CASE STUDIES           

ABSTRACT:

Wetlands are dynamic ecosystems, continually undergoing natural changes due to infilling with sediments and nutrients, subsidence, rise in sea level, etc. They sustain all life and perform some useful functions in the maintenance of overall balance of nature. Rapid urbanisation, burgeoning human population and their various activities have contributed to the decline of quality and quantity of wetlands. Hence, it is imperative to focus on preservation of these endangered habitats to achieve ecological sustainability. This study was undertaken to identify and analyze the qualitative and quantitative impact of urbanization on wetlands. Various physico-chemical and biological parameters were analyzed and a socio-economic survey was done in Rachenahalli and Amruthalli lakes to find out the pollution load and level of dependency on these lakes. In order to conserve and preserve these lakes, Geographical Information System (GIS) was used for spatial and temporal assessment, which helped in identifying and monitoring the impacts due to point and non-point source (NPS) of pollution. Remote sensing technology was used as a monitoring tool for basin management. The spatial and temporal changes in the surface water bodies are mapped using Survey of India-topographical maps and remote sensing data. Integration of water quality and quantity with socio-economic information has aided in appropriate prediction and conservation of these two lakes from point and non-point source of pollution. The results were compared with Indian Standard Specifications (NEERI) and Rachenahalli lake was found less polluted while Amruthalli lake had attained eutrophic condition.

INTRODUCTION:

Wetlands are transitional zones between land and water, a collective term for marshes, swamps, bogs and similar areas. They have been described as the “kidneys” of the landscape as they filter sediments and nutrients from surface water. Wetlands are often referred to as “biological supermarkets” because they support all life forms through extensive food webs and biodiversity (Mitsch and Gosselink, 1993). They help regulate water levels within watersheds, improve water quality, reduce flood and storm damages, provide habitat for important fish and wildlife, support hunting, fishing, other recreational activities and perform some useful functions in the maintenance of ecological balance.

Dense human population in catchments, urbanisation, and various anthropogenic activities has resulted in over exploitation of wetland resources, leading to degradation in their quality and quantity. Now, there is increasing concern to conserve and restore perishing wetlands and endangered habitats to achieve ecological sustainability.

SIGNIFICANCE OF WETLANDS:

Wetlands are among the most productive ecosystems. They directly or indirectly support millions of people and provide goods and services to them. They support important processes like the movement of water into streams and oceans; decay of organic matter; release of nitrogen, sulfur, and carbon into the atmosphere; removal of nutrients, sediment and organic matter from water moving into the wetland; and the growth and development of all organisms dependent on them. The direct benefits of wetlands are in the form of fish, agriculture, fuelwood, recreation and water supply, etc. and their indirect benefits arise from functions occurring with in the ecosystem such as flood control, ground water recharge and storm protection. The mere existence of wetlands may have great significance to some people, as they are a part of their cultural heritage. Water is required for various purposes like drinking and personal hygiene, fisheries, agriculture, navigation, industrial production, hydropower generation and recreation. Apart from these, some socio-economic values also accrue through water supply, fuel wood, medicinal plants, livestock grazing, tourism, etc. 

WETLAND LOSS AND DEGRADATION:

Wetlands are dynamic ecosystems and are estimated to occupy 8 million km² (6.4 %) of the earth’s surface with about 5 million km² in the tropics and sub-tropics. The major proportion is made up of bogs (30%), fens (26%), swamps (20%) and floodplains (15%). This estimation was compared with the area that existed in the 19^th century and it was found that around 50% of the world’s wetlands have disappeared during  the last century. The impact on wetlands may be grouped in to five main categories: loss of wetland area, changes to water regime, changes in water quality, overexploitation of wetland products and introduction of exotic or alien species. The primary factors causing degradation are sedimentation, eutrophication, pesticide pollution, salinity, heavy metal pollution, weed infestation, low dissolved oxygen and pH (UNEP, 1994).

STATUS OF WETLANDS IN BANGALORE:

Bangalore has many artificial wetlands, built for various hydrological purposes and mainly to serve the needs of irrigated agriculture. Wetlands of Bangalore occupy about 4.8% of the city's geographical area (640 sq. km) covering both urban and non-urban areas (Krishna M.B et al., 1996).  The number of these lakes has fallen from 262 (in 1960) to 81 (in 1985). The quality of water has reduced due to discharge of industrial effluents and domestic sewage (Deepa, et al, 1998). Conversion of wetlands for residential, agricultural and industrial purposes has engulfed many lakes. More than 28% of lakes suffer from various degrees of eutrophication (Krishna, et. al., 1996). Earlier investigations also revealed that between 1973 and 1996, sewage was the main source of pollution for nearly 40% of the lakes, while 13% of the lakes suffered from surrounding slums and loss of catchment affected nearly 35% (Deepa and Ramachandra, T. V., 1999).

BJECTIVES:

The main objectives of the study were to:

§         Identify the status of wetlands based on qualitative and quantitative impacts due to urbanisation and various anthropogenic activities.

§         To assess the level of dependency on the lakes.

§         Explore suitable restoration and conservation strategies based on pollution level.

STUDY AREA:

Bangalore district is located in the heart of south Deccan plateau of Peninsular India. It is situated in the south-eastern corner of Karnataka State (12^o39^’ – 13^o18^’ N latitude and 77^o22^’ – 77^o52^’ E longitude) with a geographical area of about 2,191 sq. km at an average elevation of 900 m above mean sea level. The climate of the district is salubrious with temperature ranging from mean maximum of 36^o C in April to mean minimum of 11^o C in January. The present study areas, Amruthalli and Rachenahalli lakes, are located in Bangalore North taluk.

METHODOLOGY:

The present study entailed sampling and analysing the lake water quality, and socio-economic survey of the lakes and spatio-temporal changes investigations using GIS.

The main purpose of sampling is to determine the quality of water in its natural state. Grab samples were taken at 15 days interval at various inlets, outlets and center of the lakes. Totally, four samples were taken from each lake each time using Polyethylene container (pec) and labeled as sample 1, sample 2, sample 3 and sample 4.

Physical and chemical aspects of water is required to assess and determine the quality to ascertain their suitability for various purposes like drinking, industrial processing, agricultural usage, recreation and so on.

PHYSICO-CHEMICAL PARAMETERS

Physical parameters analysed were colour, temperature, transparency, conductivity, pH, total solids, dissolved solids and suspended solids.

Chemical parameters analysed were alkalinity, acidity, dissolved oxygen, chlorides, sulphate, total hardness, calcium, magnesium, iron, sodium, potassium, nitrates and phosphates.

FIELD MEASUREMENTS

The parameters that were analysed during sampling were colour, temperature, pH and transparency.

The analysis of the lake water was done as per the standard methods of NEERI (Ramteke, and Moghi, 1988) and American Public Health Association (APHA). Color was measured using visual comparison method; temperature was determined using Mercury thermometer; pH was measured using a pH meter; electrical conductivity using a conductivity meter; total solids, total suspended solids, and total dissolved solids were determined using Gravimetric method; and dissolved oxygen was estimated using the Winkler’s method.   Sodium and potassium were analysed by using flame-photometer.  Alkalinity and acidity were determined by titration method prescribed by NEERI. Total hardness, calcium and magnesium, were determined using EDTA titration method; chlorides using Argentometric method; sulphates using turbidimetric method using Spectrophotometer at 420 nm; nitrates using Phenol Di sulfonic Acid method using Spectrophotometer at 410 nm and phosphates, was determined using Ammonium Molybdate method using Spectrophotometer at 690 nm.

Socio-economy survey was conducted

§         To quantify the value of wetland resources ; and

§         To determine the economic dependency of the people living in the surrounding areas on these lakes

Approximate valuation of wetland resources based on its use values (human interactions with the wetland resources) and non-use values (no interactions with the wetland resources) were determined by conducting interviews with local communities (Edward B Barbier, et. al, 1997). A random survey of the houses around the lake was carried out using a standard questionnaire format designed for this purpose. Totally five areas were selected in this regard, namely Amruthalli around Amruthalli lake; Rachenahalli, Mestripalya, Srirampura and Dasarahalli around Rachenahalli lake. The valuation of wetland products was done using market prices method and contingent valuation method. This assessed the requirements of the local community and their economic dependency on the wetlands.

Bathymetric analysis was carried out to find the depth profile, which was done by dividing the lake in to different segments as transects. The depth at various points is found by using plumb bob or a rope tied to a stone at one end and a measuring tape. Volume of the lake can be computed with the depth and area data.

Geographic Information System (GIS) is a computer-based tool for mapping and analysing by integrating common data base operations. It is a powerful tool for collecting, storing, analyzing and displaying the information layers of data. GIS is used for spatial and temporal assessment, which helps in identifying and monitoring the impacts, due to anthropogenic stress, etc. The spatial and temporal changes in the surface water bodies are mapped using Survey of India 1:50,000 scale, topographical maps. Remote sensing is used as a monitoring tool for basin management. The SOI 1:50,000 scale, toposheet number 57 G/12 is used for topographical information, for collecting field data (ground control points) and for the preparation of base maps. Topographical information and field data were converted to digital format. This information along with remote sensing data helped in generating various thematic layers. These layers were overlaid using Mapinfo 5.5 to generate final layers to assess the spatial and temporal changes.  Integration of thematic layers of water quality and quantity along with socio-economic, land use and population information provide information on the current status and socio economic aspects of the wetlands.

RESULTS DISCUSSION AND SUGGESTIONS

CHARACTERISTICS OF WATER:

Tables 1 and 2 show the characteristics of water in Rachenahalli and Amruthalli lakes respectively.

Results of the analysis show that dissolved oxygen ranges from 2.3 to 8.2 mg/l in Rachenahalli lake and nil values in Amruthalli lake; alkalinity ranges from 135 to 175 mg/l and 175 to 355 mg/l; total hardness ranges from 136 to 278 and 185 to 392 mg/l; total suspended solids range from 6 to 92 and 31.4 to 150 mg/l; concentration of total phosphorous ranges from 0.0065 to 0.0429 and 0.09 to 0.28 mg/l and nitrate nitrogen concentration ranges from 0.10 to 0.333 and 0.204 to 0.488 mg/l in Rachenahalli and Amruthalli lakes respectively.

The results revealed that Rachenahalli lake is moderately polluted by nutrients, alkalinity and hardness, whereas Amruthalli lake is heavily polluted by nutrients resulting in weed infestation, oxygen deficiency, odour, suspended solids, alkalinity and hardness, and has attained eutrophic condition, as a result of urbanization and various anthropogenic activities in the surrounding area.

The economic dependency of the people residing closer to wetlands is shown in Table 3. The valuation of Rachenahalli and Amruthalli lakes is shown in Table 4. The values are expressed in Rupees. The economic valuation is done to assess the dependency on wetlands. In the case of Rachenahalli lake, the economic dependency of the area for irrigation and its products is about Rs. 9173.0 per day, during cropping season, while Amruthalli lake has no agriculture value on account of eutrophication and lack of water during summer.

The economic dependency of communities for fuel in Rachenahalli lake area is around Rs. 325 per day, while for Amruthalli lake it is about Rs.13 per day. The economic dependency of the communities for fish in Rachenahalli lake is about Rs. 900 per day during fishing season, while Amruthalli lake has no fish yield due to oxygen deficiency, light  (transparency) and temperature. The economic dependency for livestock in the Rachenahalli lake area is about Rs.37 per day and in the Amruthalli lake, it is about Rs. 7 per day. The eutrophic status of the lake has made the wetland resource unusable. These results show that, the economic dependency in the case of Rachenahalli lake (Rs. 10,435) is more than that of Amruthalli lake (Rs. 20) due to better water quality and ecosystem.

The ground water table in  Rachenahalli lake catchment area ranges from 50 ft in the immediate vicinity and 250 ft at farther places (2-3 kms), while the ground water table ranges from 180 – 400 ft in Amruthalli lake catchment. This is mainly due to sediments accumulated in lake bed which has become impervious hindering recharging. Sediment accumulation is due to siltation, which is a result of removal of vegetative cover in the catchment area. Apart from this, waste disposal in lake has resulted in eutrophic condition of the lake as a consequence of urbanisation and industrialisation.

Bathymetric analysis confirmed sediment accumulation resulting in reduction in depth and area (reduced considerably during last two decades). Water spread area has also declined due to encroachment of peripheral areas for agricultural purposes, settlements, construction of roads and institutions, etc.

Integration of  information through GIS provides the decision-makers a powerful tool for collecting, storing, analysing and displaying the information layers of data. Integration of spatial, demographic, water quality and quantity along with socio-economic information has aided in arriving at appropriate restoration and conservation strategies for Rachenahalli and Amruthalli lake waters. Some of the Best Management Practices (BMPs) suggested in managing and restoring wetlands include the following:

§         Pollution prevention practices can be applied to reduce the generation of non-point and point source pollution (from industrial, residential, agricultural and institutional areas) through source reduction, waste minimization and process control.

§         Afforestation with native species in desolate areas around the wetland to control the entry of silt from run off.

§         The shorelines of the lakes, lined with bricks or stones and/or pieces of concrete in an attempt to control shoreline erosion.

§         Constructed wetlands are recommended for the purpose of stormwater management and pollutant removal from the surface water flows.

§         Infiltration trenches would be useful in reducing the storm water sediment loads to downstream wetlands by temporarily storing the runoff.

§         Extended detention basins are required for removing pollutants primarily through the settling of suspended solids.

§         Promoting public awareness programmes regarding proper use and disposal of household and agricultural hazardous waste materials.

§         Prevention of encroachments through legal actions and public participation.

Apart from these, some of the restoration methods like desiltation, aeration, harvesting of macrophytes and prevention of pollution by waste water treatment (methods like screening, aerated lagoon and constructed wetlands) are also suggested to improve the catchment conditions and the quality of water (Chatrath, 1992)

CONCLUSION:

The following conclusions could be arrived at based on the analysis carried out during the study period.

§         Physico-chemical analysis showed that, Amruthalli lake was polluted severely by phosphate (0.28 mg/l), weed infestations, oxygen deficiency (less than 2 mg/l), odour, suspended solids (150 mg/l), alkalinity (355 mg/l) and hardness (392 mg/l) from sewage, waste water through storm water drainage and industrial effluents.

§         The socio-economic survey showed that the economic dependency in the case of Rachenahalli lake (Rs.10, 435) is more than that of Amruthalli lake (Rs. 20) due to better water quality.

§         The socio economic investigations reveal that people are very much dependent on water bodies to meet their day to day requirements for fuel, food and fodder.

§         Water spread areas of both the lakes have been considerably reduced during last two decades, due to sedimentation and encroachments for developmental activities.

§         Eutrophic condition is seen in Amruthalli lake due to excessive input of nutrients and organic matter resulting from sewage, storm water drainage, industrial effluents and dumping of organic waste materials from the surrounding areas.

Hence, there is an immediate need to restore, conserve and preserve these existing wetlands to maintain and improve the ecological balance. Best Management Practices (BMPs) are suggested in managing and restoring wetlands. Restored wetlands could be used for recreational purposes such as boating and fishing; and for agricultural purposes on condition that care is taken to prevent point and non-point source of pollution that drain in to these wetlands.

REFERENCES:

Abbassi, S.A, 1997, Wetlands Of India –Status of Wetlands in India, Ecology and Threats, Volume I, Discovery Publishing House, New Delhi. pp.84-86.

Chatrath, K.J.S, 1992, Wetlands Of India – Major threats faced by wetlands of India and their conservative measures, Ashish Publication House, New Delhi.pp.22-32.

Deepa, R. S, Kiran, R, and Ramachandra, T. V (1997), Status of Wetlands in Bangalore - An Overview was presented at the International Seminar on Ecorestoration, Biodiversity Conservation and Sustainable Development", organized by the Environmental Research Academy, Vishakapatnam and International Socio-Environmental Awareness Studies Bangalore, held at Bangalore during December 1997.

Deepa, R.S., Ramachandra, T.V. and Kiran, R. (1998), Anthropogenic stress on Wetlands of Bangalore, in proceedings of the National seminar on " Environmental Pollution: Causes & Remedies ", P. E. S. Institute of Technology, Bangalore, pp: 166-182.

Deepa, R. S, and Ramachandra, T. V. (1999), Impact of Urbanisation in the interconnectivity of wetlands, in proceedings of the National Symposium on Remote Sensing Applications for Natural Resources: Retrospective and perspective, (Jan 19-21, 1999) organized by Indian Society of Remote Sensing, Bangalore, pp. 343-351.

Edward B Barbier, Mike Acreman and Duncan Knowler, 1997, Economic Valuation of Wetlands, A Guide for Policy Makers and Planners, IUCN Publication Unit, Ramsar Convention Bureau Gland, Switzerland. pp 1- 46, 81- 97 and 110- 127.

Krishna, M.B, Chakrapani, B.K and Srinivasa, T.S, 1996, Water Birds and Wetlands of Bangalore, Karnataka State Forest Department, Bangalore, pp 4- 10, 17- 25, 42 –43 & 49- 57.

Mitsch, W. J, and Gosselink, J. G, 1993, Wetlands. Van Nostrand Reinhold, New York.

Ramteke, D.S and Moghi, C.A, 1988, Manual On Water And Wastewater Analysis, National Environmental Engineering Research Institute (NEERI), Nehru Marg, Nagpur.

United Nations Environmental Programme, UNEP, 1994, The Pollution of Lakes And Reservoirs, Environmental Library NO.12, Nairobi, Kenya. pp 9-33.

TABLE 1: RACHENAHALLI LAKE WATER QUALITY RESULTS

TABLE 2: AMRUTHALLI LAKE WATER QUALITY RESULTS

Table 3: Socio-economic details:

TABLE 4:  VALUATION OF RACHENAHALLI AND AMRUTHALLI LAKES