Hydrogeological and Morphological Characterization of Río Cuarto Maar Lake in Costa Rica: An analysis of lake geometry, water balance and groundwater interaction

Sammanfattning

Volcanic crater lakes are important freshwater systems, but their hydrological functioning is often difficult to understand due to limited monitoring data and uncertainty in groundwater contribution. Río Cuarto Lake, located in the north part of Costa Rica, is a volcanic crater lake where the sources and movement of water are not fully known. This master’s thesis aimed to describe the lake’s morphology, water balance and water quality conditions and investigate if available hydrological and chemical observations could indicate interaction between groundwater and the lake. The study methodology combined field measurements and spatial analysis to develop an overall understanding of the lake system. Bathymetric data was collected using sonar and GPS and used in GIS analysis to estimate depth, area and volume of the lake. A conceptual water balance was developed by using precipitation, evaporation, inflow and recharge estimates based on meteorological data and the Schosinsky soil water balance method. Water samples were collected from different depths and analysed in both field and laboratory to examine differences in water quality in the water column and to identify potential indicators of groundwater influence. The results showed that Río Cuarto Lake has a steep-sided basin with a deep central area and stable stratification in the water column. Differences in water chemistry between surface and deeper water layers, together with the imbalance observed in the water balance calculations suggest that additional water sources besides direct rainfall and surface inflow could contribute to the lake system. However, uncertainties related to catchment area, simplified modelling assumptions and limited monitoring data limit the ability to prove groundwater interaction in the lake. Overall, the study provides new baseline information on the hydrology and water quality of Río Cuarto Lake and highlights the importance of continued monitoring and improved hydrological measurements for understanding lake behaviour in volcanic environments over the long haul.