New insights into the controlling factors of nitrate spatiotemporal characteristics in groundwater of Dagu aquifer in Qingdao, China.

Identifying spatiotemporal variation of groundwater NO-N and its primary controlling factors are vital for groundwater protection. This study, under the data scarce conditions and based on time series monitoring data in Dagu aquifer, applied methods including hydrochemical ion ratio, multiple linear regression, support vector regression and grey relational analysis and dedicated to revealing primary controlling factors of temporal variation patterns of groundwater NO-N. The results showed that agricultural and manure fertilizer are the main sources of NO-N in north and central area (vegetable farming area), and that domestic sewage discharge and manure fertilizer are the main sources of NO-N in south area (residential and grain planting area).