Imprints of long-range-transported pollution on high-altitude Eastern Himalayan lake water chemistry

摘要

Pangang Teng Tso Lake, located at an altitude of 3962 m in the Eastern Lesser Himalaya, was monitored for seasonal variation in hydrogeochemical processes, major ions and levels of trace elements to understand the imprints of long-range-transported contamination. Results revealed that major cations except Na decreased, whereas major anions except NO3- and PO43- increased in the post-monsoon. ANOVA indicated that pH, EC, TDS, Na ?, HCO3 -, Cl- and NO3-, PO43- showed significant seasonal variation in the P. T. Tso Lake. Wet precipitations of aerosols were found to be the most important source of major ions. Lake water chemistry is attributed to long-range transport of air pollutant through dry precipitation in the pre-monsoon, and by chemical weathering, biological and mineralization processes in post-monsoon. In pre-monsoon, trace elements were found to be in the order of Fe > Mn > Zn > Pb > Cu > Cr > Cd with slight change in Pb, Cd, Cr and Cu in post-monsoon. Hybrid Single-Particle Lagrangian Integrated Trajectory ( HYSPLIT) model developed by NOAA's Air Resources Laboratory was used to understand the long-range transport and depositions of aerosols. The results of HYSPLIT back-trajectory model illustrate that air arriving in the vicinity of the lake has an origin from the southeast direction and the mid-Gangetic plain during pre-monsoon and post-monsoon season, respectively. The interrelationship among trace elements in the projection of factor 1 and 2 implies that natural weathering and metal-containing aerosols transported from elsewhere may be the governing processes for lake water chemistry. The study suggests that seasonal changes in water chemistry of high-altitude lakes can reflect the imprints of change introduced through long-rangetransported pollution. Long-term monitoring programs are recommended for periodic evaluation of the high-altitude lakes worldwide in order to trace climate change impacts.