Natural　organic　matter　(NOM)　with　the　size　approaching　to　membrane　pore　size　is　commonly　considered　as　the　crucial　component　leading　to　severe　pore　blocking　and　superfluous　energy　consumption.　Aquatic　metal　ions　coexisting　with　this　NOM　constituent　(target　NOM)　exert　a　significant　influence　on　membrane　filtration　performance;　however,　little　work　elucidated　their　interactions　and　the　impacts　on　nanofiltration　(NF).　Therefore,　we　systematically　investigated　this　issue　by　titrating　three　environmentally-relevant　metal　ions　(Al3+,　Fe3+　and　Cu2+)　into　the　target　NOM　sample　obtained　by　pre-filtering　using　NF　membrane.　Fast　spectrophotometric　techniques　were　employed　to　observe　the　interactive　performance.　Results　suggested　that　all　metal　ions　at　their　critical　concentrations　caused　severe　flux　decline;　Cu2+　at　a　very　low　concentration　of　5　mu　M,　Al3+　and　Fe(3+)at　20　mu　M.　NF　performance　recovered　when　the　concentrations　were　beyond　their　critical　values,　and　was　improved　at　excessive　concentration　when　flocs　formed.　Relationship　between　spectroscopic　characteristics　and　NF　performance　was　particularly　addressed.　UV-vis　spectrum　can　be　expected　to　be　useful　and　predictive　in　membrane　fouling　control　when　Al3+　or　Fe3+　presented.　However,　fluorescence　fingerprint　was　not　likely　that　effective　since　fluorescence　intensity　continuously　reduced　with　the　increasing　metal　ion　concentration,　attributed　to　their　quenching　effect　on　NOM　fluorophores.　(C)　2019　Elsevier　B.V.　All　rights　reserved.