A long‐term study of stable isotopes as tracers of processes governing water flow and quality in a lowland river basin: the upper Thames,UK          下载免费PDF全文

W. George Darling  Michael J. Bowes 《水文研究》2016,30(13):2178-2195

A long‐term study of O, H and C stable isotopes has been undertaken on river waters across the 7000‐km² upper Thames lowland river basin in the southern UK. During the period, flow conditions ranged from drought to flood. A 10‐year monthly record (2003–2012) of the main River Thames showed a maximum variation of 3‰ (δ¹⁸O) and 20‰ (δ²H), although interannual average values varied little around a mean of –6.5‰ (δ¹⁸O) and –44‰ (δ²H). A δ²H/δ¹⁸O slope of 5.3 suggested a degree of evaporative enrichment, consistent with derivation from local rainfall with a weighted mean of –7.2‰ (δ¹⁸O) and –48‰ (δ²H) for the period. A tendency towards isotopic depletion of the river with increasing flow rate was noted, but at very high flows (>100 m³/s), a reversion to the mean was interpreted as the displacement of bank storage by rising groundwater levels (corroborated by measurements of specific electrical conductivity). A shorter quarterly study (October 2011–April 2013) of isotope variations in 15 tributaries with varying geology revealed different responses to evaporation, with a well‐correlated inverse relationship between Δ¹⁸O and baseflow index for most of the rivers. A comparison with aquifer waters in the basin showed that even at low flow, rivers rarely consist solely of isotopically unmodified groundwater. Long‐term monitoring (2003–2007) of carbon stable isotopes in dissolved inorganic carbon (DIC) in the Thames revealed a complex interplay between respiration, photosynthesis and evasion, but with a mean interannual δ¹³C‐DIC value of –14.8 ± 0.5‰, exchange with atmospheric carbon could be ruled out. Quarterly monitoring of the tributaries (October 2011–April 2013) indicated that in addition to the aforementioned factors, river flow variations and catchment characteristics were likely to affect δ¹³C‐DIC. Comparison with basin groundwaters of different alkalinity and δ¹³C‐DIC values showed that the origin of river baseflow is usually obscured. The findings show that long‐term monitoring of environmental tracers can help to improve the understanding of how lowland river catchments function. Copyright © NERC 2015. Hydrological Processes © 2015 John Wiley & Sons, Ltd.  相似文献   

Amino acid racemization dating of fossil bones,I. inter-laboratory comparison of racemization measurements     

Jeffrey L. Bada  E. Hoopes  D. Darling  Graham Dungworth  Henk J. Kessels  Keith A. Kvenvolden  David J. Blunt 《Earth and Planetary Science Letters》1979,43(2):265-268

Enantiomeric measurements for aspartic acid, glutamic acid, and alanine in twenty-one different fossil bone samples have been carried out by three different laboratories using different analytical methods. These inter-laboratory comparisons demonstrate that D/L aspartic acid measurements are highly reproducible, whereas the enantiomeric measurements for the other amino acids show a wide variation between the three laboratories. At present, aspartic acid measurements are the most suitable for racemization dating of bone because of their superior analytical precision.  相似文献   

In vitro screening for endocrine disruptive activity in selected South African harbours and river mouths     

JC Truter  JH van Wyk  BK Newman 《African Journal of Marine Science》2015,37(4):567-574

Various waterborne anthropogenic contaminants disrupt the endocrine systems of wildlife and humans, targeting reproductive pathways, among others. Very little is known, however, regarding the occurrence of endocrine disruptive activity in South African freshwater ecosystems, and coastal ecosystems have not been studied in this regard. In a first attempt to investigate endocrine disruptive activity in South African coastal waters, surface water samples collected from harbours, river mouths and estuaries in three metropolitan municipalities, eThekwini (which includes Durban), Nelson Mandela (specifically Port Elizabeth Harbour) and City of Cape Town, were screened for (anti) oestrogenicity and (anti)androgenicity using recombinant yeast bioassays. Moreover, levels of the female hormone 17β-(o)estradiol (E2) were determined in all samples, as well as a selection of hydrocarbons in the eThekwini samples. A high proportion of samples collected from eThekwini were oestrogenic, whereas none from Port Elizabeth Harbour and only a single river mouth sampled in the City of Cape Town were oestrogenic. E2 was detected in all the samples tested, but at higher concentrations at the eThekwini and City of Cape Town localities than Port Elizabeth Harbour. In addition, the recombinant yeast assays revealed that anti-androgenicity was widespread, being detected in the majority of samples screened apart from those representing Port Elizabeth Harbour. Conversely, no anti-oestrogenic or androgenic activity was detected. Anti-androgenicity did not associate with hydrocarbon loads, providing evidence that other anti-androgens were responsible for the observed activity. The present data suggest potential reproductive disruption in marine and estuarine fauna inhabiting the eThekwini and City of Cape Town regions.  相似文献   

Shallow impact: Isotopic insights into crustal contributions to the Sudbury impact melt sheet     

J.R. Darling  C.J. Hawkesworth  C.D. Storey 《Geochimica et cosmochimica acta》2010,74(19):5680-45

The largest known terrestrial impact melt sheet occurs within the 1850 Ma Sudbury Structure, Ontario. In order to evaluate the relative contributions of different target lithologies to the melt sheet, we have investigated the Pb isotope compositions of feldspar separates from early-formed quartz diorite magmas within Offset Dykes from around the impact structure. The samples define a linear array on plots of age-corrected ²⁰⁶Pb/²⁰⁴Pb versus ²⁰⁷Pb/²⁰⁴Pb. Samples from Offset Dykes hosted by the Huronian Supergroup (South Range) have a range of ²⁰⁶Pb/²⁰⁴Pb₁₈₅₀ from 15.424 to 17.255 and ²⁰⁷Pb/²⁰⁴Pb₁₈₅₀ from 15.390 to 15.801, whilst those hosted by Archean gneisses of the Superior Province (North Range) cluster around ²⁰⁶Pb/²⁰⁴Pb₁₈₅₀ ≈ 14.8 and ²⁰⁶Pb/²⁰⁴Pb₁₈₅₀ ≈ 15.1. These values can be approximated by binary mixing between the two major groups of target lithologies. A mix of 60-70% of Superior Province gneisses with 30-40% of Huronian metasedimentary material closely matches the Pb isotope compositions of North Range Offset Dyke samples, whereas in the South Range the required Huronian component is up to ca. 80%.These mixing proportions are consistent with Sr, Nd and Os isotope and trace element constraints. A third minor component, either locally-exposed Paleoproterozoic mafic rocks or the lower crust is also required. However, the isotopic, trace element and Ni-Cu-platinum group element characteristics of the melt sheet can be accommodated without the involvement of an average lower crustal or meteoritic component.A major contribution of Huronian supracrustal material, which had a pre-impact thickness of up to 12 km, is required to explain the chemical characteristics of the impact melts, which also have a strong upper crustal affinity (e.g. Eu/Sm = 0.22, Rb/Sr = 0.2-0.35). As such, a shallower level of melting is apparent than that predicted by many previous impact models for the Sudbury event. This can be accommodated by considering approach trajectories for the impactor oblique to the Earth’s surface. In addition, the isotopic and trace element variability identified indicates that the melt sheet was heterogeneous at an early stage, and may not have been completely homogenised during crater formation. Our findings have significant implications for the nature of the Sudbury impact event, the evolution of the melt sheet and the crustal sources of metals contained in Sudbury’s world class Ni-Cu-PGE sulphide ores.  相似文献   

Using environmental tracers to assess the extent of river–groundwater interaction in a quarried area of the English Chalk     

W.G. Darling  D.C. Gooddy  J. Riches  I. Wallis 《Applied Geochemistry》2010

The Swanscombe area of Kent, SE England represents a typical example of a heavily quarried Chalk area currently undergoing re-development. Because the Chalk is also an important aquifer, a good understanding of groundwater movement is required if environmental impacts are to be minimised and the water resource maximised. In particular, the nature of the relationship between the River Darent and groundwater in the Swanscombe Chalk Block requires better characterisation. Here, ‘environmental tracers’ in the form of ambient concentrations of stable isotopes, chlorofluorocarbons (CFCs), sulphur hexafluoride (SF₆) and tritium (³H) are used to investigate this and other aspects of groundwater movement in the vicinity of the quarries. Stable isotopic contrasts indicate little evidence for widespread river infiltration to the regional Chalk aquifer, although stable isotope and ³H data suggest that 20–35% of the abstraction by river-valley public water supply boreholes may be derived from the river. The CFCs, while present at above-modern concentrations in almost all groundwaters, can be used as tracers, indicating basically S–N flowpaths in the area south of the quarries, though sub-karstic conduits associated with areas of Palaeogene cover add a level of uncertainty at the local scale. Simple piston flow residence times based on SF₆ range from 1 to 17 a, but the data are probably better interpreted in terms of mixing between varying amounts of modern recharge derived from the south and deeper stored groundwater. The information gained from environmental tracers can therefore contribute to effective resource management.  相似文献   

Erratum to: Interaction between groundwater, the hyporheic zone and a Chalk stream: a case study from the River Lambourn, UK     

David J. Allen  W. George Darling  Daren C. Gooddy  Daniel J. Lapworth  Andrew J. Newell  Ann T. Williams  Debbie Allen  Corinna Abesser 《Hydrogeology Journal》2010,18(5):1301-1301

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Significance of “stretched” mineral inclusions for reconstructing P–T exhumation history     

Kyle T. Ashley  Robert S. Darling  Robert J. Bodnar  Richard D. Law 《Contributions to Mineralogy and Petrology》2015,169(6):1-9

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Science with ASKAP     

S. Johnston  R. Taylor  M. Bailes  N. Bartel  C. Baugh  M. Bietenholz  C. Blake  R. Braun  J. Brown  S. Chatterjee  J. Darling  A. Deller  R. Dodson  P. Edwards  R. Ekers  S. Ellingsen  I. Feain  B. Gaensler  M. Haverkorn  G. Hobbs  A. Hopkins  C. Jackson  C. James  G. Joncas  V. Kaspi  V. Kilborn  B. Koribalski  R. Kothes  T. Landecker  A. Lenc  J. Lovell  J.-P. Macquart  R. Manchester  D. Matthews  N. McClure-Griffiths  R. Norris  U.-L. Pen  C. Phillips  C. Power  R. Protheroe  E. Sadler  B. Schmidt  I. Stairs  L. Staveley-Smith  J. Stil  S. Tingay  A. Tzioumis  M. Walker  J. Wall  M. Wolleben 《Experimental Astronomy》2008,22(3):151-273

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Isotopic evidence for palaeowaters in the British Isles     

W.G. Darling  W.M. Edmunds  P.L. Smedley 《Applied Geochemistry》1997,12(6):813-829

Before the 20th century, groundwater circulation in the aquifers of the British Isles had largely adjusted to the temperate maritime climate and sea levels established over the past 10 ka since the end of the Pleistocene. However, in the last 100 a this natural regime has been disturbed by abstraction of water for public supply and industrial use, and palaeowaters from earlier recharge episodes are now becoming a factor to be considered in water balance estimates. This paper presents a synthesis of the existing palaeowater distribution in the British Isles, based on isotopic evidence (δ¹⁸O, δ²H and and¹⁴C). As such, it has relevance to palaeoclimatic studies in addition to the water resource implications.The Triassic basins of England and Northern Ireland contain saline waters beyond the range¹⁴C dating (>; 40 ka). Stable isotopic ratios show enrichment in some basins and depletion in others, without an overall pattern that would explain all the observed compositions. The results for the Wessex basin suggest recharge in pre-Quaternary times, but for the other basins some flushing by Pleistocene or Holocene meteoric waters is indicated. Isolated occurrences of apparently long-residence waters are found elsewhere throughout the British Isles, for example from Carboniferous and Lower Palaeozoic strata. In such cases, environmental isotopes are more useful as constraints on hydrogeological models than as indicators of palaeoconditions.Major water supply aquifers are restricted almost entirely to England. The two sandstone formations (Triassic Sherwood Sandstone and Cretaceous Lower Greensand) have a greater range of stable isotopic values between phreatic and confined conditions than the two carbonate formations (Jurassic Lincolnshire Limestone and Cretaceous Chalk). This indicates that the sandstone aquifers are better archives of information on palaeoconditions than the carbonate aquifers. They show that atmospheric circulation patterns over Britain have probably remained the same since the late Pleistocene. However,¹⁴C data from all four of the major aquifers emphasise the hiatus in recharge during periglacial conditions which occurred between the late Pleistocene and early Holocene.  相似文献   

The practicalities of using CFCs and SF₆ for groundwater dating and tracing     

W.G. Darling  D.C. Gooddy  A.M. MacDonald  B.L. Morris 《Applied Geochemistry》2012

Knowledge of groundwater residence time is important in understanding key issues in the evolution of water quality, whether this occurs due to water–rock interaction or simply by mixing or contamination. The build-up in the atmosphere of the trace gases chlorofluorocarbons (CFCs) and sulphur hexafluoride (SF₆) from the middle of the last century offers a convenient way of dating waters up to ∼60 a old. The gases are well-mixed in the atmosphere so their input functions are not area-specific as is the case with ³H. While any one of these trace gases can in principle provide a groundwater age, when two or more are measured on water samples the potential exists to distinguish between different modes of flow including piston flow, exponential flow and simple end-member mixing. As with all groundwater dating methods, caveats apply. Factors such as recharge temperature and elevation must be reasonably well-constrained. Primarily for SF₆, the phenomenon of ‘excess air’ also requires consideration. Primarily for the CFCs, local sources of contamination need to be considered, as do redox conditions. For both SF₆ and the CFCs, the nature and thickness of the unsaturated zone need to be factored into residence time calculations. However, as an inexpensive dating method, the trace gases can be applied to a wide range of groundwater problems where traditional age indicators might once have been used more sparingly. Examples include tracing flowlines, detecting small modern inputs in ‘old’ waters, and pollution risk assessment. In the future, with the main CFCs already declining in the atmosphere, new anthropogenic trace gases are likely to take their place.  相似文献