Dynamics of chemical characteristics of solubilized organic matter in wetland soils under aerobic or anaerobic conditions Asmaa Rouwane, Isabelle Bourven, Marion Rabiet, Gilles Guibaud and Malgorzata GRYBOS* University of Limoges, GRESE (Groupe de Recherche Eau-Sol-Environnement), 87060 Limoges, France. *malgorzata.grybos@unilim.fr Size distribution of dissolved organic matter Fig.3. Evolution of DOC (a), OM aromaticity (b), pH (c), redox potentiel (d) and Fe(II) under aerobic (red) and anaerobic (black) conditions. The data shown are from three independent replicates. 3D fluorescence fingerprints of DOM Soil sampling and characteristics Dissolved organic matter release from wetland soil Wetlands soils are large terrestrial organic matter (OM) pool. Accumulation of OM in these area is due to the temporal or permanent flooding and the decrease of microbial decomposition/mineralization processes under anaerobic conditions compared with OM production (1). Wetlands soils are recognized as an important source of dissolved organic matter (DOM) to aquatic ecosystem (2,3). In fact, limitation of O 2 availability in waterlogged soil, involve a reduction of oxidized elements to the corresponding reduced form. Thus, the Fe(III)-bearing minerals are reductively dissolved and adsorbed DOM mobilized. The release of DOM in reduced soils is accentuated by a decrease of the positive net surface charge at mineral surfaces in response to H + consumption during reduction reactions and DOM desorption from mineral surfaces (4,5). Fig.2. Waterlogging of superficial horizons during winter-spring time (a), batch incubations under aerobic and anaerobic conditions (b). Colored soil water is due to the mobilization of DOM and organo-mineral colloids. Fig.4. 3D Excitation-Emission Matrix fluorescence intensity plots as a function of time. Spectral localization of (I) humic-like acid, (II) fulvic-like acid, (III) aromatic proteins-like and (IV) soluble microbial metabolites. 1)Reddy & DeLaune, 2004; 2)Evans et al., 2005; 3)Worrall et al., 2005; 4)Avena & Koopal 1998; 5) Grybos et al., 2009; * calculated according Weishaar et al., 2003; **apparent molecular weight Three main size fractions (F) of DOM were indentified: - F 1 with an aMW** >10kDa: constituted of protein-like compounds, - F 2 with an aMW from 1kDa up to 10kDa: composed of a mixture of protein derived compounds and humic-like substances, - F 3 with an aMW < 1kDa: composed of a mixture of proteins derived compounds and humic-like substances. DOM increase under anaerobic conditions was due to the release of F 2 . Fig.6. Comparison of fluorescence and UV254 chromatograms for masse weight distribution of mobilized DOM under aerobic (non-reduced soil) and anaerobic conditions (reduced soil). Red chromatograms corresponds to the beginning (T=0h) and the end (T=864h) of incubations. The data shown are from three independent replicates. 700m 400m 100m Adopted from PDPG de la Haute Vienne Wetland Downstream Grazed grassland Forest 50 m N Upstream Forest N 0 100 200 300 400 500 600 700 800 900 20 40 60 80 100 120 DOC (anaerobic incubation) DOC (aerobic incubation) DOC (mg.L -1 ) time (hours) 0 100 200 300 400 500 600 700 800 900 20 25 30 35 40 45 50 55 60 65 70 75 Aromaticity (aerobic incubation) Aromaticity (anaerobic incubation) Aromaticity (%) time (hours) a b The incubations were carried out on an acidic (pH=5.5), OM rich (20%) pseudogley. Soil suspension was prepared at soil:solution ratio of 1:20. Solution contained NO 3 - ,SO 4 2- and Cl - (5, 15 and 18 mg/L respectively) to mimic the anion composition of the soil solution of wetland during a period of water table rise. OM release from wetland soil was tested under aerobic and anaerobic incubations simulating temporarily (non- reduced) and permanently (reduced) flooded soil. 0 100 200 300 400 500 600 700 800 900 -100 -50 0 50 100 150 200 250 300 350 400 450 500 550 600 Eh (aerobic incubation) Eh (anaerobic incubation) Eh (mV) time(hours) 0 100 200 300 400 500 600 700 800 900 0 5 10 15 20 25 30 35 40 45 Fe (II) (aerobic incubation) Fe (II) (anaerobic incubation) Fe(II) (mg.L -1 ) time (hours) 0 100 200 300 400 500 600 700 800 900 5,0 5,5 6,0 6,5 7,0 7,5 8,0 pH (anaerobic incubation) pH (aerobic incubation) pH time (hours) c d e Anaerobic incubations involved strong release of DOC to the soil solution (2mgC/g soil ), which was correlated with an increase of solution pH (from 6.0 to 7.5) and Fe reduction. Aerobic incubations induced smaller DOM release (0.8 mgC/g soil ) and was accompanied by pH decrease (from 6.0 to 5.0). Released DOM under both experimental conditions had an increasing trend in aromaticity. DOM released under anaerobic conditions had more aromatic character. 0 20 40 60 80 100 120 140 160 180 mg.L -1 Proteins Humic substances T=0h T=864h 0 20 40 60 80 100 120 140 160 180 mg.L -1 Proteins Humic substances T=0h T=864h Aerobic incubations Anaerobic incubations 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Fulvic-like fluorescence 240nm – 445nm 0 200 400 600 800 1000 1200 1400 1600 1800 2000 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Humic-like fluorescence 322nm – 414nm 0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 4 5 6 7 8 9 10 11 12 13 14 15 16 17 UV 254nm absorbance 0 60 120 180 240 300 360 420 480 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Protein-like fluorescence 235nm – 345nm 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Fulvic-like fluorescence 240nm – 445nm 0 200 400 600 800 1000 1200 1400 1600 1800 2000 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Humic-like fluorescence 322nm – 444nm 0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 4 5 6 7 8 9 10 11 12 13 14 15 16 17 UV 254nm absorbance 0 60 120 180 240 300 360 420 480 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Protein-like fluorescence 235nm - 345nm Anaerobic incubations Aerobic incubations Anaerobic incubations Aerobic incubations Anaerobic incubations Aerobic incubations Anaerobic incubations Aerobic incubations Fig.5. Amounts of proteins and humic substances released from wetland soil upon aerobic and anaerobic conditions at the beginning (T=0h) and the end (T=864h) of incubations. The data shown are from three independent replicates. Fig.1. Sketch map showing location of the La Roselle subcatchment and of the soil sampling site (Limousin, France). a b DOM increase under anaerobic conditions was due to the release of humic substances. Proteins had little contribution in DOM pool. Anaerobic condi,ons Aerobic condi,ons T 0 =0h T 3 =270h T 5 =530h T 7 =864h I II III IV Soil aeration regulate the amount, chemical characteristics and mass weight distribution of DOM in waterlogged soils. Anaerobic conditions: - generate higher release of DOM to the soil solution, - are suitable for the release of aromatic OM contained a mixture of humic substances and proteins-derived compounds Reduced wetland soils is a potential source of DOM input to surface water. View publication stats View publication stats