Study on chemical hydrography, chlorophyll-a and primary productivity in Liaodong Bay, China

A field study was carried out during the summer of 2013 in Liaodong Bay, China to determine the dynamics of the phytoplankton in the bay and the extent to which primary production in the bay was constrained by environmental factors. There was little or no evidence of limitation of phytoplankton production by nutrient concentrations at any of the sampling stations, with the possible exception of a few offshore stations where phosphate concentrations were less than 30 nM. This assessment was consistent with the results of nutrient enrichment experiments and the values of light-saturated photosynthetic rates and areal photosynthetic rates. To examine the effects of irradiance and temperature on light-saturated photosynthetic rates normalized to chlorophyll a concentrations (Poptb) at twelve stations where photosynthetic rates were measured by 14C method, light-conditioned values were modeled as a function of the temperature with a satisfactory fit to our field data (R2 = 0.60, p = 0.003). According to this model, the light-conditioned Poptb values increased with temperatures from 22 °C to roughly 25 °C but declined precipitously at higher temperatures, and Poptb values and corresponding areal photosynthetic rates at all 66 stations were estimated to be 7.6 ± 2.4 g C g−1 Chl a h−1 and 532 ± 429 gC m−2 d−1 in average, respectively. The quanta absorbed per carbon atom fixed averaged 14 ± 2 and 37 ± 10 at six coastal stations and six estuarine stations, respectively. The relatively high Poptb values and low quantum requirements at the coastal stations implied the highly efficient usage of absorbed light by phytoplankton under nutrient-replete conditions and favorable temperatures. Comparatively, the low Poptb values and high quantum requirements at the estuarine stations suggested rather extreme light limitation and lowly efficient usage of absorbed light in photosynthesis in the Liaohe River estuary. Areal production in Liaodong Bay appears to be controlled by a combination of temperature and light limitation.