Controls on the chemistry of runoff from an upland peat catchment     

Fred Worrall  Tim Burt  John Adamson 《水文研究》2003,17(10):2063-2083

This study uses 2 years of data from a detailed weekly water sampling programme in a 11·4 km² upland peat catchment in the Northern Pennines, UK. The sampling comprised precipitation, soil‐water samples and a number of streams, including the basin outlet. Samples were analysed for: pH, conductivity, alkalinity, Na, K, Ca, Mg, Fe, Al, Total N, SO₄, Cl and colour. Principal component analysis (PCA) was used to identify end‐members and compositional trends in order to identify controls on the development of water composition. The study showed that the direct use of PCA had several advantages over the use of end‐member mixing analysis (EMMA) as it combines an analysis of mixing and evolving waters without the assumption of having to know the compositional sources of the water. In its application to an upland peat catchment, the study supports the view that shallow throughflow at the catotelm/acrotelm boundary is responsible for storm runoff generation and shows that baseflow is controlled by cation exchange in the catotelm and mixing with a base‐rich groundwater. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Electrochemical strengthening of clayey sandy soils     

Lucas G. Adamson  Donald W. Quigley  H. Ross Ainsworth  George V. Chilingar 《Engineering Geology》1966,1(6):451-459

Most previous studies and applications of electrochemical stabilization of soils through electroosmosis have been made on clayey soils. The object of this investigation was to find out if relatively small amounts of clay (1.5%–3.5%, by weight) present in a sandy soil would be enough for stabilization and strengthening to be possible. The results indicate increases of cohesion of the order of 100–200 lb./sq.ft. X-ray analyses of treated soils indicate that sheet structures of clays are reduced and silicates destroyed upon treatment by electroosmosis. Newly-formed minerals also cement the soil. These neoformations include gibbsite, limonite, calcite, hydrohematite, hydrogoethite (hydrolepidocrocite), hisingerite, allophane, allophanoid, gypsum, hematite, magnetite, nontronite, trona and natron (Na₂ CO₃, 10H₂O). The process seems to be irreversible.  相似文献   

Drought and the rebound effect: a Murray–Darling Basin example     

Adam Loch  David Adamson 《Natural Hazards》2015,79(3):1429-1449

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JHK observations of faint standard stars in the Mauna Kea Observatories near-infrared photometric system     

S. K. Leggett  M. J. Currie  W. P. Varricatt  T. G. Hawarden  A. J. Adamson  J. Buckle  T. Carroll  J. K. Davies  C. J. Davis  T. H. Kerr  O. P. Kuhn  M. S. Seigar  T. Wold 《Monthly notices of the Royal Astronomical Society》2006,373(2):781-792

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Long-term variability in the date of monsoon onset over western India     

George C. D. Adamson  David J. Nash 《Climate Dynamics》2013,40(11-12):2589-2603

The date of onset of the southwest monsoon in western India is critical for farmers as it influences the timing of crop plantation and the duration of the summer rainy season. Identifying long-term variability in the date of monsoon onset is difficult, however, as onset dates derived from the reanalysis of instrumental rainfall data are only available for the region from 1879. This study uses documentary evidence and newly uncovered instrumental data to reconstruct annual monsoon onset dates for western India for the period 1781–1878, extending the existing record by 97 years. The mean date of monsoon onset over the Mumbai (Bombay) area during the reconstruction period was 10 June with a standard deviation of 6.9 days. This is similar to the mean and standard deviation of the date of monsoon onset derived from instrumental data for the twentieth century. The earliest identified onset date was 23 May (in 1802 and 1839) and the latest 22 June (in 1825). The longer-term perspective provided by this study suggests that the climatic regime that governs monsoon advance over western India did not change substantially from 1781 to 1955. Monsoon onset over Mumbai has occurred at a generally later date since this time. Our results indicate that this change is unprecedented during the last 230 years. Following a discussion of the results, the nature of the relationship between the date of monsoon onset and the El Niño-Southern Oscillation is discussed. This relationship is shown to have been stable since 1781.  相似文献   

Trends in 1,4-Dioxane Analyses: Implications for Identification and Characterization of Contaminated Groundwater Sites     

David T. Adamson PhD  PE  Grayson Uhlir BS  Sharon R. Rauch BA  Tessa Klein BS  Anthony S. Danko PhD  PE 《Ground Water Monitoring & Remediation》2021,41(3):29-40

1,4-Dioxane is a contaminant of emerging concern, and there is significant uncertainty about how its environmental occurrence in groundwater is being assessed given the various analytical methods available. This study compiled public sampling records from 2000 to 2019 that included >106,000 analyses of 1,4-dioxane from 822 different U.S. sites. The 1,4-dioxane detection frequency in the entire dataset (including all methods) was 45%, and the median detected concentration was 10 μg/L, highlighting the dilute nature of 1,4-dioxane in environmental media and the importance of selecting methods with adequate sensitivity. The annual distribution of samples analyzed by each method type confirmed a shift towards methods designed for semi-volatile compounds (Method 8270 and Method 8270 SIM) that exhibited consistently lower reporting limits (median reporting limit for each year typically ≤1 μg/L). In contrast, the method designed for volatile compounds (Method 8260) exhibited less sensitivity for 1,4-dioxane (median reporting limit per year between 40 and 100 μg/L) and its use declined significantly over time with increasing use of the moderately sensitive Method 8260 SIM in later years. This shift contributed to an increase in the 1,4-dioxane detection frequency over time, with a strong correlation between the annual detection frequency and the median reporting limit. Sites where 1,4-dioxane was analyzed but not detected overwhelmingly used less-sensitive methods that may not have been adequate for the expected concentration levels. Given the sub-μg/L groundwater criteria issued for 1,4-dioxane by some regulatory agencies, more sensitive and accurate methods will be increasingly needed to assess compliance.  相似文献   

Grain alignment in dense interstellar environments: spectropolarimetry of the 4.67-μm CO-ice feature in the field star Elias 16 (Taurus dark cloud)     

J. H. Hough  D. K. Aitken  D. C. B. Whittet  A. J. Adamson  A. Chrysostomou 《Monthly notices of the Royal Astronomical Society》2008,387(2):797-802

We present spectropolarimetry of the solid CO feature at 4.67 μm along the line of sight to Elias 16, a field star background to the Taurus dark cloud. A clear increase in polarization is observed across the feature with the peak of polarization shifted in wavelength relative to the peak of absorption. This shows that dust grains in dense, cold environments (temperatures ∼20 K or less) can align and produce polarization by dichroic absorption. For a grain model, consisting of a core with a single mantle, the polarization feature is best modelled by a thick CO mantle, possibly including 10 per cent water-ice, with the volume ratio of mantle to bare grain of ∼5. Radiative torques could be responsible for the grain alignment provided the grain radius is at least 0.5 μm. This would require the grain cores to have a radius of at least 0.3 μm, much larger than grain sizes in the diffuse interstellar medium. Sizes of this order seem reasonable on the basis of independent evidence for grain growth by coagulation, as well as mantle formation, inside dense clouds.  相似文献   

Long-Term Evaluation of Mulch Biowall Performance to Treat Chlorinated Solvents     

Kenneth L. Walker Jr.  Travis M. McGuire  David T. Adamson  R. Hunter Anderson 《Ground Water Monitoring & Remediation》2020,40(1):35-46

Permeable reactive barriers (PRBs), such as mulch biowalls, have been installed at numerous groundwater cleanup sites, and laboratory and field studies have demonstrated biotic and abiotic processes that degrade chlorinated volatile organic compounds (CVOCs) in groundwater passing through these engineered remedies. However, the longevity of mulch biowalls remains a fundamental research question. Soil and groundwater sampling at seven mulch biowalls at Altus Air Force Base (AFB) approximately 10 years after installation demonstrated the ongoing degradation of CVOCs. Trichloroethene was not detected in five of seven groundwater samples collected from the biowall despite upgradient detections above federal drinking water standards. Microbial sampling established the presence of key dechlorinating bacteria and the abundance of genes encoding specific enzymes for degradation, high methane concentrations, low sulfate concentrations, and negative oxidation-reduction potential, all indicative of highly reducing conditions within the biowalls and favorable conditions for CVOC destruction via microbial reductive dechlorination. High cellulose content (>79%) of the mulch, elevated total organic carbon (TOC) content in groundwater, and elevated potentially bioavailable organic carbon (PBOC) measurements in soil samples further supports an ongoing, long-lived source of carbon. These results demonstrate the ongoing and long-term efficacy of the mulch biowalls at Altus AFB. In addition, concentrations of bacteria, TOC, PBOC, and other geochemical parameters suggest a modest impact of the biowalls downgradient. The continued presence of CVOCs downgradient may be attributable to back diffusion from low-permeability shale. However, the biowalls continue to provide benefits by removing CVOCs in groundwater, thus reducing further CVOC loading to the downgradient, low-permeability strata.  相似文献   

On‐Site Vapor‐Phase Analysis as a Novel Approach for Monitoring Groundwater Wells     

David T. Adamson  Thomas E. McHugh  Michal W. Rysz  Roberto Landazuri  Mir Ahmad Seyedabbasi  Patrick E. Haas  Charles J. Newell 《Ground Water Monitoring & Remediation》2014,34(2):42-59

The results of comprehensive field testing of on‐site vapor‐phase‐based groundwater monitoring methods are presented to demonstrate their utility as a robust and cost‐effective approach for rapidly obtaining volatile organic compounds (VOCs) concentration data from a monitoring well. These methods—which rely on sensitive, commercially available field equipment to analyze vapor in equilibrium with groundwater—proved easy to implement and can be tailored to site‐specific needs, including multilevel sampling. During field testing, low‐flow groundwater concentrations could be reasonably estimated using submerged passive vapor diffusion samplers or field equilibration of collected groundwater (R² = 0.85 to 0.96). These two methods are not as reliant on in‐well mixing to overcome vertical stratification within wells as simpler headspace methods. The importance of well and aquifer‐specific factors on concentration data (and therefore method selection) is highlighted, including the effect of changing in‐well patterns due to seasonal temperature gradients. Results indicated that vertical stratification was relatively limited within the set of wells included in these studies, resulting in similar performance for short depth‐discrete passive vapor diffusion samplers (constructed from 40‐mL vials) and longer samplers (2.5 to 5 feet in length) designed to cover a larger portion of the screened interval. A year‐long, multi‐event evaluation demonstrated that vapor‐phase‐based monitoring methods are no more variable than conventional groundwater monitoring methods, with both types subject to similar spatial and temporal variability that can be difficult to reduce. Vapor sampling methods represent a promising approach for estimation of groundwater concentrations by reducing the cost liabilities associated with monitoring while providing a more sustainable approach.  相似文献   

Pfiesteria shumwayae (Pfiesteriaceae) in New Zealand     

Lesley L. Rhodes  Joann M. Burkholder  Howard B. Glasgow  Parke A. Rublee  Coy Allen  Janet E. Adamson 《新西兰海洋与淡水研究杂志》2013,47(3):621-630

Pfiesteria shumwayae Steidinger et Burkholder is now known to be present in New Zealand and occurs in estuaries around the country. The presence of Pfiesteria was initially determined by a polymerase chain reaction (PCR)‐based detection assay, using oligonucleotide primers targeted at ribosomal DNA extracted from estuarine water and sediments. Presence was confirmed by isolation from fresh sediments in the presence offish (Oreochromis mossambicus), followed by identification by scanning electron microscopy. The New Zealand isolates of P. shumwayae were ichthyotoxic in bioassays, but there is no historic evidence offish kills in New Zealand associated with the dinoflagellate.  相似文献