Change in the concentrations of iron in different size fractions during a phytoplankton bloom in controlled ecosystem enclosures

Citation
J. Nishioka et al., Change in the concentrations of iron in different size fractions during a phytoplankton bloom in controlled ecosystem enclosures, J EXP MAR B, 258(2), 2001, pp. 237-255
Citations number
31
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Aquatic Sciences
Journal title
JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY
ISSN journal
0022-0981 → ACNP
Volume
258
Issue
2
Year of publication
2001
Pages
237 - 255
Database
ISI
SICI code
0022-0981(20010415)258:2<237:CITCOI>2.0.ZU;2-7
Abstract
To observe micronutrient dynamics in the plankton ecosystem, controlled eco system enclosure (CEE) experiments were conducted in Saanich Inlet, B.C., C anada. Two CEEs (2.5 m in diameter, 16 m in length, one for Fe studies and the other for biological studies) were launched for the period 22 July to 5 August 1996 and enriched with 10 muM nitrate and 5.2 nM Fe (13% of total F e) on day 1. Sampling from three integrated depths, intervals 0-4, 4-8 and 8-12 m, was performed on days 0, 1, 2, 3, 4, 5, 7, 9 and 11. Iron concentra tions were measured for five size fractions: > 25 mum particles, 2-25 mum p articles, 0.2-2 mum particles, 0.2 mum-200 kDa small colloidal particles an d < 200 kDa soluble species. The sediment in the Fe enclosure was also coll ected on every sampling day after day 2 and its Fe was determined. Size-fra ctionated particulate organic carbon and total chlorophyll-a were also anal yzed. The Fe in small colloidal particles (200 kDa-0.2 <mu>m) comprised 78% of th e traditionally defined dissolved phase (< 0.2 <mu>m) on day 1. Of all the size fractions of Fe, the small colloidal particulate fraction decreased mo st significantly during the phytoplankton bloom. In the dissolved fraction (< 0.2 <mu>m), the small colloidal particle fraction comprised 79% of the d ecrease. The decrease in concentration of Fe in small colloidal particles w as larger than that of total Fr from day 1 to day 4. In contrast, the > 25 mum Fe particles increased over the same period. These results suggest that Fe in small colloidal particles changed to > 25 mum Fe particles during ph ytoplankton growth. A large amount of Fe was kept in the surface layer with the phytoplankton, and transported to the deep layer by phytoplankton sedi mentation, at the end of the bloom. From these results, the small colloidal particulate Fe seems to be the most dynamic size fraction and a high perce ntage of Fe in small colloidal particles changed to large particles due to chemical/physical aggregation and/or physical adsorption to suspended parti cles such as phytoplankton cells. (C) 2001 Elsevier Science B.V. All rights reserved.