Nitrogen is an essential element for plant growth, while its application and associated pollution is a worldwide concern. Generally, diffuse source pollution and its impacts on ecosystem health are difficult to monitor and regulate. Here we used the grey water footprint (GWF) and water pollution level (WPL) indicators, based on a soil nitrogen balance approach to differentiate between surface and groundwater, in order to better understand and quantify the pressure that nitrogen fertilisation generates on freshwater. For the first time, we compared the results of these indicators with actual nitrogen concentration data in surface and groundwater bodies, showing in both cases a positive significant correlation according to Spearman correlation coefficient. This means that the theoretical WPL results might be valuable to anticipate and identify nitrate pollution in surface and groundwater bodies. However, several factors influence the N-related processes that should be considered, such as natural attenuation. We estimated the agricultural and livestock nitrogen loads delivered to freshwater and the associated GWFs and WPLs at the municipality level in Navarra. Large GWFs are observed in southern Navarra, particularly in intensive agricultural regions such as Ribera Alta-Aragón and Ribera Baja. We estimated that 64% of the GWF related to nitrogen loads came from artificial fertilisers, 16% from manure, 11% from atmospheric deposition and the remaining 9% from biological fixation, seeds and other organic fertilisers. Among the crops, cereals had the largest contribution to the nitrogen-related GWF (54%) followed by vegetables (17%) and fodder (11%).

Agriculture is the largest fresh water consuming sector, and maize is the most produced and consumed crop worldwide. The water footprint (WF) methodology quantifies and evaluates the water volumes consumed and polluted by a given crop, as well as its impacts. In this work, we quantified for the first time the green WF (soil water from precipitation that is evapotranspired) and the green virtual water exports of maize from Buenos Aires province, Argentina, during 2016–2017, due to the relevance of this region in the world maize trade. Furthermore, at local level, we quantified the green, blue (evapotranspired irrigation), and grey (volume of water needed to assimilate a pollution load) WF of maize in a pilot basin. The green WF of maize in the province of Buenos Aires ranged between 170 and 730 m³/ton, with the highest values in the south following a pattern of yields. The contribution of this province in terms of green virtual water to the international maize trade reached 2213 hm³/year, allowing some water-scarce nations to ensure water and water-dependent food security and avoid further environmental impacts related to water. At the Napaleofú basin scale, the total WF of rainfed maize was 358 m³/ton (89% green and 11% grey) and 388 m³/ton (58% green, 25% blue, and 17% grey) for the irrigated crop, showing that there is not only a green WF behind the exported maize, but also a Nitrogen-related grey WF.

Livestock production systems are major consumers of freshwater, potentially compromising the sustainability of water resources at production sites. The water footprint (WF) quantifies the water consumed and polluted by a product or service. The aim of this study was to evaluate the WF of steer production from the cradle to the farm gate in representative intensive, extensive, and mixed farms located in the southeast of Buenos Aires province, Argentina. The WF to produce a live steer varied between 4247 and 5912 m³/animal. The extensive system contains the highest green WF but is also the most sustainable compared to industrial and mixed productions since it does not have an associated pollutant load or blue water. This work is the first approach to calculating the WF of live steers in Argentina carried out with local and detailed data and focuses on grey WF related to nitrogen leaching from effluents in intensive systems, showing that the blue and grey footprints increase as production intensifies. The information may be relevant for consumers and producers to make more informed decisions. Furthermore, it is essential for governments to promote sustainable practices in livestock farming, recognizing the dependence on water resources both domestically and throughout international supply chains, in order to assess their environmental policies and ensure national food security.