Nitrate concentrations in soil solutions below Danish forests |
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| Institution: | 1. Section of Critical Care, Department of Pediatrics, University of Colorado School of Medicine, Aurora, CO;2. Department of Epidemiology, Colorado School of Public Health, University of Colorado Denver, Aurora, CO;3. Section of Cardiology, Department of Pediatrics, University of Colorado School of Medicine, Aurora, CO;4. Section of Pulmonary Medicine, Department of Pediatrics, University of Colorado School of Medicine, Aurora, CO;5. The Pediatric Heart-Lung Center, Department of Pediatrics, University of Colorado School of Medicine, Aurora, CO;6. Perinatal Institute, Cincinnati Children''s Hospital Medical Center, Cincinnati, OH;1. BRGM, 3 avenue C. Guillemin, BP 6009, 45060 Orléans, France;2. BRGM Service Géologique Régional Bretagne, 2 rue de Jouanet, 35700 Rennes, France;3. Aix-Marseille Université, CNRS, IRD, CEREGE UM 34, Aix-en-Provence 13545, France;1. State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing 100875, China;2. Advanced interdisciplinary Institute of Environment and Ecology, Beijing Normal University, Zhuhai 519087, China;3. Institute of Environment and Sustainable Development in Agricultural, Chinese Academy of Agricultural Sciences, Beijing 100081, China;4. School of Geographic and Ocean Sciences, Key laboratory of Wetland Ecological Functions and Ecological Security, Yanbian University, Yanji, Jilin 133000, China |
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| Abstract: | Nitrate in the soil water below the root zone is a pre-condition for nitrate leaching, and it indicates loss of nutrients from the forest ecosystem. Nitrate leaching may potentially cause eutrophication of surface water and contamination of ground water. In order to evaluate the extent of nitrate leaching in relation to land-use, a national monitoring programme has established sampling routines in a 7×7 km grid including 111 points in forests. During winters of 1986–1993, soil samples were obtained from a depth of 0–25, 25–50, 50–75 and 75–100 cm. Nitrate concentrations in soil solutions were determined by means of a 1 M KCl extraction. The influence of forest size, forest-type, soil-type, tree species and sampling time on the nitrate concentrations was analysed in a statistical model. The analysis focused on data from depth 75–100 cm, as nitrate is considered potentially lost from the ecosystem at this depth. The range of nitrate concentrations was 0–141 mg NO?3–N dm?3 and the estimated mean value was 1.51 mg NO?3–N dm?3. The concentration was influenced by (1) forest size (concentrations in forests <10 ha were higher than concentrations in forests >50 ha), (2) forest-type (afforested arable land had higher concentrations than forest-type `other woodland'), (3) soil-type (humus soils showed above average concentrations, and fine textured soils had higher concentrations than coarse textured soils), and (4) sampling time. Unlike other investigations, there was no significant effect of tree species. A few sites deviated radically from the general pattern of low concentrations. The elevated concentrations recorded there were probably caused by high levels of N deposition due to emission from local sources or temporal disruptions of the N cycle. The nitrate concentration in the soil solution below the root zone was mostly rather low, indicating that, generally, N saturation has not yet occurred in Danish forest ecosystems. However, median concentrations exceeding drinking water standards (11.3 mg NO?3–N dm?3) were found at 7% of the sites. Furthermore, 30% of the sites had median concentrations above 2 mg NO?3–N dm?3, suggested as an elevated level for Danish forest ecosystems, equalling annual N losses of more than 2–6 kg ha?1 year?1. |
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