AdvectAs: Mobilisierung und Retention von Arsen an Redoxfronten bei advektivem Transport - Ein integrativer, multidisziplinärer Ansatz

01.01.2017 bis 31.12.2019

Elevated levels of arsenic (As) in groundwater are a health problem affecting over 100 million people worldwide, particularly in the densely populated river deltas of South and Southeast Asia. To date, selectively tapping aquifers that are low in As is the most effective way of lowering human exposure. Aquifers containing low and high As levels are characterized by highly contrasting redox conditions that are often separated by Fe-dominated transition zones. Such redox fronts play a crucial role with regard to As advection and retention, consequently preventing safe aquifers from contamination with As. However, because of the constantly growing water demand and increasing groundwater abstraction, aquifers currently low in As are at high risk of becoming As-polluted in the future.
Despite more than a decade of research, it remains largely unknown to which extent sorption of As onto aquifers sands delays the contamination of low-As aquifers. Without addressing this key issue in a comprehensive, multidisciplinary manner, it is not possible to make meaningful predictions about the time scale over which low-As aquifers are likely to become contaminated by incursion of water from neighboring high-As aquifers.
We hypothesize that the stability and persistence of the redox transition zones in space and time are largely controlled by the mutual interaction of (a) transport processes, (b) microbial activity and (c) the stability of As host mineral phases (mainly Fe-bearing). We postulate that the abundance and type of Fe minerals as well as of As species vary across the transition zones as a result of the availability of electron donors and acceptors, the activity of specific microbial community members, and the overall water and solute transport. Furthermore, we expect that external sources of dissolved organic carbon, e.g. from vertical exchange across aquifer-aquitard interfaces, add to As mobilization and enrichment in groundwater.
The overarching goal of this proposed multidisciplinary research project is to assess potential future As contamination of currently safe aquifers by understanding and predicting the long-term mobility of As under enhanced hydraulic forcing across Fe-dominated redox transition zones in aquifer systems.
Data obtained from the simultaneous characterization of the decisive microbial, geochemical, mineralogical, hydrological/hydraulic and hydrochemical processes and interactions will be integrated in a reactive-transport model to formulate a unifying numerical model approach that couples all key physical transport and biogeochemical reaction processes. This quantitative framework will be used for spatially and temporally resolved predictions of the future evolution of redox fronts and the fate of As. To our knowledge, such a comprehensive, multidisciplinary approach involving all decisive disciplines has not been pursued to date and will revolutionize our understanding and our ability to predict As mobility in aquifers.