Redox potential (𝐸𝐸ℎ) measurements are widely used as indicators of the dominant reduction-oxidation reactions occurring underground. Yet, 𝐸𝐸ℎ data are mostly used in qualitative terms, as actual values cannot be used to distinguish uniquely the dominant redox processes at a sampling point, and should therefore be combined with a detailed geochemical characterization of water samples. In this work, we have intensively characterized the redox potential of the first meter of soil in an infiltration pond recharged with river water using a set of in-situ sensors measuring every 12 min during a one-year period. This large amount of data combined with hydrogeochemical campaigns allowed developing a reactive transport model capable of reproducing the redox potential in space and time together with the site hydrochemistry. Our results showed redox processes were mainly driven by the amount of Sedimentary Organic Matter in the system as well as by seasonal variation of temperature. As a subsidiary result, our work emphasizes the need to use a fully coupled model of flow, heat transport, solute transport and the geochemical reaction network to fully reproduce the 𝐸𝐸ℎ observations in the topsoil.
Managed aquifer recharge (MAR) is a well-known technique for improving water quality and increasing groundwater resources. Denitrification (i.e. removal of nitrate) can be enhanced during MAR by coupling an artificial recharge pond with a permeable reactive layer (PRL). In this study, we examined the suitability of a multi-isotope approach for assessing the longterm effectiveness of enhancing denitrification in a PRL containing vegetal compost. Batch laboratory experiments confirmed that the PRL, installed in 2011, was continuing to enhance denitrification. At the field scale, changes in redox indicators along a flow path and below the MAR-PRL system was monitored over 21 months during recharge (RP) and non-recharge (NRP) periods. Our results showed that the PRL was still releasing non-purgeable dissolved organic carbon five years after installation. Nitrate concentration and isotope data indicated that denitrification was occurring under and close to the infiltration area where recharge water and native groundwater mix. Furthermore, longer operational periods of the MAR-PRL system increased denitrification. Multi-isotope analysis might be useful in identifying and quantifying denitrification in MAR-PRL systems.
Subsurface microorganisms must deal with quite extreme environmental conditions. 13The lack of light, oxygen, and potentially nutrients are the main environmental stresses 14 faced by subsurface microbial communities. Likewise, environmental disruptions 15 providing an unbalanced positive input of nutrients force microorganisms to adapt to 16 varying conditions, visible in the changes in microbial community diversity. In order to 17 test microbial community adaptation to environmental changes, we performed a study 18 in a surface Managed Aquifer Recharge facility, consisting of a settlement basin (two-19 day residence time) and an infiltration pond. Data on groundwater hydrochemistry, soil 20 texture, and microbial characterization was compiled from surface water, groundwater, 21 and soil samples at two distinct recharge operation conditions. 22Multivariate statistics by means of Principal Component Analysis (PCA) was the 23 technique used to map the relevant dimensionality reduced combinations of input 24 variables that properly describe the system behavior. The methodology selected allows 25 including variables of different nature and displaying very different range values. Strong 26 differences in the microbial assemblage under recharge conditions were found, 27 coupled to hydrochemistry and grain-size distribution variables. Also, some microbial 28 groups displayed correlations with either carbon or nitrogen cycles, especially showing 29 *Manuscript Click here to view linked References abundant populations of denitrifying bacteria in groundwater. A significant correlation 30 was found between Methylotenera mobilis and the concentrations of NO 3 and SO 4 , and 31 also between Vogesella indigofera and the presence of DOC in the infiltrating water. 32 Also, microbial communities present at the bottom of the pond correlated with 33 representative descriptors of soil grain size distribution. 34 , 2009). Actually, the unsaturated zone, and more specifically the topsoil, 39 supports the highest microbial activity and biomass of all compartments within the 40 subsurface environment (Lapworth et al., 2012). Likewise, microorganisms are 41 responsible for most biological processes in aquifers (Stein et al., 2010). 42 LuedersSeveral studies evidence microbial adaptation to groundwater extreme environments 43 (thermal or hypersaline) (e.g., Rothschild and Mancinelli, 2001) or disturbed by human 44 activities (Meckenstock et al., 2015). Human activities have caused disruption in 45 aquifer dynamics to some extent (Griebler and Lueders, 2009;, with 46 biological implications as indigenous microorganisms can acclimate (Pett-Ridge and 47Rodriguez-Escales and Sanchez-Vila, 2016), (2) determining the physical and 56 hydrochemical conditions that can govern the behavior of specific microbial groups 57
Abstract. Managed Aquifer Recharge (MAR) is a technique used worldwide to increase the availability of water resources. We study how MAR modifies microbial ecosystems and its implications for enhancing biodegradation processes to eventually improve groundwater quality. We compare soil and groundwater samples taken from a MAR facility located in NE Spain during recharge (with the facility operating continuously for several months) and after 4 months of no recharge. The study demonstrates a strong correlation between soil and water microbial prints with respect to sampling location along the mapped infiltration path. In particular, managed recharge practices disrupt groundwater ecosystems by modifying diversity indices and the composition of microbial communities, indicating that infiltration favors the growth of certain populations. Analysis of the genetic profiles showed the presence of nine different bacterial phyla in the facility, revealing high biological diversity at the highest taxonomic range. In fact, the microbial population patterns under recharge conditions agree with the intermediate disturbance hypothesis (IDH). Moreover, DNA sequence analysis of excised denaturing gradient gel electrophoresis (DGGE) band patterns revealed the existence of indicator species linked to MAR, most notably Dehalogenimonas sp., Nitrospira sp. and Vogesella sp.. Our real facility multidisciplinary study (hydrological, geochemical and microbial), involving soil and groundwater samples, indicates that MAR is a naturally based, passive and efficient technique with broad implications for the biodegradation of pollutants dissolved in water.
Abstract. Managed Aquifer Recharge (MAR) is a worldwide used technique to increase the availability of water resources.We study how MAR modifies microbial ecosystems, and its implications for enhancing biodegradation processes to eventually improve groundwater quality. We compare soil and groundwater samples taken from a MAR facility located in NE Spain during recharge (with the facility operating continuously for several months) and after four months of no recharge. The study demonstrates a strong correlation between soil and water microbial prints with respect to sampling location along the mapped 5 infiltration path. In particular, managed recharge practices disrupt groundwater ecosystems by modifying diversity indices and the composition of microbial communities, indicating that infiltration favors the growth of certain populations. Analysis of the genetic profiles showed the presence of nine different bacterial phyla in the facility, revealing high biological diversity at the highest taxonomic range. In fact, the microbial population patterns under recharge conditions agree with the Intermediate Disturbance Hypothesis. Moreover, DNA sequence analysis of excised DGGE band patterns revealed the existence of indicator 10 species linked to MAR, most notably Dehalogenimonas sp, Nitrospira sp and Vogesella sp. Our real facility multidisciplinary study (hydrological, geochemical and microbial), involving soil and groundwater samples, support that MAR is a naturallybased, passive, and efficient technique with broad implications for the biodegradation of pollutants dissolved in water.
Managed Aquifer Recharge (MAR) is a technique used worldwide to increase the availability of water resources. We study how MAR modifies microbial ecosystems and its implications for enhancing biodegradation processes to eventually improve groundwater quality. We compare soil and groundwater samples taken from a MAR facility located in NE Spain during recharge (with the facility operating continuously for several months) and after 4 months of no recharge. The study demonstrates a strong correlation between soil and water microbial prints with respect to sampling location along the mapped infiltration path. In particular, managed recharge practices disrupt groundwater ecosystems by modifying diversity indices and the composition of microbial communities, indicating that infiltration favors the growth of certain populations. Analysis of the genetic profiles showed the presence of nine different bacterial phyla in the facility, revealing high biological diversity at the highest taxonomic range. In fact, the microbial population patterns under recharge conditions agree with the intermediate disturbance hypothesis (IDH). Moreover, DNA sequence analysis of excised denaturing gradient gel electrophoresis (DGGE) band patterns revealed the existence of indicator species linked to MAR, most notably Dehalogenimonas sp., Nitrospira sp. and Vogesella sp.. Our real facility multidisciplinary study (hydrological, geochemical and microbial), involving soil and groundwater samples, indicates that MAR is a naturally based, passive and efficient technique with broad implications for the biodegradation of pollutants dissolved in water.
Managed Aquifer Recharge (MAR) is a technique used worldwide to increase the availability of water resources. We study how MAR modifies microbial ecosystems and its implications for enhancing biodegradation processes to eventually improve groundwater quality. We compare soil and groundwater samples taken from a MAR facility located in NE Spain during recharge (with the facility operating continuously for several months) and after 4 months of no recharge. The study demonstrates a strong correlation between soil and water microbial prints with respect to sampling location along the mapped infiltration path. In particular, managed recharge practices disrupt groundwater ecosystems by modifying diversity indices and the composition of microbial communities, indicating that infiltration favors the growth of certain populations. Analysis of the genetic profiles showed the presence of nine different bacterial phyla in the facility, revealing high biological diversity at the highest taxonomic range. In fact, the microbial population patterns under recharge conditions agree with the intermediate disturbance hypothesis (IDH). Moreover, DNA sequence analysis of excised denaturing gradient gel electrophoresis (DGGE) band patterns revealed the existence of indicator species linked to MAR, most notably Dehalogenimonas sp., Nitrospira sp. and Vogesella sp.. Our real facility multidisciplinary study (hydrological, geochemical and microbial), involving soil and groundwater samples, indicates that MAR is a naturally based, passive and efficient technique with broad implications for the biodegradation of pollutants dissolved in water.
<div> <p>Redox potential measurements are a sink of multiple processes and factors related to the hydrochemistry of a water.&#160; Normally, by themselves, they do not provide enough information to describe all the processes occurring in a system and they are considered only as &#8220;an indicator&#8221; that combined with a more detailed hydrochemistry can provide information of the driving processes. There are different reasons why these measurement are not quantitatively valid. First of all, sampling plays an important role. The most common method to determine Eh in groundwater is by using an Eh probe and a cell flow, which implies, by itself, mixing of waters. On the other hand, the Eh reproducibility is also conditioned by the amount of processes considered in a numerical model. Eh depends on several geochemical processes, which at the same time, they are depending on flow and heat transport. The last achievements in sensoring science has allowed to develop sensor probes that allows the Eh measurements in a non-invasive and a continuous way.</p> </div><p>Considering this, in this work we have monitored intensively an infiltration pond (in the context of Managed Aquifer Recharge) in order to develop a proper model to reproduce the Eh. The monitoring was based in the use of non-invasive Eh probes, which registered the Eh every 15 min during a year. During that year, four hydrochemical campaigns were also developed in order to quantify the hydrochemistry of the site. On the other hand, the model considered the flow of the system, the heat transport and a set of geochemical processes which were also depending on temperature. The main processes were the generation of organic matter in the own system, the oxidation of organic carbon using different TEAPs, nitrification and different secondary geochemical processes related, specially, to iron and manganese geochemistry.</p>
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