RESUMEN
This paper presents a spatially explicit model for simulating the fate of nitrogen (N) in soil and groundwater and nitrous oxide (N(2)O) production in groundwater with a 1 km resolution at the European scale. The results show large heterogeneity of nitrate outflow from groundwater to surface water and production of N(2)O. This heterogeneity is the result of variability in agricultural and hydrological systems. Large parts of Europe have no groundwater aquifers and short travel times from soil to surface water. In these regions no groundwater denitrification and N(2)O production is expected. Predicted N leaching (16% of the N inputs) and N(2)O emissions (0.014% of N leaching) are much less than the IPCC default leaching rate and combined emission factor for groundwater and riparian zones, respectively.
Asunto(s)
Desnitrificación , Agua Subterránea/química , Modelos Químicos , Dióxido de Nitrógeno/química , Nitrógeno/química , Contaminantes Químicos del Agua/química , Monitoreo del Ambiente , Europa (Continente) , Nitrógeno/análisis , Dióxido de Nitrógeno/análisis , Contaminantes Químicos del Agua/análisisRESUMEN
Denitrification is a critical process regulating the removal of bioavailable nitrogen (N) from natural and human-altered systems. While it has been extensively studied in terrestrial, freshwater, and marine systems, there has been limited communication among denitrification scientists working in these individual systems. Here, we compare rates of denitrification and controlling factors across a range of ecosystem types. We suggest that terrestrial, freshwater, and marine systems in which denitrification occurs can be organized along a continuum ranging from (1) those in which nitrification and denitrification are tightly coupled in space and time to (2) those in which nitrate production and denitrification are relatively decoupled. In aquatic ecosystems, N inputs influence denitrification rates whereas hydrology and geomorphology influence the proportion of N inputs that are denitrified. Relationships between denitrification and water residence time and N load are remarkably similar across lakes, river reaches, estuaries, and continental shelves. Spatially distributed global models of denitrification suggest that continental shelf sediments account for the largest portion (44%) of total global denitrification, followed by terrestrial soils (22%) and oceanic oxygen minimum zones (OMZs; 14%). Freshwater systems (groundwater, lakes, rivers) account for about 20% and estuaries 1% of total global denitrification. Denitrification of land-based N sources is distributed somewhat differently. Within watersheds, the amount of land-based N denitrified is generally highest in terrestrial soils, with progressively smaller amounts denitrified in groundwater, rivers, lakes and reservoirs, and estuaries. A number of regional exceptions to this general trend of decreasing denitrification in a downstream direction exist, including significant denitrification in continental shelves of N from terrestrial sources. Though terrestrial soils and groundwater are responsible for much denitrification at the watershed scale, per-area denitrification rates in soils and groundwater (kg N x km(-2) x yr(-1)) are, on average, approximately one-tenth the per-area rates of denitrification in lakes, rivers, estuaries, continental shelves, or OMZs. A number of potential approaches to increase denitrification on the landscape, and thus decrease N export to sensitive coastal systems exist. However, these have not generally been widely tested for their effectiveness at scales required to significantly reduce N export at the whole watershed scale.
Asunto(s)
Nitratos/metabolismo , Nitrógeno/metabolismo , Agricultura , Fertilizantes , Agua Dulce , Sedimentos Geológicos , Fijación del Nitrógeno , Oxígeno , Agua de Mar , SueloRESUMEN
Data for the historical years 1970 and 1995 and the FAO-Agriculture Towards 2030 projection are used to calculate N inputs (N fertilizer, animal manure, biological N fixation and atmospheric deposition) and the N export from the field in harvested crops and grass and grass consumption by grazing animals. In most industrialized countries we see a gradual increase of the overall N recovery of the intensive agricultural production systems over the whole 1970-2030 period. In contrast, low N input systems in many developing countries sustained low crop yields for many years but at the cost of soil fertility by depleting soil nutrient pools. In most developing countries the N recovery will increase in the coming decades by increasing efficiencies of N use in both crop and livestock production systems. The surface balance surplus of N is lost from the agricultural system via different pathways, including NH3 volatilization, denitrification, N(2)O and NO emissions, and nitrate leaching from the root zone. Global NH(3)-N emissions from fertilizer and animal manure application and stored manure increased from 18 to 34 Tg x yr(-1) between 1970 and 1995, and will further increase to 44 Tg x yr(-1) in 2030. Similar developments are seen for N(2)O-N (2.0 Tg x yr(-1) in 1970, 2.7 Tg x yr(-1) in 1995 and 3.5 Tg x yr(-1) in 2030) and NO-N emissions (1.1 Tg x yr(-1) in 1970,1.5 Tg x yr(-1) in 1995 and 2.0 Tg x yr(-1) in 2030).
Asunto(s)
Agricultura/métodos , Nitrógeno/química , Especies de Nitrógeno Reactivo , Animales , Animales Domésticos , Productos Agrícolas , Ambiente , Monitoreo del Ambiente/métodos , Predicción , Humanos , Estiércol , Modelos Teóricos , Nitratos/químicaRESUMEN
Abstract Data for the historical years 1970 and 1995 and the FAO-Agriculture Towards 2030 projection are used to calculate N inputs (N fertilizer, animal manure, biological N fixation and atmospheric deposition) and the N export from the field in harvested crops and grass and grass consumption by grazing animals. In most industrialized countries we see a gradual increase of the overall N recovery of the intensive agricultural production systems over the whole 1970-2030 period. In contrast, low N input systems in many developing countries sustained low crop yields for many years but at the cost of soil fertility by depleting soil nutrient pools. In most developing countries the N recovery will increase in the coming decades by increasing efficiencies of N use in both crop and livestock production systems. The surface balance surplus of N is lost from the agricultural system via different pathways, including NH3 volatilization, denitrification, N20 and NO emissions, and nitrate leaching from the root zone. Global NH3-N emissions from fertilizer and animal manure application and stored manure increased from 18 to 34 Tg x yr(-1) between 1970 and 1995, and will further increase to 44 Tg x yr(-1) in 2030. Similar developments are seen for N2O-N (2.0 Tg x yr(-1) in 1970, 2.7 Tg x yr(-1) in 1995 and 3.5 Tg x yr(-1) in 2030) and NO-N emissions (1.1 Tg x yr(-1) in 1970, 1.5 Tg x yr(-1) in 1995 and 2.0 Tg x yr(-1) in 2030).
Asunto(s)
Agricultura , Ambiente , Nitrógeno , Especies de Nitrógeno Reactivo , Agricultura/métodos , Animales , Animales Domésticos , Productos Agrícolas , Humanos , Modelos TeóricosRESUMEN
Global 0.5- by 0.5-degree resolution estimates are presented on the fate of nitrogen (N) stemming from point and nonpoint sources, including plant uptake, denitrification, leaching from the rooting zone, rapid flow through shallow groundwater, and slow flow through deep groundwater to riverine systems. Historical N inputs are used to describe the N flows in groundwater. For nonpoint N sources (agricultural and natural ecosystems), calculations are based on local hydrology, climate, geology, soils, climate and land use combined with data for 1995 on crop production, N inputs from N fertilizers and animal manure, and estimates for ammonia emissions, biological N fixation, and N deposition. For point sources, our estimates are based on population densities and human N emissions, sanitation, and treatment. The results provide a first insight into the magnitude of the N losses from soil-plant systems and point sources in various parts of the world, and the fate of N during transport in atmosphere, groundwater, and surface water. The contribution to the river N load by anthropogenic N pollution is dominant in many river basins in Europe, Asia, and North Africa. Our model results explain much of the variation in measured N export from different world river basins.