A detailed analytical study of the physico-chemical parameters of melt water draining from glaciers of Langtang Valley with an elevation ranging from 1395 m a s l to 4200 m a s l in Rasuwa district, Nepal was carried out in order to study the seasonal and altitudinal variation in hydro-chemistry along the Langtang River and glacial melts from the Lirung and the Khimsung Glaciers. The study was carried out during 6 - 10 April and 30 June-3 July, 2014 at 11 sites. A total of 22 composite samples were collected. The concentration of cations and anions of the Langtang Valley were found in the order Ca 2+ > K + > Na + > Mg 2+ and , respectively. Significant seasonal variation in electrical conductivity (EC), turbidity, dissolved oxygen (DO), calcium (Ca), sodium (Na), magnesium (Mg), chloride (Cl), sulphate (SO4) and total phosphorus (TP-PO4) and altitudinal variation in EC, total dissolved solids (TDS), DO and Na was found out. The concentrations of the heavy metals (As, Al, Mn, Zn, Cd, Cr) were below the detection limit except Fe (0.5 to 18.1 mg/l), which was highly variable. Calcium carbonate weathering was found out to be the major source of dissolved ions in the region. The elemental ratios (Ca/Si and K/Na) were typical of glacial melt water and the low Na/Cl and K/Cl ratios indicated major contribution from atmospheric precipitation to the observed dissolved ions of melt waters. The study showed an increase in the concentration of cations as compared to previous studies, which could be attributed to increasing weathering rates due to temperature increase. Elevated concentration of NO3 and TP-PO4 compared to previous studies show the effect of human impact in the region. Differences in the melt water composition between the debris covered and clean type glacier was found out.
Glaciers form one of the components of the hydrological budget playing an important role in buffering stream flow [
Melt waters from mountain glaciers of the Himalayas are one of the dominant water resources for Nepal along with rainfall and ground water [
The study was carried out in the Langtang River basin which lies in the Langtang National Park, Nepal. It is a sub-basin of Ganges River basin and lies in between the longitudes 85˚15'E to 86˚E and latitude 28˚N to 28˚20'N. The Lirung Glacier is the fourth largest debris-covered glacier in this valley [
Water samples for the analysis of major cations (Ca, Mg, Na, K), major anions (HCO3, Cl, SO4, NO3, TP-PO4), heavy metals (Fe, As, Al, Mn, Zn, Cd, Cr) and total silica (Si) were sampled in Langtang region in pre-monsoon season (6-10 April 2014) and monsoon season (30 June-3 July 2014) at 11 sites. Therefore, a total of 22 composite samples were collected and analyzed for different parameters. The samples were collected, preserved and analyzed following standard procedures [
One way ANOVA and Mann Whitney tests were performed to find out the seasonal and altitudinal variations of the parameters using SPSS 15.0 and Rock Works 16 is used to create the Piper plot diagram [
The chemical characteristics of glacial melt waters draining from Langtang Valley are given in
Similarly, Mann Whitney test revealed a significant variation of TDS with respect to altitude (p < 0.05) with higher values in lower altitude ranging from 4 ppm (KO, July 2014) to 80.33 ppm (L6, April 2014); whereas turbidity showed a significant variation with season (p < 0.05) with higher values during monsoon. Decrease in TSS and turbidity with distance from glaciers was observed during pre-monsoon season, where they were higher
S.N. | Location | Sample Code | Altitude (m a s l) |
---|---|---|---|
1. | Khimsung Pond | KP | 4200 |
2. | Khimsung Outlet | KO | 4163 |
3. | Lirung Pond | LP | 3982 |
4. | Lirung Outlet | LO | 3883 |
5. | Point of contact between Lirung and Khimsung Glacier | LK | 3875 |
6. | Helambu Bridge (Langtang River before Kyanjing) | L1 | 3779 |
7. | DHM Station/Kyanjing Hydrostation | L2 | 3646 |
8. | Riverside | L3 | 2757 |
9. | Welcome Bridge (Before Bamboo) | L4 | 2143 |
10. | Tiwari, New Bridge (Before Syaphrubesi) | L5 | 1547 |
11. | Chilimi Hydropower (After Syaphrubesi) | L6 | 1395 |
Parameter | Max | Min | Average | SD |
---|---|---|---|---|
pH | 8.30 | 7.70 | 8.01 | 0.16 |
EC | 163.33 | 8.67 | 65.47 | 38.36 |
TDS | 80.33 | 4.00 | 27.45 | 15.99 |
DO | 11.43 | 7.70 | 9.60 | 1.10 |
Turbidity | 112.33 | 2.00 | 33.42 | 36.17 |
TSS | 584.00 | 18.00 | 141.18 | 145.37 |
Ca2+ | 25.70 | 2.24 | 10.77 | 5.53 |
Mg2+ | 4.46 | 0.25 | 1.64 | 1.27 |
Na+ | 5.30 | 0.50 | 1.89 | 1.26 |
K+ | 6.00 | 0.80 | 2.08 | 1.48 |
78.10 | 12.93 | 36.63 | 15.15 | |
38.40 | 6.36 | 18.01 | 7.45 | |
19.00 | 0.40 | 4.97 | 5.31 | |
Cl− | 12.00 | 5.00 | 8.24 | 2.26 |
7.50 | 1.46 | 3.06 | 1.67 | |
TP- | 0.80 | 0.05 | 0.29 | 0.24 |
Si | 13.10 | 1.80 | 5.14 | 2.98 |
Fe | 18.10 | 0.50 | 5.88 | 5.54 |
As | 0.01 | 0.01 | 0.01 | 0.00 |
Mn | 0.20 | 0.05 | 0.13 | 0.07 |
Zn | 0.10 | 0.06 | 0.08 | 0.03 |
Al | 0.20 | 0.05 | 0.11 | 0.07 |
Cd | 0.02 | 0.02 | 0.02 | 0.00 |
TZ+ | 1.48 | 0.41 | 0.81 | 0.29 |
TZ− | 1.42 | 0.73 | 0.99 | 0.21 |
near glaciers, with highest at the KO (24.67 NTU and 180 mg∙L−1, respectively) attributing to glacial silt, and lowest at L5 (4 NTU and 40 mg∙L−1, respectively).
The DO ranged from 7.7 mg∙L−1 (LP, April 2014) to 11.43 mg∙L−1 (L4, April 2014). One way ANOVA revealed a significant seasonal and altitudinal variation in DO (p < 0.05). DO was significantly higher during Monsoon and at lower altitudes. The decrease in DO during the pre-monsoon season is due to decrease in water levels resulting in less mixing of air with water [
The concentration of the major cations in the Langtang valley were found out in the order of Ca2+ > K+ > Na+ > Mg2+. Ca was significantly (p < 0.05) lower during monsoon season; whereas Na was significantly (p < 0.05) lower during monsoon season and at higher altitude. The dominance of the major anions in the Langtang valley was found out in the order of
Weathering of rocks is the dominant mechanism controlling the hydro-chemistry of drainage basins which occur when water flows at the ice-rock interface [
The piper plot diagram (
and anion respectively. The Pearson’s r value shows that calcium has positive significant (p < 0.05) relationship with bicarbonate. These results confirm that the calcium carbonate weathering is the major source of dissolved ions in the region. Correlations among the divalent cations and HCO3 probably reflect common geologic sources [
The elemental ratios of the Langtang Valley are given in the
The relative importance of two major proton producing reactions―carbonation and sulphide oxidation can be evaluated on the basis of the C-ratio (HCO3/HCO3 + SO4). The Carbon ratio is closer to 1, which indicates the significance of carbonation reaction involving acid hydrolysis and pure dissolution, consuming protons from atmospheric CO2 [
where (g), (1), (aq), and (s) denote gaseous, liquid, aqueous and solid phases respectively.
In general, concentration of major cations (particularly Ca), anions (NO3 and TP-PO4) and total silica showed an increasing trend (
Ca/Si | K/Na | Na/Cl | K/Cl | C ratio | |
---|---|---|---|---|---|
Average | 2.26 | 1.20 | 0.23 | 0.26 | 0.84 |
SD | 0.73 | 0.33 | 0.12 | 0.13 | 0.09 |
Min | 1.40 | 0.53 | 0.07 | 0.11 | 0.65 |
Max | 4.06 | 1.85 | 0.41 | 0.46 | 0.95 |
The NO3 and TP-PO4 concentration were higher in monsoon season than pre-monsoon. Nutrients, such as nitrogen and phosphorus, are supplied onto the glacier surface by dry and wet depositions [
The chemical characteristics of melt water draining from the Khimsung and Lirung glacier of Langtang valley are given in
Khimsung Glacier | Lirung Glacier | ||||||||
---|---|---|---|---|---|---|---|---|---|
Parameter | Unit | Max | Min | Average | SD | Max | Min | Average | SD |
pH | - | 8.60 | 7.50 | 7.90 | 0.29 | 8.50 | 7.70 | 8.07 | 0.22 |
EC | µS∙cm−1 | 45.00 | 8.00 | 25.08 | 14.76 | 79.00 | 20.00 | 51.67 | 28.09 |
TDS | ppm | 18.00 | 4.00 | 10.58 | 5.58 | 35.00 | 11.00 | 23.00 | 11.07 |
DO | mg/l | 9.50 | 8.40 | 8.82 | 0.37 | 9.80 | 7.21 | 8.76 | 1.02 |
Turbidity | NTU | 41.70 | 12.50 | 23.63 | 11.74 | 20.00 | 11.00 | 15.74 | 2.94 |
TSS | mg∙L−1 | 180.00 | 34.00 | 108.50 | 60.19 | 80.00 | 18.00 | 40.00 | 28.33 |
Ca2+ | mg∙L−1 | 9.20 | 2.24 | 5.66 | 3.45 | 15.50 | 2.40 | 8.66 | 6.85 |
Mg2+ | mg∙L−1 | 1.98 | 0.44 | 1.10 | 0.67 | 1.75 | 0.50 | 1.08 | 0.62 |
Na+ | mg∙L−1 | 0.80 | 0.50 | 0.68 | 0.15 | 2.00 | 0.60 | 1.25 | 0.70 |
K+ | mg∙L−1 | 1.40 | 0.80 | 1.03 | 0.26 | 2.60 | 0.80 | 1.58 | 0.83 |
mg∙L−1 | 36.60 | 12.93 | 24.89 | 13.53 | 29.30 | 18.79 | 24.11 | 6.00 | |
mg∙L−1 | 18.00 | 6.36 | 12.24 | 6.65 | 14.40 | 9.23 | 11.85 | 2.95 | |
mg∙L−1 | 5.00 | 0.40 | 2.45 | 2.40 | 19.00 | 1.20 | 7.65 | 8.39 | |
Cl− | mg∙L−1 | 11.00 | 5.00 | 8.50 | 2.65 | 12.00 | 7.00 | 9.25 | 2.63 |
mg∙L−1 | 2.60 | 2.30 | 2.45 | 0.21 | 7.50 | 3.40 | 5.45 | 2.90 | |
TP- | mg∙L−1 | 0.20 | 0.06 | 0.12 | 0.07 | 0.50 | 0.09 | 0.30 | 0.29 |
Si | mg∙L−1 | 4.00 | 1.80 | 2.60 | 1.22 | 9.30 | 2.50 | 4.65 | 3.18 |
Fe | mg∙L−1 | 5.20 | 3.00 | 4.05 | 1.22 | 7.20 | 2.20 | 3.88 | 2.27 |
Mn | mg∙L−1 | 0.06 | 0.05 | 0.06 | 0.01 | 0.08 | 0.08 | 0.08 | - |
Al | mg∙L−1 | 0.07 | 0.07 | 0.07 | - | 0.20 | 0.20 | 0.20 | - |
Hydro-chemistry of glacial melt waters of the Langtang Valley was studied. The alkaline nature of pH, high DO, variable TSS and Turbidity were seen typical of the headwaters. Calcium and bicarbonate ions were the dominant cation and anion respectively. Calcium carbonate weathering was the major source of dissolved ions in the region. There has been an increase in the concentration of cations from the past few years, which may be due to increase in chemical weathering due to temperature increase in the basin. Elevated concentration of nitrates and total phosphates are seen compared to previous studies, the effect of human impact in the region. The elemental ratios (Ca/Si and K/Na) were typical of glacial melt water and the low Na/Cl and K/Cl ratios indicated major contribution from atmospheric precipitation to the observed dissolved ions of melt waters. Carbonation reaction involving acid hydrolysis and pure dissolution, consuming protons from atmospheric CO2 were the main proton supplying geochemical reactions controlling the rock weathering in the study area. The average concentrations of most of the cations and anions were comparatively higher in Lirung Glacier than Khimsung Glacier.
We are very grateful to the Partnership for Enhanced Engagement in Research (PEER) Science Project funded by the United States Agency for International Development (USAID) through the National Science Foundation (NSF), USA for supporting this research. We are also thankful to the Department of National Park and Wild Life Conservation, GoN and all the members of Himalayan Cryosphere, Climate and Disaster Research Center, Kathmandu University for their kind cooperation while conducting this research.