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Homan T, Howden NJK, Barden R, Kasprzyk-Hordern B, Hofman J. A perceptual approach to address complex water management issues in lowland permeable catchments. Water Res 2024; 254:121406. [PMID: 38452526 DOI: 10.1016/j.watres.2024.121406] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/29/2023] [Revised: 01/04/2024] [Accepted: 02/29/2024] [Indexed: 03/09/2024]
Abstract
Water quality management is a pressing global concern, and an increasingly complex issue due to climate and land-use change, legacy pollution, and the persistent release of well-known and emerging contaminants from diffuse and point sources. The increasing availability of high-frequency monitoring data is leading existing, often heuristic approaches, to be judged inadequate. Water managers frequently rely on simple qualitative and/or quantitative approaches for decision-making, but a lack of tangible improvement in freshwater quality outcomes is demanding new and innovative approaches that rely more on physical process understanding, rather than precedent. In this study, we drew upon local geological, hydrogeological, and hydrological data to infer a high-level perceptual model of surface/groundwater interactions in a chalk stream in Dorset, UK. We used the perceptual model to interrogate spatial and temporal trends in historical water quality data and to construct reach-scale nutrient mass balances. Through novel representation with Sankey diagrams, the perceptual model highlighted the relative importance of different hydrological features. Surface/groundwater interactions were found to occur predominantly by spring flow. We demonstrate that river flow accretion was dominated by the Chalk aquifer despite only occupying ca. 15 % of the surface bedrock area, and that spring sources, whilst vital to dilute treated sewage inputs in baseflow conditions, were also major sources of legacy nitrate. Nutrient mass balances showed that sewage treatment works contributed ca. 13 % to soluble reactive phosphorus load, with groundwater accounting for ca. 48 %. Thus, a determinand often associated with point-source pollution was shown to be diffuse dominated in this river. The study demonstrated how a multi-disciplinary approach to water management, based on a comprehensive perceptual modelling approach, could identify hitherto unknown sources and relative contributors to freshwater pollution and allow flow and load apportionment studies to provide useful decision-support to manage nutrient pollution. The novel application of perceptual modelling tools, such as the Sankey diagram, allows different source attributions to be presented in an accessible manner, and can be readily transferred to other study areas.
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Affiliation(s)
- Thomas Homan
- Department of Chemical Engineering, University of Bath, Claverton Down, Bath BA2 7AY, UK; Water Innovation and Research Centre (WIRC), University of Bath, Bath BA2 7AY, UK
| | | | | | - Barbara Kasprzyk-Hordern
- Water Innovation and Research Centre (WIRC), University of Bath, Bath BA2 7AY, UK; Department of Chemistry, University of Bath, Bath BA2 7AY, UK
| | - Jan Hofman
- Department of Chemical Engineering, University of Bath, Claverton Down, Bath BA2 7AY, UK; Water Innovation and Research Centre (WIRC), University of Bath, Bath BA2 7AY, UK.
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Whelan MJ, Linstead C, Worrall F, Ormerod SJ, Durance I, Johnson AC, Johnson D, Owen M, Wiik E, Howden NJK, Burt TP, Boxall A, Brown CD, Oliver DM, Tickner D. Is water quality in British rivers "better than at any time since the end of the Industrial Revolution"? Sci Total Environ 2022; 843:157014. [PMID: 35772542 DOI: 10.1016/j.scitotenv.2022.157014] [Citation(s) in RCA: 17] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2022] [Revised: 06/15/2022] [Accepted: 06/23/2022] [Indexed: 06/15/2023]
Abstract
We explore the oft-repeated claim that river water quality in Great Britain is "better now than at any time since the Industrial Revolution". We review available data and ancillary evidence for seven different categories of water pollutants: (i) biochemical oxygen demand (BOD) and ammonia; (ii) heavy metals; (iii) sewage-associated organic pollutants (including hormone-like substances, personal care product and pharmaceutical compounds); (iv) macronutrients (nitrogen and phosphorus); (v) pesticides; (vi) acid deposition and (vii) other variables, including natural organic matter and pathogenic micro-organisms. With a few exceptions, observed data are scarce before 1970. However, we can speculate about some of the major water quality pressures which have existed before that. Point-source pollutants are likely to have increased with population growth, increased connection rates to sewerage and industrialisation, although the increased provision of wastewater treatment during the 20th century will have mitigated this to some extent. From 1940 to the 1990s, pressures from nutrients and pesticides associated with agricultural intensification have increased in many areas. In parallel, there was an increase in synthetic organic compounds with a "down-the-drain" disposal pathway. The 1990s saw general reductions in mean concentrations of metals, BOD and ammonia (driven by the EU Urban Waste Water Treatment Directive), a levelling out of nitrate concentrations (driven by the EU Nitrate Directive), a decrease in phosphate loads from both point-and diffuse-sources and some recovery from catchment acidification. The current picture is mixed: water quality in many rivers downstream of urban centres has improved in sanitary terms but not with respect to emerging contaminants, while river quality in catchments with intensive agriculture is likely to remain worse now than before the 1960s. Water quality is still unacceptably poor in some water bodies. This is often a consequence of multiple stressors which need to be better-identified and prioritised to enable continued recovery.
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Affiliation(s)
- M J Whelan
- University of Leicester, United Kingdom of Great Britain and Northern Ireland.
| | - C Linstead
- WWF-UK, United Kingdom of Great Britain and Northern Ireland
| | - F Worrall
- University of Durham, United Kingdom of Great Britain and Northern Ireland
| | - S J Ormerod
- Cardiff University, Water Research Institute, United Kingdom of Great Britain and Northern Ireland
| | - I Durance
- Cardiff University, Water Research Institute, United Kingdom of Great Britain and Northern Ireland
| | - A C Johnson
- UKCEH, Wallingford, United Kingdom of Great Britain and Northern Ireland
| | - D Johnson
- The Rivers Trust, United Kingdom of Great Britain and Northern Ireland
| | - M Owen
- Angling Trust, United Kingdom of Great Britain and Northern Ireland
| | - E Wiik
- Ronin Institute, United States of America
| | - N J K Howden
- University of Bristol, United Kingdom of Great Britain and Northern Ireland
| | - T P Burt
- University of Durham, United Kingdom of Great Britain and Northern Ireland
| | - A Boxall
- University of York, United Kingdom of Great Britain and Northern Ireland
| | - C D Brown
- University of York, United Kingdom of Great Britain and Northern Ireland
| | - D M Oliver
- University of Stirling, United Kingdom of Great Britain and Northern Ireland
| | - D Tickner
- WWF-UK, United Kingdom of Great Britain and Northern Ireland
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Granger SJ, Yang Y, Pfahler V, Hodgson C, Smith AC, Le Cocq K, Collins AL, Blackwell MSA, Howden NJK. The stable oxygen isotope ratio of resin extractable phosphate derived from fresh cattle faeces. Rapid Commun Mass Spectrom 2018; 32:703-710. [PMID: 29490108 PMCID: PMC5900733 DOI: 10.1002/rcm.8092] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/19/2017] [Revised: 02/16/2018] [Accepted: 02/16/2018] [Indexed: 05/31/2023]
Abstract
RATIONALE Phosphorus losses from agriculture pose an environmental threat to watercourses. A new approach using the stable oxygen isotope ratio of oxygen in phosphate (δ18 OPO4 value) may help elucidate some phosphorus sources and cycling. Accurately determined and isotopically distinct source values are essential for this process. The δ18 OPO4 values of animal wastes have, up to now, received little attention. METHODS Phosphate (PO4 ) was extracted from cattle faeces using anion resins and the contribution of microbial PO4 was assessed. The δ18 OPO4 value of the extracted PO4 was measured by precipitating silver phosphate and subsequent analysis on a thermal conversion elemental analyser at 1400°C, with the resultant carbon monoxide being mixed with a helium carrier gas passed through a gas chromatography (GC) column into a mass spectrometer. Faecal water oxygen isotope ratios (δ18 OH2O values) were determined on a dual-inlet mass spectrometer through a process of headspace carbon dioxide equilibration with water samples. RESULTS Microbiological results indicated that much of the extracted PO4 was not derived directly from the gut fauna lysed during the extraction of PO4 from the faeces. Assuming that the faecal δ18 OH2O values represented cattle body water, the predicted pyrophosphatase equilibrium δ18 OPO4 (Eδ18 OPO4 ) values ranged between +17.9 and +19.9‰, while using groundwater δ18 OH2O values gave a range of +13.1 to +14.0‰. The faecal δ18 OPO4 values ranged between +13.2 and +15.3‰. CONCLUSIONS The fresh faecal δ18 OPO4 values were equivalent to those reported elsewhere for agricultural animal slurry. However, they were different from the Eδ18 OPO4 value calculated from the faecal δ18 OH2O value. Our results indicate that slurry PO4 is, in the main, derived from animal faeces although an explanation for the observed value range could not be determined.
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Affiliation(s)
| | - Yuguo Yang
- Queen's School of EngineeringUniversity of BristolSenate House, Tyndall AvenueBristolBS8 1THUK
| | | | | | - Andrew C. Smith
- NERC Isotope Geoscience LaboratoryBritish Geological SurveyKeyworthNottinghamNG12 5GGUK
| | - Kate Le Cocq
- Rothamsted ResearchNorth WykeOkehamptonEX20 2SBUK
| | | | | | - Nicholas J. K. Howden
- Queen's School of EngineeringUniversity of BristolSenate House, Tyndall AvenueBristolBS8 1THUK
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Noacco V, Wagener T, Worrall F, Burt TP, Howden NJK. Human impact on long-term organic carbon export to rivers. J Geophys Res Biogeosci 2017. [PMID: 0 DOI: 10.1002/2016jg003614] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Affiliation(s)
- Valentina Noacco
- Department of Civil Engineering; University of Bristol; Bristol UK
| | - Thorsten Wagener
- Department of Civil Engineering; University of Bristol; Bristol UK
- Cabot Institute; University of Bristol; Bristol UK
| | - Fred Worrall
- Department of Earth Sciences; Durham University; Durham UK
| | - Tim P. Burt
- Department of Geography; Durham University; Durham UK
| | - Nicholas J. K. Howden
- Department of Civil Engineering; University of Bristol; Bristol UK
- Cabot Institute; University of Bristol; Bristol UK
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5
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Hartley IP, Hill TC, Wade TJ, Clement RJ, Moncrieff JB, Prieto-Blanco A, Disney MI, Huntley B, Williams M, Howden NJK, Wookey PA, Baxter R. Quantifying landscape-level methane fluxes in subarctic Finland using a multiscale approach. Glob Chang Biol 2015; 21:3712-3725. [PMID: 25969925 PMCID: PMC4989475 DOI: 10.1111/gcb.12975] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/08/2014] [Accepted: 04/27/2015] [Indexed: 06/04/2023]
Abstract
Quantifying landscape-scale methane (CH4 ) fluxes from boreal and arctic regions, and determining how they are controlled, is critical for predicting the magnitude of any CH4 emission feedback to climate change. Furthermore, there remains uncertainty regarding the relative importance of small areas of strong methanogenic activity, vs. larger areas with net CH4 uptake, in controlling landscape-level fluxes. We measured CH4 fluxes from multiple microtopographical subunits (sedge-dominated lawns, interhummocks and hummocks) within an aapa mire in subarctic Finland, as well as in drier ecosystems present in the wider landscape, lichen heath and mountain birch forest. An intercomparison was carried out between fluxes measured using static chambers, up-scaled using a high-resolution landcover map derived from aerial photography and eddy covariance. Strong agreement was observed between the two methodologies, with emission rates greatest in lawns. CH4 fluxes from lawns were strongly related to seasonal fluctuations in temperature, but their floating nature meant that water-table depth was not a key factor in controlling CH4 release. In contrast, chamber measurements identified net CH4 uptake in birch forest soils. An intercomparison between the aerial photography and satellite remote sensing demonstrated that quantifying the distribution of the key CH4 emitting and consuming plant communities was possible from satellite, allowing fluxes to be scaled up to a 100 km(2) area. For the full growing season (May to October), ~ 1.1-1.4 g CH4 m(-2) was released across the 100 km(2) area. This was based on up-scaled lawn emissions of 1.2-1.5 g CH4 m(-2) , vs. an up-scaled uptake of 0.07-0.15 g CH4 m(-2) by the wider landscape. Given the strong temperature sensitivity of the dominant lawn fluxes, and the fact that lawns are unlikely to dry out, climate warming may substantially increase CH4 emissions in northern Finland, and in aapa mire regions in general.
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Affiliation(s)
- Iain P Hartley
- Geography, College of Life and Environmental Sciences, University of Exeter, Exeter, EX4 4RJ, UK
| | - Timothy C Hill
- Department of Earth and Environmental Science, University of St Andrews, St Andrews, KY16 9AL, UK
| | - Thomas J Wade
- School of Geosciences, University of Edinburgh, Edinburgh, EH3 3JN, UK
| | - Robert J Clement
- School of Geosciences, University of Edinburgh, Edinburgh, EH3 3JN, UK
| | - John B Moncrieff
- School of Geosciences, University of Edinburgh, Edinburgh, EH3 3JN, UK
| | - Ana Prieto-Blanco
- Department of Geography, University College London, London, WC1E 6BT, UK
| | - Mathias I Disney
- Department of Geography, University College London, London, WC1E 6BT, UK
- NERC National Centre for Earth Observation (NCEO)
| | - Brian Huntley
- NERC National Centre for Earth Observation (NCEO)
- School of Biological and Biomedical Sciences, University of Durham, Durham, DH1 3LE, UK
| | - Mathew Williams
- School of Geosciences, University of Edinburgh, Edinburgh, EH3 3JN, UK
- NERC National Centre for Earth Observation (NCEO)
| | | | - Philip A Wookey
- School of Life Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, UK
| | - Robert Baxter
- School of Biological and Biomedical Sciences, University of Durham, Durham, DH1 3LE, UK
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Haygarth PM, Jarvie HP, Powers SM, Sharpley AN, Elser JJ, Shen J, Peterson HM, Chan NI, Howden NJK, Burt T, Worrall F, Zhang F, Liu X. Sustainable phosphorus management and the need for a long-term perspective: the legacy hypothesis. Environ Sci Technol 2014; 48:8417-9. [PMID: 25001016 DOI: 10.1021/es502852s] [Citation(s) in RCA: 65] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Affiliation(s)
- Philip M Haygarth
- Lancaster Environment Centre, Lancaster University , Lancaster, LA1 4YQ, U.K
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Howden NJK, Burt TP, Worrall F, Mathias SA, Whelan MJ. Farming for Water Quality: Balancing Food Security and Nitrate Pollution in UK River Basins. ACTA ACUST UNITED AC 2013. [DOI: 10.1080/00045608.2013.754672] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Worrall F, Davies H, Burt T, Howden NJK, Whelan MJ, Bhogal A, Lilly A. The flux of dissolved nitrogen from the UK--evaluating the role of soils and land use. Sci Total Environ 2012; 434:90-100. [PMID: 22424770 DOI: 10.1016/j.scitotenv.2012.01.035] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/09/2011] [Revised: 12/21/2011] [Accepted: 01/12/2012] [Indexed: 05/31/2023]
Abstract
Fluvial dissolved nitrogen (dissolved organic nitrogen [DON], nitrate and ammonium) fluxes from the terrestrial biosphere of the UK to surrounding oceans are explained on the basis of combined predictions of soil to water transfer and in-stream loss. The flux of different nitrogen species from land to surface waters is estimated using an export coefficient model employing catchment soil, land use and hydroclimatic characteristics, fitted to flux estimates derived from the Harmonised Monitoring Scheme between 2001 and 2007 for 169 UK catchments. In-stream losses of DON, nitrate and ammonium were estimated using a transit time filter in the fluvial network. Comparisons of modelled land to water N flux (2125 ktonnes N yr(-1)) with estimates of N fluxes to estuarine and ocean systems at the tidal limit (791 ktonnes N yr(-1)) suggest that significant in-channel N losses occur. These in transit losses are equivalent to up to 55 kg N ha(-1) yr(-1).
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Affiliation(s)
- Fred Worrall
- Department of Earth Sciences, Durham University, Durham, UK.
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Howden NJK, Burt TP, Worrall F, Whelan MJ. Monitoring fluvial water chemistry for trend detection: hydrological variability masks trends in datasets covering fewer than 12 years. ACTA ACUST UNITED AC 2011; 13:514-21. [DOI: 10.1039/c0em00722f] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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10
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Burt TP, Howden NJK, Worrall F, Whelan MJ, Bieroza M. Nitrate in United kingdom rivers: policy and its outcomes since 1970. Environ Sci Technol 2011; 45:175-181. [PMID: 20681541 DOI: 10.1021/es101395s] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Modern conventional farming provides Western Europe and North America with reliable, high quality, and relatively cheap supplies of food and fiber, increasingly viewed as a potential source of fuel. One of the costs is continued widespread pollution of rivers and groundwater-predominantly by nutrients. In 1970, in both the United States and UK, farming was focused on maximizing yield and management practices were rapidly modernizing. Little attention was paid to the external impacts of farming. In 2010, diffuse pollution from agriculture is being seriously addressed by both voluntary and statutory means in an attempt to balance environmental costs with the continued benefits of agricultural production. In this paper we consider long-term changes in the concentration and flux of nitrate in five rural UK rivers to demonstrate the impact of agricultural intensification and subsequent policies to reduce diffuse pollution on river water quality between 1970 and 2010.
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Affiliation(s)
- T P Burt
- Department of Geography, Durham University, Durham DH1 3LE, UK.
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Holman IP, Howden NJK, Bellamy P, Willby N, Whelan MJ, Rivas-Casado M. An assessment of the risk to surface water ecosystems of groundwater P in the UK and Ireland. Sci Total Environ 2010; 408:1847-1857. [PMID: 19945150 DOI: 10.1016/j.scitotenv.2009.11.026] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/10/2009] [Revised: 11/04/2009] [Accepted: 11/09/2009] [Indexed: 05/28/2023]
Abstract
A good quantitative understanding of phosphorus (P) delivery is essential in the design of management strategies to prevent eutrophication of terrestrial freshwaters. Most research to date has focussed on surface and near-surface hydrological pathways, under the common assumption that little P leaches to groundwater. Here we present an analysis of national patterns of groundwater phosphate concentrations in England and Wales, Scotland, and the Republic of Ireland, which shows that many groundwater bodies have median P concentrations above ecologically significant thresholds for freshwaters. The potential risk to receptor ecosystems of high observed groundwater P concentrations will depend on (1) whether the observed groundwater P concentrations are above the natural background; (2) the influence of local hydrogeological settings (pathways) on the likelihood of significant P transfers to the receptor; (3) the sensitivity of the receptor to P; and, (4) the relative magnitude of P transfers from groundwater compared to other P sources. Our research suggests that, although there is often a high degree of uncertainty in many of these factors, groundwater has the potential to trigger and/or maintain eutrophication under certain scenarios: the assumption of groundwater contribution to river flows as a ubiquitous source of dilution for P-rich surface runoff must therefore be questioned. Given the regulatory importance of P concentrations in triggering ecological quality thresholds, there is an urgent need for detailed monitoring and research to characterise the extent and magnitude of different groundwater P sources, the likelihood for P transformation and/or storage along aquifer-hyporheic zone flow paths and to identify the subsequent risk to receptor ecosystems.
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Affiliation(s)
- I P Holman
- Natural Resources Department, Cranfield University, Bedford, UK
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12
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Howden NJK, Bowes MJ, Clark ADJ, Humphries N, Neal C. Water quality, nutrients and the European union's Water Framework Directive in a lowland agricultural region: Suffolk, south-east England. Sci Total Environ 2009; 407:2966-2979. [PMID: 19217145 DOI: 10.1016/j.scitotenv.2008.12.040] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/26/2008] [Revised: 12/11/2008] [Accepted: 12/13/2008] [Indexed: 05/27/2023]
Abstract
The water quality of 13 rivers in the lowland, agricultural county of Suffolk is investigated using routine monitoring data for the period 1981 to 2006 collected by the Environment Agency of England and Wales (EA), and its predecessors, with particular emphasis on phosphorus (as total reactive phosphorus, TRP) and total (dissolved and particulate) oxidised nitrogen (TOxN--predominantly nitrate NO3). Major ion and flow data are used to outline fundamental hydrochemical characteristics related to the groundwater provenance of base-flow waters. Relative load contributions from point and diffuse sources are approximated using Load Apportionment Modelling for both TRP and TOxN where concurrent flow and concentration data are available. Analyses indicate a mixture of point and diffuse sources of TRP, with the former being dominant during low flow periods, while for TOxN diffuse sources dominate. Out of 59 sites considered, 53 (90%) were found to have annual average TRP concentrations greater than 0.05 mg P l(-1), and 36 (61%) had average concentrations over 0.120 mg P l(-1), the upper thresholds for 'High' and 'Good' ecological status, respectively. Correspondingly, for TOxN, most of the rivers are already within 70% of the 11.3 mg N l(-1) threshold, with two rivers (Wang and Ore) being consistently greater than this. It is suggested that the major challenge is to characterise and control point-source TRP inputs which, being predominant during the late spring and summer low-flow period, coincide with the peak of primary biological production, thus presenting the major challenge to achieving 'good' ecological status under the Water Framework Directive. Results show that considerable effort is still required to ensure appropriate management and develop tools for decision-support.
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Affiliation(s)
- Nicholas J K Howden
- National Soil Resources Institute, Natural Resources Department, School of Applied Sciences, Cranfield University, Cranfield, Bedfordshire MK430AL, United Kingdom.
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13
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Howden NJK, Burt TP. Temporal and spatial analysis of nitrate concentrations from the Frome and Piddle catchments in Dorset (UK) for water years 1978 to 2007: evidence for nitrate breakthrough? Sci Total Environ 2008; 407:507-26. [PMID: 18947858 DOI: 10.1016/j.scitotenv.2008.08.042] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/03/2008] [Revised: 08/26/2008] [Accepted: 08/27/2008] [Indexed: 05/12/2023]
Abstract
This paper analyses time series of nitrate concentration for 35 sites throughout the Frome and Piddle catchments in southern England for the period 1978--2007. The Piddle catchment lies wholly within the Chalk aquifer in its upper reaches, whereas the headwaters of the Frome are a mixture of Chalk and other lithologies; both rivers flow across Palaeogene sands and clays in their lower reaches, before discharging into Poole Harbour. At each site sources of observed variation arise from differences between sample month (seasonality) and year (underlying trend). Considering water year mean concentrations, there is a strong and highly significant positive correlation with year for all but two sites. The annual rate of increase tends to be higher in the Piddle than the Frome, and in both catchments the annual rate of increase tends to decrease downstream; both these effects relate to the degree of groundwater influence. In addition to the strong upward trend, there is also a clear seasonal cycle in nitrate concentration at most sites; amplitude generally increases downstream. Laying aside the assumption of linearity, solute breakthrough curves (S-curves) are fitted to 34 of the 36 nitrate time series. Results show that application of S-curves is an appropriate description of changes in annual mean concentrations over time and provides improvements over linear models in most cases. The interpretation of rising nitrate concentrations in these groundwater-dominated catchments moves from a statistical to a hydrological process base, providing valuable insight into lowland catchment function.
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Affiliation(s)
- N J K Howden
- Department of Natural Resources, School of Applied Sciences, Cranfield University, Cranfield, Bedfordshire, MK43 0AL, UK.
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