With regard to variation in groundwater NO3-N concentrations
associated with changes in land use and irrigation water, in 2007
the concentration increased with a change from Awm to Wwm
than that with no change (Wwc–Wwc). The same phenomenon
was observed with the changes fromAwmto Wf and fromWwmto
Wf compared to no change. This indicates that once land had been
irrigated using sewage, the increasing trend of groundwater nitrate
concentration could not be immediately halted with a change to
well irrigation. One possible interpretation may be that the rate of
nitrate removal from the aquifer is rather slow (Claudio et al.,
2007).