Watershed-scale evaluation for land-based nonpoint source nutrients management in the Bohai Sea Bay, China

Abstract

A watershed-scale approach was used to evaluate the land-based nonpoint source nutrients in the Bohai Sea Bay, which plays a vital ecological and economic role on regional scale in China. This study firstly defined the watershed boundary of the Bohai Sea Bay with an area of approximately 676,000 sq km. Loads and source apportionment of land-based nonpoint source nutrients from the 13 coastal cities, seven major watersheds, and five sub-sea areas were quantified. The land-based nonpoint source total nitrogen (TN) and total phosphorus (TP) loads from the 13 coastal cities contributed only 16.9% and 12.5% of the total land-based nonpoint source TN and TP loads entering the Bohai Sea. Land-sea integration was highlighted for managing land-based nonpoint source TN and TP loads entering the Bohai Sea. Soil losses, livestock and poultry breeding should be regulated for land-based nonpoint source TN load management while soil losses, livestock and fertilizer use should be controlled for land-based nonpoint source TP load management. Several critical source areas for land-based nonpoint source TN and TP loads were identified where management measures to reduce nutrient should be directed. The findings of this study would be helpful in gaining insights into water quality issues derived from land-based nonpoint source pollution in the BSBW from a holistic perspective, thereby providing scientific support for land-based management in the Bohai Sea.