Nitrate source identification in the Baltic Sea using its isotopic ratios in combination with a Bayesian isotope mixing model

Autor: F. Korth, B. Deutsch, C. Frey, C. Moros, M. Voss
Jazyk: angličtina
Rok vydání: 2014
Předmět:
Zdroj: Biogeosciences, Vol 11, Iss 17, Pp 4913-4924 (2014)
Druh dokumentu: article
ISSN: 1726-4170
1726-4189
DOI: 10.5194/bg-11-4913-2014
Popis: Nitrate (NO3−) is the major nutrient responsible for coastal eutrophication worldwide and its production is related to intensive food production and fossil-fuel combustion. In the Baltic Sea NO3− inputs have increased 4-fold over recent decades and now remain constantly high. NO3− source identification is therefore an important consideration in environmental management strategies. In this study focusing on the Baltic Sea, we used a method to estimate the proportional contributions of NO3− from atmospheric deposition, N2 fixation, and runoff from pristine soils as well as from agricultural land. Our approach combines data on the dual isotopes of NO3− (δ15N-NO3− and δ18O-NO3−) in winter surface waters with a Bayesian isotope mixing model (Stable Isotope Analysis in R, SIAR). Based on data gathered from 47 sampling locations over the entire Baltic Sea, the majority of the NO3− in the southern Baltic was shown to derive from runoff from agricultural land (33–100%), whereas in the northern Baltic, i.e. the Gulf of Bothnia, NO3− originates from nitrification in pristine soils (34–100%). Atmospheric deposition accounts for only a small percentage of NO3− levels in the Baltic Sea, except for contributions from northern rivers, where the levels of atmospheric NO3− are higher. An additional important source in the central Baltic Sea is N2 fixation by diazotrophs, which contributes 49–65% of the overall NO3− pool at this site. The results obtained with this method are in good agreement with source estimates based upon δ15N values in sediments and a three-dimensional ecosystem model, ERGOM. We suggest that this approach can be easily modified to determine NO3− sources in other marginal seas or larger near-coastal areas where NO3− is abundant in winter surface waters when fractionation processes are minor.
Databáze: Directory of Open Access Journals
Externí odkaz: