Seasonal nutrient chemistry in an integrated multi-trophic aquaculture region: case study of Sanggou Bay from North China

Seasonal distribution of dissolved nutrients (, , , , ) was measured in the Sanggou Bay (SGB), China. In order to understand the impact of rivers and of the Yellow Sea (YS) and the role of integrated multi-trophic aquaculture (IMTA) in nutrient reduction and dynamics. Seasonal surveys were conducted in spring (April), summer (August), autumn (October) and winter (January) in 2011–2012 along 19 stations covering culture areas. The summer was highly impacted by excess water discharge and aquaculture activities than benthic sediments source; however other seasons were mostly influenced by the YS. Results showed that nutrients were vertically mixed and IMTA helped in reducing the elevated nutrient concentration generated by water discharge and the mixing process. The N/P ratio indicated phosphate as a limiting nutrient. Historical values of nutrient data showed that the concentration of , and increased while decreased with slightly higher uptake rate of in the bay during the last decade. A simple mass-balance model was employed to determine the nutrient budget which showed that nutrients were mostly from the river input. This implies an increase in the anthropogenic activities and assimilation of in the SGB. Such increasing trends in nutrient concentration could cause eutrophication in the bay.