The multi-annual nitrogen budget of a peat-covered catchment — Changing from sink to source?

摘要

Only a few studies have considered the N budget of peat soils and this in turn has limited the ability of studies to consider the impact of changes in climate and atmospheric deposition upon the N budget of a peat soil. This study considered the total N budget of an upland peat-covered catchment over the period 1993 to 2009. The study has shown: i) Over the period of study the total N atmospheric deposition declined from 3.5 to 0.7 tonnes N/km~2/yr. ii) The total fluvial export of N at soil source varied from 0.41 to 1.85 tonnes N/km~2/yr with the fluvial flux being greater than the atmospheric input in 3 years of the study, implying significant internal processing. iii) Measuring the C:N ratio of organic matter pools in the ecosystem shows that gross primary productivity and litter decomposition represent outputs of N from the soil while DOC production and humi-fication represent inputs of N. iv) Overall, the total N budget of the peat ecosystem varies from -1.0 to +2.5 tonnes N/km~2/yr, i.e.in some years the ecosystem is a net source of N. The time series of the total N budget suggests that the ecosystem is responding to the occurrence of severe droughts with a long-term decline in N storage that could be interpreted as a response to long-term high N deposition rates, even if those rates have now diminished.