Carbon and nitrogen balances in Danish forest and agro ecosystems

Abstract

Carbon exchange between the terrestrial biosphere and the atmosphere is one of the key processes that needs to be assessed in relation to the greenhouse effect. At the same time nitrogen plays an important role for turnover processes in the carbon cycle. This study presents data of net ecosystem carbon exchange which confirm that forest and agro ecosystems in Denmark act as carbon sinks, but only to a minor degree compared to the emission of carbon dioxide from fossil fuels. The annual carbon balance ranges from 1–2 t C per ha per year. The study also includes measurements of methane and water mediated carbon fluxes. Their contribution to the carbon balance of the ecosystems are of minor importance. The input of nitrogen to the forest and agroecosystems was 16–25 kg N per ha per year, highest in the forest due to dry deposition. The leaching of nitrate from the forest ecosystem was only a few kg N per ha per year, whereas it amounted to 50–70 kg N per ha per year from agricultural fields. The findings point to the conclusion that afforestation on agricultural fields will improve the groundwater quality with respect to nitrate content, but may also lead to formation of less groundwater due to higher evapotranspiration in forests.