In the Rafsanjan plain, Iran, the excessive use of groundwater for pistachio irrigation since the 1960s has led to a severe water level decline as well as land subsidence. In this study, the advantages of InSAR analyses and groundwater flow modeling are combined to improve the understanding of the subsurface processes causing groundwater-related land subsidence in several areas of the region. For this purpose, a calibration scheme for the numerical groundwater model was developed, which simultaneously accounts for hydraulic aquifer parameters and sediment mechanical properties of land subsidence and thus considers the impact of water release from aquifer compaction. Simulation results of past subsidence are calibrated with satellite-based InSAR data and further compared with leveling measurements. Modeling results show that land subsidence in this area occurs predominantly in areas with fine-grained sediments and is therefore only partly dependent on groundwater level decline. During the modeling period from 1960 to 2020, subsidence rates of up to 21 cm year−1 are simulated. Due to the almost solely inelastic compaction of the aquifer, this has already led to an irreversible aquifer storage capacity loss of 8.8 km3. Simulation results of future development scenarios indicate that although further land subsidence cannot be avoided, subsidence rates and the associated aquifer storage capacity loss can be reduced by up to 50 and 36%, respectively, by 2050 through the implementation of improved irrigation management for the pistachio orchards.

Biogeochemical redox processes control the chemical behavior of many major and trace elements, making their comprehension crucial for predicting and protecting environmental health. Nitrogen (N) is especially susceptible to changes in soil redox conditions and affects the cycles of other redox‐sensitive species. Elevated N concentrations, in nitrate form, in agricultural soils and associated freshwater ecosystems constitute a problem in many parts of the world. Although a wide variety of measures have been adopted, their assessment through concentration measurements in groundwater and surface water of the different monitoring networks has shortcomings. Nitrate, as a non‐point pollutant, is subject to several processes (e.g., transformation and retardation) before it is detected, making it impossible to evaluate measurements’ effectiveness reliably. Thus, we designed and constructed a monitoring station featuring commercially available products and self‐manufactured components at an agricultural site for the in situ assessment of nitrate‐related processes by high‐resolution monitoring of hydraulic (soil water content, matric potential, groundwater head) and hydrogeochemical variables (oxidation‐reduction potential and groundwater and pore water chemistry) within the vadose zone and the shallow aquifer. The monitoring station has proven to be a reliable tool. Changes over depth and time of measured variables have been identified, allowing the detection of the transient behavior of the redox reactive zone and the interpretation of ongoing denitrification processes and other redox nitrate‐triggered phenomena, such as uranium roll‐front and selenium accumulation at the redox interface. Measuring both geochemical and soil water variables allows for the calculation of in situ solute inputs into the groundwater and their reaction rates.

<p>Biogeochemical redox processes control the chemical behavior of many major and trace elements. Nitrogen is particularly sensitive to changes in soil redox conditions and its presence also affects the cycles of other redox-sensitive species, which causes its excessive application through agricultural fertilizers to be a multi-faceted problem.</p><p>To assess these processes, we constructed a high-resolution monitoring station at an agricultural site featuring sensors and sampling facilities for analyzing hydraulics and hydrogeochemistry in the vadose zone and shallow groundwater. Monitoring has been performed for over two years during which different types of crops such as dill, spinach, wheat, and sunflower have been grown on the site. Observed variations of the oxidation-reduction potential over time and depth confirm the transient behavior of the redox reactive zone, whose variation is consistent with the fluctuation of the groundwater level. Also, a strong decrease in NO<sub>3</sub><sup>- </sup>concentrations could be observed. This corresponds to changes over depth<sup></sup>in both the sulfate<sup></sup>concentration and δ<sup>34</sup>S-SO<sub>4</sub><sup>2-</sup> signatures, which<sup></sup>confirms the presence of autotrophic denitrification using sulfur as an electron donor. Moreover, a hydraulic model coupled with a heat transport model was set up for the estimation over depth of water fluxes, water content, and temperatures. In combination with the monitored concentrations, this allows us to estimate solute fluxes.</p><p>Preliminary results indicate an average nitrate input to groundwater of 200 kg·ha<sup>-1</sup>·a<sup>-1</sup>, which is almost completely reduced in the shallow groundwater. However, at the same time, a production of only 25 kg·ha<sup>-1</sup>·a<sup>-1</sup> of sulfate is estimated, which indicates that not only sulfur serves as an electron donor, and thus heterotrophic denitrification must also be taking place. This can be confirmed based on increased bicarbonate concentrations in the reactive zone. Furthermore, other nitrate-triggered redox processes were detected, including selenium accumulation at the redox interface, presumably resulting from seleno-pyrite-driven denitrification and geogenic uranium roll-front mobilization.</p>

<p>Over the last two decades there has been a growing interest in the occurrence and fate of emerging organic contaminants (EOCs) in groundwater globally. Managed aquifer recharge (MAR) has been recognized as one of the possible causes of pollution, because of the use of insufficiently or partially treated waters as infiltration source.</p><p>Biofilms are one of the most widely distributed modes of life on Earth, and they drive biogeochemical cycling processes of most elements in water, soil, sediment and subsurface environments. Biofilms are aggregates of microorganisms in which cells are frequently embedded in a self-produced matrix of extracellular polymeric substances (EPS). Biofilms partially cover the underlying material, changing the sorption behavior of the soil surface and giving a proper environment to microorganisms for the degradation of EOCs.</p><p>To understand the role of biofilms in the transport processes of EOCs, we performed batches studies and a set of three saturated column experiments where biofilms were established. Two of the columns were filled with a soil having a high organic content (0.6% organic carbon) and the third one contained the same soil but muffled, to characterize the role of organic matter in the growth of biofilms. The feed water consisted of ten-fold diluted synthetic wastewater (SWW) without EOCs, and in the case of one of the organic columns, sodium azide was spiked to have an abiotic control. The columns were equipped with automated sensors (high resolution oxidation-reduction potential, water pressure and soil pH) to link these variables to biofilm development. Several tracer experiments were run during the duration of the experiments and analysis of major ions, organic carbon and trace elements were performed as well. After hydrogeochemical equilibrium was reached in each column, inflow SWW was spiked with a cocktail of five EOCs in environmental concentrations (µg/L), covering different hydrophobicity, speciation and biodegradability parameters: Carbamazepine, Metoprolol, BP3, Ibuprofen and Diclofenac.  Breakthrough curves of the EOCs were measured, and double porosity models were fitted to compare retardation factors and rates of degradation of each system. Post experiments analysis allowed the determination of the biofilms on each column by means of EPS extraction and quantification. Differences in the transport behavior of most of the compounds were observed between the columns, concluding that biofilms and biological structures can be an important factor in the transport of EOCs in soils.</p>

<p>Managed aquifer recharge (MAR) via infiltration basins to replenish aquifers is an important part of the integrated water resource management (IWRM) toolbox. Soil aquifer treatment managed aquifer recharge (SAT-MAR) basins are used to improve water quality during infiltration. However, SAT-MAR can also pose the risk of contaminating the aquifer, by infiltrating treated wastewater effluent, which may still contain high concentrations of e.g., nutrients (N and P) and emerging organic compounds (EOCs), e.g., pharmaceuticals. In order to assess these potential risks and to be able to take measures, it is important to understand the SAT-MAR system. In this context, it is necessary to study the degradation and sorption capacity of natural conditions as well as modified regimes, e.g., by incorporating reactive layers. While laboratory column experiments are widely used and provide detailed process understanding under controlled conditions, transferring the results to field size and conditions remains challenging. On the other end, in-situ field experiments give great insights into real systems while they often study only one SAT-MAR site under distinct environmental settings which hinders to transfer knowledge to other sites. One way to bridge this gap between the two scales is through large tank experiments. However, there are few such large tank experiments in research on MAR that seek to combine the representativeness of in-situ experiments with the controlled characteristics of laboratory column studies.</p><p>Therefore, we designed and conducted a large-scale tank experiment consisting of three tank replicates for the purpose of analyzing SAT infiltration basins using treated wastewater effluent under controlled conditions. The three tanks are packed with fine sand and comprise a vadose zone as well as a saturated zone. The vadose zone of two tanks incorporates a mixed layer of biochar/fine sand as reactive layer, while the third tank consists solely of fine sand and acts as reference. The tanks are equipped with various sensors (high resolution oxidation-reduction potential, water pressure, soil moisture content, electrical conductivity, water pressure, and temperature). To be able to measure the concentration of solutes along the flow path, several suction cups and small-diameter wells allow sampling in the vadose zone and saturated zone, respectively. The infiltrating water in this study is treated wastewater while the groundwater flowing continuously in the lower part of the tank consists of local groundwater. A set of six EOCs (carbamazepine, diclofenac, ibuprofen, naproxen, gemfibrozil, and triclosan) act as model substances as they cover a wide range of physicochemical parameters and degradation potentials.</p><p>Preliminary results are presented on the influence of operational regimes and reactive barriers on the attenuation of EOCs, as well as on nutrients, dissolved organic carbon, and major ions in both the vadose zone and groundwater.</p>