Estimation of Lacustrine Groundwater Discharge (LGD) to an urban Himalayan lake using environmental tracers (222Rn, δ18O, EC)

Abstract

Lacustrine Groundwater Discharge (LGD) is a complex process that controls lake characteristics and plays a dominant role in modifying the hydrological and chemical budget of a lake. The current study was carried out with the aim to assess the groundwater discharge component of the hydrological budget of an urban Himalayan lake. We used natural tracers including radioisotope of radon (222Rn), stable water isotopes (δ2H and δ18O), electrical conductivity and water temperature to identify the potential groundwater discharge zones in a lake. The obtained LGD results, based on radon mass balance model (RMB) and end member mixing analysis (EMMA) of stable water isotopes in combination with physical parameters, show temporal as well as spatial variation. The total LGD to the Dal Lake, estimated from RMB, was 62.25 ± 9 × 104 m3/d (24 ± 3 %) and 33 ± 6 × 104 m3/d (36 ± 4 %) during high and low flow periods, respectively. The results suggested that the stream water is the dominant contributor accounting for 75 % (±7) and 55 % (±8), followed by groundwater as 22 % (±5) and 40 % (±4), during high and low flow periods, respectively. However, the contribution from direct precipitation is very little (3–4 %). High groundwater flux towards northeastern side of the lake is substantiated by more aquifer thickness and high hydraulic gradient. The current study offers first in-depth understanding about LGD of an urban Himalayan lake and could be applicable for lake ecosystem protection policies and water resource management plans in the region and elsewhere.