Standing stock and production of phytoplankton in the estuary of the Chang-jiang (Yangste River) and the adjacent East China Sea

Abstract

We determined cell density and dominant species of eukaryotic phytoplankton, chlorophyll concentration and primary production in the Changjiang estuary and dilution zone in January and July 1986. In winter, phytoplankton was dominated by small cells (< 10 pm), closely associated to particulate matter. In summer, the most striking feature of chlorophyll and primary production distributions was the presence of sharp maxima localized about 100 km offshore at salinities between 25 and 30 960 and related to diatom populations. The critical factor responsible for these maxima was the increased light avadability following sedimentation of the particulate matter oriqnating from the river, as observed in front of other major world rivers such as the Zaire and the Amazon. This photosynthetic activity resulted in high oxygen concentrations and phosphate depletion in the surface layer. In both seasons, in situ area1 productivity and light availability were related by a simple empirical relationship similar to that established for other medium-sized estuaries.

Nutrients in the Changjiang River

“…The high density area of phytoplankton would move toward the river's mouth with very high concentration of nutrients, and possibly arouse abnormal proliferation of phytoplankton (Shen et al 1992). Zhang et al(1999) thought that the Three Gorges Dam may reduce considerably the sediment load to the estuary, which in turn affects the region where photosynthesis is in radiation limitation and facilitates the primary production sustained by riverine nutrient supply (Ning et al 1988). Chen (2000) suggested that whether the East China Sea will become eutrophicated, actually depends on the amount of phosphorus supply supported by on-shore advection.…”

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“…NPP rates in the Zaire plume were at least an order of magnitude lower, ranging from 0.05 to 0.25 g C m 22 d 21 (Cadée 1978). The much higher NCP rates observed in the Mississippi River plume may be attributable to the higher nutrient (DIN) concentrations in the plume (0-32 mmol kg 21 at salinities 20-30) than in the cases for the Amazon and Zaire plumes (0-12 and 0-8 mmol kg 21 , respectively; Van Bennekom et al 1978;DeMaster and Pope 1996;Lohrenz et al 1999), and lower turbidity than that of the Changjiang and Zaire River plumes (Eisma et al 1978;Ning et al 1988;Trefry et al 1994).…”

“…For example, NCP rates of 0.9-1.6 g C m 22 d 21 were reported for the Amazon plume (Ternon et al 2000), and NPP rates of 1.5 g C m 22 d 21 were observed in the Changjiang plume in a warm season (Ning et al 1988). NPP rates in the Zaire plume were at least an order of magnitude lower, ranging from 0.05 to 0.25 g C m 22 d 21 (Cadée 1978).…”

Biogeochemical processes controlling nutrients at the turbidity maximum and the plume water fronts in the Changjiang Estuary

“…This kind of distribution is specific to upwelling areas or, at least, indicates intense vertical convection carrying nutrients released from sediments up to the surface, providing a basis for primary production. Ning et al (1988) and Tian (1989) have reported high primary production in this area. Additionally, activities of nekton and zooplankton, which produce NH: (Gu 1982;Shi 1986) can contribute to the formation of this high NH: region.…”

“…Ning et al (1988) and Tian (1989) reported a highest primary production region just outside the plume water fronts in the Changjiang Estuary. According to the turbidity measurements performed during the cruise, the content of suspended matter was below 10 mg/l outside the plume water fronts in surface waters whereas it was above 100 mg/l inside, with some values higher than 500 mg/l at the turbidity maximum.…”