Thin Soil Research Articles

Differences and mechanism of dynamic changes of Cd activity regulated by polymorphous sulfur in paddy soil

Sulfur (S) can decrease the bioavailability of Cd in paddy soil, and therefore reduce Cd uptake by rice. However, the dynamic influence mechanism of different forms of sulfur on the bioavailability of cadmium in soil has not been systematically studied. In this study, we used Diffusive gradients in thin films (DGT) technology and soil pore water sampling technology to investigate the effects of different types of S application on the bioavailability of Cd. The three forms of S are elemental sulfur (S0), sodium sulfate (SO42−), and mercapto-grafted palygorskite (MP), which have been treated in six ways according to CK, SL, SH, SO42L, SO42H, MP (L and H are the low and high levels of treatments). The results showed that soluble and labile Cd concentration was quickly fixed after flooding but activated after rice transplantation. Both MP and SL treatments increased the content of dissolved organic carbon (DOC) and significantly reduced the accumulation of Cd in roots and grains. The Cd content of roots treated with MP was only 0.50 mg kg−1, which was 77.6% lower than the Cd content in CK (2.22 mg kg−1). S promotes the reduction and dissolution of Fe, and the formation of FeS/FeS2 is also one of the reasons for the low bioavailability of Cd, while the SH treatment has a greater effect on lowering pH, so the effect of fixing Cd is not obvious. In addition, SO42− treatment delays the soil reduction process, so it cannot effectively fix Cd. At the stage of rice maturity, dissolved Cd increased in S treatment, but MP treatment did not have this phenomenon. The possible reason was the consumption of DOC or the oxidation of CdS which caused Cd to enter the soil solution. Taken together, Fe–S play a critical role in controlling the mobilization of Cd in paddy systems.

Organochlorine Pesticides in Karst Soil: Levels, Distribution, and Source Diagnosis.

Excessive reclamation and improper use of agrochemicals in karst areas leads to serious non-point source pollution, which is of great concern and needs to be controlled, since contaminants can easily pollute groundwater due to the thin patchy soil and developed karst structures. The occurrences of organochlorine pesticides (OCPs) in karst soil were investigated by analyzing 25 OCPs in the karst soils near the Three Gorges Dam, China. The total concentrations of OCPs ranged 161–43,100 (6410 ± 9620) pg/g, with the most abundant compounds being p,p′-DDT and mirex. The concentration differences between the orchard and vegetable field and between upstream and downstream presented the influences of land-use type and water transport on the OCP spatial distributions. Composition analysis indicated the possible fresh inputs of lindane, technical DDT, aldrin, endrin, mirex, and methoxychlor. Their illegal uses implied an insufficient agrochemical management system in undeveloped karst areas. Principal component analysis with multiple linear regression analysis characterized the dominant sources from current agricultural use and current veterinary use in the study area. OCPs in the soils might not pose significant cancer risk for the residents, but they need to be controlled due to their illegal uses and bioaccumulation effect via the food chain.

Effect of soil-rock interface position on seismic response of subway station structure

For subway stations in a site with thin soil layers on the engineering rock, the lower part of the subway station is embedded in the hard rock mass and the upper part is buried in the soil layers. The presence of the soil-rock interface may lead to significant increase to the seismic responses of the adjacent soil masses and underground structures. In this paper, the effect of the soil-rock interface position on the seismic response of a two-story and three-span subway station structure is investigated by numerical analyses. It is found from the numerical analyses that a most detrimental soil-rock interface position exists and makes the underground structure have maximum responses under a given artificial earthquake motion. For the upper floor, the most detrimental soil-rock interface position is near the middle slab. For the lower floor, the most unfavorable soil-rock interface position is near the bottom slab. Softer site generally leads to greater structural responses under the same intensity of ground motion excitation. On the basis of the above findings, three earthquake motions included above an artificial earthquake motion and other two real earthquake motions and three burial depths of structure are further studied. Same conclusions can be obtained for the structure with different burial depths or subjected to different input earthquake motions. The conclusions drawn from the numerical examples of this paper may be useful for seismic design of subway station structure buried in shallow soil layers on rock.

Experimental Investigation on the Mechanism of Piping in Different Two-Stratum Levee Foundations with Weak Spots

Abstract Earthen levees along rivers may break down because of piping; this is especially the case for levees built on two-stratum levee foundations with an impervious stratum and an underlying pervious substratum. However, the initial stage of this piping is difficult to recognize because finding the piping outlets along the whole levee is challenging. Practical experience confirms that weak spots, such as holes or thickness reductions in the blanket stratum, usually occur at the levee toe. Some of these are harmless, whereas others are not. This study takes weak spots into consideration and provides a detailed description and evaluation of the piping features. Experiments were conducted on three models with different pervious conditions in a flume. Weak spots caused by holes, a thickness reduction, or exposure of the substratum at the levee toe were tested. The results show that the thickness reduction influences the formation of continuous sand boiling once the confined water bursts the blanket stratum. The potential for piping is reduced when the pervious substratum is composed of thin and uniform soil. In the absence of a covering stratum, piping happens with sand boiling. Three typical phenomena, namely sand boiling near the levee toe, a pressure decrease of the confined water, and a rise in the hydraulic gradient in the pervious substratum, could be used as indicators of the occurrence of piping.

Modelling of Irrigation Return Flow in Unconfined Aquifer of Dharoi Command in Mehsana District of Gujarat, India

Surface water flow and subsurface flow have traditionally been investigated separately and simulators have been developed over the years, to model each of these systems. Growing interest in conjunctive water management, and need for simulations of surface/subsurface flow and their interactions has lead to the linking of models of the respective domains. This study from Dharoi command area, using MODFLOW, showed pertaining to the second layer of the calibrated model. The first layer is a thin soil cover layer of about 3 m uniform thickness. Top layer is kept under unconfined water table condition, where as the next layer is given the scope of transforming between water table to confined state and vice versa depending upon the fluctuation of the computed water level with respect to the bottom boundary of the top layer. No recharge and discharge options other than a single boundary condition of average May water level in the extreme north-east grid has been allowed. This calibration is based upon matching the observed and computed average gradient of the water table (hydraulic gradient) and nothing to do with matching the point to point values of the observation wells as that could lead to misappropriation in respect of hydrologic condition. Over all gradient of the water table in the area of interest is computed as 0.23 m per km in comparison to an observed hydraulic gradient of 0.3 m per km. The rivers such as Sabarmati downstream of Dharoi dam and up to Bijapur, Rupen and Pushpawati are activated in the transient run. Conductance value is considered as 0.0001 m/sec for all the rivers. proximity of the second layer under unconfined state. Comparisons of water levels in selected locations. Overall match between the trends and the point values indicate that the calibrated model transient run can be considered as base case and various options can be studied with this model. Visual MODFLOW is very effective to know the present scenario of ground water flow, water level of aquifer, wells, also point values indicate that the calibrated model transient run can be considered as base case and various options can be studied with this model. Visual MODFLOW is very effective to know the present scenario of ground water flow, water level of aquifer, wells, also distribution of spatial recharge, specific yield distribution. It gives very close result to the observed value.

Determining the Height of Water-Flowing Fractured Zone in Bedrock-Soil Layer in a Jurassic Coalfield in Northern Shaanxi, China

The height of the water-flowing fractured zone is the most important technical parameter for water prevention and control in a coal mine. Due to the numerous factors affecting the water-flowing fractured zone, it is difficult to accurately identify the zone. Currently, no effective way exists for determination of the water-flowing fractured zone in a soil layer. To accurately determine the development law of the water-flowing fractured zone in the bedrock-soil layer of a Jurassic coalfield in northern Shaanxi, China, we conducted a comprehensive study using microresistivity scanning imaging technology, apparent density logging, long-range gamma logging, observation on drilling flushing fluid consumption, physical simulation, and numerical simulation. The following results were obtained: (1) The ratio of the height of the water-flowing fractured zone to the mining height was 28.3–28.5, which was obtained by microresistivity scanning imaging technology, whereas the ratio of the height of the water-flowing fractured zone to the mining height was 28.1–29.1, determined by apparent density logging, long-range gamma logging, physical simulation, and numerical simulation. The microresistivity scanning imaging results were consistent with those obtained by other methods. (2) Based on the thickness of the soil layer and the bedrock, the height model of the water-flowing fracture zone was divided into four regions, that is, the thick bedrock-thick soil layer region, thick bedrock-thin soil layer region, thin bedrock-thin soil layer region, and thin bedrock-thick soil layer region. A mathematical model describing the difference between the thickness of the water-flowing fractured zone and the bedrock and the thickness of the soil under the condition of bedrock-soil was established. (3) We conclude that microresistivity scanning imaging technology can accurately detect the height of the water-flowing fractured zone in a soil layer, and the apparent density logging and long-range gamma logging can precisely detect the height of the water-flowing fractured zone in bedrock. This is a new comprehensive method for research on the height of the water-flowing fractured zone that can provide a reliable basis for water prevention and control in mines.

Robust identification and characterization of thin soil layers in cone penetration data by piecewise layer optimization

Cone penetration testing (CPT) is a preferred method for characterizing soil profiles for evaluating seismic liquefaction triggering potential. However, CPT has limitations in characterizing highly stratified profiles because the measured tip resistance (qc) of the cone penetrometer is influenced by the properties of the soils above and below the tip. This results in measured qc values that appear “blurred” at sediment layer boundaries, inhibiting our ability to characterize thinly layered strata that are potentially liquefiable. Removing this “blur” has been previously posed as a continuous optimization problem, but in some cases this methodology has been less efficacious than desired. Thus, we propose a new approach to determine the corrected qc values (i.e. values that would be measured in a stratum absent of thin-layer effects) from measured values. This new numerical optimization algorithm searches for soil profiles with a finite number of layers which can automatically be added or removed as needed. This algorithm is provided as open-source MATLAB software. It yields corrected qc values when applied to computer-simulated and calibration chamber CPT data. We compare two versions of the new algorithm that numerically optimize different functions, one of which uses a logarithm to refine fine-scale details, but which requires longer calculation times to yield improved corrected qc profiles.

Soils of mountain-forest landscapes of the Zeysky Nature Reserve

The article describes the properties and modern classification position of mountain-forest soils at the eastern end of the Tukuringra Range. Based on morphological analysis, three groups of soils have been identified within the study area: Cambisols, Gleysols and Podzols. The soils of the Cambisols group are associated with the slopes of the southern exposure and are characterized by the presence of humus horizon, good drainage, expressed rockiness, and formation of an aggregated metamorphosed layer of brown colour in the middle part of the profile. Soils of the Gleysols group are formed in permafrost areas within the lower part of the western exposure slopes. The lower part of the soil profile is characterized by intense thixotropy. The northern exposure slopes are characterized by high prevalence of permafrost, thin rank soils, and bedrock exposures. Under these conditions, soils of the Podzols group are described within the smooth slopes and floodplain terraces of mountain rivers. These soils are formed on colluvial deposits; they have light granulometric composition and good drainage. In the upper part of the profile, the dry peaty layer is well developed as a result of conservation of organic residues.

Long Term Application of Fertilizers in Eastern Amazon and Effect on Uranium and Thorium Levels in Soils

In recent years, the use of fertilizers has increased in the Amazon. Phosphate fertilizers, which are commonly used, can present high concentrations of radioelements. In the present study, the activity concentrations of uranium (U) and thorium (Th) in Oxisols and Ultisols cultivated with citrus (Citrus sinensis (L.) Osbeck), oil palm (Elaeis guineensis Jacq.) and black pepper (Piper nigrum L.), with 26, 10 and 5 years of implantation, respectively, were evaluated. The potential risk of contamination was estimated by the enrichment (EF) and bioaccumulation (BAF) factors. Pearson’s correlation coefficients indicated a significant relationship between the concentrations of U and Th in soil and plant and the soil properties pH, Ca2+, Mg2+, K+ and P. The enrichment (EF < 2) and bioaccumulation (0.01 < BAF < 0.05) factors were low. In plant tissues, the concentrations of 238U followed the order: citrus > black pepper > oil palm, and the concentrations of 232Th followed the sequence: black pepper >> citrus > oil palm. The activity concentrations of 238U and 232Th in the soil cultivated with black pepper, as well as in the soil of the reference area close to the citrus plantation, were higher than the world average values of 35 and 30 Bq kg−1, respectively, established by the United Nations Scientific Committee on Effects of Atomic Radiation. Perennial crops that are fertilized annually must be monitored by environmental agencies due the accumulation of elements that can promote potential risks to human health.

Watershed Sediment Yield Following the 2018 Carr Fire, Whiskeytown National Recreation Area, Northern California

AbstractWildfire risk has increased in recent decades over many regions, due to warming climate and other factors. Increased sediment export from recently burned landscapes can jeopardize downstream infrastructure and water resources, but physical landscape response to fire has not been quantified for some at‐risk areas, including much of northern California, USA. We measured sediment yield from three watersheds (13–29 km2) that drain to Whiskeytown Lake, California, within the area burned by the 2018 Carr Fire. Structure‐from‐Motion photogrammetry on aerial images combined with sonar bathymetric mapping of submerged areas indicated first‐year post‐fire sediment yields of 4,080 ± 598 t/km2 (Brandy Creek), 2,700 ± 527 t/km2 (Boulder Creek), and 305 ± 58.0 t/km2 (Whiskey Creek)—some of the first post‐fire yields measured in northern California and 64, 42, and 4.8 times greater than pre‐fire yields, respectively. These were measured during a wet year and resulted largely from rilling erosion and fluvial sediment transport, without post‐fire debris flows. Rilling preferentially developed in contact with dirt roads, aided by thin soils and exposed bedrock, and on slopes vegetated by chaparral pre‐fire. The second post‐fire year (a dry year) was characterized by fluvial reworking and delta progradation of the first‐year deposits and relatively little new sediment export. First‐year sedimentation of 111,000 m3 represented minor loss of storage capacity in Whiskeytown Lake but would be detrimental to smaller reservoirs; in general, increased sediment yields from western US watersheds as fire and extreme rainfall increase will likely pose risks to water quality and storage.

Comparison of models for predicting cleaning of viscoplastic soil layers by impinging coherent turbulent water jets

Different approaches to model the cleaning of (i) very thin and (ii) thin soil layers by impinging water jets are compared to evaluate their predictive capabilities. Cleaning experiments were performed with coherent 2 mm and 3 mm diameter water jets (Re > 10,000) impinging on flat layers of an insoluble, viscoplastic petroleum jelly. The jelly exhibited creep below the yield stress and Herschel-Bulkley behaviour above it. A two-film shear-driven model for case (i) gave very poor predictive capability, partly due to the complex soil rheology. Case (ii) data were compared to modified versions of the phenomenological model of Fernandes and Wilson (2020), and a fully-coupled CFD model of the liquid and soil motion using the volume of fluid method. The modifications to the former did not improve its accuracy. The latter gave a good prediction of the initial cleaning behaviour for the case considered: the high computational cost precluded extensive testing.

10Be and 14C data provide insight on soil mass redistribution along gentle slopes and reveal ancient human impact

PurposeSpatial and temporal patterns of past erosional events are a useful and needed information to explain observed soil patterns in different landscapes. Soil thickness reflects the overall expression of pedogenesis and erosion. Forested soils of Northern Germany exhibit varying soil thicknesses with thin soils on crest positions and buried soils at the footslope. The aim of this study is to reconstruct the complex soil mass redistribution and soil patterns of this forested area due to different periods of erosion and stability.MethodsWe explored the explanatory power of both 10Be (in situ and meteoric) on a hillslope and we 14C-dated buried horizons at different depths.ResultsThe 10Be depth profiles did not show an exponential decrease with depth. They had a ‘bulge’ shape indicating clay translocation and interaction with oxyhydroxydes (meteoric 10Be), bioturbation and soil mass redistribution (in situ 10Be). The combined application of both 10Be and 14C dating revealed progressive and regressive phases of soil evolution. Although Melzower Forest is protected (same vegetation) since the past 250 years, both 10Be clearly indicated major soil mass redistribution along the investigated catena.ConclusionA strong erosion impulse must have occurred between 4.5 and 6.8 kyr BP indicating an earlier human impact on soil erosion than previously postulated (~ 3 kyr earlier). Our findings correlate in fact with the first settlements reported for this region (~ 6.8 kyr BP) and show their immediate effect on soils. The overall soil redistribution rates in this forest are surprisingly similar to those obtained from a nearby agricultural area.

Effects of different tree species on infiltration and preferential flow in soils developing at a clayey spoil heap

Soil recovery is crucial for successful ecosystem restoration at post-mining sites. Water infiltration and preferential flow in soil are important but little studied soil characteristics. In this study, we explore effects of tree species on infiltration, geometry of preferential flows, size distribution and origin of pores, and related properties of soil. An experiment was conducted at post-mining sites developing under monocultures of three tree species (alder, oak and spruce) after lignite mining near Sokolov, Czech Republic. A key hydraulic parameter of soil, field saturated hydraulic conductivity (Ks), measured in topsoil, was highest under alder (mean value of 6.9 × 10−5 ms−1) and lowest under spruce (mean value of 1.9 × 10−5 ms−1). In subsoil, there were no significant differences in Ks between tree species. For the alder site, dye tracer tests showed that water penetrates almost uniformly to the top 15 cm of soil depth and with the greatest lateral flow. In a deeper part of the alder soil profile, preferential flow was concentrated around earthworm burrows and roots, where the two often occur together. Thin soil sections of alder soil show that earthworm casts and burrows substantially contribute to porosity around the roots (59 % of dyed worm-created structures in alder-root microsite). A similar situation was observed in oak, but preferential flows along roots started from the surface and cross section of preferential flow was smaller than in alder soil. In spruce, preferential flow was concentrated around roots and cracks in claystones and the cross section was even smaller. Comparison among the forest stands indicates that overall porosity does not correspond with infiltration of dye tracer and Ks, which seem to be more driven by pore size distribution and pore connectivity. This is consistent with larger occurrence of macropores (>300 μm) in alder. The results show that trees affect infiltration and preferential flow in soil by their specific root systems and to a large extent indirectly by effect of litter quality on earthworm populations, which then enhance macroporosity and pore connectivity.

Latent Heat Flux (Evapotranspiration) in Summer Season on Rooftop Greening Soil with Bamboo Charcoal Sublayer at a Building in West Japan

The effect of a thin and light greening system with bamboo charcoal layer for water retention on heat fluxes, in particular latent heat flux (evapotranspiration rate), under no irrigation condition, on the rooftop of a building in Higashi-Hiroshima, West Japan, was investigated. In April 2019, lawn seeds (Zoysia tenuifolia) were sown which were germinated, reached a height of 70 mm by May when 100% of the vegetation area was covered. The air temperature and humidity at two different heights (0.3 m and 1.8 m) above greening soil surface, latent, and sensible heat fluxes were estimated. Bowen ratio was employed to collect the data on surface heat balance and soil water content during the summer season (June to September) in 2019 on the rooftop of a building in Higashi-Hiroshima, West Japan. The latent heat during daytime for a week without rainfall in each month was compared with the evapotranspiration rate. Owning to the vegetation development, the ground heat flux on greening soil surface decreased from -400 W/m2 to -200 W/m2 (flux from air to soil) during sunny daytime in July, and it was less than -100 W/m2 in August, although net radiation was maintained around 800 W/m2 over the season except in September. The monthly net radiation flux for an entire day (daytime and nighttime) ranged between 55 and 125 W/m2 (average: 95 W/m2) for the summer season of which 32-66% (average: 48%) was occupied by latent heat. Evapotranspiration from greening soil ranged between 1.24 and 1.82 mm/day, averaged at 1.51 mm/day throughout the season, which corresponded to about 26% of total rainfall over the season ( r 2 = 0.88 , p < 0.01 ; S . E = 0.06 ) between the estimated and measured values. These observations suggested that the thin and bamboo coal light soil layer greening system, even without constant irrigation, could maintain the development of lawn grass and transformed more than half of net radiation to latent heat, i.e., evapotranspiration, insulating most ground heat in midsummer, which may be mostly due to bamboo charcoal sublayer.

A laboratory-scale phytocover system for municipal solid waste landfills

ABSTRACT A tremendous increase in municipal solid waste (MSW) generation and its poor management is observed in almost all the developing countries. Landfilling, though undesirable, is an unavoidable disposal option with leachate generation and landfill gas (LFG) emissions as its major inescapable consequences. To evade these dismal outcomes of waste contentment, plant-soil based cover options are being studied widely. In the present study, an attempt was made to employ locally available plants for the phytoremediation of landfills. The experimental set-up was designed using 100 kg of MSW which was laid over with a thin soil layer of 30 cm. The efficiency of the laboratory-scale experimental set-up of 1 m3 volume was assessed in terms of trace element remediation and LFG oxidation. The initial and final parameters were finally assessed and compared. Plant species were found to develop a strong root zone, thereby reducing the infiltration of water into the waste mass. The present study showed a reduction in LFG emissions of 11.12%, 54.38%, and 32.12% in the deep zone, root zone, and topsoil zone, respectively. Furthermore, the study of the microbes, influencing soil chemical characteristics, could be helpful for designing an appropriate phytocover under diverse climatic conditions of India.

Subsurface Moisture Regulates Himalayan Groundwater Storage and Discharge

AbstractThrough the release of groundwater, most mountain rivers run year‐round despite their small catchments and sporadic precipitation. This makes mountain ranges important sources of reliable freshwater for downstream populations in many parts of the world. However, due to a lack of ground instrumentation, little is known about groundwater dynamics in mountainous landscapes. Recent research has shown that the amount of moisture trapped in the soil and weathered rocks in the vadose zone can significantly buffer groundwater recharge and runoff but the wider recognition of this effect on major mountain systems has not been yet established. In this study, we test whether the moisture reservoir has an impact on hydrological fluxes in a steep Himalayan catchment during three monsoon seasons. We measured an array of parameters including relative seismic velocity changes from ambient noise correlations. This noninvasive technique allows us to monitor groundwater dynamics in conjunction with classical hydrological measurements. We found that the moisture saturation in the vadose zone controls the onset of groundwater recharge and runoff and therefore determines the annual water availability supplied by monsoon precipitation. We model this dynamic using a surface layer that has a finite storage capacity that controls the connectivity of surface flux to groundwater. The extension of this concept, which is thought to apply widely in flat and undulating landscapes, to steep mountain topography with thin and discontinuous soils underlain by regolith and bedrock has important implications for mountain hydrology.

Disastrous Flash Floods Triggered by Moderate to Minor Rainfall Events. Recent Cases in Coastal Benguela (Angola)

The present work focuses on two recent flash floods in coastal Benguela (Angola), both triggered by moderate rainfall but which had disastrous consequences for local populations (namely 71 deaths in 2015 and 17 in 2019). The research involved a regional survey to establish the effects of these floods combined with a geomorphological and socio-economic analysis of the most affected areas to understand the main forcing factors. The two flash floods produced major damage in restricted sectors within very small coastal catchments (<16 km2). The prevalence of fine-grained sedimentary rocks, relatively steep hills, thin soil cover, and vegetation scarcity are natural factors that promote surface runoff. However, socio-economic conditions are most likely the main reasons of flood damage. Namely, rapid population growth with poor planning and making use of low-quality construction materials, the high waste yields that are not properly managed and the absence of flood risk awareness. In the small valleys around the fast-growing cities of coastal Benguela, hazardous flash floods occur recurrently, even after moderate precipitation. Most affected areas are determined by local conditions that compromise drainage at the time of the rainfall event, being very difficult to predict.

Climatic and biotic influences on isotopic differences among topsoil waters in typical alpine vegetation types

Hydrogen and oxygen isotopes have been widely used to investigate global hydrologic cycles. However, the most studies of soil water isotopes have overlooked the importance of O-horizon that may potentially influence the accurate evaluation of hydrologic processes, especially in the alpine ecosystem with thin soil layers. To address this knowledge gap, soils were sampled from the O-horizon and the 0–10 cm soil layer from 107 sites in the grasslands and woodlands of the Western Sichuan alpine ecosystem in order to evaluate the influence of climatic and biotic factors on the isotopic differences (expressed as the logarithmic of effect sizes, lnRR), which represented the difference of δ2H and δ18O between the O-horizon and the 0–10 cm soil layer. The isotopic differences between the O-horizon and the 0–10 cm soil layer were significantly different in the grasslands, but not in the woodlands. The influence of climatic factors on the lnRR was limited relative to the biotic factors, and the influence of climate contrasted with expectations based on an evaporation principle. Rather, aboveground biomass (AGB) was significantly correlated with the lnRR between and within the soil water from different vegetation types. Consequently, the observed differences were mainly related to the vegetation conditions that influence the microclimates within canopies. Therefore, the investigations of hydrological processes may inaccurately estimate their influences when not separately considering the especially high stable isotope values of the O-horizon in grasslands of alpine regions with thin soil layers. In particular, the influence of O-horizon should be considered in the areas where AGB is less than 100 t/hm2.

Co-evolution of xylem water and soil water stable isotopic composition in a northern mixed forest biome

Abstract. Plant–soil water isotopic dynamics in northern forests have been understudied relative to other forest types; nevertheless, such information can provide insight into how such forests may respond to hydroclimatic change. This study examines the co-evolution of xylem water and soil water stable isotopic compositions in a northern mixed forest in Ontario, Canada. Gross precipitation, bulk soil water and xylem water were sampled from pre-leaf out to post-senescence in 2016 for eastern white cedar, eastern hemlock, red oak and eastern white pine. Near-bole soil water contents and mobile soil water isotopic compositions were measured for the last three species. Mobile soil water did not deviate significantly from the local meteoric water line (LMWL). In contrast, near-surface bulk soil water showed significant evaporative enrichment relative to the LMWL from pre-leaf out to peak leaf out under all tree canopies, while xylem water was significantly depleted in 18O and particularly 2H relative to bulk soil water throughout the growing season. Inter-species differences in deviation of xylem water from the LMWL and their temporal changes emerged during the growing season, with coniferous species xylem water becoming isotopically enriched, while that of red oak became more depleted in 2H and 18O. These divergences occurred despite thin soil cover (generally <0.5 m depth to bedrock) which would constrain inter-species differences in tree rooting depths in this landscape. Isotopic fractionation at the tree root and fractionation of xylem water via evaporation through the tree bark are among the most plausible potential explanations for deviations between xylem and soil water isotopic compositions. Differences in the timing and intensity of water use between deciduous and coniferous trees may account for inter-specific variations in xylem water isotopic composition and its temporal evolution during the growing season in this northern forest landscape.

Evaluation of cool-season binary mixtures as pasture: Herbage yield, nutritive value, and beef cattle performance

• Hybrid bromegrass-legume mixtures produced 54% more biomass than Russian wildrye-legume mixtures at Lanigan site, while biomass did not differ between mixtures at Swift Current site. • Legume contribution to total biomass was greater at Swift Current than at Lanigan site, and alfalfa contributed more to biomass than sainfoing at Lanigan site. • Crude protein tended to be greater for RWR mixtures than HBG mixtures at Lanigan site. • Beef steer gain was similar for all binary mixtures at Swift Current site, however steer gain was greater at Lanigan site for sainfoin mixtures, suggesting inclusion of legume in pasture was beneficial. • Results demonstrate that all four binary mixtures appear to be suitable for late summer and fall grazing. ABSTRACT A 3-year study (2016, 2017, and 2018) was conducted to compare the effects of alfalfa (ALF; cv. Yellowhead) (Medicago falcata L.) or sainfoin (SF; cv. AAC Mountainview) (Onobrychis viciifolia Scop.) in mixtures with either Russian wildrye (RWR; cv. Tom) (Psathyrostachys junceus [Fisch.]) or hybrid bromegrass (HBG; cv. Success) (Bromus riparius Rehm × B . inermis Leyss) on herbage dry matter yield (DMY) and nutritive value, and beef yearlings performance at two sites: Swift Current (Brown soil zone) and Lanigan (Thin Black soil zone), Saskatchewan, Canada. In 2015, in each site, sixteen 0.7-ha (in Lanigan) or 0.8-ha (in Swift Current) paddocks were established with replicated ( n = 4) ALF-HBG, ALF-RWR, SF-HBG, or SF-RWR binary mixtures. Each year in August, yearling steers (16 ± 1 month and BW = 391 ± 1.7 kg and 350 ± 0.04 kg for Swift Current and Lanigan sites, respectively) were allocated to paddocks for an average 30-d grazing trial to utilize 40–60% of available herbage. The DMY (3629 ± 154 kg/ha) did not differ ( P > 0.05) among mixtures at Swift Current. The HBG included (ALF-HBG and SF-HBG) mixtures produced 54% more ( P < 0.01) DMY than RWR included (ALF-RWR and SF-RWR) mixtures (4542 vs. 2943 kg/ha, SEM = 303) at Lanigan. Legume contribution to DMY was greater at Swift Current than at Lanigan (33.1% ± 2.1% vs. 14.0 ± 1.7%), and ALF contributed more to DMY than SF at Lanigan (18.0 vs. 10.1%). Crude protein tended ( P = 0.10) to be greater for RWR mixtures than HBG mixtures (93.5 vs. 83.4 g/kg DM for RWR and HBG mixtures, respectively) at Lanigan. The yearling steers had similar ( P = 0.25) ADG (0.78 ± 0.03 kg/d) for the treatments at Swift Current. However, at Lanigan, the animal ADG differed ( P < 0.01) with 0.88 and 0.90 kg/d for ALF-RWR and SF-RWR and 0.53 and 0.63 kg/d for ALF-HBG and SF-HBG mixtures, respectively. The HBG mixtures (ALF-HBG and SF-HBG) produced approximately 10 more grazing days (GD) (AUD/ha) than the RWR (ALF-RWR and SF-RWR) mixtures at both, Swift Current (95 vs. 88 AUD/ha, SEM = 9) and Lanigan (112 vs. 101 AUD/ha, SEM = 7) sites. Sainfoin-grass mixtures produced 8 and 3 GD less (AUD/ha) than ALF-grass mixtures at Swift Current and Lanigan, respectively. Overall, these results demonstrate that all 4 binary mixtures appear to be suitable for late summer and fall grazing to provide sufficient nutritive value and beef cattle steer performance in both soil zones of Saskatchewan, Canada.