Factors controlling nitrogen leaching from a large central European catchment during 1900–2010.

Jiri Kopacek1, Josef Hejzlar1, Maximilian Posch2
1 Biology Centre AS CR, Institute of Hydrobiology, Na Sádkách 7, 37005 České Budějovice, Czech Republic
2 Coordination Centre for Effects, RIVM, P.O.Box 1, NL-3720 BA Bilthoven, The Netherlands

O 10.3 in Links between the N cycle and other elements

17.07.2014, 12:20-12:40, H20

Nitrogen (N) concentrations and forms have been monitored at outlet from a large heterogeneous catchment (upper Vltava River, Czech Republic, ~13,000 km2) irregularly since the 1900s and regularly in 3‑week intervals since 1959. The catchment reflects the typical development in central and eastern European countries, which witnessed socio-economic shifts from a market to a planned economy in the 1950s and back to a market economy in the 1990s. The first shift was accompanied by an increase in N inputs to agricultural and forest areas of 60–160 and 14–30 kg ha–1 yr–1, respectively, during the 1950s–1980s, and with intensive draining of farmland.1 An intensity of drainage, tilling, and fertilizing increased in parallel until the late 1980s, but have been declining at different rates since the early 1990s as a result of the second economic shift. The associated changes in agricultural practice resulted in and abrupt ~40% reduction of N inputs to farmland, while draining ceased, and the proportion of the drained soils remained stable. In parallel, atmospheric N inputs to forests decreased by ~50% due to decreasing N emissions in the region.2 This large-scale “experiment” enabled (i) comparing responses of forest and agricultural areas to the reduced N inputs and (ii) disentangling of individual effects of N fertilization and drainage on N leaching from agricultural soils.

The terrestrial N export from agricultural land and forests exhibited several similar patterns, being dominated by NO3-N, increasing with N inputs, and having similar inter-annual variability related to hydrology. The N losses from forests were, however, stable (19% of N input on average), while those from agricultural land increased from ~10% in the 1960s up to 32% in the 2000s, due probably to the previous extensive drainage and tillage of waterlogged fields and pastures. These land use changes reduced the water residence time in agricultural land, elevated mineralization of soil organic matter (and organic N), and reduced N immobilization in farmland due to continuously decreasing organic C pools in the drained soils. Modelling of N losses from farmland showed that N leaching was more related to mineralization of soil organic N pools due to drainage and tillage, than to the N input during 1959–2010.3

1. Kopáček J., Hejzlar J., Posch M. 2013. Quantifying nitrogen leaching from diffuse agricultural and forest sources in a large heterogeneous catchment. Biogeochemistry, 115:149–165.
2. Kopáček J., Posch M., Hejzlar J. et al. 2012. An elevation-based regional model for interpolating sulphur and nitrogen deposition. Atmos. Environ. 50: 287–296.
3. Kopáček J., Hejzlar J., Posch M. 2013. Factors controlling the export of nitrogen from agricultural land in a large central European catchment during 1900−2010. Environ. Sci. Technol. 47, 6400−6407.

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last modified 2014-06-19