Spatial and temporal distribution of carbon dioxide flux in Amagasaki Canal, Japan

Abstract

ABSTRACT Recently, blue carbon – carbon captured by coastal ecosystems – has been gaining increased research attention for its potential to sequester anthropogenic CO2. The Amagasaki Canal, in the inner part of Osaka Bay, Japan, has high nutrient concentrations and phytoplankton abundance; primary production by phytoplankton is high in such hypertrophic environments. This could lead to the enhanced absorption of atmospheric CO2. This study investigated the temporal changes and spatial variability in water quality and CO2 flux in the Amagasaki Canal, and it analyzed factors affecting the partial pressure of CO2 (pCO2) in canal water using covariance structure analysis. The CO2 flux in the canal varied between −24.9 and 66.8 mmol-C/m2/d. There were seasonal changes in water quality, with a tendency of CO2 release during autumn and winter. In spring and summer, when phytoplankton were active and chlorophyll-a concentrations were high, concentrations of dissolved inorganic carbon were low and atmospheric CO2 was absorbed into the water. Covariance structure analysis indicated that biological processes indirectly influenced pCO2 via pH and dissolved oxygen concentrations, pointing to the contribution of the primary production rate as part of the biological processes.