[A-HW19] Tracer Hydrology: Advances in Measurement and Modelling

[AHW19-05] Investigating Mediterranean Wetland Catchment Hydrodynamics through Tracer Hydrology

*Angela Ruth Welham¹、Jared van Rooyen^1,2,3、Andrew Watson⁴、Alakendra Roychoudhury¹、Reynold Chow^5,1 (1.Department of Earth Sciences, Stellenbosch University, Western Cape, South Africa、2.Swiss Federal Institute of Aquatic Science and Technology (Eawag), 8600 Dübendorf, Switzerland、3.Hydrogeology, Department of Environmental Sciences, University of Basel - Basel, Switzerland、4.School for Climate Studies, Stellenbosch University, Western Cape, South Africa、5.Soil Physics and Land Management Group, Wageningen University, the Netherlands)

キーワード：Tritium , Noble Gases , Residence Time, Surface water, Wetland, Mediterranean

Wetland catchments that experience a Mediterranean climate have been identified as areas of concern (i.e., water quality, availability, and hydrodynamics) under the ever-growing anthropogenic and climatic pressures. Although the majority of these climates are located in southern Europe, Western Australia and Northern Africa, one such region exists in the Western Cape of South Africa. This semi-arid region is dependent on winter rainfalls to sustain domestic, industrial, and ecological water demands (e.g., in wetlands). During recent droughts, surface water resources were stressed to critical levels, fostering an increased dependence on groundwater resources. This pressure is exerted on both the hydrological system and ecosystem function, leading to water security issues. Sustainable water management in a perturbed hydrological system requires an understanding of the system's baseline functioning as well as the degree and rate at which the system is changing. Hydrological tracers have proven effective tools to constrain such behaviours in modified catchments that are affected by climate change. A tracer-based approach was applied to the highly modified Eerste River Catchment in the Western Cape, to assess the catchment’s recharge, transport and discharge dynamics that support the estuarine Macassar Wetland. Over time, wastewater treatment plant developments, informal/formal domains, and water diversion schemes have negatively impacted wetland health. In addition to a year of stable isotope monitoring, three sample campaigns were conducted during the dry and wet seasons in March, June, and September 2023. Shallow and deep aquifers were targeted for tritium (55 samples), tritium/helium age (4 sites) and dissolved noble gas (10 sites) analyses. Additionally, 5 surface water sites were sampled for dissolved noble gases. Tracer data effectively identified areas of recharge, lateral flow, and discharge of groundwaters. Furthermore, when simulated against localised lumped parameter models it enabled a revision of the catchment’s conceptual groundwater-surface water interaction mechanics as well as determining a residence time distribution between recharge and discharge information. The application of stable and radiogenic tracers as well as dissolved noble gases, provided insights transferable to analogous Mediterranean environments, promoting effective water resources management to support wetland health, particularly under forecasted drought episodes.