441 / 2024-03-18 11:26:01

Effects of River Migration and water-sediment regulation scheme on total nitrogen transport in the Yellow River Estuary

river migration; Water-Sediment Regulation Scheme; 2D hydrodynamic model; Yellow River Estuary; total nitrogen

Subtheme 7: Sediment Regulation and Management > Topic 7: Sustainable Sediment Management and Integrated Utilization

River migration and anthropogenic controls on hydrological processes may play important roles in estuarine system transformations and nutrient diffusion. We used a two-dimensional shallow water equation hydrodynamic model to simulate total nitrogen (TN) transport under the situations of river migration and the “Water-Sediment Regulation Scheme” (WSRS). The results showed that: (1) River migration changed the diffusion direction of high TN concentration water in the Yellow River Estuary (YRE) from the east-west diffusion in 2009 to the north-south diffusion in 2019. Water with high TN concentration at the eastern outlet of the Yellow River Delta spread southward mainly within 3 km of the coast under tidal currents in 2017 and 2019. (2) River migration and whether the implementation of WSRS could not change the Gudong Coast was one of the main areas of TN diffusion. (3) For the years with WSRS (2009 and 2019), the diffusion range of high TN concentration water (>1.05 mg/L) was consistent with the transport distance of the estuarine plume. The TN concentrations of 0.5 mg/L (2009) and 1.05 mg/L (2019) corresponding to 25-26 °C could be used as the longest threshold in different river directions. (4) In the year without WSRS (2017), the TN concentration of YRE was lower than 2 mg/L from June to July, which was lower than the average concentration during WSRS in 2019. (5) The amount of water discharge directly determines the diffusion range of TN in the YRE, and the average runoff during WSRS in 2019 was 6.88 times that of the same period in 2017, resulting in a higher diffusion distance of TN concentration in 2019. River migration, especially the change of estuary, can determine the direction of nutrient diffusion. Besides, human influence, such as that triggered by WSRS should also thus be considered when studying biogeochemical processes and nutrient budgets in situations like the YRE.