Assessing the Napo Karst Formation vulnerability in the Western Amazon River Basin

Karst environments are susceptible to contamination and directly affected by anthropogenic pressures. Remediation efforts are expensive, time-consuming, and often impractical. Hence, vulnerability maps can be valuable tools for protecting and preventing the aquifer’s degradation. This study aims to evaluate the vulnerability of the Napo Karst Formation (NKF), in the western Amazon basin in Ecuador, using three vulnerability models: EPIK, DRASTIC, and DRASTIC-LUC. The difference between the three models lies in the parameters used and how each one of them address the vulnerability. Because assigning values to each parameter depends on the author's expertise and the available data, these models can produce varying outcomes, which we analyze using spatial and sensitivity analysis. Our results showed that DRASTIC and EPIK classified 45.76% and 35.38% of the NKF area as highly vulnerable, respectively, while DRASTIC-LUC classified most of the NKF areas under moderate vulnerability (57.47%). The sensitivity analysis determined that the depth to water table (D) and the infiltration conditions (I) were the most critical parameters for the vulnerability assessment. The moderate-to-high vulnerability of the NKF raises a warning, as the impacts on surface and groundwater may affect local populations that directly depend on its water. This is the first study that evaluates the vulnerability to the contamination of karst formation in the Ecuadorian Amazon. The results of this research can be used as a baseline for future research and as technical information for decision-makers to reduce the activities that could aggravate surface and groundwater quality in Western Amazonia.