Study On The Concentrations Of Dissolved Iron And Its Natural Organic Ligands In The Seawater Of Jiaozhou Bay

As the one of the essential micronutrients for phytoplankton，iron plays animportant role in the process of biochemistry of phytoplankton. Organic ligands areparamount in defining Fe biogeochemical cycling and its control on oceanic primaryproductivity. In this paper, cathodic stripping volattmetry was used as themeasurement method to determine the concentration of dissolved iron and its organicligand. Parameters were discussed in the paper for the determination of dissolved ironand its organic ligand at the existence of other metals, and optimum parameters werefound for the measurenment. For the determination of the orangic ligand, competitiveligand equilibration/adsorptive cathodic stripping voltammetric (CLE-ACSV) wasused to measure the concentration of organic ligand of dissolved iron, and parameterswere optimized. Two voyages were taken for the sampling of iron in Jiaozhou Bay, onJuly19,2011and May10,2012, respectivly. Based on the method optimized, theconcentration of dissolved iron and its organic ligand in Jiaozhou Bay seawater weredetermined, and the conditional stability constant of dissolved iron and its organicligand was calculatec then. The main results are as follows:(1) When the pH value between8.0-8.1, the current peak of Fe-DHN wasobvious and independent, the concentration of DHN (2,3-dihydroxynaphthalene)was40.0μmol/L, the optimum electrochemical parameters: deposition potential-0.5V, deposition time90s, scanning rate60mV/s, balancing time50min. On thiscondition, the detection limit for the determination of iron in seawater is0.015nmol/L,and the average sensitivity is14.82±0.73nA L/nmol (n=9).(2) From the surface to the bottom, the average concentrations of dissolved iron(D-Fe) in Jiaozhou Bay in summer were23.03±7.19,19.78±7.48and18.37±5.93nmol/L, respectively; in spring, the average concentration of D-Fe were19.73±22.00,15.34±11.20and15.56±11.17nmol/L, respectively. The changes of the concentrationof D-Fe in summer were small，and the highest value were in the northwest and the baymouth of Jiaozhou Bay, from the surface to the bottom. While the changes of theconcentration of D-Fe were large, and the highest value were in the east of the Bay,the esturies of Licun River and Haibo River.(3) From the surface to the bottom, the average concentrations of organic ligand(D-L) in Jiaozhou Bay in summer were42.04±16.78,46.97±25.91and62.57±62.00nmol/L, respectively; in spring, the average concentration of D-L were62.41±39.86,59.09±16.97and55.53±34.72nmol/L, respectively. The changes of the concentrationof D-L in summer were small，and the highest value were in the northwest and theeast of Jiaozhou Bay, from the surface to the bottom. While the changes of theconcentration of D-L were large, and the highest value were in the east of the Bay, theesturies of Licun River and Haibo River.(4) From the surface to the bottom, the average value of conditional stabilityconstant (logK′FeL) of D-Fe and D-L in summer were11.97±0.64,11.22±0.42and11.26±0.61, respectively; in spring，the average value of logK′FeLwere11.25±0.56,11.15±0.35and11.10±0.44, respectively.