Hillslope scale surface runoff,sediment and nutrient losses associated with tramline wheelings     

Martyn Silgram  D.R Jackson  Alison Bailey  John Quinton  Carly Stevens 《地球表面变化过程与地形》2010,35(6):699-706

Research on arable sandy loam and silty clay loam soils on 4° slopes in England has shown that tramlines (i.e. the unseeded wheeling areas used to facilitate spraying operations in cereal crops) can represent the most important pathway for phosphorus and sediment loss from moderately sloping fields. Detailed monitoring over the October–March period in winters 2005–2006 and 2006–2007 included event‐based sampling of surface runoff, suspended and particulate sediment, and dissolved and particulate phosphorus from hillslope segments (each ～300–800 m²) established in a randomized block design with four replicates of each treatment at each of two sites on lighter and heavier soils. Experimental treatments assessed losses from the cropped area without tramlines, and from the uncropped tramline area, and were compared to losses from tramlines which had been disrupted once in the autumn with a shallow tine. On the lighter soil, the effects of removal or shallow incorporation of straw residues was also determined. Research on both sandy and silty clay loam soils across two winters showed that tramline wheelings represented the dominant pathway for surface runoff and transport of sediment, phosphorus and nitrogen from cereal crops on moderate slopes. Results indicated 5·5–15·8% of rainfall lost as runoff, and losses of 0·8–2·9 kg TP ha^?1 and 0·3–4·8 t ha^?1 sediment in tramline treatments, compared to only 0·2–1·7% rainfall lost as runoff, and losses of 0·0–0·2 kg TP ha^?1 and 0·003–0·3 t ha^?1 sediment from treatments without tramlines or those where tramlines had been disrupted. The novel shallow disruption of tramline wheelings using a tine once following the autumn spray operation consistently and dramatically reduced (p < 0·001) surface runoff and loads of sediment, total nitrogen and total phosphorus to levels similar to those measured in cropped areas between tramlines. Results suggest that options for managing tramline wheelings warrant further refinement and evaluation with a view to incorporating them into spatially‐targeted farm‐level management planning using national or catchment‐based agri‐environment policy instruments aimed at reducing diffuse pollution from land to surface water systems. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Separation of Platinum from Palladium and Iridium in Iron Meteorites and Accurate High‐Precision Determination of Platinum Isotopes by Multi‐Collector ICP‐MS          下载免费PDF全文

Alison C. Hunt  Mattias Ek  Maria Schönbächler 《Geostandards and Geoanalytical Research》2017,41(4):633-647

This study presents a new measurement procedure for the isolation of Pt from iron meteorite samples. The method also allows for the separation of Pd from the same sample aliquot. The separation entails a two‐stage anion‐exchange procedure. In the first stage, Pt and Pd are separated from each other and from major matrix constituents including Fe and Ni. In the second stage, Ir is reduced with ascorbic acid and eluted from the column before Pt collection. Platinum yields for the total procedure were typically 50–70%. After purification, high‐precision Pt isotope determinations were performed by multi‐collector ICP‐MS. The precision of the new method was assessed using the IIAB iron meteorite North Chile. Replicate analyses of multiple digestions of this material yielded an intermediate precision for the measurement results of 0.73 for ε¹⁹²Pt, 0.15 for ε¹⁹⁴Pt and 0.09 for ε¹⁹⁶Pt (2 standard deviations). The NIST SRM 3140 Pt solution reference material was passed through the measurement procedure and yielded an isotopic composition that is identical to the unprocessed Pt reference material. This indicates that the new technique is unbiased within the limit of the estimated uncertainties. Data for three iron meteorites support that Pt isotope variations in these samples are due to exposure to galactic cosmic rays in space.  相似文献   

Nutrient budgets for European seas: a measure of the effectiveness of nutrient reduction policies   总被引：3，自引：0，他引：3  

Artioli Y  Friedrich J  Gilbert AJ  McQuatters-Gollop A  Mee LD  Vermaat JE  Wulff F  Humborg C  Palmeri L  Pollehne F 《Marine pollution bulletin》2008,56(9):1609-1617

Socio-economic development in Europe has exerted increasing pressure on the marine environment. Eutrophication, caused by nutrient enrichment, is evident in regions of all European seas. Its severity varies but has, in places, adversely impacted socio-economic activities. This paper aims to evaluate the effectiveness of recently adopted policies to reduce anthropogenic nutrient inputs to European seas. Nitrogen and phosphorus budgets were constructed for three different periods (prior to severe eutrophication, during severe eutrophication and contemporary) to capture changes in the relative importance of different nutrient sources in four European seas suffering from eutrophication (Baltic Proper, coastal North Sea, Northern Adriatic and North-Western Black Sea Shelf). Policy success is evident for point sources, notably for P in the Baltic and North Seas, but reduction of diffuse sources has been more problematic.  相似文献   

A Forward Modeling Approach for Interpreting Impeller Flow Logs     

by Alison H. Parker  L. Jared West  Noelle E. Odling  Richard T. Bown 《Ground water》2010,48(1):79-91

A rigorous and practical approach for interpretation of impeller flow log data to determine vertical variations in hydraulic conductivity is presented and applied to two well logs from a Chalk aquifer in England. Impeller flow logging involves measuring vertical flow speed in a pumped well and using changes in flow with depth to infer the locations and magnitudes of inflows into the well. However, the measured flow logs are typically noisy, which leads to spurious hydraulic conductivity values where simplistic interpretation approaches are applied. In this study, a new method for interpretation is presented, which first defines a series of physical models for hydraulic conductivity variation with depth and then fits the models to the data, using a regression technique. Some of the models will be rejected as they are physically unrealistic. The best model is then selected from the remaining models using a maximum likelihood approach. This balances model complexity against fit, for example, using Akaike's Information Criterion.  相似文献   

Diagenesis of the Gully Oolite (Lower Carboniferous), South Wales     

Alison Searl 《Geological Journal》1989,24(4):275-293

Deposition of the Gully Oolite was locally interrupted by emergence and a regionally extensive palaeosol is present at the top of the unit. Early diagenetic phases include isopachous, fibrous submarine cements, nonluminescent vadose cements, and mixing zone dolomite. Subsequent nonferroan phreatic cements are non- to dully luminescent and in restricted vertical intervals predate significant compaction. More usually, however, phreatic cements postdate extensive overpacking of allochems. Ooid isotopic composition (δ¹⁸O=-7·80° to -3·10° and δ¹³C = -2·38° to +3·28°) is similar to that of associated phreatic cements and the data suggest that the bulk of ooid stabilization and cementation occurred within meteoric groundwaters. The extensive allochem overpacking appears to have occurred during the first few tens of metres of burial and intergranular macroporosity was eliminated prior to deep burial. Fracturing of the Gully Oolite during the Hercynian Orogeny and subsequent post-orogenic uplift led to localized dolomitization, several generations of calcite veins, and the restricted occurrence of ¹⁸O depleted cements in inter- and intragranular microporosity. Some of the veins clearly relate to Triassic exhumation of the Carboniferous Limestone, but others may be related to post-Mesozoic uplift and erosion of South Wales. Fracture-associated dolomitization may have occurred within a large-scale post-orogenic groundwater system, with Mg²⁺ being supplied through the release of deeply buried diagenetic brines.  相似文献   

Marine Metapopulations     

Celeste Benham  Alison M. Cawood  Geoffrey S. Cook  Ange Darnell  Peter C. Davison  Miriam C. Goldstein  Ayana Elizabeth Johnson  Talina Konotchick  Elisa M. Maldonado  Alexis L. Pasulka  Jennifer C. Prairie  Serena M. Moseman  Vera Tai  Christina A. Tanner  Tali Vardi  Tara S. Whitty  & Lisa A. Levin 《Marine Ecology》2008,29(2):319-320

  相似文献   

广州小北路黑人聚居区社会空间分析   总被引：37，自引：6，他引：31  

李志刚  薛德升  Michael Lyons  Alison Brown 《地理学报》2008,63(2):207-218

1978 年改革开放带来中国城市的快速转型。近年来, 针对经济转型背景下中国大城市 的社会空间研究很多, 但对在全球化影响下出现的跨国移民族裔聚居区的研究尚不多见。对 广州黑人聚居区展开研究, 以越秀区小北路为例, 探讨其社会空间特征与演进机制。研究采 用微观视角, 针对典型案例进行问卷调查和半结构式访谈。研究表明, 广州黑人聚居区与西 方同类族裔社会区存在诸多差异。小北路黑人聚居区因全球化下新的“自下而上”的跨国经 济联系而生, 因广州城市的商贸文化、宗教历史、贸易网络和地理气候条件而兴, 其跨国移 民多为来自西非地区的族裔散居者/ 漂泊者(Diaspora), 其人口构成异质多元, 且流动性强。 小北路的社会空间机制既包含被动隔离也包含主动聚居, 其经济形态已经开始向“族裔聚居 区经济”(ethnic enclave economy) 发展。  相似文献   

An interface-condition substitution strategy for theoretical study of dissolution-timescale reactive infiltration instability in fluid-saturated porous rocks     

Chongbin Zhao  Bruce E. Hobbs  Alison Ord 《国际地质力学数值与分析法杂志》2019,43(8):1576-1593

A theoretical study of reactive infiltration instability is conducted on the dissolution timescale. In the present theoretical study, the transient behavior of a dissolution-timescale reactive infiltration system needs to be considered, so that the upstream region of the chemical dissolution front should be finite. In addition, the chemical dissolution front of finite thickness should be considered on the dissolution timescale. Owing to these different considerations, it is very difficult, even in some special cases, to derive the first-order perturbation solutions of the reactive infiltration system on the dissolution timescale. To overcome this difficulty, an interface-condition substitution strategy is proposed in this paper. The basic idea behind the proposed strategy is that although the first-order perturbation equations in the downstream region cannot be directly solved in a purely mathematical manner, they should hold at the planar reference front, which is the interface between the upstream region and the downstream region. This can lead to two new equations at the interface. The main advantage of using the proposed interface-condition substitution strategy is that through using the original interface conditions as a bridge, the perturbation solutions for the dimensionless acid concentration, dimensionless Darcy velocity, and their derivatives involved in the two new equations at the interface can be evaluated just by using the obtained analytical solutions in the upstream region. The proposed strategy has been successfully used to derive the dimensionless growth rate, which is the key issue associated with the theoretical study of dissolution-timescale reactive infiltration instability in fluid-saturated porous rocks.  相似文献   

Past,present and future nutrient loads of the North Sea: Causes and consequences     

Jan E. Vermaat  Abigail McQuatters-Gollop  Marieke A. Eleveld  Alison J. Gilbert 《Estuarine, Coastal and Shelf Science》2008

Comprehensive, aggregate nutrient budgets were established for two compartments of the North Sea, the shallow coastal and deeper open regions, and for three different periods, representing pre-eutrophication (∼1950), eutrophication (∼1990) and contemporary (∼2000) phases. The aim was to quantify the major budget components, to identify their sources of variability, to specify the anthropogenic components, and to draw implications for past and future policy. For all three periods, open North Sea budgets were dominated (75%) by fluxes from and to the North-East Atlantic; sediment exchange was of secondary importance (18%). For the coastal North Sea, fluxes during the eutrophication period were dominated by sediment exchange (49% of all inputs), followed by exchange with the open sea (21%), and anthropogenic inputs (19%). Between 1950 and 1990, N-loading of coastal waters increased by a factor of 1.62 and P-loading by 1.45. These loads declined after 1990. Interannual variability in Atlantic inflow was found to correspond to a variability of 11% in nutrient load to the open North Sea. Area-specific external loads of both the open and coastal North Sea were below Vollenweider-type critical loads when expressed relative to depth and flushing. External area-specific load of the coastal North Sea has declined since 1990 from 1.8 to about 1.4 g P m⁻² y⁻¹ in 2000, which is close to the estimate of 1.3 for 1950. N-load declined less, leading to an increase in N/P ratio.  相似文献   

Variable Tl,Pb, and Cd concentrations and isotope compositions of enstatite and ordinary chondrites—Evidence for volatile element mobilization and decay of extinct 205Pb          下载免费PDF全文

Emeliana Palk  Rasmus Andreasen  Mark Rehkämper  Alison Stunt  Katharina Kreissig  Barry Coles  Maria Schönbächler  Caroline Smith 《Meteoritics & planetary science》2018,53(2):167-186

New Tl, Pb, and Cd concentration and Tl, Pb isotope data are presented for enstatite as well as L- and LL-type ordinary chondrites, with additional Cd stable isotope results for the former. All three chondrite suites have Tl and Cd contents that vary by more than 1–2 orders of magnitude but Pb concentrations are more uniform, as a result of terrestrial Pb contamination. Model calculations based on Pb isotope compositions indicate that for more than half of the samples, more than 50% of the measured Pb contents are due to addition of modern terrestrial Pb. In part, this is responsible for the relatively young and imprecise Pb-Pb ages determined for EH, L, and LL chondrites, which are hence only of limited chronological utility. In contrast, four particularly pristine EL chondrites define a precise Pb-Pb cooling age of 4559 ± 6 Ma. The enstatite chondrites (ECs) have highly variable ε^114/110Cd of between about +3 and +70 due to stable isotope fractionation from thermal and shock metamorphism. Furthermore, nearly all enstatite meteorites display ε²⁰⁵Tl values from −3.3 to +0.8, while a single anomalous sample is highly fractionated in both Tl and Cd isotopes. The majority of the ECs thereby define a correlation of ε²⁰⁵Tl with ε^114/110Cd, which suggests that at least some of the Tl isotope variability reflects stable isotope fractionation rather than radiogenic ingrowth of ²⁰⁵Tl from ²⁰⁵Pb decay. Considering L chondrites, most ε²⁰⁵Tl values range between −4 and +1, while two outliers with ε²⁰⁵Tl ≤ −10 are indicative of stable isotope fractionation. Considering only those L chondrites which are least likely to feature Pb contamination or stable Tl isotope effects, the results are in accord with the former presence of live ²⁰⁵Pb on the parent body, with an initial ²⁰⁵Pb/²⁰⁴Pb = (1.5 ± 1.4) × 10⁻⁴, which suggests late equilibration of the Pb-Tl system 26–113 Ma after carbonaceous chondrites (CCs). The LL chondrites display highly variable ε²⁰⁵Tl values from −12.5 to +14.9, also indicative of stable isotope effects. However, the data for three pristine LL3/LL4 chondrites display an excellent correlation between ε²⁰⁵Tl and ²⁰⁴Pb/²⁰³Tl. This defines an initial ²⁰⁵Pb/²⁰⁴Pb of (1.4 ± 0.3) × 10⁻⁴, equivalent to a ²⁰⁵Pb-²⁰⁵Tl cooling age of 55 + 12/−24 Ma (31–67 Ma) after CCs.  相似文献