Abstract. In this paper, results from three different interpolation techniques based on Geostatistics (ordinary kriging, kriging with external drift and conditional simulation) and one deterministic method (inverse distances) for mapping total monthly rainfall are compared. The study data set comprised total monthly rainfall from 1998 till 2001 corresponding to a maximum of 121 meteorological stations irregularly distributed in the region of Galicia (NW Spain). Furthermore, a raster Geographic Information System (GIS) was used for spatial interpolation with a 500×500 m grid digital elevation model. Inverse distance technique was appropriate for a rapid estimation of the rainfall at the studied scale. In order to apply geostatistical interpolation techniques, a spatial dependence analysis was performed; rainfall spatial dependence was observed in 33 out of 48 months analysed, the rest of the rainfall data sets presented a random behaviour. Different values of the semivariogram parameters caused the smoothing in the maps obtained by ordinary kriging. Kriging with external drift results were according to former studies which showed the influence of topography. Conditional simulation is considered to give more realistic results; however, this consideration must be confirmed with new data.

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Carbon (C) levels in waters allow us to assess the risk of pollution of streams and water bodies. The aim of this study was to assess the temporal changes in the concentrations of three different carbon forms (total, organic, and inorganic) at the outlet of an agroforestry catchment under Atlantic climate conditions. This research was conducted at Valiñas River catchment in Coruña (NW Spain), a periurban area. Data sets range from March 2007 to December 2009. A total of 205 samples were collected: 57 in 2007, 88 in 2008, and 60 in 2009. Carbon forms were determined using a total organic carbon analyzer. Total carbon values ranged from 7.39 to 7.94 mg L −1 , inorganic carbon varied between 4.91 and 5.61 mg L −1 , and organic carbon varied between 2.03 and 2.84 mg L −1 during the studied years. Significant correlations were observed between the three considered carbon forms during the study period, except that of inorganic and organic carbon in 2007. The lowest mean values of the three carbon forms were observed in winter 2007, winter 2009, and autumn 2008, whereas the greatest concentrations were observed in autumn 2007, summer 2008, and summer 2009. Year did not affect carbon concentrations in water; however, season influenced these concentrations, maybe because of the rainfall distribution.