Catchment land use effects on fluxes and concentrations of organic and inorganic nitrogen in streams
2015
Vogt, Esther | Braban, Christine F. | Dragosits, Ulrike | Durand, Patrick | Sutton, Mark. A. | Theobald, Mark. R. | Rees, Robert M. | Mcdonald, Chris | Murray, Scott | Billett, Michael F. | Centre for Ecology and Hydrology | Scotland's Rural College (SRUC) | Institute of Atmospheric and Environmental Science [Edinburgh] ; The University of Edinburgh | Sol Agro et hydrosystème Spatialisation (SAS) ; Institut National de la Recherche Agronomique (INRA)-AGROCAMPUS OUEST | Higher Technical School of Agricultural Engineering ; Universidad Politécnica de Madrid (UPM) | Biological and Environmental Sciences, School of Natural Sciences ; University of Stirling | NitroEurope Integrated Project; European Commission; Centre for Ecology Hydrology; Scotland's Rural College; UK Department for Environment, Food & Rural Affairs (Defra); COST 729; NinE network of the European Science Foundation
We present annual downstream fluxes and spatial variation in concentrations of dissolved inorganic nitrogen (NH4+ and NO3-) and dissolved organic nitrogen (DON) in two adjacent Scottish catchments with contrasting land use (agricultural grassland vs. semi-natural moorland). Inter- and intra-catchment variation in N species and the relation to spatial differences in agricultural land use were studied by determining catchment N input through agricultural activities at the field scale and atmospheric inputs at a 25 m grid resolution. The average agricultural N input of 52 kg N ha(-1) yr(-1) to the grassland catchment was more than 4 times higher than the input of 12 kg N ha(-1) yr(-1) to the moorland catchment, supplemented by 123 and 8.2 kg N ha(-1) yr(-1) through atmospheric deposition, respectively. The grassland catchment was associated with an annual downstream total dissolved nitrogen (TDN) flux of 14.4 kg N ha(-1) yr(-1), which was 66% higher than the flux of 8.7 kg ha(-1) yr(-1) from the moorland catchment. This difference was largely due to the NO3- flux being one order of magnitude higher in the grassland catchment. Dissolved organic N fluxes were similar for the two catchments (7.0 kg ha(-1) yr(-1)) with DON contributing 49% to the TDN flux in the grassland compared with 81% in the moorland catchment. The results highlight the importance of diffuse agricultural N inputs to stream NO3- concentrations and the importance of quantifying all the major aquatic N species for developing a better understanding of N transformations and transport in the atmosphere-soil-water system.
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