{"id":4785,"date":"2025-08-22T10:00:07","date_gmt":"2025-08-22T09:00:07","guid":{"rendered":"https:\/\/www.bgs.ac.uk\/groundwater\/?page_id=4785"},"modified":"2026-03-04T14:38:02","modified_gmt":"2026-03-04T14:38:02","slug":"nitrate-storage-in-the-unsaturated-zone","status":"publish","type":"page","link":"https:\/\/www.bgs.ac.uk\/groundwater\/quality\/diffuse-pollution\/nitrate-contamination-of-groundwater\/nitrate-storage-in-the-unsaturated-zone\/","title":{"rendered":"Global patterns of nitrate storage in the unsaturated zone"},"content":{"rendered":"\t\t\t<section class=\"hero-section hero-section-with-social\">\n\t\t\t\t\t\t\t\t<div class=\"hero-info-wrap\">\n\t\t\t\t\t<div class=\"container\">\n\t\t\t\t\t\t<div class=\"row\">\n\t\t\t\t\t\t\t<div class=\"col-12\">\n\t\t\t\t\t\t\t\t<div class=\"hero-info\">\n\t\t\t\t\t\t\t\t\t<h1>Global patterns of nitrate storage in the unsaturated zone<\/h1>\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t\t\t\t<\/div>\n\t\t\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t\t\t\t\n\t\t\t<div class=\"social-wrap social-wrap-inline-them\">\n\t\t\t\t<div class=\"sea-background-f\">\n\t\t\t\t\t<span>Share this article<\/span><a target=\"_blank\"  href=\"https:\/\/www.facebook.com\/sharer\/sharer.php?u=https:\/\/www.bgs.ac.uk\/groundwater\/quality\/diffuse-pollution\/nitrate-contamination-of-groundwater\/nitrate-storage-in-the-unsaturated-zone\/\"><span class=\"icon-facebook\"><span class=\"hidden\">Facebook<\/span><\/span><\/a><a target=\"_blank\"  href=\"https:\/\/twitter.com\/intent\/tweet?text=Global%20patterns%20of%20nitrate%20storage%20in%20the%20unsaturated%20zone&#038;url=https:\/\/www.bgs.ac.uk\/groundwater\/quality\/diffuse-pollution\/nitrate-contamination-of-groundwater\/nitrate-storage-in-the-unsaturated-zone\/\"><span class=\"icon-twitter\"><span class=\"hidden\">Twitter<\/span><\/span><\/a><a   onclick=\"javascript:void( (function() {var e=document.createElement('script' );e.setAttribute('type','text\/javascript' );e.setAttribute('charset','UTF-8' );e.setAttribute('src','\/\/assets.pinterest.com\/js\/pinmarklet.js?r='+Math.random()*99999999);document.body.appendChild(e)})());\"  href=\"javascript:void(0);\"><span class=\"icon-pinterest\"><span class=\"hidden\">Pinterest<\/span><\/span><\/a><a target=\"_blank\"  href=\"https:\/\/wa.me?text=https:\/\/www.bgs.ac.uk\/groundwater\/quality\/diffuse-pollution\/nitrate-contamination-of-groundwater\/nitrate-storage-in-the-unsaturated-zone\/\"><span class=\"icon-whatsapp\"><span class=\"hidden\">WhatsApp<\/span><\/span><\/a><a   href=\"mailto:?subject=Global%20patterns%20of%20nitrate%20storage%20in%20the%20unsaturated%20zone&#038;body=%20(https:\/\/www.bgs.ac.uk\/groundwater\/quality\/diffuse-pollution\/nitrate-contamination-of-groundwater\/nitrate-storage-in-the-unsaturated-zone\/)\"><span class=\"icon-mail\"><span class=\"hidden\">Email<\/span><\/span><\/a><a href=\"#\" data-copy=\"https:\/\/www.bgs.ac.uk\/groundwater\/quality\/diffuse-pollution\/nitrate-contamination-of-groundwater\/nitrate-storage-in-the-unsaturated-zone\/\" class=\"copy-url-on-click\"><span class=\"icon-link\"><span class=\"hidden\">Copy Link<\/span><\/span><\/a><\/div><\/div>\t\t\t\t\t\t\t<\/section>\n\t\t\t\n\n\n<section class=\"wp-block-bgs-blocks-content-container content-section\"><div class=\"container\"><div class=\"row\"><div class=\"col-12\">\n<p>The unsaturated or &#8216;vadose&#8217; zone between the base of the soil and the water table can be an important store of nitrate. Water moves slowly downward through the unsaturated zone and a large store of nitrate can accumulate if the water contains nitrate derived from surface sources such as fertiliser. Release of this store can affect ground- and surface-water quality for decades; it can also continue for a long time after changes to farming practices that reduce nitrate leaching.<\/p>\n\n\n\n<p>To better understand the extent of the problem, BGS made the first global-scale quantification of nitrate stored in the vadose zone between 1900 and 2000.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Increases in nitrate storage<\/h2>\n\n\n\n<p>To estimate nitrate stored in the unsaturated zone, we linked mathematical models of nitrate leaching from the base of the soil zone with estimates of groundwater recharge, unsaturated-zone porosity and the depth to groundwater.<\/p>\n\n\n\n<p>Our modelling showed a substantial, continuous increase in nitrate stored in the unsaturated zone over the last century. The peak nitrate storage in 2000 was estimated to be up to 1814 teragrams (Tg) of nitrogen. This is equivalent to up to 200 per cent of the inorganic nitrogen stored in soils. <\/p>\n\n\n\n<p>Spatially, the unsaturated-zone nitrate storage is greatest in North America, China and central and eastern Europe, where the depth to the water table is large and there is an extensive history of agricultural fertiliser use.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Nitrate storage patterns<\/h2>\n\n\n\n<p>To better understand trends in nitrate storage, we grouped the nitrate storage responses for river catchments across the globe. The groups show clear differences and trends, with a distinct split between developed (USA; Europe) and developing (Africa; East Asia) countries. <\/p>\n\n\n\n<p>In the developed group, current nitrate leaching into the unsaturated zone is decreasing as a result of improved regulation and farming practice. In contrast, in the developing countries, nitrate leaching shows continuous increases associated with rapid, early development and growing intensification of fertilised agriculture.<\/p>\n\n\n\t\t\t\t<div  class=\"owl-carousel carousel-primary-color carousel owl-theme thumbs-carousel-js\">\n\t\t\t\t\t<div class=\"item\"><figure  class=\"img-wrap\"><a href=\"https:\/\/www.bgs.ac.uk\/groundwater\/wp-content\/uploads\/sites\/4\/2025\/08\/global-increase-graph.jpg\" data-toggle=\"lightbox\" data-footer=\"&lt;p&gt;Global increase in nitrate stored in the unsaturated zone. BGS \u00a9 UKRI.&lt;\/p&gt;\n\" data-gallery=\"gallery_2563\"><img decoding=\"async\" src=\"https:\/\/www.bgs.ac.uk\/groundwater\/wp-content\/uploads\/sites\/4\/2025\/08\/global-increase-graph.jpg\" class=\"attachment-medium size-medium\" alt=\"A graph showing the increase in nitrate in the vadose zone from 1900 to 2000\" \/><\/a><figcaption class=\"caption sm-line\">\n\t\t\t\t\t<div class=\"caption-icon\">\n\t\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.bgs.ac.uk\/groundwater\/wp-content\/themes\/bgs\/img\/info-caption.svg\" alt=\"Information icon\">\n\t\t\t\t\t<\/div>\n\t\t\t\t\t<div class=\"caption-text\"><p>Global increase in nitrate stored in the unsaturated zone. BGS \u00a9 UKRI.<\/p>\n<\/div>\n\t\t\t\t\t<div class=\"expand-box expand-box-top\"><a href=\"https:\/\/www.bgs.ac.uk\/groundwater\/wp-content\/uploads\/sites\/4\/2025\/08\/global-increase-graph.jpg\" ><img decoding=\"async\" src=\"https:\/\/www.bgs.ac.uk\/groundwater\/wp-content\/themes\/bgs\/img\/expand.svg\" alt=\"Expand icon\"><\/a><\/div>\n\t\t\t\t<\/figcaption><\/figure><\/div><div class=\"item\"><figure  class=\"img-wrap\"><a href=\"https:\/\/www.bgs.ac.uk\/groundwater\/wp-content\/uploads\/sites\/4\/2025\/08\/spatial-distribution.jpg\" data-toggle=\"lightbox\" data-footer=\"&lt;p&gt;Spatial distribution of nitrate stored in the unsaturated zone. BGS \u00a9 UKRI.&lt;\/p&gt;\n\" data-gallery=\"gallery_2563\"><img decoding=\"async\" src=\"https:\/\/www.bgs.ac.uk\/groundwater\/wp-content\/uploads\/sites\/4\/2025\/08\/spatial-distribution.jpg\" class=\"attachment-medium size-medium\" alt=\"Four maps of the world showing global nitrate distribution in 1925, 1950, 1975 and 2000\" \/><\/a><figcaption class=\"caption sm-line\">\n\t\t\t\t\t<div class=\"caption-icon\">\n\t\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.bgs.ac.uk\/groundwater\/wp-content\/themes\/bgs\/img\/info-caption.svg\" alt=\"Information icon\">\n\t\t\t\t\t<\/div>\n\t\t\t\t\t<div class=\"caption-text\"><p>Spatial distribution of nitrate stored in the unsaturated zone. BGS \u00a9 UKRI.<\/p>\n<\/div>\n\t\t\t\t\t<div class=\"expand-box expand-box-top\"><a href=\"https:\/\/www.bgs.ac.uk\/groundwater\/wp-content\/uploads\/sites\/4\/2025\/08\/spatial-distribution.jpg\" ><img decoding=\"async\" src=\"https:\/\/www.bgs.ac.uk\/groundwater\/wp-content\/themes\/bgs\/img\/expand.svg\" alt=\"Expand icon\"><\/a><\/div>\n\t\t\t\t<\/figcaption><\/figure><\/div><div class=\"item\"><figure  class=\"img-wrap\"><a href=\"https:\/\/www.bgs.ac.uk\/groundwater\/wp-content\/uploads\/sites\/4\/2025\/08\/storage-clusters.jpg\" data-toggle=\"lightbox\" data-footer=\"&lt;p&gt;Nitrate storage groups or clusters. BGS \u00a9 UKRI.&lt;\/p&gt;\n\" data-gallery=\"gallery_2563\"><img decoding=\"async\" src=\"https:\/\/www.bgs.ac.uk\/groundwater\/wp-content\/uploads\/sites\/4\/2025\/08\/storage-clusters.jpg\" class=\"attachment-medium size-medium\" alt=\"A map of the world showing clusters of nitrate storage globally\" \/><\/a><figcaption class=\"caption sm-line\">\n\t\t\t\t\t<div class=\"caption-icon\">\n\t\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.bgs.ac.uk\/groundwater\/wp-content\/themes\/bgs\/img\/info-caption.svg\" alt=\"Information icon\">\n\t\t\t\t\t<\/div>\n\t\t\t\t\t<div class=\"caption-text\"><p>Nitrate storage groups or clusters. BGS \u00a9 UKRI.<\/p>\n<\/div>\n\t\t\t\t\t<div class=\"expand-box expand-box-top\"><a href=\"https:\/\/www.bgs.ac.uk\/groundwater\/wp-content\/uploads\/sites\/4\/2025\/08\/storage-clusters.jpg\" ><img decoding=\"async\" src=\"https:\/\/www.bgs.ac.uk\/groundwater\/wp-content\/themes\/bgs\/img\/expand.svg\" alt=\"Expand icon\"><\/a><\/div>\n\t\t\t\t<\/figcaption><\/figure><\/div>\t\t\t\t<\/div>\n\t\t\t\t\n\n\n<h2 class=\"wp-block-heading\">Implications for environmental policy<\/h2>\n\n\n\n<p>The large store of nitrate in the unsaturated zone means that the use of soil-nitrate leaching estimates alone as an indicator of nitrate pollution is likely to be inappropriate. The distribution of unsaturated-zone nitrate storage can give policy- and decision makers a first global indication of where this store may be significant and where delays in improvements in groundwater and surface water quality can be expected. This is important for assessing the effectiveness of nitrate management measures and timescales for achieving environmental objectives.<\/p>\n\n\n\n<p>The different nitrate storage characteristics observed highlight the need for different management strategies to tackle nitrate pollution across developing and developed countries. However, in both cases, it is essential that catchment retention processes, such as unsaturated-zone storage, are considered. Other temporary stores of nitrate, such as storage in soil organic matter and in riparian zones, also need to be quantified if fully integrated pollution-management strategies are to be developed.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Further reading<\/h2>\n\n\n<div  class=\"accordions\">\n\t\t\t\t<div class=\"acc-wrap\">\n\t\t\t\t\t<button class=\"acc-top secondary-background icon-arrow button no-btn\"><span class=\"button-content\" tabindex=\"-1\">References<\/span><\/button>\n\t\t\t\t\t<div class=\"acc-body sea-background-e\">\n\t\t\t\t\t\t<p>Ascott, M. 2018. <a href=\"http:\/\/dx.doi.org\/10.5285\/800dd09b-5848-4803-a70c-cd15d5590f16\">Gridded model estimates of nitrate-N stored in the vadose (unsaturated) zone at the global scale from 1900 to 2000<\/a>. British Geological Survey. DOI: http:\/\/dx.doi.org\/10.5285\/800dd09b-5848-4803-a70c-cd15d5590f16<\/p>\n<p>Ascott, M J, Gooddy, D C, Wang, L, Stuart, M E, Lewis, M A, Ward, R S, and Binley, A M. 2017. <a href=\"https:\/\/doi.org\/10.1038\/s41467-017-01321-w\" target=\"_blank\" rel=\"noopener\">Global patterns of nitrate storage in the vadose zone<\/a>. <em>Nature Communications<\/em>, Vol. 8(1), 1416. DOI: https:\/\/doi.org\/10.1038\/s41467-017-01321-w<\/p>\n<p>Ascott, Matthew J.; Gooddy, Daren C<strong>.<\/strong>;\u00a0Fenton, Owen;\u00a0Vero, Sara; Ward, Rob S.;\u00a0Basu, Nandita B.;\u00a0Worrall, Fred;\u00a0Van Meter, Kimberly;\u00a0Surridge, Ben W.J.. 2021 <a href=\"https:\/\/nora.nerc.ac.uk\/id\/eprint\/530138\/\">The need to integrate legacy nitrogen storage dynamics and time lags into policy and practice.<\/a>\u00a0<em>Science of The Total Environment<\/em>, 781, 146698. DOI: https:\/\/doi.org\/10.1016\/j.scitotenv.2021.146698<\/p>\n<p>Ascott, M.J.; Wang, L.; Stuart, M.E.; Ward, R.S.;\u00a0Hart, A.. 2016 <a href=\"https:\/\/nora.nerc.ac.uk\/id\/eprint\/512268\/\">Quantification of nitrate storage in the vadose (unsaturated) zone: a missing component of terrestrial N budgets.<\/a>\u00a0<em>Hydrological Processes<\/em>, 30 (12). 1903-1915. DOI: https:\/\/doi.org\/10.1002\/hyp.10748<\/p>\n\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t<\/div><\/div><\/div><\/div><\/section>\n\n\n<section class=\"cta-section  sea-background-e \">\n\t<div class=\"container\">\n\t\t<div class=\"row md-row\">\n\t\t\t<div class=\"col-12\">\n\t\t\t\t<h2>Need more information?<\/h2>\t\t\t\t\t\t\t\t<div class=\"btn-wrap\"><a href=\"https:\/\/www.bgs.ac.uk\/people\/lapworth-daniel\/\"  class=\"button primary-background   \">Contact Dan Lapworth<\/a><\/div>\t\t\t<\/div>\n\t\t<\/div>\n\t<\/div>\n<\/section>\n\t","protected":false},"excerpt":{"rendered":"","protected":false},"author":7,"featured_media":0,"parent":70,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_acf_changed":false,"_relevanssi_hide_post":"","_relevanssi_hide_content":"","_relevanssi_pin_for_all":"","_relevanssi_pin_keywords":"","_relevanssi_unpin_keywords":"","_relevanssi_related_keywords":"","_relevanssi_related_include_ids":"","_relevanssi_related_exclude_ids":"","_relevanssi_related_no_append":"","_relevanssi_related_not_related":"","_relevanssi_related_posts":"1","_relevanssi_noindex_reason":"","footnotes":""},"tags":[],"class_list":["post-4785","page","type-page","status-publish","hentry"],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.2 - 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