Effects of four decades of fire manipulation on woody vegetation structure in Savanna

The amount of carbon stored in savannas represents a significant uncertainty in global carbon budgets, primarily because fire causes actual biomass to differ from potential biomass. We analyzed the structural response of woody plants to long-term experimental burning in savannas. The experiment uses a randomized block design to examine fire exclusion and the season and frequency of burn in 192 7-ha experimental plots located in four different savanna ecosystems. Although previous studies would lead us to expect tree density to respond to the fire regime, our results, obtained from four different savanna ecosystems, suggest that the density of woody individuals was unresponsive to fire. The relative dominance of small trees was, however, highly responsive to fire regime. The observed shift in the structure of tree populations has potentially large impacts on the carbon balance. However, the response of tree biomass to fire of the different savannas studied were different, making it difficult to generalize about the extent to which fire can be used to manipulate carbon sequestration in savannas. This study provides evidence that savannas are demographically resilient to fire, but structurally responsive.     

Flow and transport in fractured tuff at Yucca Mountain: numerical experiments on fast preferential flow mechanisms

Recent discovery of bomb-related ³⁶Cl at depth in fractured tuff in the unsaturated zone at the Yucca Mountain candidate high-level waste (HLW) repository site has called into question the usual modeling assumptions based on the equivalent continuum model (ECM). A dual continuum model (DCM) for simulating transient flow and transport at Yucca Mountain is developed. In order to ensure properly converged flow solutions, which are used in the transport simulation, a new flow solution convergence criteria is derived. An extensive series of simulation studies is presented which indicates that rapid movement of solute through the fractures will not occur unless there are intense episodic infiltration events. Movement of solute in the environs of the repository is enhanced if the properties of the tuff layer at the repository horizon are modified from current best-estimate values. Due to a large advective–dispersive coupling between the matrix and fractures, the matrix acts as a major buffer which inhibits rapid transport along the fractures. Consequently, fast movement of solutes through the fractures to the repository depth can only be explained if the matrix–fracture coupling term is significantly reduced from a value that would be calculated on the basis of data currently available.     

Assessing the organic composition of urban surface films using nuclear magnetic resonance spectroscopy

Recently it has been shown that urban surfaces are covered with a thin film which mediates the fate, distribution and accumulation of semi-volatile organic compounds in the environment. In this study we apply a combination of solution, semi-solids, and solid state nuclear magnetic resonance (NMR) methods to provide a general overview of the organic constituents. In surface film collected from 30 m2 of outside windows over an area of 12 km2 in downtown Toronto, we roughly estimate that the organic carbon is approximately 35% carbohydrate, approximately 35% aliphatics, approximately 20% aromatics, and approximately 10% carbonyl groups. Various aliphatic groups can be identified including a number of acids, alcohols, alkanes, and alkenes. Also, numerous intact aliphatic esters are apparent that have not been observed before, as well as carbohydrates. The aromatic species include a small portion that appears to be derived from a polymer of styrene, in addition a larger fraction is consistent with polyhydroxylated PAH derived material, although this assignment is tentative and based solely on 1-D NMR data only. In addition, signals from polybutadiene are present and while accurate quantification is not possible, it appears that this polymer may be up to a few percents by weight of the total organic material.     

Sensory allometry, foraging task specialization and resource exploitation in honeybees

Insect societies are important models for evolutionary biology and sociobiology. The complexity of some eusocial insect societies appears to arise from self-organized task allocation and group cohesion. One of the best-supported models explaining self-organized task allocation in social insects is the response threshold model, which predicts specialization due to inter-individual variability in sensitivity to task-associated stimuli. The model explains foraging task specialization among honeybee workers, but the factors underlying the differences in individual sensitivity remain elusive. Here, we propose that in honeybees, sensory sensitivity correlates with individual differences in the number of sensory structures, as it does in solitary species. Examining European and Africanized honeybees, we introduce and test the hypothesis that body size and/or sensory allometry is associated with foraging task preferences and resource exploitation. We focus on common morphological measures and on the size and number of structures associated with olfactory sensitivity. We show that the number of olfactory sensilla is greater in pollen and water foragers, which are known to exhibit higher sensory sensitivity, compared to nectar foragers. These differences are independent of the distribution of size within a colony. Our data also suggest that body mass and number of olfactory sensilla correlate with the concentration of nectar gathered by workers, and with the size of pollen loads they carry. We conclude that sensory allometry, but not necessarily body size, is associated with resource exploitation in honeybees and that the differences in number of sensilla may underlie the observed differences in sensitivity between bees specialized on water, pollen and nectar collection.     

A novel enzyme-linked immunosorbent assay system for the quantitative analysis of Carassius auratus vitellogenin

A sandwich enzyme-linked immunosorbent assay (ELISA) was developed to quantitatively detect Carassius auratus vitellogenin (VTG) levels. The protein levels in fish plasma are useful aquatic biomarkers of estrogenic compounds. This procedure involved an ELISA using monoclonal antibodies of CVmA2 and CVmA7 against Carassius auratus VTG, and CVmA7 conjugated to horseradish peroxidase as the detection antibody. The assay range was between 1 and 401.5 ng/ml and the recovery of the VTG added to Carassius auratus plasma was 92.5-109%. An in vitro assay was performed to measure low levels of the VTG, using primary hepatocytes of Carassius auratus induced by 17-beta estradiol (E2). The detection limit was 1 ng/ml and 137 ng/ml at the maximum. Within each sex of wild Carassius auratus, VTG levels from the river next to sewage treatment works (STWs) were much higher than those from the feeding stream. The Carassius auratus VTG bioassay could be a sensitive and useful tool for quantification of estrogenic principles in aquatic environments.     

Isolation and fractionation of soil humin using alkaline urea and dimethylsulphoxide plus sulphuric acid

Humin, the most recalcitrant and abundant organic fraction of soils and of sediments, is a significant contributor to the stable carbon pool in soils and is important for the global carbon budget. It has significant resistance to transformations by microorganisms. Based on the classical operational definition, humin can include any humic-type substance that is not soluble in water at any pH. We demonstrate in this study how sequential exhaustive extractions with 0.1 M sodium hydroxide (NaOH) + 6 M urea, followed by dimethylsulphoxide (DMSO) + 6% (v/v) sulphuric acid (H₂SO₄) solvent systems, can extract 70–80% of the residual materials remaining after prior exhaustive extractions in neutral and aqueous basic media. Solid-state ¹³C NMR spectra have shown that the components isolated in the base + urea system were compositionally similar to the humic and fulvic acid fractions isolated at pH 12.6 in the aqueous media. The NMR spectra indicated that the major components isolated in the DMSO + H₂SO₄ medium had aliphatic hydrocarbon associated with carboxyl functionalities and with lesser amounts of carbohydrate and peptide and minor amounts of lignin-derived components. The major components will have significant contributions from long-chain fatty acids, waxes, to cuticular materials. The isolates in the DMSO + H₂SO₄ medium were compositionally similar to the organic components that resisted solvation and remained associated with the soil clays. It is concluded that the base + urea system released humic and fulvic acids held by hydrogen bonding or by entrapment within the humin matrix. The recalcitrant humin materials extracted in DMSO + H₂SO₄ are largely biological molecules (from plants and the soil microbial population) that are likely to be protected from degradation by their hydrophobic moieties and by sorption on the soil clays. Thus, the major components of humin do not satisfy the classical definitions for humic substances which emphasise that these arise from microbial or chemical transformations in soils of the components of organic debris.     

Drainage Impacts on Surficial Water Retention Capacity of a Prairie Pothole Watershed

Wetland restoration has been proposed as a tool to mitigate excess runoff and associated nonpoint source pollution in the Upper Midwestern United States. This study quantified the surficial water retention capacity of existing and drained wetlands for the Greater Blue Earth River Basin (GBERB), an intensively drained agricultural watershed. Using airborne light detection and ranging, the historic depressional storage was determined to be 152 mm. Individual depression analysis suggested that the restoration of most drained areas would have little impact on the storage capacity of the GBERB because the majority (53%) of retention capacity was in large depressions (>40 ha) which comprised only a small proportion (<1.0) of the observed depressions. Accounting for change in storage and the difference in annual evapotranspiration (ET) between wetlands and the croplands that replaced them, restoration of all depressions in the Minnesota portion of GBERB would provide a maximum of 131 mm additional capacity over and above the modern day capacity (193 mm; 56 mm depressional storage; 60 mm wetland ET; and 77 mm cropland ET). Considering that depressional depths in smaller areas are within the range of uncertainty of the lidar digital elevation models and larger depressions have the most storage, we conclude that efforts to increase the surficial water‐holding capacity of the GBERB would be best served in the restoration of large (>40 ha) depressions.