Inhaltszusammenfassung

The relevance of indirect N2O emission is a controversial topic which is subject to much uncertainty. Only a small number of studies measure the indirect N2O emission at the interface from soil to stream. In addition, the majority of studies undertaken only cover a short-term period (<1 year). Therefore, limited information is available regarding the influence of seasonal or event effects, nor is there much information as to whether indirect N2O emissions are reflected by NO in soil solutions...The relevance of indirect N2O emission is a controversial topic which is subject to much uncertainty. Only a small number of studies measure the indirect N2O emission at the interface from soil to stream. In addition, the majority of studies undertaken only cover a short-term period (<1 year). Therefore, limited information is available regarding the influence of seasonal or event effects, nor is there much information as to whether indirect N2O emissions are reflected by NO in soil solutions. The present study aimed at clarifying these two questions along with the general relevance of dissolved nitrous oxide. A wetness gradient involving soil solutions of different soil types and surface waters within an N-saturated forest catchment (3.2 ha) was monitored over a period of 1 year. N2O concentrations in soil solutions (0.09-16.6 mu g N1(-1)) were affected by events such as dry-wet cycles but did not reflect to the actual, indirect N2O emission at the soil-stream interface. It was assumed that N2O emission was due to N transformation processes. The N2O concentration at the spring was three times higher than the N2O concentrations in the soil solutions. Nevertheless, indirect N2O emission was still subordinate (< 1%) to the direct emission of N2O. The weekly amount of indirect N2O emissions depended only on the stream flow rate (62% of the total annual amount). For this reason it was necessary to measure indirect NO emission at short intervals and at the interface between soil and stream over a longer time period. Our results and the results of the reviewed studies show that the default IPCC emission factor (EF5-g = 1.5%) overestimates the indirect N2O emission from ecosystems. The emission factor should therefore be lowered to about 0.1-0.3%. In addition, the results indicate that indirect N2O emission is an insignificant pathway in the N cycle of most ecosystems. However, final judgement will depend on long-term studies. (c) 2005 Elsevier Ltd. All rights reserved. » weiterlesen» einklappen

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