Water Table Oscillations Research Articles

Hydrological control of rock carbon fluxes from shale weathering

Shale bedrocks hold Earth’s largest carbon inventory. Although water is recognized for cycling elements through terrestrial environments, understanding how hydrology controls ancient rock carbon (Crock) release is limited. Here we measured depth- and season-dependent subsurface water fluxes and pore-water and pore-gas geochemistry (including radiocarbon) over five vastly different water years along a hillslope. The data reveal that the maximum depth of annual water table oscillations determines the weathering depth. Seasonally varying subsurface water fluxes determine the export forms and rates of weathered Crock. Eighty percent of released Crock is emitted as CO2 to the atmosphere primarily during warmer and lower water table seasons and 20% of released Crock as bicarbonate exports mostly during months of snowmelt to the hydrosphere. Thus, the rates and forms of Crock weathering and export are clearly controlled by climate via hydrologic regulation of oxygen availability and subsurface flow. The approaches developed here can be applied to other environments.

Controls on rapid rare earth element enrichment in sediments deposited by a continental-scale river system

Clay-hosted rare earth element (REE) deposits, generally considered products of extended subtropical weathering of REE-rich igneous protoliths, are a critical source of REEs globally.The Koppamurra deposit of southeast South Australia, in contrast, is developed in Pleistocene lacustrine clays overlying a REE-poor marine limestone. Here we examine the REE + Y (REY) sources and enrichment mechanisms of this unusual setting. We find that the greatest REY enrichment (up to 5000 ppm) occurs in lacustrine clays at the base of a ∼1–2 m thick contact zone with the underlying limestone. This zone features an increased proportion of leachable REYs (>50 %), increased smectite abundance and a sharp increase in pH from ∼5.0 to ∼8.3. Co-variation of HREEs with a suite of clay-specific elements demonstrates that HREEs are hosted mainly by Fe-rich smectite, with separate sorbed vs structurally bound HREE pools that are of similar magnitude. LREEs are mainly hosted in secondary LREE carbonates, these are preferentially intergrown with smectite but are only rarely present in kaolinite domains. Cerium occurs mainly as cerianite. The narrow range and overlapping εNd of samples within and above the REY enriched zone suggests that enrichment is related to internal redistribution within the clay unit. The clays are isotopically incompatible with local igneous or metasedimentary rocks, but 87Sr/86Sr and εNd isotopic fingerprinting shows that they were deposited by the Murray River, Australia’s largest river system. Murray sediments are enriched in REY due to the presence of material eroded from the Lachlan Orogen granites of southeast Australia. Deposition of these sediments occurred in a coastal lacustrine setting analogous to the modern-day Coorong, with tectonic uplift and shoreline progradation allowing the onset of subaerial weathering ∼1–2 Mya. We propose that vertical and lateral solute transport allowed for the concentration of REEs in local depressions in the karst-weathering surface which separates the limestone and overlying clay, facilitated by water table oscillation and pore water redox cycling driven by seasonally contrasted rainfall. Poor soil drainage, evaporative concentration of soil waters and alkaline pH adjacent to the limestone immobilized REEs in secondary carbonates and Fe-rich smectite. Our findings illustrate that REE mobilization and enrichment in clay deposits can occur more rapidly, over a larger area and in a broader range of host phases and geologic settings than is currently appreciated, with important implications not only for REE exploration but also for the use of REEs as tracers in the Earth Sciences.

Unraveling the sedimentation environment of Marajó island: Insights from geochemical studies and implications for the origin of potentially toxic element in soils

Marajó Island, located at the mouth of the Amazon and Tocantins rivers, is the largest fluvial maritime island on Earth. Its unique location within the Amazon biome and its complex sedimentary dynamics makes it a region of great ecological and socio-economic importance. However, the island is facing significant challenges due to climate change, with projections suggesting permanent flooding of its floodplains in the coming decades. Despite numerous studies on soil geochemistry in the Amazon biome, there is a lack of research specifically focused on Marajó Island. Our study aims to investigate the soil's geochemical properties on the major parent materials in the eastern portion of Marajó Island, seeking to unravel the nature of its complex sedimentary environment, elemental relationships, origin and implications of potentially toxic elements. Samples from seven soil profiles representative of the eastern portion island were collected in a chronosequence, to conduct physical and chemical analyzes: selective dissolution of Fe oxides by sodium citrate-bicarbonate-dithionite and ammonium acid oxalate; quantification of major, trace and rare earth elements (REE) performed by multi-acid digestion and determination in ICP-OES/MS; characterization of weathering intensity by the chemical index of alteration (CIA), chemical weathering index (CWI), plagioclase index of alteration (PIA), chemical proxy of alteration (CPA), and index of compositional variability (ICV); and assessment of potentially toxic elements using enrichment factor and geoaccumulation index. The results indicated that the geochemical variation of soils reflected particularities of the parent material influenced by marine transgression events, and by the current conditions of water table oscillation and humid tropical climate. Holocene Sediments (HS) revealed enrichment by light REE. In soils on Post-Barreiras (PB), Laterite Formation (LF) and Lateritic Debris (LD), the main elements were Al, Fe, and Ti. Due to intense weathering and leaching, negative anomalies were observed in nearly all elements, including the REE. Arsenic enrichment in HS soils was due to the past estuarine influence and the current hydromorphic conditions, while soils on PB, LF and LD are naturally enriched by the parent material.

Sinkhole risk mapping and early warning: the case of Camaiore (Italy)

Introduction: Sinkholes are ground collapses that can cause significant damage to infrastructure and buildings. Part of the risk represented by sinkholes is related to their abruptness and the difficulty in spotting in advance their exact location within a sinkhole-prone area. For this reason, urban planning informed by an accurate risk mapping and monitoring is one of the most effective ways to reduce the risk.Methods: In this study, we propose a two-folded procedure based on the examination of ground displacement data measured by a ground-based interferometric radar and on the generation of a sinkhole risk zonation map. We examined 11 years’ worth of ground displacement data measured by a ground-based interferometric radar to search for sinkhole precursors. The analysis was based on averaged displacement time series retrieved from high-coherence pixels scattered around Camaiore, Italy, a test site where a catastrophic sinkhole occurred in 1995. To generate a sinkhole risk map, we evaluated the susceptibility map as derived from a set of predisposing environmental parameters, the vulnerability derived from the thickness of the sedimentary cover that can be linked to the abruptness of the collapse, and the value of the elements at risk from the Italian Real Estate Market Observatory integrated with land cover information for the non-built up areas.Results: The analysis of ground displacement data revealed that Camaiore had not experienced subsidence relatable to incoming sinkholes in the monitored period. However, few cm of vertical movements, which are well correlated with water table oscillations, have been measured and are expected to be of the same order of magnitude of sinkhole precursor deformations. This implies that a phenomenon of the size and velocity of the 1995 event could have likely been detected before its final collapse. The sinkhole risk map identified specific areas that should be closely monitored using in situ and remote sensing instrumentation.Discussion: The sinkhole risk zonation map generated in this study can be used to inform urban planning and risk management strategies. The study also shows the potential of ground-based interferometric radar to detect sinkhole precursors and the importance of integrating different mitigation approaches. Overall, this study can provide insights for sinkhole risk assessment and management in sinkhole-prone areas.

Snížení základního odtoku kvůli evapotranspiraci povrchové a podzemní vody z mokřadu v povodí Liběchovky: porovnání měření a výpočtu Oudinovou metodou

This study is focused on the base flow decrease due to surface water and groundwater evapotranspiration (ET) in wetlands of the Liběchovka catchment. Evapotranspiration in wetlands can significantly affect stream discharge, and its influence will probably still increase in the future due to the global rise of temperatures caused by climate change. The study site is located in the upper part of Liběchovka catchment (Fig. 1). This wetland hosts a small stream supplied by rather steady groundwater inflow, representing the favourable site for detection of the effect of ET. V notch weir and two piezometers were used to monitor stream discharge and wetland water table in 30 minute periods (Fig. 2). Diurnal periodical oscillations of water flow and water table caused by ET were observed (Fig. 3). They occurred in the summer part of the year, especially on sunny days without rain. The amplitude of water table level oscillation was increasing with increasing temperature (Fig. 4). Calculation showed that evapotranspiration reduced the water flow, on average, by 15 % on the warm sunny days. The maximum daily reduction was up to 32 %. Direct measurements were compared with the potential ET calculated using the Oudin’s method (Oudin 2005). The ET from the measurement was 45 % of the potential ET calculated by Oudin’s method. In the next step, the Oudin’s method was used to calculate the potential ET of all wetlands in Liběchovka catchment upstream from the Želízy village, where gauging station of ČHMÚ is situated. The original discharge not reduced by the wetland ET was defined as the sum of the wetland potential ET and the mean annual measured discharge. Due to the ET from wetlands (years 2015–2020), the discharge was reduced on average by 13 %. If only the summer months of July and August were considered, it was reduced, on average, by 26 % and by 39 % in the driest day recorded in this period. To estimate the role of groundwater abstraction on the Liběchovka stream during the period of 2015–2020, the sum of measured stream discharge, groundwater abstraction and wetland ET was calculated. From this sum, 71.5 % represented the directly measured water flow, 18.2 % was the groundwater abstraction, and 10.3 % was the wetland ET (Fig. 8).

Numerical study on the effects of groundwater table oscillation beneath the “Palazzaccio” courthouse in Rome

This work aims to evaluate the settlement induced by the river Tiber groundwater table oscillations. A representative section of the subsoil beneath the courthouse “Palazzaccio”, close to the river in the city centre of Rome, is analysed via the finite element method with a fully coupled hydro-mechanicalmodel. The effects of wetting-drying cycles induced by the water table oscillation are accounted for by adopting the Barcelona Basic Model for the unsaturated layers, whose model parameters are calibrated using experimental results on saturated and unsaturated samples and literature data. The variation of the river Tiber level is reconstructed according to the “Tevere – Ripetta” hydrometric station records between 2005 and 2008, and it is applied as a boundary condition at the boundary of the model domain.

Spatio-temporal evolution of ground motion intensity caused by reservoir-induced seismicity at the Pertusillo artificial lake (southern Italy)

We investigate the spatiotemporal evolution of ground motion caused by reservoir-induced seismicity at the Pertusillo artificial lake in southern Italy. The area has a strong seismogenic potential, having been affected in the past by the 1857, Mw 7.0 Basilicata earthquake. We consider ∼1,000 microearthquakes that occurred from 2001 to 2018 and were recorded by a local network of nine seismic stations. The ground motion intensity associated with microseismicity allows us to identify two periods, each lasting approximately 2 years. They are characterized by a high rate of events but exhibit different source properties and spatial distributions. In the first period, the seismicity is spatially clustered close to the lake, on faults with different orientations and kinematics. In the second period, the seismicity is distributed along the Monti della Maddalena faults. Comparing the ground motion intensities of the two periods, we observe that events that occurred in the first period are associated with higher stress levels than others, in agreement with the b-values of the respective frequency-magnitude distributions. We compare the temporal evolution of the ground motion intensity with the rainfall and water levels measured at the artificial lake, as well as with the discharge of a ∼80 km distant spring, which is strictly controlled by climate trends. The results provide information about the regional processes acting on the southern Apennines. Our results show that the microseismicity is clearly associated with the Pertusillo artificial lake in the first period, whereas in the second period is a result of a combination of local effects due to water table oscillations of the lake itself, regional tectonics, and the poroelastic and elastic phenomena associated with carbonate rocks hosting aquifers.

The Tim Mersoï Basin uranium deposits (Northern Niger): Geochronology and genetic model

The Tim Mersoï uranium province in northern Niger is one of the world’s largest uranium reserves and fourth-highest uranium producer. The main uranium deposits (Arlit, Akouta, and Imouraren) are located in continental siliciclastic formations. The regional north–south-trending fault (the Arlit Fault) strongly controls them, as well as secondary discontinuity networks oriented NNE-SSW, ENE-WSW, and WNW-ESE. The Arlit and Akouta uranium-ores are hosted in reduced Carboniferous formations and occur as reduced U4+ phase mineralizations. Besides, the Imouraren deposit is hosted by an oxidized Jurassic formation with a predominance of U6+ silicate and vanadate minerals and relics of reduced mineralization. New U-Pb SIMS data have been obtained on the three deposits, and the results reveal two main stages of uranium deposition and ore metallogenesis. (i) the 90–145 Ma Lower Cretaceous mineralization is related to a significant tectonothermal event, synchronous with the Atlantic rifting that induced the deformation and brine migration from Triassic formations. Primary uraninite and chalcocite are formed by fluid mixing in a reduced environment at that stage at a depth of 1 km at less at a temperature 115–150 °C, hotter than that of the reservoir. (ii) During later Cenozoic exhumation of the basin, a series of remobilizations of primary uranium stock resulted in the formation of much younger uraninites under reduced conditions at Arlit-Akouta around 50 Ma. At Imouraren, younger uraninites formed between 34 and 8 Ma under locally reduced conditions, and were followed by secondary U-minerals from 21 Ma up to 3–1.6 Ma during supergene events. These ages are close or superimposed with the main oxidation stages, affecting West Africa during the Cenozoic, and attest of water table oscillations.

Development of an argillic horizon in polygenetic paleosols in the Marília Formation (Maastrichtian), Brazil: Precautions for paleoenvironmental interpretation

A study of paleosols with argillic horizons found in the Marília Formation associated with Maastrichtian in the Cretaceous is presented herein. This study aims to investigate the polygenetic processes involved in argillic horizon formation under paleoclimatic conditions from arid to semiarid in the Brazilian Cretaceous and considers morphological soil attributes, such as evidence of cementation, macromorphological data (horizons, matrix color, structure, clay coatings, nodules, and bioturbations), micromorphological data (coarse/fine patterns, b-fabric, clay coatings, infillings, and nodules), and water table oscillation. Seven representative profiles of paleosols were selected in the São Paulo state, Brazil, and soil samples of lithified paleosols were collected to determine their macromorphological–micromorphological and chemical properties. Clay illuviation, carbonate accumulation, and gleization were dominant processes in the paleosols. Clay illuviation was identified from clay coatings along grain and ped surfaces. Carbonates occurred as nodules and rhizoliths and as coatings on peds. Red mottles, gray rhizohaloes with red oxidation rims, oxidic nodules, an iron-depleted matrix, and iron oxide depletion hypocoatings confirmed gleization. The argillic horizon polygenesis in the Marília Formation is usually interpreted as evidence of high-moisture events under arid/semiarid climates or climate change toward moister conditions than arid/semiarid. Thus, argillic horizon paleosols in the sedimentary records of the Marília Formation are not necessarily reliquial characteristics of wet paleoenvironments but are associated with changes in dominant granulometry, types of macroaggregates–microaggregates, carbonate accumulation in horizons, and/or water table oscillation. Thus, the presence of Bt horizons does not necessarily imply wet conditions with changes in the depositional system, as proposed by some authors.

Prediction of Slow-Moving Landslide Mobility Due to Rainfall Using a Two-Wedges Model

In the present study, the landslides cyclically reactivated by water-table oscillations due to rainfall are dealt with. The principal kind of motion that usually characterizes such landslides is a slide with rather small velocity. As another feature, soil deformations are substantially accumulated inside a narrow shear zone situated below the landslide body so that the latter approximately slides rigidly. Within this framework, a new approach is developed in this paper to predict the mobility of this type of landslides due to rainfall. To this end, a two-wedges model is used to schematize the moving soil mass. Some analytical solutions are derived to link rain recordings with water-table fluctuations and in turn to landslide displacements. A well-documented landslide frequently activated by rainfall is studied to check the forecasting capacity of the proposed method.

Data-Driven Modelling of Water Table Oscillations for a Porous Aquifer Occasionally Flowing under Pressure

Modelling of shallow porous aquifers in scenarios where boundary conditions change over time can be a difficult task. In particular, this is true when data modelling is pursued, i.e., models are directly constructed by measured data. In fact, data contain not only the information related to the physical phenomenon under investigation, but also the effects of time-varying boundary conditions, which work as a disturbance. This undesired component conditions the training of data-driven models, as they are fitted by models, which can produce predictions diverging from measured data. Here, a very shallow porous aquifer is modelled in terms of its response to water table to precipitation. The aquifer is characterized by the presence of a low permeability silty top layer covering the lower sandy strata, where the aquifer normally flows. Therefore, when the piezometric level increases up to the low permeability layer, the aquifer changes its behavior from phreatic to confined. This determines the changing boundary condition, which makes the response of the aquifer to rain precipitations complex, as it is related to a two-fold condition: confined or phreatic. The aquifer here is investigated by two machine learning approaches, the earlier based on an evolutionary modeling, and the latter based on artificial neural networks. Evolutionary modeling returned explicit equations with a fitness efficiency up to 0.8 for 1 month for predictions and 0.48 for simulations, while neural networks arrived at 0.85 and 0.28, respectively. The aim of this study is to get an explicit model of the response of the piezometric heights of the aquifer to the precipitations, which is useful for planning the use of groundwater resources.

Progressive failure in elastic–viscoplastic media: from theory to practice

In the risk assessment of soil movement, the comprehension of unexpected collapses involving creeping landslides is crucial. The transition from creeping to fast landslides is very hard to justify theoretically and simulate numerically. In this paper, the authors intend to demonstrate that even the integration of a basic elastic strain softening constitutive relationship under simple shear conditions is sufficient to capture such a transition. With this aim, an infinite slope, a homogeneous cemented/bonded soil and an oscillating water table level are considered. The onset of instability is shown to be anticipated by a local increase in strain rate within the shear band, behaving like a precursory signal. The size of the shear band, evolving with time and not depending only on the material grain size distribution, is governed by both the amplitude of the imposed perturbation and the material constitutive parameters.

Arsenic release from pyrite ash waste over an active hydrogeological system and its effects on water quality.

Arsenic is a potentially toxic element of concern for environmental compartments, and it is a frequent pollutant in many abandoned industrial sites. In this study, geochemical and hydrogeological tools were used to determine the long-term effects of As-rich pyrite ash disposal (83,000 m3 as estimated by geostatistical tools) in a brownfield located over a quaternary alluvial aquifer. Throughout the site, soil pollution and water table oscillation led to leachates in the form of both run-off and infiltration waters, thereby reducing (ground)water quality (e.g. pH, electrical conductivity) and, in particular, increasing the concentration of arsenic (average approx. 4000 μg/l for one hydrological year). By means of laboratory and in situ measurements, the main mechanisms through which the sulphide remaining in the pyrite ash leaches were identified. In addition, to evaluate the effects of the polluted groundwater on the nearby main river, a mathematical approach using the Domenico analytical groundwater transport model revealed potential concentrations of 49 μg/l of arsenic in the junction between the study aquifer and the river, equivalent to an annual quantity of 49 kg of this element.

Food web reconstruction through isotopic compositions of fossil faeces: Insights into the ecology of a late Barremian freshwater ecosystem (Las Hoyas, Cuenca, Spain)

A total of 54 coprolites with different morphologies from the Konservat-Lagerstätte of Las Hoyas (upper Barremian, Cuenca, Spain) were analysed for stable isotopes (δ15N and δ13Corg) to examine the food-web structure of this ancient wetland. The Las Hoyas wetland exhibited wetter and drier periods that indicated water table oscillations. Differences in the δ15N values of coprolites collected from wetter and drier facies were probably due to different baseline δ15N values during the dry periods (higher) compared to those of the wetter periods. The δ13Corg values indicated that aquatic food resources were the most commonly used by the animals from Las Hoyas. Assuming a Trophic Enrichment Factor (TEF) of + 2.5 ‰, three trophic levels were established for the coprolite association. All the specimens of circular, ellipsoidal, elongated, and rosary morphotypes fell into the same trophic level, whereas other morphotypes (cylinder, irregular, and thin lace) exhibited a wide range of δ15N values and the highest % N concentrations. The covariation between δ15N and δ13Corg values describe a wide spectrum of values across the middle and upper part of the ecosystem's food web structure, suggesting that the Las Hoyas ecosystem hosted specialist feeders and omnivorous and/or opportunistic feeders, the latter being the majority. The variation of δ15N values within the specimens of some morphotypes showed that the larger coprolites do not exhibit any correspondence between the faecal size and δ15N values.

Predicting sedimentary bedrock subsurface weathering fronts and weathering rates

Although bedrock weathering strongly influences water quality and global carbon and nitrogen budgets, the weathering depths and rates within subsurface are not well understood nor predictable. Determination of both porewater chemistry and subsurface water flow are needed in order to develop more complete understanding and obtain weathering rates. In a long-term field study, we applied a multiphase approach along a mountainous watershed hillslope transect underlain by marine shale. Here we report three findings. First, the deepest extent of the water table determines the weathering front, and the range of annually water table oscillations determines the thickness of the weathering zone. Below the lowest water table, permanently water-saturated bedrock remains reducing, preventing deeper pyrite oxidation. Secondly, carbonate minerals and potentially rock organic matter share the same weathering front depth with pyrite, contrary to models where weathering fronts are stratified. Thirdly, the measurements-based weathering rates from subsurface shale are high, amounting to base cation exports of about 70 kmolc ha−1 y−1, yet consistent with weathering of marine shale. Finally, by integrating geochemical and hydrological data we present a new conceptual model that can be applied in other settings to predict weathering and water quality responses to climate change.

Oncoids and groundwater calcrete in a continental siliciclastic succession in a fault-controlled basin (Early Permian, Northern Italy)

Lower Permian continental deposits of the fault-controlled Orobic Basin (Central Southern Alps; Northern Italy) include alluvial fan facies interfingering with muddy basin-floor deposits, consisting of three facies associations: heterolithic fine-grained siliciclastic facies, laminated sandstone facies, and oncoidal limestone facies. Besides oncoidal and microbial limestones, carbonates occur as nodules in sandy tabular beds within the laminated sandstone facies association. Microfacies analyses distinguish several types of oncoidal carbonate (consisting of an alternation of microbial carbonate and fibrous calcite) and carbonate nodules. Each type of carbonate has been characterized in terms of δ18O and δ13C. The two types of carbonate in the oncoids record a stable δ18O and a slightly varying δ13C, whereas the isotope composition of the calcite in nodules is completely different. Carbonate nodules in sandy beds of the laminated sandstone facies association have a diagenetic origin as indicated by cross-cutting relationships between nodules and lamination; the nodules are interpreted as groundwater calcrete, formed in the subsurface at the top of the unconfined water table. The exclusive sedimentation of oncoidal carbonate facies within siliciclastic deposits indicates that when oncoids were formed in ephemeral shallow ponds, siliciclastic input was minimal. The sedimentological and geochemical characteristics of the studied succession and the stable isotopic composition of the oncoids (the absence of covariance between δ18O and δ13C excludes deposition in evaporating basins) indicate persistent stable conditions for sufficient time to permit growth of centimeter-sized oncoids. Oncoids are interpreted to have formed in spring-fed ponds and outflow channels, with flowing, clean water, at the toe of major alluvial fans. Episodes of rapid delivery of sand and silt-sized sediments by flash floods, with an oscillating water table, caused the observed facies alternation. The precipitation of calcareous cements close to the water table surface produced nodules in sandy layers. Carbonate precipitation within laminated sandstone reduced porosity and permeability, causing a strong compartmentalization in the well-bedded continental succession.

An Approximate Model for Predicting the Specific Yield Under Periodic Water Table Oscillations

AbstractPredicting specific yield for a given aquifer remains a great challenge due to its dynamic characteristics, especially under periodic (e.g., seasonal and diurnal) groundwater level fluctuations. In this study, a dimensionless period of groundwater level fluctuations, which depends on the saturated hydraulic conductivity, the length of the groundwater level fluctuation period, and the soil water retention properties, is first introduced. Then, the relationship between the predicted specific yield and the dimensionless period of groundwater level fluctuations is defined based on the theory of variably saturated flow. The proposed approximate formula is tested by series of simulations of variably saturated flow within homogeneous and isotropic porous media with the Hydrus‐1D program. The results of numerical experiments demonstrate an invariant relationship between the predicted specific yield and the dimensionless period for a wide range of changes in the dimensionless period of groundwater level oscillations. Furthermore, the sensitivity analysis of the dependence of the predicted specific yield on the van Genuchten parameters indicates the applicability of estimating the specific yield via van Genuchten parameters, which can be predicted by the soil texture classes for a given length of the oscillation period and a known saturated hydraulic conductivity in the zone of groundwater level fluctuations. The proposed model can be used for predicting the dynamics of the specific yield under seasonal or diurnal groundwater level fluctuations.

Role of Redox Processes in the Pedogenesis of Hypersaline Tidal Flat Soils on the Brazilian Coast

Core Ideas Iron and Mn movement followed by oxidation impose strong control on soil transformations. Sulfidization is not an active process in hypersaline tidal flat (HTF) soils. Coprecipitation of Mn and ferrihydrite controls the geochemistry of Mn in HTF soil. Hypersaline tidal flats (HTFs) represent transitional ecosystems where the ocean, land, and freshwater meet. These places are globally widespread and their soils are an important environmental component controlling chemical reactions in wetland ecosystems. Here, we present a pedogenic study of two HTFs on the Brazilian coast (northeast and southeast) based on the solid‐phase geochemistry of Fe and Mn and morphological studies. Broken and irregular topographies and strong expression of redoximorphic concentrations (e.g., mottles, nodules, and pore linings) are present throughout the soil profiles. Although lepidocrocite is the most abundant Fe fraction in these soils (more than 50% of all extractions), deeper horizons show pyrite as the main Fe fraction caused by the presence of buried mangrove soils. The more oxidizing conditions in these deeper horizons indicate that pyrite is not stable and is undergoing degradation. Iron released in this process is moving upward and precipitating as Fe oxides in more oxidized portions of the soil profile. Coprecipitation of Mn and ferrihydrite seems to be an important process controlling the geochemistry of Mn in HTFs. Our data indicate that deeper horizons have been transforming, driven mainly by water table oscillation and, consequently, redox processes. This process allows translocation of Mn2+ and Fe2+ throughout the soil profile, followed by oxidation and precipitation of Mn3+/4+ and Fe3+ oxides in preferential sites.

Validating the KAGIS black‐box GIS‐based model in a Mediterranean karst aquifer: Case of study of Mela aquifer (SE Spain)

AbstractKarst Aquifer GIS‐based model (KAGIS model) is developed and applied to Mela aquifer, a small karst aquifer located in a Mediterranean region (SE Spain). This model considers different variables, such as precipitation, land use, surface slope and lithology, and their geographical heterogeneity to calculate both, the run‐off coefficients and the fraction of precipitation which contributes to fill the soil water reservoir existing above the aquifer. Evapotranspiration uptakes deplete water, exclusively, from this soil water reservoir and aquifer recharge occurs when water in the soil reservoir exceeds the soil field capacity. The proposed model also obtains variations of the effective porosity in a vertical profile, an intrinsic consequence of the karstification processes. A new proposal from the Nash–Sutcliffe efficiency index, adapted to arid environments, is presented and employed to evaluate the model's ability to predict the water table oscillations. The uncertainty in the model parameters is determined by the Generalized Likelihood Uncertainty Estimation method. Afterwards, when KAGIS is calibrated, wavelet analysis is applied to the resulting data in order to evaluate the variability in the aquifer behaviour. Wavelet analysis reveals that the rapid hydrogeological response, typical of a wide variety of karst systems, is the prevailing feature of Mela aquifer. This study proves that KAGIS is a useful tool to quantify recharge and discharge rates of karst aquifers and can be effectively applied to develop a proper management of water resources in Mediterranean areas.

Estimates of evapotranspiration from contrasting Wisconsin peatlands based on diel water table oscillations

AbstractEvapotranspiration rates (ET) from contrasting Wisconsin bogs (one forested bog, one open bog) were compared over 4 years by analyzing diel oscillations of their water tables. Daily rates of ET from peatlands were also compared to rates of evaporation (E) from encircled bog ponds. We hypothesized that ET would be higher in the forested bog due to the greater leaf area index of forest canopy relative to moss and ericaceous shrubs. We also hypothesized that ET in peatlands would exceed the physical process of E from encircled ponds. Field data supported the first hypothesis, but the second only proved true for the forested peatland. Daily estimates of peatland ET varied widely, ranging from ~1 to >10 mm/d; but average ET was higher in the forested peatland (4.04 vs. 3.09 mm/d; p < .01). Average ET in the forested peatland was also higher than E during summer (4.04 vs. 3.31 mm/d; p < .05); whereas in the open peatland, average ET was slightly lower than E for all measured seasons (p < .01). Methodologically, the performance of three equations used to estimate ET from daily water table fluctuations was similar. The specific yield of peat (S*y), which is a critical variable in all three equations, was found to be an exponential function of water table depth; and absent an empirically derived S*y, errors in estimates of peatland ET can be large. Given landscape composition across this northern temperate region (13% lakes, 20% peatland, and 54% upland forest) and estimates of forest ET gleaned from the literature, our findings suggest that the regional feedback of water to the atmosphere increases from open waters to peatlands to upland forest, consistent with prior observations that the biological process of transpiration dominates continental ET.