Preprints

URI permanente para esta colecciónhttp://10.0.96.45:4000/handle/11056/20514

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Tracer-aided modelling reveals quick runo generation and groundwater losses producing young stream ow ages in a tropical rainforest catchment
(2021-05-29) Mayer-Anhalt, Leia; Birkel, Christian; Sanchez-Murillo, Ricardo; Shulz, Stephan
There is still limited understanding of how waters mix, where waters come from and for how long they reside in tropical catchments. In this study, we used a tracer-aided model (TAM) and a gamma convolution integral model (GM) to assess runogeneration, mixing processes, water ages and transit times (TT) in the pristine humid tropical rainforest Quebrada Grandecatchment in central Costa Rica. Models are based on a four-year data record (2016 to 2019) of continuous hydrometric and stable isotope observations. Both models agreed on a young water component of fewer than 95 days in age for 75% of the study period. The streamow water ages ranged from around two months for wetter years (2017) and up to 9.5 months for drier (2019) years with a better agreement between the GM estimated TTs and TAM water ages for younger waters. Such short TTs and water ages result from high annual rainfall volumes even during drier years with 4,300 mm of annual precipitation (2019)indicating consistent quick near-surface runo generation with limited mixing of waters and a supra-regional groundwater ow of likely unmeasured older waters. The TAM in addition to the GM allowed simulating streamow (KGE > 0.78), suggesting an average groundwater contribution of less than 40% to streamow. The model parameter uncertainty was constrained in calibration using stable water isotopes (d2H), justifying the higher TAM model parameterization. We conclude that the multi-model analysis provided consistent water age estimates of a young water dominated catchment. This study represents an outlier compared to the globally predominant old water paradox, exhibiting a tropical rainforest catchment with higher new waterfractions than older water.
Tracing groundwater-surface water interactions in a volcanic maar lake using stable isotopes and radon-222
(Authorea (Nueva Jersey), 2024-05-08) Esquivel-Hernández, Germain; Montealegre-Viales, Emanuel; Sánchez-Gutiérrez, Rolando; Villalobos Forbes, Mario; Pérez-Salazar, Roy; Sánchez-Murillo, Ricardo; Mena-Rivera, Leonardo; Birkel, Christian; Ortega, Lucia
Abstract. Groundwater-surface water interactions are important in controlling lake water residence time, biogeochemistry, and water availability for downstream communities in tropical volcanic catchments. To better understand these complex seasonal interactions, a multi-tracer approach including water and inorganic carbon stable isotopes (δ2H, δ18O, δ13CDIC), hydrochemistry, and 222Rn was applied in Lake Hule, northern Costa Rica. Seasonal isotope mass balance calculations using lake, stream, precipitation, and groundwater isotope compositions were supplemented with local hydrometeorological information. Evaporation to inflow ratios (E/I) revealed a small variability between the dry (December-April) and wet seasons (May-November), with relatively low evaporation losses, 2.9±1.0 % and 3.2±1.8 %, respectively. Bayesian end-member analysis indicated that annual inputs from groundwater, precipitation, and runoff represented 61.3±8.1%, 24.4±8.4, and 14.3±5.9% of total inflow, respectively. Temporal variations of δ13CDIC also confirmed the key role carbonate buffering plays in this lake and indicated greater CO2 degassing from groundwater sources in the wet season. This first tracer-aided assessment in a volcanic lake maar of northern Costa Rica provides evidence of previously unknown groundwater-surface water interactions and poses a promising tool for estimating seasonal variability of groundwater discharge into natural lakes across the volcanic front of Central America.

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