DISCUSSION

Residents residing in the catchment of Varthur lake for nearly 30 years to more than 200 years and at least 60% of the families persist for over 100 years². It plays a significant role in providing daily requirements for the local inhabitants such as for domestic use of water, irrigation, fuel and fodder for livestock; while undergoing the stress sequentially due to anthropogenic activities. Higher values of BOD, COD, Nitrates and Phosphates reveal that lake water is severely contaminated. DO of lake was quite low (1.06 ppm) in inlet mainly due to increased inflow of organic material through untreated sewage. DO decreases due to presence of inorganic reducing agents such as Hydrogen sulphide (H₂S), ammonia, nitrites and certain oxidizable substances²¹.  Profuse growth of macrophytes mainly water hyacinth, limits air water interface, light penetration and consequently there is a drop in the penetration of atmospheric oxygen as well as algal photosynthetic activities. This maximizes the probability of hypoxic and anoxic conditions in the lake making difficult for survival of aquatic organisms in the water. Higher values of alkalinity show the presence of more carbonates, bicarbonates and hydroxyl ions. Water quality analysis of Varthur during 2002 also reported similar conditions of low dissolved oxygen, alkaline pH and high nutrient inputs (Nitrates, phosphates and Ammonia). Varthur contains significant amounts of the macronutrients in large quantities in order to grow and survive aquatic plants under higher concentrations of nitrates and phosphate. Elevated amount of nutrients mainly fortify the contamination of water with sewage and non-point sources -fertilizers². Amplified water quality degradation observed when current status was compared with that of past study (as listed in table 5), explaining due to the sustained and enhanced inflow of contaminants over time.
Calculation: Rs. 9554000/220 ha /year
                        = Rs. 43427.28/ha/year
                        = Rs. 118.978/ha/day

Table 5: Comparison of major water quality parameters of Varthur (2003 and 2009)

(Source: Ramachandra et al., 2003 and current survey)

Water pollution

Varthur Wetland receives 450-500 MLD of sewage from households and industrial wastewater directly into wetland from Bellandur and surrounding localities. These contribute enriched nutrients and increased amount of toxic substances (heavy metals). Enhanced land cover changes have contributed to siltation and consequent sedimentation decreasing lake’s depth. The degree of soil saturation of the wetland depends on the consistency of its freshwater flow. Effluents loading have gone beyond the ability to assimilate contaminants, further degrading the quality water. Along with effluents form households and industrial waste, household garbage, plastics and solid waste from commercial places are being dumped in lake bed.

Valuation of ecosystem highlights that due to the severe contamination of water the wetland’s goods and services has declined impinging livelihood of dependent population and also local economy. Even though residing community is dependent on lake for manifold use as mentioned in Table 3 at the same time many problems are faced by the wetland for being beneficial. The total economic value of varthur resources accounts to Rs 95, 54,000/220 ha/year (ie. Rs. 118.98/ha/day), which is much lower compared to a relatively unpolluted lake (Rs 10,450/ha/day) ³. The dependency value on wetland water for domestic and agricultural use is maximum compared to other use values.

Causes of depreciation in lake values

Dumping of garbage and other non-degradable waste materials, inflow of untreated sewage from the residential areas and open defecation are the problems accountable for water quality. Such substances liberate toxic in to the water body; remains suspended; gets dissolved in water or set down on the water bed contributing to groundwater pollution. This majorly deteriorates water quality impinging on aquatic ecosystems. Few effects of these environments are discussed:

• Utilization of contaminated lake water for irrigation purposes has a negative effect on the quality as well as the quantity of crops and this has influenced the major source of income for farmers reliant on agriculture.
• Possibility of contaminants especially heavy metals getting to food chain through fish (which accumulates higher concentrations of heavy metals- bioaccumulation²²).
• Dumping of municipal solid waste in the lake catchment and letting untreated sewage and effluents into lake has affected the health of the local population due to increase of disease vectors and pathogens (mosquito -Plasmodium sp. causing Malaria) and flies population around Varthur region. Current survey also reports health problems like fever, dysentery and skin diseases (dermatitis) in most of the houses. Due to mosquito problem and health hazards, residents spend more than 30,000 per year in purchase of mosquito repellants (according to survey). Incidence of bacterium Escherica coli in water sample indicates the fecal matter contaminates3. Fecal contamination is often associated with other types of pathogenic bacteria and viruses found in untreated sewage and survives for a prolonged period in turbid, warm temperature, mildly alkaline pH, and low oxygen levels in lake water.
• Profuse growth of exotic plant species such as water hyacinth (Eichornia crassipes) and exotic fish culture have also contributed to extinction of native species of fauna. Prolific macrophytes growth has roofed water surface completely lessening dissolved oxygen level and hindered photosynthesis process. Algal communities depending on photosynthetic activity have declined together with mortality of sensitive life stages inside water. Disturbance in food chain may also lead to changes in algal community and its metabolism.
• Poaching of waterfowl such as Purple moorhen (Gallinula chloropus), Spot billed Pelican (Pelecanus philippensis), Common coot (Fulica atra) and White breasted waterhen (Amaurornis phoenicurus)  by poachers were observed, resulting in its decline.

Dominant fish species reported in 1962, 1998 and 2009 are listed in table 6. Clarias batrachus, Heteropneustes fosslis, Mystus dittatus and so on which once contributed substantially to fish community in earlier years has dwindled in their representation in the catches now. The invasive species currently harboring water body are Catla catla (Catla), Labeo rohita (Rohu), Cirrhinus mrigala (Mrigal), Clarias gariepinus (African catfish), Oreochromis mossambica (Tilapia) and medium sized carps. Enhanced sewage and effluents inflow coupled with the overexploitation of wetland goods are prime reasons for the decline in indigenous fish species and consequent prevalence of invasive species during the last two decades.

Table 6: List of major fish species in Varthur wetland during 1962, 1998 and 2009

(Source: current survey. “+” indicates presence and “-“  indicates absence of fish species.)

Comparative analysis of polluted and unpolluted wetlands reveals difference in fish composition and associated economic value.  Varthur lake harbors only Clarias gariepinus (African catfish), whereas Catla catla (Catla), Labeo rohita (Rohu), Cirrhinus mrigala (Mrigal) and Oreochromis mossambica (Tilapia) were found in Rachenahalli while another eutrophic lake at Amruthahalli did not have any species. Varthur and Amruthahalli being eutrophicated with heavy sewage contamination and Rachenahalli is relatively unpolluted. Invasive exotic species, African catfish in Varthur water body has predated native fish and survive under eutrophic condition with the macrophytes covering the entire lake. Subsequently, huge amount of waste along with metals and ions (toxic substances) are accumulated inside fish gut due to bioaccumulation²³.  Consumption of fish rich in heavy metals has carcinogenic influence on humans. Accordingtofishermen, varthur provides 200-300 kg/day of catfish costing Rs. 50-60 /kg/day due to absence of fish variety while Rachenahalli accounts for Rs. 75 /kg/day specified by varieties of fishes mentioned above⁹. Economic value of Fish in Varthur is less than in Rachenahhali mainly because of exotic species and decline of native species, water accomplished with sewage and prolific macrophytes growth in Varthur.

The socio economic studies on Rachenahalli and Amruthalli lake showed that the economic dependency in the case of Rachenahalli lake (Rs. 10,435/ha/day) which is more than that of polluted Amruthalli lake (Rs. 20/ha/day). This is mainly because of better water quality in former lake while water quality with severe pollution by phosphates, weed infestations and oxygen deficiency in later case. Although in Varthur, Sorahumase and Valepura village, the land irrigated by utilizing the wetland water amounts to 4211.6/day with water quality indicating eutrophic lake containing high concentrations of organic wastes and phosphorus².

Management of wetlands to sustain goods and services

This study highlights the need to manage the wetlands to enhance the use value of an ecosystem. The strategies shall include

• Restoration of wetlands – removal of contaminants
• Letting only treated sewage to the wetlands
• Letting the treated water through series of wetlands further improves the water quality
• Maintaining food chain in the ecosystem – involves removal of excess growth of macrophytes (if any) and exotic fish species, African cat fish, etc.
• Regular water quality monitoring involving local schools. This would also help in functioning as watchdog to prevent any contamination (solid waste dump, direct inflow of sewage, etc.)