Increasing Soil Development Research Articles

Aggregate stability of south Chilean volcanic ash soils – A combined XPS, contact angle, and surface charge analysis

Soils developed from volcanic ash deposits vary extremely in physical and chemical soil properties and are known to degrade easily through erosion or soil compaction, which limits intensive utilization. Our objective was to test if aggregate stability, AS, as a key factor for erodibility, can be assessed from surface parameters, namely particle wettability in terms of the solid–water contact angle, CA, and the specific surface charge, SSC. To relate wettability to the chemical composition of particle interfaces, the amount of polar and nonpolar carbon (C) species within the particle interface layer was assessed by X-ray photoelectron spectroscopy, XPS. Samples were taken from four locations in southern Chile (40° south) along a 120 km transect from the central volcano range to the coastal mountain region. Sites were different in stage of soil development and land use. Aggregates (8–12 mm) were sampled on forest, meadow or arable plots from upper top- and subsoil. To increase the natural range of SSC and CA, soil pH was modified by treatment with HCl and NH3 gas, respectively. Results showed a general trend of increasing AS with increasing soil development, i.e. decreasing bulk density and increasing clay and soil organic carbon, SOC, content. A clear relation was also found between CA and AS with a wide range of AS (about 9 to >90%) at CA < 35° and always high AS for CA > 35°. XPS analysis showed that CA was closely related to the amount of nonpolar C species. Interestingly, the relation between CA and AS was still consistent after pH variation (initial pH ≅ 6, modified to pH 2 to 9) which led to net changes in SSC from around 0 C g−1 (pH 6) to values between +10 and −8 C g−1, respectively. CA for negative SSC were still in the range from 0° to >90°, similar to untreated soil, whereas positive SSC reduced the maximum CA to <40°. Increasing or decreasing SSC caused higher AS, while the least stable aggregates were found at point of zero charge, PZC. XPS analysis showed that a relative increase in interfacial C content increased AS (r2 = 0.77) and CA (r2 = 0.98) significantly. Generally, CA was revealed to be a significant parameter that allows rapid assessment of the present status and possible modifications of AS for a wide range of environmental conditions.

Characterization and Classification of Soils of Tipukjan Watershed of the Upper Brahmaputra Valley of Assam

Nine soil profiles collected from low hill (P1), piedmont plain (P2, P3, P4 and P5) and alluvial plain (P6, P7, P8 and P9) of Tipukjan watershed of Assam were studied for characterization and pedogenic development. The soils varied considerably in morphological, physical and chemical properties. The dominant hue of soil colour was 10YR, the value varied from 2 to 7 and chroma varied from 1 to 8. The soil texture ranged from loam to silty clay loam in the surface and loamy sand to clay in the sub-surface horizons. The structure of the soils was subangular blocky except in the surface horizons of rice cultivated soils, in C horizons and in all horizons of P7 where the structure was massive. Red (2.5YR 5/6) to yellowish brown (10YR 5/6) mottles were observed in all the soils except P2 and P6. Thin patchy clay cutans and few Fe-Mn glaebules were observed in the sub-surface horizons of soils except P2, P7 and P9. The organic carbon (OC) content in the soils varied from 1.5 to 17.1 g kg-1. The soils were acidic in nature (pH 4.1 to 5.4). Exchangeable Ca2+ was the dominant basic cation followed by exchangeable Mg2+, Na+ and K+. The cation exchange capacity (CEC) of soils ranged from 7.11 to 16.15 cmol(p+)kg-1 and the base saturation varied from 20.7 to 57.9%. The soils were classified as Ultic Hapludalfs (P1), Typic Dystrudepts (P2), Oxyaquic Hapludults (P3), Typic Endoaquults (P4), Aeric Endoaqualfs (P5), Oxyaquic Hapludalfs (P6 and P8), Typic Endoaquents (P7) and Ruptic-Alfic Dystrudepts (P9). The mean relative horizon distinctness (RHD) value was minimum in P7 and maximum in P9. Relative profile development (RPD) values of a soil profile increased in the order: Entisols (RPD 12) < Inceptisols (RPD 19-40) < Ultisols (RPD 31-35) < Alfisols (31-54). The profile weighted mean of exchangeable Al3+, exchangeable acidity and Al-saturation increased with increasing soil development.

Successional patterns along soil development gradients formed by glacier retreat in the Maritime Antarctic, King George Island

Maritime Antarctica is severely affected by climate change and accelerating glacier retreat forming temporal gradients of soil development. Successional patterns of soil development and plant succession in the region are largely unknown, as are the feedback mechanisms between both processes. Here we identify three temporal gradients representing horizontal and vertical glacier retreat, as well as formation of raised beaches due to isostatic uplift, and describe soil formation and plant succession along them. Our hypotheses are (i) plants in Antarctica are able to modulate the two base parameters in soil development, organic C content and pH, along the temporal gradients, leading to an increase in organic carbon and soil acidity at relatively short time scales, (ii) the soil development induces succession along these gradients, and (iii) with increasing soil development, bryophytes and Deschampsia antarctica develop mycorrhiza in maritime Antarctica in order to foster interaction with soil. All temporal gradients showed soil development leading to differentiation of soil horizons, carbon accumulation and increasing pH with age. Photoautptroph succession occurred rapidly after glacier retreat, but occurrences of mosses and lichens interacting with soils by rhizoids or rhizines were only observed in the later stages. The community of ground dwelling mosses and lichens is the climax community of soil succession, as the Antarctic hairgrass D. antarctica was restricted to ornithic soils. Neither D. antarctica nor mosses at the best developed soils showed any sign of mycorrhization. Temporal gradients formed by glacier retreat can be identified in maritime Antarctic, where soil development and plant succession of a remarkable pace can be observed, although pseudo-succession occurs by fertilization gradients caused by bird feces. Thus, the majority of ice-free surface in Antarctica is colonized by plant communities which interact with soil by litter input rather than by direct transfer of photoassimilates to soil.

Soil chemical features as key predictors of plant community occurrence in a Mediterranean coastal ecosystem

Modelling the relationships between soil chemical factors and vegetation in coastal areas provides a significant contribution to understanding the ecology and conservation of these ecosystems in the Mediterranean basin. The present study relates coastal plant communities and soil chemistry using multivariate analysis and generalized additive models (GAMs) in order (a) to determine the relationships between soil factors and plant community occurrence along a coastline-lagoon gradient; (b) to build best models of soil chemical predictors for coastal plant community occurrence. Distance from coastline was the primary driver of changes in plant community composition and soil factors on the Mediterranean coast. Field capacity, pH, CaCO3, NaCl and soil organic matter were the major parameters related to the pattern of vegetation distribution. Along the costaline-lagoon gradient, however, plant community and soil changes agreed for two main sequences of habitats. The first was in the sand dune environment, involving plant communities, the species composition of which varied in response to increasing soil development. The second was near lagoons, where vegetation responded to soil salinity, acting independently of other soil factors. Coastal plant community occurrence was explained by GAMs, using a few soil chemical predictors: pH and CaCO3 were the main predictors for dune communities but only partly explained their occurrence, whereas NaCl was the key factor for salt marsh community occurrence and largely contributed to the model. The results suggest that soil chemical changes can be detected through vegetation distribution, particularly in saline habitats. Thus, habitat-based models could be a useful tool to identify the key factors for different types of vegetation occurrence in coastal habitats.

The magnetic properties of Serbian loess and its environmental significance

This paper reports a loess-paleosol sequence located in the Danube River basin, Serbia, which formed at least since the latest part of the early Pleistocene, and before the paleomagnetic B/M boundary. Various magnetic parameters of the Serbian V-L1-V-S4 loess-paleosol sequence have been measured and analyzed in the Titel Loess Plateau. These parameters show a very similar magnetic behavior compared with that of the Chinese loess. There is a general positive relationship between magnetic susceptibility (χ) and pedogenesis. The main contributors to χ are the magnetic grains of SP (superparamagnetic) and SD (single domain) magnetic domains, while MD (multi domain) contributes only a small percentage. The difference in χ between loess and paleosol mainly is caused by pedogenesis. The very fine magnetic minerals increase gradually with increasing soil development (from loess to soil), and they lead to higher χ. The thermomagnetic curves show thatmagnetic minerals in the loess layers are magnetite and maghemite, both providing a major contribution to χ. In contrast the paleosol layers mainly are composed of magnetite, with almost no or a very small amount of maghemite, as implied by a reversible thermomagnetic behavior. This indicates that pedogenic conditions during V-S3 and V-S4 strong soil development have resulted in maghemite that is no longer stable, and has been resolved or converted to other stable phase minerals. This likely indicates that soil moisture during V-S3 and V-S4 development exceeded a critical condition of maghemite stability.

Soil development on marine terraces near Metaponto (Gulf of Taranto, southern Italy)

For decades, the marine terraces in the Metaponto area have been the subject of discussions concerning their number, sedimentology, genesis and age. This paper contributes to landscape history reconstruction from a pedogenetic view. The marine terraces are generally covered by loamy sediments, which have been interpreted in previous works as lagoonal and/or alluvial sediments, deposited shortly after the emergence of the land surface above sea level. Pedogenetic investigation, including field observations (e.g. soil colour, intensity of weathering, precipitation of secondary carbonates) and Fe d/Fe t ratio, silt/clay ratio and carbonate content, reveals that the usual sedimentation history on the terraces includes a period of soil formation between the deposition of the marine and that of the alluvial sediments. Most likely, soil formation began after the relative sea level maximum within the same interglacial during which the marine terrace formed. Later, alluvial sediments accumulated during a time of periodic flooding, while soil development in the underlying marine sediments probably continued at reduced rates. One central question of this study is whether soil formation indicates progressive ages of the terraces. The complex landscape history involving several sedimentation and erosion phases makes the correlation of soil development stages with terrace ages difficult. Nevertheless, maximum Fe d/Fe t ratios and (Ca + Mg + K + Na)/Al ratios of the soils developed in the different sediments plotted vs. assumed terrace age indicate increasing soil development. The relationship between Fe d/Fe t ratios and terrace age can be best described by power ( R 2 = 0.89) or logarithmic functions ( R 2 = 0.72), both describing a strong increase in pedogenic iron in the first 100 ka which slows down afterwards. (Ca + Mg + K + Na)/Al ratios follow a logarithmic decrease with time ( R 2 = 0.99), indicating progressive silicate weathering, associated with element release and leaching.

Mineralogy and Magnetic Properties of Basaltic Substrate Soils: Kaho'olawe and Big Island, Hawaii

Magnetic behavior of soils can seriously hamper the performance of geophysical sensors. Currently, we have little understanding of the types of minerals responsible for the magnetic behavior, as well as their distribution in space and evolution through time. This study investigated the magnetic characteristics and mineralogy of Fe‐rich soils developed on basaltic substrate in Hawaii. We measured the spatial distribution of magnetic susceptibility (χlf) and frequency dependence (χfd%) across three test areas in a well‐developed eroded soil on Kaho'olawe and in two young soils on the Big Island of Hawaii. X‐ray diffraction spectroscopy, x‐ray fluorescence spectroscopy (XRF), chemical dissolution, thermal analysis, and temperature‐dependent magnetic studies were used to characterize soil development and mineralogy for samples from soil pits on Kaho'olawe, surface samples from all three test areas, and unweathered basalt from the Big Island of Hawaii. The measurements show a general increase in magnetic properties with increasing soil development. The XRF Fe data ranged from 13% for fresh basalt and young soils on the Big Island to 58% for material from the B horizon of Kaho'olawe soils. Dithionite‐extractable and oxalate‐extractable Fe percentages increase with soil development and correlate with χlf and χfd%, respectively. Results from the temperature‐dependent susceptibility measurements show that the high soil magnetic properties observed in geophysical surveys in Kaho'olawe are entirely due to neoformed minerals. The results of our studies have implications for the existing soil survey of Kaho'olawe and help identify methods to characterize magnetic minerals in tropical soils.

Sand dynamics in coastal dune landscapes constrain diversity and life‐history characteristics of spiders

SummaryIn fragmented landscapes where natural disturbance acts at the local level, community composition can be altered either by ‘species‐by‐species matching’, with community‐wide character displacement, or by ‘constrained species sorting’, whereby disturbance favours species with distinct ecological traits. It is necessary to understand such species shifts when aiming to detect bottlenecks associated with changing disturbance dynamics at different spatial levels. Such an understanding also provides insight into the underlying ecological mechanisms in operation and allows identification of species of conservation concern.This approach to understanding species’ shifts was applied to a study of spider diversity and life‐history variation in relation to sand dynamics in stabilized and dynamic grey dune landscapes located along the coasts of France, Belgium and the Netherlands.Local (α) diversity appeared to decrease with increasing local sand dynamics in both stable and dynamic landscapes. In dynamic dune landscapes, β‐diversity decreased significantly and approached regional (γ) diversity under local grey dune stabilization; in stabilized landscapes, β‐diversity was not affected by local sand dynamics.Comparative analyses of ecological traits revealed shifts in life‐history patterns, suggesting that patterns in local diversity resulted from species sorting. Species from fragments characterized by high sand dynamics showed narrower niche breadths, larger body sizes and longer generation times, while summer‐active species tended to become residential after sand stabilization. This provides evidence for constrained species sorting in which natural disturbance (through local sand dynamics) allows only species with distinct ecological traits to persist.Synthesis and applications. Species with larger body sizes, longer generation times and a higher degree of habitat specialization (i.e. related to dispersal ability) would be expected to be more vulnerable at dynamic sites and more prone to extinction than their counterparts from stabilized fragments. In particular, species with a burrowing lifestyle would be expected to go extinct locally as a result of increasing soil development and soil hardness. Shifts in species composition were found to be more pronounced in dynamic landscapes. Hence ensuring conservation of sand dynamics at a landscape level rather than at a local level is of prime importance when aiming to conserve typical psammophilous spider species within local assemblages in grey dune habitats.

Adsorption of Dissolved Organic and Inorganic Phosphorus in Soils of a Weathering Chronosequence

Leaching of dissolved organic matter (DOM) and associated nutrients can be a significant loss from developing ecosystems. We studied how the adsorption of dissolved organic P (DOP) and PO4 changes during the development of young andesitic soils and determined which soil characteristics are responsible for these changes. We sampled 77, 255, 616, and about 1200+ yr‐old andesitic soils at the 0‐ to 10‐, 30‐ to 40‐, and 140‐ to 150‐cm soil depths and performed adsorption isotherm analyses that were described using a modified Langmuir (for DOP) or linear equation (for PO4). We also sampled soil solution at the 10‐ to 20‐, 40‐, and 150‐cm soil depths during the main snow melt period in 2001 and 2002 and analyzed it for DOP and PO4 The ability of the soils to adsorb DOP and PO4 increased with soil age. Stepwise multiple regression analyses between the adsorption capacity for DOP, or the slope of the adsorption isotherm for PO4, and several soil parameters showed that allophane concentrations control the adsorption of DOP and PO4 in these soils. Tests of preferential adsorption of DOP vs. PO4 and DOC vs. DOP showed that the adsorption strength increased in the following order: DOC &lt; DOP &lt; PO4 The preferential adsorption of PO4 vs. DOP and DOP vs. DOC increased significantly with increasing soil development, whereas the soil depth did not have a consistent and significant effect. Significant correlations between the null‐point adsorption of DOP or PO4 and field soil solution concentrations indicated that the results obtained in laboratory experiments were applicable to field conditions. Consequently, the tendency of DOP and PO4 to leach from these andesitic soils decreases as soils and ecosystem develop.

Adsorption of Dissolved Organic and Inorganic Phosphorus in Soils of a Weathering Chronosequence

Leaching of dissolved organic matter (DOM) and associated nutrients can be a significant loss from developing ecosystems. We studied how the adsorption of dissolved organic P (DOP) and PO4 changes during the development of young andesitic soils and determined which soil characteristics are responsible for these changes. We sampled 77, 255, 616, and about 1200+ yr-old andesitic soils at the 0- to 10-, 30- to 40-, and 140- to 150-cm soil depths and performed adsorption isotherm analyses that were described using a modified Langmuir (for DOP) or linear equation (for PO4). We also sampled soil solution at the 10- to 20-, 40-, and 150-cm soil depths during the main snow melt period in 2001 and 2002 and analyzed it for DOP and PO4 The ability of the soils to adsorb DOP and PO4 increased with soil age. Stepwise multiple regression analyses between the adsorption capacity for DOP, or the slope of the adsorption isotherm for PO4, and several soil parameters showed that allophane concentrations control the adsorption of DOP and PO4 in these soils. Tests of preferential adsorption of DOP vs. PO4 and DOC vs. DOP showed that the adsorption strength increased in the following order: DOC < DOP < PO4 The preferential adsorption of PO4 vs. DOP and DOP vs. DOC increased significantly with increasing soil development, whereas the soil depth did not have a consistent and significant effect. Significant correlations between the null-point adsorption of DOP or PO4 and field soil solution concentrations indicated that the results obtained in laboratory experiments were applicable to field conditions. Consequently, the tendency of DOP and PO4 to leach from these andesitic soils decreases as soils and ecosystem develop.

SOILS ON QUATERNARY TERRACES OF THE TALLAPOOSA RIVER, CENTRAL ALABAMA

Fluvial terrace chronosequences provide excellent opportunities for evaluating pedogenesis. We evaluated soil development on Quaternary terraces of the Tallapoosa River of central Alabama. Our objective was to ascertain pedogenic markers for these relatively low terraces. Past studies and other evidence suggest landscape ages ranging from contemporary floodplains to mid- to late Pleistocene terraces. The six pedons evaluated ranged from Typic Udifluvents and Fluventic Dystrudepts on the floodplain to fine-loamy and coarse-loamy Typic Paleudults on relatively higher terraces. Soil physical properties (particle size, bulk density, 15 bar H 2 O content), soil chemical properties (total and extractable elements, cation exchange capacity, Fe and Al extractions, heavy mineral content), morphological properties, and micromorphological properties were evaluated. Many soil physical and chemical properties (averaged for B horizons) are related to the soil chronosequence, including properties established in earlier studies as being indicative of soil development. The effective cation exchange capacity and cation exchange capacity 100 g -1 clay (P ≤ 0.05 and 0.01, respectively), oxalate-extractable Fe (P ≤ 0.05), oxalate-extractable Fe/dithionite extractable Fe (P ≤ 0.10), and total K/total Ti (P ≤ 0.05) all decreased at higher levels. In addition, Mehlich extractable Cu (P ≤ 0.10), Fe (P ≤ 0.05), and Zn (P ≤ 0.05), along with total Mg (P ≤ 0.01), Mn (P ≤ 0.10), and Ca (P ≤ 0.10) decreased with higher terrace levels. Principal component analysis and cluster analysis indicated that soils on terrace levels 5500 years B.P. are similar. The first principal factor, which accounted for 65% of the variance and is composed of both chemical and physical properties, separated terrace levels satisfactorily. The results are generally consistent with decreasing inherent fertility with increasing soil development.

The role of lignite in the carbon cycle of lignite-containing mine soils: evidence from carbon mineralisation and humic acid extractions

In many mine soils, lignite carbon is present as a potential carbon source for micro-organisms. Although the establishment of an active microbial community in reclaimed mine soils was recognised to be of great importance to reclamation success, the organic substrates available for micro-organisms have never been characterised in terms of bioavailability. The objective of this study was to examine if lignite in mine soils is decomposed and transformed during biodegradation. A chronosequence of lignite-rich mine substrates consisting of lignite-containing overburden material (parent substrate for soil development), a 14 years old mine soil and a 37 years old mine soil, both rich in lignite in addition to recent carbon were sampled and incubated for 16 months. Carbon mineralisation was monitored and the soil-respired CO 2 subjected to 14C activity measurements. Additionally the 14C activity of humic acids extracted from the soils was determined. With the 14C activity data, lignite carbon contribution was estimated. These results show that lignite was decomposed in the lignite-containing parent substrate as well as in the 14 and 37 years old mine soil over the whole incubation period, the average decay rate of lignite being 0.025 and 0.007 g lignite C kg −1 C year −1. Lignite carbon was part of the humic acid fraction, indicating that lignite in the soil is oxidized during biodegradation A higher portion of lignite can be extracted as humic acids with increasing soil development. Thus, lignite in soil can be mineralised as well as humified and must be considered in the soil carbon cycle.

Fine silt and clay mineralogical changes of a soil chronosequence in the Langtang valley (Central Nepal)

AbstractChemical and mineralogical properties of a soil chronosequence in the high mountain zone between 3857 m and 4120 m a.s.l. in Central Nepal (Langtang valley) are presented. The soils have been developed in moraine deposits which consist of acid gneisses. They were classified as Entisols, and Spodosols. XRD analyses of the clay and fine silt fraction show increasing changes with distance from the recent Lirung glacier, depending on the time of deposition, resp. soil age. Alteration of illite to interstratified minerals and to hydroxy‐Al interlayered minerals or pedogenic chlorite with increasing soil development could be observed. The interstratified minerals could be identified as random and regular illite‐interlayered vermiculite mixed‐layer minerals. Intensification of the X‐ray signals of the fine silt fraction is given compared to the clay. With increasing soil development differences between the clay and fine silt fraction seem to increase. Indications are given of interstratification of the mica‐pedogenic chlorite and chloriteinterlayered vermiculite type in the more intensively weathered soils.

SOIL DEVELOPMENT ON LATE PLEISTOCENE MORAINES AT PINE CREEK, EAST-CENTRAL SIERRA NEVADA, CALIFORNIA

Late Pleistocene moraines at Pine Creek in the east-central Sierra Nevada Range are differentiated into three separate relative-age groups using soil morphological properties, with increasing soil development on progressively older deposits. Tiogaage soils (oxygen-isotope stage-2 equivalent) are weakly developed with A/AB/Bw/Cox profiles. Organic material extracted from Tioga-age till matrix has a conventional radiocarbon age of 19,570 ± 420 years B.P. Soils formed on Tahoe-age moraines (stage 4) show A/2BA/2Bw1/2Bwq2/2BC/2Cox horizonation with rubification to about 50 cm depth and slight clay enrichment. Organic matter from the Tahoe-age till matrix yields an infinite radiocarbon age (>38,000 years B.P.). Rovana moraines (stage 6) have moderate soil development, with A1/A2/2Bt1/2Bw2/2BC/2Cox profiles, conspicuous rubification down to about 103 cm, and significant clay accumulation in the Bt horizon. A soil-profile development index reflects the chronologic trend; however, lithologic and climatic variabil...

Water movement in desert soil traced by hydrogen and oxygen isotopes, chloride, and chlorine-36, southern Arizona

Understanding soil water movement is important for water resource management and for analyzing pollutant transport in the vadose zone. Seasonal variations in shallow soil profiles may have profound effects on deep soil water and solutes. We have investigated seasonal soil water movement in the top meter of undisturbed desert soil in the southern Arizona using 2H, 18O, Cl, and bomb- 36C1. Six soil profiles were sampled from a young terrace (Holocene) during 1991 to 1992 on a seasonal basis. One soil profile was sampled from an older terrace (latest Pleistocene) in October 1992, and one from a yet older fan surface (late Pleistocene) in March 1992. The results indicate that repeated seasonal cyclic movement of soil water in the top 60–80 cm active zone tends to produce a consistent stable isotope composition for the soil water below the active zone in different seasons. The deep δ 18O on the oldest surface is about 6‰. heavier than on the younger surfaces, probably resulting from greater evaporative loss due to the larger proportion of fines in the older soil. This deep isotopic composition is closely related to the composition of the local average annual precipitation. An annual average evaporation rate of 35 mm year −1 was estimated using a steady-state diffusion model, whereas the actual regional evapotranspiration rate is 175–250 mm year −1. This suggests that about 80% of the soil water is lost through transpiration and first-stage evaporation before quasi steady-state is reached. The long-term average infiltration rate below the active zone is about 4 mm year −1 for the younger terrace, based on both chloride mass balance and bomb 36Cl, and 0.02 mm year −1 for the older terrace and the fan surface, based on chloride mass balance. The correlation between the deep δ 18O, the reduction of downward flux and the surface age suggests that increasing soil development has resulted in a significant decrease of soil water infiltration and hence an increase in evaporation and surface runoff.

A study of two soil development sequences located in a montane area of Canterbury, New Zealand, III. Soil phosphorus transformations

Two soil development sequences in a montane area of Canterbury were studied with a view to determining quantitative data on phosphorus (P) transformations in soils formed in geologically layered parent materials. Data from soil P fractionation are presented. The results are discussed in terms of changes in P content from that of the “initial state” of each individual soil profile. All soils have undergone a net loss of P. Soils in the low rainfall area show a trend of increasing P loss with increasing soil development, whereas soils in the higher rainfall area show trends related to differences in vegetation history. The results indicate that contrasting pathways of soil P transformation are followed by soils in low and high rainfall areas. Soils in the low rainfall area show increasing losses of P from B horizons with increasing soil development. Soils in the high rainfall area show a pattern of net gain and subsequent loss of P from the B horizon. Acid extractable P is transformed rapidly to secondary forms relative to the rate of loss of P during soil development.

Ecology of a coastal lagoon to dune forest sequence, south Westland, New Zealand

Abstract The vegetation and floristic patterns in and around a coastal lagoon are described from quadrat sampling and related to several environmental factors (elevation, water depth, soil organic content, and pH). A cluster analysis was used to identify 14 communities while a detrended correspondence analysis ordinated the quadrats. The ordination's Axis 1 was correlated with water depth/elevation, while Axis 2 was correlated with soil organic content and, in the opposite direction, with soil pH. Two vegetation development sequences are proposed for the dune hollow-ridge system: one in the hollows involving stages of aquatic, bog, and forest vegetation; the second on the ridges where forest composition changes in response to increasing soil development. Rates of succession arepresumably very slow. Formal protection of the lagoon within the World Heritage area is justified because of its ecological, conservation, and scenic values; in light of diminishing natural wetlands; and the common occurrence of a v...

Rubidium in Surface Horizons of Illinois Soils

AbstractThe mean total Rb content in 223 surface horizons of upland soils was 88.8 mg kg−1 and contents were normally distributed. Rubidium tended to be highest at sites where loess is very thin or absent and illitic Wisconsinan till is present. Surface horizons of soils in areas of thick loess commonly have about 80 mg Rb kg−1. The pattern of increasing soil development associated with decreasing loess thickness characteristic of Illinois is reflected by Rb concentrations that first increase with declining loess thickness and then decrease in the most intensely weathered soils. Minerals derived from the basin of Des Moines River of Iowa, which were incorporated in loess below its confluence with Mississippi River, are especially rich in Rb and gave rise to the highest levels observed (110–115 mg kg−1).

Soil development on recent end moraines of the Klutlan Glacier, Yukon Territory, Canada

Data on soils with six Neoglacial moraines of the Klutlan Glacier have been compared with those from moraines at the warm, moist coastal site of Glacier Bay, 160 km south. Percentage organic matter increases rapidly for the first 100 to 150 yr of soil development and then continues to rise gradually for the next 100 yr. Soil pH falls from 8.0 in recent till to approximately 6.0 in 200-yr-old soils. Nitrogen levels in the mineral soil increase from near zero in recent tills to 0.7% in soils 175–200 yr old; organic horizons of soils associated with spruce forests in later successional stages contain approximately 1% nitrogen. Concentrations of certain inorganic phosphate ions in the different-aged soils increase continually throughout the succession. Data for nine chemical variables were subjected to a principal components analysis; the major pattern in the data reflects the differences between soils of low organic content and high pH present in early successional stages, and nutrient-rich soils with high organic content and low pH present after succession has progressed toward the spruce forest. These trends in soil development with time are strikingly similar to those reported from Glacier Bay, except that the changes in soil properties appear to be delayed by 50–100 yr at the Klutlan terminus. Although numerous signs of nitrogen deficiency have been identified in plants growing on new soils at Glacier Bay, none was observed visually in living plants or in nutrients measured in samples of foliage from three plant taxa ( Epilobium latifolium, Salix spp., and Populus balsamifera) taken from the Klutlan moraines. Concentrations of nitrogen and other nutrients (Ca, Mg, K, total P) in the foliage samples show no clear trends with increasing soil development. Low temperatures, a short growing season, and very low mean annual precipitation probably limit plant growth and account for the delayed soil development on the Klutlan moraines.

CHANGES IN MOLECULAR WEIGHT DISTRIBUTION OF SOIL ORGANIC MATTER DURING SOIL DEVELOPMENT

SummaryTen different topsoils representing members of three soil chronosequences were pre‐treated with 0.1 M HC1 and extracted with neutral 0.1 M Na4P2O7 followed by 0.5 M NaOH. Extracts were purified and fractionated into five different nominal molecular weight fractions using gel filtration. With increasing soil development, the proportion of large molecules (&gt;200 000) in the organic matter decreased with an increase in the proportion of intermediate size molecules (200 000 – 10 000). This effect was more evident in the mild Na4P2O7 extracts than in the subsequent NaOH extracts, and in soils of the Manawatu chronosequence than in those of the other two chronosequences and are attributed to changes in the nature and humification of soil organic matter during soil development.