Modeling Summer Hypoxia Spatial Distribution and Fish Habitat Volume in Artificial Estuarine Waterway

Abstract

This study analyzes the dissolved oxygen (DO) depletion or hypoxia formation affecting the ecological vulnerability of Gyeongin-Ara Waterway (GAW), an artificial estuarine waterway. The physical, chemical, and biochemical factors affecting the summer hypoxia dynamics and distribution are simulated and the habitat volumes of major fish species are calculated. CE-QUAL-W2, a two-dimensional hydrodynamic and water quality model, is applied for the simulation. Comparison with observation reveals that the salinity stratification, vertical DO gradient, and summer hypoxia characteristics are realistically reproduced by the model. Comprehensive analysis of the spatial distributions of the residence time, salinity, and DO concentration reveal that the residence time is longest at the bottom of a freshwater inflow zone. Accordingly, residence time is identified as the physical factor having the greatest influence on hypoxia. It is also clear that a hypoxic water mass diffuses towards the entire waterway during neap tides and summer, when the seawater inflow decreases. Based on the modeling results, the DO depletion drivers are identified and the hypoxic zone formation and distribution are sufficiently explained. Finally, fish habitat volumes are calculated. In particular, the survival habitat volume of Mugil cephalus is found to decrease by 32–34% as a result of hypoxia from July to August. The model employed in this study could be utilized to establish an operational plan for the waterway, which would increase fish habitat volumes.

Potential Influence of Shading in Freshwater Ponds on the Water Quality Parameters and the Hematological and Biochemical Profiles of Nile tilapia (Oreochromis niloticus Linnaeus, 1758)

“…However, breathing reduces dissolved oxygen, resulting in a lower dissolved oxygen concentration in the early morning [38]. Furthermore, the rates of both photosynthesis and respiration increase with increasing temperature, which is why both severe hypoxia and hypoxia are common in summer and less frequently encountered in cooler months [39]. This was similar to the results seen in the study wherein morning and afternoon DO concentrations were far apart.…”

Advanced flow simulations of estuarine water resources responding to changes in societal demands

“…On the other hand, as urbanization progresses along the ARA waterway, the demand for cultural tourism naturally increases, which means that the function of this artificial waterway changes over time. However, the recent water quality of this artificial channel is not up to the level where waterfront activities are possible among river water quality grades in South Korea, and the occurrence of algae blooms is a particular problem [3]. Therefore, further efforts are needed to utilize this waterway as a waterfront space for water leisure, sports, and tourism.…”