Abstract

The integrated nitrous oxide (N2O) and methane (CH4) grassland project aims to estimate and explain emissions of these greenhouse gases from two ecosystems, namely drained agricultural peat soil under grass at the experimental farm Zegveld and undrained peat in the nature preserve Nieuwkoopse Plassen. Peat soils were chosen because of their expected considerable contribution to the greenhouse gas budget considering the prevailing wet and partial anaerobic conditions. The emission dynamics of these ecosystems are considered representatives of large peat areas because the underlying processes are rather general and driven by variables like organic matter characteristics, water and nutrient conditions and type of vegetation. The research approach comprises measerements and modelling at different integration levels relating to the microbiology of the production and consumption of N2O and CH4 (laboratory studies), their movement through peat soil (rhizolab and field studies), and the resulting fluxes (field studies). Typical emissions from drained soil were 15-40 kg ha-1 y-1 N2O and virtually zero for CH4. The undrained soil in the nature preserve emitted 100-280 kg ha-1 y-1 CH4, and probably little N2O. The process knowledge collected and partly integrated in the models helps to explain these data. For example, the low methane emissions from drained peat can more coherently be understood and extrapolated because (i) upper soil layers are aerobic, thus limiting methane production and stimulating methane oxidation, (ii) absence of aerenchymatous roots of wetland plants that connect deeper anaerobic soil layers where methane is produced to the atmosphere and supply labile carbon, (iii) a low methane production potential in deep layers due to the low decomposability of organic matter, and (iv) long anaerobic periods needed in the topsoil to develop a methane production potential.