Effects of the Japanese Nitrate Directive Plan (NDP) to curb groundwater nitrate-nitrogen content in the Miyakonojo River basin
There are urgent needs to evaluate different management techniques to improve groundwater quality. To maintain a good quality of groundwater in the Miyakonojo River Basin (MRB), Japan, the Nitrate Directive Plan (NDP) was implemented in 2004. To assess the efficiency of this plan, we performed multivariate times-series analyses on 26 years (1996–2021) of groundwater nitrate-nitrogen (NO3−-N) data