Variations in time budget of the polychaete Nereis virens as a function of density and acclimation after introduction to a new burrow

Behavioural patterns of Nereis virens (Sars) were monitored in the laboratory to determine variations in the time budget (i.e., percentage of time spent in various activities) as a function of density and acclimation period (number of days following the introduction of worms into experimental enclosures). Experiments were carried out from 17 June to 13 August 1989, using worms collected from intertidal sand flats of l'Anse à l'Orignal in the lower Saint Lawrence estuary, Canada. Inactivity, locomotion and irrigation were, in that order, the most frequent behaviours for solitary individuals. Correlations between the time spent in the various activities and time of day indicated a general increase in activity during the night (21.00 to 06.00 hrs). Locomotory activity increased at night, inactivity during the daytime. A general sequence of behaviour of N. virens was revealed. Inactivity, locomotion and irrigation were still the most frequent activities for individuals observed in high-density conditions, but their respective importance differed significantly (locomotion, irrigation and inactivity, in that order). There was also less variability in the time spent for each behaviour in the high-density aquarium. Comparisons between behaviour and time of day suggested fewer correlations among the different components of the time budgets under conditions of high density. Finally, the time budget varied but little over time (number of days alloved for acclimation) in the low-density aquarium as opposed to the high-density aquarium. Our study revealed that population density and acclimation are important in determining behavioural patterns of N. virens.     

A comparison of speciated atmospheric mercury at an urban center and an upwind rural location

Gaseous elemental mercury (GEM), particulate mercury (PHg) and reactive gaseous mercury (RGM) were measured every other hour at a rural location in south central Wisconsin (Devil's Lake State Park, WI, USA) between April 2003 and March 2004, and at a predominantly downwind urban site in southeastern Wisconsin (Milwaukee, WI, USA) between June 2004 and May 2005. Annual averages of GEM, PHg, and RGM at the urban site were statistically higher than those measured at the rural site. Pollution roses of GEM and reactive mercury (RM; sum of PHg and RGM) at the rural and urban sites revealed the influences of point source emissions in surrounding counties that were consistent with the US EPA 1999 National Emission Inventory and the 2003-2005 US EPA Toxics Release Inventory. Source-receptor relationships at both sites were studied by quantifying the impacts of point sources on mercury concentrations. Time series of GEM, PHg, and RGM concentrations were sorted into two categories; time periods dominated by impacts from point sources, and time periods dominated by mercury from non-point sources. The analysis revealed average point source contributions to GEM, PHg, and RGM concentration measurements to be significant over the year long studies. At the rural site, contributions to annual average concentrations were: GEM (2%; 0.04 ng m(-3)); and, RM (48%; 5.7 pg m(-3)). At the urban site, contributions to annual average concentrations were: GEM (33%; 0.81 ng m(-3)); and, RM (64%; 13.8 pg m(-3)).     

Use of microbial activity measurements for monitoring RBC biofilms

Fixed biomass technologies, such as rotating biological contactors or biodiscs, have been applied for wastewater depuration both in large and medium–small-sized agglomerations. Biofilm’s composition and microorganism activity are essential parameters for the successful operation and control of these systems. Biofilm’s thickness and total dry weight have been widely used for biofilm’s characterization but, actually, are not sufficient to describe biofilm activity. In fact, biofilm’s activity is not proportional to the quantity of fixed biomass, but increases with the thickness of biofilm up to a determined level called the “active thickness”. Above this level, the diffusion of nutrients through the film becomes a limiting factor. A stable, thin, and active biofilm thus offers numerous advantages in water and wastewater treatment. Different parameters have been used to evaluate biofilm’s activity. The specific oxygen uptake rate, INT-dehydrogenase activity, and the ratio active/total cells have been applied for that purpose. These methods are not only simple and rapid but also sensitive, precise, and representative. The results obtained confirm the potential of the microbial activity measurements studied for an accurate biofilm’s characterization and biomass activity estimation in fundamental research and for the practical operation and control of fixed biomass depuration systems.     

Representation of complex visual stimuli in the brain

A method was developed to investigate transfer properties of neurons in the visual system using pictures of complex visual stimuli. The picture is moved over the receptive field of a neuron so that it can scan it along programmed lines. The activity of the neuron during the scanning procedure is presented in a two-dimensional dot display on scale with the original picture. By superposition of the stimulus and the transfer pattern, one can find out to which detail of a stimulus the neuron responds. Neurons in the first intracerebral relay of the visual system, the lateral geniculate body, reduce a complex stimulus, such as a photograph of a natural environment, to its contours. Cortical cells only respond to contours either of a limited or of a wider range of orientations (simple and complex cells, respectively). But the course of contours is only described by a continuous representation of these contours in the cortical map of the visual field. This is done by the simple cells, which have small receptive fields and thus a higher resolving power, whereas complex cells with their large receptive fields monitor the approximate location of a moving stimulus. The function of these two classes of neurons is discussed in terms of visual behavior, i.e., for fixation, hold, and binocular vergence movements (simple cells), and for detection of moving objects and motor command signals towards these objects (complex cells). These functions are an important condition for foveal vision which is the basis of perception in primates. An important function of orientation sensitivity of simple cells may be the binocular alignment of contours in binocular fusion and stereoscopic vision.     

Effects of tree size and spatial distribution on growth of ponderosa pine forests under alternative management scenarios

Forest ecosystems may be actively managed toward heterogeneous stand structures to provide both economic (e.g., wood production and carbon credits) and environmental benefits (e.g., invasive pest resistance). In order to facilitate wider adoption of possibly more sustainable forest stand structures, defining growth expectations among alternative management scenarios is crucial. To estimate the effect of tree size and spatial distributions on growth for forest structures commonly considered in uneven-aged forest stand management, large (0.2 ha+) plots were established in 14 uneven-aged ponderosa pine stands in eastern Montana. All study trees were stem-mapped and measured for diameter and 10-year sapwood and basal area increment. A generalized growth model was developed to predict both total and merchantable 10-year basal area increment for nine hypothetical stand structures [three diameter distributions (reverse-J, irregular, flat) × three spatial distributions (clumpy, partial clumpy, uniform)]. Results indicate that the size and spatial distributions of individual trees have a considerable effect on overall stand growth. The greatest total stand growth was in stands with reverse “J” shaped tree size distributions, while the greatest merchantable stand growth was in stands with “flat” diameter distributions and uniform spatial distributions. Through better comprehension of generalized uneven-aged stand growth dynamics, forest managers may better assess the effects of alternative stand structures on stand growth while providing forest stand structures that may be more resilient in a changing climate.     

SOIL MOISTURE ACCOUNTING COMPONENT OF THE USDAHL-74 MODEL OF WATERSHED HYDROLOGY1

ABSTRACT: Soil moisture in two layers of a soil near Chickasha, Oklahoma, was simulated, using USDAHL-74 Model of Watershed Hydrology. Weekly values computed for both layers compared well with those observed during the 15-month period. Certain key parameters required adjustments in the model which illustrate the need for accurate input information. The experiment demonstrates that the model, which has previously given good results in continuous streamflow prediction on watersheds up to 100 square miles, can also compute soil moisture continuously at a site. This capability suggests other model uses, for example, in monitoring the disposition of applied chemicals.     

Reconstruction of historical trends of PCDD/Fs and PCBs in the Venice Lagoon, Italy

Historical trends of PCDD/Fs and PCBs from the year 1900 have been reconstructed for the Venice Lagoon area by using a fugacity-based dynamic multimedia model. A novel approach to estimate the inputs to the system was applied. Emissions to the lagoon were estimated by studying dated sediment cores taken from salt marshes located in the lagoon area. These cores have recently proven to be a suitable tool to reconstruct the temporal trends of atmospheric deposition of POPs. According to the model, concentrations of PCBs and PCDD/Fs in air and water reflect the trends of their production and usage, peaking during the 1960s. The peaks in the sediment were delayed by 5-40 years depending on the congener. Predicted concentrations are in good agreement with experimental results. The most important input parameters, identified by a sensitivity analysis, are the degradation constants, K(ow), the Henry's law constant, vapour pressure, active sediment depth, sediment resuspension, and deposition rates, and water residence time in the lagoon.     

Comparison of Canadian firefighters and healthy controls based on submaximal fitness testing and strength considering age and gender

Introduction. Few studies have addressed whether firefighters are fitter than the general population and possess sufficient levels of aerobic capacity and muscle strength to perform on-duty tasks in a safe and efficient manner, considering age and gender. We aimed to evaluate the fitness levels of Hamilton firefighters, and to determine the effects of age and gender. Methods. In total, 89 participants were recruited. The modified Canadian aerobic fitness test was used to determine participants’ estimated maximal oxygen consumption (V_O2max) levels. For upper and lower body strength levels, a calibrated J-Tech hand-held dynamometer and a National Institute for Occupational Safety and Health (NIOSH) lifting device was used respectively. Results. Firefighters’ mean (SD) V_O2max level was 40.30?±?6.25?ml·kg^?1·min^?1. Age proved to have a statistically significant impact on V_O2max (p?<?0.001). Gender displayed statistically significant effects on strength levels. Firefighters’ age was the only statistically significant independent variable, and accounted for 61.00% of the variance in firefighters’ aerobic capacity levels. Conclusions. Firefighters possessed somewhat similar aerobic capacities but much higher levels of body strength when compared with the general population. With age, firefighters’ aerobic capacities decreased; however, their upper and lower body strength levels remained the same.