Distribution and Speciation of Iron in Natural Waters: Transition from River Water to a Marine Environment, British Columbia, Canada

Total and "HCl reactive" iron has been determined for particulate and soluble forms in freshwater and seawater samples along a profile extending from Hope, British Columbia, 100 miles up the Fraser River, to a station in the Northeast Pacific Ocean, 60 miles west of Cape Flattery, Washington. Complementary data were taken on salinity, dissolved oxygen, pH, and temperature. Observations covered periods of high and low river runoff from June 1962 to June 1963.Total particulate iron concentrations in the Fraser River were highest during the maximum runoff period in summer, while total soluble iron concentrations did not significantly increase at this time. Admixture of saline water with fresh water at the river mouth caused the expected abrupt decrease in particulate iron below the upper 2 m.Both the total particulate and total soluble iron concentrations in seawater samples decreased from the Strait of Georgia seaward through Juan de Fuca Strait out into the Pacific Ocean. In summer, the total soluble iron was higher than in winter while the total particulate iron was lower. The seasonal fluctuations of the sum of the total particulate and total soluble iron were not significant.The high amounts of the soluble forms of iron and the concurrent low particulate iron concentrations in summer may be partially explained by the assimilation of particulate iron during periods of high phytoplankton productivity, mainly by diatoms, with release of soluble forms during lysis of these organisms.The mean annual total iron discharged by the Fraser River was 1.90 × 105 kg/day, the bulk of which was immediately laid down in the river delta.There was no evident correlation of the iron distribution with that of pH, oxygen, or density, excepting in the region immediately adjacent to the mouth of the Fraser River.