Do experimental conditions bias plankton responses to increased concentration of dissolved organic matter (DOM)? A meta-analytical synthesis of the published results

During their atmospheric lifetime, organic compounds within aerosols are exposed to sunlight and undergo photochemical processing. This atmospheric aging process changes the ability of organic aerosols to form cloud droplets and consequently impacts aerosol–cloud interactions. We recently reported changes in the cloud forming properties of aerosolized dissolved organic matter (DOM) due to a photomineralization mechanism, transforming high-molecular weight compounds in DOM into organic acids, CO and CO2. To strengthen the implications of this mechanism to atmospheric aerosols, we now extend our previous dataset and report identical cloud activation experiments with laboratory-generated secondary organic aerosol (SOA) extracts. The SOA was produced from the oxidation of α-pinene and naphthalene, a representative biogenic and anthropogenic source of SOA, respectively. Exposure of aqueous solutions of SOA to UVB irradiation increased the dried organic material's hygroscopicity and thus its ability to form cloud droplets, consistent with our previous observations for DOM. We propose that a photomineralization mechanism is also at play in these SOA extracts. These results help to bridge the gap between DOM and SOA photochemistry by submitting two differently-sourced organic matter materials to identical experimental conditions for optimal comparison.

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Use of Iron (II) Salts and Complexes for the Production of Soil Amendments from Organic Solid Wastes

International Journal of Chemical Engineering ◽

10.1155/2012/701728 ◽

2012 ◽

Vol 2012 ◽

pp. 1-9 ◽

Cited By ~ 1

Author(s):

Amerigo Beneduci ◽

Ilaria Costa ◽

Giuseppe Chidichimo

Keyword(s):

Organic Matter ◽

Dissolved Organic Matter ◽

Solid Waste ◽

Waste Treatment ◽

Organic Matrix ◽

Reaction Chamber ◽

Organic Substrate ◽

Experimental Conditions ◽

Organic Solid ◽

Organic Matrices

A method to obtain rapidly stabilized composts for crops from solid organic wastes is evaluated. Here we used a laboratory scale reaction chamber where solid waste treatment was performed under strictly controlled temperature and pressure conditions. The row organic waste was mixed with acid solutions containing iron (II) ions either in the fully hydrated form or in the form of complexes with the diethylentriaminopentaacetic acid. Data from elemental analysis distribution and GC/MS analysis of the polar and non polar dissolved organic matter, clearly showed that Fe(II) ions significantly enhance organic substrate oxidation of the initial solid waste, compared to a material obtained without the addition of the Fe(II) ions to the raw organic matrix. These results suggest that Fe(II) ions might be involved in a catalytic oxidation pathway that would be activated under the experimental conditions used. The extent of the oxidation process was evaluated by the value of the C/N ratio and, qualitatively, by the molecular composition of the dissolved organic matter. After about 6 hours of incubation, dark-brown and dry organic matrices were obtained with C/N ratio as low as 12 and a high degree of oxidative decomposition into low-molecular-weight compounds at high oxidation state.

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Reproducible determination of dissolved organic matter photosensitivity

10.5194/bg-2020-207 ◽

2020 ◽

Author(s):

Alec W. Armstrong ◽

Leanne Powers ◽

Michael Gonsior

Keyword(s):

Organic Matter ◽

Dissolved Organic Matter ◽

Terrestrial Ecosystems ◽

Freshwater Wetlands ◽

Experimental Conditions ◽

Time Resolved ◽

Precise Control ◽

C And N ◽

Aquatic Food ◽

Dom Composition

Abstract. Dissolved organic matter (DOM) connects aquatic and terrestrial ecosystems, plays an important role in C and N cycles, and supports aquatic food webs. Understanding DOM chemical composition and reactivity is key to predict its ecological role, but characterization is difficult as natural DOM is comprised of a large but unknown number of distinct molecules. Photochemistry is one of the environmental processes responsible for changing the molecular composition of DOM and DOM composition also defines its susceptibility to photochemical alteration. Reliably differentiating the photosensitivity of DOM from different sources can improve our knowledge of how DOM composition is shaped by photochemical alteration and aid research into photochemistry's role in various DOM transformation processes. Here we describe an approach to measure and compare DOM photosensitivity consistently based on the kinetics of changes in DOM fluorescence during 20h photodegradation experiments. We assess the influence of experimental conditions that might affect reproducibility, discuss our modelling approach, offer guidelines for adopting our methods, and illustrate possible applications for ecological inferences. Central to our approach is the use of a reference material, precise control of conditions, leveraging actinometry to estimate photon dose, and frequent (every 20 minutes) fluorescence and absorbance measurements during exposure to artificial sunlight. We compared DOM from freshwater wetlands, a stream, an estuary, and Sargassum sp. leachate and observed differences in sensitivity that could help identify or explain differences in their composition. Finally, we offer an example applying our approach to compare DOM photosensitivity in two adjacent wetlands as seasonal hydrologic changes alter their DOM sources. Our approach may improve reproducibility when compared to other methods and captures time-resolved changes in optical properties that may have been missed previously.

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