56
R. Chettri et al.
is hardly used for drinking purpose. Brief description of the water quality of these
sacred lakes has been discussed in the following sections.
4 Results and Discussion
As already mentioned, water of these six sacred lakes is not used for drinking or
irrigation purpose. However, in order to assess the state of purity or level of pollution, their water chemistry has been analysed and interpreted through comparison
with the BIS (1991) and WHO (2014) standards for drinking water. Most of the
hydrochemical parameters in these six sacred lakes are found to vary within the
acceptable/permissible limits of BIS and WHO standards/guidelines for drinking
water. However, variation could be found in the lake water chemistry. The pH of the
water is found to vary between 6.4 and 7.2, which is more or less within the permissible limit. However, concentration of DO and DO 5 is found to be relatively low in
two out of six lakes, particularly in the Khechiopalri and Lamapokhari lakes. While
Khechiopalri is one of the most sacred lakes in Sikkim, Lamapokhari lake is used
mostly for social and aesthetic purposes such as boating. Surprisingly, the DO and
DO 5 values are found to be much higher in the water of Kupup lake and Gurudrongmar lake, in spite of their higher elevation (Kupup: 3983 m; Gurudrongmar:
5300 m). Among other parameters, only TDS is found to be high and comparatively
higher in Khecheopalri lake and Kathok lake, both of which are extensively used for
religious purpose. Comparatively higher concentrations of carbonate and bicarbonate
are also found in samples from Khecheopalri lake (Table 1).
The Hill–Piper diagram (Piper 1944) [6] shows that water samples of all the six
lakes have high concentrations (60 to 80%) of Ca, moderate concentration (30 to
50%) of Mg and lower concentrations (20 to 40%) of Na and K (Fig. 8). In most
of the samples, chloride and sulphate are found to be low to moderate (20 to 40%),
and concentrations of carbonate and bicarbonates are relatively much higher (60 to
80%). Combined water-chemistry statistics of the six lakes is presented further for
better understanding (Table 2).
A statistical analysis (correlation) has further revealed strong or very strong
(positive or negative) association between certain chemical parameters and weak
or moderate association between other parameters (Table 3). For example, pH values
are correlated inversely with K, Mg, SO 4 and PO 4 but positively with DO and DO 5
and their associations are strong. Dissolved oxygen is found to display inverse relationship with all other parameters, and the inverse relation is strongest with PO 4 . On
the contrary, TDS shows positive correlation with most of the parameters, which is
significantly strong with Na, Ca, Cl, HCO 3 and PO 4 . Among the ions, Na, Cl, HCO 3
and PO 4 are strongly correlated with each other and the correlation is positive. Mg
is strongly correlated with K and SO 4 . Correlation of Ca is positive with HCO 3 but
negative with SO 4 . Again, SO 4 shows strong positive correlation with PO 4 and strong
negative correlation with HCO 3 .
R. Chettri et al.
is hardly used for drinking purpose. Brief description of the water quality of these
sacred lakes has been discussed in the following sections.
4 Results and Discussion
As already mentioned, water of these six sacred lakes is not used for drinking or
irrigation purpose. However, in order to assess the state of purity or level of pollution, their water chemistry has been analysed and interpreted through comparison
with the BIS (1991) and WHO (2014) standards for drinking water. Most of the
hydrochemical parameters in these six sacred lakes are found to vary within the
acceptable/permissible limits of BIS and WHO standards/guidelines for drinking
water. However, variation could be found in the lake water chemistry. The pH of the
water is found to vary between 6.4 and 7.2, which is more or less within the permissible limit. However, concentration of DO and DO 5 is found to be relatively low in
two out of six lakes, particularly in the Khechiopalri and Lamapokhari lakes. While
Khechiopalri is one of the most sacred lakes in Sikkim, Lamapokhari lake is used
mostly for social and aesthetic purposes such as boating. Surprisingly, the DO and
DO 5 values are found to be much higher in the water of Kupup lake and Gurudrongmar lake, in spite of their higher elevation (Kupup: 3983 m; Gurudrongmar:
5300 m). Among other parameters, only TDS is found to be high and comparatively
higher in Khecheopalri lake and Kathok lake, both of which are extensively used for
religious purpose. Comparatively higher concentrations of carbonate and bicarbonate
are also found in samples from Khecheopalri lake (Table 1).
The Hill–Piper diagram (Piper 1944) [6] shows that water samples of all the six
lakes have high concentrations (60 to 80%) of Ca, moderate concentration (30 to
50%) of Mg and lower concentrations (20 to 40%) of Na and K (Fig. 8). In most
of the samples, chloride and sulphate are found to be low to moderate (20 to 40%),
and concentrations of carbonate and bicarbonates are relatively much higher (60 to
80%). Combined water-chemistry statistics of the six lakes is presented further for
better understanding (Table 2).
A statistical analysis (correlation) has further revealed strong or very strong
(positive or negative) association between certain chemical parameters and weak
or moderate association between other parameters (Table 3). For example, pH values
are correlated inversely with K, Mg, SO 4 and PO 4 but positively with DO and DO 5
and their associations are strong. Dissolved oxygen is found to display inverse relationship with all other parameters, and the inverse relation is strongest with PO 4 . On
the contrary, TDS shows positive correlation with most of the parameters, which is
significantly strong with Na, Ca, Cl, HCO 3 and PO 4 . Among the ions, Na, Cl, HCO 3
and PO 4 are strongly correlated with each other and the correlation is positive. Mg
is strongly correlated with K and SO 4 . Correlation of Ca is positive with HCO 3 but
negative with SO 4 . Again, SO 4 shows strong positive correlation with PO 4 and strong
negative correlation with HCO 3 .