Well-developed Soils Research Articles

Study of flow in vadose zone from electrical resistivity surveys

Among the indirect methods applied to environmental monitoring, electrical resistivity has played an important role in accessing water flow in the non-saturated zone of the soil and, consequently, aquifer recharge. This work evaluates the influence of some pedo-geomorphologic properties in the infiltration and percolation of water through the superficial soil horizons by means of multitemporal electrical resistivity sections. The experiments were carried out in two areas of distinct pedo-geomorphological characteristics developed on the crystalline basement of southeastern Brazil. The first is situated in a hollow -shaped slope where lixisols predominate; the second, in a nose -shaped slope where well-developed soils (ferralsols ) predominate. The results proved the efficiency of the electrical resistivity method to delimit percolation of tropical soils, even when subtle differences are found in the hydraulic properties of the soil. It was also possible to establish that in the nose slope percolation is faster than in the hollow.

Evaluation of Soil Properties and Hydric Soil Indicators for Vernal Pool Catenas in California

Vernal pool soils in California's Mediterranean climate experience extremes in pedogenesis driven by prolonged saturation to extended desiccation. Four northern California vernal pool soil catenas (summit, rim, and basin) were assessed to determine how soil properties and hydric soil indicators vary in response to duration of standing water and landscape position. Each catena had differences in parent material or degree of soil development. Soil properties differed subtly across each microtopographic sequence. In the well‐developed soils, the geochemical signature of horizons overlying the duripans changed sharply compared with horizons below the restrictive layers, suggesting polygenic origins of the soil profiles. The presence and abundance of redoximorphic features (RMFs) in profiles corresponded poorly with the duration of standing water at the four sites. Instead, the abundance of RMFs coincided better with the thickness of the soil above the restrictive horizons in all settings with duripans. Hydric soils were identified in the basin positions of each catena. Most rim positions contained hydric soils and most summit positions had soils that were not hydric. Indicators F8 (redox depressions) and TF2 (test indicator for red parent materials) were most commonly applied. None of the vernal pool catena soils met F9 (vernal pools hydric soil indicator), thus the hydric soil criteria for vernal pools may need to be revised.

Periglacial cover beds and soils in landslide areas of SW-Germany

At the slopes of the Jurassic cuesta scarp in SW-Germany, pedological and mineralogical investigations were carried out in landslide areas. So far, it is possible to distinguish two well-defined landslide areas, one of them belonging to the Pleistocene, the other one characterised by Holocene movements. In general, the distribution of soils and sediments is strongly linked to the age of landslide deposits. In Pleistocene landslide areas, the parent material of the studied soils is formed by periglacial cover beds of Late Pleistocene age, consisting of Jurassic, aeolian and volcanic components. The Upper Periglacial Cover Bed was recognised as the most important marker horizon in the studied slope areas. There, the existence of minerals originating from the eruption of the Laacher See volcano, dated to 12,900 yr BP, could be demonstrated for the first time. Most of the Pleistocene landforms are characterised by well-developed soils, like Clayic and Vertic Cambisols, whereas relic soils exclusively occur in the oldest parts of landslide deposits. Landslide areas affected by Holocene slope processes do not exhibit periglacial layers, as mass movements removed periglacial sediments and former soils extensively. As a consequence, the parent material is different from those of Pleistocene landslide areas. Therefore, sediments in these areas are characterised by Jurassic components and only initial soils are present.

Plant litter decomposition and microbial characteristics in volcanic soils (Mt Etna, Sicily) at different stages of development

Soils at different developmental stages were sampled from eight sites on the slopes of Mt Etna, Sicily (Italy) and characterized for total C, microbial biomass and microbial respiration. The values of these parameters were greatest for the most developed soils, but differences in recent management and site characteristics limited analysis of trends with soil development across the eight sites. The decomposition kinetics of both intact leaf litter and the water-insoluble fraction of leaf litter from three common species on Etna [Etnean broom (Genista aetnensis), European chestnut (Castanea sativa), and Corsican pine (Pinus nigra)] were determined in four of the soils (the two with the smallest and the two with the largest organic C contents) in a laboratory experiment over 168 days to test two hypotheses. First, that the readily mineralized fraction of added plant C is greater when the plant material decomposes in well-developed soils compared to less developed soils, and second, that the microbial communities in less developed soils are less efficient at mineralizing C from low quality plant residues. The first hypothesis held for Genista and Pinus litter, but not Castanea litter. The second hypothesis was supported for the Castanea and Pinus litter, but not for the Genista litter. Thus, the general applicability of the hypotheses was dependent on the precise source and characteristics of the litter.

Soil disturbance and hydrologic response at the National Training Center, Ft. Irwin, California

Military training exercises at the National Training Center (NTC), Ft. Irwin, California have led to the degradation of large areas of the Mojave Desert. Soil physical properties in areas subjected to low and high disturbance at interspace and plant ( Larrea tridentata) mound microsites were quantitatively compared to undisturbed surfaces of both well-developed soils formed on Pleistocene age alluvial deposits and weakly developed soils formed on Holocene age alluvial deposits. Results indicate that geomorphically young and old soils differ in hydraulic and pedogenic properties with and without anthropogenic disturbance. Multi-tension infiltrometers showed that young coarser textured surfaces had saturated conductivities ( K sat) that were nearly twice those of older surfaces. Mound microsites were more sand-rich than interspace locations although K sat was not significantly different. After both low and high disturbance by tracket vehicles, bulk density was significantly increased from 1.54 to 1.62 and 1.80 g cm −3, respectively. Similarly, penetration resistance increased following low and high disturbance from 1.32 to 1.47 and 3.90 kg cm −2, respectively. Although low disturbance increased K sat, high disturbance resulted in significant reductions in both K sat (2.4 to 1.3 cm h −1 ( p<0.05)) and mean Gardner's α (0.20 to 0.10 ( p<0.001)) at all sites. The resulting decrease in α is indicative of a loss in macroporosity from mixing and compaction of the soil matrix. In general, young interspaces were less sensitive to disturbance than older well-developed interspace soils. Although results showed that K sat on these older surfaces was not dramatically reduced despite large losses of fines and increased bulk densities, the overall morphology of the soil was dramatically impacted. Disking or ripping are common methods to alleviate soil strength prior to restoration activities. However, results indicate that these practices may result in further destruction of the soil structure.

Physicochemical characterization and mercury speciation of particle-size soil fractions from an abandoned mining area in Mieres, Asturias (Spain)

Soils from old cinnabar mining areas usually exhibit high Hg contents, whose mobility depends on soil parameters and environmental conditions. This paper presents the study of the Hg speciation in soil samples from an abandoned Hg mine and metallurgical plant in Mieres (Asturias, Spain), in relation to their mineralogical and chemical composition and their particle-size distribution. A characterization of samples was made by X-Ray Diffraction Spectrometry, Scanning Electron Microscopy and Atomic Absorption and Emission Spectroscopy analyses. A sequential extraction method was applied to establish Hg mobility in the samples and their grain-size subsamples. The highest Hg mobility was found in well-developed soils, as a consequence of the adsorption processes by iron and manganese oxides, whereas in those more contaminated soils, a higher proportion of Hg was leached in the non-mobile fraction. A higher Hg mobility was found in the finest grain-size subsamples, probably due to the accumulation of clay minerals and oxides in these ranges.

Problems arising from fixed-depth assessment of deeply weathered sandy soils

Practicality dictates a limit to the depth of routine soil examination, but for some deeply weathered soils the prescribed depth is not sufficient to establish a full genetic context. Failure to account for all related soil features on a landscape by ignoring features below a fixed depth (e.g., 2 m) can result in (i) inconsistent genetic interpretations and (ii) an inaccurate and disjointed depiction of soils on the landscape. The upper boundary of some B horizons in sandy soils undulates above and below 2-m depth on the same landform. Considering only the upper 2 m of such soils yields a truncated, “tip of the iceberg” impression. Some Quartzipsamments on older surfaces have horizons below 2 m that are contiguous with B horizons of spatially associated Ultisols or Spodosols. They hence are well-developed soils rather than undeveloped “A–C” soils, with an illuvial layer below the depth of consideration. An E horizon of an Ultisol or Spodosol does not change to a C horizon as the illuvial horizon dips below an arbitrary depth (2 m) and as the Order changes to Entisol. Quartzipsamments, however, are often described in such settings as A–C soils. Soil taxonomic systems can be validly applied with fixed depth maxima as long as full-context genetic interpretations are made prior to and independently of the classification. It is not necessary to bore routinely below conventional limits, since deep horizons can generally be inferred from (i) periodically encountering them at shallower depths and (ii) observing them regionally in deep excavations.

On the response of two populations of Quercus coccifera to ozone and its relationship with ozone uptake

Abstract Ozone (O3) effects on the growth and gas exchange-related parameters of two ecotypes of Quercus coccifera L. presenting different traits in the field were assessed during a 2-years exposure experiment. One-year-old seedlings grown from the acorns collected at a rock (rock ecotype) or at a well-developed soil (garrigue ecotype) were continuously exposed in open-top chambers to three different O3 treatments: charcoal filtered air, non-filtered air and non-filtered air supplemented with 40 nl l−1. Above-ground relative growth rate (RGR) and gas-exchange-related parameters were measured during each growth season. Above- and below-ground biomass were also measured at the beginning and the end of the experiment. Ozone exposure did not induce any significant effect on RGR or any biomass-related parameters. However, the two populations differed in their sensitivity to O3 regarding gas-exchange-related parameters. The observed responses were related with accumulated O3 exposure or cumulative O3 uptake. Although the re-parameterisation of the existing European Monitoring and Evaluation Programme O3 uptake model improved its performance by 30%, O3 accumulated exposure was a better predictor of the observed responses than O3 uptake. The results of the present experiment indicate the need of taking into account the intraspecific variations in plant sensitivity to O3 when assessing the potential risks or impacts of this pollutant.

Arsenic mobility in groundwater/surface water systems in carbonate-rich Pleistocene glacial drift aquifers (Michigan)

Within the Lower Peninsula of Michigan, groundwaters from the Marshall Formation (Mississippian) contain As derived from As-rich pyrites, often exceeding the World Heath Organization drinking water limit of 10 μg/L. Many Michigan watersheds, established on top of Pleistocene glacial drift derived from erosion of the underlying Marshall Formation, also have waters with elevated As. The Huron River watershed in southeastern Lower Michigan is a well characterized hydrogeochemical system of glacial drift deposits, proximate to the Marshall Fm. subcrop, which hosts carbonate-rich groundwaters, streams, and wetlands (fens), and well-developed soil profiles. Aqueous and solid phase geochemistry was determined for soils, soil waters, surface waters (streams and fens) and groundwaters from glacial drift aquifers to better understand the hydrogeologic and chemical controls on As mobility. Soil profiles established on the glacial drift exhibit enrichment in both Fe and As in the oxyhydroxide-rich zone of accumulation. The amounts of Fe and As present as oxyhydroxides are comparable to those reported from bulk Marshall Fm. core samples by previous workers. However, the As host in core samples is largely unaltered pyrite and arsenopyrite. This suggests that the transformation of Fe sulfides to Fe oxyhydroxides largely retains As and Fe at the oxidative weathering site. Groundwaters have the highest As values of all the waters sampled, and many were at or above the World Health limit. Most groundwaters are anaerobic, within the zones of Fe 3+ and As(V) reduction. Although reduction of Fe(III) oxyhydroxides is the probable source of As, there is no correlation between As and Fe concentrations. The As/Fe mole ratios in drift groundwaters are about an order of magnitude greater than those in soil profiles, suggesting that As is more mobile than Fe. This is consistent with the dominance of As(III) in these groundwaters and with the partitioning of Fe 2+ into carbonate cements. Soil waters have very low As and Fe contents, consistent with the stability of oxyhydroxides under oxidizing vadose conditions. When CO 2 charged groundwaters discharge in streams and fens, dissolved As is effectively removed by adsorption onto Fe-oxides or carbonate marls. Although Fe does not display conservative behavior with As in groundwaters, a strong positive correlation exists between As and Sr concentrations. As water–rock interactions proceed, the As/Fe and Sr/Ca ratios would be expected to increase because both As and Sr behave as incompatible elements. Comparisons with groundwater chemistries from other drift-hosted aquifers proximate to the Marshall sandstone are consistent with these relations. Thus, the Sr content of carbonate-rich groundwaters may provide useful constraints on the occurrence, origin and evolution of dissolved As in such systems.

Hydrological processes in a small arid catchment: scale effects of rainfall and slope length

Many studies have been concerned with the scale issue in geomorphology and hydrology. Most studies focus on the possibility of data transfer from small to large watersheds. Less attention has been given to the scale problem within very small watersheds where differences in slope length may seriously affect the spatial distribution and extent of runoff-contributing areas to the channel. It is usually assumed that runoff and erosion increase as slope length and angle increase. However, field observations in the Negev Highlands show positive relationships between slope length and deposition rates, regardless of slope angles. Short hillslopes are devoid of colluvial mantle, while thick colluvial deposits, with well-developed soil profiles indicative of long-term stability, are found at the base of long hillslopes. The hypothesis advanced is that temporal variations in effective rainfall control the spatial structures of surface properties that further enhance the effects of temporal variations in rainfall. Long-term monitoring of rainfall and runoff (1982–1998), conducted at spatial scales varying from few hundreds of m 2 up to 0.3 km 2, show a decrease in runoff at the hillslope scale. The low efficiency of runoff and erosion processes on long hillslopes is because the concentration time required for continuous flow along such slopes is longer than the duration of most effective rain showers prevailing in the area. Field data lead to the notion that runoff and erosion models in which a positive relationship between slope length and angle and runoff and erosion rates is assumed should not be applied to arid and semiarid areas. More attention should be given in latter areas to the complex hydrological relationships between rainfall scales and spatial scales. The implications of data obtained regarding the spatial distribution of areas contributing to channel flow, at a geological time scale and under changing climatic conditions, are discussed.

An approach to the description and interpretation of ichnofabrics in palaeosols

Abstract Studies on ichnofabrics have focused mainly on marine environments. Attempts to apply the ichnofabric methodology and theoretical framework to continental deposits bearing palaeosols are few and poorly developed. Methodologies analysed in this contribution include the applicability of current ichnofabric indexes and diagrams, the assessment of the destruction of the original bedding by ichnofabrics and by other soil characters separately, and the relationships between different stages of palaeosol and ichnofabric development. Many soil features may be formed without the intervention of bioturbation, or may be the result of interactions of physical, chemical and biological processes, in which traces of organisms may have only a subsidiary role. Ichnofabrics can be well developed in palaeosols devoid of other soil characters and, conversely, palaeosols showing a well-developed soil structure can bear almost no trace fossils. This fact adds a third component to classical methods that normally consider only original bedding and ichnofabrics. Theoretical analysis includes the possibility of recording composite ichnofabrics in palaeosols, and the value of individual ichnotaxa as possible indicators of subaerial conditions and environmental changes. The ecological preferences and requirements of trace-makers provide the key to understanding composite ichnofabrics; however, only complex traces can be certainly attributed to particular modern taxa. Insect nests, pupal chambers and earthworm burrows are the most reliable indicators of subaerial exposure and, in many cases, very particular environmental conditions.

Rainfall infiltration on hilly slopes under various lithology and its effect on tree growth in the dry-hot valley

Revegetation is very difficult in dry-hot valleys in China. Rainfall infiltration capability on hilly slopes is one of the key factors determining soil moisture conditions and tree growth in the dry-hot valley. Low rainfall infiltration often results in soil drought on slopes under the dry-hot valleys climate. Rainfall infiltration capability varies greatly with the difference of slope lithologic porosity. The infiltration rates of five lithologic slope-types, Schist Slope, Grit Slope, Gravel Slope, the slightly eroded Mudstone Slope and the intensively eroded Mudstone Slope, are 1.40-8.67, 6.33, 0.69-2.20, 0.6-1.3 and 0.03-0.63 mm/min, respectively. With its viscid compact soil body and low infiltration capability which causes little infiltrating rainfall, mudstone slope can afford little effective supply to soil water and leads to serious drought of soil in dry seasons, resulting in cessation of growth or even wide-spread death of trees due to physiological damage for the excessive deficit of water in dry season and also the low productivity of stands. Hence, it is extremely difficult to restore vegetation on this type of slope. The other four lithologic slope-types, however, with well-developed soil crevice, high infiltration capability and thus more infiltrating rainfall, can afford more available soil water supply and the trees on them can obtain better growth and relatively higher productivity, compared with those on Mudstone Slope. Revegetation in dry-hot valleys is controlled by the soil moisture conditions of different slope-types, and it can be implemented by relying on the dominative life-form plant species, the suitable spatial arrangement of different life-forms of arbor-shrub-herb species, and the establishment of ecological community relationship between vegetation and soil moisture in habits. On the other hand, ground making measures for forestation and the runoff-collecting engineering measures to increase the rainfall infiltration are the major keys of revegetation techniques in dry-hot valleys.

In situ measurements of erosion shear stress and geotechnical shear strength of the intertidal sediments of the experimental managed realignment scheme at Tollesbury, Essex, UK

Managed realignment is one of several ‘soft’ engineering options which may reduce the costs of coastal defence, provide a more ‘natural’ response to the problem of rising sea levels and at the same time deliver environmental, specifically nature conservation, benefits. The success of this technique depends on the ability of the soils and sediments within the site to resist the erosive action of waves and tidal currents and allow sediment accretion to occur, at least at a rate equal to mean sea-level rise. Once a critical shear stress, τ 0 crt exerted by the moving fluids over the bed, is exceeded erosion will occur. A cohesive strength meter (CSM) and the fall-cone method were used to gather data, in situ on the strength and stability of sediments from an experimental managed realignment site and an adjacent, established saltmarsh in south-east England. Following six years of regular tidal cover, the underlying agricultural soil appeared both very strong (mean surface shear strength, τ f =228 kPa ) and highly resistant to erosion ( τ 0 crt =6.23 N m −2 ). During this period much of the site had been covered by sediment, and saltmarsh plants ( Salicornia europaea) had become established above the mean high water neap tide (MHWN) level. Above MHWN level (tidal cover time <15%) sediments had greater bulk densities and lower water contents which resulted in a moderate shear strength (τ f =11.6 kPa) and resistance to erosion (τ 0 crt =2.45 N m −2) . Below MHWN, where sediment accretion rates were greatest, poor consolidation resulted in very high water contents and low bulk densities. These areas were at the highest potential risk of erosion (τ 0 crt =1.5 N m −2) and had very low shear strengths (τ f =0.33 kPa) . Where sediment exceeded 25 cm depth, gullies formed allowing their banks and adjacent margins to drain faster than the surrounding sediment. This led to a significant increase in bed strength (τ f =10.8 kPa) and stability (τ 0 crt =4.3 N m −2) . These gullies were probably the early stages of the complex creek patterns characteristic of the adjacent, established saltmarsh. The established saltmarsh was rich in plants and had a well-developed (aggregated) soil structure. These soils had a moderate to high resistance to erosion (τ 0 crt =2.45 N m −2) and shear strength (τ f =25.6 kPa) . Undrained sediment shear strength, τ f, obtained with the fall-cone apparatus can also provide a useful indication of critical erosion shear stress, τ 0 crt . Values of τ 0 crt , measured across this site were all relatively large compared with computed bed stresses arising from locally generated waves. Thus this experimental managed realignment site was found to be primarily depositional and was thus successfully achieving the twin aims of protecting the coast from erosion and extending a rich ecosystem.

The Status, Habitat, and Response to Grazing of Water Vole Populations in the Big Horn Mountains of Wyoming, U.S.A.

Microtus richardsoni, the water vole, was listed as a sensitive species in Region 2 of the USDA Forest Service in 1994. Historical records indicate water voles were found in the Big Horn Mountains, but little was known about their current status. The purpose of this study was to locate water voles in the Big Horn Mountains of Wyoming, develop a habitat profile, and evaluate the extent to which livestock grazing affects them. Accessible creeks with habitat requirements for water voles were surveyed. Water voles were not captured below 2440 m. Grazed and ungrazed sites occupied by water voles were matched and analyzed for percent plant cover, dry weight biomass, riparian classification, mean stream depth, channel type, elevation, precipitation, and temperature. Capture success was significantly greater in ungrazed areas. Percent cover by ferns and thallophytes was significantly greater in areas where water voles were more abundant, and bare ground was significantly greater at grazed locations. Water voles were most abundant on Rosgen B or E streams with a willow/wet Carex riparian class that is found on relatively undisturbed sites with stable, well-developed soils and bank structure. In the Big Horn Mountains, water vole captures were low in comparison to the Beartooth Mountains and synergistic effects of grazing and drying might negatively impact this species.

Ant predation on intertidal polychaetes in a SW Atlantic estuary

Polychaetes in soft-bottom intertidal habitats of the Mar Chiquita coastal lagoon (38° 00' S, 57° 30' W, Argentina) are the prey of shorebirds, fishes and crabs. Based on 3 yr of field sampling, we observed that the fire ant Solenopsis richteri is another important predator of poly- chaetes (mostly Laeonereis acuta) during the summer (December to March). Ants use intertidal areas adjacent to terrestrial habitats which have well-developed soils and are characterized by inland veg- etation (i.e. pampas grasses), but appear to be excluded from habitats with the burrowing crab Chas- magnathus granulata. Ants build intertidal galleries perpendicular to the shoreline that are used to transport polychaetes to the nest. The ants attacked the polychaetes in burrows with diameters larger than their own abdomen. They selected larger polychaete sizes, attacking up to 66% of the poly- chaetes in the high intertidal. Based on our observations, and given the wide range of this species and related fire ants, we believe that this terrestrial-marine interaction between fire ants and polychaetes could be a common phenomenon.

Archaeological and Palaeo-environmental Investigations of the Upper Allen Valley, Cranborne Chase, Dorset (1998–2000): a New Model of Earlier Holocene Landscape Development

A combination of on- and off-site palaeo-environmental and archaeological investigations of the upper Allen valley of Dorset conducted in 1998–2000 has begun to reveal a different model of landscape development than those previously put forward. A combination of off-site geoarchaeological and aerial photographic survey and palynological analyses of two relict palaeochannel systems, and sample investigations of four Bronze Age round barrows and a Neolithic enclosure, have been combined with inter-regional summaries of the archaeological and molluscan records to re-examine the prehistoric landscape dynamics in the study area. Preliminary results suggest that woodland development in the earlier Holocene appears to have been more patchy than the presumed model of full climax deciduous woodland. With open areas still present in the Mesolithic, the area witnessed its first exploitation of the chalk downs, thus slowing and altering soil development of the downlands. Consequently, many areas perhaps never developed thick, well structured, clay-enriched soils (or argillic brown earths), but rather thin brown earths. By the later Neolithic these under-developed soils had become thin rendzinas, largely as a consequence of human exploitation. The presence of thinner and less well-developed soils over large areas of downland removes the necessity for envisaging extensive soil erosion and thick aggraded deposits in the valley bottom in later prehistory. The investigations have suggested that, if there were major changes in vegetation and soil complexes, these had already occurred by the Neolithic rather than in the Bronze Age as suggested by previous researchers, and the area has remained relatively stable since.

Soil Organic Matter Decomposition and Turnover in a Tropical Ultisol: Evidence from δ13C, δ15N and Geochemistry

Soil organic matter (SOM), leaf litter, and root material of an Ultisol from the tropical rainforest of Kakamega, Kenya, were analyzed for stable carbon (δ13C) and nitrogen (δ15N) isotopic values as well as total organic carbon (TOC) and total nitrogen (TN) contents in order to determine trends in SOM decomposition within a very well-developed soil under tropical conditions. In addition, we quantified mineralogy and chemistry of the inorganic soil fraction. Clay mineralogical variation with depth was small and the abundance of kaolin indicates intense weathering and pedoturbation under humid tropical conditions. The soil chemistry was dominated by silica, aluminium, and iron with calcium, potassium, and magnesium as minor constituents. The relative depletion of base cations compared with silica and aluminium is an indicator for intense weathering and leaching conditions over long periods of time. Depth profiles of δ13C and δ15N showed a distinct enrichment trend down profile with a large (average 13δC = 5.0 and average 15δN= 6.3) and abrupt offset within the uppermost 10–20 cm of the soil. Isotopic enrichment with depth is commonly observed in soil profiles and has been attributed to fractionation during decomposition. However, isotopic offsets within soil profiles that exceed 3 are usually interpreted as a recent change from C4 to C3 dominated vegetation. We argue that the observed isotopic depth profiles along with data from mineralogy and chemistry of the inorganic fraction from the Kakamega Forest soil are a result of intense weathering and high organic matter turnover rates under humid tropical conditions.

Iron geochemistry of loess and red clay deposits in the Chinese Loess Plateau and implications for long-term Asian monsoon evolution in the last 7.0 Ma

Abstract Recently, some groups of authors have demonstrated that the Tertiary red clay deposits underlying the Pleistocene loess–paleosol sequence in the Chinese Loess Plateau are wind-blown in origin, thus extending the eolian record in the Plateau from 2.6 Ma back to about 7.0 Ma, and providing a good opportunity to reconstruct long-term monsoon changes. As magnetic susceptibility, the widely used paleomonsoon proxy of loess deposits, is problematic in reconstructing the monsoon history recorded in the red clay, the development of other proxies is urgently needed. In this study, we analyzed the ratios of citrate–bicarbonate–dithionite (CBD)-extractable Fe2O3 to total Fe2O3 concentrations in four loess sections along a north–south transect of the Loess Plateau, and in the Lingtai loess–red clay sequence of ∼305 m thick. The Fe2O3 ratio in the loess sections clearly shows higher values in soil units than in loess horizons, and a southward increase in this ratio is also remarkable along the transect. These are in good agreement with the temporal–spatial variations in the East Asia summer monsoon intensity identified by other monsoon proxies and soil development observations. The Fe2O3 ratio thus attests to being a good proxy indicator of the summer monsoon evolution. The Lingtai Fe2O3 ratio record shows high values over three time intervals: ∼4.8–4.1 Ma, ∼3.4–2.6 Ma, and during the interglacial periods of the past 0.8 Ma. The increase in summer monsoon intensity over the three intervals also coincides with the well-developed soil characteristics. It is therefore concluded that the East Asia summer monsoon has experienced a non-linear evolution since the late Miocene. The occurrence of a monsoon prime at about 4.8–4.1 Ma implies that the Tibetan Plateau, one of the most important boundary conditions in maintaining the monsoon circulation, must have been uplifted to a critical height at that time.

Soil properties of Imperata grasslands and prospects for tree-based farming systems in Northeast Luzon, The Philippines

Ambiguity in the potential of soils under Imperata cylindrica grass contributes to the slow pace of grassland development in Northeast Luzon. The aim of this study is to investigate the soil properties of Imperata grassland and the prospects for tree-based farming systems in northeastern Luzon. Soils are developed over Miocene-Pliocene sedimentary rock and Plio-Pleistocene volcanic and fluvial deposits. There is a clear distinction between relatively well-developed fertile soils (Cambisols, Luvisols) along hill slopes, clayey soils in lowlands (Vertisols) and inferior leached soils (Planosols) restricted to palaeo terraces and elevated surfaces. Low soil organic matter content is a regional constraint to grassland development. Other constraints mainly occur on a local level and are associated with soil physical, rather than soil chemical, properties such as low infiltration, surface crusting, gully formation, limited soil depth, and stony surfaces. It is argued that variable soil conditions and topography are inadequately considered in regional attempts to develop and rehabilitate grasslands. Fertile, low-angle foot slopes are most suitable to permanent cultivation with crop rotation and husbandry practices such as mulching of crop residues, efficient use of animal manure and inclusion of nitrogen-fixing plants. Enrichment of natural forest patches is proposed, together with mixed tree plantations on rocky and steep terrain, field boundaries and stream banks in cultivated areas. Less fertile palaeo terraces, watersheds and upper slopes are most suitable to silvipastoral systems.

Use of a new 10Be and 26Al inventory method to date marine terraces, Santa Cruz, California, USA

Marine terraces along active continental margins reflect the interplay between sea-level oscillations and rock uplift. Well-dated marine terraces record the timing of sea-level highstands and delimit both uplift and geomorphic rates. Cosmogenic radionuclides provide a new tool for dating previously undatable terraces. Because the five marine terraces north of Santa Cruz, California, are capped by well-developed soils formed in regressive marine sands, both predepositional cosmogenic radionuclide inheritance and bioturbation of the profile must be accounted for. We present a new cosmogenic radionuclide inventory method that uses the depth-integrated cosmogenic radionuclide concentration to determine the terrace age. This method yields terrace ages that correlate well with sea-level highstands of marine oxygen isotope stages 3, 5a, 5c, 5e, and 7. The implied uplift rate is steady at 1.1 mm/yr, and is two to three times higher than rates suggested by earlier studies.