Spatial and temporal variability of nitrate concentration in seepage water under a mature Norway spruce [Picea abies (L.) Karst] stand before and after clear cut

Abstract

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.

Ion concentrations and fluxes of seepage water before and after clear cutting of Norway spruce stands at Ballyhooly, Ireland, and Höglwald, Germany

“…At HW, the forest floor was covered nearly exclusively by mosses (Table 4), and so herbs could not occupy the clear cut rapidly enough to reduce NO 3 -concentrations more effectively. Similar results were found at a further clear-cut experiment at Höglwald, which was performed in close vicinity some years later (Kohlpaintner et al 2009). However, even when measuring places were significantly covered with ground vegetation ([60% coverage) the average reduction in nitrate concentration was small.…”

“…Average peak concentrations were up to 2018 lmol c L -1 (BH) and 2595 lmol c L -1 (HW), with up to 3675 lmol c L -1 at single suction cups (HW). Similar results were observed following a later clear cut at HW (see Kohlpaintner et al 2009); however, higher NO 3 -concentrations were found after liming of the spruce stand (see Huber et al 2006b), where large amounts Clear cut and replant 1989-1994 1995-1999 1996 1997 1998 1999 1995 Jan Höglwald Ballyhooly Fig. 9 Potassium (K ? )…”

“…2); higher concentrations of NO 3 -are usually found close to the stem (Huber et al 2004c), however, heterogeneity in the interstem area is quite significant before and after the clear cut. The reasons for this observation are not entirely understood; the results of Kohlpaintner et al (2009) at a clear-cut plot nearby HW indicate that sites with dryer conditions, thinner surface humus layers and higher coverage of vascular plants exhibited lower NO 3 -concentrations. While a higher coverage of plants may indicate a higher N-uptake, patterns with drier conditions and thinner surface humus layers may have lower net and gross nitrification, which were found to correlate with NO 3 -in seepage water at the HW clear cut plot (Matejek et al 2008).…”

“…However, even when measuring places were significantly covered with ground vegetation ([60% coverage) the average reduction in nitrate concentration was small. At measuring spots with 0% coverage with ground vegetation the average NO 3 -concentration was 135.9 mg L -1 , while at spots with [60% coverage the mean NO 3 -concentration was 117.4 mg L -1 (see Kohlpaintner et al 2009). …”

Is Biomass Accumulation in Forests an Option to Prevent Climate Change Induced Increases in Nitrate Concentrations in the North German Lowland?

“…The validation of simulated NO 3 − concentrations at single sampling locations is generally difficult due to the high variability of NO 3 − concentrations in seepage water [104][105][106][107]. Therefore, the losses with seepage water [111].…”