Thames River Research Articles

Multi-method Modeling Framework for Support of Integrated Water Resources Management

The contemporary definition of integrated water resources management (IWRM) is introduced to promote a holistic approach in water engineering practices. IWRM deals with planning, design and operation of complex systems in order to control the quantity, quality, temporal and spatial distribution of water with the main objective of meeting human and ecological needs and providing protection from water related disasters. This paper examines the existing decision making support in IWRM practice, analyses the advantages and limitations of existing tools, and, as a result, suggests a generic multi-method modeling framework that has the main goal to capture all structural complexities of, and interactions within, a water resources system. Since the traditional tools do not provide sufficient support, this framework uses multi-method simulation technique to examine the codependence between water resources system and socioeconomic environment. Designed framework consists of (i) a spatial database, (ii) a traditional process-based model to represent the physical environment and changing conditions, and (iii) an agent-based spatially explicit model of socio-economic environment. The multi-agent model provides for building virtual complex systems composed of autonomous entities, which operate on local knowledge, possess limited abilities, affect and are affected by local environment, and thus, enact the desired global system behavior. Agent-based model is used in the presented work to analyze spatial dynamics of complex physical-social-economic-biologic systems. Based on the architecture of the generic multi-method modeling framework, an operational model for the Upper Thames River basin, Southwestern Ontario, Canada, is developed in cooperation with the local conservation authority. Six different experiments are designed by combining three climate and two socio-economic scenarios to analyze spatial dynamics of a complex physical-social-economic system of the Upper Thames River basin. Obtained results show strong dependence between changes in hydrologic regime, in this case surface runoff and groundwater recharge rates, and regional socio-economic activities.

Numerical rivers: A synthetic streamflow generator for water resources vulnerability assessments

AbstractThe vulnerability of water supplies to shortage depends on the complex interplay between streamflow variability and the management and demands of the water system. Assessments of water supply vulnerability to potential changes in streamflow require methods capable of generating a wide range of possible streamflow sequences. This paper presents a method to generate synthetic monthly streamflow sequences that reproduce the statistics of the historical record and that can express climate‐induced changes in user‐specified streamflow characteristics. The streamflow sequences are numerically simulated through random sampling from a parametric or a nonparametric distribution fitted to the historical data while shuffling the values in the time series until a sequence matching a set of desired temporal properties is generated. The desired properties are specified in an objective function which is optimized using simulated annealing. The properties in the objective function can be manipulated to generate streamflow sequences that exhibit climate‐induced changes in streamflow characteristics such as interannual variability or persistence. The method is applied to monthly streamflow data from the Thames River at Kingston (UK) to generate sequences that reproduce historical streamflow statistics at the monthly and annual time scales and to generate perturbed synthetic sequences expressing changes in short‐term persistence and interannual variability.

Improved Weather Generator Algorithm for Multisite Simulation of Precipitation and Temperature

AbstractThe KnnCAD Version 4 weather generator algorithm for nonparametric, multisite simulations of temperature and precipitation data is presented. The K‐nearest neighbor weather generator essentially reshuffles the historical data, with replacement. In KnnCAD Version 4, a block resampling scheme is introduced to preserve the temporal correlation structure in temperature data. Perturbation of the reshuffled variable data is also added to enhance the generation of extreme values. The Upper Thames River Basin in Ontario, Canada is used as a case study and the model is shown to simulate effectively the historical characteristics at the site. The KnnCAD Version 4 approach is shown to improve on the previous versions of the model and offers a major advantage over many parametric and semiparametric weather generators in that multisite use can be easily achieved without making statistical assumptions dealing with the spatial correlations and probability distributions of each variable.

William Basse's Polyhymnia and the Poetry of Service

The career of the little-known seventeenth-century poet William Basse (c. 1583-1653?) combined two distinctive elements. He served, in the first instance, as a ‘retainer’ to the Wenman family of Thame Park in Oxfordshire for a period of more than forty years. He was also, however, a published poet who produced a substantial body of verse which reflected and intertwined with his career in service. The article aims to stimulate interest in Basse by drawing attention to a manuscript collection of his poems which remains unpublished and has until now been considered ‘lost’ in scholarly accounts of the poet. The Polyhymnia , held at Chetham’s Library in Manchester, was prepared as a gift in the late 1640s or early 1650s for relations of the Wenmans who lived on the nearby Rycote estate. It brought together poems from across the course of Basse’s career, and displayed him writing in a wide variety of forms and genres. The article summarises current knowledge of Basse’s life in service, sets out the context of the Polyhymnia as a manuscript apparently designed to fortify the links between Thame Park and Rycote, and explores the importance of Basse’s perspective as a servant to some of the more intriguing poems in the collection. It concludes by suggesting some of the ways in which a renewed focus upon Basse might contribute to study of the links between service and literature in the future.

Revealing Photographs, Intimate Spaces: The Aura of Aesthetic Interiors as a Self-portrait

ABSTRACTNestled on top of a bluff, Eldon House overlooks the Thames River in London, Ontario, Canada. During the last decade of the nineteenth century Milly Harris (1868–1959), the last resident of the home, carefully arranged souvenirs, bric-a-brac, and natural specimens within her bedroom. Through an idiosyncratic application of Aesthetic principles, Harris cultivated a powerful aura among her collection. The intimate space is further mediated through the act of photography. Harris's roll in the domestic decoration and the precise composition of the images speak to her artistic intentions. An examination of the discursive space surrounding the photograph and album can lead to a more nuanced understanding of the material depicted. Examining representations of the interior in the popular press and amateur domestic scenes contextualizes Harris's work. Additional meaning is accrued by placing her photographs in an album. Susan Stewart's theories about souvenirs and photography, along with Walter Benjamin's concept of object auras work together to articulate a fuller understanding of the domestic interior photographs contained in Milly Harris's album. The materiality of both photographs and nineteenth-century photo albums play a key role in revealing aspects of Harris's personality.

Validated predictive modelling of the environmental resistome.

Multi-drug-resistant bacteria pose a significant threat to public health. The role of the environment in the overall rise in antibiotic-resistant infections and risk to humans is largely unknown. This study aimed to evaluate drivers of antibiotic-resistance levels across the River Thames catchment, model key biotic, spatial and chemical variables and produce predictive models for future risk assessment. Sediment samples from 13 sites across the River Thames basin were taken at four time points across 2011 and 2012. Samples were analysed for class 1 integron prevalence and enumeration of third-generation cephalosporin-resistant bacteria. Class 1 integron prevalence was validated as a molecular marker of antibiotic resistance; levels of resistance showed significant geospatial and temporal variation. The main explanatory variables of resistance levels at each sample site were the number, proximity, size and type of surrounding wastewater-treatment plants. Model 1 revealed treatment plants accounted for 49.5% of the variance in resistance levels. Other contributing factors were extent of different surrounding land cover types (for example, Neutral Grassland), temporal patterns and prior rainfall; when modelling all variables the resulting model (Model 2) could explain 82.9% of variations in resistance levels in the whole catchment. Chemical analyses correlated with key indicators of treatment plant effluent and a model (Model 3) was generated based on water quality parameters (contaminant and macro- and micro-nutrient levels). Model 2 was beta tested on independent sites and explained over 78% of the variation in integron prevalence showing a significant predictive ability. We believe all models in this study are highly useful tools for informing and prioritising mitigation strategies to reduce the environmental resistome.

Evaluating the Performance of Hydrological Models via Cross-Spectral Analysis: Case Study of the Thames Basin, United Kingdom

AbstractNine distributed hydrological models, forced with common meteorological inputs, simulated naturalized daily discharge from the Thames basin for 1963–2001. While model-dependent evaporative losses are critical for modeling mean discharge, multiple physical processes at many time scales influence the variability and timing of discharge. Here the use of cross-spectral analysis is advocated to measure how the average amplitude—and independently, the average phase—of modeled discharge differ from observed discharge at daily to decadal time scales. Simulation of the spectral properties of the model discharge via numerical manipulation of precipitation confirms that modeled transformation involves runoff generation and routing that amplify the annual cycle, while subsurface storage and routing of runoff between grid boxes introduces most of the autocorrelation and delays. Too much or too little modeled evaporation affects discharge variability, as do the capacity and time constants of modeled stores. Additionally, the performance of specific models would improve if four issues were tackled: 1) nonsinusoidal annual variations in model discharge (prolonged low base flow and shortened high base flow; three models), 2) excessive attenuation of high-frequency variability (three models), 3) excessive short-term variability in winter half years but too little variability in summer half years (two models), and 4) introduction of phase delays at the annual scale only during runoff generation (three models) or only during routing (one model). Cross-spectral analysis reveals how reruns of one model using alternative methods of runoff generation—designed to improve performance at the weekly to monthly time scales—degraded performance at the annual scale. The cross-spectral approach facilitates hydrological model diagnoses and development.

The Times Displayed: Late Seventeenth-Century English Commemorative Broadsheets and Media Hybridity

English broadsheet prints are often regarded as being the forerunner of modern comic strip narratives. Late seventeenth-century English broadsheets created news by displaying the manners and social rituals of their times; they were, however, designed to be accessible to multiple types of literacies, and they demonstrate a lively sense of how space and image can create meaning without words. Commemorative in the sense of recording events of national interest and significance, including the London Plague, the freezing of the Thames River, and the Pope-burning pageants, these broadsheets captured audiences through image, word and sound, employing a hybrid media modality. They functioned to preserve records of events but also through narrative strategies to convey the news of the day, to capture the action of what was important and ongoing in terms of England as a nation.

The Times Displayed: Late Seventeenth-Century English Commemorative Broadsheets and Media Hybridity

English broadsheet prints are often regarded as being the forerunner of modern comic strip narratives. Late seventeenth-century English broadsheets created news by displaying the manners and social rituals of their times; they were, however, designed to be accessible to multiple types of literacies, and they demonstrate a lively sense of how space and image can create meaning without words. Commemorative in the sense of recording events of national interest and significance, including the London Plague, the freezing of the Thames River, and the Pope-burning pageants, these broadsheets captured audiences through image, word and sound, employing a hybrid media modality. They functioned to preserve records of events but also through narrative strategies to convey the news of the day, to capture the action of what was important and ongoing in terms of England as a nation.

Catchment-scale biogeography of riverine bacterioplankton.

Lotic ecosystems such as rivers and streams are unique in that they represent a continuum of both space and time during the transition from headwaters to the river mouth. As microbes have very different controls over their ecology, distribution and dispersion compared with macrobiota, we wished to explore biogeographical patterns within a river catchment and uncover the major drivers structuring bacterioplankton communities. Water samples collected across the River Thames Basin, UK, covering the transition from headwater tributaries to the lower reaches of the main river channel were characterised using 16S rRNA gene pyrosequencing. This approach revealed an ecological succession in the bacterial community composition along the river continuum, moving from a community dominated by Bacteroidetes in the headwaters to Actinobacteria-dominated downstream. Location of the sampling point in the river network (measured as the cumulative water channel distance upstream) was found to be the most predictive spatial feature; inferring that ecological processes pertaining to temporal community succession are of prime importance in driving the assemblages of riverine bacterioplankton communities. A decrease in bacterial activity rates and an increase in the abundance of low nucleic acid bacteria relative to high nucleic acid bacteria were found to correspond with these downstream changes in community structure, suggesting corresponding functional changes. Our findings show that bacterial communities across the Thames basin exhibit an ecological succession along the river continuum, and that this is primarily driven by water residence time rather than the physico-chemical status of the river.

Seasonal Abundance of the CtenophoreMnemiopsis leidyiin Relation to Water Temperature and Other Zooplankton in the Thames River Estuary, Connecticut

I examined seasonal patterns in the abundance of the ctenophore Mnemiopsis leidyi (Atlantic Comb Jelly) to determine whether unusually early ctenophore blooms occur outside the range in which they were originally reported (Narragansett Bay, RI) and whether ctenophore abundance is correlated with sea surface temperature (SST) or with declines in zooplankton prey. Sampling was conducted from 23 April to 16 November 2004 in the Thames River Estuary, CT. Adult (≥1 cm) ctenophores first appeared in the estuary on 20 May 2004, with a seasonal peak in mean (± SD) density (9.9 ± 2.5 individuals m-3, n = 7 stations) and biovolume (26.6 ± 9.9 ml m-3, n = 7 stations) on 9 July 2004. Adult Atlantic Comb Jelly abundance was positively correlated with SST, but only during the spring and early summer. Food availability also likely played an important role in ctenophore-population growth early in the year. However, I observed a delay between copepod density and ctenophore biovolume, possibly due to unusually cold winter temperatures that reduced ctenophore survivorship in the months preceding the study. Ctenophore diets in 2004 consisted primarily of copepods. I observed an inverse correlation between ctenophore biovolume and copepod density, but my data suggest that adult Atlantic Comb Jellies consumed only 0.0–2.2% of the copepod standing stock per day. Overall, my results are consistent with the hypothesis that early summer ctenophore blooms occured over a relatively large spatial scale; however, trophic impacts in the Thames River Estuary in 2004 appeared to be relatively low.

Changes in the preferences for the ecosystem service use and the effects in a city located along a river: a preliminary study based on the example of Toruń (Poland) compared to the Isle of Dogs in London

Ecosystem services originated from various ecological units, local as well as global, hierarchically, they depend on the structure and functions of the ecosystem under study and its human community. They are involved in controlling and maintaining the development of natural resources in the ecosystem, human activities and prosperity through the use of material and non-material benefits. The technology brought in as well as developed by the application of those benefits, enhance the ecological capacity for our human community and in consequences may depend on the decisions brought about by private and public interests. Other forms of ecosystem services also immerge as a direct and indirect product from human pressure on the environment, because the ecosystem exploited by man is most often from a sink of destructive chemical and physical factors, they result in ecosystem services out of an unhealthy environmental state.This study deals with applicability of the ecosystem service paradigm, and presents the results obtained in Toruń, a city developing close to the Vistula River from medieval times. Preference of choice among a wide variety of ecosystem services can be provided in this setting, so it is interesting to compare Toruń to other cities where exceptional results are obtained. The reference point in this comparison is a system of similar size but which has developed within a much bigger and stronger urban ecosystem. This is the Isle of Dogs on the Thames River in London.Our analysis shows that currently, there are strong differences between the two cities in their demand for ecosystem services and their interaction with the public sphere, design and art. On the Isle of Dogs, there is a stronger connection between the ecosystems and the design of space to create an interesting streetscape in comparison to Toruń. The connection between the public and private zones to achieve the attractiveness to the city and to combine art and design with environmental solutions has brought about excellent results in London.

PCB and organochlorine pesticide burden in eels in the lower Thames River (UK)

Thirty-five European eels (Anguilla anguilla), caught in 2007 in the river Thames upstream and downstream of both London and the tidal limit, were analysed for PCBs and organochlorine pesticides. Most chemicals were detectable in every fish, although they have been banned or severely restricted for many years. In general, the tidal eels were more contaminated than upstream ones, which was related to their higher lipid contents.The ICES7 indicator PCB concentrations ranged overall from 4.2 to 124μgkg−1 fresh weight with averages of 33 and 56μgkg−1 for the upstream and tidal eels; 3.5–104μgkg−1, average 26 and 48μgkg−1 of that were ICES6 PCBs. Total DDT was on average 16μgkg−1 (1.7–38μgkg−1) upstream and 18μgkg−1 (8.6–35μgkg−1) downstream with about half of that provided by pp′DDE. Lindane (γ-HCH) was found at up to 2.8μgkg−1 (averages 0.58 and 1.1μgkg−1 upstream and downstream) and hexachlorobenzene (HCB) was on average 1.9 and 2.5μgkg−1 in the two groups with a maximum of 6.4μgkg−1 in each. Therefore all individuals passed the European Environmental Quality Standard (EQS) of 10μgkg−1 for HCB. PCB contamination was fairly typical for recent UK eel data, whilst DDE and lindane concentrations were lower than most previous UK eel studies, perhaps reflecting a downward trend.Although not as highly contaminated as some eels from previous UK and European studies, the presence of so many of these chemicals, with their known health effects may represent a stress for the fish or higher predators, such as birds.

Model assessment of present-day Phaeocystis colony blooms in the Southern Bight of the North Sea (SBNS) by comparison with a reconstructed pristine situation

We performed simulations with the existing MIRO&CO-3D ecological model to assess the present-day magnitude and geographical extent of undesirable Phaeocystis colony blooms in the Southern Bight of the North Sea (SBNS) receiving anthropogenic nutrient inputs from large European rivers that mix with the inflowing Atlantic waters. The criterion of 4·106Phaeocystis colonial cells L−1 of Lancelot et al. (2009) is used to scale the presence of undesirable bloom. These simulations are compared with a reconstructed pristine SBNS ecosystem making use of nutrient inputs calculated with the Seneque/Riverstrahler model of the river system when all human activities on the watershed have been erased. Interannual variability is considered by performing model runs for two contrasted meteorological years: wet (2001) and dry (2005). Results show a large excess of nitrogen (N) and phosphorus (P) delivery to the SBNS, i.e., 12 and 5 times the pristine situation respectively. In contrast, the total silicon (Si) input is decreased with respect to natural conditions due to freshwater diatom growth in some eutrophied rivers. Qualitatively, rivers deliver nutrients in large Si excess for pristine condition but N excess for both 2001 and 2005, when scaled to the N, P and Si requirement of coastal diatoms.Responding to the river nutrient inputs, either natural or of anthropogenic origin, phytoplankton blooms are simulated in the vicinity of the river mouths, especially in the eastern SBNS receiving 78–98% of the direct river inputs. In this area nutrients cumulate along a SW-NE gradient and the bloom is forming a wide ribbon parallel to the coast. A short time-delay is simulated between the western and eastern SBNS due to light limitation imposed by the amount of suspended particles carried by the Thames River. A spring diatom-Phaeocystis succession is simulated for both present-day and pristine condition. Diatoms dominate the bulk of the pristine phytoplankton community; Phaeocystis colonies develop in the whole domain, especially in the Thames and Scheldt river plume though their biomass remains low and never exceed the threshold of 4·106cellsL−1. In contrast, present-day Phaeocystis colonies start growing when diatoms attain their maximum in April, co-occur with and supplement them in May and June, reaching colonial cells densities >4·106cellsL−1 in many locations of the SBNS. Overall, Phaeocystis colonies are favored by wet meteorological conditions that enhance river N delivery. The geographical extent of undesirable Phaeocystis blooms thus varies between dry and wet years and affects 72% of the modeled SBNS domain distributed in three areas: the eastern band (90%), the Thames plume (6%) and a small offshore area (4%) possibly connected to the eastern band.

Controls on the basin-scale distribution of hydraulic conductivity of superficial deposits: a case study from the Thames Basin, UK

Controls on the basin-scale distribution of hydraulic conductivity of superficial deposits are assessed in the context of hydrological setting and basin evolution and are investigated using a case study from the Thames Basin, UK. A conceptual model of superficial deposits across the Thames Basin is used to define six lithostratigraphic classes of superficial deposits: pre-Anglian Clay-with-Flint deposits; pre-Anglian River Terrace Deposits associated with the ancestral River Thames and its tributaries; Tills formed during the Anglian glaciations; glacio-fluvial sand and gravel deposits formed during the Anglian; post-Anglian River Terrace Deposits associated with the modern-day River Thames and tributaries; post-Anglian alluvium associated with the modern-day River Thames and tributaries. Hydraulic conductivity of the superficial deposits has been estimated from grain-size distribution data, originally collected for mineral resource assessments, using the Kozeny–Carman method. Based on 6411 samples from 1416 boreholes, estimated hydraulic conductivity ranges from 0.2 to 5942 m day –1 , median and mean hydraulic conductivities are 1.67 and 26.72 m day –1 respectively, and the overall distribution of hydraulic conductivity values has a strong positive skew An apparent reduction in mean hydraulic conductivity with increasing age of the deposit is observed, particularly for the River Terrace Deposits. A reduction in maximum hydraulic conductivity at depths >10 m is also observed and the relationship between hydraulic conductivity and depth is controlled by the type of superficial deposit. At the catchment to basin scale, variation in hydraulic conductivity with depth may be explained with reference to both the deposit types and the age of the deposits. Where hydraulic conductivity is found to be intimately linked to the Quaternary evolution of the basin, through contrasts in age and deposit type, permeability variations at the basin scale may be constrained by applying a suitably refined conceptual model of the superficial deposits.

Multi-site, multivariate weather generator using maximum entropy bootstrap

Weather generators are increasingly becoming viable alternate models to assess the effects of future climate change scenarios on water resources systems. In this study, a new multisite, multivariate maximum entropy bootstrap weather generator (MEBWG) is proposed for generating daily weather variables, which has the ability to mimic both, spatial and temporal dependence structure in addition to other historical statistics. The maximum entropy bootstrap (MEB) involves two main steps: (1) random sampling from the empirical cumulative distribution function with endpoints selected to allow limited extrapolation and (2) reordering of the random series to respect the rank ordering of the original time series (temporal dependence structure). To capture the multi-collinear structure between the weather variables and between the sites, we combine orthogonal linear transformation with MEB. Daily weather data, which include precipitation, maximum temperature and minimum temperature from 27 years of record from the Upper Thames River Basin in Ontario, Canada, are used to analyze the ability of MEBWG based weather generator. Results indicate that the statistics from the synthetic replicates were not significantly different from the observed data and the model is able to preserve the 27 CLIMDEX indices very well. The MEBWG model shows better performance in terms of extrapolation and computational efficiency when compared to multisite, multivariate K-nearest neighbour model.

Identifying priorities for nutrient mitigation using river concentration–flow relationships: The Thames basin, UK

Summary The introduction of tertiary treatment to many of the sewage treatment works (STW) across the Thames basin in southern England has resulted in major reductions in river phosphorus (P) concentrations. Despite this, excessive phytoplankton growth is still a problem in the River Thames and many of its tributaries. There is an urgent need to determine if future resources should focus on P removal from the remaining STW, or on reducing agricultural inputs, to improve ecological status. Nutrient concentration–flow relationships for monitoring sites along the River Thames and 15 of its major tributaries were used to estimate the relative inputs of phosphorus and nitrogen from continuous (sewage point sources) and rain-related (diffuse and within-channel) sources, using the Load Apportionment Model (LAM). The model showed that diffuse sources and remobilisation of within-channel phosphorus contributed the majority of the annual P load at all monitoring sites. However, the majority of rivers in the Thames basin are still dominated by STW P inputs during the ecologically-sensitive spring-autumn growing season. Therefore, further STW improvements would be the most effective way of improving water quality and ecological status along the length of the River Thames, and 12 of the 15 tributaries. The LAM outputs were in agreement with other indicators of sewage input, such as sewered population density, phosphorus speciation and boron concentration. The majority of N inputs were from diffuse sources, and LAM suggests that introducing mitigation measures to reduce inputs from agriculture and groundwater would be most appropriate for all but one monitoring site in this study. The utilisation of nutrient concentration–flow data and LAM provide a simple, rapid and effective screening tool for determining nutrient sources and most effective mitigation options.

A cost-effectiveness analysis of water security and water quality: impacts of climate and land-use change on the River Thames system

The catchment of the River Thames, the principal river system in southern England, provides the main water supply for London but is highly vulnerable to changes in climate, land use and population. The river is eutrophic with significant algal blooms with phosphorus assumed to be the primary chemical indicator of ecosystem health. In the Thames Basin, phosphorus is available from point sources such as wastewater treatment plants and from diffuse sources such as agriculture. In order to predict vulnerability to future change, the integrated catchments model for phosphorus (INCA-P) has been applied to the river basin and used to assess the cost-effectiveness of a range of mitigation and adaptation strategies. It is shown that scenarios of future climate and land-use change will exacerbate the water quality problems, but a range of mitigation measures can improve the situation. A cost-effectiveness study has been undertaken to compare the economic benefits of each mitigation measure and to assess the phosphorus reductions achieved. The most effective strategy is to reduce fertilizer use by 20% together with the treatment of effluent to a high standard. Such measures will reduce the instream phosphorus concentrations to close to the EU Water Framework Directive target for the Thames.

A 9000-year record of vertical and lateral accretion on the floodplain of the lower Thames River, southwestern Ontario, Canada, and implications for archaeological research

Results of ground-penetrating radar and grain size analysis of sediments from three, 5–7 m-long cores generally support a classic, fining-up point bar model of floodplain development on a reach of the lower Thames River, a single-thread, meandering channel that flows southwest into Lake St Clair (bankfull discharge = 411 m3 s−1). Four radiocarbon dates on organic material recovered from cores indicate that floodplain development in this reach occurred over at least the past 9000 years. These results are not typical for southern Ontario channels. Previous studies have shown that some other large rivers in southern Ontario have low-energy, cohesive-bank channels with floodplains strongly dominated by vertical accretion. The distribution of culturally diagnostic archaeological artifacts on the floodplain surface dating back to the Middle Archaic period, but mostly confined to the Early Woodland period or later, suggests that human settlement of the floodplain was restricted to the later Holocene. The observation that a Middle Archaic site component is located in what should be a younger part of the floodplain challenges the notion that a simple lateral channel migration occurred with orderly (channelward) emplacement of sediment by the river. There is a possibility that the channel was anabranching in this reach of the river.

Spatial and temporal relationships between Eocene sand horizons and iron contamination in stream water in the Thames Basin west of London, UK

Analyses of stream water samples associated with Tertiary (Eocene) sands of the Bracklesham Formation 30–60 km west of London showed numerous occurrences of groundwater containing elevated iron(II) concentrations (1–15 mg/l Fe), which oxidise to red-brown ferrihydrite in localised wetlands and streams and join onward flows towards the River Thames. GIS mapping of iron concentrations in relation to topographical and geological data within a 20×30 km project area indicated some 168 km of iron-contaminated water. The results are consistent with downward permeation of groundwater through contained Camberley, Windlesham and Bagshot sand horizons and predominant W-E groundwater flow of up to 35 km in the Bagshot horizon, which rests on impermeable London Clay. Glauconite, comprising up to 70% of the sand near the base of the Windlesham horizon, apparently provides the main source of soluble iron in the near-anoxic, near-neutral, conditions normally prevailing. Pyrite is also a possible source, especially where quarrying or other excavation releases water from previously isolated volumes, simultaneously causing elevated sulphate and acidity levels via relatively rapid sulphide oxidation. Mechanisms proposed are underpinned through comparison with reports on analogous systems in the UK and abroad. Streams and lakes in the vicinity of seepages are highly visible and of decreased biodiversity. However, because of their natural origin, they are not subject to the same public concern and environmental control as compositionally similar near-neutral water from many former coal mines elsewhere - where iron derives primarily from pyrite. Also, while comparatively persistent, they appear destined for rapid depletion in geological terms: the unusual isolation of the sands until the Quaternary indicates a short leaching period and suggests a reason why iron-rich water from natural ferruginous sands is seldom of sufficient significance to be reported.