INMS guidance document on nitrogen impact assessment methods

This document provides guidance for assessing nitrogen (N) impacts on the environment and humans at all scales from local to regional to global and was compiled with input from scientists worldwide. Nitrogen provides benefits to humans as an essential nutrient for food production and to the environment by stimulating ecosystem productivity. Too much or too little reactive N in the environment causes positive and negative impacts to water quality, air quality, greenhouse gas balance, ecosystems and biodiversity, and soil quality (Sutton et al. 2013). In this document, we describe impacts on greenhouse gases, human health, terrestrial ecosystems, agricultural products, aquatic ecosystems, cultural services and non- agricultural products. Nitrogen takes multiple forms in the environment and behaves dynamically and interactively at different spatial and temporal scales depending on its source (industry, power generation, agriculture, transportation, natural), its forms (oxidised, reduced), and its receptors (humans, natural terrestrial, freshwater and marine ecosystems, the atmosphere, managed ecosystems including agriculture, human-made structures). Reactive N is highly mobile and can move from its original sources through many receptors and impacts before being chemically transformed back to the chemically inert di-nitrogen (N2), a process described as the nitrogen cascade (Galloway et al. 2003). The general background and overall concepts of N impacts are described in Chapter 1. The ‘Pathways to Reactive Nitrogen Impacts’ model is introduced as a general framework showing the transformation processes of drivers, pressures and impacts to describe and analyze the positive and negative effects of altered reactive N cycles in different environments (Figure 1.4). It is based on the concept of DPSIR (Drivers, Pressures, States, Impacts, Responses) described in Chapter 3 (Kristensen 2004). In Chapter 2, the functions across N pressures, states and impacts are summarised. Integrated methodologies, including DPSIR, to assess reactive N impacts are described in Chapter 3. Several other integrated methods, including Input- Output Budgets (Section 3.2), Nitrogen Footprint approaches (Section 3.3), Nitrogen Use Efficiency (NUE) assessments (Section 3.4), planetary boundary approaches (Section 3.5) and Critical Loads (Section 3.6) are also described. Chapter 4 presents assessment methods of individual N impacts on water quality, air quality, greenhouse gas balance, ecosystems and biodiversity, soil quality, food and non-food agricultural products, and (bio)energy. Each subchapter includes a summary, background on the consequences of N for each response variable, methods, and, where applicable, interactions of N with other types of disturbances. Chapter 5 provides cases where N impact methodologies have been applied for policy or management issues, receptors and scales. One of the central features of this guidance document is to link the multiple dimensions, sources, impacts and policy responses for nitrogen. This breadth highlights new connections, such as between ecosystems, human health, climate and materials. It also highlights the importance of emerging nitrogen flows, such as industrial nitrogen flow, where ongoing development could increase future global flows by a factor 3-4 (Section 4.7). It is our intent that this guidance document provides background support for research and assessment programs that describe and analyze the multiple positive and negative effects of reactive N at multiple scales (from local, national, regional to global). It serves as the foundation for improved integrated assessment and policy support, including support to the regional demonstration activities of the GEF/UNEP project, ‘Towards an International Nitrogen Management System’, as a contribution to the wider INMS process.