Impact of polychaetes (Nereis spp. and Arenicola marina) on carbon biogeochemistry in coastal marine sediments

Known effects of bioturbation by common polychaetes (Nereis spp. and Arenicola marina) in Northern European coastal waters on sediment carbon diagenesis is summarized and assessed. The physical impact of irrigation and reworking activity of the involved polychaete species is evaluated and related to their basic biology. Based on past and present experimental work, it is concluded that effects of bioturbation on carbon diagenesis from manipulated laboratory experiments cannot be directly extrapolated to in situ conditions. The 45–260% flux (e.g., CO₂ release) enhancement found in the laboratory is much higher than usually observed in the field (10–25%). Thus, the faunal induced enhancement of microbial carbon oxidation in natural sediments instead causes a reduction of the organic matter inventory rather than an increased release of CO₂ across the sediment/water interface. The relative decrease in organic inventory (G _b /G _u) is inversely related to the relative increase in microbial capacity for organic matter decay (k _b /k _u). The equilibrium is controlled by the balance between organic input (deposition of organic matter at the sediment surface) and the intensity of bioturbation. Introduction of oxygen to subsurface sediment and removal of metabolites are considered the two most important underlying mechanisms for the stimulation of carbon oxidation by burrowing fauna. Introduction of oxygen to deep sediment layers of low microbial activity, either by downward irrigation transport of overlying oxic water or by upward reworking transport of sediment to the oxic water column will increase carbon oxidation of anaerobically refractory organic matter. It appears that the irrigation effect is larger than and to a higher degree dependent on animal density than the reworking effect. Enhancement of anaerobic carbon oxidation by removal of metabolites (reduced diffusion scale) may cause a significant increase in total sediment metabolism. This is caused by three possible mechanisms: (i) combined mineralization and biological uptake; (ii) combined mineralization and abiogenic precipitation; and (iii) alleviation of metabolite inhibition. Finally, some suggestions for future work on bioturbation effects are presented, including: (i) experimental verification of metabolite inhibition in bioturbated sediments; (ii) mapping and quantification of the role of metals as electron acceptors in bioturbated sediments; and (iii) identification of microbial community composition by the use of new molecular biological techniques. These three topics are not intended to cover all unresolved aspects of bioturbation, but should rather be considered a list of obvious gaps in our knowledge and present new and appealing approaches.     

Influence of bare soil and cultivated land use types upstream of a bank gully on soil erosion rates and energy consumption for different gully erosion zones in the dry-hot valley region,Southwest China

This study assessed temporal variation in soil erosion rates in response to energy consumption of flow (ΔE). It employed an in situ bank gully field flume experiment with upstream catchment areas with bare (BLG) or cultivated land (CLG) that drained down to bare gully headcuts. Water discharge treatments ranged from 30 to 120 L Min⁻¹. Concentrated flow discharge clearly affected bank gully soil erosion rates. Excluding minimal discharge in the CLG upstream catchment area (30 L min⁻¹), a declining power function trend (p ≤ 0.1) was observed with time in soil erosion rates for both BLG and CLG upstream catchment areas and downstream gully beds. Non-steady state soil erosion rates were observed after an abrupt collapse along the headcut slope after prolonged scouring treatments. However, as the experiment progressed, ΔE and energy consumption of flow per unit soil loss (ΔEu) exhibited a logarithmic growth trend (p < 0.1) at each BLG and CLG position. Although similar temporal trends in soil erosion and infiltration rates were observed, values clearly differed between BLG and CLG upstream catchment areas. Furthermore, Darcy–Weisbach friction factor (f) values in the CLG upstream catchment area were higher than the corresponding BLG area. In contrast to the BLG upstream catchment area, lower ΔEu and higher soil erosion rates were observed in the CLG upstream catchment area as a result of soil disturbances. This indicated that intensive land use changes accelerate soil erosion rates in upstream catchment areas of bank gullies and increase soil sediment transport to downstream gullies. Accordingly, reducing tillage disturbances and increasing vegetation cover in upstream catchment areas of bank gullies are essential in the dry-hot valley region of Southwest China.

     

Downward migration of Chernobyl-derived radionuclides in soils in Poland and Sweden

Vertical profiles of ¹³⁷Cs and ^239,240Pu were measured in soils collected from two sites in southern Sweden and three sites in southern Poland and were modeled using both a solute transport model and a bioturbation model to better understand their downward migration. A time series of measured ¹³⁷Cs profiles indicates that ¹³⁷Cs from Chernobyl was found at the soil surface in 1986 but it has migrated progressively downward into the soil 4.5-25.5 cm since. However, because of dispersion during the migration and mixing following Chernobyl deposition and the much higher activities of ¹³⁷Cs from Chernobyl, stratospheric fallout of ¹³⁷Cs from the 1960s cannot be identified as a second ¹³⁷Cs activity maximum lower in the soil column at any of the sites. Conversely, the ²⁴⁰Pu/²³⁹Pu ratio indicates that no Chernobyl-derived Pu is present in any of the cores with the exception of one sample in Sweden. This difference may be attributed to the nature of the release from Chernobyl. Cesium volatilized at the reactor temperature during the accident, and was released as a vapor whereas Pu was not volatile and was only released in the form of minute fuel particles that traveled regionally. Both the solute diffusion and the bioturbation models accurately simulate the downward migration of the radionuclides at some sites but poorly describe the distributions at other sites. The distribution coefficients required by the solute transport model are about 100 times lower than reported values from the literature indicating that even though the solute transport model can simulate the profile shapes, transport as a solute is not the primary mechanism governing the downward migration of either Cs or Pu. The bioturbation model uses reported values from the literature of the distribution coefficients and can simulate the downward migration because that model buries the fallout by placing soil from depth on top and mixing it slightly throughout the mixing zone (0.6-2% per year of mixing). However, mixing in that model predicts concentrations in the top parts of the soil profiles which are too high in many cases. Future progress at understanding the downward migration of radionuclides and other tracers will require a more comprehensive approach, combining solute transport with bioturbation and including other important soil processes.     

Remote Sensing of Biologically Reworked Sediments: A Laboratory Experiment

The present study aims to test the application of remote sensing to address the impact of bioturbation on physical sediment properties. Therefore, a laboratory experiment was developed, using microcosms mimicking a marine intertidal water–sediment interface to test the influence of Corophium volutator densities on sediment properties. Three main variables (water content, clay content, and mean grain size) were measured in three treatments (no Corophium, 5,000 Corophium per square meter, and 20,000 Corophium per square meter) after 16 days of bioturbation. Results obtained with conventional—destructive—techniques showed a significant increase of water content and a significant, but small decrease of clay content in the presence of Corophium. The remote sensing technique detected the impact of Corophium on water content as an increase in absorption at 1,450 nm, but was not able to detect the animal impact on clay content. This study demonstrates that remote sensing data could be significantly modified by bioturbation activities and that remote sensing can be applied in the laboratory to address the impact of bioturbation on sediment properties. This possibly opens new perspectives for long-term experiments concerning the role of bioturbation on sedimentary processes.     

Quantitative evaluation of soil processes using in situ-produced cosmogenic nuclides

In situ-produced cosmogenic nuclides provide a means for quantitative evaluation of a wide range of weathering and sediment transport processes. Although these nuclides have received attention for their power as geochronometers of surface exposure, it may be argued that they are more broadly suited for study of surface processes. In many environments, they may be used to evaluate collapse, erosion, burial, bioturbation, and creep, as well as providing a qualitative basis for distinguishing allochthonous from autochthonous materials. In addition, these nuclides can provide quantitative information on rates of erosion on scales of landforms and drainage basins. Here, we review the systematics of cosmogenic nuclide production within the Earth's surface, and present field examples demonstrating the utilization of in situ-produced cosmogenic nuclides distributions for evaluation of a range of soil evolution processes. To cite this article: E.T. Brown et al., C. R. Geoscience 335 (2003).     

An analytical model for chemical diffusion in layered contaminated sediment systems with bioreactive caps

An analytical model for contaminant transport in multilayered capped contaminated sediments including the degradation of organic contaminant is presented. The effect of benthic boundary layer was treated as a Robin-type boundary condition. The results of the proposed analytical model agree well with experimental data. The biodegradation of contaminant in bioturbation layer shows a significant influence on the flux at the surface of system. The maximum flux for the case with t_1/2,bio = 0.07 year can be 4.5 times less than that of the case without considering the effect of biodegradation. The thickness of bioturbation layer has a significant effect on the performance of the capped contaminated sediment. The maximum flux for the case with l_bio = 15 cm can be 17 times larger than that of the case without bioturbation layer. This may be because the effective diffusion coefficient of sand cap can be 28 times lower than D_bio. The mass transfer coefficient should be considered for the design of the capping system as the contaminant concentration at the top of system for the case with k_bl = 2.5 × 10⁻⁵ cm/s can be 13 times greater than that of the case with k_bl = 10⁻⁴ cm/s. The proposed analytical model can be used for verification of complicated numerical methods, evaluation of experimental data, and design of the capping contaminated sediment systems with reactive cap layers.     

The ichnology of carbonate drifts

Carbonate drifts have so far not been as intensely investigated as their siliciclastic equivalents, especially from an ichnological perspective. The aim of this work is therefore to provide an overview of the different bioturbation styles in carbonate drifts for ichnologists and sedimentologists working in such deposits. Different types of carbonate drifts from the Maldives were studied to address this objective. The cores recovered during International Ocean Discovery Program Expedition 359 were examined to provide the sedimentological and ichnological data for a detailed analysis of the ichnology of carbonate drifts. The ichnological characteristics of the Maldives drifts are compared to other carbonate drifts in order to discuss similarities and differences, and thus provide an overview of the general characteristics of carbonate drift ichnology. These drifts are located in the Santaren Channel which lines Great Bahama Bank, along the Marion Plateau in Australia, in the Limassol and Larnaca basins in Cyprus and in the Danish Basin in Denmark. The common characteristics of bioturbation in carbonate drifts are: (i) the complete bioturbation of the sediment with bioturbation indexes between four and six; (ii) the occurrence of distinctive trace fossils limited to facies contacts or condensed intervals; (iii) a typical ichnoassemblage consisting of Thalassinoides, Scolicia, Planolites, Zoophycos, Chondrites, Phycosiphon and Palaeophycus; (iv) the contiguous occurrence of ichnogenera from different tiers, with only Zoophycos and Chondrites as deep tiers; and (v) distinct infills of the traces including particulate organic matter, pyrite, silica and celestine. In addition, the main ichnofacies of carbonate drifts is the Zoophycos ichnofacies. Ichnofabrics grade from coarse‐grained and completely bioturbated to ichnofabrics with present to rare trace fossils and preserved sedimentary structures. The type and intensity of the bioturbation is controlled by the amount of organic matter and the oxygenation at the sea floor that is determined by the action of bottom currents and the sea‐level fluctuations affecting the carbonate factory in carbonate platforms bordering the basins where the carbonate drifts form. The study of the bioturbation in core and outcrop provides palaeoenvironmental information about carbonate‐drift deposits that complement the classical sedimentological data.     

The relative mobility of natural (Th,Pb and Po) and fallout (Pu,Am, Cs) radionuclides in the coastal marine environment: results from model ecosystems (MERL) and Narragansett Bay

The relative mobility of nuclides of Pb, Th, Pu, and Cs, which are widely used as geochemical tracers for sedimentation and bioturbation. was investigated in artificial microcosm tanks (MERL) and in Narragansett Bay. Their mobility was characterized by their removal rates from the water column, their affinity toward particles and their degree of penetration into the surface sediments. Pb, Th, and Pu transport was controlled predominantly by the affinity of these elements to particles, and the transport parameters of the particles themselves (i.e. sediment resuspension and mixing rates). Because of its low distribution coefficient, transport of Cs was controlled by molecular diffusion through pore water in the winter, while in summer, Cs transport was enhanced due to bioturbation. The increase with depth of the $\text{Cs}\text{Pu}$ ratio in core profiles of MERL and Narragansett Bay sediments is thus caused primarily by the higher mobility of Cs.     

Tracing mechanisms controlling the release of dissolved silicon in forest soil solutions using Si isotopes and Ge/Si ratios

The terrestrial biogenic Si (BSi) pool in the soil-plant system is ubiquitous and substantial, likely impacting the land-ocean transfer of dissolved Si (DSi). Here, we consider the mechanisms controlling DSi in forest soil in a temperate granitic ecosystem that would differ from previous works mostly focused on tropical environments. This study aims at tracing the source of DSi in forest floor leachates and in soil solutions under various tree species at homogeneous soil and climate conditions, using stable Si isotopes and Ge/Si ratios. Relative to granitic bedrock, clays minerals were enriched in ²⁸Si and had high Ge/Si ratios, while BSi from phytoliths was also enriched in ²⁸Si, but had a low Ge/Si ratio. Such a contrast is useful to infer the relative contribution of silicate weathering and BSi dissolution in the shallow soil on the release of DSi in forest floor leachate solutions. The δ³⁰Si values in forest floor leachates (−1.38‰ to −2.05‰) are the lightest ever found in natural waters, and Ge/Si ratios are higher in forest floor leachates relative to soil solution. These results suggest dissolution of ²⁸Si and Ge-enriched secondary clay minerals incorporated by bioturbation in organic-rich horizons in combination with an isotopic fractionation releasing preferentially light Si isotopes during this dissolution process. Ge/Si ratios in soil solutions are governed by incongruent weathering of primary minerals and neoformation of secondary clays minerals. Tree species influence Si-isotopic compositions and Ge/Si ratios in forest floor leachates through differing incorporation of minerals in organic horizons by bioturbation and, to a lesser extent, through differing Si recycling.     

Determination of diffusion coefficients associated with the transport of210Pb radionuclides in lake bed sediments

An iterative least-squares optimization technique is utilized in conjunction with a one-dimensional representation of the mass transport equation to generate theoretical²¹⁰Pb concentration/depth profiles beneath the water-sediment interface that are best-fit approximations to directly measured²¹⁰Pb concentration/depth profiles at various locations within the Great Lakes system. The outputs of such an optimization analysis are the diffusion coefficientsD _M (molecular) andD _B (bioturbation) associated with the transport of²¹⁰Pb radionuclides in lake bed sediments. For all stations studied, the estimated values ofD _B are consistently larger than the estimated values ofD _M , emphasizing the importance of accounting for the effects of bioturbation in the modelling of contaminant transport through lake bed sediments.     

Quaternary corals from reefs in the Wakatobi Marine National Park,SE Sulawesi,Indonesia, show similar growth rates to modern corals from the same area

We have used digital photography, image analysis and measurements in the field to determine the growth rates of Quaternary corals in the Wakatobi Marine National Park, Indonesia, and compared them to growth rates of similar corals in the same area. In the Quaternary deposits it was possible to measure the growth rates of two massive coral genera Porites and Favites. For each genus, the corals reworked from better‐illuminated upslope environments had higher growth rates than the in situ fossil corals. The calculated radial growth rates for the in situ Porites are slightly lower than, but of the same order of magnitude as, the modern Porites growing in 10 m water depth at Hoga (10.04 ± 3.34 mm yr^?1 ± 1 s.d.; n = 3) and Kaledupa (15.26 ± 4.83 mm yr^?1 ± 1 s.d.; n = 3). Sedimentation rates and underwater visibility are inferred to have been similar in the fossil site to that at the modern Kaledupa site. Decreasing light penetration due to increased water depth is inferred to have been a major influence on growth rates. The in situ massive corals with good growth banding are inferred to have grown in a comparable environment to modern Kaledupa and Hoga. The study highlights that it is possible to compare coral growth rates, and their influencing parameters, from modern and well‐preserved ancient examples. Copyright © 2006 John Wiley & Sons, Ltd.     

Elemental and mineralogical changes in soils due to bioturbation along an earthworm invasion chronosequence in Northern Minnesota

Minnesota forested soils have evolved without the presence of earthworms since the last glacial retreat. When exotic earthworms arrive, enhanced soil bioturbation often results in dramatic morphological and chemical changes in soils with negative implications for the forests’ sustainability. However, the impacts of earthworm invasion on geochemical processes in soils are not well understood. This study attempts to quantify the role of earthworm invasion in mineral chemical weathering and nutrient dynamics along an earthworm invasion chronosequence in a sugar maple forest in Northern Minnesota. Depth and rates of soil mixing can be tracked with atmospherically derived short lived radioisotopes ²¹⁰Pb and ¹³⁷Cs. Their radioactivities increase in the lower A horizon at the expense of the peak activities near the soil surface, which indicate that soil mixing rate and its depth reach have been enhanced by earthworms. Enhanced soil mixing by earthworms is consistent with the ways that the vertical profiles of elemental and mineralogical compositions were affected by earthworm invasion. Biologically cycled Ca and P have peak concentrations near the soil surface prior to earthworm invasion. However, these peak abundances significantly declined in the earthworm invaded soils presumably due to enhanced soil mixing. It is clear that enhanced soil mixing due to earthworms also profoundly altered the vertical distribution of most mineral species within A horizons. Though the mechanisms are not clear yet, earthworm invasion appears to have contributed to net losses of clay mineral species and opal from the A horizons. As much as earthworms vertically relocated minerals and elements, they also intensify the contacts between organic matter and cations as shown in the increased amount of Ca and Fe in organically complexed and in exchangeable pools. With future studies on soil mixing rates and elemental leaching, this study will quantitatively and mechanically address the role of earthworms in geochemical evolution of soils and forests’ nutrient dynamics.     

The variation of soil temperature and water content of seasonal frozen soil with different vegetation coverage in the headwater region of the Yellow River, China

The variation and distribution of temperature and water moisture in the seasonal frozen soil is an important factor in the study of both the soil water cycle and heat balance within the source region of the Yellow River, especially under the different conditions of vegetation coverage. In this study, the impact of various degrees of vegetation coverage on soil water content and temperature was assessed. Soil moisture (θ _v) and soil temperature (T _s) were monitored on a daily basis. Measurements were made under different vegetation coverage (95, 70–80, 40–50 and 10%) and on both thawed and frozen soils. Contour charts of T _s and θ _v as well as a θ _v–T _s coupling model were developed in order to account for the influence of vegetation cover and the interaction between T _s and θ _v. It was observed that soil water content affected both the overall range and trend in the soil temperature. The regression analysis of θ _v versus T _s plots indicated that the soil freezing and thawing processes were significantly affected by vegetation cover changes. Vegetation coverage changes also caused variations in the θ _v–T _s interaction. The effect of soil water content on soil temperature during the freezing period was larger than during the thawing period. Moreover, the soil with higher vegetation coverage retained more water than that with lower coverage. In the process of freezing, the higher vegetation coverage reduced the rate of the reduction in the soil temperature because the thermal capacity of water is higher than that of soil. Areas with higher vegetation coverage also functioned better for the purpose of heat-insulating. This phenomenon may thus play an important role in the environmental protection and effective uses of frozen soil.     

Uptake and fixation of Zn, Pb, and Cd by Thlaspi caerulescens: application in the cases of old mines of Mibladen and Zaida (West of Morocco)

Contaminated soils and mine tailings pose major environmental and agricultural problems worldwide. These problems may be partially solved by an emerging new technology: phytoremediation. This technique uses plants to extract soil contaminants from the ground. Thlaspi caerulescens is known to accumulate in their tissues several heavy metals from soil and aerial deposition. This study was conducted to screen plants growing on a contaminated site to determine their potential for metal accumulation. Seeds of T. caerulescens metallicolous have been collected in the vicinity of F.T. Laurent le Minier in the Pb–Zn mining district of les Malines (North of Montpellier, Southern France), and seeds of T. caerulescens non-metallicolous were sampled on Larzac Plateau (North of Montpellier, Southern France). Soil substrates were collected from a mine site of Mibladen and Zaida (West, Morroco). Cultivated plant and surface soil samples were analyzed for zinc, lead, and cadmium concentrations by inductively coupled plasma mass spectrometry. A non-metallicolous (NM) ecotype of T. caerulescens and a metallicolous (M) ecotype are compared for Pb, Cd, and Zn accumulation in shoot and root in five metal-contaminated soils and one uncontaminated soil. The growth of individuals from uncontaminated soil was greater than that of individuals from metal-contaminated soils. The NM populations had markedly higher root/shoot ratio compared to M populations. The results indicate that both ecotypes of T. caerulescens are highly tolerant of zinc and Cd. Ecotype NM had constitutively higher Zn uptake capacity than the M ecotype. T. caerulescens species accumulate higher amount of Zn and Cd in their tissues in polluted soil and, in both of the two ecotypes, the root Pb concentrations were much greater than those of the shoot Pb contents. From both uncontaminated and metal-contaminated soils, we conclude that T. caerulescens are interesting material for phytoremediation of zinc and cadmium.     

Ichnofabric characterization of a deep‐marine clastic system: a subsurface study of the Middle Eocene Ainsa System,Spanish Pyrenees

This paper documents a subsurface trace fossil and ichnofabric study of the proximal parts of a structurally confined and channelized sand‐rich, lower slope and proximal basin‐floor deep‐marine system in the Middle Eocene Ainsa basin, Spanish Pyrenees. Five depositional environments are recognized based on sedimentary facies associations, depositional architecture and stratigraphic context (channel axis, channel off‐axis, channel margin, leveé‐overbank and interfan), as well as a channel abandonment phase. Each environment is characterized by distinct and recurring ichnofabrics. Ichnological measurements and observations were recorded from six cores recovered from six wells drilled at a spacing of between 400 m and 500 m at outcrop, and totalling 1213 m in length. From channel axis to levée‐overbank environments, there is a trend of increasing bioturbation intensity and ichnodiversity. Ichnofabrics in channel axis and channel off‐axis environments are characterized by low bioturbation intensity and low ichnodiversity. Thalassinoides‐dominated firmground ichnofabrics associated with erosive sediment gravity flows are common in these environments. In contrast, channel margin and levée‐overbank environments are characterized by ichnofabrics associated with high bioturbation intensity and ichnodiversity. Sediments of the interfan are characterized by the highest bioturbation intensity, associated with burrow mottling and an absence of primary sedimentary structures. This paper demonstrates that in core‐based studies, ichnofabric analysis is an important and valuable tool in discriminating between different environments in channelized deep‐marine siliciclastic systems. The results of this study should find wide applicability in reservoir characterization studies in the petroleum industry, in field‐based analogue ichnofabric studies and other core‐based studies in deep‐water siliciclastic systems worldwide such as the Integrated Ocean Drilling Program.     

Pesticides and lipids occurrence in Tangier agricultural soil (northern Morocco)

This study evaluates pesticide occurrence in Tangier agricultural soil (northern Morocco). Soil samples were measured for alpha endosulfan, beta endosulfan, endosulfan sulfate, alpha HCH, beta HCH, gamma HCH, aldrin, dieldrin, endrin, o,p′ DDT, p,p′ DDD, p,p′ DDE and p,p′ DDT. The analyses were performed by gas chromatography coupled with mass spectrometry (GC/MS). Endosulfan isomers (alpha and beta) and endosulfan sulfate were detected in soil samples, in which the beta isomer showed the highest concentrations. Some DDT metabolites (o,p′ DDT and p,p′ DDE) and alpha HCH were also detected in the analyzed soil. The lipid fraction of the soil samples was extracted by accelerated solvent extraction and fractionated using chromatographic techniques. The principal biomarkers obtained were alcohols, esters, ketones, aldehydes, fatty acids and hydrocarbons. Lipid biomarkers were characterized to determine soil organic matter sources. Experimental results showed that the organic matter was mainly of plant origin, although the bacterial contribution was significant.     

Patterns of mangrove forest structure and soil nutrient dynamics along the Shark River estuary, Florida

The basal area and productivity of managrove wetlands are described in relation to selected soil properties to understand the general pattern of optimum forest stature at the mouth of estuaries in the Everglades, such as the Shark River Slough, Florida (U.S.). The basal area of mangroves decreases from 40.4 m² ha⁻¹ and 39.7 m² ha⁻¹ at two stations 1.8 km and 4.1 km from the estuary mouth to 20.7 m² ha⁻¹ and 19.6 m² ha⁻¹ at two sites 9.9 km and 18.2 km from the mouth, respectively. The gradient in basal area at these four sites is mostly the result of approximately 34 yr of growth since Hurricane Donna. Wood productivity is higher in the lower estuary (10.7 Mg ha⁻¹ yr⁻¹ and 12.0 Mg ha⁻¹ yr⁻¹) than in the upper estuary (3.2 Mg ha⁻¹ yr⁻¹ and 4.2 Mg ha⁻¹ yr⁻¹). Porewater salinity among these four mangrove sites during seasonal sampling in 1994 and 1995 ranged from 1.6 g kg⁻¹ to 33.5 g kg⁻¹, while sulfide was generally<0.15 mM at all sites. These soil values indicate that abiotic stress cannot explain the decrease in forest structure along this estuarine gradient. Concentrations of nitrogen (N) and phosphorus (P) are more closely related to patterns of forest development, with higher soil fertility at the mouth of the estuary as indicated by higher concentrations of extractable ammonium, total soil P, and available P, along with higher ammonium production rates. The more fertile sites of the lower estuary are dominated by Laguncularia racemosa, whereas the less fertile sites in the intermediate and upper estuary are dominated by Rhizophora mangle. Relative N mineralization per unit of total N is higher in the lower estuary and is related positively to concentrations of available P, indicating the importance of turnover rates and nutrient interactions to soil fertility. Concentrations of Ca-bound P per volume soil in the lower estuary is 40-fold higher than in the upper estuary, and along with an increase in residual P in the upper estuary, indicate a shift from mineral to organic P along the estuarine gradient. Mineral inputs to the mouth of Shark River estuary from the Gulf of Mexico (rather than upland inputs) apparently control the patterns of mangrove structure and productivity.     

Tolerable versus actual soil erosion rates in Europe

Erosion is a major threat to soil resources in Europe, and may impair their ability to deliver a range of ecosystem goods and services. This is reflected by the European Commission's Thematic Strategy for Soil Protection, which recommends an indicator-based approach for monitoring soil erosion. Defined baseline and threshold values are essential for the evaluation of soil monitoring data. Therefore, accurate spatial data on both soil loss and soil genesis are required, especially in the light of predicted changes in climate patterns, notably frequency, seasonal distribution and intensity of precipitation. Rates of soil loss are reported that have been measured, modelled or inferred for most types of soil erosion in a variety of landscapes, by studies across the spectrum of the Earth sciences. Natural rates of soil formation can be used as a basis for setting tolerable soil erosion rates, with soil formation consisting of mineral weathering as well as dust deposition. This paper reviews the concept of tolerable soil erosion and summarises current knowledge on rates of soil formation, which are then compared to rates of soil erosion by known erosion types, for assessment of soil erosion monitoring at the European scale.A modified definition of tolerable soil erosion is proposed as ‘any actual soil erosion rate at which a deterioration or loss of one or more soil functions does not occur,’ actual soil erosion being ‘the total amount of soil lost by all recognised erosion types.’ Even when including dust deposition in soil formation rates, the upper limit of tolerable soil erosion, as equal to soil formation, is ca. 1.4 t ha^− 1 yr^− 1 while the lower limit is ca. 0.3 t ha^− 1 yr^− 1, for conditions prevalent in Europe. Scope for spatio-temporal differentiation of tolerable soil erosion rates below this upper limit is suggested by considering (components of) relevant soil functions. Reported rates of actual soil erosion vary much more than those for soil formation. Actual soil erosion rates for tilled, arable land in Europe are, on average, 3 to 40 times greater than the upper limit of tolerable soil erosion, accepting substantial spatio-temporal variation. This paper comprehensively reviews tolerable and actual soil erosion in Europe and highlights the scientific areas where more research is needed for successful implementation of an effective European soil monitoring system.     

Impacts of zerovalent iron application on the adsorption behavior of alachlor and metalaxyl in water and soil systems

Alachlor and metalaxyl contaminations of environmental and agricultural water and soil systems cause potential threats to human health. However, information on the pesticide adsorption quantity–intensity (Q/I) relationships in water and soil systems is limited. Therefore, adsorption behavior and the fate of alachlor and metalaxyl in the systems as influenced by the application of zerovalent iron (ZVI, Fe⁰) were investigated using the pesticide adsorption Q/I relationships. After treating ZVI in the systems, the concentration of alachlor rapidly decreased within a few days and then it disappeared at approximately 5–7 experiment days; whereas metalaxyl concentration was reduced by approximately 40–45% during the 28 day experimental period. In particular, ZVI adsorbed more metalaxyl in the aqueous system than in the soil-solution system. The alachlor concentration in the water and soil solution drastically decreased with increasing ZVI treatment, while metalaxyl concentration was relatively slow in its decrease. Adsorption mechanism of the pesticides in the soil-solution system was shown as multiple-site adsorption Q/I fitting. Buffering capacity (BC) of the pesticides increased with ZVI treatment in all sorption sites. The BC values in sandy soil were escalated with increasing ZVI application rates, so that the values were rather higher in sandy soil than in clayey soil. In addition, changes in alachlor concentration with applying ZVI were due to both dechlorination and adsorption; whereas metalaxyl concentration was dependent upon adsorption reaction. Thus, the pesticide adsorption Q/I relationships in different soil-solution systems were critically affected by the ZVI treatment.     

The Lower Permian Wasp Head Formation,Sydney Basin: high‐latitude,shallow marine sedimentation following the late Asselian to early Sakmarian glacial event in eastern Australia

The Lower Permian Wasp Head Formation (early to middle Sakmarian) is a ～95 m thick unit that was deposited during the transition to a non‐glacial period following the late Asselian to early Sakmarian glacial event in eastern Australia. This shallow marine, sandstone‐dominated unit can be subdivided into six facies associations. (i) The marine sediment gravity flow facies association consists of breccias and conglomerates deposited in upper shoreface water depths. (ii) Upper shoreface deposits consist of cross‐stratified, conglomeratic sandstones with an impoverished expression of the Skolithos Ichnofacies. (iii) Middle shoreface deposits consist of hummocky cross‐stratified sandstones with a trace fossil assemblage that represents the Skolithos Ichnofacies. (iv) Lower shoreface deposits are similar to middle shoreface deposits, but contain more pervasive bioturbation and a distal expression of the Skolithos Ichnofacies to a proximal expression of the Cruziana Ichnofacies. (v) Delta‐influenced, lower shoreface‐offshore transition deposits are distinguished by sparsely bioturbated carbonaceous mudstone drapes within a variety of shoreface and offshore deposits. Trace fossil assemblages represent distal expressions of the Skolithos Ichnofacies to stressed, proximal expressions of the Cruziana Ichnofacies. Impoverished trace fossil assemblages record variable and episodic environmental stresses possibly caused by fluctuations in sedimentation rates, substrate consistencies, salinity, oxygen levels, turbidity and other physio‐chemical stresses characteristic of deltaic conditions. (vi) The offshore transition‐offshore facies association consists of mudstone and admixed sandstone and mudstone with pervasive bioturbation and an archetypal to distal expression of the Cruziana Ichnofacies. The lowermost ～50 m of the formation consists of a single deepening upward cycle formed as the basin transitioned from glacioisostatic rebound following the Asselian to early Sakmarian glacial to a regime dominated by regional extensional subsidence without significant glacial influence. The upper ～45 m of the formation can be subdivided into three shallowing upward cycles (parasequences) that formed in the aftermath of rapid, possibly glacioeustatic, rises in relative sea‐level or due to autocyclic progradation patterns. The shift to a parasequence‐dominated architecture and progressive decrease in ice‐rafted debris upwards through the succession records the release from glacioisostatic rebound and amelioration of climate that accompanied the transition to broadly non‐glacial conditions.