Water Percolation Research Articles

Influence of spatially heterogeneous deterioration patterns on strength and ductility of corroded reinforced concrete bridge piers

This work reports on some preliminary results obtained within the framework of a wide research project aimed to study the influence of the corrosion of in Reinforced Concrete (RC) piers on the overall seismic performances of bridges. In this context, after the statistical evaluation of a large database of real structures, a consistent set of bridges and piers has been selected as a sample representative of typical bridge profiles, pier heights and cross-sections as well as of material properties. In the first part of the project, pushover analyses of isolated piers with different corrosion patterns and intensity are carried out to evaluate the residual strength and ductility of corroded piers. In the second part, nonlinear static and dynamic seismic analyses of bridges with corroded piers are carried out to evaluate the influence of the deterioration on the overall seismic performance. Due to specific environmental conditions exposure or to water percolation from the superstructures, it is often the case that corrosion is non-uniformly distributed over piers producing non-homogeneous spatial deterioration patterns. The nonlinear modeling of this type of situations represents specific challenges related to the description of the deterioration patterns and the calibration of material properties. To this end, a multi-level modeling approach based on fiber-based finite elements has been developed and implemented in a specific OpenSeesPy software that allows users to accurately model RC piers subject to arbitrary corrosion patterns, up to their ultimate limit states. In this work, a specific case study of a typical RC rectangular hollow bridge extracted from the mentioned above database subject to different corrosion intensity and patterns is studied. In particular, the influence of the corrosion-induced deterioration on residual strength and ductility are studied. Results show that depending on the intensity and on the patterns significant variations of both strength and ductility can be observed with respect to the undamaged conditions.

Quantification of global Digital Elevation Model (DEM) – A case study of the newly released NASADEM for a river basin in Central Vietnam

Study regionLai Giang River basin, Central Vietnam Study focusThe Digital Elevation Models (DEM) is essential in hydrological modeling and water cycle understanding. There are several unanswered questions regarding the impact of DEM on the models’ quality of hydrological applications. This study develops a comprehensive framework for evaluating impacts of six global DEM products: MERIT, NASA, SRTM, ASTER GDEM2, AW3D30, and TanDEM-X using the semi-distributed model SWAT for the Lai Giang River basin, Central Vietnam, in which four criteria have been used (i) statistical analysis, (ii) river basin characteristics, (iii) effects of DEM uncertainty on streamflow using hydrological simulations, and (iv) cross-validation’s impacts on hydrological applications. New hydrological insights for the regions(1) NASA and SRTM 30 DEM were ranked as most accurate DEMs among the chosen products; (2) ASTER GDEM2 performed the worst, with more uncertainty in river networks delineation; (3) MERIT, ASTER GDEM2, and SRTM 90 m provided inaccurate basin delineations, particularly for the intersection subbasin; (4) DEM resolution and source are insensitive to most of the hydrological components, except for lateral flow, groundwater flow, water percolation, and sediment yield. Moreover, a proposed cross-validation approach for the DEM performance has been introduced, showing that the calibrating parameters of higher-resolution DEM would positively impact the hydrological simulations of lower-resolution DEMs and the opposite, especially in terms of flood peak observation.

Long term monitoring of rainwater harvesting tanks: Is multi‐years management possible in crystalline South Indian aquifers?

AbstractIn semi‐arid regions as in India, where agriculture relies on groundwater abstraction, increase of water resources availability through managed aquifer recharge (MAR) or rainwater harvesting (RWH) is often perceived as a major solution. Studies on these structures’ efficiency exists but despite the interest, limited information is available on the temporal variation of their replenishment. In a monsoon driven climate, the inter‐annual variations are crucial to assess the potential of water storage and multi‐year management especially for these structures. Here, we aim at developing a methodology to reconstruct water storage of RWH tanks to further improve our understanding on long term efficiency and multi‐years drought management. To tackle this issue, long‐term monitoring of a RWH tank located in Telangana in Southern India is achieved by a combination of field monitoring over 2 years (tanks surface and water levels) and a daily water balance compared to LANDSAT measurements of the tank area. The procedure allows reconstructing the tank filling dynamic over a 14‐years period at a daily time step and show the extreme variability of the tank filling level. During this period, the yearly maximum tank volume ranges from 8650 to ~200 000 m3. On the 14‐years period, the tank reach its maximum capacity only once and, for 1/3 of the time, yearly maximum replenishment is below 15% of its capacity. The surface water availability remains limited in time since the tank dries‐up annually, except for 2 years. However, water percolation to the aquifer is slightly enhanced for some years. During this monitoring period, very few extreme raining events (6) contribute for more than 50% of the collected volume. This observation highlights (1) the dependency of the structure to extreme storm events, (2) the limited capacity for a multi‐year's management and (3) the farmers vulnerability to successive droughts.

Optimizing phosphate fertilizer input to reduce phosphorus loss in rice-oilseed rape rotation.

Identifying the major sources and critical periods of P loss from agricultural fields provides important guidance for reducing P loss. A rice-oilseed rape rotation with no P fertilization (NP, control), medium P fertilization (MP, 90kg P2O5 ha-1 season-1), and high P fertilization (HP, 180kg P2O5 ha-1 season-1) was conducted from 2019 to 2021 in the middle Yangtze River Basin. Runoff and leaching P losses were measured simultaneously using runoff event monitoring and a percolation device. Applying P fertilizer increased the P concentration in the field ponding water and percolation water of the rice-oilseed rape rotation. During the rice growing season, total P (TP), dissolved P (DP), and particulate P (PP) concentrations in the field ponding water and percolation water peaked 1day after P was applied, and then decreased rapidly. After 10days of fertilization, P concentration in the field ponding water of the MP treatment decreased to a minimum and stabilized, while the HP treatment extended this period to 20days. The highest P concentration in percolation water was observed at the first sampling during the oilseed rape season, and then it continued to decrease. Inputting P fertilizer increased P loss by 55.0-109.9% compared to the NP treatment, with annual P losses of 0.89-1.10kg P ha-1, of which runoff loss accounted for 61.7-62.9%. Fertilization and precipitation resulted in varied P loss within and between seasons. Runoff from heavy precipitation during the rice season was the main source of P loss, while PP accounted for 54.7-77.6% of runoff P loss. The strong utilization of soil P by rice resulted in a lower demand for exogenous P fertilizer than oilseed rape. Excessive P input increased the soil P surplus and vertical migration. Therefore, reducing rice season P fertilizer inputs to achieve annual P balance in rice-oilseed rape rotation can effectively reduce soil P surplus and loss while ensuring crop P demand, and the initial 10 d after fertilization in the rice season was a critical period for reducing P runoff loss.

Application of electrical resistivity tomography (ERT) in uranium mining earth dam

Abstract Dams are built to contain water or mining tailings and provide several benefits to society. The safety and stability of these structures are essential since eventual accidents can generate catastrophic damage. The main cause of ruptures is associated with abnormal seepage, which can progress to an internal erosion process. To assess the stability and safety of dams, periodic inspections are carried out, which typically include visual inspections and geotechnical instrumentation. Some geophysical methods have the potential to assist conventional geotechnical instrumentation using non-destructive and rapid acquisition investigations. The present study applied a finite element forward modeling to evaluate the percolation conditions and water stability in an earth dam of a decommissioned uranium mine in Brazil. The dam is the final structure of the contention system of mine water treatment. The electrical resistivity data were acquired using electrical resistivity tomography (ERT) and Schlumberger array. The results were presented from the inversion of data in 3D models. The data were processed by open-source software (modeling and inversion of geophysical data). The results indicate the presence of water in the vertical filter located in the crest area. The different levels of investigation indicated water infiltration in the rock mass of the dam foundation. These results are supported by structural surveys carried out in the area that indicate a fracturing pattern in the rock mass of the mine area. The results of the study were satisfactory for the desired purposes and demonstrate that geophysical methods constitute an important complementary tool for the geotechnical monitoring dams.

Investigation into percolation and liquid water content in a multi-layered snow model for wet snow instabilities in Glacier National Park, Canada

Water percolation in snow plays a crucial role in the avalanche risk assessment. Liquid water content and wetting front are hard to measure in the field; hence, accurate simulation of the phenomena can be of great help to forecasters. This study was the first to evaluate water percolation simulations with the SNOWPACK model using Richards’ scheme on Mount Fidelity, Glacier National Park, Canada. The study highlights that, at this site, an updated configuration on precipitation phase transition and new snow density can significantly improve simulations of the snow cover, and water percolation in particular, which can be relevant in an era of an increased occurrence of rain-on-snow (ROS) events. More specifically, emphasis was put on the quality of the input data and parameters. The analysis of the precipitation phase temperature threshold showed that a value of 1.4°C was the best suited to track the rain/snow transition on site. A 10-year analysis of 24-h precipitation measured using the rain gauge and 24-h new snow water equivalent showed an excellent correlation. New snow density sub-models were evaluated using the 24-h new snow density values taken by the park technicians. The BELLAIRE model performed best and was used to drive the snow simulations. Two SNOWPACK snow simulations were evaluated using 1) rain gauge precipitation amount (PCPM) and 2) automatic snow height measurement (HS) at the same site. Both runs simulated the main snowpack layers observed during the dry season (i.e., before spring percolation was observed), and both simulated the snow properties with good accuracy. The water equivalent of snow cover, used as a proxy for a first-order characterization of the simulations generated by both simulations, was slightly underestimated compared with four manual measurements taken on-site during the winter. Nevertheless, the comparison of both measured density and modeled bulk density showed great correspondence. The percolation timing and wetting front depth were evaluated using field measurements from field campaigns and continuous observations from on-site instruments. The main percolation events were correctly simulated and were coincident with the observed wet avalanche cycles. The results highlight the need for accurate input data on valid simulation of the wetting front and percolation timing on site. Good percolation information generated using the SNOWPACK model and Richards’ scheme could be used to assess the snowpack stability by forecasters in areas where such data are available.

Formation of pyromorphite by hydroxyapatite during lead migration in soil with different phosphorus sorption abilities

Chemical immobilization using hydroxyapatite is one of the promising approaches to handling soil with high-level lead contamination. To enhance the effectiveness of lead immobilization by hydroxyapatite, it is important to understand how lead reacts with hydroxyapatite and forms pyromorphite, insoluble lead phases. The up-flow suction percolation test was conducted in this study by the combined application of an X-ray diffraction analysis using fine-grained and sandy soils. The aim of the test was to understand how the availability of lead and phosphorus depends on the formation of pyromorphite in water-unsaturated soil. The results revealed that the available phosphorus derived from hydroxyapatite remained in the sandy soil after the percolation test, but it did not remain in the fine-grained soil. The X-ray diffraction analysis was able to quantify the amounts of lead as pyromorphite formed during the water percolation test. The presence of hydroxyapatite suppressed 48% and 76% of the lead leaching from the contaminated fine-grained and sandy soils, respectively. In the fine-grained soil, much of the pyromorphite formed in the soil near the inflow side; however, as the distance from the inflow side increased, the pyromorphite formation decreased, and lead, as water-soluble, remained. In contrast, in the sandy soil, phosphorus added as hydroxyapatite was extracted, as available. Therefore, pyromorphite homogeneously formed regardless of the distance from the inflow side, resulting in no lead as the water-soluble phases. Thus, hydroxyapatite application for lead immobilization is suitable for soil with a low phosphorus sorption ability.

Experimental study on the drainage gas recovery of an environmentally friendly nanofluid in tight gas reservoirs

AbstractThe efficiency of gas recovery in tight gas reservoirs has been a challenge in the oil and gas industry for the past decade because conventional drainage or water‐controlled gas recovery technologies typically have poor performance in low‐permeability reservoirs. To solve this problem, self‐made nanofluid was introduced to enhance drainage gas recovery in a tight gas reservoir. In this paper, nanofluid was prepared by phase reversal technology for application in a tight gas reservoir. Its thermal, acidic, alkaline, and salty stabilities were systematically investigated by using light transmittance as a shortcut index. At the same time, its biodegradability and biotoxicity were evaluated based on the industry/national standard, and the effectiveness of its drainage gas recovery was studied by dynamic gas–water percolation. The results showed that the self‐made nanofluid can be effectively used for drainage gas recovery in tight gas reservoirs. The nanofluid has chemical stability and is environmentally friendly, which fully conforms to the contemporary development trend of the oil and gas industry. The nanofluid can shift the isotonic point of the gas–water relative permeability to the left (its minimum is 1.83% at 6.25 wt.% and maximum is 4.78% at 100 wt.%) and reduce the irreducible water saturation (its minimum is 8.84% at 6.25 wt.% and maximum is 4.28% at 100 wt.%), achieving the purpose of the enhancement of drainage gas recovery. The research results provide technical support for the application of nanofluid to improve the gas production in tight gas reservoirs.

Dairy Manure Application Effects on Water Percolation, Nutrient Leaching and Rice Yield Under Alternate Wetting and Drying Irrigation

Dairy Manure Application Effects on Water Percolation, Nutrient Leaching and Rice Yield Under Alternate Wetting and Drying Irrigation

Variations in hydrological variables using distributed hydrological model in permafrost environment

The Yangtze River Source Region (YaRSR) is located in the third polar region, the most threatened zone by global warming after the Arctic. Permafrost covers eighty percent of the total area of YaRSR, while the rest is seasonally frozen ground. Due to a significant rise in air temperature, degradation of the permafrost could occur. Permafrost coverage in a river basin greatly controls its hydrology. This study focuses on hydrological modeling in this permafrost environment using the Soil and Water Assessment Tool (SWAT). The SWAT model was calibrated (1985–2000) and validated (2001–2015) on a daily time step. The results were also compared on a monthly time scale. An impermeable layer was introduced within the SWAT model to represent the permafrost conditions. The streamflow is strongly dependent on the seasonal variation of precipitation and temperature, and the rising limb of the hydrograph shows the melting of snow, the contribution of soil water, and thawing of permafrost during the spring-summer season. The permafrost layer well restricted the deep percolation of water. During the spring season, streamflow mainly consists of surface runoff because of the frozen soils. Permafrost and frozen ground thawing lead to an increase in the contribution of groundwater flow to streamflow. Ultimately, the frozen ground depletes as the temperature gets close to the freezing point. This study also describes the SWAT model application to better analyze and understand the hydrology of the permafrost/frozen ground with limited data availability.

The Impact of Coating Defects on Water Transport in the Gas Diffusion Layer of PEM Fuel Cells

Present study suggests that the breakthrough pressure of a mixed-non-wetting (MNW) meniscus is highly sensitive to the extent of coating defects. On the other hand, the wetting meniscus breakthrough pressure showed little sensitivity to the geometry of the pore. Hydrophobic coatings such as PTFE are used to improve the water transport behaviour of the gas diffusion layer. Improved performance is typically associated with high breakthrough pressure, as evidenced by experiments. Simulations employing pores consider the influence of the pore geometry, and that of heterogeneous wetting and pinning conditions of the water droplets in contact with the GDL fibrous matrix. This model examines the water percolation behaviour at pore level, the pore being defined as a contact line of an evolving droplet in contact with fibers. In contrast with the pores of a pore-network model, the pore-level model captures the evolution of a liquid-gas interface having both pinned and free contact line segments. The mixed-non-wetting behaviour is caused by the hydrophobic coating which allows parts of the meniscus contact line to deform freely in contact with the fibers, while other parts of the meniscus remain pinned due to coating defects. The MNW meniscus is critical to establishing a high breakthrough pressure and a small characteristic droplet volume. The influence of the coating defects is simulated by MNW menisci having various ratios of pinned-to-free contact line segments.

Transfer of water and contaminants in the Chalk unsaturated zone – underground quarry of Saint-Martin-le-Nœud

Abstract The aim of this study is to understand the water and contaminant (nitrate and atrazine) transfer in the unsaturated zone (UZ) of Chalk. For this, the underground quarry of Saint-Martin-le-Nœud is an exceptional site because it permits entry to the aquifer at the limit between the UZ and the saturated zone (SZ). It provides direct access to the water table: underground lakes and the output of the UZ (percolation water at the ceiling). The thicknesses of the UZ and the clay-with-flints (CwF) layer that overlie the Chalk, vary along the 1200 m length of the quarry. From 2012, the chemical evolution and the flow variability of groundwater are characterized for 16 sites with different UZ properties. Chalk groundwater has highly spatially variable hydrodynamic behaviour and geochemical properties. A peak of contaminants is observed in the UZ around 15–20 m depth, with differing behaviours of nitrate and atrazine. The downward matrix water velocity is estimated to be from 0.3 to over 0.72 m a −1 , and the water table is mainly composed of ‘old’ water resulting from transfer through the matrix. A thick CwF layer modifies (1) the transfer processes: surface water is stored in a sort of ‘near-surface perched groundwater’, the infiltration is concentrated by preferential pathways; and (2) water quality: pesticides degradation processes occur in the perched groundwater.

The Impact of Coating Defects on Water Transport in the Gas Diffusion Layer of PEM Fuel Cells

Present study suggests that the breakthrough pressure of a mixed-non-wetting (MNW) meniscus is highly sensitive to the extent of coating defects. On the other hand, the wetting meniscus breakthrough pressure showed little sensitivity to the geometry of the pore. Hydrophobic coatings such as PTFE are used to improve the water transport behaviour of the gas diffusion layer. Improved performance is typically associated with high breakthrough pressure, as evidenced by experiments. Simulations employing pores consider the influence of the pore geometry, and that of heterogeneous wetting and pinning conditions of the water droplets in contact with the GDL fibrous matrix. This model examines the water percolation behavior at pore level, the pore being defined as a contact line of an evolving droplet in contact with fibers. In contrast with the pores of a pore-network model, the pore-level model captures the evolution of a liquid-gas interface having both pinned and free contact line segments. The mixed-non-wetting behaviour is caused by the hydrophobic coating which allows parts of the meniscus contact line to deform freely in contact with the fibers, while other parts of the meniscus remain pinned due to coating defects. The MNW meniscus is critical to establishing a high breakthrough pressure and a small characteristic droplet volume. The influence of the coating defects is simulated by MNW menisci having various ratios of pinned-to-free contact line segments.

Study on Nitrogen Loss Rules of Paddy Fields under Different Irrigation and Drainage Modes in Southern China

With the growing problem of agricultural nonpoint source pollution, it is an urgent issue to explore irrigation and drainage modes suitable for rice-growing areas in southern China. Barrel experiments were conducted to study the variation of NH4+-N, NO3−-N and TN concentrations in surface drainage and deep percolation water, as well as the rules of nitrogen runoff losses and leaching losses. Treatments included frequent and shallow irrigation (FSI), drought planting with straw mulching (DPS) and water catching and controlled irrigation (WC-CI). The results showed that the trends of NH4+-N, NO3−-N and TN concentrations in surface drainage were similar, and the N concentration gradually decreased with increasing drainage frequency. The trends of NH4+-N, NO3−-N and TN concentrations in deep percolation water were similar, rising to a peak within 5~7 days after fertilization and then gradually decreasing. NH4+-N loss load was the main form of N loss load in surface drainage and deep percolation water, which accounted for 42.06~89.16%. Compared with FSI, DPS significantly increased surface drainage and N runoff loss loads by 98.67% and 125.86%, respectively, while WC-CI significantly reduced them by 59.21% and 66.38%, respectively. Deep percolation water was reduced by 68.59% and 37.99% for DPS and WC-CI, respectively, and N leaching loss loads were reduced by 74.69% and 43.23%, respectively. Compared with FSI, the total TN loss load was significantly reduced by 76.69% and 43.34% for DPS and WC-CI, respectively, and the pollution control was better for DPS. WC-CI significantly increased rice yield by 7.31%, while DPS decreased by 0.95 % due to long-term water stress. Comprehensively considered, WC-CI has obvious advantages, which can reduce nitrogen loss and maintaining a high yield.

The seasonality of nitrate and phosphorus leaching from manure and chemical fertilizer added to a chernozemic soil in Canada.

Identifying seasons sensitive to nutrient losses could help farmers and policymakers to formulate effective nutrient loss reduction strategies. This long-term study monitored water percolation as well as nitrate (NO3 -N) and total phosphorus (TP) leaching from liquid swine manure and chemical fertilizer applied to intact core lysimeters in a sandy loam soil in Manitoba, Canada. Water percolation, NO3 -N, and TP leaching were monitored from 2005 to 2016. Chemical fertilizer showed greater average annual mean water percolation (p=.01), annual flow-weighted mean concentration (FWMC) of NO3 -N (22mg L-1 ; p<.001), and annual NO3 -N leaching (36kg N ha-1 ; p=.002) compared with the manure treatment (FWMC NO3 -N, 15mg L-1 ; NO3 -N leaching load, 22kg N ha-1 ). Average annual mean TP loss did not differ between treatments (p=.86). Spring (April-June) was the most sensitive season, when>75% of annual percolation,>80% of annual NO3 -N, and>68% of annual TP leaching losses occurred from both manure and chemical fertilizer. Annual NO3 -N and TP leaching increased exponentially with cumulative winter and spring precipitation (control, r2 =.69; manure, r2 =.79; chemical fertilizer, r2 =.63) and decreased with winter and spring air temperatures. The largest spring NO3 -N and TP leaching losses were observed in 2013, which followed the dry year of 2012, indicating the potential for nutrient flushing. The findings emphasize the need for environmentally sound N and P management strategies in cold North American regions underlain by coarse-textured soils, particularly during the spring season.

Pengolahan Lindi Menggunakan Advanced Oxidation Process (AOPs) Berbasis Ozon

Leachate can be formed from the percolation of water that passes through the garbage. The high content of organik and metallic substances in leachate can cause environmental damage, so it must be treated first before being discharged into the environment. This study aims to determine the effectiveness of ozonation in neutralizing pH and reducing the levels of TSS, BOD, COD in the leachate of the Griyo Mulyo landfill using the AOPs method based on ozonation. Studies on ozonation in leachate treatment have been carried out by varying the ozonation time (15, 30, 45, and 60 minutes). Parameters that have been observed are pH, TSS, BOD, COD. The results showed that the best ozonation time for leachate pH was at 15 minutes with a value of 7, the best ozonation time for leachate TSS was at 15 minutes with a value of 56 mg/L. The best ozonation time for BOD and COD was at 45 minutes with values ​​of 511 mg/L and 1260 mg/L, respectively. The best percentage of removal efficiency for TSS, BOD and COD reached 67%; 84.1%; and 88.41%.

A dual-porosity model for coupled rainwater and landfill gas transport through capillary barrier covers

A two-dimensional dual-porosity model for coupled rainwater and landfill gas transport through capillary barrier covers (CBCs) was established. The proposed model was partially verified using published data from a laboratory loess column test. By fitting the field-measured data using the proposed model, the optimal dual-porosity parameters of the in-situ loess of a loess/gravel CBC in Northwest China were determined to be wf = 0.1 (volume fraction of macropore system), Kf/Km = 150 (intrinsic permeability ratio of macropore to micropore system) and Re = 1 (reduction factor of mass exchange at the interface between macropore and micropore systems). This model was used to predict the performance of the CBC experiencing a 15-day rainfall period followed by a 30-day no-rainfall period. Results showed that the presence of macropores induced an earlier occurrence of percolation accompanied with a higher percolation rate. The cumulative percolation and CH4 emission rate derived from the dual-porosity model were about 50 % and one order of magnitude higher than those predicted by the single-porosity model, respectively. In addition, the existence of gravel layer had remarkable influence on minimizing water percolation and CH4 emission, but these were practically independent of its thickness. The results of this study can provide an effective method, crucial parameters and guidelines for the design of CBCs.

Improvement in potassium budget with water outflow reduction through reducing excessive irrigation in a paddy field

ABSTRACT Countermeasures to reduce radiocesium uptake by crops have been implemented in farmlands affected by the accident at Tokyo Electric Power Company’s Fukushima Daiichi Nuclear Power Plant in 2011. A widely practiced countermeasure is the application of K. Long-term maintenance of soil K is crucial due to the long physical half-life of 137Cs (30 years). Plant-available K budgets can be used as an indication of sustainable maintenance. Our previous study found that large water outflow, especially percolation, associated with excessive irrigation caused major K outflow and a negative K budget in a paddy field in Fukushima in 2018. The present study evaluated whether decreasing the water outflow by reducing the irrigation volume from 6300 to 1900 mm reduced K outflow and improved the K budget in the field during the cropping period in 2019. K concentrations in soil solution were comparable in both years, and the percolation water volume decreased to 37% that of 2018, resulting in a 53% reduction in the K output from 392 to 184 kg ha–1. The input via irrigation also decreased (−35 kg ha–1), but the output via surface runoff showed a greater reduction (−58 kg ha–1) owing to a 70% decrease in the water volume compared with 2018. Consequently, the K budget was substantially improved (from −289 to −57 kg ha–1), highlighting the importance of controlling water outflow, particularly percolation, for soil K maintenance in paddy fields with high permeability.

Genesis and soil environmental implications of intact in-situ rhizoliths in dunes of the Badain Jaran Desert, northwestern China

Desert rhizoliths are generally found as weathered, broken and scattered samples on dune field surface, but rarely in-situ in their initial states buried under the soil of desert in the Badain Jaran Desert, northwest China. This study offers an assessment of the morphological, mineralogical, and chemical properties of intact and in-situ rhizoliths found in soils of swales and depressions among dune chains. The characteristics of these rare and precious objects were assessed using optical polarizing microscopy, cathodoluminescence, scanning electronic microscopy, radiocarbon dating, and stable isotopic analyses, providing the opportunity for discussion of the rhizolith formation mechanisms and associated environmental conditions. Field and laboratory investigations showed that the in-situ intact rhizoliths were formed only in the places where Artemisia shrubs are living, and the remaining root relicts within rhizoliths belong to this species. The spatial distribution of rhizoliths also suggested that low topographic positions on a landscape provided soil moisture, and redox environments favored rhizolith formation. A semi-closed redox environment in the subsoil at swales and depressions, where water is always present, along with the sandy soil texture, facilitated fast water percolation to deeper depths and condensation. Such a soil environment not only provides water for Artemisia growth, but also for the weathering of minerals such as felspars and calcite from primary carbonates, and for the decomposition of root relicts. Furthermore, harsh climatic conditions, such as strong winds and solar radiation, led to water evaporation through dead root channels and triggered the calcification along the root relicts. The entrapped lithogenic carbonates and to a lesser extent the decomposition of Artemisia roots provided the carbon sources for the rhizoliths formation, while the weathering of soil minerals, particularly feldspars and carbonates, was the main source of Ca. Rhizoliths in the Badain Jaran desert formed relatively quickly, probably over a few soil drying episodes. This led to the entrapment of a large quantity of lithogenic carbonates (more than 90% of carbon) within rhizolith cement. The re-dissolution of the entrapped lithogenic carbonates in rhizolith tubes should be taken into account in the paleoenvironmental interpretation of 14C ages, the latter suggesting that rhizoliths formed during the Holocene (~ 2053 years cal BP, based on root organic relicts).

The response of aquatic fauna to variable environmental conditions in Ghețarul de la Vârtop cave (Apuseni Natural Park, Romania)

Caves with permanent and temporary ice formations exists at mid-to-high northern latitudes, at elevations between 0 and &amp;gt;3000 meters above sea level. In such caves, rare and endemic species or glacial relicts strictly tied to cold microclimates habitat conditions have evolved and the negative temperatures have contributed significantly in shaping the structural pattern of both terrestrial and aquatic communities. Aquatic dwellers inhabiting ice caves are likely to show resistance and have special physiological adaptation to cope with constantly low air and water temperatures. Ghețarul de la Vârtop cave is a short (340 m) cave located in the Apuseni Natural Park (northwest Romania) that hosts temporary ice formations near its entrance. In 2021, we have initiated a study aiming to understand how low temperatures in the cave are shaping the structure of underground fauna, along a temperature gradient through the cave. The sampling design imply monthly monitoring of air temperature (hourly measurements using data loggers), water physical and chemical characteristics and the structure of aquatic fauna communities. In this paper we present preliminary data on the environmental conditions and aquatic invertebrate communities present in percolation water and associated gours from the cave. Aquatic fauna is represented by nematodes, oligochaetes and several crustacean species the majority stygobites, of which at least three are potentially new to science. The surprising presence of Acanthocyclops reductus, considered a Tertiary relict living in warm water raises discussions on its tolerance to highly variable temperatures but also on the colonisation history of the caves on a regional scale. Investigations of cave aquatic fauna in caves with permanent and temporary ice offer hints to understand the ecology of the fauna, and also to further assess the mechanisms involved in adaptations of species to cope with constantly low-water temperatures.