Characterisation of organic carbon in mire and heath soils at the Elgea-Urkilla Wind Farm, northern Spain

Abstract

This paper describes a detailed comparative study of carbon storage in mire and heath soils within the Elgea-Urkilla Wind Farm (Basque Country, northern Spain). Different methods for estimating organic C stocks in the uppermost 15 cm of the soil profile were evaluated in an attempt to determine whether there was any spatial variability. The dominant vegetation of the study area was acidophilic and Atlantic heathland, with scattered areas of mire vegetation associated with spring lines. Soils were classified as Haplic Leptic Umbrisols (Oxyaquic, Molliglosic). Two sampling plots (900 m2 and 600 m2) were established adjacent to wind turbines. Mire vegetation was present in the larger plot (PLOT-A) and absent from the smaller one (PLOT-B). Fourier-transformed infra-red (FTIR) spectra indicated no noteworthy structural dissimilarities in the organic matter characteristics of the soils beneath the two types of vegetation. Soil samples were taken every week at systematically chosen points lying on fixed transects. Estimates of organic C stocks based on single sampling dates were 94–141 t C ha-1 for PLOT-A and 70–105 t C ha-1 for PLOT-B, and tended to increase as the weather became drier. When the estimates were derived from samples taken on several dates but from single transects, the range of the estimate for each plot was reduced to 111–116 t ha-1 for PLOT-A and 81–89 t ha-1 for PLOT-B. The results suggest that organic C stocks vary seasonally, and highlight difficulties that may be encountered in attempting to detect long-term changes in C storage.

Keywords

• Basque Country
• Fourier-transformed infra-red spectroscopy
• FTIR
• organic carbon stocks
• spatial variability
• temporal variability