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981.
Relationship between water repellency and native and petroleum-derived organic carbon in soils 总被引:1,自引:0,他引:1
Some soils develop severe and persistent water repellency following contamination with crude oil. This study was conducted to characterize and compare the spatial distribution of soil water repellency and residual oil contamination at 12 such sites. The molarity of ethanol droplet (MED) test was used to assess soil water repellency and the content of dichloromethane-extractable organics (DEO) was used to quantify residual oil in soil. We found a relatively strong positive correlation between MED and DEO in soil (r2 = 0.74). Both variables tended to decrease abruptly with depth at 11 of the 12 study sites. Dichloromethane-extractable organics similarly decreased with depth in control adjacent soil (MED = 0 M), but from an average concentration one to two orders of magnitude lower than in water-repellent soil. Using data from corresponding control adjacent and water-repellent soils, we determined that approximately 29 and 10% of measured total organic carbon in water-repellent A- and B-horizon soil, respectively, consists of dichloromethane-insoluble organic carbon of petroleum origin. We propose that this fraction contains most of the causative agents of soil water repellency at the studied sites. 相似文献
982.
Woodard KR French EC Sweat LA Graetz DA Sollenberger LE Macoon B Portier KM Rymph SJ Wade BL Prine GM Van Horn HH 《Journal of environmental quality》2003,32(3):996-1007
In northern Florida, year-round forage systems are used in dairy effluent sprayfields to reduce nitrate leaching. Our purpose was to quantify forage N removal and monitor nitrate N (NO3(-)-N) concentration below the rooting zone for two perennial, sod-based, triple-cropping systems over four 12-mo cycles (1996-2000). The soil is an excessively drained Kershaw sand (thermic, uncoated Typic Quartzip-samment). Effluent N rates were 500, 690, and 910 kg ha(-1) per cycle. Differences in N removal between a corn (Zea mays L.)-bermudagrass (Cynodon spp.)-rye (Secale cereale L.) system (CBR) and corn-perennial peanut (Arachis glabrata Benth.)-rye system (CPR) were primarily related to the performance of the perennial forages. Nitrogen removal of corn (125-170 kg ha(-1)) and rye (62-90 kg ha(-1)) was relatively stable between systems and among cycles. The greatest N removal was measured for CBR in the first cycle (408 kg ha(-1)), with the bermudagrass removing an average of 191 kg N ha(-1). In later cycles, N removal for bermudagrass declined because dry matter (DM) yield declined. Yield and N removal of perennial peanut increased over the four cycles. Nitrate N concentrations below the rooting zone were lower for CBR than CPR in the first two cycles, but differences were inconsistent in the latter two. The CBR system maintained low NO3(-)-N leaching in the first cycle when the bermudagrass was the most productive; however, it was not a sustainable system for long-term prevention of NO3(-)-N leaching due to declining bermudagrass yield in subsequent cycles. For CPR, effluent N rates > or = 500 kg ha(-1) yr(-1) have the potential to negatively affect ground water quality. 相似文献
983.
Geographically explicit analysis tools are needed to assess forest health indicators that are measured over large regions. Spatial scan statistics can be used to detect spatial or spatiotemporal clusters of forests representing hotspots of extreme indicator values. This paper demonstrates the approach through analyses of forest fragmentation indicators in the southeastern United States and insect and pathogen indicators in the Pacific Northwest United States. The scan statistic detected four spatial clusters of fragmented forest including a hotspot in the Piedmont and Coastal Plain region. Three recurring clusters of insect and pathogen occurrence were found in the Pacific Northwest. Spatial scan statistics are a powerful new tool that can be used to identify potential forest health problems. 相似文献
984.
Agricultural Land Use Effects on Sediment Loading and Fish Assemblages in Two Minnesota (USA) Watersheds 总被引:1,自引:1,他引:0
We examined the relationship between water quality and fish communities within two agricultural areas using a computer simulation model. Our analyses focused on a coolwater stream, Wells Creek in southeastern Minnesota, and a warmwater stream, the Chippewa River in western Minnesota. We used the Agricultural Drainage and Pesticide Transport (ADAPT) model in relation to land use to calculate instream suspended sediment concentrations using estimates of sediment delivery, runoff, baseflow and streambank erosion, and quantified the effects of suspended sediment exposure on fish communities. We predicted the effects of agricultural practices on stream fish communities under several possible land use scenarios, with reference to current conditions. Land use changes led to reductions in sediment loading of up to 84% in Wells Creek and 49% in the Chippewa River. The reduction in sediment loading across scenarios may be directly related to a reduction in runoff by about 35% in both study areas. We found a 98% decrease in lethal concentrations of suspended sediment on fish in Wells Creek with an increase in conservation tillage, riparian buffers, and permanent vegetative cover. However, the effects of suspended sediment did not significantly decrease in the Chippewa River. This difference between study areas was likely due to differences in tolerance to suspended sediment between coolwater and warmwater fish communities and differences in topography, runoff and bank erosion between the two streams.
The Minnesota Cooperative Fish and Wildlife Research Unit is jointly sponsored by the US Geological Survey, the University of Minnesota, the Minnesota Department of Natural Resources, and the Wildlife Management Institute. 相似文献
985.
Mike?H.?AllsoppEmail author Johan?N.?M.?Calis Willem?J.?Boot 《Behavioral ecology and sociobiology》2003,54(6):555-561
Sections of brood from colonies of the Cape honeybee ( Apis mellifera capensis), the African honeybee ( A. m. scutellata), and hybrid bees of the two races were exchanged between colonies to study the effect of different brood-origin/nurse-bee combinations on development of caste characters. When Cape larvae were raised by African workers the amount of food provided almost doubled in comparison with Cape larvae reared by their own workers. In contrast, African larvae raised by Cape workers were provided with only half the amount they received from their own workers. After the bees emerged, we found a large degree of plasticity in characters related to caste differentiation, which corresponded closely to the amount of food provided. Super-fed Cape bees had enlarged spermathecae, were heavier than normal workers and developed more rapidly, and had reduced pollen combs, all typical for a more queen-like condition. Ovariole numbers did not appear to be enhanced by additional feeding. Cape bees that behave as social parasites in African bee colonies were most queen-like in the characters studied, albeit within the range that was found for Cape bees from normal colonies, suggesting within-colony selection for characters that enhance reproduction.Communicated by R. Page 相似文献
986.
Integrated effects of applied pressure,time, and polymer doses on alum sludge dewatering behaviour 总被引:2,自引:0,他引:2
In this study, combinations of applied pressure, pressing time and polymer dose were examined in an air pressure plate apparatus to explore their integrated influence on the dewatering of an alum sludge. Results of the investigation demonstrated that dewatering can be enhanced by increases in pressure and time. However, a point is reached at which continued increases in pressure and time offer little benefit. The data also confirmed that polymer affects the rate of water release rather than the extent of dewatering. Increased rates of water release due to increasing polymer dose can be attributed to the aggregation of sludge particles by polymer addition. It was also evident in this study that the initial sludge depth has a major impact on the average cake moisture content at a given dewatering time. It was apparent that once the initial sludge thickness exceeds about 2 cm, the water release follows a fairly similar pattern, which can be represented by a simple empirical model. 相似文献
987.
Clow David W. Striegl Robert G. Nanus Leora Mast M. Alisa Campbell Donald H. Krabbenhoft David P. 《Water, Air, & Soil Pollution: Focus》2002,2(2):139-164
A chemical survey of 69 high-altitude lakes in seven national parks in the western United States was conducted during the fallof 1999; the lakes were previously sampled during the fall of 1985, as part of the Western Lake Survey. Lakes in parks in the Sierra/southern Cascades (Lassen Volcanic, Yosemite, Sequoia/Kings Canyon National Parks) and in the southern RockyMountains (Rocky Mountain National Park) were very dilute; medianspecific conductance ranged from 4.4 to 12.2 S cm-1 andmedian alkalinity concentrations ranged from 32.2 to 72.9 eqL-1. Specific conductances and alkalinity concentrations were substantially higher in lakes in the central and northernRocky Mountains parks (Grand Teton, Yellowstone, and GlacierNational Parks), probably due to the prevalence of more reactivebedrock types. Regional patterns in lake concentrations of NO3 and SO4 were similar to regional patterns in NO3 and SO4 concentrations in precipitation, suggestingthat the lakes are showing a response to atmospheric deposition.Concentrations of NO3 were particularly high in Rocky Mountain National Park, where some ecosystems appear to be undergoing nitrogen saturation. 相似文献
988.
Edwin D Geetha VR Vishwanathan H Usha Rani MV 《Journal of environmental biology / Academy of Environmental Biology, India》2002,23(4):373-376
Common use of antimutagens and anticarcinogens in everyday life is an effective measure for preventing human cancer and genetic diseases. Antioxidant properties of tea have vast potential as protective agents against diverse toxic effects. The present study was aimed to evaluate the role of aqueous clonal tea extracts (green tea, oolong tea and black tea) in modulating the genotoxic damage induced by cyclophosphamide (CP), a commonly used chemotherapeutic drug and a well-known mutagen and clastogen. All the three tea extracts at 1 and 2% concentration did not increase the frequency of micronucleated polychromatic erythrocytes (MPE) in bone marrow cells of mice when administered individually. The tea extracts decreased the micronuclei (MN) induced by CP. Therefore, regular intake of tea may improve the antioxidant status in in vivo and thereby reduce the risk of cancer and coronary heart disease. 相似文献
989.
Water, even in its natural environment, contains some level of impurities. Water is nearly a universal solvent. It contains dissolved solids and gases, and hosts a number of micro-organisms. The exploitation of groundwater by means of boreholes for supplying small user groups and rural communities with water has been widely applied in certain parts of the world for several decades. In recent years this practice has spread all over the globe, and hundred of thousands of boreholes have beendrilled to tap low-yield aquifers. It is evident that such boreholes require pumps for lifting thewater. In developing countries these are usually handpumps, butsolar as well as other systems with submersible pumps are also used, depending upon the energy sources available and the financial means of the beneficiaries. This article gives a general overview of groundwater quality with regard to itsphysico-chemical composition. The results presented originatefrom the experience gained from handpump equipped boreholes within the UNICEF through German Centre for Technical EducationTransfer executed inter-regional UNDP-Handpumps Project inWest African Regions. Particular attention is paid to presenting corrosion onthe water quality of wells in terms of iron concentrationand other parameters. Furthermore, the corrosion attack ongalvanised iron, the effect of biofilms on the corrosionrate, and the difference between internal and externalcorrosion of rising mains are shown. 相似文献
990.
Grulke NE Preisler HK Fan CC Retzlaff WA 《Environmental pollution (Barking, Essex : 1987)》2002,119(2):163-175
In highly polluted sites, stomatal behavior is sluggish with respect to light, vapor pressure deficit, and internal CO2 concentration (Ci) and poorly described by existing models. Statistical models were developed to estimate stomatal conductance (gs) of 40-year-old ponderosa pine at three sites differing in pollutant exposure for the purpose of calculating O3 uptake. Gs was estimated using julian day, hour of day, pre-dawn xylem potential and photosynthetic photon flux density (PPFD). The median difference between estimated and observed field gs did not exceed 10 mmol H2O m(-2) s(-1), and estimated gs within 95% confidence intervals. 03 uptake was calculated from hourly estimated gs, hourly O3 concentration, and a constant to correct for the difference in diffusivity between water vapor and 03. The simulation model TREGRO was also used to calculate the cumulative 03 uptake at all three sites. 03 uptake estimated by the statistical model was higher than that simulated by TREGRO because gas exchange rates were proportionally higher. O3 exposure and uptake were significantly correlated (r2>0.92), because O3 exposure and gs were highly correlated in both statistical and simulation models. 相似文献