Abstract
European groundwater reservoirs are frequently subject to reactive nitrogen pollution (Nr) owing to the intensive use of nitrogen (N) fertilizer and animal manure in agriculture. Besides its risk on human health, groundwater Nr loading also affects the carbon (C) and N cycle of associated ecosystems. For a temperate grassland in Germany, the long-term (12 years) annual average exports of Nr in form of harvest exceeded Nr inputs via fertilization and deposition by more than 50 kgN ha−1. We hypothesize that the resulting deficit in the N budget of the plant-soil system could be closed by Nr input via the groundwater. To test this hypothesis, the ecosystem model LandscapeDNDC was used to simulate the C and N cycle of the respective grassland under different model setups, i.e., with and without additional Nr inputs via groundwater transport. Simulated plant nitrate uptake compensated the measured N deficit for 2 of 3 plots and lead to substantial improvements regarding the match between simulated and observed plant biomass and CO2 emission. This suggests that the C and N cycle of the investigated grassland were influenced by Nr inputs via groundwater transport. We also found that inputs of nitrate-rich groundwater increased the modelled nitrous oxide (N2O) emissions, while soil water content was not affected.
Highlights
Carbon dioxide (CO2 ) and nitrous oxide (N2 O) are two potent greenhouse gases (GHGs) whose atmospheric concentrations are on the rise involving fundamental adaptations of global biogeochemical
A further consequence of the enhanced use of N fertilizer is that nitrate (NO3 − ) accumulates in the soil and subsequently leaches into groundwater bodies leading to groundwater pollution and eutrophication of nearby surface water bodies
We begin with identification of the most sensitive parameters for each model setup and the that form the basis of the plot-dependent uncertainty ranges of the annual NO3 − uptake and the four intersection sizes for each model setup and plot
Summary
Carbon dioxide (CO2 ) and nitrous oxide (N2 O) are two potent greenhouse gases (GHGs) whose atmospheric concentrations are on the rise involving fundamental adaptations of global biogeochemicalAtmosphere 2018, 9, 407; doi:10.3390/atmos9100407 www.mdpi.com/journal/atmosphereAtmosphere 2018, 9, 407 cycles [1]. In 2011, average atmospheric concentrations of CO2 and N2 O were approx. Agricultural soils are with about 60% the strongest contributors to total anthropogenic N2 O emissions [4]. While N2 O production has always been associated with nitrogen (N) turnover, e.g., nitrification and denitrification, [5] intensification of agriculture during recent decades has considerably increased soil N2 O production and emissions [1]. This is mainly attributable to profuse or improper N fertilizer application for crop yield improvements. Erisman et al [6]
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