Redistribution Of Organic Matter Research Articles

Impact of Chondrites on trace metal distribution in the sapropel S7 (ODP Site 966): Implications for paleoenvironmental and paleoceanographic reconstructions

Organic-rich deposits are valuable paleo-archives, recording significant paleoceanographic changes linked to past climate variations and marine deoxygenation events. The deposition of organic-rich sediments stops when bottom-water reventilation/oxygenation occurs. This impedes organic matter preservation, enabling macro and micro burrowing-organisms to recover and bioturbate the seafloor. In this sense, highly bioturbated sediments require particular attention when sampling is done for geochemical analyses, as sediments can be considerably mixed. While avoiding trace fossils during sampling for geochemical analyses is easy for large traces (e.g. Planolites, Thallasinoides, and Zoophycos), it becomes challenging for smaller and complex traces (< 0.5 cm), as is the case with Chondrites. Chondrites-producers have an opportunistic behavior, being one of the first organisms to colonize the seafloor after an anoxic event. As a result, Chondrites are commonly and sometimes abundantly found in the upper layers of organic-rich sediments, including sapropels and black shales.This study focuses on sapropel S7, which was deposited between ∼198.5 and 191.9 ka at the top of Eratosthenes Seamount and exhibits abundant Chondrites. For this sapropel, we demonstrated that Chondrites-producers can bioturbate significant volumes of organic-rich sediments (over 35%), introducing oxic/dysoxic material downward into anoxic sediments enriched in redox-sensitive trace metals and organic matter. This process can dilute up to 18% the original concentration of redox-sensitive trace metals (e.g. Mo, U and V). This dilution is especially important to consider when calculating trace metals and organic matter burial flux from bulk sediment data. Therefore, Chondrites-producers can play a crucial role in altering the sediment texture and distribution of minerals and organic matter at sub-cm scale, and may thus impact paleoenvironmental and paleoceanographic reconstructions based on geochemical signals. Furthermore, the subsequent redistribution of organic matter and redox-sensitive trace metals (including oligoelements) within the sediment can affect carbon and nutrient cycling, microbial activity, organic matter degradation in deep-marine sediments, and the overall sedimentary biogeochemistry.

Stylolitization structures as possible migration routes of organic matter in microbial genesis sedimentary deposites

It was studied that the possibilities of preservation, migration and transformation of organic matter (OM) in rocks of Precambrian age, the textural and structural characteristics of which are inextricably linked with the physiological characteristics of microorganisms, and the role of stylolithization structures in these processes. The similarity of modern stromatolites with ancient ones in the mechanism of deposition of carbonate micrite and the formation of porous frameworks allowed us to establish that a significant amount OM of cyanobacterial lamins could be preserved after the buildings were immersed in the sedimentation basin and transformed into sedimentary strata. OM was concentrated on numerous relict surfaces between micrite carbonate secretions deposited by microorganisms during life. Subsequent transformations were expressed in the recrystallization of the carbonate substance, accompanied by a significant loss of primary voidness, oustion and redistribution of OM, as well as clay material deposited from the suspension. During detailed petrographic studies, it was observed how clay-organic material (COM), displaced by recrystallization, concentrated on the crystal faces and in intercrystalline pores in certain areas and composed numerous lenticular layers in contact with each other, forming surfaces of complex configurations - rudimentary microstylolites. According to the authors, recrystallization is one of the main catalysts of stillolithization processes, because it creates mineral aggregates in which the pressure on the COM enclosed between them varies greatly at different points. This contributes to the occurrence of the phenomenon of differentiated dissolution under pressure, more intensive transformation of OM in areas with maximum load and, as a consequence, excessive release of CO, which in turn leads to saturation of pore solutions with carbon dioxide and initiation of chemical dissolution. Probably, this is how stylolites and associated fractured voidness are formed in stromatolites, which is available for the migration of OM.

Top-down controls on nutrient cycling and population dynamics in a model estuarine photoautotroph-heterotroph co-culture system.

Viral lysis and protistan grazing are thought to be the major processes leading to microbial mortality in aquatic environments and thus regulate community diversity and biogeochemical cycling characteristics. Here, we studied nutrient cycling and bacterial responses to cyanophage-mediated photoautotroph lysis and ciliate predation in a model Synechococcus-heterotroph co-culture system. Both viral lysis and Euplotes grazing facilitated the transformation of organic carbon from biomass to dissolved organic matter with convention efficiencies of 20%-26%. The accumulation of ammonium after the addition of phages and ciliates suggested the importance of recycled NH4+ occurred in the interactions between Synechococcus growth and heterotrophic bacterial metabolism of photosynthate. The slower efficiency of P mineralization compared to N (primarily ammonium) indicated that P-containing organic matter was primarily integrated into bacterial biomass rather than being remineralized into inorganic phosphate under C-rich conditions. In the cyanophage addition treatment, both Fluviicola and Alteromonas exhibited rapid positive responses to Synechococcus lysing, while Marivita exhibited an apparent negative response. Further, the addition of Euplotes altered the incubation system from a Synechococcus-driven phycosphere to a ciliate-remodelled zoosphere that primarily constituted grazing-resistant bacteria and Euplotes symbionts. Top-down controls increased co-culture system diversity and resulted in a preference for free-living lifestyles of dominant populations, which was accompanied by the transfer of matter and energy. Our results indicate top-down control was particularly important for organic matter redistribution and inorganic nutrient regeneration between photoautotrophs and heterotrophs, and altered bacterial lifestyles. This study consequently sheds light on marine biogeochemical cycling and the interaction networks within these dynamic ecosystems.

Long-term response of tropical Andisol properties to conversion from rainforest to agriculture

Short-term changes in tropical rainforest soil properties and their impact on C cycling following land-use conversion to agriculture have received intensive study. However, long-term, land-use changes have not been explored for tropical Andisols, whose high carbon stocks and several distinctive properties may differ in their response to land-use conversion. Thus, the primary objective of this study was to assess changes in selected soil properties of Andisols in response to long-term (>100 years) changes of land use from tropical rainforests to agriculture. Soils were sampled by horizon to a depth of 110–140 cm in pine forests (PF), tea plantation (TP) and horticultural crops with either intensive cultivation (IH) or bare fallow (FH) cropping systems. Selected physical, chemical and biological soil properties were characterized, including microbial biomass carbon (MBC) and laboratory CO2 mineralization rates. Results showed that land-use change from rainforest to agriculture resulted in increased soil bulk density and meso/micropores that contributed to increased plant-available water retention capacity. Soil carbon and nitrogen stocks in the upper 1 m of soil were higher in agricultural soils (25–29 kg C m−2; 1.7 – 2.3 kg N m−2) than pine forest soil (17 kg C m−2; 1 kg N m−2) with a redistribution of organic matter from topsoil to subsoil horizons. Organic matter quality was also affected by land-use conversion with the horticultural soils having lower rates of carbon mineralization per unit soil carbon (PF > TP > IH > FH) and lower microbial biomass, especially in topsoil horizons. The MBC sharply decreased in the topsoil horizon due to land-use change from forest (330 mg kg−1) to agricultural production (<118 mg kg−1). The intensive horticultural soil receiving recent additions of horse manure had higher extractable mineral N (especially NO3), reduced P fixation, increased available P, higher pH, and higher concentrations of exchangeable base cations (Ca2+, Mg2+ and K+) and micronutrients (Zn, Mn and Cu). The Andisols in this study demonstrated strong resilience to long-term degradation of soil properties following conversion from rainforest to agronomic land use. Further, this study demonstrates the ability of these Andisols to sequester additional C upon conversion to selected agriculture practices, thereby providing a positive impact on C mitigation.

Ефективність агроекологічних заходів у сівозмінах на зрошуваних землях півдня України

Ефективність агроекологічних заходів у сівозмінах на зрошуваних землях півдня України

Exotic earthworm community composition interacts with soil texture to affect redistribution and retention of litter-derived C and N in northern temperate forest soils

Exotic earthworm impacts on temperate forest soils are influenced by earthworm community composition and are likely constrained by the degree of organic matter redistribution following earthworm introductions across different soil types; however, the relative importance of these factors remains unknown. We examined how exotic earthworm communities affected leaf litter carbon (C) and nitrogen (N) mineralization and transport in two Spodosols with contrasting textures and organic matter contents. In reconstructed soil mesocosms, we measured organic C pools, quantified 13C and 15N transport from isotopically labeled red maple (Acer rubrum) leaf litter, and linked leaf litter redistribution to sub-surface burrow system structures following 150-day incubations. Transport of C and N from surface litter into soil was greatest with multi-species earthworm communities, and A-horizon and burrow pools functioned as dominant sinks for this material. Litter-derived C:N recovery ratios of soil pools revealed higher retention of litter-derived N over litter-derived C; recovery of litter N (mg 15N m−2) transported from surface litter was greater in the sandy loam (98.2 ± 2.73 %) than in the sandy soil (66.2 ± 4.92 %) following earthworm community additions. Earthworm biomass was as a minor sink for litter C (mg 13C m−2) and N transported from surface litter (0.56 ± 0.13 and 2.26 ± 0.31 %, respectively). Recovery of litter-derived C and N in earthworm biomass increased with the degree of direct leaf litter consumption (A. trapezoides < E. fetida < L. terrestris). Surface-dwelling epigeic and mineral-soil dwelling endogeic species produced burrow systems with the highest volume, surface connectivity, and density in the A-horizon; these properties were associated with greater CO2 losses and with greater litter C and N transport into A-horizons and burrows. Burrow systems with high continuity and large burrows produced by vertical-burrowing anecic species were associated with greater litter C and N transport into B-horizons, and greater dissolved organic C leaching losses. This study shows that the degree of organic matter redistribution in temperate forest soils following earthworm introductions is directly related to earthworm community composition, while the preferential retention of N over C and the potential stabilization of this material is determined by soil type.

Impact of storm-induced remobilization on grain size distribution and organic carbon content in sediments from the Blanes Canyon area, NW Mediterranean Sea

Interactions between organic carbon and mineral particles are known to play a key role for the preservation of organic carbon in marine sediments. In this study we combine meteorological, hydrological and oceanographic information with grain size and geochemical analyses (organic carbon, OC, its stable isotope δ13C, and the nitrogen to OC ratio) in different grain size fractions of surface sediments to determine the impact of a major storm on organic matter redistribution in a deep continental margin of the NW Mediterranean Sea. Sediment cores were obtained from the continental shelf, along the axis of the Blanes submarine canyon (BC), and in the adjacent southern open slope before (November 2008) and after (February and May 2009) the occurrence of one of the most severe coastal storms recorded in the last century in the study area.The storm occurred the 26 of December 2008 and dramatically impacted the North Catalan coast and its offshore area. The high shear stress produced by this event on the shelf floor led to sediment erosion and, subsequently, to its transport and deposition into BC. While sand and gravel-sized particles up to 2500μm in diameter were deposited at 300m of water depth in the canyon head, the finer particles (<4μm) were transported farther offshore towards the deep margin reaching at least 1500m depth.The results obtained show that the hydrodynamic processes that controlled the sorting and differential deposition of particles according to their grain size also controlled the redistribution of particles with different loads of OC. Thus, whereas coarse particles transported to the canyon head were poorly loaded with OC, fine particles reaching greater depths were relatively rich in OC, a significant proportion of which was of marine origin (i.e. derived from marine primary production). This adds to evidence that the physical action of waves and currents during storms plays a key role in determining the amount of OC stored in surface sediments not only in the shelf but also in the deep margin and possibly deeper.

Characteristics of soil organic carbon and nitrogen distributed in different density fractions of mollisols under long-term continuous cropping and natural restoration

本文以海伦农田生态系统国家野外科学观测站长期定位试验的黑土为研究对象, 通过对不同作物连作(玉米、大豆、小麦)和自然恢复(草地、裸地)下土壤及其密度分组中有机碳、氮含量的测定, 比较分析了土壤总有机碳、全氮以及密度组分碳、氮分布的变化特征。结果表明不同作物连作下土壤总有机碳的含量差异不显著。0~10 cm和10~20 cm土层农田土壤游离态轻组有机碳含量具有显著差异(<i>P</i><0.05)。大豆连作的农田土壤游离态轻组有机碳主要分布在0~10 cm土层, 而小麦连作的土壤游离态轻组有机碳主要分布在10~20 cm土层。不同作物连作下土壤闭蓄态轻组有机碳含量差异不显著。不同组分中氮素具有与碳相似的分布特征。游离态轻组与闭蓄态轻组C/N比值之间呈显著负相关(<i>P</i><0.05)。草地与农田、裸地相比显著提高了土壤总有机碳和全氮的含量。草地土壤游离态轻组、闭蓄态轻组和重组有机碳含量显著高于农田和裸地。作物连作和自然恢复导致土壤碳、氮的重新分配, 改变了土壤碳、氮的赋存特征。

Density effects on the clearance rate of the zebra mussel Dreissena polymorpha: flume study results

Zebra mussel filtration rates and regulating factors have been addressed earlier in a number of studies. Still, only a few of them have taken into consideration the refiltration phenomenon, and therefore the direct extrapolation of experimental results may only give the potential filtering capacity, and hence, over- or underestimate the actual amount of seston being removed by zebra mussels in an ecosystem. The current experimental study aimed to gain insight into the refiltration effect on the clearance rate of the zebra mussels at relatively high seston concentrations, and its potential role in controlling the filtration efficiency of the zebra mussel population. The experiment was conducted in a laboratory flume following the Latin squares design with one fixed (mussel density) and three random factors (initial total particulate matter (TPM) concentration, flume “wall effect” and distance from the flume inflow area) considered. The results showed the significant effects of mussel density and the TPM concentration on the effective clearance rate (ECR) of zebra mussels. The higher ECR values were obtained at denser mussel clumps and lower TPM concentrations. The flume “wall effect” had no significant effect on the ECR, whereas the distance from the flume inflow area appeared to have a significant impact. A positive relationship between ECR and the zebra mussel density was most evident in the proximity of the TPM source. Based on the results, we assume that at high TPM concentration, refiltration may assert itself by the elevated net clearance rate of mussels within dense clumps compared to that of mussels at relatively low individual densities. This should be taken into consideration while modelling and assessing the role of the zebra mussel in energy flow and redistribution of organic matter in an ecosystem.

Monitoring the sedimentary carbon in an artificially disturbed deep-sea sedimentary environment

An area of 0.6 km(2) in the manganese nodule field of the Central Indian Basin was physically disturbed and sediments discharged in the near bottom waters to simulate seabed mining and study its impact on benthic ecosystem. An estimated 2 to 3 tonnes of sedimentary organic carbon (C(org)) was resuspended into the water column during a 9-day experiment. The majority of the sediment cores from within the disturbed area and areas towards the south showed a ~30% increase in C(org) content as well as an increase in carbon burial rates after disturbance, though with a reduction in carbon/phosphorus ratios. High specific surface area (SSA~25 m(2) g(-1)) and low C(org)/SSA ratios (mostly <0.5) are typical of deep-sea sediments. The increased C(org) values were probably due to the organic matter from dead biota and the migration and redeposition of fine-grained, organic-rich particles. Spatial distribution patterns of C(org) contents of cores taken before and after disturbance were used to infer the direction of plume migration and re-sedimentation. A positive relationship was observed between total and labile C(org) and macrobenthos density and total bacterial numbers prior to disturbance, whereas a negative relationship was seen after disturbance owing to drastic reduction in the density of macrofauna and bacteria. Overall decrease in labile organic matter, benthic biota and redistribution of organic matter suggest that the commercial mining of manganese nodules may have a significant immediate negative effect on the benthic ecosystem inducing changes in benthic community structure.

Sedimentary organic matter distributions, burrowing activity, and biogeochemical cycling: Natural patterns and experimental artifacts

The coupling between biogenic reworking activity and reactive organic matter patterns within deposits is poorly understood and often ignored. In this study, we examined how common experimental treatments of sediment affect the burrowing behavior of the polychaete Nephtys incisa and how these effects may interact with reactive organic matter distributions to alter diagenetic transport – reaction balances. Sediment and animals were recovered from a subtidal site in central Long Island Sound, USA. The upper 15 cm of the sediment was sectioned into sub-intervals, and each interval separately sieved and homogenized. Three initial distributions of sediment and organic substrate reactivity were setup in a series of microcosms: (1) a reconstituted natural pattern with surface-derived sediment overlying sediment obtained from progressively deeper material to a depth of 15 cm (Natural); (2) a 15 cm thick sediment layer composed only of surface-derived sediment (Rich); and (3) a 15 cm thick layer composed of uniformally mixed sediment from the original 15 cm sediment profile (Averaged). The two last treatments are comparable to that used in microcosms in many previous studies of bioturbation and interspecific functional interaction experiments. Sediment grain size distributions were 97.5% silt-clay and showed no depth dependent patterns. Sediment porosity gradients were slightly altered by the treatments. Nepthys were reintroduced and aquariums were X-rayed regularly over 5 months to visualize and quantify spatial and temporal dynamics of burrows. The burrowing behaviour of adult populations having similar total biovolume, biomass, abundance, and individual sizes differed substantially as a function of treatment. Burrows in sediment with natural property gradients were much shallower and less dense than those in microcosms with altered gradients. The burrow volume/biovolume ratio was also lower in the substrate with natural organic reactivity gradients. Variation in food resources or in sediment mechanical properties associated with treatments, the latter in part coupled to remineralization processes such as exopolymer production, may explain the burrowing responses. In addition to demonstrating how species may respond to physical sedimentation events (substrate homogenization) and patterns of reactive organic matter redistribution, these experiments suggest that infaunal species interactions in microcosms, including the absolute and relative fluxes of remineralized solutes, may be subject to artifacts depending on exactly how sediments are introduced experimentally. Nonlocal transport and cylinder microenvironment transport – reaction models readily demonstrate how the multiple interactions between burrowing patterns and remineralization rate distributions can alter relative flux balances, decomposition pathways, and time to steady state.

Occurrence of Organic Matter in Calcimicrobialites across Permian–Triassic Boundary in Huayingshan Region, Sichuan, South China

Calcimicrobialites across the Permian-Triassic boundary in Huayingshan region were investigated using the fluorescence microscopic measurements to understand the occurrence of organic matter. The microbialites are composed of micrite matrix and coarse spar cement. Abundant rhombic or magnetic needle-like carbonate minerals were observed adrift within the cement. The fluorescence microscopic measurement indicates the micrite matrix in microbialites shows the most abundant organic matter, with the rhombic or magnetic needle-like carbonate minerals and coarse spar cement coming to the 2nd and the 3rd, respectively. Organic matter is mainly preserved in the space between the grains of the micrite minerals but almost evenly distributed in the rhombic or magnetic needle-like carbonate minerals. As one of the common diagenesis types, dolomitization is observed to occur in the microbialites in Huayingshan. However, the carbonate cement in microbialites still has high content of element Sr as shown by the microprobe analysis, reflecting that the dolomitization might have happened in a restricted environment. Observation under the fluorescence microscope shows that dolomitization just led to the redistribution of organic matter in the grain space of dolomite minerals, inferring that the diagenesis has a slight effect on the preservation, and thus on the content of organic matter in the microbialites.

Influence of aquaculture of mussels on the benthic and planktonic communities in the White Sea

Structural and functional parameters of planktonic and benthic communities in the White Sea were studied both at the sites of industrial mussel cultivation farms (MF) and in aquaculture free areas. Redistribution of organic matter in pelagic and bottom systems close to MF was shown to result in changes of the structure of the surrounding biocoenoses. The consumption of proteins by mussels led to a drastic decrease in the relative abundance of planktonic bacteria, while the composition and abundance of the zooplanktonic community were not affected by MF. A significantly uneven distribution was found in the bottom habitats, which results in organic contamination and, in some cases, in degradation of benthic communities.

Properties of intertidal marsh sediment mobilized by rainfall

We conducted sprinkler irrigation experiments on a low‐tide marsh to investigate the effects of rainfall on the redistribution of organic matter (OM) and nutrients in the intertidal zone. We irrigated 1‐ × 2‐m plots at highmarsh, low‐marsh, and channel bank sites and flood‐irrigated 1‐ × 3‐m plots in the high marsh and low marsh. We measured particulate density, OM content, organic carbon (OC) content, and nitrogen (N) content and calculated OM particulate density and atomic C:N ratios. The content of OM, OC, and N in rainfall‐mobilized sediment was consistently higher than in the substrate. C:N ratios ranged from 13 to 15 and were consistently lower than the sediment substrate (16–21). These observations indicate that rainfall can mobilize N preferentially over OC; hence, rainfall events deplete the marsh substrate of OM, OC, and nutrients. Despite variability in the density of mobilized particulates, the calculated OM densities and the C:N ratios remained unchanged during the irrigation experiments. These results indicate that rainfall runoff processes preferentially and consistently mobilize OM‐rich particulates with low C:N ratios, characteristic of mixed algal or vascular plant sources. The short‐term OC fluxes during these rainfall experiments represent 3–20% of annual primary productivity.

Influence of earthworm invasion on soil microbial biomass and activity in a northern hardwood forest

Recent invasion and activity of exotic earthworms has profoundly altered the chemical and physical environment of surface soils in northern hardwood forests that previously had mor humus horizons. We investigated the influence of earthworm invasion on soil microbial biomass and activity in surface soils of Allegheny northern hardwood forests in central New York state. Earthworm activity in these sites had transformed surface soils with clear Oi, Oe, and Oa horizons (forest floor) overlying mineral soil, to more uniformly mixed organic-enriched A horizons. The highest concentrations of microbial biomass and activity occurred in the forest floor. Microbial biomass (assayed by chloroform fumigation–extraction) nearly doubled in surface (0–5 cm) mineral soils in response to earthworm activity, an effect that corresponded directly to redistribution of organic matter from forest floor into the mineral soil. Microbial activity in surface mineral soils was even more sensitive to the presence of earthworms than microbial biomass. For example, substrate-induced respiration (or maximum initial respiratory rate, MIRR) was 6.7-fold greater, basal respiration was 5-fold greater, and microbial respiration per unit microbial biomass (metabolic quotient, qCO 2) was almost 3-fold greater in surface mineral soils where earthworms were present than in earthworm-free sites. Of the activity indices, only MIRR was higher when expressed on an organic matter basis. Surface mineral soils where earthworms were present thus appear to retain a high proportion of the microbial biomass and activity found in mor organic horizons. Our findings suggest that earthworm activity stimulates the activity of soil microorganisms, probably by enhancing organic C availability via processing and mixing of litter. The relative pattern in microbial properties did not change over the growing season; however, there were some seasonal changes in the proportional differences between worm and no-worm soils. Our results indicate interactions among earthworms, organic matter, and soil microbial activity that should alter the carbon and nutrient balance of northern hardwood forest surface soils, relative to non-invaded soils.

Partitioning of copper onto suspended particulate matter in river waters

Suspended particles and river water from the Susquehanna River, White Clay Creek and the Delaware River were collected to experimentally study the partitioning of copper. The effects of many factors that may influence the partitioning coefficient ( K d) including pH, total suspended solids (TSS), total copper concentration ([Cu] T), dissolved organic matter (DOM), particulate organic matter (POM), hardness, and ionic strength were investigated by performing batch adsorption experiments. The results implied that organic matter binding sites in both the aqueous and solid phases play the most important role in controlling copper partitioning. Other major factors governing the partitioning are pH and TSS. K d increases with pH in the pH range 3–8. TSS increases caused decreases in K d values, which may be attributed to the decrease in the quantity of available binding sites caused by interparticle interactions, rather than by the redistribution of organic matter between solid and solution phases with the variation of TSS. K d decreases slightly when total Cu concentration increases; however, K d can be considered to be independent of Cu concentration when TSS is high. The effects of calcium competition and ionic strength on partitioning are small.

Impacts of forest harvesting on biological processes in northern forest soils

Resume Soil is the habitat of plant roots and the home of numerous microflora, including viruses, bacteria, fungi and blue-green algae, and a host of animals from unicellular protozoans to small vertebrates. Simple communities of soil organisms, present from the earliest stages of forest soil genesis, become more complex and grow to astronomical numbers in mature forest soils. Here, they are essential for the maintenance and productivity of these soils, which unlike agricultural systems, generally receive less mechanical treatments and chemical inputs. The soil microflora and fauna complement each other in the comminution of litter, mineralization of essential plant nutrients, and conservation of these nutrients within the soil system. Harvesting directly affects these processes through the reduction and redistribution of organic matter, compaction, changes in plant cover, and modification of microclimate, all of which affect the distribution, composition and activity of the soil biological communities. Although most information is available for clearcut forests, the limited data from other systems indicate that severity of impacts of forest harvesting practices generally follow the sequence: clearcuts > shelterwood systems > extended rotation systems. However, all practices generally affect soil organisms over the short term. Changes over the longer-term are less obvious because of gradual recovery of most biological components with canopy closure. Long-term impacts are more difficult to interpret because these are often influenced by natural changes in population dynamics of soil organisms with forest succession, drought, and the invasion of exotic species. Responses are complex, with various groups being affected differently. Even within a taxon, individual species may behave differently. Although the relationships among floral composition, faunal diversity and sustained soil fertility are not always clear, there are indications that a simplified soil biological system will adversely affect nutrient cycling, tree growth, and forest health. Decomposition rate is generally positively correlated with faunal biomass, and a diverse fauna is required for interacting with microorganisms to enhance microbial diversity. Also, feeding on microflora by the fauna concurrently controls certain plant pathogens. Destruction of mycorrhizae, essential for the establishment of coniferous seedlings, can lead to serious reforestation problems. It is therefore prudent to discourage any qualitative or quantitative changes in the soil biota. Concepts in ‘new forestry’ attempt to mitigate against adverse affects of conventional forest harvesting practices on soil organisms by maintaining plant biodiversity, minimizing soil compaction, avoiding extreme microclimatic conditions, providing refugia for re-colonization by the biota, and directly introducing desirable microflora and fauna.

Megafauna Can Control the Quality of Organic Matter in Marine Sediments

On the highly productive Oman Margin of the Arabian Sea, where an intense permanent oxygen minimum impinges on the continental slope, there is no relationship between oxygen concentration and sedimentary organic-carbon content. However, we provide photographic and molecular evidence that benthic invertebrates play a significant role in the redistribution of organic matter. High densities of spider crabs and brittle stars characterize a narrow band near the base of the oxygen minimum zone, where sediments have depleted organic carbon contents and a remarkable lipid composition that is indicative of metabolic alteration of phytoplankton-derived sterols by invertebrate detritivores. The distributions of sedimentary sterols and the high abundances of epifaunal crabs and brittle stars suggest that the metabolism of the megabenthos profoundly influences the quality of organic matter in underlying sediments.

The depositional environment and mineralogical and chemical compositions of high ash brown coal resting on early Tertiary saprock (Schirnding Coal Basin, SE Germany)

The late Tertiary high ash brown coal ( R r=0.26%) of the Schirnding Seam Zone is mainly composed of huminite. The seam is underlain by a thick saprock (mica saprock⇒kaolinite-mica saprock) some tens of meters thick which gradually developed from phyllitic basement rocks and a thin Footwall Series of coarse-grained clastic sediments which, however, occur only in a few places. The roof rocks ` Hanging Wall Series' abruptly appear on top of the seam and consist of massive gray mudstones and arenites, intercalated with some tuffites. These Tertiary series were studied in open-pit mines operated for coal and clay and in bore holes. Chemical investigation involved the analyses of TOC, TSC, Ni, Co, Pb, Zn, Ga, Be, V, Cr, U, Th, P, Zr, REE and organic compounds of extracted organic matter (=OM). Early Tertiary chemical weathering was responsible for the monotonous kaolinite-mica-goethite mineral assemblage in the saprock and the footwall series. In the coal-bearing basin a more variegated mineral association including, pyrite, kaolinite, illite, smectite, illite-smectite mixed layers and siderite was brought about by volcanic processes, intrastratal solution set free in course of coalification and early diagenesis and by meteoric waters infiltrating the coal-bearing series from uplifted parts of the basin, which underwent strong oxidation. The environment of deposition is interpreted in terms of peatswamps that were fed by small streams and crevasse splays of a meandering drainage system grading towards the basin margin into a braided stream system on an alluvial fan plain. Strongly fluctuating water levels were responsible for the pronounced cyclicity to be encountered across the coal-bearing series. The processes of element redeposition and element migration in the Schirnding Basin are operative across the interface coal-saprolite (detrital influx of heavy minerals and intrastratal solution, hydrocarbon infiltration and redistribution of organic matter, reworking of duricrusts), in the saprolite proper (weathering leachats) and across the redox boundaries between the Schirnding Seam Zone and the Hanging Wall Series (input of physils and diagenetic alteration) as well as its strongly oxidized stratigraphic equivalents at the basin edge (volcanic influx, intrastratal solutions). Chemical and mineralogical variations across the coal basin which are directly controlled by the variation in the environment of deposition, weathering and groundwater movements may be directly correlated to changes in the saprock due to the immediate contact between coal and bedrock.

Benthic denitrification and nitrogen cycling at the slope and rise of the N.W. European Continental Margin (Goban Spur)

The rate of benthic denitrification in slope and rise sediments of a transect across the N.W. European Continental Margin (Goban Spur) was evaluated from 31 pore water nitrate profiles obtained during six cruises between May and October. All profiles had well separated zones of nitrification and denitrification. High near-surface nitrate concentrations prevented the influx of nitrate from the bottom water. The denitrification rates obtained from steady-state-modelling ranged from 0.13 to 2.56 μmol N cm −2 y −1 and showed an exponential increase both with decreasing water depth and with increasing rate of organic carbon degradation. Denitrification rates in a nearby canyon, which did not follow these relationships, were estimated to be much higher as a result of erosion and redistribution of organic matter. Denitrification at the Goban Spur slope and rise is much lower than previously reported for similar environments in the Pacific resulting predominantly from the different oxygen and nitrate concentrations in the bottom water. A weighted average for the whole slope and rise sediment system shows that 17% of the particulate organic nitrogen input (8.93 μmol N cm −2 y −1) is denitrified and only 1% is buried, the rest being released as nitrate. Although being ten times higher compared with basin sediments, denitrification on the slope and rise is several times lower than on the adjacent shelf.