Shallow Soil Profile Research Articles

Strengthen farmers' fertilizer self-sufficiency in the tourist area with a reduce-reuse-recycle system

Mining activities at Tebing Breksi are a vital source of income for the community in Sambirejo village, Sleman Regency, Yogyakarta. However, these activities have caused several environmental issues, such as lowered pH levels, reduced soil fertility, shallow soil profiles, and water scarcity. Additionally, mining has led to biodiversity loss and land degradation, making post-mining reclamation essential to restore the area's environmental and social functions. This project aimed to enhance the community’s skills in soil analysis and the production of liquid organic fertilizer using effective methods. The activities took place in the Tebing Breksi tourist area, located in Nglengkong, Sambirejo Village, Prambanan District, Sleman Regency. The project included a Focus Group Discussion (FGD), soil fertility analysis using test kits, and the creation of liquid organic fertilizer from household waste. During the FGD, it was discovered that the local community had not received prior training on producing fertilizer from household and organic waste. Until then, they relied on expensive commercial fertilizers to quickly stabilize soil pH. Through this training, the community learned how to perform rapid soil chemical analysis and produce liquid organic fertilizer independently. As a result, they can now apply the fertilizer locally, improving soil conditions and reducing their reliance on costly commercial products.

Identifying the nitrate transport and transformations under apple orchards in the loess depositusing stable isotopes of water and nitrate

Understanding the behavior of nitrate in the unsaturated zone is critical for predicting groundwater nitrate pollution. Although this issue has been intensively investigated for shallow soil profiles, it remains poorly understood in deep soils. We collected soil samples up to 20 m depth under farmland and apple orchards with trees that were 16 and 22 years old (A16 and A22). We then determined soil-water content, stable isotopes (δ2H and δ18O) and nitrate content under two land use types. The stable isotopes of nitrate under two apple orchards were measured to a depth of 16 m. The mean nitrate contents in the shallow soils (0–6 m) under apple orchards (78.8 ± 87.8 mg kg−1 for A16, 180 ± 155 mg kg−1 for A22) were significantly higher than that of farmland (2.40 ± 1.56 mg kg−1) (p < 0.01), whereas the nitrate contents in the deep soils (6–20 m) were almost similar between apple orchards and farmland. Ammonium or urea-based nitrogen (N) fertilizers (30–61%) were the predominant contributors to nitrate in the shallow soil layers, followed by soil organic N and manure & sewage, whereas the soil organic N (mean 34%) was the primary source of nitrate in deep soils. Isotopic data revealed that the N transformation was controlled by nitrification, and denitrification was not apparent throughout the soil profiles. The downward transport of nitrate lagged behind soil-water. Nitrate was leached by piston flow in the vadose zone, and the nitrate from N application since the 1980 s has only infiltrated to 6 m depth. The difficulty in recharging deep soils mitigates the transport of nitrate to lower depths. The combination of water-nitrate stable isotopes provides new insights for identifying nitrate sources, transformation, and transport in the thick unsaturated zone.

Geothermal gradients in a high-organic content landfill

Geothermal gradients in a high-organic content landfill

Environmental fate of chlorpyrifos in Rhodic Ferralsol grown with corn during summer and winter seasons under high-intensity rainfall

The interactions between pesticides' physicochemical properties and edaphoclimatic factors influence their distribution into the environment. Understanding how those factors interact in a changing environment is crucial for mitigating environmental and agronomic problems. Thus, a percolation lysimeter with undisturbed soil and suction lysimeters were used to conduct a field study to evaluate the distribution of chlorpyrifos sprayed in a corn crop cultivated in a Rhodic Ferralsol in simulated extreme rainfall conditions. The mobility of chlorpyrifos was evaluated under simulated precipitation (150 mm h−1), 24 h and 48 h after applying the chlorpyrifos in different phenological stages of corn during the summer and winter crops in two agricultural years. In addition, GC-ECD determined the residual concentration of chlorpyrifos in the runoff and leached samples. Finally, a laboratory adsorption study was conducted with Rhodic Ferralsol to find the chlorpyrifos adsorption capacity in different temperatures, with and without soil organic matter. Our results show that soil organic matter is essential in chlorpyrifos adsorption, responsible for approximately 5% pesticide retention, which could be 25% higher during winter. High-intensity rainfalls positively affect runoff and leaching; nevertheless, these are responsible for only 0.2% of all chlorpyrifos amounts, as the soil is the major reservoir of chlorpyrifos by retention into clays and organic matter. Furthermore, the corn growth stages directly affect chlorpyrifos transportation, with higher amounts observed in runoff and leaching during the first and last corn growth stages. Therefore, in the conditions such as high-intensity rainfall, exposed soil, shallow soil profile, and temperatures below 20 °C, attention should be paid to chlorpyrifos spray with special regard to the weather forecast, avoiding its spray near rainfall events. Further studies should be conducted in other soil classes and rainfall conditions to validate our observations.

Probabilistic and deterministic-based approach for liquefaction potential assessment of layered soil

In the present study, deterministic and probabilistic approaches have been used for the assessment of liquefaction potential of ground during an earthquake. The deterministic approach was used to analyze and assess the liquefaction of loose saturated river bed deposit with emphasis on two benchmark locations. A wide range of earthquake data in the form of peak ground acceleration (PGA) values of 0.18 g, 0.37 g, 0.6 g and 0.75 g was used as input motions. The dynamic properties of soil were evaluated using standard penetration test (SPT) data obtained from the bore logs. The shear stress induced within soil deposit due to the seismic excitation was calculated in the form of cyclic stress ratio (CSR) and cyclic resistance ratio (CRR) in order to calculate the factor of safety (FOS) against liquefaction. In addition, liquefaction potential index (LPI) and probability of liquefaction (PL) were also calculated using input motion. It was observed, based on the probability analysis and liquefaction indices, that the shallow layer soil profile is safe against liquefaction, whereas deep layer soil profile is unsafe.

Pedogenesis at the coastal arid-hyperarid transition deduced from a Late Quaternary chronosequence at Paposo, Atacama Desert

Under hyperarid climate conditions, pedogenesis is driven by the atmospheric deposition and subsequent accumulation of easily to moderately soluble salts forming extreme types of Aridisols. In contrast, the processes and timescales of soil formation in coastal desert environments are as yet not well understood. Therefore, a soil chronosequence at the arid-hyperarid transition in the south-central coastal Atacama Desert is investigated. We measured physicochemical soil parameters of shallow soil profiles on four generations of a multi-stage alluvial fan system, assisted by micromorphological analysis, allowing to deduce the soil-forming processes. We further established a geochronological framework by applying 10Be cosmogenic nuclide exposure dating on the abandoned surface generations, which allowed to infer the timescales for soil formation. The results indicate initial yet clearly identifiable pedogenesis occurring since MIS 5e–c. Along the Late Quaternary chronosequence, physicochemical soil properties show decreasing trends with growing age for the median grain size, salinity, long-term pH development, and CaCO3 contents. Contrarily, organic carbon, the ratio of organic to total phosphorus, the redness, and the contents of total and poorly crystalline pedogenic iron oxides tend to increase with age. This provides evidence for soil formation under an arid to hyperarid coastal climate characterized by (i) redistribution of salts by leaching causing topsoil desalinization; (ii) decalcification coupled with (iii) dealkalinization in totally decalcified horizons; (iv) accumulation of soil organic matter; (v) initial rubification through formation of pedogenic iron oxides (i.e. hematite); and (vi) initial loamification that, in turn, might have impeding effects on the translocation of soil constituents on timescales larger than 105 a. Furthermore, in situ pedogenesis might be superimposed considerably by aeolian dust influx. At Atacama’s south-central coast, the state of pedogenic alteration scales with the cumulative precipitation received throughout the entire Late Quaternary, yet evolved strongest between MIS5 and the MIS4/3-transition.

Environmental controls on the hydrogen isotopic composition of volcanic glass from the Southern Afar rift, eastern Ethiopia

Hydrogen stable isotope values of hydrated volcanic glass as a proxy for the isotopic composition of past meteoric waters provide an opportunity for reconstructing past climates. Here we present new hydrogen stable isotope values from 63 individual tuffs from the Afar region in the lower Awash Valley of eastern Ethiopia. The hydrogen isotopic results from volcanic glass spanning the last 6.4 Ma show a wide distribution with values ranging between −89 and − 32 ‰ (VSMOW). The variability is consistent with the observed paleo-depositional setting (i.e., lower values for fluvial settings while higher values are recorded in lacustrine settings). The reconstructed hydrogen isotopic values of parent waters are considerably lower than those of modern meteoric waters, suggesting a bias toward lower values during the hydration of volcanic glass.Reconstructed hydrogen stable isotope values of water derived from volcanic glass differ from other proxies of regional climate in northeast Africa, pointing to the controls of local meteoric waters on the hydrogen isotopic composition of volcanic glass. There is agreement between the reconstructed isotopic composition of parent waters and the lowest hydrogen isotopic values of modern precipitation in the Awash catchment that correspond to periods of large rainfall. This correspondence probably indicates that volcanic glass is preferentially hydrated during the wettest seasons. To test this idea, we compared the isotopic results from volcanic glass with the reconstructed isotopic composition of surface waters from soil carbonates deposited during the Pliocene and Pleistocene in the lower Awash Valley. The comparison reveals a considerable difference between proxies, with volcanic glass recording lower isotopic values than soil carbonates. Evaporative isotopic enrichment of water in shallow (<1 m) soil profiles probably accounts for the elevated values in soil carbonates. In contrast, the presence of smectite-rich vertisols above volcanic deposits appears to retard infiltration of meteoric waters deep into the subsurface. During rainfall events, vertisols swell and prevent all but the largest rainfall events from penetrating deep (>1 m) into the profiles and promoting the hydration of volcanic glass that display systematically lower isotopic values of meteoric waters than the mean annual rainfall.

Revisiting Michael Bonell's work on humid tropical rainforest catchments: Isotope tracers reveal seasonal shifts in catchment hydrology

It has been almost 50 years since the foundational work at the Babinda catchments in North Queensland kickstarted the field of tropical hydrology globally. To expand upon this work and build a more generalized hydrological understanding of steep rainforest catchments, we studied the seasonal evolution of hydrological response from two catchments with broadly similar characteristics to the Babinda catchments. Both hydrometric and water stable isotope data were collected at relatively high frequencies during one wet season (Thompson Creek) and a 3-year period (Atika Creek). The longer dataset spans a wide range of environmental conditions experienced in the humid tropics, including events that cover the wetting-up transitional period of the wet season and tropical cyclones (TC). Both catchments displayed a fast streamflow response to rainfall with the shallow upper soil profile responding quickly to rainfall at Atika Creek. New findings from this study include the importance of pre-event water (>50% using the two component hydrograph separation technique) for overall event flows, especially when the catchment was wet. Rainfall, surface runoff and groundwater isotope and specific electrical conductivity (SEC) compositions varied between rainfall events with the most complex bivariate mixing plots observed for multi-peak events that occurred at the start of the wet season and after a dry period within the wet season. Two-tracer, 3 component hydrograph separations did not provide satisfactory results in identifying source water contributions to streamflow. These results highlighted the time-variant and non-conservative behaviour of the rainfall, surface runoff and shallow groundwater source waters over the seasonal timescale, with soil water being an important unidentified source contributor. Our findings highlight the need for high frequency multi-source sampling to accurately interpret catchment behaviour and the importance of soil water contributions to streamflow. We propose a framework to describe the seasonal evolution of streamflow response in steep tropical rainforest catchments experiencing seasonal rainfall activity.

Soil Related Factors Controlling Erosion And Landslides In Malaysia

The high temperature and rainfall in Malaysia results in intensive tropical weathering and depending on the parent material, the resultant soil can have deep or shallow soil profiles. Thus, a variety of soils can form with different textures (clay content), structure and porosity. With the high rainfall, soils in steep terrain are subjected to surface erosion when exposed or landslides if the rainwater percolates into the soil profile. Key soil-related factors controlling soil erosion and landslides include local climate, parent material of soils and depth of the weathered profile. Slope and geomorphology, vegetation and land use as well as land management practices also influence erosion and landslides. Measures used to control soil erosion and stabilize slopes require improved understanding of soil weathering, erosion, landslide and their linkages in steep terrain.

GEOPHYSICAL SURVEY AS A TOOL TO REVEAL SUBSURFACE STRATIFICATION AT A SMALL AGRICULTURAL HEADWATER CATCHMENT: A CASE STUDY

Catchment drainage area is a basic spatial unit in landscape hydrology within which the authorities estimate a water balance and manage water resources. The catchment drainage area is commonly delineated based on the surface topography, which is determined using a digital elevation model. Therefore, only a flow over the surface is implicitly considered. However, a substantial portion of the rainfall water infiltrates and percolates through the soil profile to the groundwater, where geological structures control the drainage area instead of the topography of the soil surface. The discrepancy between the surface topography-based and bedrock-based drainage area can cause large discrepancies in water balance calculation. It this paper we present an investigation of the subsurface media stratification in a headwater catchment in the central part of the Czech Republic using a geophysical survey method - electrical resistivity tomography (ERT). Results indicate that the complexity of the subsurface geological layers cannot be estimated solely from the land surface topography. Although shallow layers copy the shape of the surface, the deeper layers do not. This finding has a strong implication on the water transport regime since it suggests that the deep drainage may follow different pathways and flow in other directions then the water in shallow soil profile or shallow subsurface structures.

Assessing hillslope sediment generation potential by tree throw: a preliminary field study along a small river valley in the Jura Mountains, northwest Switzerland

Abstract. A preliminary field-based investigation was undertaken in a small (&lt; 10 km2) river valley located in the mountainous Jura region of northwest Switzerland. The aims of the work were to assess sediment generation and annual sediment transport rates by tree throw on forested hillslopes and to document surface hydrology characteristics on four fresh tree throw mounds associated with recent tree throws over a 24 d monitoring period. For the tree throw mounds, average sediment recovery ranged from 7.7–28.2 g (dry weight), equivalent to a suspended sediment concentration of 145.2–327.8 g L−1, and runoff coefficients ranged from 1.0 %–4.2 %. Based on a soil bulk density value of 1044 kg m−3, upslope runoff generation areas were denuded by an average of 0.14 mm within the 24 d monitoring period, representing an erosion rate equivalent to 2.1 mm a−1. This means that a ca. 50 cm high tree throw mound could theoretically persist for around 200–250 years. For tree throw work, the dimensions of 215 fallen trees were measured and their locations mapped in 12 separate locations where tree throw was prominent along the river valley, representing a cumulative area equivalent to 5.3 ha (average density equivalent to 43 trees ha−1). The 215 tree throws generated a total of 20.1 m3 of fine sediment (&lt; 2 mm dia.), or the equivalent of 3.8×10-4 m3 m−2. The process of tree throw was originally attributed to two extreme weather events that occurred across west and central Europe in late December 1999. Taking the 18-year period since both storms, this represents an annual sediment transport rate of 2.7×10-5 m3 m−1 a−1. Exploring the relationship with wind on fall direction, however, 65.5 % of mapped tree throws (n= 143) generally fell in a downslope direction irrespective of hillslope aspect on which they were located. Given the similar fall orientation for most trees, this infers that severe storms may not have been responsible for the majority of tree throws, but instead, their upheave might be related to root failure. Given the relative maturity (average age 41 years) of fallen trees in this river valley, our data suggest that once trees attain a certain age, their physiognomy (i.e. height, mass, and centre of gravity) compromises their ability to remain securely anchored. We tentatively attribute this possibility to the presence of bedrock close to the surface, and to the shallow soil profile overlaying the steep rocky slopes. More in-depth studies are required to firstly confirm our findings, and secondly, tree throw studies should be undertaken in other Jura mountain river valleys to assess whether these results are representative.

Stable oxygen isotope analysis of the water uptake mechanism via the roots in spring maize under the ridge–furrow rainwater harvesting system in a semi-arid region

Root water uptake plays an important role in plant growth and the water cycle in ecosystems, and it is greatly affected by the morphology and spatial distribution of the roots. The ridge–furrow rainwater harvesting system (RFRH) is an effective strategy in semi-arid regions, but the mechanism of spring maize root water uptake remains unclear. Therefore, we conducted a two-year experiment in a semi-arid region of northwestern China to study the soil water content (SWC), spring maize root morphology and spatial distribution, and water uptake in different root zones using the 18-oxygen stable isotope (δ18O) under RFRH. The root zones were investigated in three locations around a maize plant: (1) ridge (RF-R), (2) border of the ridge and furrow (RF-B), and (3) furrow (RF-F). The results showed that RFRH changed the symmetrical soil water distribution in the maize rows and significantly increased the SWC in RF-F, especially in the shallow soil profile (0–60 cm), which where the enhanced root growth in the shallower soil layers (0–40 cm) under RF-F and the roots reached deeper into the soil under RF-R. The roots reached deeper to absorb water as they developed vertically in the advanced of growth stage. The contributions of different soil layers to the total soil water uptake in the root zone exhibited a similar trend to the root proportion according to δ18O analysis. In the filling stage, the maize roots under RF-R and RF-B acquired 64.1% and 65.8% of the water from the 40–60 cm layer in 2018, respectively, and 74.5% and 65.5% in 2019, whereas the amounts under RF-F were 49.9% and 27.6% from the 40–60 cm layer, and 30% and 53.9% from the 20–40 cm layer in 2018 and 2019. Thus, spring maize root water uptake was positively correlated with the root distribution, and the roots under the furrow absorbed more water from the shallower soil layers than the ridge, and less from the deeper soil layers than the ridge.

Climate Signals in Earlywood, Latewood and Tree-Ring Width Chronologies of Sessile Oak (Quercus petraea (Matt.) Liebl.) from Majdanpek, North–Eastern Serbia

In this article, the dependence of the sessile oak (Quercus petraea (Matt.) Liebl.) radial growth (tree-ring, earlywood, and latewood widths) on climate (the mean monthly temperature and precipitation totals) was studied in the Majdanpek area, north-eastern Serbia. The growth response of the oak trees to the prevailing climate conditions was dendroecologically investigated, by applying the correlation and response function, as well as by pointer years analysis. The site chronology covered 159 years (1855-2013). We found that latewood and total tree-ring width contain the imprinted positive response to the amount of precipitation in summer months (June and July) of the current growing season. The earlywood width showed no direct dependence on climate data, but it was significantly affected by the previous-year latewood width. Moreover, 40 % of the variation in the latewood width is explained by the earlywood variation in the same season. The temperature was not found to have any significant effect on the growth of oak at the study site. The use of pointer years, determined by applying several calculation procedures, has highlighted previous results, indicating that the precipitation in summer months was the deciding climate factor leading to the occurrence of the years with exceptionally wide or narrow tree-rings and latewood. To enhance our understanding of the response of the sessile oak growth at south-oriented sites with a shallow soil profile to precipitation and temperature variations, and expand the current database and knowledge, future studies should be undertaken.

Sediment generation and soil mound denudation in areas of high-density tree throw along a river valley in the Jura Mountains, Switzerland

A preliminary field-based investigation was undertaken in a small (< 10 km2) river valley located in the mountainous Jura region of northwest Switzerland. The aims of the work were to assess sediment generation and annual sediment transport rates by tree throw on forested hillslopes, and to document surface hydrology characteristics on four fresh soil mounds associated with recent tree throws over a 24-day monitoring period. For the soil mounds, average sediment recovery ranged from 7.7–28.2 g (dry weight), equivalent to a suspended sediment concentration of 145.2–327.8 g L−1, and runoff coefficients ranged from 1.0%–4.2%. Based on a soil bulk density value of 1,044 kg m−3, upslope runoff generation areas were denuded by an average 0.14 mm by the end of the 24-day monitoring period, representing an erosion rate equivalent to 2.1 mm yr−1. A ca. 50 cm high soil mound could therefore feasibly persist for around 200–250 years. For tree throw work, the dimensions of 215 individual tree throws were measured and their locations mapped in 12 separate locations along the river valley representing a cumulative area equivalent to 5.3 ha (av. density, 43 per ha). Tree throws generated a total of 20.1 m3 of fine-sediment (< 2 mm diameter), or the equivalent of 3.8 × 10−4 m3 m−2. The process of tree throw was originally attributed to two extreme weather events that occurred in west and central Europe in late December 1999. Taking the 18-year period since both storms, this represents an annual sediment transport rate of 2.7 × 10−5 m3 m−1 yr−1. Exploring the relationship with wind on fall direction, 65.5% of tree throws (143) generally fell in a downslope direction irrespective of hillslope aspect on which they were located. This infers that individual storms may not have been responsible for the majority of tree throws, but instead, could be associated with root failure. Given the high density of tree throws and their relative maturity (average age 41 years), we hypothesise that once trees attain a certain age in this river valley, their physiognomy (i.e. height, mass and centre of gravity) compromises their ability to remain securely anchored. We tentatively attribute this possibility to the presence of bedrock close to the surface, and to the shallow soil profile overlaying steep hillslopes.

Simulating and assessing the effects of seasonal fallow schemes on the water-food-energy nexus in a shallow groundwater-fed plain of the Haihe River basin of China

The increasing dependency on groundwater, especially in irrigated regions, has highlighted the notable place of groundwater resources within the water-food-energy nexus (WFEN). This role is particularly relevant in the Haihe River basin of China, a globally representative area that is experiencing rapid aquifer depletion. The winter wheat (Triticum aestivum L.) fallow strategy may have the potential to limit withdrawal in this region. Based on information from multiple sources, this paper proposed six kinds of fallow schemes—under the same triple-cropping system consisting of winter wheat and summer maize (Zea mays L.) followed by fallow and summer maize in two years (WW–SM/F–SM) but with different irrigation schemes—as scenarios to conduct detailed simulation by a modified Soil and Water Assessment Tool (SWAT) model. Then, the water balance components of the shallow aquifer and soil profile (2 m) under different scenarios were analyzed to quantify the variations in hydrological processes caused by changes in cropping system and pumping intensity. Furthermore, through 17 indices that could quantitatively describe the changes related to the WFEN, the effects of seasonal fallow schemes on shallow groundwater drawdown mitigation, grain yield reduction, and energy consumption savings were evaluated. Based on these evaluation outcomes, linear programming was used to optimize the fallow schemes at the subbasin scale. As a result, to satisfy the constraint of stopping groundwater drawdown as well as improving water and energy productivities, the minimum reduction in the annual average winter wheat yield would be 55% compared with the basic scenario, while the summer maize yield would remain basically stable. Under the optimized fallow scheme pattern, 66% of the well-irrigated cropland should adopt the WW–SM/F–SM system with two irrigation applications for winter wheat and a rain-fed scheme for summer maize; additionally, 24% of the well-irrigated cropland should adopt the WW–SM/F–SM system with one irrigation application for winter wheat and a rain-fed scheme for summer maize, and the recommended fallow schemes for the other 10% of well-irrigated cropland varied spatially. Compared to the basic scenario, the optimized fallow scheme pattern could decrease shallow groundwater exploitation by 36.5 × 108 m3 a−1 (i.e., to realize shallow groundwater equilibrium), reduce the diesel consumption of agricultural machines and electricity consumption of pumping wells by 32% and 90%, respectively, and save energy costs by approximately 873 yuan ha−1. These results could provide a quantitative reference for policy-making in this watershed and serve as a typical case for similar areas that wish to implement fallow strategies to achieve groundwater sustainability.

Modeling the hydrologic effects of watershed-scale green roof implementation in the Pacific Northwest, United States

Green roofs are among the most popular type of green infrastructure implemented in highly urbanized watersheds due to their low cost and efficient utilization of unused or under-used space. In this study, we examined the effectiveness of green roofs to attenuate stormwater runoff across a large metropolitan area in the Pacific Northwest, United States. We utilized a spatially explicit ecohydrological watershed model called Visualizing Ecosystem Land Management Assessments (VELMA) to simulate the resulting stormwater hydrology of implementing green roofs over 25%, 50%, 75%, and 100% of existing buildings within four urban watersheds in Seattle, Washington, United States. We simulated the effects of two types of green roofs: extensive green roofs, which are characterized by shallow soil profiles and short vegetative cover, and intensive green roofs, which are characterized by deeper soil profiles and can support larger vegetation. While buildings only comprise approximately 10% of the total area within each of the four watersheds, our simulations showed that 100% implementation of green roofs on these buildings can achieve approximately 10–15% and 20–25% mean annual runoff reductions for extensive and intensive green roofs, respectively, over a 28-year simulation. These results provide an upper limit for volume reductions achievable by green roofs in these urban watersheds. We also showed that stormwater runoff reductions are proportionately smaller during higher flow regimes caused by increased precipitation, likely due to the limited storage capacity of saturated green roofs. In general, green roofs can be effective at reducing stormwater runoff, and their effectiveness is limited by both their areal extent and storage capacity. Our results showed that green roof implementation can be an effective stormwater management tool in highly urban areas, and we demonstrated that our modeling approach can be used to assess the watershed-scale hydrologic impacts of the widespread adoption of green roofs across large metropolitan areas.

Sap flow of Amorpha fruticosa: implications of water use strategy in a semiarid system with secondary salinization

A. fruticosa (Amorpha fruticosa L.) is widely used for revegetation in semiarid lands that undergo secondary salinization. Understanding A. fruticosa plants response to soil water and salt stress is essential for water irrigation management and proper revegetation practices. In this study, we measured sap flow, stomatal conductance, meteorological and soil characteristics in an A. fruticosa community that recently experienced secondary salinization in northwestern China. Results of our study showed that daytime and nocturnal sap flows averaged 804.37 g·cm−2·day−1 and 46.06 g·cm−2·day−1, respectively, during the growing season. Within individual days, the highest sap flow appeared around noon local time and followed a similar pattern of photosynthetically active radiation (PAR). Despite the significant effect of meteorological factors on the characteristics of sap flow, our study highlighted that the sap flow of A. fruticosa is strongly regulated by the availability of soil relative extractable water (REW). The daytime sap flow, which is predominant compared to nocturnal sap flow, was strongly affected by PAR, air temperature and vapor-pressure deficit. With water stress in the top 40 cm of the soil (REW0–40 cm < 0.4), daytime sap flow displayed a strong relationship with soil water content (SWC) (positive) and soil electrical conductivity (EC) (negative) in the relatively shallow soil profile (up to 40 cm). For the nocturnal sap flow, our results suggest that in the absence of soil water stress (REW0–40 cm > 0.4), the nocturnal sap flow is mainly used to replenish the stem water content and sustain nocturnal transpiration. Under soil water stress, nocturnal sap flow is mainly used to replenish stem water content. The results of our study indicate that it is necessary to shorten the irrigation cycle during the primary growing period (May–July) of A. fruticosa. Moreover, in the absence of soil water stress (REW0–40 cm > 0.4), A. fruticosa can survive well in an saline environment with soil EC < 5 mS·cm−1.

Canopy isotopic investigation reveals different water uptake dynamics of maples and oaks

Variations in drought responses exhibited by cohabiting tree species such as Acer sacharrum and Quercus alba have often been attributed to differences in rooting depth or water accessibility. A. sacharrum is thought to be a shallow rooted species, and is assumed to not have access to the deep and stable water resources available to Q. alba. As such, A. sacharrum conserves water by minimizing stomatal conductance under drought conditions whereas Q. alba does not. However, detailed records of sufficient temporal resolution which integrate water accessibility, meteorological drivers, and leaf level parameters (e.g., photosynthesis, stomatal conductance) are lacking, making such assumptions—though plausible— largely untested. In this study, we investigated the water accessibility of both maples (A. sacharrum) and oaks (Q. alba) during the late growing season using novel canopy stable isotope measurements. Our results showed that maples can draw from the same water pool as cohabitating oaks, but can also switch to a shallow water source in response to available moisture in the shallow soil profile. We also found that maples tended to use a deep water source under high vapor pressure deficit even when shallow soil water was available. On the other hand, oaks had consistent deep water access during our study period. It is noted that our measurements do not cover the whole growing season and should be extrapolated with caution. Such findings indicate that differences in leaf functions during drought between maples and oaks may be due to both soil water accessibility and atmospheric water demand.

Root production, mortality and turnover in soil profiles as affected by clipping in a temperate grassland on the Loess Plateau

Abstract Aims Clipping or mowing for hay, as a prevalent land-use practice, is considered to be an important component of global change. Root production and turnover in response to clipping have great implications for the plant survival strategy and grassland ecosystem carbon processes. However, our knowledge about the clipping effect on root dynamics is mainly based on root living biomass, and limited by the lack of spatial and temporal observations. The study aim was to investigate the effect of clipping on seasonal variations in root length production and mortality and their distribution patterns in different soil layers in semiarid grassland on the Loess Plateau. Methods Clipping was performed once a year in June to mimic the local spring livestock grazing beginning from 2014. The minirhizotron technique was used to monitor the root production, mortality and turnover rate at various soil depths (0–10, 10–20, 20–30 and 30–50 cm) in 2014 (from 30 May to 29 October) and 2015 (from 22 April to 25 October). Soil temperature and moisture in different soil layers were also measured during the study period. Important Findings Our results showed that: (i) Clipping significantly decreased the cumulative root production (P &lt; 0.05) and increased the cumulative root mortality and turnover rates of the 0–50 cm soil profile for both years. (ii) Clipping induced an immediate and sharp decrease in root length production and an increase in root length mortality in all soil layers. However, with plant regrowth, root production increased and root mortality decreased gradually, with the root production at a depth of 30–50 cm even exceeding the control in September–October 2014 and April–May 2015. (iii) Clipping mainly reduced root length production and increased root length mortality in the upper 0–20 cm soil profile with rapid root turnover. However, roots at deeper soil layers were either little influenced by clipping or exhibited an opposite trend with slower turnover rate compared with the upper soil profile, leading to the downward transport of root production and living root biomass. These findings indicate that roots in deeper soil layers tend to favour higher root biomass and longer fine root life spans to maximize the water absorption efficiency under environmental stress, and also suggest that short-term clipping would reduce the amount of carbon through fine root litter into the soil, especially in the shallow soil profile.

Characteristics and Triggering Conditions for Naturally Deposited Gravelly Soils that Liquefied following the 2008 Wenchuan Mw 7.9 Earthquake, China

The 2008 Mw 7.9 Wenchuan, earthquake caused naturally deposited ravelly soils to liquefy over a wide area. Although liquefaction of gravely soils is recognized by the geotechnical profession, observations of liquefaction and nonlique-faction case histories within the literature are few. Through several years of systematic study following the 2008 Wenchuan earthquake (Mw 7.9), 92 locations of gravel liquefaction were identified, described, and mapped. These locations lie within an approximately 3,000 km2 area of the Chengdu Plain. Peak ground accelerations estimated at the sites range from 0.15 g to 0.49 g. Taken collectively, these studies reveal the necessary conditions for liquefaction triggering in gravelly materials. Grain size analyses indicates that the ejecta was much finer than the gravels that liquefied. Gravel contents of liquefied soils ranged from 5% to more than 85%. The liquefied gravelly soils were loose, but their measured shear wave velocities range from 133 m/s to 267 m/s, with corrected values ranging from 154 m/s to 31 4m/s. The unique depositional conditions under Chengdu Plain provide favorable conditions for extensive liquefaction of gravelly soils. The shallow soil profiles consist of a 0.5 m to 5.5 m impermeable soil (i.e., the capping layer) overlying gravels ranging in thickness from a few meters to hundreds of meters.