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 (delta N-15- and delta O-18-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.