NITRATE SOURCE DISTRIBUTION IN RIVERS, ESTUARIES AND GROUNDWATER USING A DUAL ISOTOPE APPROACH AND A BAYESIAN ISOTOPE MIXING MODEL

Identification and quantification of nitrate (NO3 -) sources in rivers, estuaries and shallow groundwater (SG) may help implementation in the water quality control measures.In this study, a dual isotope approach ( 15 N-and  18 O-NO3 -) and Bayesian isotope mixing model (SIAR) have applied to estimate the proportional contributions of NO3 -from precipitation (NP), NO3 -fertilizer (NF), ammonia nitrogen (NH4 + ) from fertilizer and rain (NF&R), soil N (Soil), and manure and sewage (M&S) for six rivers, two estuaries and SG in a coastal municipality in northern China.The combination of "M&S" (17-56%), "Soil" (21-37%), and "NF&R (14-25%)" contributions occupied more than 60% in total, and were considered as the dominant NO3 -sources for the rivers and estuaries.The mean proportions of "NF" ranged from 6 to 20% and "NP" ranged from 2 to 11%, respectively.For SG, the mean proportions of "M&S" (27%), "Soil" (22%), and "NF&R" (21%) occupied about 70% in total, while the residual two NO3 -sources occupied about 19% for "NF" and 11% for "NP".We suggest that this approach can be easily modified determine NO3 -sources and help to develop better N management practices in other environments where NO3 -is a major N contributor.