WATER QUALITY ANALYSIS OF THE BAGMATI RIVER, KATHMANDU, NEPAL

The Bagmati River is a precipitation-fed river that encompasses a 650 km² watershed located in the Kathmandu Valley, Nepal’s largest and most populated urban area. The purpose of this project was to evaluate the relative importance of natural versus anthropogenic sources of solutes found in the river water. Samples were collected during the monsoon season (time of maximum flow), along a transect extending from the headwaters of the Bagmati River near Sundarijal downstream to Chobhar located 5 km downstream of the population center. A second sample transect was conducted along the Seti River in Pokhara, Nepal. Samples were processed and initially analyzed within 1-5 days of collection at Tribuhvan University, Center Department for Environmental Science. Additional analyses were run on samples returned to the Smith College Center for Aqueous Biogeochemistry Research. Samples were analyzed for dissolved organic (DOC) and inorganic carbon (DIC), trace metals (As, Pb, Fe, Ba, Al, Mn), major base cations (Ca⁺², Mg⁺², Na⁺, K⁺) and anions (Cl^-, SO₄^-2, NO₃^-, F^-).

In the Bagmati River, most solute concentrations (As, Ca⁺, Na⁺, F^-, SiO₂, K⁺, Cl^-, SO₄ ^-2) increased downstream toward the center of population, then decreased after the center of urbanization was passed. At the center, only Mn and Fe had concentrations above the U.S. EPA’s Maximum Contaminant Level (MCL). Low concentrations of Ca, Na, and Mg at the upstream sites reflect minimal weathering of the resistant underlying gneiss that outcrops in the headwater regions. Downstream, lacustrine clays minimize groundwater additions to the river.

In the Seti River the concentrations of all solutes except calcium are lower than those found in the Bagmati. There are no urban areas within the Seti River watershed and the high calcium concentrations can be directly attributed to the presence of limestone in the underlying bedrock A comparison of the chemistry of these two rivers shows that the urbanized areas within the Kathmandu Valley are having a significant impact on the chemistry of the Bagmati River.