Shallow Soil Layers Research Articles

Quantifying Drought Propagation from Soil Moisture to Vegetation Dynamics Using a Newly Developed Ecohydrological Land Reanalysis

Despite the importance of the interaction between soil moisture and vegetation dynamics to understand the complex nature of drought, few land reanalyses explicitly simulate vegetation growth and senescence. In this study, I provide a new land reanalysis which explicitly simulates the interaction between sub-surface soil moisture and vegetation dynamics by the sequential assimilation of satellite microwave brightness temperature observations into a land surface model (LSM). Assimilating satellite microwave brightness temperature observations improves the skill of a LSM to simultaneously simulate soil moisture and the seasonal cycle of leaf area index (LAI). By analyzing soil moisture and LAI simulated by this new land reanalysis, I identify the drought events which significantly damage LAI on the climatological day-of-year of the LAI’s seasonal peak and quantify drought propagation from soil moisture to LAI in the global snow-free region. On average, soil moisture in the shallow soil layers (0–0.45 m) quickly recovers from the drought condition before the climatological day-of-year of the LAI’s seasonal peak while soil moisture in the deeper soil layer (1.05–2.05 m) and LAI recover from the drought condition approximately 100 days after the climatological day-of-year of the LAI’s seasonal peak.

An experimental irrigation tool for creating a water gradient across soil depths under terminated rainfall conditions

An experimental irrigation tool to research the response of plants to soil drying from deep to shallow soil layers observed under limited rainfall conditions was tested. Water was supplied from the tips of 4-mm-diameter tubes measuring 0.1, 0.3, 0.6, and 0.85 m in the length inserted into the soils. Each tube was set from shallowest to deepest at intervals of 1.5–3.0 m in the field. Control by the irrigation system was evaluated in rice and spring wheat fields under rain-protected shelters, where two cultivars with different root depths were planted. The irrigation tool created a series of different soil water profiles in which wet soil layers decreased with increasing irrigation depth due to the inserted tube lengths in both fields. In fine sandy soils more than sand, continuous decreases in soil water content were well simulated. Leaf conductance, leaf green color (SPAD value), and aboveground plant dry weight in both fields decreased with increasing irrigation depth in shallow root cultivars to a greater extent than that in deep root cultivars. The lower reducing effect of deep irrigation on plant dry weight in wheat compared to that in rice suggested that the irrigation depth based on tube length should be changed depending on the root distribution traits in the tested crops. These results indicated that the irrigation tool can conveniently simulate a diverse and continuous soil water content profile closer to that of an actual water gradient under limited rainfall conditions and contribute to studies on crop responses to different soil water absorption traits.

Investigation of local site responses at the Bodrum Peninsula (Southwest of Turkey) using the mainshock and aftershocks of the 20 July 2017 Mw6.6 Bodrum-Kos earthquake

Bodrum Peninsula located in the province of Mugla is situated in southwest Turkey. T he peninsula is one of the most populated touristic centers of the southwest coast of Turkey, near the Aegean Sea. However, t his region is surrounded by numerous active seismic entities. All of those systems have capability of producing large magnitude earthquakes and pose a great threat to settlements in and around of this region. Considering the high seismic risk and population of the peninsula, a strong ground motion monitoring system was deployed in June 2015. So far the network recorded many earthquakes in different magnitude and distances. In this study, a dataset with 51 events with moment magnitudes from 4.0-6.6 occurred within 100 km epicentral distances were selected for site effect calculation. This dataset includes the mainshock and its significant aftershocks records of the Mw6.6 Bodrum-Kos earthquake (20 July 2017, 22:31 UTC) . Predominant frequencies and amplification values of shallow soil layers under the stations were estimated through Horizontal to Vertical Spectral Ratio and Standard Spectral Ratios. The results indicate that predominant frequencies change between 2.1 - 2.7 Hz for soft soils, where it is 4.8 Hz for the reference site B5, and relative amplifications are in the range of 1.0 to 6.6. Then, sediments thicknesses beneath the stations were empirically calculated by using p redominant frequencies . In addition, the damage distribution of the Bodrum-Kos earthquake was discussed with its relation to the estimated resonance frequencies and relative amplifications. O bservations regarding to the Mw6.6 earthquake have revealed that unreinforced masonry structures, in particular, old stone houses were damaged while there were generally no apparent structural damage at reinforced buildings.

Soil water and root distribution of apple tree (Malus pumila Mill) stands in relation to stand age and rainwater collection and infiltration system (RWCI) in a hilly region of the Loess Plateau, China

Soil water status and fine root distribution is the basis of implementing water management in semiarid rain-fed orchards. Exploitation of rainwater is an effective avenue for alleviating water scarcity in semiarid regions since ground water is generally unavailable there. Through the method of space-for-time substitution, we investigated the soil moisture and root distribution along a range of stand ages (6, 9, 12, 18 and 21 years) in rain-fed apple (Malus pumila Mill) orchards and the effects of rainwater collection and infiltration systems (RWCI) on root-zone soil water and fine root distributions in matures apple orchards (21 years) in the semiarid Loess Plateau of China. The results showed that the mean soil moisture content (SMC) in the shallow layer (<2 m) decreased with apple tree age (6 to 18 years); the deep SMC (>2 m) was higher than shallow soil layers (<2 m) in most cases and the SMC increased with depth in stands of all ages. Fine roots (<2 mm diameter) showed an obvious trend of extending deeper with apple tree age - nearly 8 m in a 12-yr-old apple plantation and >8 m in plantations >12 years old. Dry root weight density (RWD) decreased sharply with depth, but densities at each depth were greater in older stands. The RWCI system significantly increased SMCs from the surface down to the maximum rainfall infiltration depth (MRID) (2 m depth) (P < 0.05), especially in the 0.2–1 m soil layer. Further, we found that apple tree water requirements could be sustainably met when RWCI system and a low-volume of irrigation water was applied. The distribution of root system was greatly affected by the RWCI system, which led to higher root densities close to the wetted area in the shallow soil layers (2 m soil depth) under RWCI system, down to a depth of 3 m in the soil. Overall, the application of RWCI system could be an effective water management strategy for providing sustainable water resources for semiarid orchards.

Nitrogen Budget and Topographic Controls on Nitrous Oxide in a Shale‐Based Watershed

AbstractThe high spatial and temporal variabilities of nitrous oxide (N2O) emissions from the soil surface have made it difficult to predict flux patterns at the ecosystem scale, leading to imbalances in nitrogen (N) budgets at all scales. Our research sought to quantify topographic controls on the sources or sinks of N2O in the soil profile to improve our ability to predict soil‐atmosphere N2O fluxes and their contribution to watershed N budgets. We monitored surface‐to‐atmosphere N2O fluxes for 2 years in the Susquehanna Shale Hills Critical Zone Observatory in central Pennsylvania. Topographically convergent flow path locations had significantly higher surface N2O flux rates than nonconvergent flow path locations in the summer, but not other seasons. Overall, N2O fluxes were a large percentage (~19%) of total ecosystem N losses, and nearly twice as large as stream N export. Surface N2O fluxes were better correlated with concentrations of O2, N2O, and NO3− in shallow soil layers (&lt;30 cm) than deeper soils. Following decades of anthropogenic atmospheric deposition and additional N from shale weathering, watershed N inputs (~8 kgN ha−1 yr−1) are greater than outputs (~3.7 kgN ha−1 yr−1). Our research revealed patterns of N cycling that are distinct from many other watersheds that have been extensively studied to understand N saturation; despite showing no other symptoms of N saturation, the watershed had high upland N2O losses, especially in convergent flow paths during summer. High upland N gas losses may be a mechanism that maintains N limitation to biota in the Shale Hills catchment.

Monitoring of a Full-Scale Embankment Experiment Regarding Soil–Vegetation–Atmosphere Interactions

Slope mass-wasting like shallow slides are mostly triggered by climate effects, such as rainfall, and soil–vegetation–atmosphere (SVA) interactions play a key role. SVA interactions are studied by a full-scale embankment with different orientations (North and South) and vegetation covers (bare and vegetated) in the framework of the prediction of climate change effects on slope stability in the Pyrenees. A clayey sand from the Llobregat river delta was used for the construction of the embankment and laboratory tests showed the importance of suction on the strength and hydraulic conductivity. Sixty sensors, which are mostly installed at the upper soil layer of the embankment, registered 122 variables at four vertical profiles and the meteorological station with a 5 min scan rate. Regarding temperature, daily temperature fluctuation at the shallow soil layer disappeared at a depth of about 0.5 m. There was great influence of orientation with much higher values at the South-facing slope (up to 55 °C at −1 cm depth) due to solar radiation. Regarding rainfall infiltration, only long duration rainfalls produced an important increase of soil moisture and pore water pressure, while short duration rainfalls did not trigger significant variations. However, these changes mostly affected the surface soil layer and decreased with depth.

Exploration of S-wave velocity profiles at strong motion stations in Eskisehir, Turkey, using microtremor phase velocity and S-wave amplification

We have explored 1D S-wave velocity profiles of shallow and deep soil layers over a basement at strong motion stations in Eskisehir Province, Turkey. Microtremor array explorations were conducted at eight strong motion stations in the area to know shallow 1D S-wave velocity models. Rayleigh wave phase velocity at a frequency range from 3 to 30 Hz was estimated with the spatial autocorrelation analysis of array records of vertical microtremors at each station. Individual phase velocity was inverted to a shallow S-wave velocity profile. Low-velocity layers were identified at the stations in the basin. Site amplification factors from S-wave parts of earthquake records that had been estimated at the strong motion stations by Yamanaka et al. (2017) were inverted to the S-wave velocities and Q-values of the sedimentary layers. The depths to the basement with an S-wave velocity of 2.2 km/s are about 1 km in the central part of the basin, while the basement becomes shallow as 0.3 km in the marginal part of the basin. We finally discussed the effects of the shallow and deep sedimentary layers on the 1D S-wave amplification characteristics using the revealed profiles. It is found that the shallow soil layers have no significant effects in the amplification at a frequency range lower than 3 Hz in the area.

Exposure Corrosion Test of Metal Pile for Shallow Soil Layer

Exposure Corrosion Test of Metal Pile for Shallow Soil Layer

Root responses to elevated CO2, warming and irrigation in a semi‐arid grassland: Integrating biomass, length and life span in a 5‐year field experiment

Abstract Plant roots mediate the impacts of environmental change on ecosystems, yet knowledge of root responses to environmental change is limited because few experiments evaluate multiple environmental factors and their interactions. Inferences about root functions are also limited because root length dynamics are rarely measured. Using a 5‐year experiment in a mixed‐grass prairie, we report the responses of root biomass, length and life span to elevated carbon dioxide (CO2), warming, elevated CO2 and warming combined, and irrigation. Root biomass was quantified using soil cores and root length dynamics were assessed using minirhizotrons. By comparing root dynamics with published results for soil resources and above‐ground productivity, we provide mechanistic insights into how climate change might impact grassland ecosystems. In the upper soil layer, 0–15 cm depth, both irrigation and elevated CO2 alone increased total root length by twofold, but irrigation decreased root biomass and elevated CO2 had only small positive effects on root biomass. The large positive effects of irrigation and elevated CO2 alone on total root length were due to increases in both root length production and root life span. The increased total root length and life span under irrigation and elevated CO2 coincided with apparent shifts from water limitation of plant growth to nitrogen limitation. Warming alone had minimal effects on root biomass, length and life span in this shallow soil layer. Warming and elevated CO2 combined increased root biomass and total root length by c. 25%, but total root length in this treatment was lower than expected if the effects of CO2 and warming alone were additive. Treatment effects on total root length and root life span varied with soil depth and root diameter. Synthesis. Sub‐additive effects of CO2 and warming suggest studies of elevated CO2 alone might overestimate the future capacity of grassland root systems to acquire resources. In this mixed‐grass prairie, elevated CO2 with warming stimulated total root length and root life span in deeper soils, likely enhancing plant access to more stable pools of growth‐limiting resources, including water and phosphorus. Thus, these root responses help explain previous observations of higher, and more stable, above‐ground productivity in these projected climate conditions.

Determining the effects of nitrogen rate on cotton root growth and distribution with soil cores and minirhizotrons.

Cotton root growth can be affected by different nitrogen fertilizer rates. The objective of the present study was to quantify the effects of nitrogen fertilization rate on cotton root growth and distribution using minirhizotron and soil coring methods. A secondary objective was to evaluate the minirhizotron method as a tool for determining nitrogen application rates using the root distribution as an index. This study was conducted on a Bt cotton cultivar (Jimian 958) under four nitrogen fertilization rates, i.e., 0, 120, 240 and 480 kg ha-1 (control, low, moderate and high levels, respectively), in the Yellow River basin of China from 2013–2015. The sampling process, details of each method as well as the root morphology and root distribution were measured. The operational processes, time and labor needed for the soil core method were all greater than those for the minirhizotron method. The total root length density and the length density in most soil layers, especially in the upper soil layers, first increased but then decreased as nitrogen fertilization increased, and the same trend was observed for both methods. Compared with N0, the total root length density under moderate nitrogen fertilization by the soil coring method increased by more than 94.82%, in 2014 and 61.11% in 2015; while by the minirhizotron method the corresponding values were 28.24% in 2014 and 57.47%, in 2015. Most roots were distributed in the shallow soil layers (0–60 cm) in each method. However, the root distribution with the soil coring method (>73.11%) was greater than that with the minirhizotron method (>47.07%). The correlations between the root morphology indexes of shallow soil depth measured using the two methods were generally significant, with correlative coefficients greater than 0.334. We concluded that the minirhizotron method could be used for cotton root analysis and most cotton roots distributed in upper soil layers (0-60cm). In addition, a moderate nitrogen rate (240 kg ha-1) could increase root growth, especially in the shallow soil layers. The differences observed with the minirhizotron method were clearer than those observed with the soil coring method.

Contrasting response of coexisting plant's water-use patterns to experimental precipitation manipulation in an alpine grassland community of Qinghai Lake watershed, China.

Understanding species-specific changes in water-use patterns under recent climate scenarios is necessary to predict accurately the responses of seasonally dry ecosystems to future climate. In this study, we conducted a precipitation manipulation experiment to investigate the changes in water-use patterns of two coexisting species (Achnatherum splendens and Allium tanguticum) to alterations in soil water content (SWC) resulting from increased and decreased rainfall treatments. The results showed that the leaf water potential (Ψ) of A. splendens and A. tanguticum responded to changes in shallow and middle SWC at both the control and treatment plots. However, A. splendens proportionally extracted water from the shallow soil layer (0–10cm) when it was available but shifted to absorbing deep soil water (30–60 cm) during drought. By contrast, the A. tanguticum did not differ significantly in uptake depth between treatment and control plots but entirely depended on water from shallow soil layers. The flexible water-use patterns of A.splendens may be a key factor facilitating its dominance and it better acclimates the recent climate change in the alpine grassland community around Qinghai Lake.

Soil water storage compensation potential of herbaceous energy crops in semi-arid region

Large-scale vegetation construction has generally led to soil desiccation in arid and semi-arid regions. Energy crops with high biomass and water use efficiency are generally beneficial to agriculture and the environment. It is necessary to understand how to maintain the dynamic balance of soil moisture and biomass production on herbaceous energy croplands. In this study, soil moisture data at different depths of soil were obtained from long-term field observations for two energy crops, i.e., Panicum virgatum and Miscanthus sinensis, and a forage crop-Medicago sativa. Relative aridity of the soil and plant biomass were compared among different vegetation types, transects, and cultivation years. Medicago sativa soil was severely, even extremely, desiccative with increasing cultivation years, whereas there was nearly no desiccation in the soil of energy crops. The values of compared soil water storage compensation indexes in deep soil layers were higher than those in shallow soil layers, with the evaluated soil water storage compensation index being the smallest in the 40–80 cm layer. Energy crops had significantly higher aboveground biomass, mostly exhibiting more than 2.6 kg m−2, while the aboveground biomass of M. sativa was only above 0.5 kg m−2. Furthermore, the water use efficiencies of energy crops were obviously higher than that of M. sativa (P < 0.05). Our results indicated that deep soil moisture conditions were mainly determined by field crop types. Energy crops may be suitable candidates for compensating soil water storage and maintaining high biomass production in semi-arid regions.

Water use strategies of Populus euphratica seedlings under groundwater fluctuation in the Tarim River Basin of Central Asia

Riparian vegetation in arid regions is subject to frequent water environmental fluctuations and plays an important role in maintaining the riparian ecosystem. In recent decades, Populus euphratica (P. euphratica) has been threatened by decreasing groundwater levels, and large areas of P. euphratica seedlings are withered. To better understand the adaptive mechanism underlying hydrological process alterations, we designed an experiment to identify the water sources of P. euphratica seedlings using δ18O values (plant stem xylem, soil water and groundwater) under different groundwater scenarios by simulating the wild habitats conditions in the Tarim River bank of Central Asia. Seedlings were grown in lysimeters (2.0 m tall × 0.4 m inner diameter) under varying hydrological conditions. P. euphratica seedlings generally took up water from the shallow soil layer (0–80 cm). Under the T. ramosissima disturbance, the water source depths of the P. euphratica seedlings moved down as the groundwater depth increased. With increasing groundwater depth, the proportions of groundwater used by P. euphratica seedling monocultures (only P. euphratica seedlings) and P. euphratica seedling mixtures (P. euphratica and T. ramosissima seedlings) were reduced. Under shallow groundwater treatment (W1: 25 cm), the plant height growth of the P. euphratica seedlings slowed, and their biomass accumulation decreased. The aboveground and total biomasses of the non-coexistence seedlings under W2 (75 cm) treatment were maximized, while the maximum value for coexistence seedlings occurred under W3 (125 cm) treatment. Thus, we suggest that shallow groundwater depth is not beneficial to P. euphratica seedling growth, and appropriately decreasing the groundwater depth may promote their growth. Such information will be valuable to provide the configuration of water resources for a typical river basin in an arid region of Central Asia based on the ecological water requirements of desert riparian vegetation.

The sign, magnitude and potential drivers of change in surface water extent in Canadian tundra

The accelerated rate of warming in the Arctic has considerable implications for all components of ecosystem functioning in the High Northern Latitudes. Changes to hydrological cycle in the Arctic are particularly complex as the observed and projected warming directly impacts permafrost and leads to variable responses in surface water extent which is currently poorly characterized at the regional scale. In this study we take advantage of the 30 plus years of medium resolution (30 m) Landsat data to quantify the spatial patterns of change in the extent of water bodies in the Arctic tundra in Nunavut, Canada. Our results show a divergent pattern of change—growing surface water extent in the north-west and shrinking in the south-east—which is not a function of the overall distribution of surface water in the region. The observed changes cannot be explained by latitudinal stratification, nor is it explained by available temperature and precipitation records. However, the sign of change appears to be consistent within the boundaries of individual watersheds defined by the Canada National Hydro Network based on the random forest analysis. Using land cover maps as a proxy for ecological function we were able to link shrinking tundra water bodies to substrates with shallow soil layers (i.e. bedrock and barren landscapes) with a moderate correlation (R2 = 0.46, p < 0.001). It has previously been reported that rising temperatures are driving a deepening of the active layer and shrinking water bodies can be associated with coarse textured soils beneath the lakes. Unlike water bodies with soil, or gravel, beneath them the water bodies that are situated on bedrock are likely cut off from ground water. Drying water bodies clustered in areas of bedrock and thin soils points to evaporation as an important driver of surface water decrease in these cases.

Water use strategies of natural Pinus sylvestris var. Mongolica trees of different ages in Hulunbuir Sandy Land of Inner Mongolia, China, based on stable isotope analysis

Natural Mongolian pine trees of different ages consistently use shallow water throughout the main growing season; therefore, water stored in the shallow soil layer is vital for maintaining their viability. Mongolian pine (Pinus sylvestris var. mongolica) plantations in sandy regions often experience dieback after 30–35 years of growth due to water deficiency, whereas natural Mongolian pine forests remain healthy during the same growth stage. However, the water use strategies of natural Mongolian pines remains unclear. Therefore, δ2H and δ18O in twig xylem water, soil water and groundwater were analyzed in 10–20, 20–30 and 30–50-year-old natural Mongolian pine trees to identify their water sources. In addition, needle δ13C was measured simultaneously to assess water use efficiency. Results showed that pine trees of different ages utilized soil water from the same depth. During the growing season (June–August), all pine trees utilized water from 0 to 20 cm soil depth, regardless of the soil water condition. During the end of growing season (September and October), even though soil moisture content in the 0–20 cm depth was higher, pine trees of different ages utilized water from the 0–60 cm soil depth in September and switched to utilize water from the 20–80 cm soil depth in October. There were no significant differences in needle δ13C among the sampling dates for trees in each age group, indicating that pine trees can absorb sufficient water to satisfy their water requirements regardless of age. These findings suggest that water stored in the shallow soil layer (0–20 cm) plays an important role in supporting tree transpiration during the growing season (June–August). Therefore, the stability of shallow soil is vital for maintaining the viability of natural Mongolian pine forests.

Modeling soil water flow and quantification of root water extraction from different soil layers under multi-chemicals application in dry land field

The combined application of different functional chemicals creates challenges both in modeling water flow in soil and quantification of water extraction by crops in dry land farming. In the present study, 2-year laboratory and field experiments were conducted in a typical dry land of northern China in order to: (i) develop a model to describe patterns of water flow in soil under two typical chemicals Superabsorbent polymer (SAP) and Fulvic acid (FA) combined applied in the soil-maize system and (ii) use the stable hydrogen and oxygen analysis method to further quantify the soil water extraction by crops as affected by SAP and FA. Two root water extraction (RWE) terms based on density of root length (DRL) and density of root nitrogen mass (DRNM), respectively, were established to describe the rate of RWE, demonstrating that the values simulated from DRNM were verified to be closer to measured values. A particular model was further developed to simulate flow of water in different soil layers, and its authenticity was confirmed for describing the patterns of soil water flow under multi-chemicals application. The results of hydrogen and oxygen isotope abundance estimated from multi-source mass balance method (IsoSource model) suggested that main depth of water extraction as affected by multi-chemicals decreased first and then increased, and mainly concentrated in the shallow soil layers, 0–20 cm soil layer for jointing stage, 20–40 cm soil layer for heading stage, 0–20 cm soil layer for grain filling stage. Combined application of SAP and FA played a synergistic role in promoting the rainfall WUE of maize.

Water use strategies for two dominant tree species in pure and mixed plantations of the semiarid Chinese Loess Plateau

AbstractUnderstanding the water sources and physiological responses to soil moisture pulses for plantation species, particularly in mixed plantations, are essential to assess the water use strategy and vegetation restoration in semiarid regions. We used hydrogen stable isotopes in plant and soil water to determine the potential water sources forPinus tabuliformisandHippophae rhamnoidesin both pure and mixed plantations in the semiarid Chinese Loess Plateau during the vigorous growing season (June–August) in 2016. Stomatal conductance (gc), midday leaf water potential (Ψm) and photosynthetic rate (Pr) were measured concurrently to analyse the physiological response. TheP. tabuliformisin the pure plantation depended largely on shallow and middle soil layers regardless of precipitation amount, permitting this species to maintain stable Ψmat the expense of Prthrough stomatal control. In contrast,H. rhamnoidesin the pure plantation shifted its water source from shallow to deep soil layers following decreases in precipitation, allowing this species to maintain stable gcand Prat the expense of Ψm. Thus,P. tabuliformisandH. rhamnoidesdisplayed isohydric and anisohydric behaviour, respectively. Additionally, both species in mixed plantations largely absorbed water from shallow soil layers and shifted to deep soil layers when precipitation decreased. Mixed afforestation significantly reduced (p &lt; .05) PrforP. tabuliformisand ΨmforH. rhamnoides. Although contrasting physiological responses were adopted by these species, the major proportion of water resources were competitively obtained from similar soil depths—indicating that their mixed afforestation requires further investigation.

Changes in soil organic and inorganic carbon stocks in deep profiles following cropland abandonment along a precipitation gradient across the Loess Plateau of China

Determining changes in soil organic carbon (SOC) and inorganic carbon (SIC) stocks following ecological restoration is important for estimating the regional carbon budget and evaluating ecological effects. However, there is limited understanding on the interacting effects of vegetation restoration and climate gradients on SOC and SIC stocks in shallow and deep soil layers over large scales. This study selected seven sites along a climate transect from the east to the west of the Chinese Loess Plateau, and the SOC and SIC stocks were measured to a depth of 300 cm in sites covered by cropland and three vegetation restoration types (grassland, shrubland and woodland). The spatial variations and controlling factors of the SOC and SIC stocks at different depths following vegetation restoration along the precipitation gradient were investigated in detail. The results indicated that the SOC and SIC stocks in the 100–300 cm layers accounted for more than 50% of the total values in the 0–300 cm profile. The total SOC stock in the 0–300 cm profiles significantly increased along precipitation gradient (p < 0.01) in all vegetation types except woodland. The total SIC stock decreased, but the change was not significant, which caused little variation in the total carbon stocks along the precipitation gradient (p > 0.05). Shrubland and woodland plantation following cropland abandonment resulted in soil carbon accumulation, whereas grassland represented carbon loss in sites with mean annual precipitation (MAP) greater than 470 mm. The changes in the SOC stock (ΔSOC) in the surface layer (0–20 cm) and those in the SIC stock (ΔSIC) in the deep layers (100–300) following revegetation significantly decreased along precipitation gradient (p < 0.05). The interactions between ΔSOC and ΔSIC stocks were evident, especially in the upper soil layers. An accumulation of 1 kg SOC was accompanied by 0.73 kg loss of SIC in the 0–40 cm layer and 1.26 kg increase of SIC in the 40–300 cm layer per square meter following revegetation. MAP and mean annual temperature (MAT) mainly affected the spatial patterns of SOC and SIC in the upper layers, while land use and soil texture mainly affected soil carbon in the deep layers. This study indicates that vegetation restoration does not always result in soil carbon sequestration at every depth after cropland abandonment, which depends on climatic conditions and varies among different vegetation types.

Subsurface shallow depth soil layers thermal potential for ground heat pumps in Poland

Subsurface shallow depth soil layer (SSDSL) is characterized by dynamic temperature changes, which may be eligible to constitute as a heat source for ground heat pumps. This paper aims to present the regime of heat flow in SSDSL and its climatic conditions in central Europe, taking into consideration the agriculture periphery characteristics of Wroclaw (Poland). Emphasis was laid on the relation between the radiative properties and heat balance of two contrasting types of analyzed active surfaces (bare soil and grassy surface). The obtained experimental results gathered across a span nine years (August 2007–July 2016) and the conducted thermal analysis aim to evaluate the utilization of SSDSL as a heat source for ground heat pumps. The heat fluxes were measured between the active surface of the soils and their lower layers on an 8 cm depth. The soil temperature data between 5 cm to 10 cm under the ground and the temperatures of the active soil surfaces are represented. The results showed that the biggest monthly sums of ground positive fluxes (G > 0) reached about 80 MJ/m2 (22.2 kWh/m2) for the bare soil from May to July and the adequate average monthly sums reached maximum 55 MJ/m2 (15.3 kWh/m2) in July. The sums for the grassy surface were nearly twice lower, with the monthly maximum equals to 42.5 MJ/m2 (11.7 kWh/m2) in June and average value of 32 MJ/m2 (8.9 kWh/m2) in July. The nine-year average annual sums for G > 0 reached 337.6 MJ/m2 (93.8 kWh/m2) for the bare soil and 170.8 MJ/m2 (59.9 kWh/m2) for the grassy surface. The heat fluxes of the 5 cm depth soil were higher than for the 8 cm and 10 cm soil. Thus, the conclusion of the study suggests that the thermal performance of SSDSL is efficient enough to be used as an environment friendly heat source for interseasonal heat pump operation.

Responses of soil moisture to vegetation restoration type and slope length on the loess hillslope

Soil moisture, a critical variable in the hydrologic cycle, is highly influenced by vegetation restoration type. However, the relationship between spatial variation of soil moisture, vegetation restoration type and slope length is controversial. Therefore, soil moisture across soil layers (0-400 cm depth) was measured before and after the rainy season in severe drought (2015) and normal hydrological year (2016) in three vegetation restoration areas (artificial forestland, natural forestland and grassland), on the hillslopes of the Caijiachuan Catchment in the Loess area, China. The results showed that artificial forestland had the lowest soil moisture and most severe water deficit in 100-200 cm soil layers. Water depletion was higher in artificial and natural forestlands than in natural grassland. Moreover, soil moisture in the shallow soil layers (0-100 cm) under the three vegetation restoration types did not significantly vary with slope length, but a significant increase with slope length was observed in deep soil layers (below 100 cm). In 2015, a severe drought hydrological year, higher water depletion was observed at lower slope positions under three vegetation restoration types due to higher transpiration and evapotranspiration and unlikely recharge from upslope runoff. However, in 2016, a normal hydrological year, there was lower water depletion, even infiltration recharge at lower slope positions, indicating receiving a large amount of water from upslope. Vegetation restoration type, precipitation, slope length and soil depth during a rainy season, in descending order of influence, had significant effects on soil moisture. Generally, natural grassland is more beneficial for vegetation restoration than natural and artificial forestlands, and the results can provide useful information for understanding hydrological processes and improving vegetation restoration practices on the Loess Plateau