Hydrochemical and dual-isotope approach to the identification of denitrification in arable field drainage in the Wensum catchment, eastern England

The global pool of reactive nitrogen has doubled in the last century in response to the need to increase food production with the consequent increase in fertiliser-derived reactive nitrogen detrimentally affecting aquatic ecosystems. This study investigates the spatial distribution and significance of denitrification in the lowland, agriculturally-impacted River Wensum catchment in eastern England as a natural attenuation process. To investigate the evidence for denitrification, the hydrochemical characteristics and dual stable isotope composition of nitrate (15N and 18O) were measured over a 15-month period, 2015–2017, in 63 samples of field drainage in predominantly clay loam and sandy clay loam soils under mainly arable cultivation. Microbially-mediated denitrification in field drainage was indicated by the gradient of the linear regression of 15NNO3 and 18ONO3 compositions with a value of 0.58. Dual fractionation of the nitrate isotopes yielded enrichment factors for δ15NNO3 (−4.52‰) and δ18ONO3, (−4.51‰) within the reported ranges for denitrification in aquatic studies. Soil type influenced denitrification, with a positive relationship between percentage clay and δ15NNO3 and δ18ONO3 values. The same relationship was observed for denitrification rates calculated via a simple mass balance approach, which ranged from 11.0 to 26.3 kg N ha−1 and accounted for 30–73% of the leached soil nitrogen. Higher denitrification rates were recorded in drainage areas with a greater soil clay content (>20% by weight). Comparing calculated dentification rates for individual drain areas with median δ15NNO3 values of drain samples demonstrated that an isotopic enrichment of +1‰ is associated with a denitrification rate of 2.6 kg N ha−1. In conclusion, sustainable agricultural practices that maintain natural attenuation processes such as denitrification, for example by preserving and increasing the soil organic carbon content, are desirable to improve overall soil health to support ecosystem services that reduce nitrate pollution

Energy and Ecosystem Service Impacts

Energy, and access to energy, are essential to human life, civilisation and development. A number of energy issues - including energy security, energy prices and the polluting emissions for energy use - now have high prominence on global agendas of policy and diplomacy. In addressing these and other global energy issues, the purpose of this book is to lay out the broad global energy landscape, exploring how these issues might develop in coming decades, and the implications of such developments for energy policy. There are great uncertainties, which will be identified, in respect of some of these issues, but many of the defining characteristics of the landscape are clear, and the energy policies of all countries will need to be broadly consistent with these if they are to be feasible and achieve their objectives. The book therefore provides information about and analysis of energy and related resources, and the technologies that have been and are being developed to exploit them that is essential to understanding how the global energy system is developing, and how it might develop in the future. But its main focus is the critical economic, social, political and cultural issues that will determine how energy systems will develop and which technologies are deployed, why, by whom, and who will benefit from them. The book has three Parts. Part I sets out the current global context for energy system developments, outlining the essential trends of global energy supply and demand, and atmospheric emissions, from the past and going forward, and their driving forces. Part II explores the options and choices, covering both energy demand and energy supply, facing national and international policymakers as they confront the challenges of the global context outlined in Part I. Part III of the book brings together the discussion in Parts I and II with consideration of possible global energy and environmental futures, and of the energy policy choices which will determine which future actually comes to pas