Article ID Journal Published Year Pages File Type
4553736 Progress in Oceanography 2007 30 Pages PDF
Abstract

Eutrophication has become an overwhelming phenomenon in the coastal environment off the Changjiang (Yangtze River) Estuary, illustrated by an increase in nutrient concentration, frequent red-tide events and hypoxia in near-bottom waters, while the open East China Sea Shelf and Kuroshio waters remain oligotrophic. Observations made in the Changjiang Estuary and the East China Sea in 1999–2003 cover a broad range of hydrographic and chemical properties. The concentration gradients of nutrients across the shelf indicate that high levels from land-sources are constrained to the coastal and inner-shelf region by the complex circulation regime. In surface waters, nutrient species gradually decrease from eutrophic coastal to oligotrophic open shelf waters, depending on the hydrographic stages of the Changjiang, although biological uptake and regeneration in the upper water column can produce patchy character of nutrient distribution. Taiwan Current Warm Water and Kuroshio Surface Water are devoid of nutrients. Remineralization of nutrient species takes place in the near-bottom waters in the inner-shelf following extensive bacterial demand for organic matter. Hence the burial efficiency is low with regard to the biogenic species, either allochthonous or autochthonous, or both. The Kuroshio Sub-surface Waters are rich in nutrients, and their incursion into the East China Sea can be tracked by salinity and temperature, reaching within water depth of 50–100 m at mid-shelf. Relative to shelf waters, the Kuroshio intrusion is characterized by high NO3-/(NH4++DON) and DIP/DOP ratios. In the water column, the ratio of DIP/DOP to NO3-/(NH4++DON) is higher than the Redfield P/N value, suggesting rapid regeneration of phosphorus relative to nitrogen in the East China Sea. The results of a box-model suggest that the East China Sea Shelf do likely not export substantial amounts of dissolved biogenic elements to the open Northwest Pacific Ocean.

Related Topics
Physical Sciences and Engineering Earth and Planetary Sciences Geology
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