Impact of Artificial Islands and Reefs on Water Quality in Jinmeng Bay, China

Abstract

Recurrent green tide has been widely studied due to its severe damage to coastal ecosystem. Jinmeng Bay, a popular resort in northeastern China, has suffered from green tide events since 2015, after the constructions of artificial islands and submerged reefs. To investigate the potential impacts of artificial islands and reefs on the water quality in Jinmeng Bay, a MIKE 21 numerical model was established by coupling a hydrodynamic model with a transport model of Chemical Oxygen Demand (COD) and nitrate ion (NO3−). The changes in the water quality in Jinmeng Bay by the initial, first-stage and current construction conditions of artificial islands and submerged reefs were simulated. The model results indicated that: (1) The artificial islands and reefs in Jinmeng Bay hinder the tidal currents and weaken the tidal actions. (2) The weakened tidal actions at the estuary lead to the accretion of COD and NO3−. The neap tides generate a littoral zone with the high concentration of COD and NO3−, and the spring tides maintain the zone at the estuary. (3) NO3− is more sensitive than COD to the variation of hydrodynamic conditions. The NO3− concentration in the north of Conch artificial island is altered significantly, where the construction of the artificial structures decrease the concentration by ~30%, while the demolition of the connection road increases the concentration beyond its initial values by 16~21%. (4) Under the current construction conditions, the rising concentrations of COD (up to 2%) and NO3− (up to 40%) increase the frequency and scale of green tides in Jinmeng Bay considerably. Therefore, continuous monitoring of water quality is required for this region.