Floor Layers Research Articles

Seasonal variations in the chemical composition of dissolved organic matter in organic forest floor layer leachates of old-growth Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.) stands in northeastern Bavaria, Germany

Organic matter dissolved in thepercolation water of forest soils contributeslargely to element cycling and transport ofnatural and anthropogenic compounds. The wayand extent to which these processes areaffected depends on the amount and the chemicalcomposition of soluble organic matter. Becausethe amount of soluble organic matter variesseasonally with changes in the microbialactivity in soil, it seems reasonable to assumethat there may be also seasonal changes in thechemical composition of dissolved organicmatter. We examined dissolved organic matter inthe seepage waters of organic forest floorlayers over a 27-month period (1997–1999) intwo forest ecosystems, a 160-year-old Scotspine (Pinus sylvestris L.) stand and a90-year-old European beech (Fagussylvatica L.) forest. The forest floorleachates were analysed for bulk dissolvedorganic C, C in hydrophilic and hydrophobicdissolved organic matter fractions,lignin-derived phenols (CuO oxidation),hydrolysable neutral carbohydrates and uronicacids, hydrolysable amino sugars, and stablecarbon isotope composition. In addition, westudied the samples by use of liquid-state13C-nuclear magnetic resonance (NMR)spectroscopy. For both investigated forest sites we foundthat the dissolved organic carbonconcentrations in forest floor leachates werelargest during summer. They peaked after rainstorms following short dry periods (106–145 mgdissolved organic C l−1). The proportionsof C in the hydrophilic fractions were largestin winter and spring whereas in summer andautumn more C was found in the hydrophobicfraction. According to liquid-state 13C-NMR spectroscopy, summer and autumn samples hadlarger abundances of aromatic and aliphaticstructures as well as larger proportions ofcarboxyl groups whereas the winter and springsamples were dominated by resonances indicatingcarbohydrates. Wet-chemical analyses confirmedthese results. Winter and spring samples wererich in neutral carbohydrates and amino sugars.The summer and autumn samples contained morelignin-derived phenols which were also strongeroxidised than those in the winter and springsamples. Seasonal changes of δ13C valueswere found to reflect the changes in thechemical composition of dissolved organicmatter. Most negative values occurred whenisotopically light lignin-derived compoundswere abundant and less negative values whencarbohydrates predominated. The different vegetation, age of thestands, and underlying mineral soils resultedin different concentrations of dissolvedorganic carbon and in differences in thedistribution between hydrophobic andhydrophilic organic carbon. Despite of this,the results suggest that the trends in temporalvariations in the composition of dissolvedorganic matter in forest floor seepage waterwere remarkably similar for both sites.Dissolved organic matter in winter and springseems to be mainly controlled by leaching offresh disrupted biomass debris with a largecontribution of bacterial and fungal-derivedcarbohydrates and amino sugars. Dissolvedorganic matter leached from the forest floor insummer and autumn is controlled by thedecomposition processes in the forest floorresulting in the production of stronglyoxidised, water-soluble aromatic and aliphaticcompounds. The chemical composition ofdissolved organic matter in forest floorseepage water in winter and spring indicateslarger mobility, larger biodegradability, andless interaction with metals and organicpollutants than that released during summer andautumn. Thus, the impact of dissolved organicmatter on transport processes may varythroughout the year due to changes in itscomposition.

Below‐ground ectomycorrhizal community structure in a recently burned bishop pine forest

Summary 1 The effects of wildfire ash on ectomycorrhizal (EM) associations were investigated by sampling bishop pine (Pinus muricata, D. Don) seedlings from control and ash‐removed plots 1.5 years after a severe fire in a northern Californian P. muricata forest. The below‐ground community composition of EM at the site was characterized using molecular techniques (PCR‐RFLP and nucleotide sequencing). 2 A total of 30 fungal taxa were observed, many of which differed in their distribution between treatment and control seedlings. However, most of the taxa that were distinctive to either treatment or control seedlings occurred only once across the site, precluding statistical detection of potential ash effects on EM community composition. There were no significant effects of ash removal on plot‐level mycorrhizal community richness or diversity, and there were no distinct treatment‐related clusters in a principal components analysis. 3 Analysis of the combined data indicated that numbers of fungal taxa per seedling, numbers of successive root depth increments colonized by the same taxon, and distances to neighbouring seedlings colonized by the same taxon, were randomly distributed across the site for the majority of mycorrhizal fungi. These distributional patterns suggest that the post‐fire mycorrhizal community structure on P. muricata arose primarily from successful colonization by randomly distributed point‐source fungal inocula within the upper mineral soil layer of the forest floor. 4 By comparison with pre‐fire studies from similar P. muricata sites nearby, our data indicate that severe wildfire disturbance resulted in marked changes in mycorrhizal community composition, and a sharp increase in the relative biomass of ascomycetous fungi.

Pools and fluxes of mercury and methylmercury in two forested catchments in Germany

Mercury (Hg) and methylmercury (CH 3Hg +) are global pollutants, but little information is available on rates of atmospheric input, distribution and mobility in soils and catchments of central Europe. The objectives of this study were to investigate input and output fluxes of these compounds in a deciduous and a coniferous catchment in NE Bavaria (Germany), and to estimate pools and mobility of total Hg (Hg tot) and CH 3Hg + at the catchment scale. Bulk precipitation, throughfall, litterfall and runoff were collected biweekly from April 1998 to April 1999. Several soil profiles were sampled to estimate pools of Hg compounds in the catchments. In both catchments highest contents of Hg tot were found in the Oa layer of the forest floor (up to 500 ng g −1) and the soil storage of Hg tot calculated for a soil depth of 60 cm was approximately 890 g ha −1 in the coniferous and 190 g ha −1 in the deciduous catchment. Highest contents of CH 3Hg + in upland soils were observed in the Oi layer of the forest floor, and soil storage of CH 3Hg + was 4.35 g ha −1 in the coniferous and 0.59 g ha −1 in the deciduous catchment. The annual total deposition of Hg tot (total deposition not measured directly but calculated from throughfall and litterfall) was 541 mg ha −1 year −1 in the coniferous and 618 mg ha −1 year −1 in the deciduous catchment. Total deposition rates of CH 3Hg + were 3.5 and 2.6 mg ha −1 year −1. The contribution of litterfall to the total deposition of Hg tot and CH 3Hg + was 55% in the deciduous catchment. In the coniferous catchment, the contribution of litterfall to total deposition was only 29% for Hg tot, but 55% for CH 3Hg +. By far the largest proportion of the deposited CH 3Hg + and Hg tot remained in the catchments (85% in the coniferous, 95% in the deciduous). As compared to remote Swedish catchments, deposition and output via runoff of Hg tot were higher, but deposition and output of CH 3Hg + were lower in our catchments. In contrast to other studies, the annual budget revealed no differences in the mobility between the two species at the catchment scale. However, temporal patterns of the runoff fluxes and converse gradients of CH 3Hg + and Hg tot contents in the forest floor indicated differences in mobility on shorter time scales.

THE SORPTION OF ORGANIC MATTER IN SOILS AS AFFECTED BY THE NATURE OF SOIL CARBON

Recent studies have shown that soil organic carbon (OC) may either hinder or favor the sorption of dissolved organic matter (DOM) in soils. Our concept was that the nature of soil OC determines these contrasting findings. To test this hypothesis, we compared the DOM sorption in soils with OC derived from biomass decomposition with that in soils with OC more likely derived from charred materials (black carbon). All the mineral soil samples in the study were from Spodosols, and the DOM was from an aqueous extract of a mor forest floor layer. Sorption was determined in batch experiments. The sorption in soils that contain large amounts of black carbon was, in general, less than the sorption in soils with decomposition-derived OC. When the DOM sorption parameters of the soils were correlated to the OC content, the black carbon soils showed a positive effect of the OC content on the DOM sorption. In the soils lacking the features of black carbon residues, the DOM sorption was negatively influenced by OC. These results lead us to assume that the nature of soil OC is a soil property that needs to be considered in the DOM sorption of soils, especially when soils have large amounts of highly aromatic OC.

Incidence of occupational asthma by occupation and industry in Finland

Systematic research on occupation or industry-specific incidence of occupational asthma (OA) is sparse. We calculated the incidence of notified OA by occupation, industry and causative agent in Finland for the years 1989-95. The numbers of cases of reported OA were retrieved from the Finnish Registry of Occupational Diseases for the population between 20 and 64 years of age. The numbers of employed workers were retrieved from Statistics Finland. Incidence rates were calculated for each occupation, industry and the total workforce. Altogether 2602 cases of OA were notified and the mean annual incidence rate was 17.4 cases/100,000 employed workers. The incidence rate was the highest in bakers, other painters and lacquerers, veterinary surgeons, chemical workers, farmers, animal husbandry workers, other food manufacturing workers, welders, plastic product workers, butchers and sausage makers, and floor layers. Cases caused by animal epithelia, hairs and secretions or flours, grains, and fodders accounted for 60% of the total. Estimation of occupation and industry-specific incidence rates forms the basis for successful prevention of OA, but necessitates collection of data over several years from well-established surveillance systems.

Influence of decomposer food web structure and nitrogen availability on plant growth

We studied the sensitivity of soil microbial communities and ecosystem processes to variation in the vertical and horizontal structure of decomposer food web under nitrogen poor and N-enriched conditions. Microcosms with humus and litter layer of boreal forest floor, birch seedlings infected with mycorrhizal fungi, and decomposer food webs with differing trophic group and species composition of soil fauna were constructed. During the second growing period for the birch, we irrigated half of the microcosms with urea solution, and the other half with de-ionised water to create two levels of N concentration in the substrate. During the experiment night time respirations of the microcosms were measured, and the water leached through the microcosms was analysed for concentration of mineral N, and nematode numbers. The microcosms were destructively sampled after 37 weeks for plant biomass and N uptake, structure of soil animal and microbial community (indicated by PLFA profiles), and physical and chemical properties of the humus and litter materials. Predatory mites and nematodes had a negative influence on the biomass of their microbivorous and microbi-detritivorous prey, and microbi-detritivores affected the biomass and community structure of microbes (indicated by PLFA-analysis). Moreover, predatory mites and nematodes increased microbial biomass and changed the microbial community structure. The decomposer food web structure affected also N uptake and growth of plants. Microbi-detritivorous fauna had a positive effect, whereas predators of microbial and detritus feeding fauna exerted a negative influence on plant N uptake and biomass production. The impact of a trophic group on the microbes and plant was also strongly dependent on species composition within the group. Nitrogen addition magnified the influence of food web structure on microbial biomass and plant N uptake. We suggest that addition of urea-N to the soil modified the animal-microbe interaction by increasing microbial growth and altering community structure of microbes. The presence of microbi-detritivores and predators reduced loss of carbon from the microcosms, and the food web structure influenced also water holding capacity of the materials. The changes in plant growth, nutrient cycling, size of N and C pools, and in the physical properties of the soil emphasize the importance and diversity of indirect consequences of decomposer food web structure.

Soil Properties of Boreal Riparian Plant Communities in Relation to Natural Succession and Clear-Cutting, Peace River Lowlands, Wood Buffalo National Park, Canada

Thirteen study sites on the floodplain and terraces ofthe lower Peace River, Wood Buffalo National Park,Canada, were examined for the effects of naturalforest succession and logging on physical and chemicalsoil properties. The principal changes in substratecharacteristics along the natural successional pathwaywere (i) development of a forest floor and (ii) burialof organic layers by floodwater deposition. Thephysical soil parameters of the forest floor andmineral soil were closely related to floodingfrequency, soil texture, stand closure, and forestfloor build-up. Significant differences in a number ofchemical soil properties between early (Barren Silt,Establishing) and late (Mature, Old-growth)successional stages were evident. The rising influenceof the developing plant community on chemical soilparameters was obvious. Organic carbon, totalnitrogen, cation exchange capacity, exchangeablecalcium, magnesium and potassium and extractablephosphorus level of forest floor and mineral soilswere highest in Mature sites; whereas pH and basesaturation were lowest. Physical and chemical soilproperties at three clear-cut sites were compared tosix undisturbed Mature/Old-growth stands. Removingvegetation had an effect on the physical soilproperties. A significant decrease in forest floornitrogen, cation exchange capacity, calcium andphosphorus occurred due to clear-cutting. Nosignificant change of chemical soil parameters wasobserved in the mineral soil at 0–20 cm depthfollowing harvesting. Significant impacts on chemicalsoil characteristics appeared to be limited to theforest floor. The absence of post-cutting sitepreparations makes the study area a useful benchmarkfor comparison with logged and scarified borealriparian sites elsewhere.

Forms of organic C and P extracted from tropical soils as assessed by liquid-state 13C- and 31P-NMR spectroscopy

Transformation of soil organic phosphorus (SOP) is linked with the transformation of soil organic carbon (SOC). Yet, it is uncertain to which SOC structures the cycling of SOP is related, especially in tropical environments. To clarify this issue, we determined the vertical distribution of extractable C and P chemical structures in 4 soil profiles using solution 13C- and 31P-nuclear magnetic resonance (NMR) spectroscopy after extraction with 0.1 M NaOH/0.4 M NaF (1 : 1). Soils were from a cabbage cultivation with annual burning of weeds, a Pinus reforestation, a secondary forest, and a primary forest in northern Thailand. For all profiles, signals due to O-alkyl and carbonyl C dominated the 13C-NMR spectra (up to 50 and 22% of total spectral area, respectively). The proportions of alkyl and aryl C decreased, whereas carbonyl and O-alkyl C increased with soil depth. Sharp resonances at 135 and 177 ppm appeared in spectra of subsoil horizons. They indicated mellitic acid, an end-product of the oxidation of charred plant residues. The SOP forms comprised mainly orthophosphate diesters in the organic layer of the forests, whereas in the mineral horizons orthophosphate monoesters dominated the chemical composition of extractable SOP. The relationships between SOC and SOP forms in the organic floor layers of the forests were clearly different from those in the mineral soil horizons, indicating changed SOM dynamics upon contact with soil minerals. In the forest mineral soils, significant correlations between monoester-P and O-alkyl C (R = 0.84, P < 0.001) were found. Diester-P, teichoic acids, and phosphonates were positively correlated with aromatic C and negatively with O-alkyl C. At the same time, teichoic acids and phosphonates were positively correlated with short range-ordered Al and Fe oxide phases. These findings can be explained through an increasing microbial decay of aryl C and diester-P compounds that may be less effectively stabilised at lower depths.

Weathering characteristics of some soils formed in White River Tephra, Yukon Territory, Canada

Soil formation under a cold, dry climate on two Late Holocene (approximately 1800 yr BP and 1150 yr BP) volcanic tephra deposits was examined to evaluate trends and rates of soil weathering. Presently under mature boreal forest, these soils are underlain by permafrost within 1 m of the soil surface. The soils are composed of buried forest floor materials and layers of coarse ashy-pumiceous rhyodacite tephra up to 60 cm thick. The bulk density in all tephra-derived horizons is less than 0.90 Mg m−3, water retention values for these horizons at 1500 kPa suction are less than 10% by weight. The mineralogy of the tephra-derived horizons is dominated by volcanic glass with lesser amounts of plagioclase, microcline and amphibole. Micromorphological investigation showed minor pitting of glass and feldspar grains and some oxyhydroxide coatings and Fe and Al-humus complexes. Several soil horizons meet glass composition, P retention and oxalate-extractable Fe and Al criteria established for andic soil material. However none of the profiles meet the thickness requirement to be classified as Andisol as specified in Soil Taxonomy. It is estimated that it would take >4000 yr under present climatic conditions to achieve such a degree of weathering. Key words: Tephra, Cryosol, andic, Yukon, Gelisol, glass

Hydrogeologic Evolution of Gale Crater and Its Relevance to the Exobiological Exploration of Mars

The presence of an Amazonian impact crater lake in the Noachian crater Gale (located in the Aeolis northwest subquadrangle of Mars) is indicated by evidence from young floor deposits, streamlined terraces, layers, and channels observed on the central sedimentary deposit. Evidence for the filling of this lake by two processes is described: (a) the drainage of the aquifer in the Aeolis Mensae region, supported by extended mass-wasting and rim sliding in the crater at the contact with the mensae and (b) the overspilling of the northern rim by an Amazonian south transgression of the Elysium Basin. This last hypothesis is supported by hydrologic features such as channels and channel-like depressions north of the crater and by the crescent-like shape of the central sedimentary deposit. The presence of an impact melt sheet and uplifted central peak may have also generated hydrothermal activity, including an early crater lake, shortly after the formation of the crater in the Noachian period. With time, decreasing heat flux, and changing climates Gale may have experienced transitions in aqueous environments from warm and wet to cold and ice-covered water that could have provided suitable oases for various communities of microorganisms. Preservation of the biological and climatic record may have been favored in this paleolacustrine environment, which probably occured episodically over two billion years.

Mercury and Methylmercury in upland and wetland acid forest soils of a watershed in NE-Bavaria, Germany

Mercury (Hg) and methylmercury (CH3Hg+) are global pollutants, but little information is available on their distribution and mobility in soils and catchments of Central Europe. The objective of this study was to investigate the pools and mobility of Hg and CH3Hg+ in different forest soils. Upland and wetland forest soils, soil solutions and runoff were sampled. In upland soils the highest contents of total-Hg were found in the Oh layer of the forest floor (>400 ng g-1) and the storage of non geogenic total-Hg (calculated for 60 cm depth) was about 120 mg/m2. The storage of total-Hg was one order of magnitude lower in wetland soils as compared to the upland soils. By far the largest proportion of total-Hg in soils was bound in immobile fractions. The depth gradients of CH3Hg+ did not correspond to those of total-Hg and the highest contents of CH3Hg+ in upland soils were observed in the litter layer of the forest floor and in the Bsv horizon. The CH3Hg+ content of the wetland soils was generally much higher in comparison with upland soils. CH3Hg+ in solution was found in the forest floor percolates of upland soils and in wetland soils, but not in soil solutions from mineral soil horizons. Gaseous losses of Hg as well as methylation of Hg are likely in wetland soils. The latter might be highly relevant for CH3Hg+ levels in runoff.

Excavation of a cropmark enclosure at Brixwold, (Dalhousie Mains), Bonnyrigg, Midlothian

Excavation recorded a large, sub-rectangular, ditched enclosure, previously identified from aerial photographic evidence as a cropmark. The deep U-shaped ditch contained waterlogged deposits with preserved organic materials. The radiocarbon dates obtained from waterlogged seeds in the ditch indicate two phases of activity, one in the fourth to second centuries BC and one in the first to second centuries AD. Analyses of the macroplant and insect assemblages from these deposits have provided evidence of the environment within, and immediately surrounding, the ditch as well as some slight evidence of human activity. No significant features or artefacts were recorded in the interior, probably as a result of extensive plough damage. A hollow feature with possible floor layers and a hearth was excavated outwith the south-west perimeter of the enclosure and is tentatively identified as a remnant sunken house floor. There are separately authored reports on: `The macroplant assemblage' by T Holden (395--6); `The invertebrate assemblage' by H Kenward, F Large, J Carrott & M Issitt (396--400); `Flint' by Thomas Rees (400); and `Animal bone' by Tanya O'Sullivan (400--1).

A flow-front instability in viscous gravity currents

We describe an instability that appears at the front of laminar gravity currents as they intrude into a viscous, miscible ambient fluid. The instability causes a current to segment into fingers aligned with its direction of flow. In the case of currents flowing along a rigid floor into a less dense fluid, the case of primary interest here, two mechanisms can produce this instability. The first is gravitational and arises because the nose of the gravity current is elevated above the floor and overrides a buoyantly unstable layer of ambient liquid. The second is a form of viscous fingering analogous to a Saffman–Taylor instability in a Hele-Shaw cell. Whereas the ambient fluid must be more viscous than the current in order for the latter instability to occur, the gravitational instability can occur even if the ambient fluid is less viscous, as long as it is viscous enough to elevate the nose of the current and trap a layer of ambient fluid. For the gravitational mechanism, which is most important when the current and ambient fluids have comparable viscosities, the wavelength when the instability first appears is proportional to a length scale constructed with the viscosity, the flux and the buoyancy. The Saffman–Taylor-type mechanism is most important when the ambient liquid is much more viscous than the current. We have carried out experiments with miscible fluids in a Hele-Shaw cell that show that, at the onset of instability, the ratio of the finger wavelength to the cell width is a constant approximately equal to 2. This result is explained by using the principle that the flow tends to minimize the dissipation associated with the finger perturbation. For the gravity currents with high viscosity ratios, the ratio of the wavelength to the current thickness is also a constant of about 2, apparently consistent with the same mechanism. But, further analysis of this instability mechanism is required in order to assess its role in wavelength selection for gravity currents.

Landscapes at Landnám: Palynological and Palaeoentomological Evidence from Ibftanes, Faroe Islands

Toftanes is a Viking age farmstead in the coastal village of Leirvík, Eysturoy. Excavations in the 1980s revealed four buildings, thousands of finds and radiocarbon dates which extend back to perhaps the 9th century AD. This is the first complex farmstead of the Viking Age landnám settlement to have been completely excavated in the Faroe Islands. Organic remains from floor layers were subjected to pollen and insect analyses in an effort to reconstruct land use associated with the farm and thewiderlandscape. The taphonomy of the deposits and their contained fossils presents diffículties for the interpretation of results.It is clear, however, that a mainly open landscape was associated with a largely pastoral economy, but cereal-type pollen is also present. The insect faunas are enigmatic in showing a very muted anthropogenic signature, yet one which displays obvious signs of anthropochorous habitats. Future palaeoecological research will include the investigation of many more samples and the analyses of seeds.

The influence of bioregulation on water quality of the prefiltered stagnant water reservoir eekhoven (Flanders, Belgium)

When the creation of a new safety reservoir for the drinking water supply of the Antwerp region was envisaged it was decided that a number of actions would be undertaken to create a favourable environment for bioregulation (biomanipulation). These were: the use of boulders for the side-walls instead of concrete or bitumen, first flooding with a shallow layer of water to leach out the minerals contained in the upper clay layer of the bottom floor, introduction of freshwater mussels and of a number of fish species (bitterlings, predators such as eels, pike-perch and pike) and of submerged, floating-leaved and emergent aquatic plant species. This paper is a report on the results of these bioregulation measures obtained so far.

The influence of bioregulation on water quality of the prefiltered stagnant water reservoir eekhoven (Flanders, Belgium)

When the creation of a new safety reservoir for the drinking water supply of the Antwerp region was envisaged it was decided that a number of actions would be undertaken to create a favourable environment for bioregulation (biomanipulation). These were: the use of boulders for the side-walls instead of concrete or bitumen, first flooding with a shallow layer of water to leach out the minerals contained in the upper clay layer of the bottom floor, introduction of freshwater mussels and of a number of fish species (bitterlings, predators such as eels, pike-perch and pike) and of submerged, floating-leaved and emergent aquatic plant species. This paper is a report on the results of these bioregulation measures obtained so far.

Soil Dissolved Organic Matter Sorption as Influenced by Organic and Sesquioxide Coatings and Sorbed Sulfate

AbstractThe sorption of dissolved organic carbon (DOC) and its fractions as influenced by organic C (OC), sesquioxides [amorphous Al(OH)3, ferrihydrite, goethite], and extractable SO2−4 was investigated by modifying the properties of the Bs horizon of an Entic Haplorthod. Coating the Bs material with OC extracted from the Oa horizon of a mor forest floor layer decreased the sorption of total DOC. The effects on the sorption of the hydrophobic DOC fraction were little, whereas the sorption of the hydrophilic fraction was strongly reduced. At the highest OC coating levels, a net release of hydrophilic DOC occurred, indicating a displacement of indigenous hydrophilic substances from the soil by the sorbing hydrophobic dissolved organic matter (DOM). Coating of the soil material with sesquioxides clearly increased the sorption of DOC and its fractions. The strongest effects occurred when amorphous Al(OH)3 was added, followed by ferrihydrite and goethite. Increased contents of extractable SO2−4 did not affect the sorption of DOC on soil material. With increasing addition of DOC, however, the concentrations of SO2−4 in the equilibrium solution increased. Adsorbing DOM seems to displace SO2−4 bound to soil materials. Thus, DOM shows a higher affinity to sorb on soil material than SO2−4.

Impacts of Timber Harvesting on Soil Organic Matter, Nitrogen, Productivity, and Health of Inland Northwest Forests

Abstract Soil organic components are important factors in the health and productivity of Inland Northwest forests. Timber harvesting and extensive site preparation (piling, windrowing, or scalping) reduces the amount of surface organic material (woody residues and forest floor layers) over large areas. Some wildfires and severe prescribed burns can have similar consequences. Such organic matter reductions can have important implications for soil chemical, biological and physical properties. A number of studies have linked substantial reduction in mycorrhizae development and tree growth to high levels of soil disturbance, or removal of organic horizons. Timber harvesting also removes a large percentage of coarse woody debris, which has unknown ramifications on soil productivity. Current woody residue guidelines in this region recommend leaving <10 to 125 Mg ha-1 on site to replace woody materials lost during harvesting operations. Large amounts of soil nitrogen (>500 kg ha-1) can also be lost from timber harvesting and site preparation, especially when using prescribed fire. The time required to replace this lost nitrogen may range from <10 to >275 yr, and depends on the severity of site treatments, presence or absence of nitrogen-fixing plants, and amounts of atmospheric deposition. Maintaining adequate amounts of organic matter on some forest sites in the Inland Northwest may temporarily increase the risk of wildfire or favor the activity of certain insects or disease fungi. However, carefully planned prescribed burns and mechanical site preparation can be practiced on most sites with relatively low impacts on soil organic levels, while accomplishing the important forest management objectives of fuel reduction, seedbed preparation, and reducing competing vegetation. Organic matter management will be the most difficult on very dry sites, with their historically low soil organic and nitrogen content, and high fire potential. The maintenance of adequate soil organic matter levels is critical for sustaining forest health and productivity under the variable moisture and temperature conditions of this region. Thus, soil organic components will become more important in the future as ecosystem management systems are developed for western forests. For. Sci. 43(2):234-251.

96/06570 Brown coal mining and water resource management in the Rhenish district. Protection of water supply in a heavy strained area

Compared to agricultural lands, forests are complex ecosystems as they can involve diverse plant species associations, several vegetative strata (overstorey, shrubs, herbaceous and other annual plant layer) and multi-layered soil profiles (forest floor, hemi-organic and mineral layers). A high degree of variability is thus generally observed in radionuclide transfers and redistribution patterns in contaminated forests. In the long term, the soil compartment represents the major reservoir of radionuclides which can give rise to long-term plant and hence food contamination. For practical reasons, the contamination of various specific forest products has commonly been quantified using the aggregated transfer factor (Tag in m2 kg−1) which integrates various environmental parameters including soil and plant type, root distribution as well as nature and vertical distribution of the deposits. Long lasting availability of some radionuclides was shown to be the source of much higher transfer in forest ecosystems than in agricultural lands. This study aimed at reviewing the most relevant quantitative information on radionuclide transfers to forest biota including trees, understorey vegetation, mushrooms, berries and game animals. For both radiocaesium and radiostrontium in trees, the order of magnitude of mean Tag values was 10−3 m2 kg−1 (dry weight). Tree foliage was usually 2–12 times more contaminated than trunk wood. Maximum contamination of tree components with radiocaesium was associated with (semi-)hydromorphic areas with thick humus layers. The transfer of radionuclides to mushrooms and berries is high, in comparison with foodstuffs grown in agricultural systems. Concerning caesium uptake by mushrooms, the transfer is characterized by a very large variability of Tag, from 10−3 to 101 m2 kg−1 (dry weight). For berries, typical values are around 0.01–0.1 m2 kg−1 (dry weight). Transfer of radioactive caesium to game animals and reindeer and the rate of activity reduction, quantified as an ecological half-life, reflect the soil and pasture conditions at individual locations. Forests in temperate and boreal regions differ with respect to soil type and vegetation, and a faster decline of muscle activity concentrations in deer occurs in the temperate zone. However, in wild boar the caesium activity concentration shows no decline because of its special feeding habits. In the late phase, i.e. at least a few months since the external radionuclide contamination on feed plants has been removed, a Tag value of 0.01 m2 kg−1 (fresh weight) is common for 137Cs in the muscles of adult moose and terrestrial birds living in boreal forests, and 0.03 m2 kg−1 (fresh weight) for arctic hare. Radiocaesium concentrations in reindeer muscle in winter may exceed the summer content by a factor of more than two, the mean Tag values for winter ranging from 0.02 to 0.8 m2 kg−1 (fresh weight), and in summer from 0.04 to 0.4 m2 kg−1. The highest values are found in the year of initial contamination, followed by a gradual reduction. In waterfowl a relatively fast decline in uptake of 137Cs has been found, with Tag values changing from 0.01 to 0.002 m2 kg−1 (fresh weight) in the three years after the contaminating event, the rate being determined by the dynamics of 137Cs in aquatic ecosystems.

Assembly of the Herpes Simplex Virus Capsid: Characterization of Intermediates Observed During Cell-free Capsid Formation

The herpes simplex virus-1 (HSV-1) capsid is an icosahedral shell approximately 15 nm thick and 125 nm in diameter. Three of its primary structural components are a major capsid protein (VP5; coded by the UL19 gene) and two minor proteins, VP19C (UL38 gene) and VP23 (UL18 gene). Assembly of the capsid involves the participation of two additional proteins, the scaffolding protein (UL26.5 gene) and the maturational protease (UL26 gene). With the goal of identifying morphological intermediates in the assembly process, we have examined capsid formation in a cell-free system containing the five HSV-1 proteins mentioned above. Capsids and capsid-related structures formed during progressively longer periods of incubation were examined by electron microscopy of thin-sectioned specimens. After one minute, 90 minutes and eight hours of incubation the structures observed, respectively, were partial capsids, closed spherical capsids and polyhedral capsids. Partial capsids were two-layered structures consisting of a segment of external shell partially surrounding a region of scaffold. They appeared as wedges or angular segments of closed spherical capsids, the angle ranging from less than 30° to greater than 270°. Partial capsids are suggested to be precursors of closed spherical capsids because, whereas partial capsids were the predominant assembly product observed after one minute of incubation, they were rare in reactions incubated for 45 minutes or longer. Closed spherical capsids were highly uniform in morphology, consisting of a closed external shell surrounding a thick scaffold similar in morphology to the same layers seen in partial capsids. In negatively stained specimens, closed spherical capsids appeared round in profile, suggesting that they are spherical rather than polyhedral in shape. A three-dimensional reconstruction computed from cryoelectron micro graphs confirmed that closed spherical capsids are spherical with T=16 icosahedral symmetry. The reconstruction showed further that, compared to mature HSV-1 capsids, closed spherical capsids are more open structures in which the capsid floor layer is less pronounced. In contrast to closed spherical capsids, polyhedral capsids exhibited distinct facets and vertices, indicating that they are icosahedral like the capsids in mature virions. Upon incubation in vitro, purified closed spherical capsids matured into polyhedral capsids, indicating that the latter arise by angularization of the former. Partial capsids, closed spherical capsids and polyhedral capsids were all found to contain VP5, VP19C, VP23, VP21 and the scaffolding protein; the scaffolding protein being predominantly in the immature, uncleaved form in all cases. Polyhedral capsids and closed spherical capsids were found to differ in λtheir sensitivity to disruption at 2°C. Closed spherical capsids were disassembled while polyhedral capsids were unaffected. Our results suggest that HSV-1 capsid assembly begins with the partial capsid and proceeds through a closed, spherical, unstable capsid intermediate to a closed, stable, icosahedral form similar to that found in the mature virion. Structures resembling HSV-1 partial capsids have been described as capsid assembly intermediates in Salmonella typhimuriumbacteriophage P22. HSV-1 capsid maturation from a fragile, spherical state to a robust polyhedral form resembles the prohead maturation events undergone by dsDNA bacteriophages including