The distribution of nutrients and salinity recorded during the June 2009 cruise in the Changjiang Estuary indicated that dilution by Changjiang River water and seawater mixing were the main factors controlling nutrient behavior. To better understand the implications of this variation, phytoplankton growth and nutrient uptake along a salinity gradient representing dilution by the Changjiang River and seawater respectively were recorded. Two water samples were collected from the sampling stations C1 and I10 (as used in the June 2009 cruise) which were representative of the freshwater and
An increase in N 2 fixation by diazotrophic organism due to increased stratification driven by climate changes, may decrease phosphate concentrations and result in P limitation in the oligotrophic upper ocean, which challenges the traditional view that nitrogen is generally the primary nutrient limiting phytoplankton productivity in oceanic waters. Which nutrient, N or P, is the most limiting nutrient for phytoplankton growth in the oligotrophic Pacific Ocean has been on debate over recent years. More studies on nutrient limitation are apparently needed to resolve this debate in the Pacific Ocean. In August and September of 2009, nutrient enrichment bioassays were conducted at two representative stations, N1 (160. 58毅 E, 21. 61毅N) in the western Pacific Ocean with extremely low nutrient ( below detect limit) and Chl a concentrations, and N2 (154. 12毅 W, 10. 12毅 N) in the eastern Pacific Ocean with shallower nutricline due to the influence of equatorial currents, in order to examine the spatial variability in the potential limiting nutrient for phytoplankton growth in the Pacific Ocean. Nutrients were added in 5 combinations in bioassays: control ( no addition) , NO 3 +PO 4 ( N +P) ; NO 3 +SiO 4 ( N + Si) , PO 4 +SiO 4 ( P+Si) , and NO 3 +PO 4 +SiO 4 ( N+P+Si) . The limiting nutrient was judged based on the response of algal biomass and nutrient depletion among treatments. Phytoplankton exhibited different response to nutrient additions at two study sites. Phytoplankton biomass increased dramatically in response to both N and P additions at station N1 where the
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