Nitrogen leaching from natural ecosystems under global change: a
Maarten C. Braakhekke1,2, Karin T. Rebel1, Stefan C. Dekker1, Benjamin Smith3, Arthur H. W. Beusen2,4, and Martin J. Wassen11Copernicus Institute of Sustainable Development, Faculty of Geosciences, Utrecht University, Heidelberglaan 2, 3584 CS, Utrecht, the Netherlands 2PBL Netherlands Environmental Assessment Agency, Postbus 30314, 2500 GH, The Hague, the Netherlands 3Department of Physical Geography and Ecosystem Science, Lund University, 22362, Lund, Sweden 4Department of Earth Sciences, Geochemistry, Faculty of Geosciences, Utrecht University, P.O. Box 80021, 3508 TA, Utrecht, the Netherlands
Received: 10 Jan 2017 – Accepted for review: 13 Mar 2017 – Discussion started: 15 Mar 2017
Abstract. In order to study global nitrogen (N) leaching from natural ecosystems under changing N deposition, climate, and atmospheric CO2, we performed a factorial model experiment for the period 1901–2006 with the N-enabled global terrestrial ecosystem model LPJ-GUESS. In eight global simulations we used either the true transient time series of N deposition, climate, and atmospheric CO2 as input, or kept combinations of these drivers constant at initial values. The results show that N deposition is globally the strongest driver of simulated N leaching, individually causing an increase of 88 % by 1997–2006, relative to pre-industrial conditions. Climate change led globally to a 31 % increase in N leaching, but the size and direction of change varied among global regions: leaching generally increased in regions with high soil organic carbon storage or high initial N status, and decreased in regions with a positive trend in vegetation productivity or decreasing precipitation. Rising atmospheric CO2 generally caused decreased N leaching (33 % globally), with strongest effects in regions with high productivity and N availability. All drivers combined resulted in a rise of N leaching by 73 % with strongest increases in Europe, eastern North America and South-East Asia, where N deposition rates are highest. Decreases in N leaching were predicted for the Amazon and Northern India. We further found that N loss by fire regionally is a large term in the N budget, associated lower N leaching, particularly in semi-arid biomes. Predicted global N leaching from natural lands rose from 13.6 Tg N yr−1 in 1901–1911 to 18.5 Tg N yr−1 in 1997–2006, accounting for land-use changes. Ecosystem N status (quantified as the reduction of vegetation productivity due to N limitation) shows a similar positive temporal trend but large spatial variability. Interestingly this variability is more strongly related to vegetation type than N input. Similarly, the relationship between N status and (relative) N leaching is highly variable due to confounding factors such as soil water fluxes, fire occurrence, and growing season length. Nevertheless, our results suggest that regions with very high N deposition rates are approaching a state of N saturation.
Braakhekke, M. C., Rebel, K. T., Dekker, S. C., Smith, B., Beusen, A. H. W., and Wassen, M. J.: Nitrogen leaching from natural ecosystems under global change: a
modelling study, Earth Syst. Dynam. Discuss., doi:10.5194/esd-2017-7, in review, 2017.