Showing papers by "Fuh-Kwo Shiah published in 2006"

Importance of planktonic community respiration on the carbon balance of the East China Sea in summer

Abstract: [1] The East China Sea (ECS) is one of the largest continental shelves in the world; however, the role that biota plays in the carbon fluxes of this shelf ecosystem is still obscure. To evaluate the organic carbon balance and the roles played by planktonic communities in organic carbon consumption, two cruises with stations covering almost the entire shelf were conducted during the high productivity and high river flow season of the ECS in June (the early summer) and August (the middle summer) 2003. Results showed that biological activity was significantly higher in the early summer. To flourish in the early summer, plankton need a significant fluvial input of dissolved inorganic nutrients and organic matter from the Chinese coast, especially from the Changjiang (aka Yangtze River), might be one of the main driving forces. Further analysis showed that most planktonic community respiration (PCR) could be attributed to phytoplankton and bacterioplankton, which accounted for over 96% of the total planktonic biomass (in carbon units) in summer. This might partially explain why mean PCR was higher in June (∼114 mg C m−3 d−1), with higher phytoplankton biomass, than in August (∼40 mg m−3 d−1). The ratio of integrated primary production to PCR (i.e., the P/R ratio) was, however, less than 1, with a mean ± SD value of 0.35 ± 0.41 for all the pooled data. This indicates a significant amount of organic carbon has been regenerated through planktonic activity in the water column. The sea-air difference in fCO2, however, changed from a mean value of −64.5 ± 61.3 ppm in June to 10.0 ± 37.5 ppm in August. To explain the contradictory results between PCR and fCO2, we suggest that the dissolved inorganic carbon regenerated through planktonic respiration could be stored in the subsurface layer and may affect the fCO2 in the surface water, which is what controls the shelf sea either as an atmospheric CO2 sink or as a source, depending on the prevailing physical forces. These results also suggest that the controversy between atmospheric CO2 sink or source in the ECS shelf needs further exploration.

Thermal effects on heterotrophic processes in a coastal ecosystem adjacent to a nuclear power plant

Abstract: During the period October 2001 to August 2002, weekly sampling on bacterial respiration (BR, 3 to 22 mg C m -3 d -1 ) and microplankton community respiration (CR, size fraction 35°C. Such a phenomenon might be related to a temperature-substrate interaction.

Effects of ChangJiang River summer discharge on bottom-up control of coastal bacterial growth

Abstract: The East China Sea (ECS) has one of the largest shelf ecosystems in the world, and among the major external forces that affect physical and biogeochemical processes over the ECS shelf is discharge from the ChangJiang (CJ) River. This is particularly true during summer when prevailing flooding leads to the annual maxima of CJ River discharge. To explore the effects of interannual variations in CJ River summer discharge on bacterial growth rate (BGR), 6 cruises were conducted over the entire width of the ECS shelf in July 1998, June 2001, June and August 2003, and June and July 2004. It was found that the spatial patterns of inorganic nutrients (e.g. nitrate: 33 psu) were positively correlated with chl a. However, the intercepts and slopes of the BGR-chl a relationship in the mixing zone were significantly higher than those in the oceanic zone. Noteworthy too is that on monthly and/or inter-annual scales, BGR-chl a coupling (i.e. the slope) in both zones changed positively with river discharge, and this coupling of the oceanic zone seems to have been more sensitive to changes in discharge. This suggests that bacterial growth in the oligotrophic zone might be more substrate-limited than that in the mixing zone. Our study is one of the few to suggest that, in summer, monthly and/or inter-annual variations in CJ River discharge might significantly alter the supply rates of inorganic nutrients and dissolved organic matter, which in turn affects the relationship between auto- and hetero-trophic processes in the ecosystem of the ECS shelf.