Nonlinear effects of food aggregation on interference competition in mallards

Previous studies of interference competition have shown an asymmetric effect on intake rate of foragers on clumped resources, with only subordinate individuals suffering. However, the food distributions in these studies were uniform or highly clumped, whereas in many field situations, food aggregation is intermediate. Here we investigated whether food distribution (i.e., uniform, slightly clumped, and highly clumped) affects the behavioral response of mallards foraging alone or competing with another. Although the amount of food was the same in all distributions, the mallards reached higher intake rates, visited fewer patches, and showed longer average feeding times in the highly clumped distribution. Competing mallards had lower intake rates on the slightly clumped than on the uniform or highly clumped food distributions. Subordinates generally visited more patches and had shorter feeding times per patch, but their intake rates were not significantly lower than those of dominants. Therefore, we propose that subordinates do not necessarily suffer from interference competition in terms of intake rate, but do suffer higher search costs. In addition, although dominants had significantly higher average feeding times on the best quality patches of the highly clumped food distribution, such an effect was not found in the slightly clumped distribution. These findings indicate that in environments where food is aggregated to a lesser extent, monopolization is not the best strategy for dominants. Our results suggest that interference experiments should use food distributions that resemble the natural situation animals are faced with in the field.     

Measuring copepod naupliar abundance in a subtropical bay using quantitative PCR

Copepod nauplii are important in plankton food web dynamics, but limited information is available about their ecology due to methodological challenges. Reported here is a new molecular method that was developed, optimized, and tested in laboratory and field samples that uses quantitative PCR (qPCR) to identify and estimate the abundance of nauplii of the planktonic copepod, Parvocalanus crassirostris. The overall approach included collection of bulk zooplankton samples in the field, size fractionation to create artificial cohorts of relatively few developmental stages, obtaining DNA copy number for each size fraction by qPCR amplification of a target gene region, and estimation of the number of animals in each fraction through application of known DNA copy number across developmental stage. Method validation studies found that our qPCR-based approach has comparable accuracy to microscope-based counts of early developmental stages. Naupliar abundance estimates obtained using the two methods on cultured populations were similar; the regression of qPCR estimates on microscope-based counts resulted in a nearly 1:1 ratio (slope = 1.09). The qPCR-based method is superior to traditional identification and quantification methods for nauplii due to its higher taxonomic resolution, sensitive detection over a range of DNA quantities, and relatively high throughput sample processing.     

Approaches to soil remediation by complexometric extraction of metal contaminants with regeneration of reagents

Complexometric equilibrations were performed with six chelating reagents to mobilise Cu, Mn, Pb and Zn from a contaminated urban soil. The metal-laden aqueous extract was treated with sodium diethyldithiocarbamate (DEDTC) to precipitate the heavy metals from solution while liberating the chelating reagent. The aqueous supernatant fraction was then re-combined with the soil particulates to extract more pollutants. A sparing quantity of EDTA (ethylenediaminetetraacetic acid; 10 mmol) mobilised 32-54% of the 5 mmol of heavy metals from the soil with three cycles but only 0.1 and 1.0% of the iron and magnesium, respectively, was removed. Whereas DPTA (1,3-diamino-2-hydroxypropane-N,N,N',N'-tetraacetic acid) and citric acid also mobilised each of the heavy metals to some extent and continued to extract these metals during all three cycles, the DTPA (diethylenetriamine pentaacetic acid), although efficient initially, could not be recycled with these conditions. ADA [N-(2-acetamido)iminodiacetate] and SCMC [(S)-carboxymethyl-L-cysteine] were selective for copper and zinc but mobilised only Cu when recycled. An alternate means of regenerating the chelating reagent involved treatment of the aqueous extract with magnesium (Mg0) granules. Excess HEDC [bis(2-hydroxyethyl)dithiocarbamate] mobilised appreciable quantities (19-57%) of heavy metals from the soil and retained its complexing activity when recycled. An appreciable fraction of the mobilised Pb and Cu and a portion of the Zn were cemented to the surfaces of the excess magnesium whereas virtually all of the Fe and Mn was removed from solution as insoluble hydroxides.     

A COLORIMETRIC METHOD FOR THE DETERMINATION OF TRACE COPPER CONCENTRATIONS IN WATER1

Trace quantities of copper (II) ion can be found in natural water as waste products from industrial, mining, and agricultural operations. Because low concentrations of copper can be toxic to plant life, many workers have devised methods of analysis for this metal in water. These methods require expensive equipment and skilled technicians. The described study illustrates a simple method in which copper (II) ion is concentrated by a batch ion exchange technique and estimated colorimetrically after formation of the blue triethylenetetramine complex. Using the visible absorption peak of the complex at 600 nm it was possible to obtain accurate estimations of original copper concentrations in the range 0.5-3 ppm. Using the complex absorption peak at 260 nm in the ultra-violet region of the spectrum increased the sensitivity by a factor of twenty. Because of the dependence of the complex formation reaction on solution acidity it is possible to optimize conditions for the detection of copper (II) in the presence of other metal ions. This type of method, which could be extended to the analysis of other metal ions, could be performed by a relatively unskilled technician under field conditions.     

Observations on organic aggregates in the vicinity of coral reefs

The abundance of organic aggregates is reported for a variety of coral-reef sites and surrounding waters. There is no net increase of aggregates forming from dissolved organic matter and streaming off the reefs into the lagoons, though the organic components and the aeration of this water might be conducive to aggregate formation. Also, although the waters flowing from the surrounding oceans across the reefs and into the lagoons contribute organic components, the concentration of organic aggregates in the latter habitats is not in excess of quantities in surrounding oceanic waters.     

Strategic Routeing and Environmental Impact Assessment for Overhead Electrical Transmission Lines

High-voltage, high-capacity overhead lines are the economic and reliable choice for the bulk transmission of electricity throughout the world. The routeing of transmission lines is a complex process, and in the UK requires a balance to be struck between statutory obligations, engineering requirements, economic viability, land use and the environment. Transmission line routeing projects can rightly generate considerable public interest and debate, but issues often focus on local effects such as visual amenity rather than the wider benefits of the project to society as a whole. Given the extent of their public and regulatory scrutiny, the environmental statements of such schemes must be objective and transparent in the approach adopted to the routeing strategy. The approach outlined is based on the premise that the major effect of an overhead transmission line is visual and the degree of visual intrusion can be reduced through careful routeing.     

Carbon Sequestration: Do N Inputs and Elevated Atmospheric CO2 Alter Soil Solution Chemistry and Respiratory C Losses?

Soil respiration is a large C flux which is of primary importance in determining C sequestration. Here we ask how it is altered by atmospheric CO₂ concentration and N additions. Swards of Lolium perenne L. were grown in a Eutric cambisol under controlled conditions with and without the addition of 200 kg NO ₃ ^– –N ha^–1, at either 350 ppm or 700 ppm CO₂, for 3 months. Soil respiration and net canopy photosynthesis were both increased by added N and elevated CO₂, but soil respiration increased proportionately less than fixation by photosynthesis. Thus, both elevated CO₂ and N appeared to increase potential C sequestration, although adding N at elevated CO₂ reduced the C sequestered as a proportion of that fixed relative to elevated CO₂ alone. Across all treatments below-ground respiratory C losses were predicted by root biomass, but not by soil solution C and N concentrations. Specific root-dependent respiration was increased by elevated CO₂, such that belowg-round respiration per unit biomass and per unit plant N was increased.     

A risk-based approach to how clean is clean

Clearly defined remedial action objectives are a key factor in successful remediation programs. Chemical-specific cleanup criteria are critical components of remedial action objectives. A common risk-based approach can be applied for developing cleanup criteria for remediations under CERCLA, RCRA, and TSCA. This approach involves four steps: identify regulatory requirements; identify chemical-specific cleanup guidelines from previous cleanups; evaluate site-specific risk considering mitigating factors for a given site; select the final cleanup criteria based on information from the first three steps. To describe this approach, this paper presents a case study on a PCB cleanup conducted under TSCA. An objective risk-based approach was used to capitalize on the flexibility built into EPA's PCB cleanup guidelines. EPA granted an exemption to the stated policy on the basis of competing risk factors using a comparative risk-assessment approach. Similarly, risk assessment can be used to take advantage of regulatory flexibility in the selection of applicable or appropriate and relevant requirements (ARARs) under CERCLA, or in the selection of media protection standards under RCRA.     

Barcelona and the delta: metropolitan infrastructure planning and socio‐ecological projects

The delta of the Llobregat river is a natural expansion area for the city of Barcelona. It has been used first for agricultural purposes and then in the twentieth century for urban and infrastructural development. The history of the delta is examined, in order to trace the changing interactions between economic and political forces and ecological processes. This includes the influence of urban planning from 1930 onwards. The paper describes the effort made by the Spanish government from 1991 to co‐ordinate investment planning in the delta with the Catalan administration and local authorities. One municipality, El Prat, has offered a partial environmentalist challenge to the dominant economic development model of other administrations. It is concluded that it would be valuable to consider this key zone in relation to alternative projects for the socio‐economic and ecological development of Catalonia and Spain as a whole.     

ESTIMATES OF MEAN CHLOROPHYLL-a CONCENTRATION: PRECISION,ACCURACY, AND SAMPLING DESIGN1

ABSTRACT: Data from 56 north-temperate lakes and reservoirs are used to develop models predicting temporal variance as a function of the mean chlorophyll-a concentration. Trophy, as estimated by mean chlorophyll-a concentration, is shown to have little effect on the sampling effort required to achieve a pre-determined level of precision for lakes sampled year-round. Collecting ten observations results in a coefficient of variation that averaged 20 percent; collecting more than ten observations yields increasingly marginal improvements in precision. The same guidelines apply to mesotrophic or eutrophic lakes sampled in the summer, whereas oligotrophic lakes sampled in the summer require fewer observations to achieve the same level of precision. The bias resulting from collecting too few observations is minimized if five or more observations are collected.