3:45 PM - 4:00 PM
[AOS17-07] Annual variation of nutrient and phytoplankton biomass at a shore site in Shido Bay, Japan: results from a high-frequency monitoring
Keywords:phytoplankton biomass, nutrient, vertical mixing, stratification
Phytoplankton is the main primary producer to support higher trophic organisms in marine environments. The turnover rates of the populations are so fast that the biomass frequently varies even in a short-term scale such as several days or a week. It is thus meaningful to reveal daily variation of the phytoplankton biomass. However, existing monitoring programs for phytoplankton biomass are generally set the sampling frequency as once a month or less and are not intended to describe the shorter time variation. In this study, we examined phytoplankton biomass with environmental parameters more than 300 days during a year period at a shore site in a seasonally stratified small bay. Based on the results of the high-frequency monitoring, we discuss how phytoplankton biomass interact with environmental status in the bay.
Monitoring site was set at a wharf in a port of Shido Bay, Japan. During each visit to the site from January to December 2022, sea surface temperature (SST) and salinity (SSS) were recorded and a surface seawater was collected. The seawater sample was used for the analysis of nutrient and chlorophyll-a (Chl-a). Incident photosynthetically available radiation (PAR) was monitored nearby the site during the study period. Data on precipitation at Takamatsu city, Kagawa Prefecture, were obtained from the web site of the Japan Meteorological Agency.
SST recorded the minimum in the late February, increased gradually thereafter, peaked in early August to early September, and then decreased with time. We thus defined March to early September and early September to February as the stratification dominated period and the mixing dominated period, respectively. Concentrations of DIN, the most insufficient nutrient, were typically <1.5 µM in the stratification dominated period, while the higher levels were usually observed in the mixing dominated period. In the stratification dominated period, abrupt decreases of SSS triggered by precipitation tended to be raised the concentration of Chl-a as well as DIN. Exception was the marked bloom caused by Karenia in August, which was not explained by the increase of DIN and the cause was unclear. In the mixing dominated period, peaks of Chl-a were observed irrespective of nutrient status, and the DIN during the periods of Chl-a peaks fell to lower levels compared to the before and after the peaks in the mixing dominated period. The results suggest that DIN status basically regulates the phytoplankton biomass in the stratification dominated period, whereas DIN status is influenced by phytoplankton biomass in the stratification dominated period in Shido Bay.
Monitoring site was set at a wharf in a port of Shido Bay, Japan. During each visit to the site from January to December 2022, sea surface temperature (SST) and salinity (SSS) were recorded and a surface seawater was collected. The seawater sample was used for the analysis of nutrient and chlorophyll-a (Chl-a). Incident photosynthetically available radiation (PAR) was monitored nearby the site during the study period. Data on precipitation at Takamatsu city, Kagawa Prefecture, were obtained from the web site of the Japan Meteorological Agency.
SST recorded the minimum in the late February, increased gradually thereafter, peaked in early August to early September, and then decreased with time. We thus defined March to early September and early September to February as the stratification dominated period and the mixing dominated period, respectively. Concentrations of DIN, the most insufficient nutrient, were typically <1.5 µM in the stratification dominated period, while the higher levels were usually observed in the mixing dominated period. In the stratification dominated period, abrupt decreases of SSS triggered by precipitation tended to be raised the concentration of Chl-a as well as DIN. Exception was the marked bloom caused by Karenia in August, which was not explained by the increase of DIN and the cause was unclear. In the mixing dominated period, peaks of Chl-a were observed irrespective of nutrient status, and the DIN during the periods of Chl-a peaks fell to lower levels compared to the before and after the peaks in the mixing dominated period. The results suggest that DIN status basically regulates the phytoplankton biomass in the stratification dominated period, whereas DIN status is influenced by phytoplankton biomass in the stratification dominated period in Shido Bay.