Improving the precision of estimating nitrate (NO 3 -) concentration in seepage water of forests by prestratification with soil samples

Michael Kohlpaintner, Christian Huber, Axel Göttlein

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1 Scopus citations


Nitrate (NO 3 -) concentrations in seepage water (SW NO3) of N saturated forests regularly show a high spatial variability. As seepage water sampling is expensive, most studies use small numbers of soil solution samplers. This implies high uncertainties of calculated concentration and flux data. At the N saturated Höglwald site we investigated, whether a preselection of seepage water sampling places by a prior intensive soil sampling can improve the precision of the estimation of SW NO3. We implemented 121 suction cups and analyzed the soil, removed with the soil auger during installation at the sampling depth of 40 cm, for water extractable NO 3 -. The NO 3 - content in soil (Soil NO3) was calculated and SW NO3 was measured. With this data set we tested the correlation between Soil NO3 and SW NO3 and simulated a random selection of sampling places (RS) as well as a prestratified sampling based on Soil NO3 (PS). With bootstrap statistics different numbers of replications (n) were tested and the 95% confidence interval (95% CI) was used to compare RS with PS. Highly significant correlations between Soil NO3 and SW NO3 were found (r = 0. 99***). It was even possible to calculate SW NO3 from Soil NO3. Here best results where achieved when Soil NO3 was determined from field moist soil samples. With PS the accuracy of the mean value of SW NO3 improved considerably. To achieve a 95% CI lower than ±10%, 250 suction cups would be needed for RS compared to n = 20 for PS. Even 6 months after implementation, precision of mean SW NO3 was higher for suction cup places selected with the PS method. A detailed description is given, how these findings may be applied in studies and monitoring programs focusing on NO 3 - leaching in forest ecosystems.

Original languageEnglish
Pages (from-to)1399-1409
Number of pages11
JournalEuropean Journal of Forest Research
Issue number5
StatePublished - Sep 2012


  • Höglwald
  • N-saturation
  • Nitrate leaching
  • Random sampling
  • Soil samples
  • Spatial variability
  • Stratified sampling


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