Experimental problems using electronic particle counters

The following scheme lists the problems which have been and will continue to be encountered in grazing experiments on natural particle assemblages. In some cases there are solutions, but many of the problems listed below remain intractable. To solve them will require innovative approaches, most probably combining the use of particle counters with other techniques to approach the problem to be solved from several angles at once. Variance between samples due to

- statistical causes (especially caused by large particles) and

- differences between experimental bottles and between experimentals and controls at start of experiment. Shifts in particle distribution during experiment due to

- increase in small particles

- growth of bacteria and other organisms due to excretion of grazers and

- breakage during handling by grazers into fragments. Processes, independent of grazing, leading to changes in particle size distribution due to

- primary production

- grazing by additional components and

- bacterial growth on detrital particles and the formation of detrital flocs.

     

Biogeographic responses and niche occupancy of microbial communities following long-term land-use change

Understanding the effects of forest-to-agriculture conversion on microbial diversity has been a major goal in soil ecological studies. However, linking community assembly to the ruling ecological processes at local and regional scales remains challenging. Here, we evaluated bacterial community assembly patterns and the ecological processes governing niche specialization in a gradient of geography, seasonality, and land-use change, totaling 324 soil samples, 43 habitat characteristics (abiotic factors), and 16 metabolic and co-occurrence patterns (biotic factors), in the Brazilian Atlantic Rainforest, a subtropical biome recognized as one the world’s largest and most threatened hotspots of biodiversity. Pairwise beta diversities were lower in pastures than in forest and no-till soils. Pasture communities showed a predominantly neutral model, regarding stochastic processes, with moderate dispersion, leading to biotic homogenization. Most no-till and forest microbial communities followed a niche-based model, with low rates of dispersal and weak homogenizing selection, indicating niche specialization or variable selection. Historical and evolutionary contingencies, as represented by soil type, season, and dispersal limitation were the main drivers of microbial assembly and processes at the local scale, markedly correlated with the occurrence of endemic microbes. Our results indicate that the patterns of assembly and their governing processes are dependent on the niche occupancy of the taxa evaluated (generalists or specialists). They are also more correlated with historical and evolutionary contingencies and the interactions among taxa (i.e., co-occurrence patterns) than the land-use change itself.

     

A preliminary comparison of two turbid coastal ecosystems: The Dollard (Netherlands-FRG) and the Cumberland Basin (Canada)

Extensive ecological studies are currently being conducted in the Ems-Dollard estuary and the upper reaches of the Bay of Fundy. The purpose, approach, results, synthesis and application of each project are compared in a preliminary fashion, with emphasis upon the Dollard and the Cumberland Basin. Both regions are turbid, shallow water environments with extensive intertidal areas. Although important differences do exist, for example greater tidal energy and suspended sediment concentrations in Cumberland Basin and pronounced import of allochthonous organic carbon in the Dollard, similar organisms and ecological processes dominate both estuaries and secondary production does not appear to be significantly different. High levels of stress in both environments favor the development of small and rapidly growing organisms. Comparison exercises such as this are extremely valuable for judging progress, evaluating results and stimulating new ideas.     

An integrated approach to patient-specific predictive modeling for single ventricle heart palliation

In patients with congenital heart disease and a single ventricle (SV), ventricular support of the circulation is inadequate, and staged palliative surgery (usually 3 stages) is needed for treatment. In the various palliative surgical stages individual differences in the circulation are important and patient-specific surgical planning is ideal. In this study, an integrated approach between clinicians and engineers has been developed, based on patient-specific multi-scale models, and is here applied to predict stage 2 surgical outcomes. This approach involves four distinct steps: (1) collection of pre-operative clinical data from a patient presenting for SV palliation, (2) construction of the pre-operative model, (3) creation of feasible virtual surgical options which couple a three-dimensional model of the surgical anatomy with a lumped parameter model (LPM) of the remainder of the circulation and (4) performance of post-operative simulations to aid clinical decision making. The pre-operative model is described, agreeing well with clinical flow tracings and mean pressures. Two surgical options (bi-directional Glenn and hemi-Fontan operations) are virtually performed and coupled to the pre-operative LPM, with the hemodynamics of both options reported. Results are validated against postoperative clinical data. Ultimately, this work represents the first patient-specific predictive modeling of stage 2 palliation using virtual surgery and closed-loop multi-scale modeling.     

Greenhouse gases emission from soil contaminated with automobile industry residue in Brazil

Solid waste of the automobile industry containing large amounts of heavy metals might affect the emission of greenhouse gases (GHG) when applied to the soil. Accumulation of inorganic chemical elements in the environment generally occurs due to human activity (industry, agriculture, mining and waste landfills). Residues from human activities may release heavy metals to the soil solution, causing toxicity to plants and other soil organisms. Heavy metals may also be adsorbed to clay minerals and/or complexed by the soil organic matter, becoming a potential source of pollutants. Not much is known about the behavior of solid wastes in tropical soil as regarded as source of greenhouse gases (GHG). The emission of GHG (CO₂, CH₄ and N₂O) was evaluated in incubated soil samples collected in an area contaminated with a solid residue from an automobile industry. Samples were randomly collected at 0 to 0.2 m (a mix of soil and residue), 0.2 to 0.4 m (only residue) and 0.4 to 0.6 m (only soil). A contiguous uncontaminated area, cultivated with sugarcane, was also sampled following the same protocol. Canonical Discriminant Analysis and Principal Component Analysis were applied to the data to evaluate the GHG emission rates. Emission rates of GHG were greater in the samples from the contaminated than the sugarcane area, particularly high during the first days of incubation. CO₂ emissions were greater in samples collected at the upper layer for both areas, while CH₄ and N₂O emissions were similar in all samples. The emission rates of CH₄ were the most efficient variables to differentiate contaminated and uncontaminated areas.     

Grassland management intensification affects the soil fauna in a subtropical highland

The conversion of natural grasslands to cultivated pastures can have a significant impact on the composition and structure of soil macro- and mesofauna groups, compromising the resilience of these organisms and the ecosystem services they provide. We studied the responses of these groups to increasing levels of soil disturbance across a gradient of four land management practices: Natural grassland (NG), Improved-natural grassland (IG), Perennial-cultivated pasture (PP), and Annual-cultivated pasture (AP). The NG area had a higher abundance of macrofauna, greater dominance of certain groups, particularly Isoptera, and a lower abundance of mesofauna. On the other hand, the IG area had a higher abundance and diversity of macro- and mesofauna, with a lower dominance of specific groups. The PP area had a higher abundance of Coleoptera, Oligochaeta, and Hemiptera, whereas the AP area, despite soil disturbance, showed a higher abundance of mesofauna, particularly mites, Collembola, and Enchytraeidae, but lower diversity. Different grassland management practices have significantly altered the composition and structure of macro- and mesofauna groups, resulting in high dissimilarity between communities. We recommend IG as a more productive and sustainable alternative to the total replacement of natural vegetation (NG) with intensified converted pastures (PP and AP), as it maintains soil fauna diversity and ecosystem services.