Identification of groundwater nitrate pollution sources in agricultural area using PCA and SIAR methods

Abstract

Groundwater nitrate sources are diverse and it is of great scientific significance to analyze the sources and respective contribution rates. However, the existed methods of source parsing have some shortcomings. Hence, this study compared principal component analysis (PCA) and Stable Isotope Analysis in R (SIAR), taking the Dagu River groundwater source in Qingdao as an example. The pollution sources analyzed by PCA are more comprehensive and more reliable than those of SIAR. For the contribution rate, the results of PCA can only provide the total contribution of the similar sources, while SIAR is able to capture the contribution rate of each pollution source. Here, we proposed a mixed method taking the advantage of the PCA and SIAR. The new approach can better determine the pollution sources and is capable of solving the contribution rate of each pollution source. Utilizing the combined method, the main sources of nitrate pollution in the Dagu River are found to be manure, NO3− fertilizer, sewage, soil N and NH4+ fertilizer, with average contribution rates 27.7, 27.3, 21.8, 13.0 and 10.2%, respectively. Through this case study, we are confirmed that this mixed method is preferred clearing pollution source and contribution rate.