A detailed study of iron concentrations measured by the reducible,
reactive ferrous, and extractable methods was conducted in Auke Bay,
Alaska during June 1973 and in Hood Canal, Washington during October
1973 and April 1974. The concentrations by each method were generally
highest at the bottom and decreased towards the surface with
occasional pockets of high iron concentration water at the surface.
In Hood Canal in October the maximum reactive ferrous iron concentration was observed at the bottom of the pycnocline. Large changes
in the iron concentration were observed between successive surveys.
The reducible iron method (range <0.8 to 187 μg Fe/L) measures colloidal
ferric hydroxide plus easily dissolvable and reducible organically
and inorganically bound iron. The reactive ferrous iron method
(range <0.04 to 4.2 μg Fe/L) measures loosely bound organic and
inorganic ferrous iron. The extractable iron method, as finally used,
(range <4 to 170 μg Fe/L) measures that iron measured by reducible iron method plus up to twice the tightly bound organic iron.
We have defined "available" iron (with quotes) as that iron
which appears to be taken up by phytoplankton as determined by the
correlation between the in situ iron concentration and the chlorophyll
a concentration. Chlorophyll a concentration maxima generally
occurred at the depth of the iron concentration minima, strongly
supporting the idea that each method measures "available" iron.
However, significant correlation coefficients for the regression of
iron concentration versus chlorophyll a only support the "availability"
of reactive ferrous iron and that phytoplankton prefer ferrous iron to
ferric iron.
This was one of the first extensive uses of Lewin and Chen's
(1973) ferrous iron method and values observed were generally 2 to
100 times less than they reported. Changes occurring during water
storage appear to be a function of p0₂. Major changes took place
during the first five hours of storage. Interstitial water was greatly
enriched in iron compared with the overlying water. The ferrous
iron concentration was particularly high due to the low Eh of the
sediments. Although the net flow of "available" iron is out of the
sediment, the flux is small (approximately 3 x 10⁻⁵ μg Fe/m²sec).
Most of the iron that appears to be coming from the sediment is
probably being produced by bacterial decomposition as in the case
of subsurface sources of iron associated with ammonia or urea maxima. Fresh water is a significant source of extractable and
reactive ferrous iron into the well-mixed surface layer. Fresh
water is also a source of organically bound iron. Zooplankton appear
to produce "available" iron by eating or excretion. Light appears
to cause the production of ferrous iron through an undetermined
mechanism. / Graduation date: 1976
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/28560 |
| Date | 09 May 1975 |
| Creators | Holden, Robert Bennett |
| Contributors | Curl, Herbert C. Jr |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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