Hydrogeochemical and socio-hydrogeological assessment of the Inle Lake catchment (Southern Shan State Myanmar)

Since 2013, the Earth and Environmental Sciences Department of Pavia University has been conducting an educational and research project in collaboration with the University of Mandalay (Myanmar), the second largest University in Myanmar. The project was initially funded through the Erasmus Mundus PANACEA program, and has continued thanks to Erasmus+ International Credit Mobility KA107 funds and CICOPS scholarships.
The study area of this project is the Inle lake (Southern Shan, Myanmar). This area is characterized by the presence of several water-dependent anthropic activities (e.g. fishery, hydroponic farming, floating markets), and it is experiencing an increasing development of tourism activities. All these activities are exerting pressure on the catchment area and contributing to the gradual reduction of the lake's surface and depth.

The overall goal of the project is to investigate the causes of this phenomenon with geo-pedological and hydrochemical analyses, whose results have already given rise to joint several publications. The main results can be summarized as follow:

• Lake waters are dominated by carbonate equilibria, are fully flushed yearly and are not stratified. The short residence time prevent the accumulation of contaminants and nutrients in lake waters (Thin et al., 2016). The high resilience of the lake to external perturbations is due to calcite precipitation, that represents an effective mechanism of P removal, combined to the low residence time of water (Re et al., 2018).

• Groundwater in the Inle lake catchment is of Mg(Ca)-HCO₃ facies. A deep groundwater circulation, in equilibrium with the dolomitic rocks of the basement, upwells in the Northern part of the basin, and contributes to Inle lake by mixing with local recharge in the aquifer and by feeding the network of artificial channels created for reclamation purposes (Re et al., 2018). 

• The Khaung Daing Hot Spring  belongs to another type of deep groundwater circulation, has a temperature of about 70°C and is of Na-HCO₃ facies (Sacchi et., 2017). It is fed by local groundwater and equilibrated with the carbonate rocks. It contains some As at high concentrations, raising some concern about potential environmental and health effects (Sacchi et al., 2017).

• Inle lake sediments identify the increased soil and bedrock erosion as a major anthropogenic impact to the lake. The sedimentation disturbance is especially evident at the main inflow, the Nanlit stream. Soil erosion is a source for Potentially Toxic Elements (As, Cr, Cu, Ni, Pb, and Zn) accumulating in the sediments at concentrations sometimes exceeding the probable effect concentrations (Thin et al., 2020a). Elevated P contents in the lake sediments show a distribution pointing to an increased anthropogenic input. Two different sources are identified: the agricultural input in the floating gardens area and the detrital input related to soil erosion (Thin et al., 2020b).

During 2017, a socio-hydrogeological assessment was also initiated. In this context, in order to understand the needs of local populations and assess the environmental impacts on their well-being, stakeholder engagement activities have been set up with meetings with civil society representatives and structured interviews regarding the use of water in the various economic sectors and wastewater management. This activity was carried out during a field mission in 2018 and the data are being processed.