Seepage Flux Research Articles

Snowmelt seepage fluxes of dissolved organic matter in forest and grassland – a molecular-level case study from the Hainich Critical Zone Exploratory, Germany

Snowfall/cover and snowmelt are essential determinants of winter soil processes/events that may force the biogeochemical dynamics of soils in temperate regions. Increasing variability of the European hydroclimate is expected to lead to more frequent intermittent warm periods, which cause snowmelt during winter and rapidly mobilize large amounts of dissolved organic matter (DOM). This study, conducted at the Hainich Critical Zone Exploratory in Germany, seeks to address a significant gap in understanding the molecular impacts of snowmelt-induced DOM flows and their ability to alter soil ecosystems rapidly. During two snowmelt events between January and March 2021, we observed that DOM concentration and composition varied more in forest soil seepage than in grassland soil seepage. Forest seepage showed a pronounced DOM flux peak and synchronous increases in the relative abundances of aromatic DOM components, indicating surface-derived transport of plant litter carbon. In the grassland, however, peak DOM fluxes were characterized by a marked increase in nitrogen-containing (N-containing) DOM components, indicating a predominance of microbial carbon. Notably, the unique DOM components specific to each ecosystem increased during peak fluxes in the forest but decreased in the grassland. We suggest that an overall higher molecular richness and the broader functional metabolic potentials in grassland may account for its relatively greater DOM stability compared to the forest during peak snowmelt events.

Interface and mixing zone between soil waters arising from upward and downward seepage - Part II: Heterogeneous total density.

Freshwater lenses in otherwise saline environments contain an important source of fresh water for natural vegetation and agricultural crops. Such lenses are regularly found in areas where both upward seeping saline groundwater and downward infiltrating fresh recharge water occur simultaneously during part of the year, resulting in shallow freshwater lenses which are highly susceptible to changes in recharge or seepage. In a series of two papers, we consider the water – and solute transport in a 2D cross-section between two parallel outflow faces. In this second part of the series, we build upon expressions presented in the first part to consider a situation where the density of seepage water exceeds that of recharge water, as typical for many deltaic areas around the world. Analytical expressions and approximations are given to obtain the steady state position of the interface between the two types of water using a sharp interface approximation, with a focus on the position midway between two outflow faces. Results show that the effect of a heterogeneous density distribution is limited when the seepage flux exceeds the density difference induced flux, but increases rapidly for ratios of the seepage flux over the density flux falling below 1. The heterogeneous density distribution then results in a decrease in freshwater lens thickness and, correspondingly, a decrease in fresh water availability. We also consider time-variant, oscillatory boundary conditions, and show that for heterogeneous density distributions the interface approaches its equilibrium position faster than for a corresponding situation with a homogeneous density distribution, indicating a higher vulnerability for changing boundary conditions. We also demonstrate that heterogeneous density distributions have limited effect on the amplitude of the interface oscillations. Analytical results obtained with the simplified model are validated using the numerical code SUTRA, which solves the full model for a numerical grid.

Carbon budget of methane seepages in the Haiyang 4 Area in the northern slope of the South China sea

Methane seepage records information of the local carbon cycle with respect to the generation, consumption and sequestration of carbon. Here presents the investigation of 7 gravity cores retrieved in 2004 during cruise SO-177 in the Haiyang 4 Area at the northern slope of the South China Sea. Porewater solutes, sulfate, methane, total alkalinity, sulfide and calcium demonstrate currently the weak seep activity. Local carbon cycling and sequestration is also revealed, that dominates by anaerobic oxidation of biogenic methane to dissolved bicarbonate inducing calcium carbonate and iron sulfide minerals (mainly pyrite) precipitation. A reactive transport model was employed to quantify the carbon cycle and budget. Model results show that current methane fluxes contribute to less than 2 wt % of authigenic carbonates and 2 wt % iron sulfide minerals being precipitated in 600–800 cm sediment depth. The sequestration of carbon could be > 50 mmol C cm−2 yr−1 under in situ condition. The observed increase of carbonate and iron sulfide minerals at ∼100 cm, however, require higher methane fluxes to shift the zone of anaerobic oxidation of methane upwards to around 1 m below the seafloor, which have occurred during sea level low stands in the geological past. The oscillation of seepage flux contributed to the formation of multiple layers of authigenic carbonates and pyrite, which indicates the high capability of carbon sink and is speculated to be induced by the dissociation of the underlying hydrates triggered by sea level drop and or temperature increase.

Experimental Study of the Effect of Molecular Collision Frequency and Adsorption Capacity on Gas Seepage Flux in Coal

Summary The differences in the transport behavior and adsorption capacity of different gases in coal play crucial roles in the evolution of coal permeability. Previous studies of coreflooding experiments failed to explain the mechanism of gas flow and have attributed the variation in gas seepage flux (flow rate) at the beginning of the experiment to the change in effective stress, while the differences in the microscopic properties of different gases, such as molar mass, molecular diameter, mean molecular free path, and molecular collision frequency, were ignored. To research the effect of these gas properties on seepage flux while circumventing the effective stress, coreflooding experiments with helium (He), argon (Ar), nitrogen (N2), methane (CH4), and carbon dioxide (CO2) were designed. The results show that the gas transport velocity in coal is affected by the combination of molecular collision frequency and dynamic viscosity, and the transport velocities follow the order of ν (CH4) > ν (He) > ν (N2) > ν (CO2) > ν (Ar). A permeability equation corrected by the molecular collision frequency is proposed to eliminate differences in the permeabilities measured with different gases. The adsorption of different gases on the coal matrix causes different degrees of swelling, and the adsorption-induced swelling strains follow the order of ε (CO2) > ε (CH4) > ε (N2) > ε (Ar) > ε (He). The reduction in seepage flux and irreversible alterations in pore structure caused by adsorption-induced swelling are positively correlated with their adsorption capacities. The gas seepage fluxes after adsorption equilibrium of coal follow the order of Q (He) > Q (CH4) >Q (N2) > Q (Ar) > Q (CO2). Like supercritical CO2 (ScCO2), conventional CO2 can also dissolve the organic matter in coal. The organic molecules close to the walls of the cleats along the direction of gas flow are preferentially dissolved by CO2, and the gas seepage flux increases when the dissolution effect on the cleat width is greater than that on adsorption swelling.

Groundwater–surface water exchange from temperature time series: A comparative study of heat tracer methods

The importance of the interaction between groundwater and surface water is increasingly being recognized for both understanding and managing water systems. Many efforts have been made to characterize and quantify groundwater–surface water exchange. In particular, temperature–based methods have quickly established themselves given their monetary and practical advantages. In the last 15 years, several methods for interpreting passive temperature time series measured in the streambed have been developed. Still, the benchmarking of these methods has only been carried out in specific and distinct hydrological conditions.This article aims to fill this research gap by benchmarking the performance of six commonly used methods for deriving seepage fluxes using a two-year-long temperature time series covering various meteorological and thermal conditions. This work compares three analytical methods that calculate seepage flux using the amplitude and/or phase of the temperature signals, and three numerical methods that use different schemes to inversely solve the one–dimensional heat transport equation in the streambed. The temperature measurements were made in the context of an international dispute between Chile and Bolivia over the status and use of the waters of the Silala River, Northern Chile. Flux estimations are tested against Darcy’s flux derived from measured hydraulic gradient and hydraulic conductivity.Flux estimations from the benchmarked methods ranged from −0.5 to 3.5 m/d (with positive fluxes directed downwards), whereas fluxes estimated using Darcy’s law ranged from 0.5 to 6 m/d. Results show that the amplitude method is the best–performing method. This method is best suited for estimating the direction of the fluxes, while the method using both the thermal amplitude and phase is best suited for monthly flux trends, and the combination of a Local Polynomial (LP) method and a Maximum Likelihood Estimator (MLE) method (LPMLEn) is appropriate for estimating flux in transient conditions.The use of heat as a tracer proved to be an effective tool for monitoring groundwater–surface water exchange in a river reach for two years, and yielded exchange flux estimates with lower point-scale variability than Darcy’s law.

Approach to tailings facility liner configuration selection: A case study

What liner configuration should you use for a tailings facility? Do you need a geosynthetic liner? Should you include overdrains above your liner? This paper presents an approach to answer these questions for a case study tailings facility in a semi-arid environment. The case study project includes a performance criterion that the seepage flux be limited below the impoundment. Four liner configurations were shortlisted, and the efficacy of each arrangement compared with numerical modelling. The configurations are: (1) tailings directly over a liner, (2) tailings on an overdrain system over a liner, (3) tailings on an overdrain system over a blinding layer over a liner, and (4) sealing the foundation with tailings slimes (i.e., no geosynthetic membrane). This paper also presents estimates of the longevity of an HDPE liner system, as this is vital in assessing performance over very long time periods. Seepage and consolidation modelling results indicate that overdrains do not improve the potential to meet the performance criterion and overdrains have a limited post-closure consolidation benefit. All configurations with geosynthetics indicated the liner system would function adequately during the period prior to geosynthetic membrane degradation. The slimes sealing case was shown to not provide an adequate impedance to flow.

Effect of metallurgical step-graded quantum barrier on the performance of InGaN-based laser diode

In this paper, a metallurgical step-graded uniform quantum barrier (QB) laser diode (LD) structure is proposed, which leads to performance enhancement in terms of reduced electron seepage current, reduced threshold current, diminished polarization charges at interfaces, and increased laser power, hole injection efficiency, optical confinement etc. The proposed LD structure demonstrated the best results among all the three structures considered in this study. The laser output power was increased from 118 mW to 160 mW in the metallurgical step-graded uniform QB LD structure as compared to the ungraded QB reference structure. The optical confinement was improved from 0.94% to 1.09% in the photon-generating region. The electron potential barrier height has increased from 191 meV to 242 meV, while the hole potential barrier height has decreased from 133 meV to 116 meV at 120 mA injection current. In addition, the electron seepage flux has reduced from 1374 A cm−2 to 768 A cm−2 at 120 mA injection current.

Magnetic properties of gas hydrate-bearing sediments and their association with iron geochemistry in the Sea of Marmara, Turkey

The anaerobic oxidation of methane, a key geochemical process that is involved in the cycling of sulfate and iron (oxyhydr)oxides in marine sediments, results in the formation of iron sulfides. Although ferrimagnetic iron sulfides have been identified in seepage systems, the link between iron migration and sediment magnetic properties remains poorly understood. Here, we investigate two cores from the Sea of Marmara to evaluate biogeochemical iron cycling and iron sulfide mineralogy in gas hydrate-bearing sediments. Magnetic analyses indicate the presence of greigite and pyrrhotite in a core from a hydrate-rich site with a high hydrocarbon flux, which contrasts with a lack of these minerals in a core characterized by only mild seepage. This is supported by the results of rock magnetic and scanning electron microscope analyses of the sediments. The presence of authigenic greigite is critical for assessing local redox records and together with the occurrence of monoclinic pyrrhotite may suggest specific diagenetic processes in gas hydrate environments. Our analysis demonstrates the usefulness of these ferrimagnetic minerals, with a high saturation isothermal remanent magnetization to magnetic susceptibility ratio (SIRM/χ > 15 kAm−1) and a high index of hysteresis parameters (DJH > 0.2) indicative of magnetic mineralogy changes, for evaluating variability in the intensity of seepage fluxes and for estimating gas hydrate distributions.

Incorporating temperature into seepage loss estimates for a large unlined irrigation canal

Quantifying seepage losses from unlined irrigation canals is necessary to improve water use and conservation. The use of heat as a tracer is widely used in quantifying seepage rates across the sediment–water interface. In this study, field observations and two-dimensional numerical models were used to simulate seepage losses during the 2018 and 2019 irrigation season in the Truckee Canal system. Nineteen transects were instrumented with temperature probes and stage recording devices for inverse modeling to derive seepage flux and volumetric losses over the 39 km length of canal. The numerical models for each transect were calibrated and validated using the two-year dataset. Soil zones and observation data were used in each numerical model to help guide calibration of vertical and lateral heat and fluid fluxes. Model simulations were used to derive multivariable regression equations that consider stage, temperature, and hydraulic gradient. The results demonstrate the value of long-term datasets that illustrate the seasonality of groundwater levels, siltation, stage, and temperature on seepage rates. Seepage rates estimated by the numerical models range from 0.16 to 4.6 m3/d m−1. Total annual volumetric losses estimated for 2018 and 2019 were 1.6 × 10-2 to 1.2 × 10-2 km3, respectively. The seepage losses estimated by this study account for 32 % to 41 % of the inflow volumes. Regression models were able to reproduce seepage time-series simulated by the numerical models reasonably well. In arid environments, water diverted into irrigation canals may be influenced by seasonal variations in temperature sufficient to influence the water accounting of conveyed surface flows.

Geophysical evidence for submarine methane seepage on the Western slope of Okinawa Trough

Identifying seafloor methane seepage efficiently has important implications for assessing environmental impact, reducing the uncertainty of top seal integrity, understanding the petroleum system, and mitigating the drilling hazards due to shallow gas influx. Pore water geochemistry analyses suggest that the study area has an extremely high methane seepage flux and active methane anaerobic oxidation processes. However, geochemical data cannot provide details about the internal seepages. The geophysical dataset from the Western slope of Okinawa Trough, including 2D high-resolution seismic, sub-bottom profiles, and bathymetry, gives us a good opportunity to understand the detailed characteristics of methane seepages in this study. Geophysical data have revealed numerous methane seepage-related features such as seismic chimneys, pockmarks, submarine domes, and amplitude anomalies, including bright spots and enhanced reflections. Pockmarks and domes are often associated with seismic chimneys, indicating that fluid migration is important in their formation. The various geophysical expressions may represent different stages of methane seepage. Fluid quickly drains, causing severe sediment deformation and forming pockmarks, whereas domes may indicate the early stages of fluid discharge. Chimneys that do not extend to the seafloor may indicate that the venting is gradual and focused. Flares linked to domes or pockmarks may indicate that the fluid migration is active. Several factors triggered the existence of methane seepages on the Western slope of the Okinawa Trough, including tectonic setting, overpressure and rapid sedimentation.

Quantifying the groundwater seepage along a glacier originated river by integrated use of radium isotopes and hydrochemistry

Glaciers, as the core part of the cryosphere, are very sensitive to climate change. As an indicator of glacier changes, the characteristics of glacier-originated rivers have profound significance to global climate change and local water resources. In this paper, the Mingyong River, a glacier-originated river replenished by groundwater, was selected to study the river hydrological cycle characteristics by integrating natural tracer radium isotopes with hydrochemical parameters. The results showed that there were significant differences in radium isotope activities and hydrochemical parameters between groundwater and river water, and the radium activities increased along the river, which reflected the fact that the river was supplied by groundwater seepage. We also found that the activity ratios of 224Ra/228Ra in river and groundwater were less than one unit, which indicated that the groundwater and river water circulated rapidly and that the radioactive equilibrium of short-time radium isotopes had not yet been reached. According to the geochemical behavior of radium in river water body, the mass balance equation of radium was established. 228Ra and 224Ra were used to estimate the groundwater seepage of different segments of the Mingyong River. The results demonstrated that the groundwater seepage fluxes calculated by 224Ra and 228Ra were similar and increased along the river from 123.12 to 657.68 m3 m−1 d−1. Our results have certain significance in revealing the characteristics of the local hydrological cycle and demonstrate that radium isotopes can be used as a tool to estimate the groundwater discharge of rivers in glacial environments.

Seasonal variations of geofluids from mud volcano systems in the Southern Junggar Basin, NW China

Variations in the chemical composition of geofluids and of gas fluxes are significant parameters for understanding mud volcanism and correctly estimate their emissions in carbon species, particularly greenhouse gas, methane. In this study, muddy water and gas samples were collected from the Anjihai, Dushanzi, Aiqigou, and Baiyanggou mud volcanoes in the southern Junggar Basin during the four seasons, around a year. This region hosts the most active mud volcanism throughout China. Gas and water were analyzed for major molecular compositions, carbon and hydrogen isotopes of the gas phase, as well as cations and anions, hydrogen and oxygen isotopes of water. The emitted gases are dominated by CH4 with some C2H6, CO2, and N2. The seasonal changes in the chemical composition and carbon isotopes of emitted gases are not significant, whereas clear variations in the amounts of cations and anions dissolved in the water are reported. These are higher in spring and summer than autumn and winter. The CH4, CO2, and C2H6 fluxes are 157.3–1108 kg/a, 1.8–390.1 kg/a, and 10.2–118.7 kg/a, respectively, and a clear seasonal trend of the gas seepage flux has been observed. In January, the macro-seepage flux of open vents is ≥65 % higher than in April, whereas the micro-seepage flux significantly decreased, probably due to the frozen shallow ground and blockage of soil fractures around the vents by heavy snow and ice during January. This probably causes an extra gas pressure transferred to the major vents, resulting in higher flux of the macro-seepage in the cold season. However, the total flux of the whole mud volcano system is generally consistent around a year.

A Simplified Method for Leakage Estimation of Clay Core Dams with Different Groundwater Levels

Clay core dams are widely applied in reservoir construction, regulating water resource and provide electric power. Leakage is a common problem in reservoir construction, and the leakage amount, which not only affects the economic benefits of the project, but also relates to the safety of the dam body, is difficult to estimate. According to Darcy’s law and stable seepage theory, an analytical method can be proposed to calculate the leakage of the clay core dam to gain the seepage flux in a short time. By making some reasonable assumptions, we propose formulae for seepage calculation in different conditions of the position of the groundwater levels, below or above the reservoir bottom. Both sets of formulae contain two parts of leakage calculation, i.e., leakage from the reservoir bottom and leakage from the dam body. By using the proposed analytical method, the leakage of clay core dams can be estimated considering the influence of the groundwater level. To prove the rationality of the analytical method, a simple numerical model can be established using Geo-studio 2020 to calculate the seepage flux of the clay core dam, where relative errors between numerical solutions and analytical solutions are less than 10%. To verify the feasibility in engineering applications, the proposed method was applied to calculate the seepage of a clay core dam in Sichuan, China, which was also calculated using numerical methods by establishing a three-dimensional model. The results show the rationality of the analytical method, which can strike a balance between precision and efficiency.

Using Automated Seepage Meters to Quantify the Spatial Variability and Net Flux of Groundwater to a Stream

AbstractWe utilized 251 measurements from a recently developed automated seepage meter (ASM) in streambeds in the Nebraska Sand Hills, USA to investigate the small‐scale spatial variability of groundwater seepage flux (q) and the ability of the ASM to estimate mean q at larger scales. Small‐scale spatial variability of q was analyzed in five dense arrays, each covering an area of 13.5–28.0 m2 (169 total point measurements). Streambed vertical hydraulic conductivity (K) was also measured. Results provided: (a) high‐resolution contour plots of q and K, (b) anisotropic semi‐variograms demonstrating greater correlation scales of q and K along the stream length than across the stream width, and (c) the number of rows of points (perpendicular to streamflow) needed to represent the groundwater flux of areas up to 28.0 m2. The findings suggest that representative streambed measurements are best conducted perpendicular to streamflow to accommodate larger seepage flux heterogeneity in this direction and minimize sampling redundancy. To investigate the ASM's ability to produce accurate mean q at larger scales, seepage meters were deployed in four stream reaches (170–890 m), arranged in three to six transects (three to eight points each) per reach across the channel. In each reach, the mean seepage flux from ASMs was compared to the seepage flux from bromide tracer dilution. Agreement between the two methods indicates the viability of a modest number of seepage meter measurements to determine the overall groundwater flux to the stream and can guide sampling for solutes and environmental tracers.

CrAssphage as an indicator of groundwater-borne pollution in coastal ecosystems

Novel approaches for monitoring coastal water quality changes and identifying associated contaminant source(s) are of growing importance as climate change and population redistribution to coastal zones continue to impact coastal systems. CrAssphage, a virus found in the human gut and shed with fecal matter, is currently gaining popularity as an indicator of human fecal contamination in surface water and groundwater. Here we demonstrate that DNA assays targeting crAssphage genetic fragments can be used to detect pollution from nearshore onsite wastewater treatment systems discharging to the ocean via submarine groundwater discharge. We integrated this novel viral monitoring tool into a field study that characterized the physical hydrogeology (hydraulic gradients, hydraulic conductivity, and seepage fluxes) and surface water and groundwater quality at a study site on the north shore of Nova Scotia, Canada. Increased use of onsite wastewater treatment systems during the summer cottage season coincided with widespread detections of crAssphage in submarine groundwater discharge (4/4 samples) and coastal surface waters (3/8 samples). Conversely, classical fecal pollution indicators based on bacterial targets (Escherichia coli and human-specific Bacteroidales genetic marker (HF183)) were sparsely detected in the samples in the coastal environment (2/12 E. coli samples, 0/12 HF183 samples), likely due to greater attenuation of bacterial contaminants within the subsurface environments. Results from this first application of crAssphage in coastal groundwater contribute to a growing body of research reporting the application of this emerging tracer in various environments impacted by sewage pollution sources.

Non‐Darcy Flow Through a Natural Streambed in a Disconnected Stream

AbstractSeepage flux from disconnected streams can be a main source of groundwater recharge in arid and semiarid regions. The seepage into the streambed will respond to a change in stream stage; however, the relationship between seepage flux and stream stage is uncertain due to a lack of in situ observations. This study investigated the change in seepage flow regime with stream stage in a natural streambed through field measurements along a 50.1 km long disconnected stream. Seepage fluxes were quantified using a seepage meter method involving the measurement and simulation of the variable stream stages in a seasonal stream. Flow regimes in the streambed were then evaluated using a developed model. Two seepage flow regimes were observed, the Darcy flow regime and the non‐Darcy flow regime, with the change of the stream stage in the streambed. Our analysis of the mechanisms of seepage flow indicates that drainable porosity and particle size of streambed media are the key factors controlling non‐Darcy seepage flow behavior. We demonstrated that the Reynolds number based on the particle diameter d30 instead of d50 can provide a more accurate criterion for non‐Darcy flow in natural heterogeneous streambeds. Model evaluation showed that predicted streambed seepage regimes and fluxes were consistent with field observations. Together, these results provide new insights into the seepage mechanisms, which have significant implications for the establishment of a better seepage model and the joint development of regional surface water and groundwater.

Understanding the Seepage Behavior of Nai Gaj Dam through Numerical Analysis

This study presents the seepage patterns of earth-fill dams, using critical situations by employing the finite element approach. The Nai Gaj dam is 65km northwest of Dadu city in Sindh Province, Pakistan. In this study, the seepage through the main dam body and foundation is computed and simulated for different scenarios, i.e. maximum, normal, and minimum reservoir level. Seepage analysis was conducted by using the SEEP/W sub-program of GEO-SLOPE software. Dam design parameters and dam geometry data were used as input data to compute the unknown seepage. The seepage behavior of the Nai Gaj dam is shown in terms of net flow which consists of equipotential lines, streamlines, velocity vectors, and phreatic lines. The results show the seepage flux, maximum seepage, and exit gradient at different reservoir levels. The results show that the average flow rate at normal, maximum, and minimum reservoir levels are 1.49×10-7cumec/m, 3.38×10-7cumec/m, and 2.108×10-8cumec/m respectively. In addition, the overall stability of the side slope of the dam is discussed.

The evolutional states of seasonally losing unclogged stream-groundwater systems

Losing streams are widespread in arid and semi-arid regions. Exploring the evolutional states of losing stream-groundwater systems is of great significance to understand the exchanges of water, mass and energy in stream-aquifer systems. This study is devoted to investigate the evolutional process of infiltration flux, pressure head and flow states of a seasonally losing stream-groundwater system with the semi-permeable streambeds missing (or without clogging). The paper constructs a new theoretical framework for the evolutional states of the system. In particular, it focuses on investigating the transition among different evolutional states including disconnected state, transitional state, negative-pressure connected state and positive-pressure connected state, and the critical conditions of transition between connected and disconnected states. The critical conditions associated with disconnection or connection are that 1) the zero-flux zone starts to disappear, 2) the unsaturated zone starts to disappear, and 3) the negative pressure zone starts to disappear. Analytical solutions of those critical conditions are proposed. The evolutional process of stream leakage is characterized into two stages: the first stage corresponds to the disconnected and transitional states in which the seepage fluxes decrease with time; the second stage corresponds to the fully connected state in which the seepage flux decreases rapidly again as time developing. Finally, the influence of various controlling parameters on the critical conditions is analyzed. The critical time (tCRI1) and critical depth (zCRI1) of changing from the disconnected state to the transitional state have nonlinear correlations with saturated hydraulic conductivity (Ks), pore-size distribution index (λ) and flux at the base of the unconfined aquifer (q). The critical time (tCRI2) and the critical depth (zCRI2) of changing from the transitional state to the negative-pressure connected state and the critical time (tCRI3) of changing from the negative-pressure connected state to the positive-pressure connected state all have nonlinear correlations with Ks and λ. zCRI1 and zCRI2 are independent of saturated water content (θs) and residual water content (θr). An innovative physical interpretation is given to system evolutional states and quantifiable criteria for those evolutional states are proposed. The findings of this study can help better understand the evolutional states of seasonally losing stream-groundwater systems, and it lays a foundation for further research on water exchange, mass transport and ecological protection in stream-groundwater systems.

The Effects of Soil Drying Out and Rewetting on Nitrogen and Carbon Leaching—Results of a Long-Term Lysimeter Experiment

As a result of global climate change, heavy rainfall events and dry periods are increasingly occurring in Germany, with consequences for the water and solute balance of soils to be expected. The effects of climate change on nitrogen and carbon leaching were investigated using 21 non-weighable manually filled lysimeters of the UFZ lysimeter facility Falkenberg, which have been managed since 1991 according to the principles of the best management practices and organic farming. Based on a 29-year dataset (precipitation, evaporation, leachate, nitrate and dissolved organic carbon concentrations), the lysimeter years 1995/96, 2018/19, and 2003/04 were identified as extremely dry years. Under the climatic conditions in northeastern Germany, seepage fluxes were disrupted in these dry years. The reoccurrence of seepage was associated with exceptionally high nitrogen concentrations and leaching losses, which exceeded the current drinking water limits by many times and may result in a significant risk to water quality. In contrast, increased DOC leaching losses occurred primarily as a result of increased seepage fluxes.

Geostatistical interpolation of streambed hydrologic attributes with addition of left censored data and anisotropy

Spatial geostatistical interpolation of point measurements of streambed attributes in the hyporheic zone may be constrained by the streambed anisotropy, and data density and spatial distribution may significantly impact the results. Spatial clustering and low spatial data density can be caused by bedrock outcropping at the streambed limiting installation of in-stream piezometers. This study examines parameter error variability of the geostatistical interpolation using anisotropic interpolation methods and increasing the data density by adding left censored values (i.e., data below measurement limit) to locations where measurements were limited by exposed bedrock lining the streambed. The reduction in relative standard error of the interpolation was determined for the spatial distributions of streambed attributes including hydraulic conductivity, seepage flux, and mercury solute flux measured in two different years along a study reach in East Fork Poplar Creek, Tennessee, USA. Two methods to impute the left censored values were compared including the conventional half the detection limit substitution method, and the Stochastic Approximation of Expectation-Maximization (SAEM) algorithm, which both had comparable results. Imputing left censored data increased the data density to recommended ranges, reduced data clustering, increased the spatial dependence for some attributes, and reduced the standard error for each of the three attributes. For the reach considered herein, addition of the left censored values resulted in a larger error reduction than the consideration of anisotropy within the interpolation, which confirms the benefit of data addition to increase data density within data-limited river corridors.