M.A. García

Soil CO2 fluxes in cereal land use of the Spanish plateau: influence of conventional and reduced tillage practices

From November 1998 to October 2000, measurements of soil respiration were performed on the Spanish plateau for two patches of non-irrigated barley, one managed with conventional tillage (CT) and the other with reduced tillage (RT). Soil CO2 flux showed seasonal variation on both patches, with an increase from March to October, peaking in May, and a decrease during the winter period by a factor of around 2. The mean value for both combined years was 2.03 and 1.70 micromol m(-2) S(-1), in the CT and RT patches, respectively. In order to analyse the influence of RT on soil CO2 flux, two tests were performed. The first one was the Kruskal-Wallis test to compare whether the differences between the medians in both patches were statistically significant. The results obtained revealed statistically significant differences during the second year, at a 85% and 95% significance level, use being made of annual data and that recorded during the period of maximum interest, March-October, respectively. The decrease in soil respiration in the RT patch was around 24%. The second test was aimed at describing and comparing the influence of soil temperature on soil CO2 flux. By using the data of both patches recorded during the first year, an empirical equation on 10-cm soil temperature was fitted and tested on the data corresponding to the second year in each of the patches. Then, a comparison between the medians of the differences between the estimated and observed values was again performed by means of the Kruskal-Wallis test. The over-prediction of the model in the RT patch, statistically significant at a 90% significance level, was roughly 23%, confirming again the decrease in soil respiration one year after this agricultural management practice had been implemented.

Analysis of wind data in the low atmosphere from a RASS sodar

This paper focuses on the ability of a sodar to describe some characteristics of the atmospheric vertical structure and presents some techniques for meteorological data evaluation. The measuring campaign took place in April 2001 and consisted of 10-min averages covering the lower atmosphere from 40 to 500 m at 20-m levels. Three methods were considered, the first of which was a scalar analysis performed using a combination of wind and temperature median profiles. A noticeable contrast between day and night was obtained. Flat wind profiles during the day were a consequence of prevailing convective conditions that determined thermal turbulence. A stable layer above 260 m capped the unstable layer situated below and guaranteed the stability of the boundary layer. During the night, the presence of a low level jet was the most significant feature. The height of the core was 340 m and the higher vertical winds defined it clearly. The second method focused on the wind vector. In this analysis, the anti-cyclonic rotation of hourly averages was considered in the lower levels where it was observed. After a translation of the origin, an empirical, robust model with two parts was then proposed for the resulting vector. The angle was described linearly and the module by a second order model for cylindrical data. Finally, as a third method, three regression analyses were investigated: vectorial, taking every wind component separately and scalar. The two first seemed to be more complete due to their description of anti-cyclonic wind rotation when height increased. Correlation coefficients also proved to be more satisfactory. As a consequence, these techniques, although less frequently used, are more suitable to study wind in the low atmosphere.

O3 and CO2 concentrations in a rural area in central Spain

This paper presents the main experimental results of ozone and carbon dioxide concentrations measured in a rural area in the upper Spanish plateau during 2000-2003 from a climatological perspective. Special attention is addressed to characterise the annual cycle and describe the trends observed during the entire period of the study.

Diffusive Sampling Of SO2 And NO2 Concentrations In Complex Terrain In Castile And Leon (Spain)

92 radial diffusive samplers were used to measure sulphur dioxide and nitrogen dioxide concentrations in July 1999. They were distributed over a well-defined 56x56 km 2 grid centred around a coal power station, covering a large stretch of the provinces of Palencia and Leon in the north of Spain. Both pollutants were quantitatively retained on cartridges coated with triethanolamine, and exposed over a period of 20 days. The trapped sulphur dioxide and nitrogen dioxide were analysed as sulphite, sulphate and nitrite by ion chromatography. In order to determine the precision and the exposure time, preliminary tests were performed. The results showed the great sensitivity of the method applied and concluded that two or three weeks were a suitable time to measure all kinds of air pollution scenarios within the area. The accuracy of the diffusive samplers was evaluated by comparison with the measurements obtained using continuous analysers. The inter-comparison yielded satisfactory results (r=0.81, for SO 2 and NO 2 ) showing a tendency to underestimate the nitrogen dioxide concentration. Spatial distribution of both pollutants across the selected grid was analysed and compared. The concentration levels of sulphur dioxide and nitrogen dioxide ranged between 3.0-39.0 and 11.2-27.7 μg/m 3 , respectively. In general, the results derived from the analysis of the concentration contours showed that the maximum concentrations of the pollutants were recorded in the prevailing wind sectors in the area and about 10 km downwind of the power station.