Long‐term growth of a valley‐bottom gully,western Iowa     

John T. Thomas  Neal R. Iverson  Michael R. Burkart  Larry A. Kramer 《地球表面变化过程与地形》2004,29(8):995-1009

Growth of a permanent, valley‐bottom gully from 1964 to 2000 was determined annually from survey and sediment‐discharge data and compared with runoff and base?ow discharges. Data were analysed to test the hypothesis that rates of gully growth decay exponentially with time in response to shrinking catchment area caused by gully enlargement. Also, monthly values of growth rates and runoff, averaged over the 36‐year record, were analysed with mass‐wasting data to determine the extent to which colluvium availability affected growth rates seasonally. From 1964 to 2000, the gully volume increased by 9200 m³, accounting for 34 per cent of sediment yield from the watershed. There were tight power‐law relationships between annual growth rates and annual runoff, with runoff exponents of 1·57 and 1·30 for headward and volumetric growth, respectively. Increases in gully length, area, and volume were ?tted successfully assuming an exponential decay in growth rate with time. Rather than being due to a decrease in catchment area, however, the decline in growth rate was caused by a 77 per cent decrease in the ratio of runoff to base?ow, which also widened the gully and reduced the mean slope of its banks. Order‐of‐magnitude seasonal changes in erosion ef?ciency, de?ned as the fraction of stream power used to evacuate sediment from the gully, were roughly correlated with colluvium availability, as indicated by seasonal changes in the number of bank mass‐wasting events. No more than 2·2 per cent of stream power was used to evacuate sediment during any month. This study demonstrates the danger of attributing declining rates of gully growth to a shrinking catchment area if corroborative runoff and base?ow data are not available. Moreover, it illustrates that stream power alone provides only a rough and physically indirect measure of erosion potential. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Do Pharmaceuticals, Pathogens, and Other Organic Waste Water Compounds Persist When Waste Water Is Used for Recharge?   总被引：3，自引：0，他引：3  

Gail E. Cordy  Norma L. Duran  Herman Bouwer  Robert C. Rice  Edward T. Furlong  Steven D. Zaugg  Michael T. Meyer  Larry B. Barber  Dana W. Kolpin 《Ground Water Monitoring & Remediation》2004,24(2):58-69

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On the vertical profile of surface radiative fluxes in southwest Germany     

M. G. Iziomon  H. Mayer  W. Wicke 《Meteorology and Atmospheric Physics》2002,79(3-4):159-172

Summary Vertical profile of surface radiative fluxes in an area of heterogeneous terrain in south-west Germany is presented. Main data sets utilized for the study were recorded during the REgio KLIma Projekt (REKLIP). Supporting observational data were provided by the German weather service and German geophysical consultant service. Elevation of the study sites ranged from 212 m a.s.l. to 1489 m a.s.l. From May to September, monthly mean albedo was generally low at the study sites, ranging from 19% to 24%. For the other months, monthly mean albedo lie between 22% and 25% at the lowland site but extended between 27% and 71% at the highly elevated mountain site. Following the altitudinal increase in surface albedo, net radiative flux and radiation efficiency declined with elevation at an annual mean of 1.15 Wm⁻²/100 m and 0.008/100 m respectively. Absorbed shortwave radiation and effective terrestrial radiation showed mean decline of 1.54 Wm⁻²/100 m and 0.34 Wm⁻²/100 m, respectively, with the mean sky-to-earth radiation deficit amounting to about 52 Wm⁻² for the lowland site and 73 Wm⁻² for the highest elevated site. Some empirical models which express shortwave and longwave radiative fluxes in terms of meteorological variables have been validated for the lowland and mountain sites. Monthly mean daily total estimates of solar radiation obtained from ?ngst?m-Prescott relation were quite consistent with observed values. Parameterisation of downward atmospheric radiation under all sky condition was achieved by extending Brutsaert clear sky atmospheric model. Relationship between outgoing longwave radiation and screen temperature at the study sites was best described by an exponential function unlike the linear relationship proposed by Monteith and Unsworth. Net radiative flux for the lowland and mountain sites has been expressed in terms of absorbed shortwave radiation, cloud amount and screen temperature. Received March 5, 2001 Revised October 29, 2001  相似文献   

Emission of Biogenic Volatile Organic Compounds: An Overview of Field, Laboratory and Modelling Studies Performed during the `Tropospheric Research Program' (TFS) 1997–2000     

J.-P. Schnitzler  N. Bauknecht  N. Brüggemann  W. Einig  R. Forkel  R. Hampp  A. C. Heiden  U. Heizmann  T. Hoffmann  C. Holzke  L. Jaeger  M. Klauer  M. Komenda  R. Koppmann  J. Kreuzwieser  H. Mayer  H. Rennenberg  G. Smiatek  R. Steinbrecher  J. Wildt  W. Zimmer 《Journal of Atmospheric Chemistry》2002,42(1):159-177

The present paper summarises results on the emission of biogenicvolatile organic compounds (BVOC) achieved within the frame of thenational `German Tropospheric Research Programme' (TFS) between 1997 and2000. Field measurements were carried out at the meteorologicalmonitoring station `Hartheimer Wald' located in the vicinity of Freiburg(upper Rhine valley), Germany, within a pine plantation dominated byScots pine (Pinus sylvestris L.). The measured BVOC emissionrates were used to determine the daily and seasonal variation of BVOCemission and its dependence on important meteorological and plantphysiological parameters. In parallel, laboratory experiments usingyoung trees of pine (P. sylvestris), poplar (Populustremula ×P. alba) and pedunculate oak (Quercusrobur L.) were performed, and the influence of abiotic (e.g.,light, temperature, seasonality, flooding) factors on the biosynthesisand emission of BVOC was quantified. Based on these data, emissionalgorithms were evaluated and a process-oriented numerical model for thesimulation of the isoprene emission by plants was developed. Inaddition, newly calculated land use and tree species distributions wereused for the calculation of an actual BVOC emission inventory ofGermany.  相似文献   

Recent vertical crustal movements from precise leveling surveys in the Blue Ridge and Piedmont Provinces, North Carolina and Georgia     

Gary P. Citron  Larry D. Brown 《Tectonophysics》1979,52(1-4)

Examination of two lines of repeated leveling in North Carolina and Georgia reveals

1. (1) apparent uplift at the Blue Ridge-Piedmont physiographic boundary (the AtlanticGulf drainage divide) relative to the Atlantic Coastal Plain on the east and the Valley and Ridge province to the west; and

2. (2) large tilts over short baselines superimposed upon the regional pattern in the vicinity of the nearby Blue Ridge—Piedmont geologic boundary (the Brevard fault zone). In the North Carolina profile a very pronounced correlation between topography and movement suggests possible systematic leveling error, but the observed movements appear to be larger than those normally attributed to leveling error. Thus, either refraction or rod errors are larger than expected, or the movement is real and strongly correlates with topography along this portion of the leveling line.

Anomalously high stream-gradients over both resistant and nonresistant lithologies are found around the drainage divide in North Carolina, and may be associated with the relative uplift inferred from releveling. The drainage divide in Georgia, also characterized by relative uplift on the movement profile, approximately separates two different types of stream patterns. In both cases evidence presented here suggests that stream morphology may be responding to contemporary deformation as implied by the observed elevation changes. The relative uplift in North Carolina also correlates with a positive Bouguer gravity anomaly of 30–40 mGal in the midst of the regional Blue Ridge gravity low, although the significance of the correlation is unclear.The close spatial correspondence between the zone of maximum uplift and the drainage divide suggests that the vertical movements and geomorphic anomalies may result from the same mechanism, although the nature of such is unclear. One possible mechanism could be displacement at depth along the nearby Brevard zone. However, on the basis of dislocation modeling it appears that the geodetic observations cannot be adequately explained by surface deformation associated with any simple models of slip on the Brevard zone.  相似文献   

Test of a model for trace element partition during closed-system solidification of a silicate liquid     

Larry A. Haskin  Randy L. Korotev 《Geochimica et cosmochimica acta》1977,41(7):921-939

Distributions of trace elements during solidification of a basalt are adequately described by the model of Helmkeet al. (1972) for crystallization as a closed system. A hypidiomorphic granular basalt was coarsely crushed to particles < 2 mm in size, was sieved, and materials from nine size fractions were analyzed by neutron activation for REE, Co, Cr, Fe, Hf, Na, Sc, and Ta. Mineral separates from one of the size fractions were also analyzed.Trace-element concentrations of analyzed samples containing statistically significant numbers of mineral grains were matched very well by a mixing model whose end-member components were the analyzed major minerals and mesostasis. Highly accurate modal analyses of the analyzed materials were obtained from the mixing model. Differences in proportions of mesostasis (range 0.57–2%) were shown to be responsible for large differences in trace element concentrations among 0.25–1 g chips from a single hand-specimen of the basalt. Ilmenite in the basalt is badly contaminated with mesostasis.The closed-system model for crystallization yields values for temperature- and composition-averaged distribution coefficients for incompatible elements that are accurate to ? 15 to + 30%, and relative to each other are accurate to a few percent. The model demonstrates why some current practices for estimating values of distribution coefficients or of parent liquid compositions lead to errors of factors of several times.  相似文献   

Phosphoraufnahme durch Potamogeton natans und submerse Makrophyten in einem Fließgewässer-Laboratoriumsmodell     

G. Weise  H.-G. Mayer  W. Jorga  I. Bahr 《洁净——土壤、空气、水》1985,13(3):307-317

The germs of macrophytes were exposed in a ring channel at 0.073 m/s, 0.085 m water level and natural daylight for 52 h in tap water whose phosphorus concentration had been increased with KH₂PO₄ to 0.325 mg/1 P. After 4, 28 and 52 h the phosphorus concentrations in water and in dry matter were determined and the relative phosphorus elimination and incorporation, as referred to the concentrations in water and in dry matter prior to the test, were calculated in 0/0. Within 52 h the following increases of the internal phosphorus pool resulted (in %): Ranunculus aquatilis April 141, Potamogeton crispus May 178, P. natans June 139, Callitriche polymorpha June 128, Ranunculus aquatilis August 118, Elodea canadensis September 124. The phosphorus uptake behaves thus parallel to the gas-metabolism-physiological activity and the subsequently made differentiation into species which are active in spring, summer and autumn. Therefore, weed removals from waters should be done at the date of the species-specific activity maximum, since the then obtained biomass with 3… 9 kg/t P in the dry matter guarantees a maximum phosphorus elimination from the water.  相似文献   

BASIN MANAGEMENT IN THE SAN BERNARDINO BASIN AREA     

Larry W. Rowe 《Ground water》1980,18(6):626-629

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The behavior of some trace elements during solidification of the Skaergaard layered series     

Theodore P. Paster  Donald S. Schauwecker  Larry A. Haskin 《Geochimica et cosmochimica acta》1974,38(10):1549-1577

Six rocks and twelve mineral separates from the layered series of the Skaergaard intrusion were analyzed by neutron activation for REE, Ag, As, Ba, Co, Cr, Cu, Ga, Mn, Ni, Sb, Sc and Zn. The logarithmic model for trace element partitioning was further developed for use in describing the behavior of the elements during solidification of the layered series. Iterations were made in order to optimize within limits of uncertainty of measured values, such parameters as bulk composition, zone size, relative proportions of cumulus plus adcumulus minerals, zone mineralogy, and distribution coefficients. Values for distribution coefficients for the elements entering the cumulus minerals were obtained and have uncertainties of ~±50 per cent. The relative size of the hidden zone is limited, according to the estimates from the model, to between 20 and 50 per cent of the mass of the layered series.  相似文献   

Crustal structure of the Middle Urals based on reprocessing of Russian seismic reflection data     

David N. Steer  James H. Knapp  Larry D. Brown  Alexander V. Rybalka  Vadim B. Sokolov 《Geophysical Journal International》1995,123(3):673-682

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