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

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 < 300 mu m, 2 to 90 mg C m(-3) d(-1)) was conducted in the inlet and outlet of Taiwan Nuclear Power Plant II (TNP-II). In addition, 3 transect surveys were conducted across the warm plume outside the TNP-II outlet. All measurements except dissolved organic carbon (DOC, 18 to 45 g C m(-3)) varied seasonally and spatially with temperature. On average, BR constituted 41% of the total CR. The BR/CR ratios were negatively correlated with CR, the first observation of this trend that we are aware of. The positive temperature responses of rate and/or biomass-normalized rate parameters indicated a very low probability of bottom-up (substrate supply) control on the growth of heterotrophic organisms in these systems. The Q(10) (i.e. the increase of rate with a temperature increase of 10 degrees C) values for BR, CR, biomass-normalized bacterial respiration (0.07 to 1.31 d(-1)) and particulate organic carbon-normalized CR (0.04 to 0.52 d(-1)) ranged from 1.3 to 3.7. Similar Arrhenius expressions of heterotrophic processes in the field surveys and short-term temperature-manipulation experiments showed that, in this high DOC system, most planktoners were eurythermal and that their respiration increased with temperature up to > 35 degrees C. Such a phenomenon might be related to a temperature-substrate interaction.