Functional　redundancy　is　considered　common　in　microbial　systems,　but　recent　studies　have　challenged　this　idea.　The　mechanism　for　this　contradictory　result　is　not　clear.　However,　in　this　study,　we　hypothesize　that　strong　environmental　filtering　which　links　to　the　anthropogenic　activities　is　able　to　weaken　microbial　functional　redundancy.　We　used　metagenome　and　16S　rRNA　gene　high-throughput　sequencing　to　investigate　planktonic　microbial　communities　in　a　subtropical　river.　We　found　that　the　weak　anthropogenic　activities　might　result　in　a　low　selection　pressure　in　the　river　upstream　area.　Therefore,　the　microbial　community　functional　attributes　were　stable　although　the　community　composition　changed　with　the　water　temperature　and　NO3-N　in　upstream　area　(this　indicates　functional　redundancy).　However,　the　strong　anthropogenic　activities　in　river　downstream　area　selected　pollutant-degraded　functions　(e.g.　nitrogen　metabolism,　toluene,　xylenes　and　ethylbenzene　degradation)　and　potentially　pollutant-degraded　(tolerant)　microbes,　and　therefore　caused　the　microbial　community　composition　synchronously　changed　with　the　variation　of　community　functional　attributes.　Our　results　reveal　that　strong　environmental　filtering　which　associates　with　the　anthropogenic　activities　not　only　has　effects　on　microbial　community　composition　and　community　functional　attributes　but　also　on　their　relationships.　These　results　provide　a　new　insight　to　refine　the　functional　redundancy　idea.