Contribution Of Dissolved Organic Matter Research Articles

CONTRIBUIÇÃO DA DECOMPOSIÇÃO DE MACRÓFITAS AQUÁTICAS (Eichhornia azurea) NA MATÉRIA ORGÂNICA DISSOLVIDA

CONTRIBUTION TO DISSOLVED ORGANIC MATTER BY DECOMPOSITION OF AQUATIC MACROPHYTES, Eichhornia azurea. Organic matter plays a fundamental role in many ecological processes and decomposition is among the main cycling routes of organic matter. The decomposition of aquatic macrophytes generates much debris, since the carbon of these algae is not easily assimilated by other organisms. Spectroscopic analyses are important in organic matter studies, because it enables satisfactory distinction between labile and refractory materials can be obtained. Through comparing the fl uorescence spectrum of the organic debris generated by a decomposing macrophyte with those of water, sediment, and soil samples from the Upper Parana River fl oodplain water bodies, we were able to estimate the contribution of decomposition to local carbon cycles. The results revealed a higher contribution of decomposition to the oligotrophic environments connected with the Parana River, while some water bodies connected with the rivers Ivinheima and Baia showed a greater participation of allochthonous organic matter, mainly derived from humus.

Contribution of dissolved organic matter to carbon storage in forest mineral soils

AbstractDissolved organic matter (DOM) is often considered the most labile portion of organic matter in soil and to be negligible with respect to the accumulation of soil C. In this short review, we present recent evidence that this view is invalid. The stability of DOM from forest floor horizons, peats, and topsoils against microbial degradation increases with advanced decomposition of the parent organic matter (OM). Aromatic compounds, deriving from lignin, likely are the most stable components of DOM while plant‐derived carbohydrates seem easily degradable. Carbohydrates and N‐rich compounds of microbial origin produced during the degradation of DOM can be relatively stable. Such components contribute much to DOM in the mineral subsoil. Sorption of DOM to soil minerals and (co‐)precipitation with Al (and probably also with Fe), especially of the inherently stable aromatic moieties, result in distinct stabilization. In laboratory incubation experiments, the mean residence time of DOM from the Oa horizon of a Haplic Podzol increased from <30 y in solution to >90 y after sorption to a subsoil. We combined DOM fluxes and mineralization rate constants for DOM sorbed to minerals and a subsoil horizon, and (co‐)precipitated with Al to estimate the potential contribution of DOM to total C in the mineral soil of a Haplic Podzol in Germany. The contribution of roots to DOM was not considered because of lack of data. The DOM‐derived soil C ranges from 20 to 55 Mg ha–1 in the mineral soil, which represents 19%–50% of the total soil C. The variation of the estimate reflects the variation in mineralization rate constants obtained for sorbed and (co‐)precipitated DOM. Nevertheless, the estimates indicate that DOM contributes significantly to the accumulation of stable OM in soil. A more precise estimation of DOM‐derived C in soils requires mineralization rate constants for DOM sorbed to all relevant minerals or (co‐)precipitated with Fe. Additionally, we need information on the contribution of sorption to distinct minerals as well as of (co‐)precipitation with Al and Fe to DOM retention.

Role of dissolved organic matter in translocation of nutrient cations from organic layer materials in coniferous and broad leaf forests

Dissolved organic matter (DOM) transports many kinds of substances in soil. In order to investigate the contribution of DOM to the transport of nutrient cations from forest organic layers to mineral soils, incubation experiments were conducted on organic layer materials of two Quercus species (broad leaves), Japanese cypress and Japanese cedar. Water leachates from the incubated organic layer materials contained far smaller amounts of mineral anions than cations. The deficit of negative charges was related to the organic anions of DOM. In the course of the decomposition, exchange sites formed on the surface of the plant residues retained some of the cations, which were prone to elution by organic anions of DOM. Potassium was least retained; 33 to 62% of the initial contents were leached with water during the 5-week incubation period. The divalent cations, Mg and Ca, were not substantially leached. Still at most 81 and 45%, for Mg and Ca, respectively, of the initial amounts were transformed into an ammonium acetate-extractable form" due to the elution by organic anions of DOM on a longer time scale. The amount of DOM controlled the total amount of eluted cations. The extent of cation mobilization differed among the four plant species, and decreased in the order of broad leaf species> cypress> cedar. A similar tendency was also observed in the distribution patterns of the cations between the organic layers and the mineral soils in fields. The production of DOM increased at higher (up to 30°C) temperature, while the increase in CO2 emissions was larger. The production of DOM and CO2 showed a linear relation for the Oe layer materials, while no correlation was detected for the Oi ones, presumably because water-soluble saccharides, the major substrates used in the Oi layer, did not produce efficiently DOM. The production of DOM and CO2 was larger in the broad leaf litter than in the coniferous one. The emission of CO2 was negatively correlated with the C/P and lignin/P ratio, while the production of DOM was positively correlated with the contents of hot water-soluble N and hemicellulose. The largest correlation coefficient was detected between CO2 and DOM production.

Significance of DOM in the translocation of cations and acidity in acid forest soils

AbstractWe estimated the contribution of dissolved organic matter (DOM) to cation leaching and the translocation of acidity in three acid forest soils. The analysis was based on monitored (2 years) concentrations of dissolved organic carbon (DOC) in the field, measured total acidities of DOM, and measured as well as predicted weighted mean dissociation constants of the organic acids. Although the forest floor solutions were strongly acidic (pH 3.47–4.10), a considerable proportion of the organic acids was dissociated and organic anions represented 22–40% of the total anions in the mineral soil input. The flux of DOM‐associated exchangeable protons from the forest floor to the mineral soil ranged from 0.35 (Wülfersreuth) to 3.72 (Hohe Matzen) kmol ha−1 yr−1. In the subsoil, this organic acidity may be neutralized by microbial decomposition of the organic acids, but a part of the hydrogen ions may dissociate and contribute to acidification of the soil solution and to weathering processes. Due to the pronounced retention of DOM in the mineral subsoil horizons, the contribution of DOM to the output of cations and acidity from the soil is much lower than in the surface horizons but still significant.?

Dissolved organic matter and terrestrial‐lotic linkages in the Central Amazon Basin of Brazil

We evaluate the hypothesis that decomposition and adsorption reactions operating in upland soils of headwater catchments control the concentration and composition of dissolved and fine particulate organic matter in rivers of the Amazon basin. In two contrasting first‐order catchments characteristic of the central Amazon basin, we analyzed plant, litter, soil, groundwater, and stream water chemistry. Our results indicate that clear and persistent differences exist in the concentration and elemental composition of dissolved organic matter (DOM) in stream waters and groundwaters from the two catchments, due mainly to corresponding differences in soil texture and chemistry. Within the more oxide and clay rich Oxisols underlying terra firme forest, groundwater DOM concentrations were uniformly low (120 μMC) and C/N ratios averaged 10. Conversely, within the oxide and clay deficient Spodosols underlying campinarana forest, groundwater DOM concentrations were greatly elevated (3000 μMC), and C/N ratios averaged near 60. We found that, in the terra firme/Oxisol terrain, the majority of DOM contributions to the stream derived from the riparian zone, while in the campinarana/Spodosol terrain, upland groundwater contributions could account for the concentration and composition of DOM in the stream. The implications of our findings are that in the terra firme terrains which dominate the region, upland soil profiles are not the site of definitive processes which impart compositional signatures to organic matter carried by the largest rivers of the Amazon basin, as was hypothesized. Instead, we suggest that definitive reactions are focused primarily in the river corridor.

Short term fluctuations in dissolved organic matter concentrations in streamflow draining a forested watershed and their relation to the catchment budget

AbstractDissolved organic matter (DOM) concentrations in throughfall, throughflow, and runoff were recorded in a small (95 ha) woodland catchment in North Warwickshire for a period of eight weeks following a prolonged dry spell. DOM is shown to be positively related to stream discharge over the sampling period, although distinctive flushing effects were identified. The net contribution of DOM to total dissolved solids load carried in the river was only 2.4 per cent, and represented significantly less than published carbon losses by mineralization of soil organic matter. Throughfall inputs were some 100 times higher than streamflow outputs from the catchment.