Sandy Sites Research Articles

Scaling the Hydraulic Functions of A Water Repellent Sandy Soil

Abstract The heterogeneity of both unsaturated hydraulic conductivity and water retention was measured with a high spatial resolution on a transect using an evaporation method. Fifteen undisturbed 100 cm3 soil cores were taken on a transect every 10 cm from the topsoil of a water repellent sandy site. Five dynamic water retention curves and four unsaturated conductivity curves were determined for each core. We conducted measurements without further saturation in the laboratory in order to achieve field-like conditions. The initial water contents were heterogeneous, indicating different hysteretic conditions and water repellent areas. The scattering of the water retention curves was high, while the heterogeneity of unsaturated conductivity curves was unexpectedly low. Two scaling approaches were used to describe the heterogeneity: one with and one without considering hysteresis. The concept of scaling applies well to describing the heterogeneity of both hydraulic functions. Including hysteresis leads to similar results than excluding hysteresis. The distribution of the hydraulic conductivity and the water retention were independent from each other. The results give important information for numerical simulation of the water flow with heterogeneous hydraulic functions.

Black spruce growth response to varying levels of biomass harvest intensity across a range of soil types: 15-year results

With a growing interest in the diversification (e.g., bioenergy, biochemicals) of the forest industry beyond the traditional product streams, concerns that higher harvest utilization levels may compromise site productivity have been heightened. This study reports on 15-year tree growth responses to varying levels of biomass removals conducted on four soil types: loamy tills, outwash sands, wet mineral, and peatlands. Experimental harvest treatments included stem-only, full-tree, full-tree chipping (a full-tree harvest with the roadside material chipped and returned to the site), and full-tree + bladed (a full-tree harvest followed by forest floor removal). Results indicated no significant effect on height growth on the loamy tills, a significant decline for the blading treatment on the sandy soils, and an increase when the blading treatment was applied to the peatland sites. At the stand level, better planted seedling survival and higher recruitment of naturals on the more extreme removal treatment (forest floor removal on sandy sites) tended to nullify any negative impacts identified in the individual-tree growth measurements. The more than doubling of the slash loading on the stem-only treatment plots compared with the full-tree plots did not result in differences in tree productivity levels between these two operational treatments. The stands, however, were just approaching crown closure by year 15, suggesting that ongoing monitoring will be required to confirm that the growth trajectories for the various harvest treatment – soil type combinations can be maintained.

Predicting the responsiveness of soil biodiversity to deforestation: a cross‐biome study

The consequences of deforestation for aboveground biodiversity have been a scientific and political concern for decades. In contrast, despite being a dominant component of biodiversity that is essential to the functioning of ecosystems, the responses of belowground biodiversity to forest removal have received less attention. Single-site studies suggest that soil microbes can be highly responsive to forest removal, but responses are highly variable, with negligible effects in some regions. Using high throughput sequencing, we characterize the effects of deforestation on microbial communities across multiple biomes and explore what determines the vulnerability of microbial communities to this vegetative change. We reveal consistent directional trends in the microbial community response, yet the magnitude of this vegetation effect varied between sites, and was explained strongly by soil texture. In sandy sites, the difference in vegetation type caused shifts in a suite of edaphic characteristics, driving substantial differences in microbial community composition. In contrast, fine-textured soil buffered microbes against these effects and there were minimal differences between communities in forest and grassland soil. These microbial community changes were associated with distinct changes in the microbial catabolic profile, placing community changes in an ecosystem functioning context. The universal nature of these patterns allows us to predict where deforestation will have the strongest effects on soil biodiversity, and how these effects could be mitigated.

Microbial residue indices down the soil profile after long-term addition of farmyard manure and mineral fertilizer to a sandy soil

Long-term organic fertilization may control the accumulation of organic matter in subsoil. The objective of this study was to evaluate the effects of long-term farmyard manure application in comparison with mineral fertilization on the accumulation of amino sugars as indices for microbial residues down to 1m depth at a sandy site that exhibits highly heterogeneous pH conditions. In relation to maximum values in topsoil at 90–100cm depth, the SOC content decreased to roughly 24% and the total N content to 16% of the maximum values, leading to an increased soil C/N ratio from 11 to values around 16 in all treatments. The relative contribution of microbial residue C to SOC decreased with depth from 68% at 0–25cm to 24% at 50–100cm. In the subsoil, the stocks of microbial residue C were increased by manure in comparison with mineral fertilization, but not the stocks of SOC. This suggests that manure-induced priming effects increase the microbial turnover at 50–100cm depth. Manure fertilization promoted the formation of bacterial residues in the topsoil at 0–25cm depth, but not in the subsoil. Below the topsoil, the fungal C to bacterial C ratio decreased from 2.6 at 0–25cm depth to 2.1 at 50–100cm depth. Below the topsoil, the ratio of fungal to bacterial residues continuously decreased with depth from 2.7 to 1.7 at 90–100cm depth, without fertilizer effects. Possible reasons for this decrease, such as effects of pH on the subsoil microbial community, a higher sensitivity of fungi to the absence of fresh organic matter or to an unfavourable composition of the subsoil atmosphere, need further investigations.

Keeping agricultural soil out of rivers: Evidence of sediment and nutrient accumulation within field wetlands in the UK

Intensification of agriculture has resulted in increased soil degradation and erosion, with associated pollution of surface waters. Small field wetlands, constructed along runoff pathways, offer one option for slowing down and storing runoff in order to allow more time for sedimentation and for nutrients to be taken up by plants or micro-organisms. This paper describes research to provide quantitative evidence for the effectiveness of small field wetlands in the UK landscape. Ten wetlands were built on four farms in Cumbria and Leicestershire, UK. Annual surveys of sediment and nutrient accumulation in 2010, 2011 and 2012 indicated that most sediment was trapped at a sandy site (70 tonnes over 3 years), compared to a silty site (40 tonnes over 3 years) and a clay site (2 tonnes over 3 years). The timing of rainfall was more important than total annual rainfall for sediment accumulation, with most sediment transported in a few intense rainfall events, especially when these coincided with bare soil or poor crop cover. Nutrient concentration within sediments was inversely related to median particle size, but the total mass of nutrients trapped was dependent on the total mass of sediment trapped. Ratios of nutrient elements in the wetland sediments were consistent between sites, despite different catchment characteristics across the individual wetlands. The nutrient value of sediment collected from the wetlands was similar to that of soil in the surrounding fields; dredged sediment was considered to have value as soil replacement but not as fertiliser. Overall, small field wetlands can make a valuable contribution to keeping soil out of rivers.

Effects of Biomass Removals on Site Carbon and Nutrients and Jack Pine Growth in Boreal Forests

As international demand for renewable energy and forest biomass increases, there is considerable debate about the effect of increased removals on long‐term soil productivity. Carbon and nutrient contents of the aboveground biomass, forest floor, and mineral soil were determined at 14 boreal forest sites in northern Ontario. At each site, three treatments were performed: tree‐length harvesting (OM0), full‐tree harvesting (OM1) and full‐tree harvesting plus forest floor removal (OM2). Theoretical and actual estimates of biomass removal for OM0 and OM1 were determined. Jack pine (Pinus banksiana Lamb.) dominant height increments from Years 10 to 15 (HD10‐15) were determined as a measure of site productivity. A nutrient budget approach was used to estimate C and nutrient removal and retention and to calculate stability ratios (i.e., ratio of nutrient removed during harvest to post‐harvest nutrient reserve) and nutrient replacement times. The OM1 treatment removed 65% of the potentially available biomass; on average 27 Mg ha−1 of unutilized biomass was burned in slash piles. The OM1 harvesting residue retention values coincided with guidelines of jurisdictions that recommend retaining one‐third of residues on site after bioenergy harvesting. The OM0 and OM1 C and nutrient removals were more similar than estimated in previous studies. Base cation stability ratios and nutrient replacement times gave opposite interpretations in terms of which sites were more sensitive to biomass removal treatments. For sandy sites with thin forest floor horizons HD10–15 responded positively to increased post‐harvest soil C reserves, but for sites with thick forest floors, organic matter accumulation became a detriment to increased growth.

Contrasting Hydraulic Strategies during Dry Soil Conditions in Quercus rubra and Acer rubrum in a Sandy Site in Michigan

Correlation analyses were carried out for the dynamics of leaf water potential in two broad-leaf deciduous tree species in a sandy site under a range of air vapor pressure deficits and a relatively dry range of soil conditions. During nights when the soil is dry, the diffuse-porous, isohydric and shallow-rooted Acer rubrum does not recharge its xylem and leaf water storage to the same capacity that is observed during nights when the soil is moist. The ring-porous, deep-rooted Quercus rubra displays a more anisohydric behavior and appears to be capable of recharging to capacity at night-time even when soil moisture at the top 1 m is near wilting point, probably by accessing deeper soil layers than A. rubrum. Compared to A. rubrum, Q. rubra displays only a minimal level of down-regulation of stomatal conductance, which leads to a reduction of leaf water potential during times when vapor pressure deficit is high and soil moisture is limiting. We determine that the two species, despite typically being categorized by ecosystem models under the same plant functional type—mid-successional, temperate broadleaf—display different hydraulic strategies. These differences may lead to large differences between the species in water relations, transpiration and productivity under different precipitation and humidity regimes.

Physical and biological controls on trace gas fluxes in semi-arid urban ephemeral waterways

Rapid increases in human population and land transformation in arid and semi-arid regions are altering water, carbon (C) and nitrogen (N) cycles, yet little is known about how urban ephemeral stream channels in these regions affect biogeochemistry and trace gas fluxes. To address these knowledge gaps, we measured carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) before and after soil wetting in 16 ephemeral stream channels that vary in soil texture and organic matter in Tucson, AZ. Fluxes of CO2 and N2O immediately following wetting were among the highest ever published (up to 1,588 mg C m−2 h−1 and 3,121 μg N m−2 h−1). Mean post-wetting CO2 and N2O fluxes were significantly higher in the loam and sandy loam channels (286 and 194 mg C m−2 h−1; 168 and 187 μg N m−2 h−1) than in the sand channels (45 mg C m−2 h−1 and 7 μg N m−2 h−1). Factor analyses show that the effect of soil moisture, soil C and soil N on trace gas fluxes varied with soil texture. In the coarser sandy sites, trace gas fluxes were primarily controlled by soil moisture via physical displacement of soil gases and by organic soil C and N limitations on biotic processes. In the finer sandy loam sites trace gas fluxes and N-processing were primarily limited by soil moisture, soil organic C and soil N resources. In the loam sites, finer soil texture and higher soil organic C and N enhance soil moisture retention allowing for more biologically favorable antecedent conditions. Variable redox states appeared to develop in the finer textured soils resulting in wide ranging trace gas flux rates following wetting. These findings indicate that urban ephemeral channels are biogeochemical hotspots that can have a profound impact on urban C and N biogeochemical cycling pathways and subsequently alter the quality of localized water resources.

Reflection-coefficient inversion for compressional- and shear-wave dispersion in porous and elastic layered media

This paper considers Bayesian inversion of seabed reflection-coefficient data for the compressional- and shear-wave velocity dispersion and attenuation-frequency dependence in arbitrarily layered porous and elastic media. The seabed is modeled using Buckingham's viscous grain shearing model which obeys causality. Seabed layers are parametrized in terms of six fundamental parameters, including thickness, porosity, compressional and shear grain-to-grain moduli, material exponent, and the compressional visco-elastic time constant. These fundamental parameters are used to compute density, compressional- and shear-wave dispersion curves, and compressional and shear attenuation-frequency curves for each layer. The curves are used in the inversion to predict spherical-wave reflection coefficients as a function of frequency (300–3000 Hz) and grazing angle (12–75 degrees), which include the effects of shear waves in arbitrarily layered media. In addition, the seabed layering is estimated from the data by applying a trans-dimensional Bayesian model. The ability to resolve shear-wave velocity and attenuation structure is studied using simulated data. Finally, compressional- and shear-wave dispersion are presented and discussed from measured reflection data at a sandy site in the Tyrrhenian Sea. [Work supported by ONR Ocean Acoustics.]

In situ measurements of sediment sound speed in the frequency band of 2–10 kHz at target and reverberation experiment site

As part of the environmental measurements for TREX13 (Target and Reverberation EXperiment 2013), in situ measurements of surfacial sediment sound speed were carried out off Panama City, Florida, using a system called Sediment Acoustic-speed Measurement System (SAMS). SAMS consists of ten fixed sources positioned just above the seafloor, and one receiver which is driven into the seabed to a known depth. During TREX13, 10 deployments were made along the main reverberation track which is about 7.5 km in length. All measurements were made at a penetration depth of 3m between 2 to 50 kHz, focusing on 2–10 kHz. Preliminary sediment sound speed results show variation from low sound speeds (muddy sites) to high sound speeds (sandy sites). A 3–5% of dispersion was observed at coarse sandy sites between 2 and 10 kHz, whereas little dispersion was observed at muddy sites. [Work supported by ONR.]

Near-bed gradients in particles and nutrients above a mussel bed in the Limfjorden: influence of physical mixing and mussel filtration

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 490:137-146 (2013) - DOI: https://doi.org/10.3354/meps10444 Near-bed gradients in particles and nutrients above a mussel bed in the Limfjorden: influence of physical mixing and mussel filtration Jens Kjerulf Petersen1, Marie Maar2,*, Tom Ysebaert3,4, Peter M. J. Herman3 1Dansk Skaldyrcenter, Øroddevej 80, 7900 Nykøbing Mors, Denmark 2Aarhus University, Department of Bioscience, PO Box 358, Frederiksborgvej 399, 4000 Roskilde, Denmark 3Royal Netherlands Institute for Sea Research (NIOZ), PO Box 140, 4400 AC Yerseke, The Netherlands 4Institute for Marine Resources and Ecosystem Studies (IMARES), PO Box 77, 4400 AB Yerseke, The Netherlands *Corresponding author. Email: mam@dmu.dk ABSTRACT: The aim of this field study was to investigate the role of mussels on near-bed layer characteristics at different hydrodynamic regimes in a micro-tidal system. At Løgstør Broad, the Limfjorden, Denmark, we deployed ‘siphon mimics’ to sample chlorophyll a (chl a), particulate organic carbon (POC) and inorganic nutrients at different distances above the bottom. This was done without disturbing water column gradients and in a manner similar to mussel incurrent flow. Mimics were deployed at 2 sites: a site with a relatively dense mussel bed and a nearby sandy site without mussels. During the 2 wk field campaign, physical conditions in the fjord varied from extremely calm weather with low waves to quite windy with high waves. Results showed that under all conditions, the vertical concentration profiles of chl a were significantly depleted towards the mussel bed due to mussel filtration, whereas the degree of chl a depletion was correlated to wave height. Nutrient profiles consistently showed increasing concentration profiles towards the bed, identifying the mussel bed and the sediment as a source of nutrients with the highest gradients during the period with high waves. In conclusion, the near-bed concentrations of seston and nutrients in this study were temporally variable and closely linked to the physical structure of the water column. KEY WORDS: Depletion · Nutrient flux · Mixing · Mussel filtration · Wind forcing · Mytilus edulis Full text in pdf format PreviousNextCite this article as: Petersen JK, Maar M, Ysebaert T, Herman PMJ (2013) Near-bed gradients in particles and nutrients above a mussel bed in the Limfjorden: influence of physical mixing and mussel filtration. Mar Ecol Prog Ser 490:137-146. https://doi.org/10.3354/meps10444 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 490. Online publication date: September 17, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.

Vegetation of Thumamah Nature Park: a managed arid land site in Saudi Arabia

Thumamah Nature Park is located at about 100 km north of Arriyadh (Saudi Arabia), having an area of 170 km2. The Park was established since 30 years ago. The aim of this study is to analyze the vegetation structure in relation to the environmental factors in different habitat types. The phenological activities around the year of the 20 dominant species were monitored. 119 species were identified, of which 51 (43 %) annuals and 68 (57 %) perennials after 30 years of exclusive human impact. The Saharo-Arabian component species were the highest among the monoregional species (64 %) in most life forms, while the Sahelien-Somali Masai attained the highest among the biregionals (46 %). The TWINSPAN, DCA and CCA analyses separated seven vegetation groups. The first two groups were dominated by psammophytic species, which occupy the lower sandy plain as shown in group I with Rhanterium epapposum–Rhazya stricta and group II with Pennisetum divisum–Haloxylon salicornicum. The escarpment habitat was characterized by three groups, viz., group III with Acacia gerrardii–Panicum turgidum, group IV with Panicum turgidum and group V with Acacia ehrenbergiana–Lasiurus scindicus. Vegetation in the upland plateau was represented by the remaining two groups; group VI with Helianthemum lippii and group VII with Helianthemum kahiricum. The environmental variables that affect the species distribution and diversity in the park include the altitude, soil texture, pH, EC, Ca, Mg and Mn. The increased plant species richness, turnover, evenness and cover were mostly due to the increase of the herbaceous species. Plant populations showed interspecific variations in their relative timing of phenological phases with reproductive activity period ranged between 3 and 6 months with unimodal flowering peak. Three flowering-fruiting activities were recorded during late winter–spring, summer and late autumn–early winter. In an attempt to explain the vegetation dynamics after 30 years conservation, the progressive succession varied among the different habitat types, including the lower sandy sites, the escarpment and the upland rocky habitats, which reflect the relationship between altitude, edaphic factors and the type of vegetation units in each habitat type after exclusion of the human impact.

Non-trophic Interactions Control Benthic Producers on Intertidal Flats

The importance of positive effects of ecosystem engineers on associated communities is predicted to increase with environmental stress. However, incorporating such non-trophic interactions into ecological theory is not trivial because facilitation of associated species is conditional on both the type of engineer and the type of abiotic stress. We tested the influence of two allogenic ecosystem engineers (lugworms, Arenicola marina L. and cockles, Cerastoderma edule L.) on the main primary producers (microphytobenthos) of the tidal flats, under different abiotic stresses controlled by reefs of blue mussels (Mytilus edulis L.). We added 25,000 cockles or 2,000 lugworms to 5 × 5 m plots, both in a muddy site with high sedimentation rates located coastward of a mussel bed, and in a sandy site without mussels and characterized by high hydrodynamic stress. After a year, cockles increased algal biomass in the sandy area, but not in the mussel bed site, where high values were measured in all plots. However, lugworms did not affect algal biomass in any of the sites. Field measurements suggest that cockles outweighed negative effects of water currents in the site without mussels by locally increasing sediment stability, whereas mussels overruled the effects of cockles in the wake of the reefs through hydrodynamic stress alleviation and/or biodeposition. Our results suggest that non-trophic interactions by ecosystem engineering bivalves control primary production of intertidal areas, and that the sediment-stabilizing effect of cockles plays a crucial role where the overruling effects of mussel beds are not present.

Dramatic losses of specialist arable plants in Central Germany since the 1950s/60s – a cross‐regional analysis

AbstractAimTo assess the consequences of agricultural intensification since the 1950s for Central Europe's plant communities of arable plants.LocationCentral Germany.MethodsWe employed a semipermanent plot design to analyse changes in 392 field interiors for 10 study regions, including sandy, limestone and loamy sites between the 1950s/60s and 2009.ResultsThe analysis revealed a reduction in the regional species pool during the 50‐year period of 23% (from 301 to 233 vascular species) and dramatic losses in plot‐level diversity (from medians of 24 to 7). Median cover of spontaneously growing arable plants decreased from 30% to 3%. Losses were disproportionally larger on limestone sites while sandy sites maintained a larger fraction of the original diversity. Archaeophytes, neophytes and most Poaceae (including some aggressive weeds) showed similarly strong losses as indigenous plants. This contradicts the assumption that grasses and neophytes are generally profiting from agricultural intensification. Crop diversity decreased from 25 crop plants present in the 1950s/60s to only 16 in 2009, while crop cover generally increased. Winter cereals, oilseed rape and maize are dominant today, while all other crop types showed strong declines.Main conclusionsVegetation change over time depended on soil substrate with once markedly different arable communities now showing more homogenized community structure. Increasing Ellenberg indicator values for nitrogen and pH point to N fertilization as a major driver of change. New conservation measures such as the establishment of field flora reserves and agri‐environment schemes with less intensive land use are thus urgently needed especially on limestone substrates to bring an end to the decline of this functionally distinct and increasingly threatened component of the Central European flora.

The influence of ground disturbance and gap position on understory plant diversity in upland forests of southern New England

The forest understory contains the majority of vascular plant diversity in eastern temperate forests, and its diversity, composition, and dynamics contribute directly to ecosystem function. Forest managers have traditionally viewed the understory as primarily affecting forest regeneration or wildlife habitat, but the growing recognition of goods and services the understory provides (e.g., ecosystem function, ecological resiliency, non-timber forest products) has increased concerns about the impacts of forest management on understory diversity. We monitored response of understory diversity to microsite position and degree of ground-level disturbance within experimental gaps for 10years. We did this at four sites with distinct soil types and topographic positions of a glacial geology in southern New England that were categorized as (i) mesic, (ii) mid-slope, (iii) outwash, and (iv) sandy-skeletal. We analyzed differences in patterns of species richness, Shannon diversity, and evenness across sites and through time. Understory species richness was generally enhanced by gap formation. Gap position was the primary factor influencing species richness across all sites, but the patterns of diversity and evenness within gaps was site specific. Ground-disturbance was influential on drier sandy sites, and more pronounced earlier in the experiment. Temporal differences were also evident across sites, with richness stabilizing at all sites 10years after gap creation. The one exception was the sandy-skeletal site, which was still increasing in richness. Resource managers interested in protecting and enhancing understory species diversity need to consider underlying site, specifically soil type when planning silvicultural treatments, as the response of the understory community to disturbance can vary greatly with site.

Application of non-linear quantile regression to macrozoobenthic species distribution modelling: comparing two contrasting basins

The occurrence and distribution of macrozoobenthos in estuaries are strongly related to sediment grain-size characteristics. However, statistical prediction of the distribution of benthic populations as a response to a single environmental gradient has proven to be difficult, because the focal variable may set upper limits to the abundance, but other (partly uncorrelated) variables may cause considerable deviation from the maximum. A multi-quantile regression approach is better suited to characterize biota–environment relationships than a single (average or boundary) estimation, because it shows the variation in responses and quantifies the relative importance of other unmeasured factors. Here, a univariate application of non-linear quantile regression is proposed to account for heteroskedasticity and non-linearity in the biological response to sediment grain size. The analysis was applied to a large macrozoobenthic dataset from the SW Delta area (The Netherlands) to compare the relationships between sediment granulometry and macrozoobenthos in 2 neighboring but differing temperate coastal ecosystems (Oosterschelde and Westerschelde). Preference of individual species for grain size was consistent between both systems, although in general, a slightly higher median grain size (ca. +60% in grain diameter) was preferred in the Oosterschelde than in the Westerschelde. The major difference in the community was, however, that mud-preferring species dominated the assemblage in the Westerschelde, and sand-preferring species dominated the Oosterschelde. Although the prevalence of muddy and sandy sediments in both systems is similar, in the Westerschelde, strong hydrodynamic stress is correlated with sandy habitats, causing impoverishment of assemblages at sandy sites. In the Oosterschelde, sandy sediments are usually associated with much more benign conditions and have the richest species assemblage.

Coarse Woody Debris Dynamics Following Biomass Harvesting: Tracking Carbon and Nitrogen Patterns During Early Stand Development in Upland Black Spruce Ecosystems

Coarse woody debris (CWD) in the boreal ecosystem has been hypothesized to play an important nutritional role following stand-replacing disturbances such as fire or harvest. Sites with shallow soil over bedrock, or those with coarse-textured soils, can be especially susceptible to overstory removal because low carbon and nutrient pools may limit stand productivity in subsequent rotations. On these site types, CWD can provide essential nutrition to the developing second growth stand, prior to internal cycling processes stabilizing at crown closure (15 years to 20 years after stand initiation) through slow and steady decomposition. The current study sites were established in 1994 and in 2008 (14 years following harvesting) and were approaching crown closure. The experimental harvest areas were designed to document carbon loss and nutrient fluxes after the application of four levels of biomass removal from mature black spruce forested stands in northwestern Ontario, Canada. Two soil types (fresh, loamy : dry, sandy), with stand replicates (blocks), were selected to test whether residual CWD represents a source or sink for nutrients, and if the decay pattern varied depending on soil type. Measurement/sampling of CWD was done immediately after the harvest treatments were applied, and again in year 4 and year 14. The biomass removal treatment with the greatest carbon loss and fastest CWD decay rate had the highest initial mass of CWD, indicating possible synergistic decay dynamics. Nitrogen concentration in the CWD continued to increase from the initial measurements to year 14 (from 900 ppm to 2400 ppm), but was largely a function of increasing carbon loss. When converted to N content in CWD (kg ha-1), however, nitrogen exhibited an initial upward trend (i.e., immobilization) through years 1to 4 (from 50 kg ha-1 up to 80 kg ha-1) and a subsequent release in years 5 to 14 (from 80 kg ha-1down to 27 kg ha-1). This trend was more apparent on the dry, sandy sites where N content peaked at almost 100 kg ha-1 at year 4, but then reduced to 26 kg ha-1 by year 14. We compared the average loss of N from CWD in years 4 to 14 (5.3 kg ha-1 yr-1) to the total soil inorganic N pool (based on a fresh K2SO4 extraction), and found that the N loss from CWD represented a substantive portion (80%) of the available N pool, particularly on the dry, sandy sites. After an initial peak in year 4, black spruce foliar N decreased significantly (p<.0001) through to year 10 but began to rebound by year 15. This increase, presumably, was in part the result of the documented release of N from CWD. These results suggest that CWD, although a small contributor to the total N pool, makes a substantial contribution to the relatively small available N pool, especially on dry, sandy soils. The trend of initial N immobilization and subsequent release shows CWD may also serve to buffer the initial leaching of nutrients from the site following harvesting and provide an available source of N to the regenerating stand prior to crown closure.

Subterranean transport and deposition of quartz by ants in sandy sites relevant to age overestimation in optical luminescence dating

An artificial layered sandy site was created using a combination of native sand and colored sand (3 parts native uncolored quartz, 1 part colored quartz) in Apalachicola National Forest near Tallahassee, Florida. Twelve layers of sand, each 1 by 1 m in horizontal extent by 10 cm in thickness were emplaced to a depth of 2 m followed by implantation at the surface of a Florida harvester ant (Pogonomymrex badius) colony (the lower two layers were 50 cm thick). The colony excavated a nest, and after 7 months, the sand layers were excavated to the base to test the hypothesis that sand grains were moved upward within the ant nest without reaching the surface. The ants penetrated 11 of the 12 colored layers reaching a depth of 130 cm. Thirty nine sticky-acetate peels of ant chamber floors were collected and colored sand grains were counted under a microscope. More than 16,000 grains were identified in layers that did not originally host them. Of these, more than 80% were unambiguously moved upward. This means that possibly as many as 54,000 upwardly mobile grains were present (ratio of 3:1 uncolored to colored). In relation to optical luminescence (OSL) dating, this means that grains that would not have been optically zeroed by transport to the surface (defined here as subterranean-transported) were present in abundance, and that if the site was ancient, there would have been found many grains that were older than the layers they presently reside in, even if only one colony of harvester ants had disturbed the layers. This is in addition to the fact that backfilling of chambers and tunnels may contribute even more significantly to the presence of a subterranean-transported component of an OSL sample. We conclude that ants can significantly affect the age distributions in sandy archaeological sites. Multiple examples of such disturbances have been documented in the literature. Most relevant to our results are recent studies of the OSL chronology of Pre-Clovis-age and Palaeoindian age archaeological sites in sandy environments in North America that may have been compromised by ant bioturbation of quartz sand grains. Here we have examined in detail the potential effects of one episode of ant nest-building on the age overestimation of affected sediments. From this we found that as few as 12 episodes of bioturbation involving backfilling of chambers in the same volume of sand could lead to the presence of 1 contaminant grain per 50 grains of sample.

Effects of grazing exclusion on carbon sequestration and the associated vegetation and soil characteristics at a semi-arid desertified sandy site in Inner Mongolia, northern China

Li, Y., Zhao, X., Chen, Y., Luo, Y. and Wang, S. 2012. Effects of grazing exclusion on carbon sequestration and the associated vegetation and soil characteristics at a semi-arid desertified sandy site in Inner Mongolia, northern China. Can. J. Soil Sci. 92: 807–819. China's Horqin Sandy Land is a region vulnerable to disturbance that has been subjected to serious desertification, mainly because of overgrazing. We investigated whether the establishment of grazing exclosures in areas with active sand dunes would benefit vegetation recovery and improve soil quality. The results showed that along the age sequence of grazing exclosure for 8, 13, and 26 yr, plant cover, species number, and above-ground biomass increased, the soil's water-holding capacity, fine particle content, organic C, total N, total P, available N and K, and electrical conductivity also increased, and the soil coarse sand content, pH, and bulk density in the top 20 cm of the soil decreased. However, the greatest improvements compared with t...

Soil Accumulation of Nitrogen and Phosphorus Following Annual Fertilization of Loblolly Pine and Sweetgum on Sandy Sites

A key question that arises following fertilization of forest plantations in the southeastern United States is whether fertilization has a long‐term effect on nutrient availability and long‐term site quality. Site quality could improve if mineral soil N and P pools are increased but is less likely if only forest floor pools are increased. Rapid forest floor decomposition and nutrient release following harvest likely lead to only rotation‐length increases in nutrient availability. To examine the impact of repeated applications of N and P, forest floor and mineral soil N and P pools were measured at a 24‐yr‐old loblolly pine (Pinus taedaL.) plantation in North Carolina (Southeast Tree Research and Education Site [SETRES]) and 13‐yr‐old loblolly pine and sweetgum (Liquidambar styracifluaL.) plantations in Georgia (Mt. Pleasant) receiving annual incremental fertilizer applications totaling &gt;1000 kg N ha−1and &gt;160 kg P ha−1. Mineral soil N pools varied only slightly. In contrast, fertilization increased forest floor N pools by 300 kg N ha−1at SETRES. Long‐term impacts on site N availability and site quality following these large N applications are unlikely. The forest floor P pool at SETRES was increased by 19.8 kg P ha−1. Fertilization also increased the mineral soil extractable P pool at SETRES to a depth of 1.5 m by 56 kg P ha−1but not at Mt. Pleasant where P fertilization during the previous rotation may have already increased this pool. Observed increases in mineral soil P from fertilization indicated a potential for increased long‐term site quality in terms of higher P availability for future rotations.