Use of a Bayesian isotope mixing model to estimate proportional contributions of multiple nitrate sources in surface water

Abstract

To identify different NO 3- sources in surface water and to estimate their proportional contribution to the nitrate mixture in surface water, a dual isotope and a Bayesian isotope mixing model have been applied for six different surface waters affected by agriculture, greenhouses in an agricultural area, and households. Annual mean δ 15N-NO 3- were between 8.0 and 19.4‰, while annual mean δ 18O-NO 3- were given by 4.5-30.7‰. SIAR was used to estimate the proportional contribution of five potential NO 3- sources (NO 3- in precipitation, NO 3- fertilizer, NH 4+ in fertilizer and rain, soil N, and manure and sewage). SIAR showed that "manure and sewage" contributed highest, "soil N", "NO 3- fertilizer" and "NH 4+ in fertilizer and rain" contributed middle, and "NO 3- in precipitation" contributed least. The SIAR output can be considered as a "fingerprint" for the NO 3- source contributions. However, the wide range of isotope values observed in surface water and of the NO 3- sources limit its applicability. © 2011 Elsevier Ltd. All rights reserved.