Atmospheric particle adsorption rates of plants in an industrial city of southwest Iran

Abstract. A significant decrease of dissolved iron (DFe) concentration has been observed after dust addition into mesocosms during the DUst experiment in a low Nutrient low chlorophyll Ecosystem (DUNE), carried out in the summer of 2008. Due to low biological productivity at the experiment site, biological consumption of iron can not explain the magnitude of DFe decrease. To understand processes regulating the observed DFe variation, we simulated the experiment using a one-dimensional model of the Fe biogeochemical cycle, coupled with a simple ecosystem model. Different size classes of particles and particle aggregation are taken into account to describe the particle dynamics. DFe concentration is regulated in the model by dissolution from dust particles and adsorption onto particle surfaces, biological uptake, and photochemical mobilisation of particulate iron. The model reproduces the observed DFe decrease after dust addition well. This is essentially explained by particle adsorption and particle aggregation that produces a high export within the first 24 h. The estimated particle adsorption rates range between the measured adsorption rates of soluble iron and those of colloidal iron, indicating both processes controlling the DFe removal during the experiment. A dissolution timescale of 3 days is used in the model, instead of an instantaneous dissolution, underlining the importance of dissolution kinetics on the short-term impact of dust deposition on seawater DFe. Sensitivity studies reveal that initial DFe concentration before dust addition was crucial for the net impact of dust addition on DFe during the DUNE experiment. Based on the balance between abiotic sinks and sources of DFe, a critical DFe concentration has been defined, above which dust deposition acts as a net sink of DFe, rather than a source. Taking into account the role of excess iron binding ligands and biotic processes, the critical DFe concentration might be applied to explain the short-term variability of DFe after natural dust deposition in various different ocean regions.

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Dust deposition: iron source or sink? A case study

Biogeosciences Discussions ◽

10.5194/bgd-7-9219-2010 ◽

2010 ◽

Vol 7 (6) ◽

pp. 9219-9272

Author(s):

Y. Ye ◽

T. Wagener ◽

C. Völker ◽

C. Guieu ◽

D. A. Wolf-Gladrow

Keyword(s):

Ecosystem Model ◽

Dust Particles ◽

Dust Deposition ◽

Colloidal Iron ◽

Size Classes ◽

Excess Iron ◽

Particulate Iron ◽

Sensitivity Studies ◽

Particle Adsorption ◽

Adsorption Rates

Abstract. A significant decrease of dissolved iron (DFe) concentration has been observed after dust addition into mesocosms during the DUst experiment in a low Nutrient low chlorophyll Ecosystem (DUNE), carried out in the summer of 2008. To understand the processes regulating the observed DFe variation, we simulated the experiment by a one-dimensional model of the Fe biogeochemical cycle, coupled with a simple ecosystem model. Different size classes of particles and particle aggregation are taken into account to describe the particle dynamics. DFe concentration is regulated in the model by dissolution from dust particles and adsorption onto particle surfaces, biological uptake, and photochemical mobilisation of particulate iron. The model reproduces the observed DFe decrease after dust addition well, choosing particle adsorption rates of 30, 150 and 750 m3 kg−1 d−1 for particles of different size classes. These adsorption rates range between the measured adsorption rates of soluble iron and those of colloidal iron, indicating both processes controlling the DFe removal during the experiment. Sensitivity studies reveal that initial DFe concentration before dust addition was crucial for the net impact of dust addition on DFe during the DUNE experiment. From the balance between sinks and sources of DFe, a critical DFe concentration, above which dust deposition acts as a net sink of DFe, rather than a source, has been estimated for the DUNE experiment. Taking into account the role of excess iron binding ligands, this concept of a critical DFe concentration might be applied to explain the short-term variability of DFe after natural dust deposition.

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