Changes In Soil Moisture Conditions Research Articles

Dynamic hydrological niche segregation: How plants compete for water in a semi-arid ecosystem

Hydrological niche segregation (HNS), specifically the variation in root water uptake depth among coexisting species, is an understudied area of research. This is especially the case in semi-arid ecosystems, such as China’s Loess Plateau (CLP), where seasonal aridity necessitates adaptive water use strategies among plant species. In this study, we conducted a two-year investigation to understand the water sources and intrinsic water use efficiency (WUEi) of four coexisting plant species: Populus simonii (tree), Caragana korshinskii and Salix psammophila (shrubs), and Artemisia ordosica (semi-shrub). We analyzed the isotopic compositions of xylem and soil water (δ2H and δ18O) and leaf δ13C to identify the water sources and WUEi, respectively, of each species. We then used the nicheROVER model to quantify HNS based on the variations in xylem water δ2H and δ18O. Our results show that the four co-existing species occupied distinct positions on a hydrological niche axis, delineated by their respective water sources and disparate WUEi. The tree P. simonii exhibited a preference for deep soil water and demonstrated a high WUEi. Both shrubs, S. psammophila and C. korshinskii, utilized intermediate and deep soil water, respectively, and with comparable WUEi. Conversely, the semi-shrub A. ordosica relied on shallow soil water and displayed a low WUEi. These differences in water sources and WUEi led to HNS between A. ordosica and the other three species in a relatively wet year. However, in a relatively dry year, HNS between A. ordosica and the other three species contracted and WUEi increased as species increased the use of deep soil water. Overall, these results demonstrate that HNS is a dynamic phenomenon that varies on at least an annual basis. It expands and contracts as plants regulate their water uptake and loss in response to changing soil moisture conditions.

A detailed stratigraphic and taphonomic reassessment of the late Paleozoic fossil flora from Promontory Butte, Arizona

A late Paleozoic, likely early Late Pennsylvanian (Missourian/early Virgilian), flora from Promontory Butte, Arizona, USA is the westernmost assemblage of this age yet described from northern Pangea. The palynological species pool is similar to that typical of more central parts of the supercontinent; in contrast, the macroflora differs by facies, reflective of original habitat differentiation. The flora is preserved in a succession that includes sandstone, siltstone, shale, and conglomerate in an upward-fining series of beds. A break between the siltstone and shale is marked by an organic-shale bed, previously described as a coal, and its underclay/paleosol. This stratigraphic unit is interpreted as an active channel fill terminating in a lake. A detailed bed-by-bed facies analysis of the macroflora, focusing on the relationship between sedimentological features and fossil-plant composition reveals that the wetland floral elements are concentrated in the upper, fine-grained beds of the fill, including the organic shale and overlying mudrock, whereas the drought-tolerant, xeromorphic plants are concentrated in siltstones and sandy siltstones below the organic-shale/underclay couplet. Palynology, in contrast, suggests a uniform flora throughout the interval, indicating that macrofloral changes within the channel-fill sequence reflect microhabitat differences resulting from local changes in soil moisture conditions rather than climate change. The palynoflora is dominated by tree ferns and compositionally suggests a Missourian (Kasimovian) age, possibly early Virgilian; rare lycospore grains, characteristic of the Middle Pennsylvanian, are likely reworked from older sediments. Earlier collecting at this site did not sort the fossils by microstratigraphy and facies types, combining all floral levels into one assemblage that indicated possible co-occurrence of wetland plants and plants tolerant of seasonal moisture stress. Furthermore, a Pennsylvanian-Permian boundary age was inferred due to the abundance of xeromorphic, drought-tolerant taxa. In light of this investigation, a late Missourian age is inferred as most likely.

Water stable isotope characteristics and water use strategies of co-occurring plants in ecological and economic forests in subtropical monsoon regions

Identifying the spatio-temporal variation in water use by co-occurring species in mixed forests can determine whether there is hydrological niche partitioning or niche overlapping, i.e., whether plant co-occurrence brings about resource complementation or interspecific competition, and provides a reference for plantation management. Water stable isotopic compositions in precipitation, soil, and four plants (xylem and leaf) in ecological and economic forests and hydrometeorological factors were continuously monitored for a year, and the water uptake by plants was determined using a Bayesian MixSIR model. The isotopic compositions of soil water and plant water in the ecological forest (Camphora camphora and Cunninghamia lanceolate) and economic forest (Castanea mollissima and Camellia pitardii) showed similar seasonal variation, and no significant difference between their mean isotopic values was found (p > 0.05). The isotopic compositions in leaf water of different plants in the two forests were controlled by xylem water isotope and meteorological factors, rather than soil moisture conditions. With decreasing soil water availability, the water sources of C. camphora, C. lanceolate, and C. pitardii changed from shallow to deep, while the water use pattern of C. mollissima was insensitive to changing soil moisture conditions. The water source overlapping between C. camphora and C. lanceolate in the ecological forest might generate water resource competition during the dry period, limiting their ecological functions. On the other hand, the water source partitioning between C. mollissima and C. pitardii in the economic forest facilitated the water resource allocation. Our study suggested that the overlapping and partitioning of hydrological niches among species in mixed forests were species-specific and provided a scientific basis for fully exploiting the ecological and economic benefits of silviculture ecosystems.

A novel genotypic selection methodology to create a breeding population for developing drought-tolerant cultivars in tree crops

With the adverse effects of climate change, selecting the best tolerant varieties to drought stress is highly necessary to sustain the yield and productivity of agricultural crops including tree crops. However, classical drought tolerance selection studies of tree crops have several limitations due to their relatively long lifespan. In this study, we propose a method to identify stable high-yielding trees under changing soil moisture conditions using yield data of existing elite tree populations. We develop this method using the data from a tropical tree palm, Coconut (Cocos nucifera L.) as a model crop. Our selection method considers individual palms as different genotypes. The method considered both mean trait values and their stability across different environments therefore, it can be effectively used to identify elite genotypes of tree crops for drought tolerance.•We propose an analysis framework to identify stable, high-yielding individuals of tree crops under limited soil moisture conditions using the data of existing tree populations.•Individual trees that produce stable and higher yields under soil moisture stress were identified based on mean yield and regression-based coefficient over different environments characterized by inter-annual rainfall variability.•Individual trees selected by this method can be used as parental populations in breeding programs that focus on developing drought-tolerant varieties.

How Weather Affects over Time the Repeatability of Spectral Indices Used for Geological Remote Sensing

Geologic remote sensing studies often targets surface cover that is supposed to be invariant or only changing on a geological timescale. In terms of surface material characteristics, this holds for rocks and minerals, but only to a lesser degree for soils (including alluvium, colluvium, regolith or weathered outcrop) and not for vegetation cover, for example. A view unobstructed by clouds, vegetation or fire scars is essential for a persistent observation of surface mineralogy. Sensors with a continuous multi-temporal operation (e.g., Landsat 8 OLI and Sentinel-2 MSI) can provide the data volume needed to come to an optimal seasonal acquisition and the application of data fusion approaches to create an unobstructed view. However, the acquisition environment always changes over time, driven by seasonal changes, illumination changes and the weather. Consequently, the creation of an unobstructed view does not necessarily lead to a repeatable measurement. In this paper, we evaluate the influence of weather and resulting soil moisture conditions over a 3-year period, with alternating dry and wet periods, on the variance of several “geological” spectral indices in a semi-arid area. Sentinel-2 MSI data are chosen to calculate band ratios for green vegetation, ferric and ferrous iron oxide mineralogy and hydroxyl bearing alteration (clay) mineralogy. The data were used “as provided”, meaning that the performance of the atmospheric correction and geometric accuracy is not changed. The results are shown as time-series for selected areas that include solid rock, beach sand, bare soil and natural vegetation surfaces. Results show that spectral index values vary not only between dry and wet periods, but also within dry periods longer than 45 days, as a result of changing soil moisture conditions long after a last rain event has passed. In terms of repeatability of measurements, an overall low soil-moisture level is more important for long-term stability of spectral index values than the occurrence of minor rain events. In terms of creating an unobstructed view, we found that thresholds for NDVI should not be higher than 0.1 when masking vegetation in geological remote sensing, which is lower than what usually is indicated in literature. In conclusion, multi-temporal data are not only important to study dynamic Earth processes, but also to improve mapping of surfaces that are seemingly invariant. As this work is based on a few selected pixels, the obtained results should be considered only indicative and not as a numerical truth. We conclude that multi-temporal data can be used to create an unobstructed view, but also to select the data that give the most repeatability of measurements. Images selection should not be based on a certain number of days without rain in the days preceding data acquisition but aim for the lowest soil moisture conditions. Consequently, weather data should be incorporated to come to an optimal selection of remote sensing imagery, and also when analyzing multi-temporal data.

Novel Approaches in Tropical Forests Mapping and Monitoring–Time for Operationalization

For more than three decades, the remote sensing scientific community has successfully generated predictive models of tropical forest attributes and ecological processes at the leaf, canopy, patch and landscape scale by linking field-measured data to remotely sensed spectral values, as well as other variables derived from remotely sensed data. The main interest of these applications is to help describe ecological and functional patterns occurring at larger geographic scales with sufficient accuracy and precision and enable scientists to better understand ecological processes, such as the relationship between atmospheric fluxes, plant structural and ecophysiological traits, soil attributes, anthropogenic use, species occurrence and animal movement. However, as the earth’s environment suffers from ever-increasing human use and abuse, detecting spatiotemporal changes in these variables has become a necessary decision-making tool in conservation action and natural resources’ management. Moving from modeling into the study of soil, plants, wildlife and socioecological processes using remotely sensed data requires the extrapolation of single time-step models to its application on a time series of data with the same expected accuracy. The challenges in this matter are not trivial, since changes in soil moisture conditions, cloud contamination, canopy and leaf-level geometry and physiology can affect the strength of the proposed models. In this context, the term ‘Operationalization’ refers to migration from single time-step models to time series but also refers to the design and implementation of user-friendly tools to increase the efficacy of communicating spatiotemporal trends to the users. [...]

The effect of biochar on the water-soil environmental system in freezing-thawing farmland soil: The perspective of complexity

The moisture content of farmland soils is closely related to the farmland soil environment. Although biochar has been widely studied for farmland soil amelioration in tropical and temperate farmland soils, its application in areas of seasonally frozen soil is rare. In this study, field experiments were conducted to explore the effect of biochar on soil temperature and soil liquid moisture content in seasonally frozen soils and its corresponding mechanism. Biochar was applied to the soil at different rates (3 kg·m-2, 6 kg·m-2, 9 kg·m-2, and 12 kg·m-2) in autumn and spring. Daily monitoring data from the 20 cm soil-layer recorded for one year from the biochar application date were analyzed. The approximate entropy was introduced to explore the complex changes in soil temperature and soil liquid moisture content under biochar application in seasonally frozen soils. According to the calculation of approximate entropy, the application of biochar increased the complexity for most treatments. In the case of ignoring the heterogeneity of snowfall and uneven land tillage to the soil, we infer that this change was caused by changes in properties of the biochar due to the freeze-thaw cycle. The treatment under mixed biochar application in spring and autumn of 9 kg·m-2 had the smallest change in water and heat complexity. And the approximate entropy of this treatment is the smallest. Moreover, in the freezing period, the soil liquid moisture content is positively correlated with the biochar amount applied and negatively correlated with the biochar and soil mixing time. In the melting period, the opposite correlations occur. The changes in soil moisture conditions caused by freezing and thawing restrict the affinity of biochar for water. Therefore, the effect of biochar addition on the soil liquid moisture content varies among different freezing and thawing periods.

The role of geochemistry in organic carbon stabilization against microbial decomposition in tropical rainforest soils

Abstract. Stabilization of soil organic carbon (SOC) against microbial decomposition depends on several soil properties, including the soil weathering stage and the mineralogy of parent material. As such, tropical SOC stabilization mechanisms likely differ from those in temperate soils due to contrasting soil development. To better understand these mechanisms, we investigated SOC dynamics at three soil depths under pristine tropical African mountain forest along a geochemical gradient from mafic to felsic and a topographic gradient covering plateau, slope and valley positions. To do so, we conducted a series of soil C fractionation experiments in combination with an analysis of the geochemical composition of soil and a sequential extraction of pedogenic oxides. Relationships between our target and predicting variables were investigated using a combination of regression analyses and dimension reduction. Here, we show that reactive secondary mineral phases drive SOC properties and stabilization mechanisms together with, and sometimes more strongly than, other mechanisms such as aggregation or C stabilization by clay content. Key mineral stabilization mechanisms for SOC were strongly related to soil geochemistry, differing across the study regions. These findings were independent of topography in the absence of detectable erosion processes. Instead, fluvial dynamics and changes in soil moisture conditions had a secondary control on SOC dynamics in valley positions, leading to higher SOC stocks there than at the non-valley positions. At several sites, we also detected fossil organic carbon (FOC), which is characterized by high C/N ratios and depletion of N. FOC constitutes up to 52.0 ± 13.2 % of total SOC stock in the C-depleted subsoil. Interestingly, total SOC stocks for these soils did not exceed those of sites without FOC. Additionally, FOC decreased strongly towards more shallow soil depths, indicating decomposability of FOC by microbial communities under more fertile conditions. Regression models, considering depth intervals of 0–10, 30–40 and 60–70 cm, showed that variables affiliated with soil weathering, parent material geochemistry and soil fertility, together with soil depth, explained up to 75 % of the variability of SOC stocks and Δ14C. Furthermore, the same variables explain 44 % of the variability in the relative abundance of C associated with microaggregates vs. free-silt- and-clay-associated C fractions. However, geochemical variables gained or retained importance for explaining SOC target variables when controlling for soil depth. We conclude that despite long-lasting weathering, geochemical properties of soil parent material leave a footprint in tropical soils that affects SOC stocks and mineral-related C stabilization mechanisms. While identified stabilization mechanisms and controls are similar to less weathered soils in other climate zones, their relative importance is markedly different in the tropical soils investigated.

Assessing Available Water Content of Sandy Soils to Support Drought Monitoring and Agricultural Water Management

In the future, according to regional climate-model simulations, the Carpathian Basin (in Central Europe) is predicted to be exposed to intensifying weather extremes that will exert a growing pressure on water resources. In recent past decades, water already has become a significant limiting factor for the natural environment and many agro-economic sectors in the southern Carpathian Basin. Therefore, there are increasing attempts to develop monitoring systems to detect water stress. In this study, changes in soil moisture conditions were monitored within two Arenosol profiles of extreme water balance during years characterised by different hydrologic conditions and under the impact of irrigation in the Great Hungarian Plain. Hourly data series of hydrometeorological parameters and soil moisture from six different soil depths during 2014–2018 were provided by on-site monitoring stations; humus, carbonate content, porosity, field capacity and wilting point were measured in the laboratory. On the basis of the newly definied so-called ‘available water percent’ (AW%) and a developed classification method, the rate, time and duration of water-shortage periods were evaluated for the years 2014–2018. The results show that drought monitoring cannot be effective without investigation of soil moisture content. Detailed analysis of available water percentage (AW%) can be used for real-time drought monitoring and as a precise indicator of the evolution of drought. This can help us prevent and manage damage from drought, and it is extremely important for agriculture.

Assessing future drought risks and wheat yield losses in England

Droughts pose a major risk to agricultural production. By comparing the outputs from an ecophysiological crop model (Sirius) with four drought severity indicators (DSI), a comparative assessment of the impacts of drought risk on wheat yield losses has been evaluated under current (baseline) and two future climate scenarios. The rationale was to better understand the relative merits and limitations of each approach from the perspective of quantifying agricultural drought impacts on crop productivity. Modelled yield losses were regressed against the highest correlated variant for each DSI. A cumulative distribution function of yield loss for each scenario (baseline, near and far future) was calculated as a function of the best fitting DSI (SPEI-5July) and with the equivalent outputs from the Sirius model. Comparative analysis between the two approaches highlighted large differences in estimated yield loss attributed to drought, both in terms of magnitude and direction of change, for both the baseline and future scenario. For the baseline, the average year differences were large (0.25 t ha−1 and 1.4 t ha−1 for the DSI and Sirius approaches, respectively). However, for the dry year, baseline differences were substantial (0.7 t ha−1 and 2.7 t ha−1). For the DSI approach, future yield losses increased up to 1.25 t ha−1 and 2.8 t ha−1 (for average and dry years, respectively). In contrast, the Sirius modelling showed a reduction in future average yield loss, down from a baseline 1.4 t ha−1 to 1.0 t ha−1, and a marginal reduction for a future dry year from a baseline of 2.7 t ha−1 down to 2.6 t ha−1. The comparison highlighted the risks in adopting a DSI response function approach, particularly for estimating future drought related yield losses, where changing crop calendars and the impacts of CO2 fertilisation on yield are not incorporated. The challenge lies in integrating knowledge from DSIs to understand the onset, extent and severity of an agricultural drought with ecophysiological crop modelling to understand the yield responses and water use relations with respect to changing soil moisture conditions.

Drying-wetting cycles consistently increase net nitrogen mineralization in 25 agricultural soils across intensity and number of drying-wetting cycles

An increase in extreme weather events such as heavy rainfall and extreme drought causes intensive and frequent drying-wetting (DW) cycles, which have strong effects on the availability of nitrogen (N) for plant growth and development. How the effects of DW cycles on N turnover vary with the intensity and number of DW cycles and soil properties has not been clearly addressed, which hinders predicting soil biogeochemical cycles in a changing world. Herein, we examined the response of net N mineralization in agricultural soils measured at a standard temperature (25 °C) to DW cycles varying in intensity and number. A total of 25 soils differing in texture and organic matter content were collected to create a soil property gradient. We also established the relationships of DW cycle effects on net N mineralization to soil properties. The DW cycles significantly increased N mineralization by 11.05 ± 0.66 mg kg−1 (+81.7%), and the increase was consistent across DW intensities and numbers for most soils. The release of inorganic N was dependent on soil properties, while the regulation of soil properties on DW effects varied with DW intensity, with stronger regulation under intense DW cycles (60% to 0% field capacity) than under moderate DW cycles (100% to 20% field capacity). The effect of intense DW cycles on NH4+ increased with clay content but decreased with soil pH and sand content. The effect on NO3− has opposite responses to these soil properties when compared with the effects on NH4+. The effect on total inorganic N increased with soil pH and inorganic N concentration. These results indicated that DW cycles have the potential to increase N availability in agricultural soils and highlighted the underestimation of N availability predicted with averaged soil moisture instead of real-time soil moisture under changing soil moisture conditions.

Influence of changes in rainfall and soil moisture on trends in flooding

Despite the expectation that increases in rainfall with climatic change will result in increases in pluvial flooding, there is more historical evidence for decreases in flood magnitude. In Australia, as in many other parts of the world, flood magnitudes are mostly decreasing, despite increasing rainfall extremes. Here, we show how changes in soil moisture have led to decreasing flood magnitudes while rainfall extremes have been increasing.Using gauged streamflow, catchment average rainfall, and modelled soil moisture data across Australia we confirm that streamflow peaks (or floods) that occur at least once a year are strongly related to both the peak rainfall causing the flood and the antecedent soil moisture conditions preceding the storm event. Regions where the magnitude of the peak flow has decreased are visually and statistically correlated to regions of decreasing soil moisture. Flood magnitudes are more likely to increase only for the rarest events, with increases in rainfall offset by decreases in soil moisture for more frequent events. A recurrence interval dependent tipping point is identified beyond which trends in catchment rainfall outweigh those of soil moisture trends and dominate the flood response. For regions where soil moisture has decreased, this tipping point occurs at an average recurrence interval of ten years or more. As most studies investigating trends in flooding generally use annual maxima, changes in soil moisture are likely to be the dominant mechanism behind observed flood trends. Hence changes in soil moisture conditions need to be considered when predicting catchment flood response due to climatic change.

Chronic dryness and wetness and especially pulsed drought threaten a generalist arthropod herbivore.

Under climate change, both wetter and drier conditions, as well as an increase in extreme events like floods or droughts are projected for many areas. So far, studies only investigate the impact of drier or wetter conditions at a single stress severity level but do not consider how different intensities and types of changes affect insect herbivores feeding on stressed plants. Further, how effects of acute stress pulses differ from milder, chronic soil moisture stress is unclear. We investigated how changing soil moisture conditions affect a generalist insect herbivore feeding on grassland plants. We transplanted multi-species sections of grassland into pots and subjected them to different intensities and durations of flooding and drying stress. We compared effects of short, extreme drought and flooding pulses against the effects of milder, but chronic stress. Constantly drier conditions decreased plant and herbivore performance at all levels of stress severity. Severe permanent wetness did not affect plant growth, but decreased pupal weight (- 23%) and survival of larvae (- 34%). Extreme pulsed drought exacerbated negative effects of chronic drying, as most larvae died before they could benefit from rewetting plants after the drought (94% mortality). Pulsed flooding did not affect plants or larval development more than chronic severe wetness. Our findings imply that plant stress negatively affects generalist chewing herbivores, even with mixed diets. Both drier and severely wet, but not mildly wetter conditions, will reduce survival of some species. Especially, extreme droughts appear to have strong negative effects on generalist grassland herbivores.

Manipulative experiments demonstrate how long-term soil moisture changes alter controls of plant water use

Tree transpiration depends on biotic and abiotic factors that might change in the future, including precipitation and soil moisture status. Although short-term sap flux responses to soil moisture and evaporative demand have been the subject of attention before, the relative sensitivity of sap flux to these two factors under long-term changes in soil moisture conditions has rarely been determined experimentally. We tested how long-term artificial change in soil moisture affects the sensitivity of tree-level sap flux to daily atmospheric vapor pressure deficit (VPD) and soil moisture variations, and the generality of these effects across forest types and environments using four manipulative sites in mature forests. Exposure to relatively long-term (two to six years) soil moisture reduction decreases tree sap flux sensitivity to daily VPD and relative extractable water (REW) variations, leading to lower sap flux even under high soil moisture and optimal VPD. Inversely, trees subjected to long-term irrigation showed a significant increase in their sensitivity to daily VPD and REW, but only at the most water-limited site. The ratio between the relative change in soil moisture manipulation and the relative change in sap flux sensitivity to VPD and REW variations was similar across sites suggesting common adjustment mechanisms to long-term soil moisture status across environments for evergreen tree species. Overall, our results show that long-term changes in soil water availability, and subsequent adjustments to these novel conditions, could play a critical and increasingly important role in controlling forest water use in the future.

A model coupling the effects of soil moisture and potential evaporation on the tree transpiration of a semi‐arid larch plantation

AbstractQuantifying the tree transpiration (T) response to the coupling effects of changing soil moisture and weather conditions provides insights into water use by forests, especially in dryland regions. This study was conducted in a semi‐arid pure larch (Larix principis‐rupprechtii) plantation in northwest China. The sap flow density of trees, weather conditions in open field, and soil moisture of main root zone (0–60 cm) were measured synchronously and continuously throughout a growing season in 2010. The response of daily T to the relative extractable soil water (REW) and potential evapotranspiration (PET) was analyzed. The T varied in the range of 0.08–2.18 mm/day during the study period. With increasing REW, it initially rose quickly and almost linearly; but after the REW reached a threshold, it leveled off and gradually approached its maximum (Tmax). However, Tmax positively related with PET. Based on the T‐REW and Tmax‐PET relationships, an integrated model (T = (−0.05PET2 + 0.65PET) × (1 − exp (−5.39REW))) was developed to describe the complex T‐REW‐PET relationship and it fit the measured data well. For the whole study period, due to the limit of PET and REW, the actual T was reduced by 32% (88.6 mm) and 16% (45.0 mm) respectively, compared with potential T. Although this model cannot be widely applied until it is validated with measured data from more sites, it does provide a way to accurately estimate the daily T using REW and PET data and to quantify the coupling effects of changing REW and PET on the T.

Impacts of river impoundment on dissolved heavy metals in floodplain soils of the Lahn River (Germany)

The effects of changing soil moisture conditions and oxidation–reduction (redox) processes on dissolved fractions of arsenic (As), cadmium (Cd), copper (Cu), iron (Fe), manganese (Mn), lead (Pb) and zinc (Zn) were studied in floodplain soils in the Lower Lahn Valley (Germany). Multiple weirs and locks affect the groundwater levels in the adjacent river banks by modifying the river’s discharge rate. Redox conditions act as a key factor for sorption and desorption processes and are strongly regulated by groundwater levels. Hence, floodplain soils situated up- and downstream of impounded river segments were characterized by various contents of their mobile heavy metal fraction. To quantify the variations of the dissolved heavy metal concentrations during seasonal and periodic fluctuations of the groundwater levels, a 2-year field study was conducted. The results indicated that higher seasonal changes of river discharge downstream of a weir caused higher amplitudes of groundwater levels, redox changes and variations in dissolved As, Fe and Mn in soil depths (50–60 cm) with a strong groundwater influence. Upstream of a weir, higher dissolved concentrations and more smooth variations of As, Fe and Mn dominated within the same depths. A high rise of capillary waters within the same study site caused significant enrichments of dissolved Cd and Zn in the middle (25–35 cm) of the soil profile. The comparison of floodplain soils along the Lahn River showed how the stream regulations influence heavy metal concentrations of soil pore waters, which may in turn influence the quality of the river water.

Measuring and predicting soil moisture conditions for trafficability

ABSTRACTThe main cause of loss of soil structural stability is vehicle operation on unpaved wet surfaces. Unfortunately, there is a lack of continuous soil moisture data in predicting trafficable conditions. To measure changes in soil moisture conditions in real time, Percostation (Adek) sensors were installed in sandy loam Stagnosol soil at different depths. Problems with soil trafficability can be expected at the plastic limit, and the soil is unable to support vehicle operations at the liquid limit in such soils. The maximum water-holding capacity of the soil is 32%, the field capacity is 25%, the plastic limit is 22%, and the liquid limit is 30%. With rainfall of more than 10 mm d−1, the moisture content reached the plastic limit in the upper 25 cm of soil. The average increase in the soil moisture content after more than 10 mm of rain was 1–2.5% in a time frame of 2–3 hours. After rain, the previous soil moisture level was obtained within 2 to 3 days in the vegetation period. Measurements also allowed soil water balance and evapotranspiration modelling data to predict soil moisture conditions with an accuracy of one day but failed to predict in a shorter period.

Paleoenvironmental analysis of the Neotropical fossil mammal site of Cerdas, Bolivia (middle Miocene) based on ichnofossils and paleopedology

The early middle Miocene (Langhian age) site of Cerdas in the southern Bolivian Altiplano has produced a diverse fauna of extinct mammals (15 species in seven orders and 11 families). In this study, we use paleosols and ichnofossils to reconstruct its paleoenvironment and the conditions in which its fossils were preserved. The described paleosols represent three pedotypes and three distinct landscape surfaces in an alluvial system. Type 1 paleosols are interpreted as Haplusteps (Inceptisols) that formed on a proximal floodplain in a subhumid to humid, patchy shrubland with seasonal variation in precipitation and associated changes in soil moisture conditions (Landscape 1). Type 2 paleosols are interpreted as Dystrudepts that formed on a well-vegetated, distal floodplain in a seasonal, humid climate with ground covering shrubland vegetation (Landscape 2). Type 3 paleosols are interpreted as Calciustolls (Mollisols) that formed in a shifting alluvial environment in a seasonal, sub-humid to semi-arid open environment (Landscape 3). Ichnofossil assemblages of Cerdas include Skolithos, Planolites, Macanopsis, Parowanichnus, rhizohaloes, and rhizotubules. These were produced by detritivorous, herbivorous, and faunivorous soil arthropods as well as plant roots and represent soil communities not normally preserved as body fossils that were living within a heterogeneous alluvial environment. The physical and geochemical properties of the paleosols and associated ichnofossil assemblages indicate that the paleolandscapes were composed of shrublands and open environments that experienced changes in moisture regimes due to seasonal precipitation and flooding events and had varying degrees of temporal stability. Our analysis is the first detailed study of pre-Pleistocene Cenozoic paleosols and trace fossils from the southern tropics (mid-latitudes) of South America and one of the few focused on important fossil-mammal bearing sediments.

Long-term changes in soil moisture conditions and their relation to atmospheric circulation in the Poyang Lake basin, China

Understanding the reasons for past changes in soil moisture conditions is key to improving forecasts of this extremely important variable coupling land and atmosphere. To contribute to this understanding, we analyzed the variability of soil moisture and its relationship to regional climate features. In this study we focused on the Poyang Lake basin, which is located on the southern bank of the Yangtze River at the junction of its middle and lower reaches in Jiangxi Province. Using in situ soil moisture observations from Nankang and Hukou stations for the period from 1998 to 2012, we tested the regional applicability of the high-resolution long-term Essential Climate Variable (ECV) soil moisture (SM) dataset (1978–2013) by means of trend and correlation analyses. We only used the ECV SM product here that is based on passive microwave technology. Both observed and ECV SM data show the same variations on monthly and inter-annual time scales including identical trend direction and strong correlations. To investigate the relationship between soil moisture conditions in the Poyang Lake basin and the Western Pacific Subtropical High (WPSH), correlation coefficients were calculated between the ECV SM data, the strength index (IS), and the northern limit index (IN) of the WPSH. The IS of the last autumn and winter shows a strong positive correlation with soil moisture during the subsequent rainy season. A strong WPSH in the preceding autumn and winter could result in more humid climate conditions in the Poyang lake basin during the following rainy season. The IN shows a strong negative correlation with concurrent soil moisture from July to September. The further the WPSH extends towards the north, the drier the area.

Moisture and temperature controls on nitrification differ among ammonia oxidizer communities from three alpine soil habitats

Climate change is altering the timing and magnitude of biogeochemical fluxes in many highelevation ecosystems. The consequent changes in alpine nitrification rates have the potential to influence ecosystem scale responses. In order to better understand how changing temperature and moisture conditions may influence ammonia oxidizers and nitrification activity, we conducted laboratory incubations on soils collected in a Colorado watershed from three alpine habitats (glacial outwash, talus, and meadow). We found that bacteria, not archaea, dominated all ammonia oxidizer communities. Nitrification increased with moisture in all soils and under all temperature treatments. However, temperature was not correlated with nitrification rates in all soils. Site-specific temperature trends suggest the development of generalist ammonia oxidzer communities in soils with greater in situ temperature fluctuations and specialists in soils with more steady temperature regimes. Rapidly increasing temperatures and changing soil moisture conditions could explain recent observations of increased nitrate production in some alpine soils.