Analysis and numerical simulation of natural and human-caused low dissolved oxygen in the Minjiang River Estuary

Abstract

The Minjiang River, a typical tidal channel in Southeast China, plays an important role in the supply of drinking water, flood control and drought relief, farming and navigation, as well as shipping and other functions. Dissolved oxygen (DO), as a basic living condition for aquatic biota, has been deteriorating in the Minjiang River in recent years. In order to understand how the spatial distribution of DO responds to river discharge, nutrient loading and water temperature, a three-dimensional Environmental Fluid Dynamics Code model was used to simulate water age and the distribution of DO in the Minjiang River. The model presented in this paper was used for water resource and water quality simulations under various physical, chemical, and biological scenarios. Sensitivity simulation results indicated that the three factors had a significant impact on the spatial distribution variation of DO in the Minjiang River. Increased river discharge or split ratio of the North Channel resulted in decreased water age and increased DO. Increased nutrient loading and water temperature caused lower DO. In order to protect coastal environments in the Minjiang River, river discharge should be increased and pollutants of local cities should be reduced during the high temperature and drought period.

Influence of Riverbed Incision and Hydrological Evolution on Water Quality and Water Age Based on Numerical Simulation: A Case Study of the Minjiang Estuary

“…The model was mainly calibrated and verified the water quality state variables, including DO, TN, TP, NH 4 + , and BOD 5 . The important water quality parameter values of the water quality module were shown in Table 1 , mainly based on the calibration results, the previous field hydrological and water quality synchronous monitoring, and the research results of the Minjiang River related model [ 7 ] and other waters [ 32 ]. The error analysis of verification results of each monitoring point in the Minjiang River ( Figure 1 ) was summarized in Table 3 .…”

“…Estuaries, as heterotrophic ecosystems where large numbers of organic substance transported by rivers and inputted from the ocean are mineralized [ 1 , 2 ], have appeared low DO and deterioration of water quality around the world [ 3 , 4 , 5 ]. Estuarine discharge, topography (volume), tides, pollutant emissions etc., playing a role in controlling the estuarine environment [ 6 , 7 ]. Different from the water bodies of lakes or inland rivers, the migration and diffusion of estuary materials is a complex process, which is not only affected by runoff and tide, but also by gravity cycle, wind-driven and unique topography.…”

“…Water age defined in this study is the time elapsed since the water parcel under consideration exited the region in which its age is prescribed to be zero, or particularly, the time elapsed since a water particle is discharged from the headwater of an estuary [ 23 ]. The aged concept of a water parcel has been used as a timescale to quantify pollutant transport in lagoons, estuaries, and oceans [ 7 , 24 ]. Flushing time of estuaries is commonly defined as the time needed to replace the freshwater already in the estuary (freshwater volume) at the rate of freshwater inflow, which expresses the ratio of freshwater volume over the freshwater flow rate, but water can never be “emptied” since estuaries constantly exchange with the sea.…”

Traceability and Emission Reduction of Dissolved Inorganic Nitrogen in Minjiang Estuary, China

“…The Minjiang River basin has a subtropical monsoon climate, with an annual runoff of 1760 m 3 ·s −1 [ 34 , 35 ]. The Shuikou Dam—as a dividing line between the middle and lower reaches of the Minjiang River—has a controlled minimum ecological flow of 308 m 3 ·s −1 that sustains the downstream water environment and improves shipping requirements [ 36 ]. The lower section of the river divides into the south channel and the north channel at the Wenshanli hydrographic station, converging at the Baiyantan water-level station.…”

Simulation of the Parameters Effecting the Water Quality Evolution of Xuanwu Lake, China

“…The famous Great Canal from Beijing to Hangzhou with a total length of 1794 km, is the longest and first manual canal in the world [ 17 ]. The water diversion project has also been implemented in more places and has played a key role in water environment protection [ 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 ].…”