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 <300 μm, 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 Q10 (i.e. the increase of rate with a temperature increase of 10°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°C. Such a phenomenon might be related to a temperature-substrate interaction. © Inter-Research 2006.