Abstract: Evaluating the relative amounts of water moving through the different components of the hydrological cycle is required for precise management and planning of water resources. An important aspect of this evaluation is the partitioning of streamflow into surface (quick flow) and base‐flow components. A prior study evaluated 40 different approaches for hydrograph‐partitioning on a field scale watershed in the Coastal Plain of the Southeastern United States and concluded that the Boughton’s method produced the most consistent and accurate results. However, its accuracy depends upon the proper estimation of: (1) the end of surface runoff, and (2) the fraction factor (α) that is function of many physical and hydrologic characteristics of a watershed. Proper identification of the end of surface runoff was accomplished by using a second derivative approach. Applying this approach to 12 years of separately measured surface and subsurface flow data from a field scale watershed (study area) proved to be accurate for 87% of the time. Estimation of the α value was accomplished in this study using two steps: (1) alpha was fitted to individual hydrographs: and, (2) a regression equation that determines these alpha values based on climatological factors (e.g., rainfall, evapotranspiration) was developed. Using these strategies improved the streamflow partitioning method’s performance significantly. 相似文献
In this study, habitat surveys were undertaken on 50 grass-based farms in SE Ireland and data digitised onto aerial photography. Additional data i.e. stocking rates, and participation (or otherwise) in the Irish Rural Environment Protection Scheme (REPS) were collected and analysed as possible explanatory variables for farm habitat composition.Results indicated that approximately 14.3% of the land area of sampled farms comprised of semi-natural habitat types, a proportion substantially greater than has been reported for many other European countries. The most frequently recorded semi-natural habitats included, field boundaries, scrub, and deciduous and riparian woodlands.Multivariate analysis of farm habitat configuration showed a strong dichotomy between dairy and non-dairy farming systems. Habitats such as intensively managed grassland and built ground were closely associated with dairy-based enterprises. In contrast, the incidence of other habitat types was associated with non-dairy and/or REPS participating enterprises. The ecological quality of field boundaries as assessed by the Field Boundary Evaluation and Grading System (FBEGS) Index was significantly greater on dairy, compared with dry-stock farms.This dichotomy in farm habitat composition is not reflected within current Agri-Environment (AE) policy. Integration of locally important drivers of habitat diversity into the design and implementation of AE policy, is integral to the successful performance of AE schemes. 相似文献
Objective: Soldiers in military vehicles subjected to underbelly blasts can sustain traumatic head and neck injuries due to a head impact with the roof. The severity of head and neck trauma can be influenced by the amount of head clearance available to the occupant as well as factors such as wearing a military helmet or the presence of padding on the interior roof. The aim of the current study was to examine the interaction between a Hybrid III headform, the helmet system, and the interior roof of the vehicle under vertical loading.
Methods: Using a head impact machine and a Hybrid III headform, tests were conducted on a rigid steel plate in a number of different configurations and velocities to assess helmet shell and padding performance, to evaluate different vehicle roof padding materials, and to determine the relative injury mitigating contributions of both the helmet and the roof padding. The resultant translational head acceleration was measured and the head injury criterion (HIC) was calculated for each impact.
Results: For impacts with a helmeted headform hitting the steel plate only, which represented a common scenario in an underbelly blast event, velocities of ≤6 m/s resulted in HIC values below the FMVSS 201U threshold of 1,000, and a velocity of 7 m/s resulted in HIC values well over the threshold. Roof padding was found to reduce the peak translational head acceleration and the HIC, with rigid IMPAXX foams performing better than semirigid ethylene vinyl acetate (EVA) foam. However, the head injury potential was reduced considerably more by wearing a helmet than by the addition of roof padding.
Conclusions: The results of this study provide initial quantitative findings that provide a better understanding of helmet–roof interactions in vertical impacts and the contributions of the military helmet and roof padding to mitigating head injury potential. Findings from this study will be used to inform further testing with the future aim of developing a new minimum head clearance standard for occupants of light armored vehicles. 相似文献
ABSTRACT: The approximate streamflow partitioning method which uses daily rainfall and streamfiow data was applied in Coastal Plain, Coastal Flatwoods, and Southern Piedmont physiographic regions for estimation of the surface and subsurface flow components of total streainflow. Sizes of the watersheds ranged from 9.6 km2 to 1,030 km. Although the streamflow partitioning method was developed and tested on the Coastal Plain physiographic region, results indicate that the procedure can be applied to other physiographic regions where available data are limited to daily values. The effect of channelization on the partitioned flow components in the Coastal Plain and Coastal Flatwoods physiographic areas was also examined. While channelization was found to decrease the storm-time base, it had no significant effect on the relative percentages of the partitioned flow components. 相似文献
Groundwater samples, taken from 73 wells in 10 counties of southeast Michigan in 1997 had arsenic concentrations in the range of 0.5 to 278 microg/L the average being 29 microg/l. About 12% of these wells had arsenic concentrations that exceeded the current USEPA's maximum contaminant level of 50 microg/l. Most (53-98%) of the arsenic detected was arsenite [As(III)] and other observations supported the arsenic species distribution (low redox potential and DO). In shallow groundwater (< 15 m), arsenic concentrations are low likely due to the formation of insoluble ferrosoferric hydroxide complex. In deep groundwater (> 15 m), the concentration of arsenic is possibly controlled by reductive dissolution of arsenic-rich iron hydroxide/oxyhydroxide and dissolution of arsenic sulfide minerals. 相似文献
Farmland habitat diversity in marginal European landscapes changed significantly in the past decades. Further changes toward
homogenization are expected, particularly in the course of European agricultural policy. Based on three alternative transfer
payment schemes, we modeled spatially explicit potential effects on the farmland habitat diversity in a marginal European
landscape. We defined (1) a scenario with direct transfer payments coupled to production, (2) a scenario with direct transfer
payments decoupled from production, and (3) a scenario phasing out all direct transfer payments. We characterized habitat
diversity with three indices: habitat richness, evenness, and rarity. The habitat pattern in 1995 served as reference for
comparison. All scenarios predicted a general trend of homogenization of the farmland habitat pattern, yet to a differing
extent. Transfer payments coupled to production (Scenario 1) favored the abandonment of agricultural production, particularly
in low-productive areas and arable land use in more productive areas. Habitat richness and habitat evenness had intermediate
values in this scenario. Decoupling transfer payments from production (Scenario 2) supported grassland as most profitable
farming system. This led to a grassland-dominated landscape with low values of all habitat diversity indices. Phasing out
transfer payments (Scenario 3) resulted in complete abandonment or afforestation of agricultural land and extremely low values
in all habitat diversity indices. Scenario results indicate that transfer payments may prevent cessation of agricultural production,
but may not counteract homogenization in marginal landscapes. Conserving high farmland habitat diversity in such landscapes
may require support schemes, e.g., Pillar Two of EU Common Agricultural Policy. 相似文献
Summary We have devised a radionuclide technique that allows the assessment of matrilineal kinship by the transfer of unique combinations of gamma-emitting radionuclides from pregnant and lactating female meadow voles (Microtus pennsylvanicus) to their offspring. A pool of prospective fathers can be established from field records of reproductively active males that were alive at the time of conception of the female's litter. Electrophoresis of 6 proteins allowed us to eliminate genetically incompatible males from the prospective pool of fathers. A log-likelihood statistic provided an estimate of the probability of paternity. In the case of numerical ties physical proximity of the males to the mother at the time of conception was used. With these techniques, we established 40 kinships in a field population of meadow voles. 相似文献
Arsenic concentrations exceeding 10 μg/l, the United States maximum contaminant level and the World Health Organization guideline
value, are frequently reported in groundwater from bedrock and unconsolidated aquifers of southeastern Michigan. Although
arsenic-bearing minerals (including arsenian pyrite and oxide/hydroxide phases) have been identified in Marshall Sandstone
bedrock of the Mississippian aquifer system and in tills of the unconsolidated aquifer system, mechanisms responsible for
arsenic mobilization and subsequent transport in groundwater are equivocal. Recent evidence has begun to suggest that groundwater
recharge and characteristics of well construction may affect arsenic mobilization and transport. Therefore, we investigated
the relationship between dissolved arsenic concentrations, reported groundwater recharge rates, well construction characteristics,
and geology in unconsolidated and bedrock aquifers. Results of multiple linear regression analyses indicate that arsenic contamination
is more prevalent in bedrock wells that are cased in proximity to the bedrock-unconsolidated interface; no other factors were
associated with arsenic contamination in water drawn from bedrock or unconsolidated aquifers. Conditions appropriate for arsenic
mobilization may be found along the bedrock-unconsolidated interface, including changes in reduction/oxidation potential and
enhanced biogeochemical activity because of differences between geologic strata. These results are valuable for understanding
arsenic mobilization and guiding well construction practices in southeastern Michigan, and may also provide insights for other
regions faced with groundwater arsenic contamination. 相似文献