In wetlands terrains, impermeable clay layers are usually found above the sandy aquifer (s), it is neccessary to determine if the groundwater in the aquifer is recharged from vertical pentration of surfcae water or from lateral flow from a nearby (upper stream) region.
The isotopic composition of groundwater (expressed as abundance of oxygen-18 and deuterium) is determined by the isotopic composition of recharge.If most of the recharge is derived from direct infiltration of precipitation, the groundwater will reflect the isotopic composition of that precipitation. However, if most of the recharge is derived from surface water (rivers or lakes) instead of from precipitation, the groundwater will reflect the mean isotopic composition of the contributing river or lake.
This isotopic composition is expected to be measurably different from that of local precipitation. The difference arises from the fact that recharge via bank filtration may represent water originating from precipitation in a distant area, for instance in a high mountain region. In high mountain regions the isotopic content of precipitation is different to that of precipitation falling on plains.
This difference in isotopic composition allows for differentiation of precipitation sources, and hence of recharge mechanisms. In addition to differences in isotopic composition of groundwater resulting from different recharge sources, there can be differences due to how recently recharge occurred. In hydrological settings in which groundwater is very old (>10 000 years), regional climatic conditions at the time of recharge may have been different from those existing today, and this is reflected in the isotope composition of the groundwater.
https://www.iaea.org/About/Policy/GC/GC55/GC55InfDocuments/English/gc55inf-5-att3_en.pdf
https://www.researchgate.net/publication/7912760_A_groundwater_separation_study_in_boreal_wetland_terrain_The_WATFLOOD_hy
Article A groundwater separation study in boreal wetland terrain: Th...
Dear Zhonghe,
Waters with diferent origings (i.e. generated by precipitation events with different vapour source such as the Atlantic and the Mediterranean) have different finger print. Nevertheless, even having waters with the same vapor source origin, the water isotopic finger print also depends on the processes afecting the recharging water (e.g. recharge from a evaporated water surface body or direct recharge from precipitation). If you know the finger print of the different water sources recharging your aquifer you could express the water isotopic content of the aquifer as a combination of the different water sources, using the isotopic content as if it was an ordinary tracer (e.g. chloride).
I hope it helps.
Dear Dr. Zhonghe,
It's as simple as expressed by Dr. Jorge above and more in details by Dr. Ebrahimi previously. You just have to measure the isotopic signature of each end-member in your system (wetland) as well as that of precipitation. Applying the mass conservation equation you would become able to compute the percentage of recharge from any component (end-member) that might contribute to recharge of your groundwater anywhere within your studied aquifer. Chloride being a conservative tracer, you could also use it in combination with isotopes (plotted vs. O-18 for instance) to assess in depth what could be happening within your system.
All the best...
I think Monitoring stable water isotopes (18O and 2H) in precipitation and surface water in the basin is important to study the complex hydrology of wetlands and have the contributions of estimates of groundwater. In any case a hydrological model is used. In this case It's possible to using the isotopic (e.g. chloride) as If It Was an ordinary plot .
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