Rajinikanth. R. and Ramachandra. T.V. *
Centre for Ecological Sciences, Indian Institute of Science Bangalore 560 012, India

RESULTS AND DISCUSSION

Table 1 shows the characteristics of Rachenahalli Lake water quality; and Table 2 shows the characteristics of Amruthalli   Lake Water quality.

 

Figure 1. and Figure 2. gives an idea about the water quality parameters value variation during different set of cycles in Rachenahalli and Amruthalli lakes respectively.

Fig.1. Rachenahalli lake water charecterstic variations during bio-monthly sampling

Fig.2. Amurthahalli lake water charecterstic variations during bio-monthly sampling

The analysis results shows that the 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 in Rachenahalli and Amruthalli lakes respectively, Total hardness ranges from 136 to 278 and 185 to 392 mg/l in Rachenahalli and Amruthalli lakes respectively, the Total suspended solids ranges from 6 mg/l to 92 mg/l in Rachenahalli lake and 31.4 to 150 mg/l in Amruthalli lake,the concentration of total phosphorous ranges from 0.0065mg/l to 0.0429 mg/l in Rachenahalli and 0.09 mg/l to 0.28 mg/l in Amruthalli lake and the Nitrate nitrogen concentration ranges from 0.10 mg/l to 0.333-mg/l and 0.204 mg/l to 0.488 mg/l in Rachenahalli and Amruthalli lakes respectively.

These results were compared with Indian Standard Specifications (NEERI) and Water quality datas of Sankey tank in Bangalore, collected during this period and that of Rachenahalli lake is slightly polluted by the parameters like nutrients, alkalinity and hardness, whereas Amruthalli lake is heavily polluted by nutrients, weed infestations, oxygen deficiency, odour, suspended solids, alkalinity and hardness, and has attained the eutrophic condition, as a results of urbanisation and various anthropogenic activities in the surrounding area.

Table 3 shows the economic dependency of the people residing closer to wetlands. The values are expressed in Rupees. Table 4 shows the valuation of Rachenahalli and Amruthalli lakes.

 

The economic valuation is done to assess the dependency on wetlands. In the case of Rachenahalli lake by surrounding villages is estimated to be about Rs. 10,435/day ( during cropping and fishing season) and Amruthalli lake is about Rs.20.0/day. This shows that, the economic dependency in the case of Rachenahalli lake is more than that of people living around the Amruthalli lake due to better water quality and ecosystem. The ground water table of Rachenahalli lake ranges from 50 ft in the immediate vicinity and 250 ft at farther places (2-3 kms), while surrounding region of Amruthalli lake ground water table ranges from 180 - 400 ft. This is mainly due to, sediments accumulated in lake bed has become impervious which hinders 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 consequence of urbanisation and industrialisation.

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