
Other species like Bacopa monnieri, Alternanthera sessilis had moderate concentrations of Cu, Fe, Ni and Pb. Hence these plants are also identified as moderate harvester of the above mentioned nutrients and heavy metals. The results could be possibly used in the restorative strategies like introduction of pollution tolerant diatoms and biological harvesting of pollutants especially heavy metals.