Effects of an Episodic Storm-Induced Flooding Event on the Biogeochemistry of a Shallow, Highly Turbid, Semi-Enclosed Embayment (Laizhou Bay, Bohai Sea)

Episodic storm-induced flooding is becoming more frequent with a warming climate, which may alter the biogeochemical properties and conditions of estuaries. However, the effects of such extreme events on semi-enclosed bay ecosystems have not been fully investigated because of the difficulty in collecting in situ samples. To address this issue, a comparative study was carried out to understand the biogeochemical changes in Laizhou Bay, a shallow, highly turbid, semi-enclosed bay, by coupling satellite data and surface water samplings collected during an episodic flooding event (August 2018) and during a non-flooding period (August 2017). The results showed that the 2018 Shouguang flood delivered large amounts of suspended solids, phosphorus, and organic matter-enriched terrigenous materials into Laizhou Bay and enhanced the offshore expansion of the low-salinity seawater plume and associated nutrient fronts. Water total suspended solid (TSS) particle and chlorophyll a (Chl-a) concentrations increased by 23.79 g/m3 and 0.63 mg/m3, respectively, on average in the freshwater mixing water plume around the Mi River. Episodic flooding is a crucial driver which temporally dominates the spatial patterns of water biogeochemistry. These results are essential to anticipate the ecosystem response of estuarine regions to the high episodic freshwater flow associated with the increasing storms.