Groundwater-surface water interactions in a volcanic maar lake (Hule maar, Costa Rica)

Description

These data include stable isotopes of carbon and water, radon-222 in water, hydrochemistry, and weather data. This study was carried out at Lake Hule, a volcanic lake in northern Costa Rica, and aimed to better understand the interactions between groundwater and surface water. Our results showed little difference in evaporation-to-inflow ratios between dry (December-April) and wet (May-November) seasons. Groundwater, precipitation, and runoff contributed ~61.3%, 24.4%, and 14.3% of total inflow to the lake, respectively. We found that carbonate buffering also played a key role in the lake chemistry, with greater carbon dioxide degassing from groundwater sources in the wet season. This study provides insight into groundwater-surface water interactions in Central America's volcanic front.

Steps to reproduce

Water samples of Lake Hule, springs, and streams were collected between March 2022 and September 2023. A passive collector was installed (Palmex Ltd., Croatia; Gröning et al., 2012) in July 2022 above the caldera wall on the east side of Lake Hule (Latitude: 10.2951°, Longitude: -84.2033°, 875 m asl) to manually collect on every rainy day in the morning (7-8 am) precipitation samples from July 2022 to September 2023. To better characterize the groundwater system in the lake basin, we collected water samples from three springs, namely Pata Gallo (982 m asl), Rio Cuarto (651 m asl), and Crucero (617 m asl). Samples were collected manually every week in the periods of March-October 2022 and March-September 2023. Water samples of streams, namely Maria Aguilar river (736 m asl), Sardinal river (453 m asl), Hule river (418 m asl), and Rio Cuarto river (417 m asl) were collected during sampling campaigns in March 2022, March 2023, and September 2023 . At Lake Hule, samples were also collected in March 2022, March 2023, and September 2023 at five sites located along a transect in the west-east direction (N=39, Figure 1). Lake samples were collected (~ 1 m below the surface) and bottom samples (in the last 1 m of the water column and as close as possible to the lake floor). The depth at which lake bottom samples were collected was in the range of 10-20 m. Water samples were collected using a 2.2 L Niskin bottle sampler (Wildco, USA). The stable isotope composition of lake, springs, streams, and precipitation samples was analyzed by CRDS spectroscopy (L2140-i, Picarro, USA). The stable isotope composition of dissolved inorganic carbon (δ13CDIC) and total alkalinity of filtered aliquots (0.45μm PTFE) were also analyzed by CRDS spectroscopy (G2201-i, Picarro, USA). Ion chromatography (Thermo Scientific ICS-5000+, CA, USA) was used to analyze ammonium, sodium, potassium, magnesium, calcium, chloride, nitrite, nitrate, and sulfate. The radon-222 activity was measured in lake, groundwater, and stream water samples using a RAD7 detector (Durridge Co., USA). Hourly meteorological variables (relative humidity, air temperature, solar radiation, wind speed and direction, and precipitation amount) were recorded at 2 m height using a Vantage Pro2 weather station (Davis Instruments, USA), which was installed next to the precipitation collector.

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