Primary productivity estimation in Liaodong Bay and Liaohe River Delta, China

Abstract:

In this study, primary productivities of phytoplankton in the areas of Liaodong Bay and Liaohe River Delta, China were investigated with chlorophyll contents and components, nutrient dynamics and all related environment parameters in July, 2013. Water samples collected from 14 typical sites were incubated under in situ or simulated in situ conditions by the ¹⁴C tracer method. Surface chl-a concentration in the coastal zone of Liaodong Bay ranged from 2.16 to 19.85 mg·m^-3, and the corresponding primary productivity of particulate organic carbon (POC) ranged from 26.82 to 204.91 mg·m^-3·h^-1. Although both our chl-a and primary productivity measurements reveal significant spatial variability across the Liaodong Bay, the release rates of dissolved organic carbon (DOC) from phytoplankton cells into seawater accounts for 4.94±1.44% of the primary productivity of total organic carbon (TOC). Furthermore, the mean and standard deviation of photosynthetic assimilation numbers were 11.65±2.33 (range = 8.78 to 14.63; n=6) with specific maxima in two sites where transparency was better than others, comparatively. In the Liaohe River Delta, it is observed that chl-a concentration and the primary productivity of POC declined from 11.20 mg·m^-3 and 89.03 mg·m^-3·h^-1 to be 1.54 mg·m^-3 and 13.22 mg·m^-3·h^-1, separately, corresponding to the increasing of salinity from 1.0 to be 6.7 in the area dominated by the salinity gradient. The maxima primary productivity of TOC in the river (99.74 mg·m^-3·h^-1) was about ten times higher than the minima primary productivity (9.73 mg·m^-3·h^-1) in the coastal area of Liaodong Bay, probably because of the significant variation of nutrient dynamics, suspended particulate matter and transparency along the river discharge. The percentage of DOC release from phytoplankton cell in the river delta area was approximately 13.71±3.62%, much higher than that in the coastal area of Liaodong Bay. The possible effect of phytoplankton community on the chl-a distribution and the spatial variation of primary productivity will be studied; meanwhile, the ability of carbon uptake and storage of phytoplankton in the process of photosynthesis and its long-term effect on the global warming and climate change will be discussed as well.