FLOOD PLAIN MODELING1

Computer simulation of river basin hydrology has rapidly progressed from an interesting academic exercise to a practical engineering procedure of increasing utility. Mathematical models of the many interrelated processes which occur in a basin have been developed along with efficient numerical procedures for their solution. The present paper is concerned with a particular model which has been used to describe the transformation of a temporally and spatially varying rainfall into a time history of stage and discharge on a flood plain. Although developed principally as a model of the physical processes involved, it is envisioned that the model can serve as one component of an information system for flood plain planning and management. The model consists of the following elements: (i) a rainfall simulation which generates stochastic inputs to the model according to specified rainfall statistics, (ii) a catchment-runoff model which converts the rainfall to surface runoff, (iii) a flood stage model which converts the surface runoff to time histories of flood stage and discharge. The model has been used to investigate the effect of various structural flood control measures in a basin and, in particular, to establish frequency-stage information for each of these. Of particular interest in development of the model have been recurring and partially unanswered questions relative to the proper balance among availability of data for use in the model, data requirements of the model and the objectives of the outputs produced by the model.     

Does the nutrition profile of vitamins, fatty acids and microelements counteract the negative impact from organohalogen pollutants on bone mineral density in Greenland sledge dogs (Canis familiaris)?

There is a great need for understanding the impact from dietary OHCs (organohalogen compounds) on bone mineral composition - and thereby osteoporosis - in especially arctic wildlife such as polar bears (Ursus maritimus) as well as humans. For that purpose, we measured BMD (bone mineral density) by DXA scanning (g/cm(-2)) in 15 age and weight normalized sledge dog (Canis familiaris) bitches and their 26 pups divided into a control group (n=26) given 50-200 g/day clean pork (Suis scrofa) fat and a treated group (n=15) given 50-200 g/day OHC polluted minke whale (Balaenoptera acutorostrata) blubber as main lipid sources. The results showed that BMD increased significantly with age (linear regression: p<0.0001, r(2)=0.83, n=41) while no sex difference was found in the F-generation (two-way ANOVA: all p>0.3). No differences in BMD(femur) or BMD(vertebrae) between exposed and control individuals in the bitch generation were found (linear mixed effect model: both p>0.38). Likewise, no difference between exposed and control subadults and juveniles in the F-generation was found (two-way ANOVA: all p>0.33). Correlation analyses between BMD(femur), BMD(vertebrae) and groups of OHCs, respectively, did not show any statistically significant relationships nor a clear or decreasing trend (Pearson's: p: 0.07-0.78; r: -0.2-0.59; n: 10-18). As the groups were similar regarding genetics, age and sex are the only factors that can explain this observation. Either the pollutants did not have an impact on BMD using the present time frame and OHC concentrations (threshold levels not reached), or the difference in food composition (mainly vitamins and n3 fatty acids) conceal the potential OHC impact on BMD. Such information is important when evaluating the positive and negative health consequences from eating polluted marine species.     

Flexibility,learning, and irreversibility in environmental decisions: A bayesian approach

The Bayes decision is characterized and studied for a two-period decision problem involving a proposed resource development project. It is assumed that development is irreversible and that expectations about benefits and costs during the second period vary with experiences resulting from the first-period action. The amount and types of learning achieved depend upon the particular action taken during the first period. Flexible sequential decision procedures are compared with fixed once-and-for-all decisions. It is shown that under this specification, optimal development decisions are not necessarily more conservative when a sequential procedure is used. The possibility of reneging on a fixed decision is formally specified and studied.     

Shunning the night to elude the hunter: diurnal fireflies and the “femmes fatales”

Summary. Lucidota atra, a diurnal firefly, shares possession of defensive steroids (lucibufagins or LBGs) with nocturnal fireflies of the genus Photinus. Photinus are protected against predators by their LBGs, but not against fireflies of the genus Photuris, the so-called firefly femmes fatales, which prey upon Photinus, thereby acquiring LBGs for their own defense. We propose that L. atra may have been prompted evolutionarily to become diurnal by the opportunity to avoid, thereby, being hunted by Photuris. Indeed, L. atra, if offered to Photuris, were eagerly devoured by the latter, which sequestered their LBG’s. In feeding on L. atra, Photuris may be driven by a gustatory affinity for LBGs. Persistent nocturnality might therefore have put L. atra at risk vis à vis Photuris. Diurnality freed the firefly from that risk, without compromising its defended status with respect to other predators. Possession of LBGs may in fact account for L. atra’s unacceptability to birds and spiders.     

Effect of bombardier beetle spray on a wolf spider: repellency and leg autotomy

Summary. Data are presented on the repellency of the spray of a bombardier beetle (Pheropsophus aequinoctialis) to a lycosid spider (Lycosa ceratiola). The secretion is shown to cause the spider to desist from its assault on the beetle within, on average, 58 ms of onset of the beetle’s secretory emission, a reaction time that is at a par with latencies previously reported for startle, escape, and avoidance reactions of cockroaches, flies, and moths. Spray ejections by the beetle, are shorter in duration (43 ms, on average) than the response time of the spider, an indication that the beetle does indeed pack a formidable “punch” into its ejection. After being hit by a beetle’s spray, L. ceratiola were found occasionally to autotomize one or two of their legs. It is argued, but not proven, that this unusually severe effect from exposure to an arthropodan defensive secretion may be caused by the high temperature of the bombardier beetle spray.     

Synthetische Nanopartikel — Entwicklungschancen im Dialog

This article provides an overview on the opportunities and risks of nanotechology. It is the outcome of a first national stakelholder dialogue carried out by the Federal Environment Ministry in October 2005. Recommendations are provided for further risk communication.     

Effects of a decrease in downwelling irradiance on the daytime vertical distribution patterns of zooplankton and micronekton

The daytime vertical distribution of several species of crustaceans, gelatinous zooplankton, and fish were monitored in situ simultaneously with measurements of downwelling irradiance in Oceanographer Canyon in July 1999. During this submersible-based research cruise, an influx of turbid water significantly decreased downwelling irradiance and had a substantial impact on the depth distributions of a number of organisms. Several species of crustaceans, (Thysanoessa gregaria and Sergestes arcticus) and gelatinous zooplankton (Salpa aspera and Salpa fusiformis) ascended over 100 m in the water column during the influx and returned to their pre-influx depths once the influx had ceased. In situ light measurements demonstrated that each of these species was associated with the same irradiance levels during the influx as they were under pre- and post-influx conditions. By contrast, a statistically significant change in temperature, salinity, and oxygen concentrations measured post-influx had no apparent impact on the depth distributions. These results indicate that these species were adjusting their depth distributions to remain within a range of preferred irradiances. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/10.1007/s002270020788     

Juvenile Survival in a Population of Neotropical Migrant Birds

Determination of population productivity of Neotropical migrant birds and assessment of breeding habitat quality have been based on population densities and nesting success. Data on juvenile survival improve our estimates of population productivity, provide information on factors during the post-fledging period that affect this productivity and, with comparative data, enable us to better assess breeding habitat quality. We present the first estimate of post-fledging juvenile survival in a population of Neotropical migrant birds. We studied post-fledging survival in a population of Wood Thrush ( Hylocichla mustelina) in southern Missouri, (U.S.) an area hypothesized to contain source populations. Nesting success during our study period was 0.266, and individual survival within the nest was 0.245. Post-fledging survival during the first 8 weeks after fledging was 0.423. Survival varied significantly between post-fledging weekly age classes, with survival of weeks 1, 2, 3, and 4 through 8 being 0.716, 0.930, 0.637, and 1.00, respectively. Probability of predation after fledging was 0.506. Probability of mortality by other causes was 0.071. Probability of predation varied by weekly age class and may have been related to behaviors occurring at different developmental stages. Post-fledging survival was not correlated with nestling mass and did not change throughout the course of the breeding season. Analysis of the source/sink status of the population based on our estimates of nesting success and post-fledging survival indicates that young were being produced below replacement levels during our study period. Large-scale management decisions should take into account potential fluctuations in the productivity of Neotropical migrant populations over time. Data on post-fledging juvenile survival are needed from other populations of Neotropical migrant birds to more accurately assess differential productivity between populations and better assess breeding habitat quality.