Concentration, Spatial-Temporal Distribution, and Bioavailability of Dissolved Reactive Iron in Northern Coastal China Seawater

Abstract

The concentrations of total dissolved iron (TdFe) and dissolved reactive iron (DrFe) in the Northern coastal China seawater (Yantai Sishili Bay) in 2018 were determined using cathodic stripping voltammetry (CSV). It was found that while the concentrations of TdFe ranged from 27.8 to 82.0 nM, DrFe concentrations changed in a much narrower range from 6.8 to 13.3 nM. The annual mean concentrations of DrFe also ranged from 7.1 to 12.6 nM at the 12 sites monitored over the 4 years of the study (2017–2020). Considering the obvious changes in temperature (T), chlorophyll a (Chl a) concentrations (Chl a contents were higher in May, July and September than in March and November), and nutrients over a year in this zone, the consumption of DrFe was expected; the supplement of DrFe observed may have resulted from the transformation of strong organically complexed iron by photoreduction and cell surface reduction. Additionally, a pre-liminary conclusion was drawn based on the theoretical calculation of Fe* that the concentration of DrFe was sufficient to meet the phytoplankton demand.