Flooding Effects on Organic Carbon Consumption in the East China Sea

English Abstract:

A central motivation for this study was to reveal how flood effects on plankton community respiration (CR) in the East China Sea (ECS). In 2010, a devastating flood occurred in July in the Changjiang River; with mean monthly discharge of 60,527 m³ s^-1. To compare, data was examined in July of 2009, when the riverine flow was low (mean monthly values = 33,955 m³ s^-1). During flood, a tremendous amount of freshwater was delivered into the ECS, and low sea surface salinity (≤ 31 psu) covered almost two third of this continental shelf. High nitrate concentration in the ECS was also measured during the flood, and it was significantly higher than that of 2009 non-flood with mean ± SD values of 6.2 ± 9.8 and 2.0 ± 5.3 μM, respectively. Although primary production in the surface water was high in 2010 flood with mean ± SD value of 62.1 ± 33.8 mg C m^-3 d^-1. Surprisingly, the mean value of Chl a was only slightly higher in 2010 than that of 2009, and bacterial biomass was even lower in 2010 compared to that of 2009. The CR was however still higher in 2010 than that of 2009, with mean (± SD) values of 105.6 (± 66.7) and 73.2 (± 76.9) mg C m^-3 d^-1, respectively. To further explore, the difference (i.e., 2010 – 2009) of variables at the same station between two sampling periods were compared. Values of difference in CR was positively and negatively linearly regressed with that of differences in Chl a and fCO₂ (all p≦0.001), respectively. These results imply that the flooding effect on higher CR during 2010 might be more attributed to phytoplankton. It also infers that the huge amount of fCO₂ absorption during 2010 flood was relative to strength of plankton activity, especially phytoplankton. These results all suggest that the devastating flood has significant effect on organic carbon consumption in the ECS. This impact might be even more pronounced when extreme rainfall events and flood magnitude have increasing dramatically throughout the world in last few decades.