Modelling nitrogen saturation and carbon accumulation in heathland soils under elevated nitrogen deposition.
A simple model of nitrogen (N) saturation, based on an extension of the biogeochemical model MAGIC, has been tested at two long-running heathland N manipulation experiments. The model simulates N immobilisation as a function of organic soil C/N ratio, but permits a proportion of immobilised N to be accompanied by accumulation of soil carbon (C), slowing the rate of C/N ratio change and subsequent N saturation. The model successfully reproduced observed treatment effects on soil C and N, and inorganic N leaching, for both sites. At the C-rich upland site, N addition led to relatively small reductions in soil C/N, low inorganic N leaching, and a substantial increase in organic soil C. At the C-poor lowland site, soil C/N ratio decreases and N leaching increases were much more dramatic, and soil C accumulation predicted to be smaller. The study suggests that (i) a simple model can effectively simulate observed changes in soil and leachate N; (ii) previous model predictions based on a constant soil C pool may overpredict future N leaching; (iii) N saturation may develop most rapidly in dry, organic-poor, high-decomposition systems; and (iv) N deposition may lead to significantly enhanced soil C sequestration, particularly in wet, nutrient-poor, organic-rich systems.
Evans
C D
CD
Centre for Ecology and Hydrology, Orton Building, Deiniol Road, Bangor LL57 2UP, UK. cev@ceh.ac.uk
Caporn
S J M
SJ
Carroll
J A
JA
Pilkington
M G
MG
Wilson
D B
DB
Ray
N
N
Cresswell
N
N
D002244:Carbon / Q000737:chemistry*; D004784:Environmental Monitoring / Q000379:methods; D006801:Humans; D008962:Models, Theoretical; D009584:Nitrogen / Q000737:chemistry*; D012989:Soil Pollutants / Q000737:chemistry*
D012989:Soil Pollutants; D002244:Carbon; D009584:Nitrogen