Long-term variation of nutrients in the southern Yellow Sea

Abstract

Nutrients play a major role in sustaining marine ecosystems. However, in the past few decades, nutrient inputs from land have significantly changed worldwide, resulting in the variations in nutrient concentrations and compositions in marginal seas. Based on historical data, the long-term variation patterns of nutrients and its compositions, as well as its potential influencing factors, were presented in the southern Yellow Sea. The concentrations of NO3-N and dissolved inorganic nitrogen (DIN) in the southern Yellow Sea have been continuously increasing from the 1980s, with a most rapid increase after the mid-1990s. While the concentrations of SiO3-Si and PO4-P generally exhibited a decreasing trend before the mid-1990s, and then gradually increased. The N/P ratio has been continuously increasing from the 1980s and run up to a level of >16 at the end of the last century. The Si/N ratio decreased rapidly from the mid-1980s to the mid-1990s and then maintained a low level of ~1 at the end of the last century and at the beginning of this century. Similar to the variation of SiO3-Si, the Si/P ratio decreased from the 1970s to the mid-1990s and then started to increase gradually. There was an evolution trend from N limitation to P and Si limitation in the southern Yellow Sea. The variations in the concentrations of nutrients were related to the variations of the riverine flux and atmospheric deposition, and especially the long-term variations of PO4-P and SiO3-Si concentrations were both consistent with the variation of precipitation. In addition, the nutrient transport from the Kuroshio Subsurface Water to the continental shelf, in combination with the cultural eutrophication in the coastal zones, may also influence the nutrient levels in the southern Yellow Sea under the global change.