Potential competition between hybrid striped bass (Morone saxatilis × M. americana) and striped bass (M. saxatilis) in the Cape Fear River estuary, North Carolina

Gillnet surveys from 1990 to 1992 and from 1996 to 1999 indicated a two-fold decrease in native striped bass (Morone saxatilis) populations and a concomitant two-fold increase in hybrid striped bass (Morone saxatilis × M. americana) in the Cape Fear River estuary, North Carolina. Gut content analysis indicated high diet overlap, and tagrecapture data suggested that hybrid striped bass participate in spawning migrations. These data provide circumstantial evidence that hybrid striped bass compete with striped bass for food and that they may compete for mates or habitat on the spawning grounds. Increasing abundance of adult hybrid striped bass in this system elevates the likelihood of hybrid introgression. We recommend that stocking of hybrid striped bass be terminated to preserve native striped bass populations.     

Decaying Scalars Emitted By A Forest Canopy: A Numerical Study

A large-eddy simulation is modified to include multiple scalars emitted by a plant canopy. Each of these scalars is subjected to varying rates of chemical loss. Presented is a detailed comparison between conservedspecies and species undergoing first- and second-order chemical loss.Profiles of mean mixing ratio, mixing-ratio variance and vertical mixing-ratio flux reveal the influence of chemical reactivity. Distribution of thescalar source through the depth of the canopy is shown to locally reducethe reaction rate for second-order species. Transport efficiencies, diffusioncoefficients, and mean source heights also exhibit chemical dependencies.Budgets of mixing-ratio variance and flux elucidate the mechanisms throughwhich chemistry modifies each. Instantaneous fields show the existence ofintermittently occurring coherent structures that are thought to enhancespecies segregation.     

On the mathematical description of glaciated valley cross sections

Morphometric analyses of glaciated valleys typically involve attempts to fit empirical data from valley cross-profiles to quadratic (parabolic) or power-law equations, with the choice of equation depending on the goal of the analysis. In assessing the relative merits of these two types of equations, some confusion has arisen because of apparent variations in coordinate system datums between studies which have made use of the power-law equation. However, we show that this confusion relates to a simple mathematical error, rather than any true difference in methodology. Of more significance, however, is the fact that in fitting a power-law equation to observed profiles, significant bias is introduced by the use of a logarithmic data transformation. Because of this implicit bias, power-law equation parameters are influenced most strongly by data points close in elevation to the centre of the valley, and so failure to account for the depositional elements which frequently occur in these areas can lead to significant errors if the aim of the analysis is to characterize the form of the erosional profile.     

A numerical technique for simulation of cloud seeding experiments

Two numerical cloud seeding experiments, using historic rainfall for the Deccan plateau region in Maharashtra state, were performed adopting different simulation techniques. The data used consisted of 1-day total rainfall for the 5-year period 1951–55. A double-area cross-over design with area randomisation was adopted. The first experiment, EXP-TR, was based on the simulation technique of Twomey and Robertson which involves about 100 hr of Robotron EC-1040 computer time. The second experiment, EXP-MMM was based on a different simulation technique proposed in the present study. The results of EXP-TR and EXP-MMM have shown close agreement. The numerical simulation technique of EXP-MMM is more promising for the following two reasons: (i) the computational time is reduced by about an order of magnitude without compromising the scientific value of the results, and (ii) a direct estimate of the lower limit of the double ratio value which can be detected at 5% level of significance is defined. The results of the two numerical experiments suggested that, for the Deccan plateau region, 15 and 20% increases in rainfall due to seeding could be detected with 80% or more probability in 5 years.     

Thermal alteration experiments on organic matter in recent marine sediment—I. Pigments

Sediment from Tanner Basin, located at the outer continental shelf off southern California, was analyzed for photosynthetic pigments and their derivatives, namely carotenes and chlorins. Samples of the sediment were also exposed to raised temperatures (65°, 100°, 150°C) for various periods of time (1 week, 1 month, 2 months). Analysis of the heat-treated sediment revealed the presence of α-ionene and 2,6-dimethylnaphthalene, thermal-degradation products of β-carotene. Chlorins were converted to nickel porphyrins of both DPEP and etio series. Possible mechanisms and geochemical significance of these transformations are presented.     

Response of Soybean and Sorghum to Varying Spatial Scales of Climate Change Scenarios in the Southeastern United States

This study examines how uncertainty associated with the spatial scale of climate change scenarios influences estimates of soybean and sorghum yield response in the southeastern United States. We investigated response using coarse (300-km, CSIRO) and fine (50-km, RCM) scale climate change scenarios and considering climate changes alone, climate changes with CO₂ fertilization, and climate changes with CO₂ fertilization and adaptation. Relative to yields simulatedunder a current, control climate scenario, domain-wide soybean yield decreased by 49% with the coarse-scale climate change scenario alone, and by26% with consideration for CO₂ fertilization. By contrast, thefine-scale climate change scenario generally exhibited higher temperatures and lower precipitation in the summer months resulting in greater yield decreases (69% for climate change alone and 54% with CO₂fertilization). Changing planting date and shifting cultivars mitigated impacts, but yield still decreased by 8% and 18% respectively for the coarse andfine climate change scenarios. The results were similar for sorghum. Yield decreased by 51%, 42%, and 15% in response to fine-scaleclimate change alone, CO₂ fertilization, and adaptation cases, respectively– significantly worse than with the coarse-scale (CSIRO) scenarios. Adaptation strategies tempered the impacts of moisture and temperature stress during pod-fill and grain-fill periods and also differed with respect to the scale of the climate change scenario.