PHYTOPLANKTON PHOSPHORUS STRESS OF JIULONGJIANG RIVER-ESTUARY AND ADJACENT WATERS SYSTEM IN SUMMER

Phosphorus stress of phytoplankton was determined by using bulk and single-cell alkaline phosphatase activity (APA) assays during summer (June—July 2010) in Jiulongjiang River-Estuary and adjacent waters system.Results showed that Chl.a-normalized APA was significantly higher in the lower Jiulongjiang River [(48.80±14.69)nmol/(h·μgChl.a)] than the estuary and adjacent coastal waters [(10.60±15.58)nmol/(h·μgChl.a) and (23.54±25.41)nmol/(h·μgChl.a),respectively],indicating that phytoplankton phosphorus stress was more serious in the lower Jiulongjiang River than that in the estuary and coastal waters.High soluble APA contribution indicated that phytoplankton suffered long-term phosphorus (P) stress in the river-estuary-coastal water system.Single-cell ELF labeling of phytoplankton showed that there was no significant difference between the estuary (20%±20%) and adjacent coastal waters (38%±20%),which was coincided with the results of bulk APA.However ELF labeling of phytoplankton in estuary-coastal waters was significantly higher than that in the lower Jiulongjiang River (9%±3%) (P0.05).