The limnology of “Swetganga” — A thermal spring of Bakreswar, West Bengal, India

Summary

The results of the limnological investigations of “Swetganga”, one of the thermal springs of Bakreswar, West Bengal, India, have formed the basis of this paper. The samples of water were collected eleven times from the month of September '67 to October '68 at regular intervals for analysis. The physical conditions like depth, temperature and chemical factors like pH, free carbon dioxide, phenolphthalein alkalinity, total alkalinity, total hardness, chloride, nitrite, nitrate, phosphate, silicate and dissolved oxygen were determined. A qualitative and quantitative analysis of plankton was also made.

The water of the Kund was found to be distinctly alkaline on all occasions. Since free carbon dioxide was absent in all samples, phenolphthalein alkalinity was always recorded in appreciable quantities.

The lower values of chloride were noted only during the monsoon months due to the dilution of water by the rain. The silicate content showed erratic fluctuations. Large amounts of phosphate were always present in the Kund. The absence of nitrite and traces of nitrate throughout, is a characteristic feature of this thermal spring.

An attempt has been made, whenever possible, to attribute the reason of the changes and also to correlate the plankton blooms with the chemical factors. The coefficient of correlation between total alkalinity and phytoplankton (−0.529) indicates a negative correlation, significant at the 10 per cent level. No significant relation between phytoplankton and pH values (r = 0.183) has been observed. An apparent inverse relation between dissolved oxygen and phytoplankton has been noted.

A list of phytoplankton and zooplankton has been incorporated. Total phytoplankton varied between 8.91 per cent and 100 per cent and the zooplankton between nil and 91.08 per cent of the total plankton bulk.