PHOSPHATE LIMITATION IN ESTUARINE AND COASTAL WATERS OF CHINA

Mesocosm experiments conducted off the southern coast of mainland China, indicate that phytoplankton growth is limited by phosphorus, rather than nitrogen. In April, when natural seawater was enclosed in mesocosms, phosphorus always reached undetectable concentrations several days before inorganic nitrogen. This was not surprising since the initial N: P (by atoms) in the seawater at the start of the experiment was ≈ 80:1, indicating about a five-fold excess nitrogen over phosphorus. Bioassay experiments also indicated P-limited phytoplankton growth for seawater in Xiamen Bay. Several other estuaries along the coast of China have N: P ratios ranging from 30 to > 80:1. The large rivers of China have high nutrient loads with nitrogen in great excess over phosphorus (e.g., N: P up to 150:1). As a consequence of these large riverine inputs, vast areas along the coast of China are P-limited for primary production. © 1990.