A review of the impact of climate change on future nitrate concentrations in groundwater of the UK

Abstract

This paper reviews the potential impacts of climate change on nitrate concentrations in groundwater of the UK using a Source-Pathway-Receptor framework. Changes in temperature, precipitation quantity and distribution, and atmospheric carbon dioxide concentrations will affect the agricultural nitrate source term through changes in both soil processes and agricultural productivity. Non-agricultural source terms, such as urban areas and atmospheric deposition, are also expected to be affected. The implications for the rate of nitrate leaching to groundwater as a result of these changes are not yet fully understood but predictions suggest that leaching rate may increase under future climate scenarios. Climate change will affect the hydrological cycle with changes to recharge, groundwater levels and resources and flow processes. These changes will impact on concentrations of nitrate in abstracted water and other receptors, such as surface water and groundwater-fed wetlands.The implications for nitrate leaching to groundwater as a result of climate changes are not yet well enough understood to be able to make useful predictions without more site-specific data.The few studies which address the whole cycle show likely changes in nitrate leaching ranging from limited increases to a possible doubling of aquifer concentrations by 2100.These changes may be masked by nitrate reductions from improved agricultural practices, but a range of adaption measures need to be identified. Future impact may also be driven by economic responses to climate change. The study draws on extensive literature mainly from the UK and so presents a UK-based perspective, although literature for other temperate climates is included to augment that from Keywordsthe UK and to demonstrate that the proposed framework and general conclusions have a wider applicability.The principal N input to UK groundwater is derived from manures, fertilisers, sewage sludges and crop residues in agricultural areas (DEFRA, 2006). There are also smaller inputs from urban point sources and aerial deposition (Wakida and Lerner, 2005). N fertiliser can be applied as urea or ammonia, as well as nitrate, but the non-nitrate forms are generally converted rapidly to nitrate in the soils of the UK (MAFF, 1999). A small percentage of applied N is lost to the atmosphere as NH 3 , NO or N 2 O (Destouni and Darracq, 2009;Skiba et al., 1997;Sommer and Hutchings, 1995). A proportion of soil N is leached as nitrate from the base of the soil. This is either stored in, or transmitted through, the unsaturated zone to groundwater. groundwater. They found that although an ensemble average suggests there will be about a 5% reduction in annual potential groundwater recharge across the study area, this was not statistically significant at the 95% confidence level and more importantly observed that the spread of results for simulated changes in annual potential groundwater recharge range from a 26% decrease to a 31% increase by the 2080s, with ten GCMs predicting a decrease and three a...

How can forage production in Nordic and Mediterranean Europe adapt to the challenges and opportunities arising from climate change?

“…In an attempt to reduce costs linked to an extra cut, farmers may decide to increase grazing. However, as N use efficiency of swards can be considerably lower under grazing compared to cutting (Nevens and Reheul, 2003), and as climate change is expected to create a higher potential for leaching in grazed grassland compared to cut grassland (Saarijärvi et al, 2004;Stuart et al, 2011), N fertilization has to be judiciously adjusted to prevailing management practices and climatic conditions in grazed systems to avoid excessive N leaching. In the current Nordic climate, excessive precipitation frequently causes problems with farm operations (Peltonen-Sainio et al, 2009;Olesen et al, 2011).…”

Macronutrient status of UK groundwater: Nitrogen, phosphorus and organic carbon

“…This is in addition to issues related to stratification, for example the screening out shallow high nitrate water allowed abstraction of older low nitrate water and maintenance of drinking water quality (Osenbrück et al, 2006). Stuart et al (2011) concluded that the implications for N leaching to groundwater as a result of climate changes are not yet well enough understood to be able to make useful predictions.…”

“…During recent decades, pools and fluxes of nitrogen (N), phosphorus (P) and carbon (C), in UK ecosystems have been transformed (Galloway et al, 2008;Vitousek et al, 1997) by the spread and fertiliser-based intensification of agriculture (Jenkinson, 2001), by atmospheric pollution (Fowler et al, 2005;Goulding et al, 1998), and now potentially by climate change (Stuart et al, 2011;Watts et al, 2015). Many terrestrial ecosystems that were previously nearly-closed with respect to N and P now permit considerable export of these nutrients (Galloway et al, 2008;Smil, 2000;Withers et al, 2001), leading to eutrophication and acidification of surface waters (Bennett et al, 2001).…”

Socio-economic Impacts—Agricultural Systems

“…This in turn may increase the risk of nitrate leaching during periods of little or no crop cover with sufficient nitrogen uptake to prevent nitrate being leached in periods of precipitation surplus (Jabloun et al 2015). This may increase the risk of nitrate leaching to surface and groundwater systems (Stuart et al 2011;Patil et al 2012). Current measures to reduce nitrate leaching may not be sufficient to maintain low leaching rates under projected climate change (Doltra et al 2014) and this could increase the risk of algal blooms and the occurrence of toxic cyanobacteria in lakes (Jeppesen et al 2011).…”