Sedimentation processes have negative socioeconomic and environmental consequences. The Compound-Specific Stable Isotopes (CSSI) technique allows for the evaluation of sediment inputs associated with different land use changes in a study region. In the present work, this technique was used in the Alhajuela Lake sub-basin, within the Panama Canal Watershed. The role of the main soil contributors to the landscape (land uses, river, runoff, slope) relevant to the sediment load within the sub-basin of Alhajuela Lake was evaluated, and the relevant indicators in the landscape were selected in order to obtain the best representative sample. The contribution levels of three (3) representative land uses (Forest, Pasture and Sediment) in the study area were evaluated for the sediments present in sixteen (16) selected mixing points. The samples collected were subjected to the standard laboratory process to obtain the carbon chain isotopic values present in the fatty acids. The results of the determinations of the carbon chain fatty acid isotope ratios were evaluated using a Bayesian mixing model that takes into account the uncertainty present in the identified source values. According to the results obtained, the source identified as Sediment has a prominent contribution in most of the mixing points. The contributions of Forest land use are important in the mixing points located north of the study area. The contributions associated with Pasture land use are relevant in the points located in the proximity of this land use. The results suggest that landslides caused by high rainfalls events (Forest and Pasture sources) cause strong sedimentation to the north of Alhajuela Lake. At the same time, a high distribution of soils deposition is observed in the area surrounding Alhajuela Lake due to the strong presence of soils with Sediment source in these places. The results obtained are consistent with observations and measurements of the sediments accumulated in Alhajuela Lake between the years 2008 and 2012.

Sedimentation processes have negative socioeconomic and environmental consequences, ranging from eutrophication phenomena, loss of water quality in surface water bodies, effects on the potential for hydroelectric generation, etc. Frequently, anthropic activity is the main cause that enhances these processes through changes in land use that can lead to landscape modifications. Therefore, it is relevant to evaluate this phenomenon and to be able to discriminate the influence of different land uses on the contributions to sediment loads at different scales. The novel Compound Specific Stable Isotopes technique allows the evaluation of sediment inputs associated with different land use changes in a study region. In the present work this technique was used in the Alhajuela Lake sub-basin, within the Panama Canal Watershed. The contribution levels of three (3) representative land uses (forest, pasture and sediment) in the study area were evaluated for the sediments present in sixteen (16) selected mixing points. The main contributions of the sources to the sediments present in the main rivers and tributaries flowing into Alhajuela Lake, in the sub-basin of the same name, were identified. The results obtained are consistent with observations and measurements of sedimentation in the study area.

Groundwater is critical for water security across the Central American Dry Corridor (CADC), particularly during recurrent El Niño-Southern Oscillation (ENSO) related droughts, yet the timescales over which regional aquifers may respond to climate variability remain poorly constrained. Here, we integrate precipitation stable isotopes, tritium, and complementary noble gas measurements to explore interannual hydroclimatic variability and groundwater recharge across the CADC. The high-resolution isotope Evaporation and Moisture Recycling Index (iEMI) shows that ENSO influences both precipitation amount and moisture provenance, with El Niño conditions generally associated with lower iEMI and greater evaporation-sourced moisture. Apparent groundwater ages ranged from 1.3 to 59.6 years (median 19.6 years), while modern recharge fractions ranged from 6.2 to 100% (median 53.7%), revealing widespread mixing of recent and decades-old recharge. Noble gases provide complementary evidence of contrasting groundwater mixing. Sub-atmospheric 3He/4He (R/Ra) ratios and low Ne/He in Honduras are consistent with continental ⁴He accumulation, whereas elevated R/Ra in Costa Rica reflects variable mantle-He inputs through a tectonically active multilayer volcanic aquifer system. Our results suggest that CADC groundwater vulnerability is influenced by ENSO cycles, hydraulic connectivity between multilayer aquifer systems, and predominant groundwater mixing. Aquifers dominated by modern recharge are potentially more vulnerable to short-term recharge deficits but may recover rapidly when wet conditions return. In contrast, older groundwater provides greater short-term climatic buffering but may recover more slowly from prolonged drought and sustained abstraction.

La implementación de programas locales de conservación de coberturas forestales en zonas de recarga hídrica y acuífera permite estudiar el ciclo hidrológico y su interacción con la vegetación y el suelo, en términos de cantidad y calidad del agua. Los objetivos de este estudio fueron: a) caracterizar la composición de la vegetación y suelo de tres sistemas de cobertura forestal (bosque, reforestación y plantación establecida), b) estimar los aportes de agua (escorrentía, percolación y evapotranspiración) y la generación de sedimentos de los tres sistemas de cobertura forestal en zona de recarga acuífera y c) evaluar escenarios de cambio de uso de suelo y sus implicaciones en la seguridad hídrica y la gestión de PSAH. Los resultados muestran que, bajo condiciones de conservación, los tres sistemas presentan patrones similares de percolación y evapotranspiración, favorecidos por suelos andisoles con alto contenido de materia orgánica. Sin embargo, los escenarios de cambio de uso de suelo hacia matorral, pradera y suelo desnudo evidencian incrementos sustanciales en la escorrentía superficial y en la generación de sedimentos, lo cual afectaría negativamente la calidad del agua destinada al consumo humano. Estos hallazgos resaltan la importancia de los esquemas de conservación, como el Pago por Servicios Ambientales Hídricos (PSAH), para la protección de zonas de recarga y la sostenibilidad del recurso hídrico en Costa Rica.