Contribution of Outer-Shelf Deep Water to the Nutrient Inventories in the Euphotic Zone of the Changjiang River Plume during Summer

摘要

The nutrient supply to the euphotic zone of high-productivity areas in the Changjiang Estuary is crucial to understanding ecological processes. Previous studies suggested that Changjiang Diluted Water (CDW) and Outer-Shelf Deep Water (ODW) are the two main sources for nutrient supply, while a quantitative estimate of each nutrient species to the euphotic zone remains unknown. Based on a field survey and an end-member mixing model, the nutrient inventories of ODW and its contribution to the model-predicted nutrient inventory in the euphotic zone of the Changjiang River plume impacted area were assessed. Upwelling of ODW was identified, indicating that it significantly contributed to nutrient inventories in the upper layer. The nutrient inventory estimate suggested that the area integrated nutrient inventories of ODW were higher than those of CDW in the euphotic zone of the plume-impacted area. As inferred from the mixing model, the contributions of ODW to the dissolved inorganic nitrogen (contains nitrate, nitrite, and ammonia)and silicate inventories in the euphotic zone were 18.2% and 28.1%, respectively, much lower than those of CDW. However, 37.6% and 39.1% of the phosphate inventory were from ODW and CDW, respectively, indicating that ODW phosphate contribution was comparable with that of CDW in the euphotic zone.