Determining the Isotopic Composition of Nitrate in the River Daugava and Loads of Nitrogen to the Gulf of Riga

• Published in: Environment. Technology. Resources. Proceedings of the International Scientific and Practical Conference
• Main Authors: Skute, Arturs, Osipovs, Sergejs, Vardanjans, Davids
• Format: Article in Journal/Newspaper
• Language: English
• Published: Rezekne Academy of Technologies 2015
• Subjects: Nitrates; Stable isotopes; Ion exchange; dvina
• Online Access: http://journals.ru.lv/index.php/ETR/article/view/249; https://doi.org/10.17770/etr2015vol2.249

The Daugava or Zapadnaya (Western) Dvina River belongs to the Baltic Sea basin. The length of the river is 1,005 km with a drainage area of 87,900 km2. It crosses three countries: Russia (323 km and 18,500 km2), Belarus (328 km and 33,100 km2) and Latvia (352 km and 24,700 km2). Water samples were collected at three points with the following coordinates: Kraslava, Daugavpils, and Riga and distance from the river mouth 320, 255, and 20 km respectively. Discharge measurements by use of acoustic Doppler current profiler (ADCP) from a moving boat were also performed in the locations indicated above. Nitrates were extracted from water samples using the ‘ion-exchange resin method’, which involves extracting NO3- from freshwater and converting it into solid silver nitrate, which is then analysed for 15N/14N and 18O/16O ratios by IRMS. Prior to passing water through an anion-exchange resin precipitation of O-bearing contaminants (mainly sulphate and phosphate) with barium chloride was carried out. The δ15NNO3 values of riverine samples varied from 7.1 to 8.6 ‰ in Kraslava, from 7.2 to 8.3 ‰ in Daugavpils, and from 8.1 to 9.0 ‰ in Riga and displayed significant differences between the three sampling points.