Global anthropogenic and natural nutrient fluxes: from local to planetary assessments

Abstract

Nutrients are recognized as one of the nine planetary boundaries, which could increase risks of unacceptable global environmental changes. In this study we developed a recent and complete high-resolution nutrient flows compilation that can be used for assessing global nutrient annual fluxes from land to sea. It consists of annual nitrogen (N) and phosphorus (P) fluxes with spatial resolution of five arc-minutes (about 10 × 10 km at the equator) centered on year 2005, assessing potential nutrient delivery to rivers, lakes and oceans. The dataset includes: nutrient inputs in agricultural areas (mineral and organic fertilization, nitrogen fixation), crop/fodder/grass harvest, nutrient inputs by domestic and industrial activities (i.e. wastewater treatment plants, industries, and phosphorus from detergents), nutrients from built-areas, nitrogen atmospheric deposition, N and P transported via erosion, and phosphorus release by weathering. The dataset was compared with other studies, was analyzed at different spatial scales showing the main environmental hotspots, and finally a qualitative uncertainty analysis was performed. The results showed that nitrogen surplus was the largest contributor to the potential losses on all continents, while for phosphorus the major contributors included the surplus, erosion and inputs from human wastewater. Hotspots were identified mainly in China and India. Rates exceeding 100 kg ha−1 of N were observed locally in Europe, Egypt and North America coinciding with intensive agriculture practices. We also showed that N and P transported via erosion, domestic and industrial nutrient emissions, as well as manure resulted in the most uncertain fluxes.