Long-term monitoring of scots pine litter decomposition rates throughout Sweden indicates formation of a more recalcitrant litter in the South.

Decomposition studies were carried out at sites throughout Sweden, including the four Integrated Monitoring sites. Scots pine needle litterbag weight loss measurements over 3 or 5 years were determined at 26 sites and repeated up to 27 times, depending on the site. Humus layer respiration rates were determined for 20 sites in 1987-1989 and repeated in 2007-2008. Partial Least Squares (PLS) regression was used to elucidate the relative importance of climatic and soil factors. Annual needle weight losses decreased only slowly (20-10%) over 3-5 years for all northern (>60°N) sites but decreased sharply from 30 to 10% in the third year in southern (<60°N) sites. Respiration rates of southern sites were less (40% on average) than those of northern sites. Humus layer N was positively correlated to needle weight loss during the first and the second years, but negatively correlated in the third year and to respiration rates. The results indicated that litter formed in southern Sweden became more recalcitrant in later stages of decomposition compared to litter produced in northern Sweden.

Modeling the effect of liming on calcium concentration in Swedish lakes.

To abate the severe acidification of Swedish lakes are about 7% directly limed (AL-lakes). These are important to include when assessing acidification. Consequently, we need to estimate their chemical status as if they were not lime-affected. We hypothesize that there is a spatial dependence for calcium (Ca) and magnesium (Mg) concentrations. Spatial variation is determined using variograms. We study lakes within two 150 * 150 km quadrates (EMEP150-grid) in the middle and southern parts of Sweden. We model Ca in AL-lakes using the Ca and Mg concentrations in nearby, unaffected lakes (UL-lakes). The mean Ca/Mg for the three or seven closest UL-lakes is used. We assume that Ca/Mg is constant for UL-lakes and that Mg unaltered by liming. For UL-lakes, Ca and Mg are spatially dependent. For AL-lakes, there is a spatial dependence for Mg, but, as anticipated, not for Ca. The modeled Ca for UL-lakes show a good correspondence with measured Ca; r2 > 0.6; slopes close to 1 and intercepts almost 0. Using three or seven nearby lakes when modeling Ca give similar results. Modeled Ca was higher than measured Ca for 36% (three closest lakes) and 38% (seven closest) of the modeled AL-lakes in the middle part of Sweden. The corresponding results for the southern part were 10% and 9%, respectively. This model is an acceptable estimator of Ca in limed lakes and for estimating critical loads and acidification status on an EMEP-scale.

Comparison of ordinary and lognormal kriging on skewed data of total cadmium in forest soils of Sweden.

Spatial statistical analysis of georeferenced data of total cadmium (TCd) in forest soils of Sweden was assumed to provide more advantageous maps than traditional interpolated maps. However, 264 measurements of TCd in O-horizon of forest soils displayed skewed frequency distribution. Since atypical observations affect badly the variogram, outliers were identified, different data transformations were tested and ordinary (OK) and lognormal kriging (LK) scenarios were compared based on cross-validation. Results were compared using overall measures of predictors, e.g. traditional mean squared prediction error (MSPE), mean of kriging variances, variance ratio, median of internally standardised residuals, and assessments of classification accuracy, such as percentage of correctly predicted samples and within-class MSPE. One outlier was identified based on the absolute value of skewness of value differences less or equal to one in data pairs separated at certain lag classes. Mapping categories characterised by percentage of correct classification and within-class MSPE were found to be essential in comparison of kriging results additionally to the overall measures. In comparison of kriging methods, OK predicted high values more accurately and LK was more effective to predict low and medium values. Thus, OK was suggested for mapping high concentration of TCd and other pollutants. Percentage of correctly predicted samples and within-class MSPE were found to be dependent on kriging method, as well as on the number and limits of categories.