Abstract
Abstract. The Integrated Model to Assess the Global Environment–Global Nutrient Model (IMAGE–GNM) is a global distributed, spatially explicit model using hydrology as the basis for describing nitrogen (N) and phosphorus (P) delivery to surface water, transport and in-stream retention in rivers, lakes, wetlands and reservoirs. It is part of the integrated assessment model IMAGE, which studies the interaction between society and the environment over prolonged time periods. In the IMAGE–GNM model, grid cells receive water with dissolved and suspended N and P from upstream grid cells; inside grid cells, N and P are delivered to water bodies via diffuse sources (surface runoff, shallow and deep groundwater, riparian zones; litterfall in floodplains; atmospheric deposition) and point sources (wastewater); N and P retention in a water body is calculated on the basis of the residence time of the water and nutrient uptake velocity; subsequently, water and nutrients are transported to downstream grid cells. Differences between model results and observed concentrations for a range of global rivers are acceptable given the global scale of the uncalibrated model. Sensitivity analysis with data for the year 2000 showed that runoff is a major factor for N and P delivery, retention and river export. For both N and P, uptake velocity and all factors used to compute the subgrid in-stream retention are important for total in-stream retention and river export. Soil N budgets, wastewater and all factors determining litterfall in floodplains are important for N delivery to surface water. For P the factors that determine the P content of the soil (soil P content and bulk density) are important factors for delivery and river export.
Highlights
Eutrophication, induced by a surge in anthropogenic nutrient loads to the global freshwater domain, has an increasingly negative impact on aquatic ecosystems
This paper describes the Integrated Model to Assess the Global Environment (IMAGE)–Global Nutrient Model (GNM), which simulates the fate of nitrogen (N) and phosphorus (P) in surface water arising from concentrated point sources, and from dispersed sources such as agricultural production systems with its fertilizer application and manure management, and natural ecosystems
The drainage network is based on the DDM30 flow direction map of Döll and Lehner (2002) and the lake characteristics taken from the Global Lakes and Wetlands Database version 1 (GLWD1) product (Lehner and Döll, 2004)
Summary
Eutrophication, induced by a surge in anthropogenic nutrient loads to the global freshwater domain (e.g., rivers, lakes and estuaries), has an increasingly negative impact on aquatic ecosystems. This paper describes the IMAGE–Global Nutrient Model (GNM), which simulates the fate of nitrogen (N) and phosphorus (P) in surface water arising from concentrated point sources (wastewater from urban and rural populations, and industrial wastewater), and from dispersed (nonpoint) sources such as agricultural production systems with its fertilizer application and manure management, and natural ecosystems This global-scale model focuses on prolonged historical periods for testing output results, and future scenarios to analyze consequences of future global change. IMAGE–GNM is a global, spatially explicit model, which uses hydrology as the basis for describing N and P delivery to surface water and in-stream transport and retention It is part of the IAM IMAGE, and used to study the impact of multiple environmental changes over time frames, which capture the mutual feedbacks between humanity and the Earth system. We compare the model behavior against observations for a number of rivers, and test its sensitivity to a range of model parameter variations to analyze the impact of changing nutrient loading, climate and hydrology
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