Evaluation of magnetic field effect on quantification of aromatic components of humic acids by 13C CPMAS NMR

2 pages, 3 figures, 2 references.-- Comunicación oral presentada al citado Congreso, celebrado del 7-11 de mayo 2007, en Río de Janeiro, Brasil.High resolution 13C NMR spectroscopy, acquired with the CPMAS technique, has been a powerful tool to analyze chemical composition of soil organic mater (SOM), since 1980. The principal application of the CPMAS technique has been the quantification of the structural components of humic substances such as tile amount of aromatic, aliphatic, carbonyl and carboxyl groups.Peer reviewe

Wildfires influence on soil organic matter in an Atlantic mountainous region (NW of Spain)

10 páginas, 5 figuras, 3 tablas, 53 referencias.-- [email protected] principal aim of this research was to determine the influence of wildfires on soil organic matter (SOM) content and composition in soils located on the northern slope of the Cantabrian Cordillera, an Atlantic mountainous region in the North West of Spain, where wildfires are frequent. Samples from soils with similar aspect, slope, elevation and vegetation characteristics, but with different wildfires histories were collected. Total organic carbon and total nitrogen contents were determined as well as the C/N ratio. Furthermore, a qualitative characterization of the soil organic carbon (SOC) was carried out by 13C variable amplitude cross polarization magic angle spinning (VACP/MAS) Nuclear Magnetic Resonance (NMR) spectroscopy. Our results show that, on the one hand, all the sampled soils can be considered important pools of carbon in this Atlantic mountainous region, especially in the heath areas. On the other hand, the fire-affected soils present higher SOM contents than their unburnt counterparts. This could be attributed to an important reaccumulation of fresh vegetal material, which is probably a consequence of the decrease of SOM decomposition rates after fire. Moreover, charred organic compounds are not found in all the burnt soils, which could be due to the long time since the last fires events took place, to different fire severities, or to different post-fire erosion processes in the studied soils.This research was financially supported by the Principado de Asturias Government, in the FICYT project “Procesos de erosión en las vertientes de la Cordillera Cantábrica: relación con los incendios forestales” (PC04-17). C. Santín was in receipt of an FPU grant from the Spanish Government.Peer reviewe

Effects of reclamation and regeneration processes on organic matter from estuarine soils and sediments

Three adjacent areas in the Urdaibai Estuary (NW Spain) comprising a reclaimed salt marsh, a natural salt marsh and a regenerated salt marsh were sampled in order to study edaphic processes and changes in organic matter (OM) composition related to reclamation and regeneration of soils and sediments in estuarine environments. For this, a general analytical description of the soil and sediment profiles was carried out and the OM was characterized using solid state 13C nuclear magnetic resonance (NMR) spectroscopy and analytical pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). The reclaimed salt marsh displayed very different characteristics from the natural salt marsh throughout the whole profile, indicating an important degree of change in soil quality and, particularly, in OM composition caused by the reclamation. At this reclaimed site, characterized by oxic conditions and a lack of tidal influence, transformation of the former salt marsh to grassland resulted in input of OM richer in carbohydrates and with a lower contribution of aromatic compounds than the OM in the salt marsh soils. On the other hand, the edaphic characteristics of the regenerated marsh were similar to those of the natural marsh and the vegetation cover was the same. However, the natural marsh accumulated twice the amount of organic carbon at the surface as the regenerated marsh. Furthermore, the natural marsh contained more aromatic material, as detected with NMR and the Py-GC/MS results indicated a greater presence of microbial material. These differences indicate that the regenerated marsh has not completely recovered its natural characteristics, despite the long period (more than 40 y) since the beginning of the regeneration process. We propose the composition of soil OM as a suitable long term indicator of reclamation and regeneration processes in the salt marsh environments.The research was partially financed by the Spanish Government (CN-04-245). C.S. was in receipt of an FPU grant from the Spanish Government.Peer Reviewe