Influence of Short-term Transfers on Nitrogen Fluxes Printer-friendly Version Interactive Discussion Influence of Short-term Transfers on Nitrogen Fluxes, Budgets and Indirect N 2 O Emissions in Rural Landscapes Influence of Short-term Transfers on Nitrogen Fluxes Printer-friendly Version Interactiv

Biogeosciences Discussions This discussion paper is/has been under review for the journal Biogeosciences (BG). Please refer to the corresponding final paper in BG if available. Abstract Spatial interactions at short-term may lead to large inputs of reactive nitrogen (N r) to oligotrophic ecosystems and induce environmental threats such as additional N 2 O emissions and global warming. The paper presents a new methodology to estimate N r fluxes, especially additional N 2 O emissions, at the landscape scale by taking into 5 account spatial interactions between landscape elements. We used the NitroScape model which integrates processes of N r transformation and short-term transfer in a dynamic and spatially distributed way to simulate N r fluxes and budgets at the landscape scale. Four configurations of NitroScape were implemented by taking into account or not the atmospheric, hydrological or both pathways of N r transfer. We simulated N r 10 fluxes, especially direct and indirect N 2 O emissions, within a test landscape including pig farms, croplands and unmanaged ecosystems. Simulation results showed the ability of NitroScape to simulate patterns of N r losses and recapture for each landscape element and the whole landscape. They made it possible to quantify the contribution of both atmospheric and hydrological transfers in N r fluxes and budgets. Indirect N 2 O 15 emissions were estimated at almost 25 % of the total N 2 O emissions. They varied within the landscape according to land use, meteorological and soil conditions as well as topography. This first attempt has proved that the NitroScape model is a useful tool to estimate the effect of spatial interactions on N r fluxes and budgets as well as indirect N 2 O emissions within landscapes. Our approach needs to be further tested by apply-20 ing NitroScape to several spatial distributions of ecosystems within the landscape and to real and larger landscapes.

atmospheric or hydrological pathways (Galloway et al., 2003).They are estimated around 20 % of the total N 2 O emissions in Europe (IPCC, 2006) and are consecutive to atmospheric deposition of ammonia (NH 3 ) and recapture of nitrates (NO − 3 ).Indirect N 2 O emissions depend on the farming system and the characteristics of the area: variations in meteorological and soil conditions, topography, spatial distribution of N r sources and sinks which are spatially heterogeneous, in intensity and nature, at a scale of several square kilometres (Beaujouan et al., 2001;Dragosits et al., 2002).For instance, atmospheric NH 3 emitted from an animal house or a field can be redeposited to the soil and foliage of nearby ecosystems (Fowler et al., 1998).Similarly, ecosystems at the bottom of slopes can recapture groundwater NO − 3 that originates in N r applied further up the slope in the groundwater.The relevant scale to study indirect N 2 O emissions is therefore an area, namely the landscape, in which interactions occur between ecosystems and farm management, resulting from atmospheric and hydrological transfers which may be large at short-term i.e., distances of several square kilometres to several tens of square kilometres.In rural areas, the landscape may include a river or stream catchment, several livestock buildings, agricultural fields and semi-natural ecosystems such as forests and wetlands (Cellier et al., 2011).Several attempts have been carried out to estimate indirect N 2 O emissions from measurements (e.g., Deurer et al., 2008, Reay et al., 2009) or from the IPCC methodology (IPCC, 2006) based on emission factors (e.g., Mosier et al., 1998;Nevison, 2000;van der Gon and Bleeker, 2005).However, those estimates are highly uncertain and rarely account for both atmospheric and hydrological interactions, as well as farm management.Modelling is helpful to study complex dynamic systems such as landscapes, where spatial interactions occur and direct measurements of N r fluxes are time and cost consuming due to the complexity of the system.Several models have been developed to simulate N r fluxes in rural landscapes.Most of them focused on aquatic ecosystems to describe N r concentrations and fluxes within and at the outlet of a catchment which may correspond to the landscape scale described above (e.g., Beven, 1997;Whitehead et al., 1998;Beaujouan et al., 2002, Vach é andMcDonnell, 2006)  larger i.e., regional scales (e.g., Arnold et al., 1998;Billen and Garnier, 2000).Recent studies have attempted to assess the effect of anthropogenic activities on aquatic and terrestrial ecosystems, especially croplands, by coupling hydrological and crop models (e.g., Beaujouan et al., 2001;Ducharne et al., 2007).Other recent modelling studies have tried to integrate all compartments of a rural landscape but focusing only on one compartment, the others being described with less detail.A few studies focused on anthropogenic transfers within the terrestrial (croplands, grasslands and farm compartments) and aquatic ecosystems (e.g., Hutchings et al., 2004).Other studies focused on atmospheric transfers between terrestrial ecosystems to assess emission, transfer and deposition of NH 3 at the landscape scale (Theobald et al., 2004;Kros et al., 2011) or indirect N 2 O emissions at the regional scale (van der Gon and Bleeker, 2005).However, none of those models dealt with both atmospheric and hydrological N r transfers in a consistent way regarding temporal and spatial scales.The NitroScape model (Duretz et al., 2011) has been therefore developed to integrate processes of N r transfer and transformation with temporal and spatial consistency between various compartments of a rural landscape: the atmosphere, several compartments of the terrestrial ecosystems (livestock buildings, croplands and grasslands) and the aquatic ecosystems (wetlands, streams and groundwater).
In this paper we describe a new approach to estimate direct and indirect N 2 O emissions in relation to spatial interactions by using the NitroScape model.We also estimate the relative contribution of indirect N 2 O emissions to the nitrogen budget of a test landscape and the relative contribution of both atmospheric and hydrological pathways to indirect N 2 O emissions.The test landscape includes livestock buildings, croplands (maize and wheat) and unmanaged ecosystems.Introduction

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Full 2 Materials and methods

The NitroScape model
The NitroScape model integrates in a spatially distributed and dynamic way four types of models representing processes of N r transfers and transformations within the four corresponding compartments of a rural landscape: the atmosphere, the hydrological network, the ecosystems and the farm buildings (Duretz et al., 2011, Fig. 1).For each compartment of NitroScape, models were selected according to their ability to simulate N r processes at the landscape scale and their consistency regarding temporal and spatial scales: the atmospheric model OPS-st (van Jaarsveld et al., 2004) is the short-term version of the OPS model which describes processes of dispersion, transfer and deposition of N r pollutants over a domain where surface characteristics may vary in space.It works at various spatial scales by combining long-term (Lagrangian) and short-term (Gaussian) modelling of pollutant transfer.We used the grid-based version of OPS working at a time step of 12 h (one day-and one night-time calculation per 24 h).OPS-st was validated for NH 3 concentrations simulated on a landscape of 3 km by 3 km (van Pul et al., 2008); the hydrological model TNT (Beaujouan et al., 2002)  the agro-ecosystem model CERES-EGC (Gabrielle et al., 2006) is a processbased model which simulates water, C and N cycles in agro-ecosystems at a daily time step and at the field scale.It models vegetation growth and development, energy balance, evapotranspiration, heat and water transfer in soil above 180 cm.It accounts for mineral and organic N inputs from the farmer and simulates NO − 3 leaching and gaseous emissions of NH 3 , NO x and N 2 O. N r transformation in soil is simulated by using the semi-empirical model NOE (H énault et al., 2005); the farm model FASSET (Berntsen et al., 2003) simulates N r species in a dynamic way and accounts for N r transfer at the farm scale and exchanges with the outside of the landscape.It was adapted by (i) including production of animal manure either in the livestock housing or in the field and manure storage and (ii) removing the ecosystem component of FASSET.The updated version of FASSET, namely FASSET-farm, runs at a daily time step and deals with a range of livestock systems, livestock housing types and manure store types.NH 3 losses from manure in animal housing and manure storage are modelled according to Hutchings et al. (1996).
Since all those processes occur simultaneously, the four models were integrated into a common modelling framework using the PALM dynamic coupler (Buis et al., 2006).They are called modules hereafter.An additional module, namely the linker, was developed and integrated into PALM to specify the exchange of data between the other four modules.It receives and sorts fluxes and enables the calculation of N r budgets.
For simulating the spatial interactions, a raster approach was used in NitroScape, in which the landscape is divided into pixels.TNT and OPS-st, which perform simulations on a grid, were directly integrated in this framework, using a one-to-one relationship between pixels.Individual runs of CERES-EGC and FASSET-farm were performed as many times as there were pixels occupied by an ecosystem or a livestock building.Exchange of data between modules was performed at the pixel scale: each ecosystem pixel receives and sends data which are different from those of its neighbouring pixels.Introduction

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Full The modules of NitroScape exchange data in a dynamic way on a daily time step (i.e., the shortest time-step common to all modules) during the simulation.Each module provides information to the other modules for the next daily time step.

The methodology to estimate indirect emissions
The relative contribution of short-term transfers of N r on N r fluxes and budgets was estimated by implementing four configurations of NitroScape in which atmospheric or hydrological or both pathways of N r transfer were cut or not: the "all transfers" (all) configuration corresponds to the reference configuration in which NH 3 and NO x are emitted, transferred and deposited through the atmospheric pathway, and NO − 3 is transferred through the hydrological pathway including runoff, throughflows and interaction with the groundwater; the "hydrological transfers" (hydro) configuration corresponds to the case in which no atmospheric short-term transfers are calculated.This was implemented by not sending the emissions of NH 3 and NO x from ecosystems and farm buildings to the atmospheric module.NH 3 and NO x transfers and deposition were not taken into account, but daily emissions of those gases were stored to be included in the final budget; the "atmospheric transfers" (atm) configuration corresponds to the case in which no hydrological short-term transfers are calculated.This was implemented by (i) not sending wet deposition and soil NO − 3 concentration to the hydrological module to prevent runoff, exfiltration and leaching and therefore saturated lateral transfers and (iii) not sending groundwater NO − 3 to prevent uptake by ecosystems.Daily NO − 3 leaching was stored to be taken into account in the final budget; the "no short-term transfer" (not) configuration corresponds to the case in which both atmospheric and hydrological transfers were cut in NitroScape.This was implemented by (i) not sending to the atmospheric module the emissions of NH 3 Introduction

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Full The total indirect N 2 O emissions in the all configuration were calculated as: where N 2 O tot,all are the total N 2 O emissions in the all configuration and N 2 O tot,not are the total N 2 O emissions in the not configuration.
The indirect N 2 O emissions due to atmospheric transfers were calculated as: where N 2 O tot,atm are the total N 2 O emissions in the atm configuration.
The indirect N 2 O emissions due to hydrological transfers were calculated as: where N 2 O tot,hydro are the total N 2 O emissions in the hydro configuration.
Indirect emission factors were calculated for croplands, unmanaged ecosystems and for the whole landscape using the following equations derived from Mosier et al. (1998):

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Full where EF 4 is the emission factor due to atmospheric deposition, EF 5g is the emission factor due to hydrological recapture, EF all is the emission factor due to both atmospheric deposition and hydrological recapture, capt NH 3 is the total atmospheric deposition, capt NO 3 is the total NO − 3 recapture by hydrological transfers and capt N is the total N r recapture due to atmospheric deposition and hydrological recapture.

The test landscape
NitroScape was applied to a simplified landscape with a size of 1.75 × 1.75 km 2 corresponding to farm management in intensive rural areas with mixed crops and pig farming (Fig. 2a).From a topographical point of view, the landscape was characterized by a linear slope with a gradient of 50 m between the highest and the lowest parts of the landscape (Fig. 2c).Meteorological data used for the simulation were measured with a meteorological station located on the Kervidy-Naizin catchment (48 • 01 N, 2 • 83 O).This catchment was characterized by humid climatic conditions (total rainfall: 1968 mm, average relative humidity: 90 %) and little temperature contrast (average temperature: 10 • C, standard deviation: 5 • C).The prevailing wind was from the northeast and south-west, with an average speed of about 1.8 m s −1 (Fig. 2b).The soil type was a uniform silt loam soil.and the maximum grid cells needed to observe atmospheric dry deposition.Within that landscape 39 fields of 49 pixels each and one field of 41 pixels were dedicated to maize crop, 39 fields of 49 pixels each and one field of 41 pixels were dedicated to wheat crop, four fields of 245 pixels each were dedicated to unmanaged ecosystems and 16 pixels were dedicated to pig buildings (Fig. 2a).One of the four unmanaged ecosystems (UM 1) was located in the north-west i.e., the highest part of the landscape; another unmanaged ecosystem was located in the centre of the landscape (UM 3), close to one of the livestock building.The other two unmanaged ecosystems were located at the bottom of the landscape: one in the north-east close to the other livestock building (UM 2) and the other in the south-east of the landscape (UM 4) (Fig. 2a).
NitroScape simulations were carried out on a whole year from 1 January to 31 December.

Nitrogen losses, recapture and indirect emissions at the landscape scale
Total NH 3 dry deposition was around 9 kg NH 3 -N ha −1 yr −1 within the whole landscape in the all and atm configurations (Table 1).Two types of N r capture resulting from groundwater interactions with soil were taken into account: (i) capillary rise and (ii) groundwater uprising when the water table rose in soil and brought water and NO Introduction

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Full (Table 1).Atmospheric and hydrological transfers led separately to an additional leaching of 16 kg NO Total NH 3 emissions by the landscape were around 39 kg NH 3 -N ha −1 yr −1 (Table 1) in the four configurations (Table 1).Atmospheric transfers led to additional emissions of 0.7 kg NH 3 -N ha −1 yr −1 .Hydrological transfers did not lead to additional NH 3 emissions.
Taking into account both types of transfer led to additional emissions of 0.5 kg NH 3 -N ha −1 yr −1 .
Total emissions of NO x were around 1 kg N-NO x ha −1 yr −1 in the four configurations (Table 1).There were no NO x emissions due to atmospheric or hydrological or both transfers.
Total N 2 O emissions were around 5 kg N 2 O-N ha −1 yr −1 in the all, atm and hydro configurations.They were around 4 kg N 2 O-N ha −1 yr −1 in the not configuration (Table 1).Atmospheric and hydrological transfers led to additional emissions of respectively 0.7 and 1.1 kg N 2 O-N ha −1 yr −1 .Taking into account both types of transfer led to additional emissions of 1.2 kg N 2 O-N ha −1 yr −1 .

Distribution of soil nitrogen capture and losses within the landscape
Average NH 3 dry deposition on soils was around 9 kg NH 3 -N ha −1 yr −1 , in the all (Fig. 3a) and atm (Fig. 3b) configurations, ranging from 0 to 360 kg NH 3 -N ha −1 yr −1 .The highest NH 3 deposition rates were found close to the farm buildings.The lowest NH 3 deposition rates were found in the north-west and the south-east of the landscape for pixels not located in the lee of the farm buildings.Deposition was zero in the not and hydro configurations.Direct NH 3 emissions by soils were around 6 kg NH 3 -N ha −1 yr −1 in the not configuration, ranging from 0 to 121 kg NH 3 -N ha −1 yr −1 (Fig. 4a).The highest emissions were found for crops in the north-east of the landscape and the lowest NH 3 emissions were found for the unmanaged ecosystems.Average indirect NH 3 emissions resulting

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Full from atmospheric transfers were 0.3 kg NH 3 -N ha −1 yr 1 , ranging from −2 to 108 kg NH 3 -N ha −1 yr −1 (Fig. 4c).Average indirect NH 3 emissions resulting from hydrological transfers were zero, ranging from −7 to 21 kg NH 3 -N ha −1 yr −1 (Fig. 4d).Average indirect NH 3 emissions due to all transfers were 0.3 kg NH 3 -N ha −1 yr −1 , ranging from −14 to 108 kg NH 3 -N ha −1 yr −1 (Fig. 4b).In the four configurations the highest indirect NH 3 emissions were simulated close to the farm buildings located in the north-east of the landscape.(Fig. 5a).Average NO − 3 inputs to soils by capillary rise and groundwater uprising were around 9 kg NO − 3 -N ha −1 yr −1 in the hydro configuration, ranging from 0 to 135 kg NO − 3 -N ha −1 yr −1 (Fig. 5b).The highest values were found for the unmanaged ecosystems in the east of the landscape.
Average NO − 3 losses to the groundwater by leaching were around 59 kg NO −
Average additional losses to the groundwater due to atmospheric transfers were −11 kg NO − 3 -N ha −1 yr −1 , ranging from −55 to 149 kg NO 3 -N ha −1 yr −1 (Fig. 6c).Average additional losses to the groundwater due to hydrological transfers were 23 kg NO −

-N ha
−1 yr −1 , ranging from −25 to 157 kg NO − 3 -N ha −1 yr −1 (Fig. 6d).Average additional losses to the groundwater due to both atmospheric and hydrological transfers were 6 kg NO − 3 -N ha −1 yr −1 , ranging from −50 to 263 kg NO − 3 -N ha −1 yr −1 (Fig. 6b).In the atm configuration the highest additional losses were simulated close to the buildings of farm 2 and for the wheat fields.In the hydro configuration the highest additional transfers were simulated for the wheat fields located in the east of the landscape while the lowest additional emissions were simulated in the unmanaged ecosystems.In the all configuration the highest additional transfers were simulated for the wheat fields located in the east of the landscape.Introduction

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Full Average N 2 O emissions by soils were 5 kg N 2 O-N ha −1 yr −1 in the not configuration, ranging from 0 to 72 kg N 2 O-N ha −1 yr −1 (Fig. 7a).The highest values of N 2 O emissions were simulated for pixels located in the north-east of the landscape which was the lowest part of the landscape.The lowest N 2 O emissions were simulated for the unmanaged ecosystems.Average indirect N 2 O emissions due to all transfers were around 1 kg N 2 O-N ha −1 yr −1 , ranging from −37 to 29 kg N 2 O-N ha −1 yr −1 (Fig. 7b).Average indirect N 2 O emissions due to atmospheric transfers were around zero, ranging from −9 to 17 kg N 2 O-N ha −1 yr −1 (Fig. 7c).Average indirect N 2 O emissions due to hydrological transfers were 1 kg N 2 O-N ha −1 yr −1 , ranging from −37 to 29 kg N 2 O-N ha −1 yr −1 (Fig. 7d).The highest indirect N 2 O emissions were simulated at different locations according to the type of transfer.Indirect emissions due to atmospheric transfers were located close to the farm buildings, especially those of the farm 1, while the highest indirect emissions due to hydrological transfers were located in the maize fields and the unmanaged ecosystems in the north-east of the landscape.The highest indirect emissions due to all transfers were located in the maize fields and the unmanaged ecosystems in the north-east of the landscape.

Indirect N 2 O emission factor
The value of the indirect N 2 O emission factor for the whole landscape was around 8, 9 and 6 % in the atm, hydro and all configurations respectively (Fig. 8).For croplands only, that value was around 10, 9 and 4 % in the atm, hydro and all configurations respectively.For the unmanaged ecosystems only, that value was around 3, 10 and 6 % in the atm, hydro and all configurations respectively.Introduction

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Full NH 3 emissions from soils were 11 % of the N r inputs.This value was lower than the expected value of 37 % of fertilizers applied (ECETOC, 1994).NH 3 emissions varied within the landscape according to the N r input patterns.The highest NH 3 emissions were simulated for crops located in the north-east of the landscape which was the lowest part of the landscape and where soil was highly saturated (not configuration, Fig. 4a).Nitrification was therefore limited, leading to high NH + 4 content (H énault et al., 2005) and therefore high NH 3 emissions (G énermont and Cellier, 1997).The lowest NH 3 emissions were found for the unmanaged ecosystems located in the north-west of the landscape where soil was not saturated.
The highest values of NO − 3 leaching were simulated for the wheat fields located in the west and the centre of the landscape (Fig. 6a, not configuration).The lowest values of NO − 3 leaching were simulated for the unmanaged ecosystems.The leaching rates mainly varied according to the land use and the N r inputs.
The value of the average direct N 2 O emission factor was higher than the expected value of 1 % given by the IPCC methodology (IPCC, 2006).The highest direct N 2 O emissions were simulated for pixels located in the north and the east of the landscape where soil was highly saturated, leading to high denitrification rates (H énault et al., 2005).Direct N 2 O emissions also varied according to the land use and N r inputs, with the highest N 2 O emissions simulated for the wheat fields receiving more N r inputs.

Re-capture
The simulated NH 3 deposition rates (Fig. 3) ranged within the same values as those observed by Fowler et al. (1998), with high deposition rates close to the downwind of the livestock buildings (Loubet et al., 2009).The lowest NH 3 deposition rates were found in the north-west and the south-east of the landscape for pixels located far from livestock buildings and receiving low N r rates from them due to wind direction distribution.Introduction

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1
Introduction Nitrous oxide (N 2 O) is mainly emitted by agricultural soils.Indirect N 2 O emissions may occur far from zones of nitrogen application and result from a cascade of transformations and transfers of reactive species of nitrogen (N r ) through the biogeochemical, Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | represents water and NO − 3 transfer in the hydrological network of a catchment.It accounts for runoff, exfiltration, leaching, deep flows and uptake from deep soils (below 180 cm).It is mainly based on the assumptions of the hydrological model TOPMODEL (Beven, 1997).It is a distributed model that takes into account dual porosity (retention and drainage porosity).Computations are performed at a daily time step, following a mono-directional (a pixel flows into only one pixel) or multi-directional (one pixel can flow into several pixels) scheme.This scheme depends directly on the surface topography and is calculated from a digital elevation model at the beginning of the simulation; Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | and NO x from ecosystems and farm buildings to prevent transfers and deposition, (ii) not sending wet deposition and soil NO − 3 concentration to the hydrological module to prevent runoff, exfiltration, leaching and saturated lateral transfers and (iii) not sending groundwater NO − 3 to prevent uptake by ecosystems.Daily NH 3 and NO x emissions as well as daily NO − 3 leaching were stored to be taken into account in the final budget.
Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Farms were mixed crop-pig farms characterized by indoor pigs(200 sows, 2000 piglets and 2000 baconers).Pig feed was mainly based on imported feed such as wheat, soybean, barley, fishmeal and fat.Baconers were also fed with barley, pea, rye and rapeseed.Croplands cultivated on the farm were wheat and maize (Fig.2a).Wheat received three applications of mineral fertilizer in February (60 kg N r ha −1 ), March (60 kg N r ha −1 ) and April (120 kg N r ha −1 ).Maize received one manure application in March (120 kg N r ha −1 ) and two mineral fertilizer applications in April (60 kg N r ha −1 ).The unmanaged ecosystems received no fertilizer or manure, but only N r deposition.This test landscape was represented by a matrix of 70 × 70 pixels of 25 × 25 m 2 each which corresponded to the minimal scale at which hydrological transfers occur Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper |deposition led to higher soil NO − 3 content leading to higher N 2 O emissions, especially in the north-east of the landscape where conditions of soil saturation were favourable to denitrification.NH 3 deposition in the east of the landscape led to lower N 2 O emissions.That might be explained by the fact that NH 3 deposition led to an increase of NO − 3 uptake by plants.Hydrological transfers and recapture did not lead to additional NH 3 emissions.Hydrological transfers and recapture led to additional NO − 3 losses to the groundwater up to 157 kg NO − 3 -N ha −1 yr −1 .The highest losses were simulated in the east of the landscape where high soil saturation led to high interaction with the groundwater and potentially high dilution by the groundwater.Hydrological transfers and recapture led to additional N 2 O emissions up to 29 kg N 2 O-N ha −1 yr −1 .The highest losses were simulated in the east of the landscape where the highly saturated soil conditions led to high interaction with the groundwater and potentially to high dilution by the groundwater.The highest indirect N 2 O emissions due to hydrological transfers were simulated for the maize fields and the unmanaged ecosystems in the north-east of the landscape.Those fields and ecosystems received higher N r from recapture and were characterized by conditions of soil saturation favourable to denitrification.Negative indirect N 2 O emissions due to hydrological transfers were simulated in the wheat fields located in the north-east of the landscape, affected by dilution in the groundwater leading to NO − 3 losses to the groundwater.The response to N r recapture varied according to the land use.The unmanaged ecosystems had a higher value of the indirect N 2 O emission factor than crops.They emitted more N 2 O than crops for the same recapture of N 2 O.That may be explained by competition for NO − 3 between plant uptake and denitrification with higher NO − 3 uptake by crops than by unmanaged ecosystems.Moreover, the high productivity of crops might be also linked to high water uptake by crops, leading to reducing soil saturation, then reducing denitrification and consequently reducing indirect N 2 O emissions by crops in comparison with unmanaged ecosystems.Another hypothesis to explain patterns of indirect N 2 O emissions is that atmospheric NH 3 deposition is more limiting Discussion Paper | Discussion Paper | Discussion Paper |distributed and dynamic model is emphasized by the high variability of N r losses and gains which were simulated within the landscape, and the effect of landscape topography and short-term processes on N r fluxes.We also showed that N 2 O emissions by unmanaged ecosystems were affected by both atmospheric deposition of NH 3 and hydrological recapture of NO − 3 , which emphasized the need to model dynamically both atmospheric and hydrological transfers of N r .Taking into account both pathways of N r transfers led to simulate high values of indirect N 2 O emissions (almost 25 % of the total N 2 O emissions).Indirect N 2 O emissions were affected by both the position of recapture within the landscape and the land use of receptors.That result indicates that the spatial distribution of ecosystems and especially the ecosystems located in the zones of N r recapture may affect N 2 O emissions.This hypothesis needs to be further tested by applying NitroScape to several spatial distributions of ecosystems within the landscape and to real and larger landscapes.Discussion Paper | Discussion Paper | Discussion Paper |

Figure 4 .
Figure 4. (a) Direct NH3 emissions by soils in the not configuration (kg NH3-N ha -1 yr -1 ).Indirect NH3 emissions in the (b) all, (c) atm and (d) hydro configurations (kg NH3-N ha -1 yr - 1 ).Negative values in (b), (c) and (d) means that NH3 emissions are lower in each of the all, atm and hydro configurations than in the not configuration.

Fig. 4 .
Fig. 4. (a) Direct NH 3 emissions by soils in the not configuration (kg NH 3 -N ha −1 yr −1 ).Indirect NH 3 emissions in the (b) all, (c) atm and (d) hydro configurations (kg NH 3 -N ha −1 yr −1 ).Negative (resp.positive) values in (b), (c) and (d) means that NH 3 emissions are lower (resp.higher) in each of the all, atm and hydro configurations than in the not configuration.

Table 1 .
Nitrogen losses and recapture in the test landscape.