Emma Gozzard

Centre for Ecology & Hydrology, Wallingford, England, United Kingdom

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Publications (12)27.3 Total impact

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    ABSTRACT: This paper describes the hydrochemistry of a lowland, urbanised river-system, The Cut in England, using in situ sub-daily sampling. The Cut receives effluent discharges from four major sewage treatment works serving around 190,000 people. These discharges consist largely of treated water, originally abstracted from the River Thames and returned via the water supply network, substantially increasing the natural flow. The hourly water quality data were supplemented by weekly manual sampling with laboratory analysis to check the hourly data and measure further determinands. Mean phosphorus and nitrate concentrations were very high, breaching standards set by EU legislation. Though 56% of the catchment area is agricultural, the hydrochemical dynamics were significantly impacted by effluent discharges which accounted for approximately 50% of the annual P catchment input loads and, on average, 59% of river flow at the monitoring point. Diurnal dissolved oxygen data demonstrated high in-stream productivity. From a comparison of high frequency and conventional monitoring data, it is inferred that much of the primary production was dominated by benthic algae, largely diatoms. Despite the high productivity and nutrient concentrations, the river water did not become anoxic and major phytoplankton blooms were not observed. The strong diurnal and annual variation observed showed that assessments of water quality made under the Water Framework Directive (WFD) are sensitive to the time and season of sampling. It is recommended that specific sampling time windows be specified for each determinand, and that WFD targets should be applied in combination to help identify periods of greatest ecological risk. This article is protected by copyright. All rights reserved.
    No preview · Article · Mar 2015 · Hydrological Processes
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    ABSTRACT: 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.The ISME Journal advance online publication, 13 February 2015; doi:10.1038/ismej.2014.237.
    Full-text · Article · Feb 2015 · The ISME Journal
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    ABSTRACT: Small-angle neutron scattering has been used to examine the settling behaviour of partially-passivated silver nanoparticles (AgNP), capped with a polyvinylpyrolidone (PVP) stabiliser, in water and domestic wastewater, in a primary clarification ‘microcosm’ as a function of time. The impact of two flocculants routinely used in the wastewater treatment process has also been studied. The settling velocity is found to be time-dependent, but always exceeds 100 mm/hr during the first hour at the point of input. Particle removal by settling is almost three times greater in wastewater than it is in pure water. The results are rationalised in terms of a generic, but synergistic, interaction between non-ionic capping agents and anionic components of wastewater, and we show how this may afford an explanation for some of the diversity of behaviour previously reported in studies of several different NPs in wastewater treatment. We conclude that AgNPs entering primary clarification with non-ionic surface coatings, whether present by design or environmental transformation, pose no threat to the viability of the biofilms in secondary wastewater treatment.
    Full-text · Article · Jan 2015
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    ABSTRACT: The total reactive phosphorus (TRP) and nitrate concentrations of the River Enborne, southern England, were monitored at hourly interval between January 2010 and December 2011. The relationships between these high-frequency nutrient concentration signals and flow were used to infer changes in nutrient source and dynamics through the annual cycle and each individual storm event, by studying hysteresis patterns. TRP concentrations exhibited strong dilution patterns with increasing flow, and predominantly clockwise hysteresis through storm events. Despite the Enborne catchment being relatively rural for southern England, TRP inputs were dominated by constant, non-rain-related inputs from sewage treatment works (STW) for the majority of the year, producing the highest phosphorus concentrations through the spring-summer growing season. At higher river flows, the majority of the TRP load was derived from within-channel remobilisation of phosphorus from the bed sediment, much of which was also derived from STW inputs. Therefore, future phosphorus mitigation measures should focus on STW improvements. Agricultural diffuse TRP inputs were only evident during storms in the May of each year, probably relating to manure application to land. The nitrate concentration-flow relationship produced a series of dilution curves, indicating major inputs from groundwater and to a lesser extent STW. Significant diffuse agricultural inputs with anticlockwise hysteresis trajectories were observed during the first major storms of the winter period. The simultaneous investigation of high-frequency time series data, concentration-flow relationships and hysteresis behaviour through multiple storms for both phosphorus and nitrate offers a simple and innovative approach for providing new insights into nutrient sources and dynamics. Crown Copyright © 2014. Published by Elsevier B.V. All rights reserved.
    Full-text · Article · Jan 2015 · Science of The Total Environment
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    Full-text · Conference Paper · Apr 2014
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    Full-text · Conference Paper · Apr 2014
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    ABSTRACT: This paper reports the results of a 2-year study of water quality in the River Enborne, a rural river in lowland England. Concentrations of nitrogen and phosphorus species and other chemical determinands were monitored both at high-frequency (hourly), using automated in situ instrumentation, and by manual weekly sampling and laboratory analysis. The catchment land use is largely agricultural, with a population density of 123 persons km−2. The river water is largely derived from calcareous groundwater, and there are high nitrogen and phosphorus concentrations. Agricultural fertiliser is the dominant source of annual loads of both nitrogen and phosphorus. However, the data show that sewage effluent discharges have a disproportionate effect on the river nitrogen and phosphorus dynamics. At least 38% of the catchment population use septic tank systems, but the effects are hard to quantify as only 6% are officially registered, and the characteristics of the others are unknown. Only 4% of the phosphorus input and 9% of the nitrogen input is exported from the catchment by the river, highlighting the importance of catchment process understanding in predicting nutrient concentrations. High-frequency monitoring will be a key to developing this vital process understanding.
    Full-text · Article · Jan 2014
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    Full-text · Conference Paper · Apr 2013
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    ABSTRACT: This paper introduces new insights into the hydrochemical functioning of lowland river systems using field-based spectrophotometric and electrode technologies. The streamwater concentrations of nitrogen species and phosphorus fractions were measured at hourly intervals on a continuous basis at two contrasting sites on tributaries of the River Thames - one draining a rural catchment, the River Enborne, and one draining a more urban system, The Cut. The measurements complement those from an existing network of multi-parameter water quality sondes maintained across the Thames catchment and weekly monitoring based on grab samples. The results of the sub-daily monitoring show that streamwater phosphorus concentrations display highly complex dynamics under storm conditions dependent on the antecedent catchment wetness, and that diurnal phosphorus and nitrogen cycles occur under low flow conditions. The diurnal patterns highlight the dominance of sewage inputs in controlling the streamwater phosphorus and nitrogen concentrations at low flows, even at a distance of 7 km from the nearest sewage treatment works in the rural River Enborne. The time of sample collection is important when judging water quality against ecological thresholds or standards. An exhaustion of the supply of phosphorus from diffuse and multiple septic tank sources during storm events was evident and load estimation was not improved by sub-daily monitoring beyond that achieved by daily sampling because of the eventual reduction in the phosphorus mass entering the stream during events. The results highlight the utility of sub-daily water quality measurements and the discussion considers the practicalities and challenges of in situ, sub-daily monitoring.
    Full-text · Article · Nov 2012 · Hydrology and Earth System Sciences
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    ABSTRACT: This paper introduces new insights into the hydrochemical functioning of lowland river-systems using field-based spectrophotometric and electrode technologies. The streamwater concentrations of nitrogen species and phosphorus fractions were measured at hourly intervals on a continuous basis at two contrasting sites on tributaries of the River Thames, one draining a rural catchment, the River Enborne, and one draining a more urban system, The Cut. The measurements complement those from an existing network of multi-parameter water quality sondes maintained across the Thames catchment and weekly monitoring based on grab samples. The results of the sub-daily monitoring show that streamwater phosphorus concentrations display highly complex, seemingly chaotic, dynamics under storm conditions dependent on the antecedent catchment wetness, and that diurnal phosphorus and nitrogen cycles occur under low flow conditions. The diurnal patterns highlight the dominance of sewage inputs in controlling the streamwater phosphorus and nitrogen concentrations at low flows, even at a distance of 7 km from the nearest sewage works in the rural, River Enborne, and that the time of sample collection is important when judging water quality against ecological thresholds or standards. An exhaustion of the supply of phosphorus from diffuse and septic tank sources during storm events was evident and load estimation was not improved by sub-daily monitoring beyond that achieved by daily sampling because of the eventual reduction in the phosphorus mass entering the stream during events. The dominance of respiration over photosynthesis in The Cut indicated a prevalence of heterotrophic algae, and the seasonal patterns in respiration and photosynthesis corresponded with those of temperature and light in this nutrient over-enriched stream. These results highlight the utility of sub-daily water quality measurements but the deployment of modified wet-chemistry technologies into the field was limited by mains electricity availability. A new approach is therefore needed to allow measurement of a wide range of analytes at a broader range of locations for the development of water quality web-sensor networks. The development and field deployment of a miniaturised "lab-on-a-chip" ion chromatograph is proposed and justified.
    Full-text · Article · May 2012 · Hydrology and Earth System Sciences Discussions
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    ABSTRACT: Chlorophyll-a and nutrient concentrations were monitored at weekly intervals across 21 river sites throughout the River Thames basin, southern England, between 2009 and 2011. Despite a 90% decrease in soluble reactive phosphorus (SRP) concentration of the lower River Thames since the 1990s, very large phytoplankton blooms still occur. Chlorophyll concentrations were highest in the mid and lower River Thames and the larger tributaries. Lowest chlorophyll concentrations were observed in the smaller tributaries, despite some having very high phosphorus concentrations of over 300 μg l(-1). There was a strong positive correlation between river length and mean chlorophyll concentration (R(2)=0.82), and rivers connected to canals had ca. six times greater chlorophyll concentration than 'natural' rivers with similar phosphorus concentrations, indicating the importance that residence time has on determining phytoplankton biomass. Phosphorus concentration did have some influence, with phosphorus-enriched rivers having much larger phytoplankton blooms than nutrient-poor rivers of a similar length. Water quality improvements may now be capping chlorophyll peaks in the Rivers Thames and Kennet, due to SRP depletion during the spring/early summer phytoplankton bloom period. Dissolved reactive silicon was also depleted to potentially-limiting concentrations for diatom growth in the River Thames during these phytoplankton blooms, but nitrate remained in excess for all rivers throughout the study period. Other potential mitigation measures, such as increasing riparian shading and reducing residence times by removing impoundments may be needed, alongside phosphorus mitigation, to reduce the magnitude of phytoplankton blooms in the future.
    Full-text · Article · Apr 2012 · Science of The Total Environment
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    ABSTRACT: Model-based assessments of the impacts of environmental change on European freshwater ecosystems are needed to aid informed resource management. This talk will focus on how such model-based assessments can be improved using the latest results from in-situ, continuous sub-daily water quality monitoring in upland and lowland UK river systems. Two catchments in the lowland Thames basin, the Enborne and The Cut, have been instrumented since November 2009 to examine the water quality dynamics using laboratory instruments (Hach-Lange; Micromac) installed in the field to produce hourly measurements of nutrient dynamics. Total Phosphorus and Total Reactive Phosphorus were measured in The Cut and nitrate was measured in the Enborne. These data were supplemented at both sites by nearby flow measurements and data collected using YSI multi-parameter sondes fitted with pH, dissolved oxygen, conductivity and water temperature probes. Experiences of installing and using these in-situ technologies will be described. The observed dynamics evident in these datasets will be compared to those identified at Plynlimon, Wales, which represent the hydrochemical functioning of an upland river-system. Both the lowland and upland data will be interpreted in terms of: the gain in information by sampling at sub-daily frequencies (and what is lost by sampling at lower frequencies); new information derived in terms of hydrochemical functioning; and the implications for progressing hydrochemical models. As part of the discussion, new opportunities from 'lab-on-a-chip' technologies will be described.
    Full-text · Conference Paper · Jan 2012