Assessing the impacts of partial mass depletion in DNAPL source zones I. Analytical modeling of source strength functions and plume response

Analytical solutions are developed for approximating the time-dependent contaminant discharge from DNAPL source zones undergoing dissolution and other decay processes. The source functions assume a power relationship between source mass and chemical discharge and can consider partial DNAPL source remediation (depletion) at any time after the initial DNAPL release. The source functions are used as a time-dependent boundary condition in an idealized chemical transport model to develop leading order approximations of the plume response to DNAPL source removal. The results suggest that partial DNAPL remediation does not tend to have a dramatic impact on the maximum extent of the plume if very low concentration values are used to define the plume boundaries. However, the solutions show that partial DNAPL removal from the source zone is likely to lead to large reductions in plume concentrations and mass, and it reduces the longevity of the plume. When the mass discharge from the source zone is linearly related to the DNAPL mass, it is shown that partial DNAPL depletion leads to linearly proportional reductions in the plume mass and concentrations.     

Sources and fate of PCDD and PCDF

PCDD and PCDF were found in urban air particulates from St. Louis and Washington, D.C., and in sediments from the Great Lakes and Siskiwit Lake, Isle Royale. The similarity between the PCDD and PCDF found in air particulates and sediment samples and the presence of PCDD and PCDF in sediment from Siskiwit Lake (a location which can receive only atmospheric inputs) suggest that these compounds are emitted to the atmosphere from combustion sources. The historical input of PCDD and PCDF to dated sediment cores shows a strong increase since 1940, and this suggests that the incineration of chlorinated organic compounds is an important source of PCDD and PCDF to the environment.     

The highs and lows of chemical communication in giant pandas (Ailuropoda melanoleuca): effect of scent deposition height on signal discrimination

The giant panda's (Ailuropoda melanoleuca) social system is not well known, but it is clear that competition and avoidance characterizes social interaction for this solitary species throughout most of the year. Chemical communication appears to play a major role in structuring these interactions. Pandas adopt four distinct marking postures that deposit anogenital gland secretions or urine at varying heights: squat, reverse, legcock and handstand. In this experiment we tested the behavioral responses of 28 captive pandas belonging to all age-sex groups to conspecific odors placed to mimic the height of these postures. We tested three odor stimuli: male urine, and male and female glandular secretions. In all cases, pandas spent more time investigating higher odors than lower odors, suggesting that pandas place more importance on gathering information about individuals that adopt elevated postures. Pandas, particularly subadult males, also showed evidence of avoiding areas where adult male urine was deposited to mimic the handstand posture. Based on these and other findings, we propose that elevated postures in pandas may function to communicate competitive ability and possibly aggressive intent. Height of odor deposition, especially in the handstand posture, may be associated with body size, a major determinant of competitive ability. Selection may favor signalers that capitalize on the assessment activities of assessors by depositing scents to emphasize height cues. If such signals of competitive ability are used to mediate aggressive interactions, subsequent selection may favor their use only when the signaler is prepared to escalate in a contest.     

A Practice-based Approach to Ecosystem Management

Ecosystem management is a rapidly evolving philosophy or paradigm of natural resource management intended to sustain the integrity of ecosystems. The problem is that principles of ecosystem management are unsatisfactory for practical purposes. Three major approaches to the problem are evaluated: (1) clarification of the goals of ecosystem management, (2) construction of a better scientific foundation for management decisions, and (3) comparative appraisal of current practices. The evaluation concludes that neither of the first two approaches is necessary or sufficient for better management decisions because better decisions depend upon the complexities of particular contexts. The third, practice-based approach makes the most of the limited human capacity to cope with the complexities of ecosystem management in order to improve principles of ecosystem management, to inform particular management decisions through improved principles, and to incorporate clearer goals and a better scientific foundation as they become available. The evaluation draws on experience and disciplines beyond conservation biology and natural resource management, including policy sciences.     

Antipredator responses of California ground squirrels to rattlesnakes and rattling sounds: the roles of sex,reproductive parity,and offspring age in assessment and decision-making rules

California ground squirrels (Spermophilus beecheyi) and northern Pacific rattlesnakes (Crotalus viridus oreganus) have an adversarial relationship. Adults are partially protected by venom resistance and harass rattlesnakes in part to defend their more vulnerable offspring. Larger, warmer snakes are more dangerous than smaller colder snakes, and in escalated conflict squirrels could benefit from risk assessment strategies. Rattlesnakes often rattle at harassing squirrels and rattling sounds produce cues related to body size and temperature. In study 1 we played back rattling sounds from snakes that varied in dangerousness and evaluated the roles of sex and parity in squirrel risk assessment strategies. In general, squirrels tail flagged and stood bipedally more, and were slower to reapproach the playback speaker following playbacks of rattling sounds from more dangerous snakes. In comparison with males and nonmothers, mothers were most responsive to rattling sounds and more sensitive to variation in snake dangerousness. Mothers tail flagged more than males and nonmothers, and this behavior tracked variation in snake dangerousness most closely, perhaps reflecting the effects of snake size and temperature on pup vulnerability. These findings suggest that many aspects of squirrel antisnake behavior are governed by their effects on descendant kin. In study 2 we tested the effects of offspring age on mothers responses to live rattlesnakes and rattling sounds. According to the offspring value hypothesis, mothers should take more risks in defense of older offspring because they are more likely to survive to reproductive age. By contrast, under the offspring vulnerability hypothesis, older offspring are less vulnerable to predators and thus mothers should take fewer risks. Risk-taking, as measured by behaviors that bring the squirrel close to the snakes strike range, was either unaffected by or negatively correlated with offspring age. Thus, our findings suggest that whereas offspring value is unimportant in squirrel antisnake behavior, offspring vulnerability may affect maternal defense. We suggest that offspring vulnerability in mammals, in comparison with birds, may play a larger role in parental defense against predators.Communicated by P.A. BednekoffAn erratum to this article can be found at     

Prenatal diagnosis of giant cystic hygroma: Prognosis,counselling, and management; case presentation and review of the recent literature

Cystic hygromas have historically been associated with a grim prognosis when discovered during prenatal sonographic study of the fetus. This same grim prognosis is not observed by the paediatric surgeon who evaluates the neonate or paediatric patient. We present a fetal patient with a massive anterior cystic hygroma discovered in the third trimester prior to 30 weeks. This case and a review of the literature suggest tailoring the prognosis by category when counselling patients: (1) first trimester, normal karyotype-good; (2) first trimester, abnormal karyotype-poor; (3) second trimester and early third-poor to guarded; and (4) mid to late third trimester-good.     

Cadmium content of shellfish of the South Carolina fishery

A survey of cadmium residues in shellfish from the Atlantic Coast of South Carolina was undertaken to see the magnitude of cadmium contamination in the South Carolina Fishery. The shellfish collected were oysters, clams, crabs, shrimps, and scallops. Shellfish samples were dissected and pieces of edible muscle tissue were incubated in reagent grade nitric acid, at a constant temperature shaking-water bath at 58°C. Cadmium levels were determined by flame atomic absorption. The distribution pattern of the element Cd in shellfish is different in various species. It seems that shellfish contained more Cd content levels than other saltwater boney fish. It was found that Cd levels were relatively higher in oysters, shrimps, and clams than crabs and scallops. Larger shellfish had higher Cd content than the smaller shellfish of the same species. Elevated levels of Cd found in these shellfish species of edible fish were not high enough to render them dangerous for human consumption.     

Stomatal uptake of O3 in aspen and aspen-birch forests under free-air CO2 and O3 enrichment

Rising atmospheric carbon dioxide (CO₂) may alleviate the toxicological impacts of concurrently rising tropospheric ozone (O₃) during the present century if higher CO₂ is accompanied by lower stomatal conductance (g_s), as assumed by many models. We investigated how elevated concentrations of CO₂ and O₃, alone and in combination, affected the accumulated stomatal flux of O₃ (AFst) by canopies and sun leaves in closed aspen and aspen-birch forests in the free-air CO₂-O₃ enrichment experiment near Rhinelander, Wisconsin. Stomatal conductance for O₃ was derived from sap flux data and AFst was estimated either neglecting or accounting for the potential influence of non-stomatal leaf surface O₃ deposition. Leaf-level AFst (AFst_l) was not reduced by elevated CO₂. Instead, there was a significant CO₂ × O₃ interaction on AFst_l, as a consequence of lower values of g_s in control plots and the combination treatment than in the two single-gas treatments. In addition, aspen leaves had higher AFst_l than birch leaves, and estimates of AFst_l were not very sensitive to non-stomatal leaf surface O₃ deposition. Our results suggest that model projections of large CO₂-induced reductions in g_s alleviating the adverse effect of rising tropospheric O₃ may not be reasonable for northern hardwood forests.     

Attachment,decay, and social network

To study decay in attachment to an organization, I analyse data on women who obtained an MBA from the University of Chicago's Graduate School of Business (GSB). I measure attachment in terms of network embedding: an alumna is attached to the GSB to the extent that people close to her graduated from the GSB. Behavioral data corroborate the network data in that alumnae measured to be more attached are more likely to have joined an alumni club and made a financial contribution to the school. The hypothesis is that alumnae attachment will decay over time, more slowly when the school is deeply embedded in an alumna's network, more quickly when disruptive events compete for the alumna's time and energy. As expected, attachment declines across the years after graduation (linearly for the first 20 years to about half its initial level), and decay is inhibited when connections with GSB graduates are embedded in stable relations of family, work, or long-term friendship. Decay is remarkably robust to events after graduation (which account for only 2 per cent of explained variance in attachment). In other words, an alumna's attachment today was largely determined while she was in school. The results should be of practical value to people who design programmes to build personal attachment to organizations, and of theoretical interest to scholars who study such connections. Copyright © 2001 John Wiley & Sons, Ltd.