EDAFOLOGIA, Vol. 11 (3), pp. 295-307, 2004



1Departamento de Edafoloxía e Química Agrícola. Facultade de Bioloxía. Universidade de Santiago de Compostela. Campus Sur s/n. 15782 Santiago de Compostela. Galicia. Es- paña. e-mail: edpombal@usc.es 2Department of Environmental Sciences, University of Wageningen, The Netherlands



Mountain peat bogs of Galicia (NW Spain) as carbon sinks Due to its ability to accumlate atmospheric carbon and to the proportion of the Earth surface they occupy, a 3% of continental lands, peatlands are an important carbon reservoir and thus have a high potential to in- fluence the greenhouse effect and the global climate. In Galicia (NW Spain) there are some 10,000 ha of mountain peatlands in which we estimate there are accumulated 10-16 106 t C. This represents a 4.7-7.5% of the carbon stored in forests biomass in Spain, and a 24-38% of the carbon stored in forests biomass and up to 6% of the carbon stored in the soils of Galicia. This numbers give a good insight into the importance of peat forming ecosystems on the C cycle in the region. Within the peat deposits, C shows a rapid increase in the superficial layers (25-60 cm) and a slow increase downwards. Nitrogen shows an opposite trend, thus C/N ratios increase with the depth/age of the peat, in contrast with the usual decrease that occurs in well aerated, mineral soils. The intensity in the change of the C/N ratio seems to be related with local factors, as for example the climatic conditions and their effect on peatland hydrology. Peatlands located at lower altitude have higher C/N ratios than those located at higher altitude. Carbon concentrations follow the opposite trend of peat bulk density, supporting the conclusion that mass loss due to the decompostion of the organic matter is implied in the relative enrichment in carbon. CPMAS 13C-NMR analysis of the peat revealed the presence of aliphatic, methoxylic, hydroxylic, acetalic, aromatic and carboxilic C functional groups. Carbohydrates (hydroxylic and acetalic groups) and aliphatics are the main components, with average proportions of 36.6% and 29.5% respectively. With increasing depth/age the proportion of carbohydrates decreases while aliphatic and aromatic carbon increase. As a re- sult, the proportion of carbohydrate-C is negatively correlated to C concentration (r= -0.86), but aromatic- C and aliphatic-C show a positive correlation (r= 0.78 and 0.63, respectively). It seems though that the increase in C concentration during peat decomposition occurs by the selective preservation and/or diagene- sis of consituents enriched in carbon.

Key words: Peatlands, Histosols, Carbon storage, Organic matter decomposition, 13C NMR studies, Galicia (NW Spain)