@misc{deek_seasonal_variations_2010, 
author={Deek, A.,Emeis, K.,Struck, U.},
title={Seasonal variations in nitrate isotope composition of three rivers draining into the North Sea},
year={2010},
howpublished = {preprint},
doi = {https://doi.org/10.5194/bgd-7-6051-2010},
abstract = {Nitrate loading of coastal ecosystems by rivers that drain industrialised catchments continues to be a problem in the South Eastern North Sea, in spite of significant mitigation efforts over the last 2 decades. To identify nitrate sources, sinks, and turnover in three German rivers that discharge into the German Bight, we determined δ 15N-NO3- and δ18O- NO3- in nitrate and δ 15N of particulate nitrogen for the period 2006–2009 (biweekly samples). The nitrate loads of Rhine, Weser and Ems varied seasonally in magnitude and δ 15N-NO3- (6.5–21‰), whereas the δ 18O-NO3- (-0.3–5.9‰) and δ 15N-PN (4–14‰) were less variable. Overall temporal patterns in nitrate mass fluxes and isotopic composition suggest that a combination of nitrate delivery from nitrification of soil ammonia in the catchment and assimilation of nitrate in the rivers control the isotopic composition of nitrate. Nitrification in soils as a source is indicated by low δ 18O-NO3- in winter, which traces the δ 18O of river water. Mean values of δ 18O-H2O were between –9.4‰ and –7.3‰; combined in a ratio of 2:1 with the atmospheric oxygen δ 18O of 23.5‰ agrees with the found δ 18O of nitrate in the rivers.},
note = {Online available at: \url{https://doi.org/10.5194/bgd-7-6051-2010} (DOI). Deek, A.; Emeis, K.; Struck, U.: Seasonal variations in nitrate isotope composition of three rivers draining into the North Sea. Biogeosciences Discussions. 2010. vol. 7, 6051-6088. DOI: 10.5194/bgd-7-6051-2010}}