STRUCTURAL EQUATION MODELING OF DYNAMICS OF NITRATE CONTAMINATION IN GROUND WATER1

ABSTRACT: Most research on the temporal aspect of nitrate pollution in water resources has focused on surface water. Comprehensive studies on the dynamics of nitrate in ground water are lacking, especially on a drainage basin scale and for relatively long periods of time. In this study, structural equation modeling is applied in investigating the influences of climate, hydrology, and nitrogen management in agricultural production on nitrate concentration in the Big Spring Basin, Iowa, over a 10-year period. The study shows that for given hydrogeological settings, nitrogen management practices and climate are the two most important factors that affect nitrate dynamics. The long-term trend of nitrate is closely related to the nitrogen input primarily determined by management practices. The potential effects of nitrogen management, however, are contingent on the variations of climate. The improvements in water quality (reduced nitrate concentration and loads) in relation to improved nitrogen management are often overshadowed by the impact of climate, especially in extremely dry or wet years. The variations of climate and hydrology have much greater impacts on the nitrate dynamics than the changes in nitrogen input. This study reveals significant seasonal variation in the relations between nitrate concentration and influencing factors, which is also closely related to the seasonal variation in climate. Assessment of management practices and resultant water quality should consider the impact of short- and long-term climate dynamics.     

Formation of chlorinated hydrocarbons during combustion of poly (vinyl chloride)

Pilot-scale experiments were carried out to study the formation of chlorinated hydrocarbons through combustion of PVC. Vinyl chloride, dichloro-, trichloro-, tetrachloro-, pentachloro-, and hexachlorobenzenes were determined by GC/ECD. Furthermore, some peaks in the chromatogram were tentatively assigned to octachlorostyrene and PCB. The total amount of lipophilic organochlorinated compounds was determined by neutron activation analysis. The results indicate that incineration of PVC is not a major source of chlorinated hydrocarbons in the environment.     

Comparative health impact assessment of local and regional particulate air pollutants in Scandinavia

The ongoing program Clean Air for Europe (CAFE) is an initiative from the EU Commission to establish a coordinated effort to reach better air quality in the EU. The focus is on particulate matter as it has been shown to have large impact on human health. CAFE requested that WHO make a review of the latest findings on air pollutants and health to facilitate assessments of the different air pollutants and their health effects. The WHO review project on health aspects of air pollution in Europe confirmed that exposure to particulate matter (PM), despite the lower levels we face today, still poses a significant risk to human health. Using the recommended uniform risk coefficients for health impact assessment of PM, regardless of sources, premature mortality related to long-range transported anthropogenic particles has been estimated to be about 3500 deaths per year for the Swedish population, corresponding to a reduction in life expectancy of up to about seven months. The influence of local sources is more difficult to estimate due to large uncertainties when linking available risk coefficients to exposure data, but the estimates indicate about 1800 deaths brought forward each year with a life expectancy reduction of about 2-3 months. However, some sectors of the population are exposed to quite high locally induced concentrations and are likely to suffer excessive reductions in life expectancy. Since the literature increasingly supports assumptions that combustion related particles are associated with higher relative risks, further studies may shift the focus for abatement strategies. CAFE sets out to establish a general cost effective abatement strategy for atmospheric particles. Our results, based on studies of background exposure, show that long-range transported sulfate rich particles dominate the health effects of PM in Sweden. The same results would be found for the whole of Scandinavia and many countries influenced by transboundary air pollution. However, several health studies, including epidemiological studies with a finer spatial resolution, indicate that engine exhaust particles are more damaging to health than other particles. These contradictory findings must be understood and source specific risk estimates have to be established by expert bodies, otherwise it will not be possible to find the most cost effective abatement strategy for Europe. We are not happy with today's situation where every strategy to reduce PM concentrations is estimated to have the same impact per unit change in the mass concentration. Obviously there is a striking need to introduce more specific exposure variables and a higher geographical resolution in epidemiology as well as in health impact assessments.     

Molecular Weight Changes and Polymeric Matrix Changes Correlated with the Formation of Degradation Products in Biodegraded Polyethylene

The molecular weight changes in abiotically and biotically degraded LDPE and LDPE modified with starch and/or prooxidant were compared with the formation of degradation products. The samples were thermooxidized for 6 days at 100°C to initiate degradation and then either inoculated with Arthobacter paraffineus or kept sterile. After 3.5 years homologous series of mono- and dicarboxylic acids and ketoacids were identified by GC-MS in abiotic samples, while complete disappearance of these acids was observed in biotic environments. The molecular weights of the biotically aged samples were slightly higher than the molecular weights of the corresponding abiotically aged samples, which is exemplified by the increase in from 5200 g/mol for a sterile sample with the highest amount of prooxidant to 6000 g/mol for the corresponding biodegraded sample. The higher molecular weight in the biotic environment is explained by the assimilation of carboxylic acids and low molecular weight polyethylene chains by microorganisms. Assimilation of the low molecular weight products is further confirmed by the absence of carboxylic acids in the biotic samples. Fewer carbonyls and more double bonds were seen by FTIR in the biodegraded samples, which is in agreement with the biodegradation mechanism of polyethylene.     

瑞典沿岸水域濒临消失的大叶藻(Zostera Marina,L.)

在瑞典斯卡格拉克海峡沿岸,大叶藻(Zostera marina)是一种生长在浅水软海底上的优势显花植物.大叶藻场是许多甲壳动物和鱼类,不管是洄游种或是稳定种的重要群落生境.在20世纪80年代期间,作为海岸带管理的基础,对瑞典西海岸有大叶藻生长的沿岸浅水区的资源进行了调查.在这次研究中我们再次考察了斯卡格拉克海峡200km沿岸的5个沿海地区中的2000hm2大叶藻场.资源调查的方法(水下测量镜)与80年代的一样,但通过使用全球定位系统(GPS)增加了绘图的精确度.这次研究的结果表明,在10～15年的时间里,大叶藻的区域延伸面积减少了58%,且地区变化很大.大叶藻的减少主要限于大叶藻场的浅水部分.本文探讨了原因和生态后果.     

Chest injuries of elderly postmortem human surrogates (PMHSs) under seat belt and airbag loading in frontal sled impacts: Comparison to matching THOR tests

Abstract

Objective: The goal of the study was to develop experimental chest loading conditions that would cause up to Abbreviated Injury Scale (AIS) 2 chest injuries in elderly occupants in moderate-speed frontal crashes. The new set of experimental data was also intended to be used in the benchmark of existing thoracic injury criteria in lower-speed collision conditions.

Methods: Six male elderly (age >63) postmortem human subjects (PMHS) were exposed to a 35?km/h (nominal) frontal sled impact. The test fixture consisted of a rigid seat, rigid footrest, and cable seat back. Two restraint conditions (A and B) were compared. Occupants were restrained by a force-limited (2.5?kN [A] and 2?kN [B]) seat belt and a preinflated (16?kPa [A] and 11?kPa [B]; airbag). Condition B also incorporated increased seat friction. Matching sled tests were carried out with the THOR-M dummy. Infra-red telescoping rod for the assessment of chest compression (IRTRACC) readings were used to compute chest injury risk. PMHSs were exposed to a posttest injury assessment. Tests were carried out in 2 stages, using the outcome of the first one combined with a parametric study using the THUMS model to adjust the test conditions in the second. All procedures were approved by the relevant ethics board.

Results: Restraint condition A resulted in an unexpected high number of rib fractures (fx; 10, 14, 15 fx). Under condition B, the adjustment of the relative airbag/occupant position combined with a lower airbag pressure and lower seat belt load limit resulted in a reduced pelvic excursion (85 vs. 110?mm), increased torso pitch and a substantially lower number of rib fractures (1, 0, 4 fx) as intended.

Conclusions: The predicted risk of rib fractures provided by the THOR dummy using the C_max and PC Score injury criteria were lower than the actual injuries observed in the PMHS tests (especially in restraint condition A). However, the THOR dummy was capable of discriminating between the 2 restraint scenarios. Similar results were obtained in the parametric study with the THUMS model.     

Changes Versus Homeostasis in Alpine and Sub-Alpine Vegetation Over Three Decades in the Sub-Arctic

Plant species distributions are expected to shift and diversity is expected to decline as a result of global climate change, particularly in the Arctic where climate warming is amplified. We have recorded the changes in richness and abundance of vascular plants at Abisko, sub-Arctic Sweden, by re-sampling five studies consisting of seven datasets; one in the mountain birch forest and six at open sites. The oldest study was initiated in 1977–1979 and the latest in 1992. Total species number increased at all sites except for the birch forest site where richness decreased. We found no general pattern in how composition of vascular plants has changed over time. Three species, Calamagrostis lapponica, Carex vaginata and Salix reticulata, showed an overall increase in cover/frequency, while two Equisetum taxa decreased. Instead, we showed that the magnitude and direction of changes in species richness and composition differ among sites.     

Brood sex ratios, female harem status and resources for nestling provisioning in the great reed warbler (Acrocephalus arundinaceus)

The theory of parental investment and brood sex ratio manipulation predicts that parents should invest in the more costly sex during conditions when resources are abundant. In the polygynous great reed warbler, Acrocephalus arundinaceus, females of primary harem status have more resources for nestling provisioning than secondary females, because polygynous males predominantly assist the primary female whereas the secondary female has to feed her young alone. Sons weigh significantly more than daughters, and are hence likely to be the more costly sex. In the present study, we measured the brood sex ratio when the chicks were 9 days old, i.e. the fledging sex ratio. As expected from theory, we found that female great reed warblers of primary status had a higher proportion of sons in their broods than females of lower (secondary) harem status. This pattern is in accordance with the results from two other species of marsh-nesting polygynous birds, the oriental reed warbler, Acrocephalus orientalis, and the yellow-headed blackbird Xanthocephalus xanthocephalus. As in the oriental reed warbler, we found that great reed warbler males increased their share of parental care as the proportion of sons in the brood increased. We did not find any difference in fitness of sons and daughters raised in primary and secondary nests. The occurrence of adaptive sex ratio manipulations in birds has been questioned, and it is therefore important that three studies of polygynous bird species, including our own, have demonstrated the same pattern of a male-biased offspring sex ratio in primary compared with secondary nests. Received: 1 June 1999 / Received in revised form: 10 January 2000 / Accepted: 12 February 2000     

Urban dose rates at Gävle, Göteborg and Lund

Besides gamma rays from ¹³⁷Cs emanating from the Chernobyl accident, gamma rays from natural radionuclides are a dominant source of radiation exposure to the public. Since people spend much more time indoors than outdoors the radiation dose obtained inside dwellings contributes greatly to individual and collective doses. Dose rate measurements were made at 20 locations within the city of Göteborg and at further 22 reference sites within a radius of 100 km. Measurements were also made at Gävle and Lund. The dose rates were measured with RNI intensimeters, TLD (LiF) meters and in in situ measurements using an HPGe. The ground cover was grass, asphalt, concrete slates or paving-stones. The dose rates varied between 0.05 and 0.25 μSv/h. Also performed in different ways, measurements made inside and outside buildings at both Göteborg and Gävle showed inside dose rates higher than outside dose rates.