The chemistry of seepage water was studied before and after small scale clear-cutting and femel cutting (removing 20% of the trees) between 1999 and 2002 at the Höglwald site in southern Bavaria. The interventions were performed in February 2000 on mature, N-saturated Norway spruce (Picea abies (L.) Karst.) stands with high NO − 3 concentrations before felling. Seepage water was collected with suction cups at 40 cm soil depth in the following treatments: (I) a mature stand (control), (II) a femel-cut, and (III) a clear-cut. In the femel cut subvariants were created with suction cups (plots) at varying distances from pre-selected spruce, which were later removed. The femel treatment was replanted with beech (Fagus sylvatica L.) saplings. On the clear-cut, subvariants of planted beech (close to the stem, interstem area), planted spruce (interstem), or natural spruce regeneration were investigated. Clear-cutting caused high NO − 3 peaks (average values up to 2750 µM) during 2000 and 2001 in all planted tree subvariants during times of comparatively low water fluxes. In contrast to peak concentrations, flux weighted yearly average concentrations showed different trends. In 2000, flux weighted yearly average NO − 3 concentrations were significantly elevated, but only on the subvariants of the interstem area, which covered in the clear-cut plot ca. 62% of the area. However, the subvariant close to the stem (31% of clear-cut area), or the natural spruce regeneration subvariant (6% of clear-cut area) exhibited no significant felling effect. With respect to the whole treatment area, this resulted in no significant felling effect as compared with the control. In the next year (2001), flux weighted yearly average NO − 3 concentrations were not significantly affected by clear-cutting, while the concentrations were even reduced for all of the clear-cut subvariants in 2002. On the subvariant natural spruce regeneration, NO − 3 concentrations remained below the European limit of drinking water (806 µM) during almost the whole investigation period. Selective cutting resulted in slightly reduced NO − 3 concentrations in 2000 and 2001 on the femel treatment. However, no significant effect could be detected for any subvariant in the femel-cut, even not for the subvariant with suction cups closest to the felled spruce. In contrast to many other investigations, clearcutting did not increase the NO − 3 problem on the treatment to a relevant extend. Quite contrary, a decline in NO − 3concentrations to values below the EU level for drinking water and levels below the control and femel treatment just 2 years after cutting were observed. Al 3+ concentrations showed nearly the same trend as NO − 3 , while Ca 2+ , Mg 2+ , and K + concentrations were affected to a lesser degree. Only in 2002 was Ca 2+ significantly lower on the clear-cut as compared to the femel treatment, but not compared to the control. Mg 2+ increased in 2000 on the clear-cut subvariants in the interstem area, but decreased in the years 2001 and 2002. Changes could be obs...

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Abstract. The time domain reflectometry technique for measuring the volumetric soil water content is highly sensitive to installation effects because the sampling volume is more heavily weighted close to the transmission line elements. To investigate changes in soil structure caused by the installation and its influence on the measurement, field and laboratory experiments covering different probe dimensions, soil types, and installation techniques were performed. The results indicate that merely pushing the probes into the soil entails a significant reduction of the measured water content up to 0.10 cm3/cm 3. The effect is strongest close to saturation since the large pores are affected most. The degree of compression differed strongly according to the varying compressibility of the investigated soils. It was smaller for the smaller probe indicating a more favorable relationship between sampling volume and compression. The compression effect could be minimized using a drill to remove the soil for the probes. X ray-computed tomography was used to visualize the installation effects and to measure the density distribution around the probes.

The spatial and temporal variability of the nitrate (NO 3 − ) concentration in seepage water below the main rooting zone of a mature spruce forest was investigated using 121 suction cups which were implemented in a 2×2 m grid at 40 cm depth in the mineral soil. Seepage was collected at least monthly during the vegetation period in 2005. In January 2006 a clear cut was performed on the plot and monthly seepage water was collected with 118 suction cups. Conventional and geostatistical methods were used to investigate the spatial and temporal variability in NO 3 − . We tried to explain the observed variability with multiple classification analysis (MCA) and multiple linear regression models (MLR) based on vegetation, stand and soil parameters, which could be measured without disturbance of the ecosystem. The NO 3 − concentration in the mature stand reached mean values up to 35.2 mg l −1 per sampling date and the distributions were positively skewed. The temporal variability was much lower than the spatial variability. NO 3 − in seepage water showed clear structural patterns over the whole vegetation period. Spatial autocorrelation ranged between 16 and 19 m and structural variance was between 65% and 80% of the whole model semivariance. However, for practical purposes it should be sufficient to consider an autocorrelation range of about 12 m as the last 5-6.5 m only explained 5% of the total structural variance of NO 3 − in seepage water. Vegetation and stand parameters such as distance and size of the trees surrounding the measuring points explained about 40% of total variability in the MCA and MLR models. After clear cut, concentration means per sampling date were below 10 mg l −1 in spring but increased to more then 150 mg l −1 until December 2006. The distribution was nearly normal. The patterns of spatial and temporal variability were reversed compared to the mature stand. Structuring was less pronounced with autocorrelation ranges decreasing from 10 m in April 2006 to values below 3 m during the following vegetation period. The structuring variance was below 30% at most sampling dates. Thickness of the humus layer and amount of water in the sampling bottles, which were not considered in the mature stand, contributed significantly to the explanation of variability after the clear cut. Together with vegetation coverage and stand parameters 30% of the total NO 3 − variability could be explained in the MCA and MLR models. The consequences for future seepage water investigations are discussed.