DISTRIBUTION OF CHLOROPHYLL a AND ESTIMATION OF RELEASING RATE OF DOC BY PHYTOPLANKTON DURING SUMMER IN LIAODONG BAY, CHINA

Based on an in situ investigation and incubation experiments using ¹⁴C as a tracer during the summer of 2013 in Liaodong Bay, China, we examined the concentrations and distributions of the environmental parameter, chlorophyll a (Chl a), and the releasing rates of dissolved organic carbon (DOC) by phytoplankton in the process of photosynthesis. Results show that the average concentration of Chl a is (6.10±0.41) mg/m³ in the surface water. Several high-and low-Chl a zones appeared in some places of the bay with possible blooms in the high-Chl a areas, which resulted in the fast consumption of nutrients. An apparent low-Chl a zone appeared nearby the mouth of Shuangtaizi River, and the weak light availability caused by sandy suspended particulate matter (SPM) was probably the limiting factor for phytoplankton growth in this region. The estimated total DOC productivities at six selected typical stations range from (1.69±0.06) to (7.59±0.94) mg/(m³·h) with an average of (3.42±0.94) mg/(m³·h), and account for 4.94%±0.59% of the total primary productivities. Regression analyses suggest that the concentration of Chl a, i.e. phytoplankton biomass, was correlated well with the primary productivities. The DOC releasing rate by phytoplankton was correlated well with the Chl a concentrations and phytoplankton photosynthesis rates, implying that regional high biomass caused by eutrophication promote the high primary productivities and high releasing rates of DOC as well in Liaodong Bay.