Floor Depth Research Articles

Mobility of Trimethyllead and Total Lead in the Forest Floor

The forest floor represents an important compartment for the accumulation of heavy metals in forest soils. To study the mobility of Pb species and their linkage to C cycling in the forest floor, we investigated concentrations of trimethyllead (C3H9Pb+) and total Pb (Pbtotal) in throughfall and forest floor percolates during 14 snow‐free wk. For our study, we used a long‐term field experiment with increased input of throughfall and litterfall at a Norway spruce [Picea abies (L.) H. Karst.] site. The concentrations of trimethyllead were highest in throughfall (106 pg Pb L−1) and decreased with depth of the forest floor. Strong correlations between trimethyllead concentrations in throughfall and forest floor percolates suggested that trimethyllead in forest floor percolates originates largely from throughfall. The partition coefficients of trimethyllead and Pbtotal, estimated as ratios of concentrations in percolates to those in forest floors, ranged from 54 to 560 and 870 to 26,400 L kg−1, respectively, indicating that the mobility of trimethyllead was greater than Pbtotal The Pbtotal concentrations were low in throughfall and often the highest in Oa horizon percolates (15.2−57.5 μg L−1). They decreased in Oi horizon percolates after increased throughfall addition. Increased litterfall resulted in increased concentrations of Pbtotal in forest floor percolates. Concurrently, dissolved organic C increased. The tight coupling of Pbtotal to dissolved organic C was also indicated by correlations (r ≥ 0.48) that were stronger than those between Pbtotal and pH (r ≤ −0.22). We concluded that the mobilization of Pbtotal from the large pool in forest floor horizons is strongly linked to the release of dissolved organic matter. Conversely, the mobility of trimethyllead is regulated by throughfall input and not by dissolved organic C.

Micro-crystalline inclusions analysis by PIXE and RBS

A characteristic feature of the nuclear microprobe using a 3MeV proton beam is the long range of particles (around 70μm in light matrices). The PIXE method, with EDS analysis and using the multilayer approach for treating the X-ray spectrum allows the chemistry of an intra-crystalline inclusion to be measured, provided the inclusion roof and thickness at the impact point of the beam (Z and e, respectively) are known (the depth of the inclusion floor is Z+e). The parameter Z of an inclusion in a mineral can be measured with a precision of around 1μm using a motorized microscope. However, this value may significantly depart from Z if the analyzed inclusion has a complex shape. The parameter e can hardly be measured optically. By using combined RBS and PIXE measurements, it is possible to obtain the geometrical information needed for quantitative elemental analysis. This paper will present measurements on synthetic samples to investigate the advantages of the technique, and also on natural solid and fluid inclusions in quartz. The influence of the geometrical parameters will be discussed with regard to the concentration determination by PIXE. In particular, accuracy of monazite micro-inclusion dating by coupled PIXE–RBS will be presented.

Long-Term Trends in Stream Nitrate Concentrations and Losses Across Watersheds Undergoing Recovery from Acidification in the Czech Republic

Stream nitrogen (N) export and nitrate \((\text {NO}^-_3) \) concentration were measured at 14 forested watersheds (GEOMON network) in the Czech Republic between 1994 and 2005. In the last several decades, emissions of sulfur (S) and N compounds have decreased throughout much of Europe. In the Czech Republic, atmospheric deposition of S has decreased substantially since the beginning of 1990s, whereas N deposition remains largely unchanged at most sites. The mean dissolved inorganic nitrogen (DIN) streamwater export ranged from 0.2 to 12.2 kg ha−1 y−1 at the GEOMON sites. Despite decades of elevated N deposition, 44–98% of DIN inputs to these watersheds were retained or denitrified, and many watersheds showed seasonal variation in nitrate concentrations. Dissolved organic N export was quantified in 1 year only and ranged from 0.05 to 3.5 kg ha−1 y−1. Spatial variability in DIN export among watersheds was best explained by spatial variability in average acidic deposition, particularly S deposition (R 2 = 0.81, P < 0.001); DIN input and forest floor carbon:nitrogen (C/N) also provided significant explanatory power. DIN export was strongly influenced by the forest floor C/N ratio and depth of the forest floor soils (R 2 = 0.72, P < 0.001). The only variable that predicted variations in forest floor C/N (R 2 = 0.32, P < 0.05) among watersheds was S deposition. Forest floor depth was also related to deposition variables, with S deposition providing the most explanatory power (R 2 = 0.50, P < 0.01). Variation in forest floor depth was also associated with climatic factors (precipitation and temperature). Temporal variability in DIN export was primarily associated with changes in acidic deposition over time; S deposition explained 41% of variability in DIN exports among all watersheds and years. Extensive acidification of forested watersheds was associated with the extraordinarily high S inputs to much of the Czech Republic during earlier decades. We hypothesize that recovery from acidification has led to improved tree health as well as enhanced microbial activity in the forest floor. As these watersheds move into a new regime with dramatically lower sulfur inputs, we expect continued declines in nitrate output.

Species and Spacing Effects of Northern Conifers on Forest Productivity and Soil Chemistry in a 50-Year-Old Common Garden Experiment

Species and Spacing Effects of Northern Conifers on Forest Productivity and Soil Chemistry in a 50-Year-Old Common Garden Experiment

Long-term effects of stump removal to control root rot on forest soil bulk density, soil carbon and nitrogen content

Removal of stumps and fertilization after harvesting have been proposed to reduce root diseases in succeeding stands. Potential impacts such as compaction and loss of soil C or N could limit the use of this technique. This research examined forest soils in five Pacific Northwest stands 22–29 years after stump removal and fertilization with N. Results show that small long-term soil bulk density increases caused by stump removal are not likely to either limit tree growth or discourage the use of stump removal to reduce root rot. However, an extended decrease was noted in mineral soil total N and C and forest floor depth caused by stump removal. The stumped areas show a mineral soil nitrogen concentration that is 20% lower than the non-stumped areas. Mineral soil carbon concentrations were 24% lower and the forest floor depth was 24% lower. A non-significant trend of lower foliar N was also observed with stump removal. These results were consistent in all five soil types. This reduction in the organic component of the soil may be a concern for nutrient cycling and long-term productivity on poor sites.

Fluxes of inorganic and organic arsenic species in a Norway spruce forest floor

To identify the role of the forest floor in arsenic (As) biogeochemistry, concentrations and fluxes of inorganic and organic As in throughfall, litterfall and forest floor percolates at different layers were investigated. Nearly 40% of total As total input (5.3 g As ha −1 yr −1) was retained in Oi layer, whereas As total fluxes from Oe and Oa layers exceeded the input by far (10.8 and 20 g As ha −1 yr −1, respectively). Except dimethylarsinic acid (DMA), fluxes of organic As decreased with depth of forest floor so that <10% of total deposition (all <0.3 g As ha −1 yr −1) reached the mineral soil. All forest floor layers are sinks for most organic As. Conversely, Oe and Oa layers are sources of As total, arsenite, arsenate and DMA. Significant correlations ( r ≥ 0.43) between fluxes of As total, arsenite, arsenate or DMA and water indicate hydrological conditions and adsorption–desorption as factors influencing their release from the forest floor. The higher net release of arsenite from Oe and Oa and of DMA from Oa layer in the growing than dormant season also suggests microbial influences on the release of arsenite and DMA.

ONTOGENY OF MOVEMENTS AND FORAGING RANGES IN THE AUSTRALIAN SEA LION

AbstractThis study tracked the movements of Australian sea lion (Neophoca cinerea) pups, juveniles, and adult females to identify home ranges and determine if young sea lions accompanied their mothers at sea. Satellite tags were deployed on nine 15‐mo‐old pups, nine 23‐mo‐old juveniles, and twenty‐nine adult female Australian sea lions at Seal Bay Conservation Park, Kangaroo Island, South Australia. Females did not travel with their offspring at sea, suggesting young Australian sea lions learn foraging behaviors independently. Although home ranges increased with age, 23‐mo‐old juveniles had not developed adult movement capacity and their range was only 40.6% of the adult range. Juveniles traveled shorter distances (34.8 ± 5.5 km) at slower speeds (2.0 ± 0.3 km/h) than adults (67.9 ± 3.5 km and 3.9 ± 0.3 km/h). Young sea lions also stayed in shallower waters; sea floor depths of mean locations were 48 ± 7 m for juveniles and 74 ± 2 m for females. Restricted to shallow coastal waters, pups and juveniles are more likely to be disproportionately impacted by human activities. With limited available foraging habitat, young Australian sea lions appear particularly vulnerable to environmental alterations resulting from fisheries or climate change.

The role of environmental factors and tree injuries in soil carbon respiration response to fire and fuels treatments in pine plantations

The need to understand how forest management practices affect soil CO2 exchange with the atmosphere (soil respiration) has increased with the recognition of a likely feedback effect of climate warming on soil respiration rates. Previous research addressing the mechanisms driving soil respiration has yielded inconsistent and/or conflicting results. This study looked to alternative above-ground forest characteristics to help explain spatial variability in soil respiration in a 30-year-old Sierra Nevada pine plantation. Fire hazard mitigation is one of the predominant management goals in these and other western US forests. Therefore, this analysis examined how fuels treatments, including shredding of understory vegetation (mastication), prescribed fire, and a combination thereof, affected soil respiration and its relationship to environmental factors and post-fire tree injuries. Multiple regression models indicated that mastication had no significant impact on soil respiration, but the roles of soil temperature and forest floor depth (O horizons) in the models increased after the treatment. Burning reduced soil respiration by ∼14%, and increased its sensitivity to tree proximity and the exposure of bare mineral soil. Scorch height in burned stands was negatively correlated with soil respiration. Models incorporating only tree injury or tree proximity parameters explained between 63% and 91% of the variability in burned plantations. This work suggests that measures of above-ground forest features can increase understanding of management impacts on soil respiration, and the mechanisms by which these impacts occur. These results are especially applicable in Mediterranean climates, where moisture stress reduces the effectiveness of soil microclimate in explaining soil respiration.

Evidence that floodwaters filled and overflowed Capri Chasma, Mars

Erosional features on a plateau in the Valles Marineris provide evidence that a lake filled Capri Chasma until it overflowed its eastern rim, carving two large spillover channels. The floodwaters surged into the adjacent lowlands of ancestral Ganges Chasma and eastern Eos Chasma. The channel floor elevation and depth of incision at Daga Vallis reveal that a 1200‐m‐deep lake water column was drained by the flooding. The width, depth, and steep energy slope (∼0.02) of Daga Vallis and the existence of several cataracts, including a 500‐m‐high dry falls, demonstrate the power of the floodwaters. We estimate a possible peak discharge rate of 1–6 × 108 m3·s−1. The catastrophic flows may have been triggered by the collapse of topographic barriers in eastern Coprates Chasma, providing a gateway for lake waters in the central Valles Marineris to pour eastward toward Capri Chasma and the lowlands beyond. These may have been among the earliest flows in Simud‐Tiu Valles, contributing discharge to a possible sea in the northern plains of Mars.

Changes in soil properties, tree growth, and nutrition over a period of 10 years after stump removal and scarification on moderately coarse soils in interior British Columbia

Silvicultural site preparation treatments that involve severe soil and forest floor disturbance may, in the long-term, reduce soil productivity and negate the initial increased forest productivity obtained by controlling root diseases or vegetation. The effect of a range of stump removal treatments on selected soil chemical and physical properties, and growth of planted lodgepole pine ( Pinus contorta) and hybrid spruce ( Picea glauca (Moench) Voss × Picea engelmanii Parry), was examined at three sites in the Interior Cedar–Hemlock (ICH) zone of British Columbia. Changes in forest floor and mineral soil chemistry and bulk density were measured 1 year after treatment and again 9 years later. Tree growth and foliar nutrient status of planted seedlings were measured 3, 5 and 10 years after planting. Forest floor mass and depth were altered by treatment, and decreased significantly between years 1 and 10. Mineral soil bulk density was greater in all stump-removal treatments than in the non-stumped treatment in year 1; however, 10 years after treatment, bulk densities had decreased and no treatment effects were apparent. Changes in forest floor chemistry that were measured in year 1 had largely disappeared by year 10. Mineral soil chemical concentrations were not affected by treatment at any time, except for a significant increase in carbon (C) concentration between years 1 and 10. Lodgepole pine height and diameter were increased over the measurement period by the most intense, scarified treatment, whereas spruce growth was largely unaffected by stump removal treatment. Both tree growth and soil measurements suggest that, on the moderately coarse soils within the climatic regime of the present study, soil limits to tree growth have not been exceeded.

A new expression for the direct calculation of the maximum wave force on vertical cylinders

Here, an easy analytical solution for the direct calculation of the instant in which the maximum wave force on a support of an offshore platform is realized, and for the direct estimation of the aforementioned maximum force. The solution is obtained thanks to an artifice. The instant is expressed t m of the maximum force as limits of a succession t m 0 , t m 1 , t m 2 , … , and it is proved that in cases of practical interests the successions converge very quickly: t m = t m 1 , less than negligible errors. The solution allows the estimate of useful synthesis to be arrived at in the preliminary phase of the project. In fact, it allows one to immediately appreciate the effects of variations of the parameters in play: the sections of the cylinder, the depth of the sea floor and the characteristics of the waves.

Marine ice-sheet dynamics. Part 1. The case of rapid sliding

Marine ice sheets are continental ice masses resting on bedrock below sea level. Their dynamics are similar to those of land-based ice sheets except that they must couple with the surrounding floating ice shelves at the grounding line, where the ice reaches a critical flotation thickness. In order to predict the evolution of the grounding line as a free boundary, two boundary conditions are required for the diffusion equation describing the evolution of the grounded-ice thickness. By analogy with Stefan problems, one of these conditions imposes a prescribed ice thickness at the grounding line and arises from the fact that the ice becomes afloat. The other condition must be determined by coupling the ice sheet to the surrounding ice shelves. Here we employ matched asymptotic expansions to study the transition from ice-sheet to ice-shelf flow for the case of rapidly sliding ice sheets. Our principal results are that the ice flux at the grounding line in a two-dimensional ice sheet is an increasing function of the depth of the sea floor there, and that ice thicknesses at the grounding line must be small compared with ice thicknesses inland. These results indicate that marine ice sheets have a discrete set of steady surface profiles (if they have any at all) and that the stability of these steady profiles depends on the slope of the sea floor at the grounding line.

Characterization/Modeling of Wire Screen Insulation for Deep-Water Pipes

The amount of oil consumption has been rapidly increas ing around the world; consequently , industries have expanded to offshore exploration in to deep sea waters . At sea floor depths , pipe insulation is essential to prevent the blockage with in the pipe due to paraffin build -up within crude oil . To maintain a proper inner crude oil temperature , ab ove the paraffin formation point, insulation techniques have been used to overcome the thermal issue , but these technologies still have limitations. In this study, the objective was to develop an analytical model for a wire screen joint which contained bo th nonconforming and conforming interfaces , and then compare the predicted results to experimental measured data for validation. The experimental study for this novel insulation techn ology consisted of a coaxial pipe fabricated from P110 -4140 steel with a low conductivity wire screen (Stainless Steel) as the interstitial insulation material inserted at the annulus .

Thinning and Prescribed Fire Effects on Fuels and Potential Fire Behavior in an Eastern Cascades Forest, Washington, USA

Prescribed fire and low thinning were applied to dry forests dominated by ponderosa pine (Pinus ponderosa) and Douglas-fir (Pseudotsuga menziesii) in the eastern Washington Cascades. Experimental design was an unbalanced analysis of variance with 4 control units, 4 thin units, 2 burn units and 2 thin/burn units. Thinning was designed to reduce basal area to 10–14 m2 ha−1 in a non-uniform pattern and burning was a low intensity spring burn. Burn coverage was spotty, ranging from 23–51%, and considered ineffective in reducing fuels at the time of application by management and research personnel. Both thinning and burning had effects on vegetation and fuels variables. Thinning reduced canopy closure, canopy bulk density, and basal area, and increased canopy base height. Burning had no influence on these canopy variables. Thinning increased 10-hr timelag (0.62–2.54 cm) fuels. Burning decreased 1-hr (0–0.62 cm) and 10-hr timelag fuels, forest floor depth and mass, and increased fuelbed depth. There were interactions between thinning and burning for 1-hr and 10-hr timelag fuels, and fuelbed depth. These differences in fuel properties did not translate into differences in simulated wildfire behavior and tree mortality. Thinning did increase potential surface fire flame length under 97 percentile weather, and active crown fire potential decreased on thinned units, but basal area survival did not significantly differ between treatments under 80 and 97 percentile weather. The scale at which data are presented has a large influence on interpretation of results. For example, torching fire behavior, expressed as an average at the unit level, was low, but 17% of the individual plots (about 30 plots total per unit) across all treatments did exhibit potential torching behavior.

Analysis of behaviour of steel beams with web openings at elevated temperatures

Beams with web openings are an attractive system for multi-storey buildings where it is always desirable to have long spans. The openings in the web of steel beams enable building services to be integrated within the constructional depth of a floor, thus reducing the total floor depth. At the same time, the increased beam depth can give high bending moment capacity, thus allowing long spans. However, almost all of the research studies on web openings have been concentrated on beam behaviour at ambient temperature. In this paper, a preliminary numerical analysis using ABAQUS is conducted to develop a general understanding of the effect of the presence of web opening on the behaviour of steel beams at elevated temperatures. It is concluded that the presence of web openings will have substantial influence on the failure temperatures of axially unrestrained beams and the opening size at the critical position in the beam is the most important factor. For axially restrained beams, the effect of web openings on the beam\'s large deflection behaviour and catenary force is smaller and it is the maximum opening size that will affect the beam\'s response at very high temperatures. However, it is possible that catenary action develops in beams with web openings at temperatures much lower than the failure temperatures of the same beam without axial restraint that are often used as the basis of current design.

Community Genomics Among Stratified Microbial Assemblages in the Ocean's Interior

Microbial life predominates in the ocean, yet little is known about its genomic variability, especially along the depth continuum. We report here genomic analyses of planktonic microbial communities in the North Pacific Subtropical Gyre, from the ocean's surface to near-sea floor depths. Sequence variation in microbial community genes reflected vertical zonation of taxonomic groups, functional gene repertoires, and metabolic potential. The distributional patterns of microbial genes suggested depth-variable community trends in carbon and energy metabolism, attachment and motility, gene mobility, and host-viral interactions. Comparative genomic analyses of stratified microbial communities have the potential to provide significant insight into higher-order community organization and dynamics.

Snag and woody debris dynamics following severe wildfires in northern Arizona ponderosa pine forests

Following severe wildfires in southwestern ponderosa pine forests, dead trees remain on the landscape and eventually fall, but relatively little is known about the quantity and quality of post-wildfire coarse woody debris (CWD). To describe post-fire conditions, we measured snags, CWD, and fine woody debris and forest floor depth on seven fires in a chronosequence from 3 to 27 years old in northern Arizona. Snags declined in density with increasing time since fire and generally followed expected patterns of decay, except that few snags stood long enough to reach a clean-bark state. The mean biomass of the surface CWD ranged from as low of 3.3 Mg ha −1 to a high of 41.3 Mg ha −1. Total CWD biomass in the surface fuel load remained roughly comparable from 8–9-year-old fires to a 27-year-old fire but the state of the CWD changed from sound to rotten. The change to a rotten condition suggests an increase in ignitability of the post-fire fuel load, but fine fuels that could support high fireline intensity were relatively low. The number of “jackstraws,” points where intersecting downed logs could create a hot spot if reburned, was slightly higher in the oldest fire. Few fire-created snags remained by the 27th year post-fire. Management options to reduce fuels after severe wildfire, such as salvage logging, prescribed burning, or passive management, should be addressed in a broad ecological context.

Stocks, Chemistry, and Sensitivity to Climate Change of Dead Organic Matter Along the Canadian Boreal Forest Transect Case Study

Improving our ability to predict the impact of climate change on the carbon (C) balance of boreal forests requires increased understanding of site-specific factors controlling detrital and soil C accumulation. Jack pine (Pinus banksiana) and black spruce (Picea mariana) stands along the Boreal Forest Transect Case Study (BFTCS) in northern Canada have similar C stocks in aboveground vegetation and large woody detritus, but thick forest floors of poorly-drained black spruce stands have much higher C stocks, comparable to living biomass. Their properties indicate hindered decomposition and N cycling, with high C/N ratios, strongly stratified and depleted δ13C and δ15N values, high concentrations of tannins and phenolics, and 13C nuclear magnetic resonance (NMR) spectra typical of poorly decomposed plant material, especially roots and mosses. The thinner jack pine forest floor appears to be dominated by lichen, with char in some samples. Differences in quantity and quality of aboveground foliar and woody litter inputs are small and unlikely to account for the contrasts in forest floor accumulation and properties. These are more likely associated with site conditions, especially soil texture and drainage, exacerbated by increases in sphagnum coverage, forest floor depth, and tannins. Small changes in environmental conditions, especially reduced moisture, could trigger large C losses through rapid decomposition of forest floor in poorly drained black spruce stands in this region.

Response of ground beetle (Carabidae) assemblages to logging history in northern hardwood–hemlock forests

We quantified differences in ground beetle (Coleoptera: Carabidae) communities in relation to forest management practices and historic forest cover changes in hardwood–hemlock forests of the north central United States. Beetles were sampled with pitfall traps in 1996 and 1997 and compared among three forest types: old-growth, and post-logging uneven- and even-aged forests. Non-metric multidimensional scaling ordination was used to assess compositional differences among forest types for 39 carabid species (43,483 individuals), which revealed distinct differences in beetle assemblages among forest types. Coarse woody debris, snag volume, gap area, understory vegetation and forest floor depth were significantly correlated with ordination axes suggesting that these variables are critical in structuring the beetle communities. Several of the species significantly associated with old-growth forests, like Carabus sylvosus, are known to favor forest habitats, whereas species commonly found in open habitats, such as Carabus nemoralis, had stronger affiliations with managed forests. Comparisons of northern hardwood–hemlock forest distribution from pre-Euroamerican settlement with current distributions reconstructed using the Forest Inventory and Analysis database indicate that old-growth habitat has declined to <1% of its original extent in this region. At the landscape level, these data suggest that the abundance of carabid species that prefer old-growth forest conditions has undergone broad-scale decline.

Spatial Distribution of Ammonium and Calcium in Optimally Fertilized Pine Plantation Soils

Commercial timber production is increasingly reliant on long‐term fertilization to maximize stand productivity, yet we do not understand the extent to which this practice homogenizes soil properties. The effects of 16 yr of optimal fertilization and optimal fertilization with irrigation (fertigation) on forest floor depth, pH, total organic carbon (TOC) and total nitrogen (TN) content, and concentrations of potentially plant available NH4+, Ca2+, Mg2+, and Al3+ in the fine root zone of monoculture loblolly pine (Pinus taeda L.) stands in North Carolina were examined. Generally, optimal fertilization significantly increased forest floor depth and the concentrations of potentially plant available NH4+, Ca2+, and Mg2+ No significant effects on TOC or TN were observed. However, differences were observed between optimally fertilized and fertigated treatments. Specifically, fertilization alone tended to retain more Ca2+ and Mg2+ in the root zone and to increase pH more than fertigation. Semivariogram analysis indicated optimal fertilization generally lead to a significant increase in the effective spatial autocorrelation ranges of NH4+ and Ca2+ at the end of the growing season, from approximately 25 m in controls to more than 100 m. However, optimally fertilized and fertigated plots differed in terms of their NH4+ and Ca2+ spatial autocorrelation ranges, with the ranges in fertigated plots being 1.5‐ to 2‐fold greater. A comparison of kriged maps of NH4+ and Ca2+ availability in fall 2000 and spring 2001 suggested that the spatial distribution of Ca2+, which has not been added to these soils for 6 yr, was stable, whereas the heterogeneity of NH4+ distribution increased post fertilization.