Dal Lake - Environmental Issues

Environmental Issues

The lake is warm monomictic (mixing type) and the pH value recorded has varied from a minimum of 7.2 to a maximum of 8.8 on the surface over a yearly period. The Dissolved oxygen value has varied from a minimum of 1.4 to a maximum of 12.3 on the surface within a year. The Recorded maximum nitrogen concentration (NH₄-N has been recorded as 1315 on the surface and 22 at the bottom of the lake. Phosphorus concentration expressed in Total-P has varied from a high of 577 to a low of 35 during the 12 months of the year. The lake water temperature has varied from a minimum of 3 °C (37 °F) in January to 26 °C (79 °F) in June at the surface. Transparency, expressed as depth in metres, has varied from a maximum of 1.95 metres (6.4 ft) in July to a minimum of 0.53 metres (1.7 ft) in March, over the 12 months period.

Studies of the water quality of the lake in 1983–84 indicate a decline in quality since the 1965–66 analysis. Scientific research over the years also reveal that Telbal, Botkal, and sewage drains are responsible for a substantial influx of nitrogen and phosphorus into the lake. Quantitatively, fifteen drains and several other sources have released a total of 156.62 tonnes (56.36 tonnes by drains alone) of phosphorus, and 241.18 tonnes of inorganic nitrogen into the lake from a discharge of 11.701 million cubic metres /year. Non-point sources, such as seepage and diffused runoff, also add to this pollution and have been recorded as further adding 4.5 tonnes of total phosphates and 18.14 tonnes of nitrogen (NO₃–N and NH₄–N) to the lake. Based on the values mentioned above, it has been inferred that the water quality of the lake has deteriorated.

The major environmental problem facing the lake is eutrophication, which has required immediate remedial measures to combat it. Alarmingly, the size of the lake has shrunk from its original area of 22 square kilometres (8.5 sq mi) to the present area of 18 square kilometres (6.9 sq mi), and there is a concerning rate of sediment deposition due to catchment area degradation. The water quality has also deteriorated due to intense pollution caused by the untreated sewage and solid waste that is fed into the lake from the peripheral areas and from the settlements and houseboats. Besides, some experts like Dr. A.A. Kazmi (Associate Professor, IIT Roorkee and in charge of the Environmental Engineering Lab) believe that deforestation in the catchment of Dal Lake and Telbal stream may have led to more nitrogen and phosphorus-rich run-off, further aiding eutrophication. Encroachments of water channels and consequent clogging has diminished the circulation and inflows into the lake, so with the building up of phosphates and nitrogen, this has led to extensive weed growth and consequences on the biodiversity of the lake.