Control of ammonia toxicity to Hyalella azteca by sodium, potassium and pH

The toxicity of ammonia to Hyalella azteca at constant pH in artificial media was controlled by sodium and potassium, and not by calcium, magnesium, or anions. Small increases in the LC50 for total ammonia (from 0.15 to 0.5 mM) occurred as sodium was increased from 0.1 to 1 mM and above, but major increases in the LC50 (to over 10 mM total ammonia) required the addition of potassium. Potassium was, however, more effective at reducing ammonia toxicity at high (1 mM) sodium than at low (0.1 mM) sodium. Ammonia toxicity was independent of pH at low sodium and potassium concentrations, when ammonia toxicity appeared to be associated primarily with aqueous ammonium ion concentrations. At high sodium and potassium concentrations, the toxicity of ammonia was reduced to the point where un-ionized ammonia concentrations also affected toxicity, and the LC50 became pH dependent. A mathematical model was produced for predicting ammonia toxicity from sodium and potassium concentrations and pH.     

Oil pollution monitoring in the Lagoon of Venice using the mussel Mytilus galloprovincialis

Gas chromatographic analyses of mussels, Mytilus galloprovincialis, from different areas of the Lagoon of Venice show that these organisms contain a very complex mixture of hydrocarbons attributable to fuel oil contamination. The measured amounts normally range from 0.8 to 8.7 mg/100 g wet weight, but values as high as 22.0 mg/100 g have been recorded. This high value indicates a saturation limit for these organisms which is considerably higher than those values normally found in mussels from the lagoon. The aliphatic hydrocarbon levels in mussels are related to distance from pollution sources and to the degree of exchange between the sea and the area sampled. On the basis of this relationship between overall hydrocarbon pollution load and level of contamination of M. galloprovincialis, it appears that this bivalve might be effectively utilized as a self-integrating monitoring index of oil pollution in the wasters of the lagoon.     

Modelling stomatal responses of spring wheat (Triticum aestivum L. cv. Turbo) to ozone and different levels of water supply

Spring wheat (Triticum aestivum L. cv. Turbo) was exposed to different levels of ozone and water supply in open-top chambers in 1991. Air was charcoal filtered (CF), non-filtered (NF) and CF plus proportional addition of ambient or twice ambient ozone (CF1, CF2). Seasonal means of O(3), taken over 24 h, were 2.3, 20.6, 17.3, and 34.5 nl litre(-1) for CF, NF, CF1 and CF2 treatments, respectively. A split-plot design was used to obtain two levels of water supply: one-half of the pots was irrigated sufficiently not to show any symptoms of drought stress; the others were exposed to low water supply and received 50% of these amounts. Using a steady-state porometer approximately 800 measurements of stomatal conductance (g(s)) were made on flag leaves from 68 to 106 days after sowing. The measurements yielded only small differences of maximum conductance between the two levels of water supply. Therefore, low water supply did not protect wheat plants against ozone injury via reduced stomatal uptake in this experiment. To describe the effects of environmental variables on the stomatal behaviour, boundary-line analysis and non-linear regression analysis were used. Besides microclimatic parameters, the ozone dose of flag leaves was introduced as an independent variable affecting stomatal aperture. A well-defined boundary line for ozone dose was found, suggesting that increasing ozone dose caused stomatal closure in wheat flag leaves. But at high ozone doses, co-acting senescence seems also responsible for the decrease in stomatal conductance. A multiplicative boundary-line model was used to predict stomatal conductance from combinations of environmental variables. In the test carried out with the measurements of stomatal conductance, the model accounted only for 40% of the variation of g(s). Generalized stomatal response patterns of the herbaceous growth form, the dependence of the variables' age and ozone dose and the lack of an important factor influencing stomatal response (water status of the plant) in the model, are suggested as explanations of the poor results of the test.     

Modeling the Entrepe?as Reservoir.

The Entrepe?as Reservoir is a monomictic reservoir located in River Tagus (Spain). The aim of this work is to establish a feasible model to predict the depth of the thermocline that is developed in the reservoir during the period of natural thermal stratification. Entrainment, eddy diffusion, inflow of external energy, and other factors are considered to calibrate the parameters of the model. The methodology involves the measure of actual temperature and electrical conductivity profiles, use of meteorological data and reservoir parameters, and selection and application of several models from the literature. The calculations and predictions are integrated to a software packet that is able to predict thermocline depth and water temperature profile during a 1-year period on a day-by-day basis. In the thermocline depth, the prediction error, on the basis of real data, is less than 6% and, in the water temperature, it is 2 degrees C.     

Extrinsic modeling and simulation of helio-photovoltaic system: a case of single diode model

Simulation of helio-photovoltaic system is continuously undergoing revolution through diverse parameter modifications which closely mimic the experimental data. In retrospect, the current work has presented a nonlinear modification of equivalent circuit parameters and simulated the same for different semiconductors (crystalline and thin films); furthermore, established a mathematical relation between the coefficients of solar irradiance and module temperature (SIMT); moreover, investigated the influence of SIMT on the model parameters. The simulation upshot reveals that increment in solar irradiance (SI) intensifies the output current whereas an increase in module temperature (MT) diminishes the output voltage; the SIMT coefficients developed validated well with the manufacturers data; the influence of SI was evident on the photon current, diode current, and shunt resistance whereas the effect of MT was pronounced on the diode current, ideality factor, and shunt resistance. Thus, the provision made by this work is essential for advanced design and simulation of helio-photovoltaic systems.