Temporal and Spatial Changes of Nutrient Content and Eutrophication Condition in Waters of the Abandoned Yellow River Delta

This study made use of the trophic state index method, the eutrophication index method, and the potential eutrophication evaluation method to analyze temporal and spatial changes of the nutrient content and the eutrophication level in waters of the Abandoned Yellow River Delta from 2010 to 2015. Findings of this study include the following: the average trophic state index in the study area remained above 3 over the years of investigation, so the study area was under eutrophication; the average eutrophication index each year was above 3, so the study area was in a medium-eutrophication state; both the average trophic state index and the average eutrophication index showed fluctuating trends and the indices were higher in each autumn than in each spring. Fourth, the study area showed a surplus of nitrogen and deficiency in phosphorus, but the N/P ratio declined from 176.68 to 32.234. The concentration of nutrients and the level of eutrophication declined from the coast to the sea and from north to south, with the estuaries marking the highest concentration and most severe eutrophication. Pollutants discharged from the rivers and development projects along the coastline are the main contributors to the high concentrations of nutrients and eutrophication.