Spatial distribution of soils determines export of nitrogen and …pure.au.dk/portal/files/52809829/Wohlfart_2012.pdf · · 2013-02-26tions were measured with a ﬁeld photometer

Biogeosciences 9 4513ndash4525 2012wwwbiogeosciencesnet945132012doi105194bg-9-4513-2012copy Author(s) 2012 CC Attribution 30 License

Biogeosciences

Spatial distribution of soils determines export of nitrogen anddissolved organic carbon from an intensively managed agriculturallandscape

T Wohlfart 1 J-F Exbrayat12 K Schelde3 B Christen3 T Dalgaard3 H-G Frede1 and L Breuer1

1Institute for Landscape Ecology and Resources Management (ILR) Research Centre for BioSystems Land Use andNutrition (IFZ) Justus-Liebig Universitat Gieszligen Germany2Climate Change Research Centre University of New South Wales Sydney New South Wales Australia3Department of Agroecology Aarhus University Denmark

Correspondence toL Breuer (lutzbreuerumweltuni-giessende)

Received 29 March 2012 ndash Published in Biogeosciences Discuss 25 June 2012Revised 28 September 2012 ndash Accepted 22 October 2012 ndash Published 15 November 2012

Abstract The surrounding landscape of a stream has cru-cial impacts on the aquatic environment This study picturesthe hydro-biogeochemical situation of the Tyrebaeligkken creekcatchment in central Jutland Denmark The intensively man-aged agricultural landscape is dominated by rotational crop-lands The small catchment mainly consist of sandy soil typesbesides organic soils along the streams The aim of the studywas to characterise the relative influence of soil type andland use on stream water quality Nine snapshot samplingcampaigns were undertaken during the growing season of2009 Total dissolved nitrogen (TDN) nitrate (NOminus

3 ) am-monium nitrogen and dissolved organic carbon (DOC) con-centrations were measured and dissolved organic nitrogen(DON) was calculated for each grabbed sample Electricalconductivity pH and flow velocity were measured duringsampling Statistical analyses showed significant differencesbetween the northern southern and converged stream partsespecially for NOminus3 concentrations with average values be-tween 14 mg N lminus1 and 96 mg N lminus1 Furthermore through-out the sampling period DON concentrations increased to28 mg N lminus1 in the northern stream contributing up to 81 to TDN Multiple-linear regression analyses performed be-tween chemical data and landscape characteristics showeda significant negative influence of organic soils on instreamN concentrations and corresponding losses in spite of theiroverall minor share of the agricultural land (129 ) Onthe other hand organic soil frequency was positively corre-lated to the corresponding DOC concentrations Croplands

also had a significant influence but with weaker correlationsFor our case study we conclude that the fractions of coarsetextured and organic soils have a major influence on N andDOC export in this intensively used landscape Meanwhilethe contribution of DON to the total N losses was substantial

1 Introduction

Agricultural land use has been found responsible for ma-jor nutrient losses from land to river systems and estuar-ies worldwide (Vitousek et al 1997) Nitrate (NOminus

3 ) is de-scribed as the main source of nitrogen (N) losses from culti-vated land because it is the most important growth regulatingnutrient and is often applied in excess to guarantee optimalcrop yields (van Kessel et al 2009 Martin et al 2004 Ran-dall and Mulla 2001 Ruiz et al 2002a Steenvoorden et al2002) The amount of NOminus3 leaching into water bodies de-pends on dry and wet climatic cycles (Randall 1998) Duringdry periods NOminus3 accumulates in soils before being releasedunder wet conditions even after many years (Randall andMulla 2001) More generally N losses naturally show a largespatial and temporal variability with minimum losses occur-ring in summer as a result of biological uptake (Edwards etal 1985) For example Vagstad et al (2004) described Nlosses ranging from 5 to 75 kg haminus1 yrminus1 in different Balticregions with the highest losses corresponding to cropland onsandy soils Indeed soil physicochemical properties such as

Published by Copernicus Publications on behalf of the European Geosciences Union

4514 T Wohlfart et al Spatial distribution of soils determines export of nitrogen

texture or organic content play an important role on N lossesRecently researchers have put more emphasis on studyingthe contribution of dissolved organic nitrogen (DON) to theN balance of landscapes (Mattson et al 2009 Cooper et al2007 Ghani et al 2007 van Kessel et al 2009 Neff et al2003 2002) Hedin et al (1995) found that organic N repre-sents a large part of the total N losses from forest ecosystemswhich was also described in other studies (van Breemen2002 Cooper et al 2007 van Kessel et al 2009 Neff etal 2003 2002) It was also found that DON can be used asN source by many plant species (Nasholm et al 2009) andtherefore could also play a substantial role in N flows of agri-cultural systems

Cooper et al (2007) pointed out that the release of DON(and DOC) is ldquostrongly influenced by a wide range of hydro-meteorological factorsrdquo As DON includes labile and recal-citrant compounds (Neff et al 2003) and has different reten-tion times in soil and water corresponding losses can sub-stantially vary between different watersheds Therefore thereis a need to better understand the fundamental role of DONin agricultural systems (Ghani et al 2007 van Kessel et al2009) and in the global N cycle (see review by Durand et al2011) including its preferential flow pathways and biologi-cal degradation mechanisms (Perakis 2002)

In this study we focused on the N and carbon (C) fluxesin the Tyrebaeligkken stream (Denmark) and the influence ofland use and soil properties on stream chemistry Agricul-ture represents a large sector of Danish economy due toa suitable climate and relatively good soils Manure is themain fertiliser source for agricultural production (Dalgaardet al 2011b) and represents more than 80 of the N sourcein Danish streams lakes and coastal waters (Kronvang etal 2005 2008 National Environmental Research Institute2006) We investigated the fractions of dissolved inorganicnitrogen (DIN) and DON within total dissolved nitrogen(TDN) concentrations and fluxes in the stream water respec-tively As DON is linked to DOC by often sharing the sameorigin of organic matter DOC values were also studied Themain concern of this investigation concentrated on answeringtwo questions

1 What is the relative influence on stream chemistry ofland use and soil properties

2 How big is the contribution of DON to TDN losses fromagriculture-dominated land

In order to unravel the impact of soil properties and land useon in-stream chemistry measurements of different C and Nsolutes with a high spatial and temporal resolution are re-quired Furthermore to get a general overview on seasonaltrends in effects of nutrient export flushing rainfall eventsneed to be excluded Therefore in our study we performedldquosnapshotrdquo sampling campaigns during stable flow condi-tions (Grayson et al 1997)

2 Materials and methods

21 Study area

The study site is located south of Bjerringbro in centralJutland Denmark Two streams run through the investi-gated area from the east towards north-west (Fig 1 Hutch-ings et al 2004) They converge to form the Tyrebaeligkkenstream that ultimately reaches the Gudena River approxi-mately 3 km downstream of the studied area The total catch-ment area is 8427 ha and outlet coordinates are 5635prime14primeprime Nand 965prime09primeprime E According to the available 2times 2 m DEMdigitised for the NitroEurope project (Dalgaard et al 2012Hansen 2004) elevation ranges from 25 to 58 m asl andtopography is gentle with a mean slope of 37 althoughlocal maximum reaches 214 The mean annual rainfall inthe area is about 712 mm with a corresponding mean evapo-transpiration of 555 mm per year Mean annual temperatureis 77C (PlanteInfo 2011)

As presented in Fig 1 three river parts were analysed thenorthern branch (sampling points 1 to 6) the southern branch(points 11 to 20) and the downstream converged part (points21 to 24) As summarised in Table 1 and depicted in Fig 1land use is dominated by 90 of intensive farming primar-ily arable cropland in rotation (70 ) Pasture is the secondmost frequent land cover (20 ) totally dominating the landuse along the stream (Cellier et al 2011) The average fer-tilisation in the area is 80 kg N haminus1 yrminus1 in the form of live-stock manure (equal amounts of pig and cattle slurry) and74 kg N haminus1 yrminus1 in the form of synthetic fertilisers with amodelled average NOminus3 leaching equal to 58 kg N haminus1 yrminus1

(Dalgaard et al 2011a) correlating to the typical croppingand management practices in this part of Denmark (moraineplateaus with arable land dominated by winter wheat cere-als and with permanent grassland on the lowland organicsoils Dalgaard et al 2012 Holl et al 2002) Accordingto Dalgaard et al (2012) atmospheric N deposition for theBjerringbro area derived from EMEP (2012) was around12 kg haminus1 yrminus1 adding another 8 of total N input whichdoes not significantly change the overall N budget The fourdominant soil textures are coarse sandy clay (27 ) coarseclayey sand (26 ) fine clayey sand (24 ) and 13 withsoil organic matter predominant (Table 1) As illustrated inFig 2 (Dalgaard et al 2002) organic soils are mostly foundnear streams The northern part is dominated by coarse andfine clayey sands whilst coarse sandy clay dominates thesouthern part (Fig 2)

22 Sample collection and analyses

A total of nine snapshot sampling campaigns (Grayson etal 1997) were carried out in 2009 Sampling periods cor-responded to stable flow conditions in April (20th 24thand 27th) August (4th 11th 13th) and September (10th17th and 25th) Twenty different locations at an approximate

Biogeosciences 9 4513ndash4525 2012 wwwbiogeosciencesnet945132012

T Wohlfart et al Spatial distribution of soils determines export of nitrogen 4515

Fig 1 Land use distribution over the Bjerringbro study areawith stream network delineated subcatchments and selected sam-pling site numbers along the stream (digitized for the NitroEuropeproject Dalgaard et al 2012)

spacing of 200 m along the stream were sampled during eachcampaign (Fig 3) Furthermore six drains (T ) that dischargedirectly into the southern stream were analysed as well astwo nearby groundwater wells (GW) (Fig 3) Geographiccoordinates of the sampled waypoints were captured with aglobal positioning system (Garmin eTrex) and imported intoa geographic information system (ArcGIS 93) The 2times 2 mDEM from the Bjerringbro area was used to delineate andcalculate the upstream contributing area corresponding toeach sampled point (Fig 3) The sampling protocol includedmeasuring in-stream flow velocity with an electromagneticflow meter (FloMate 2000 Marsh McBirney Frederick US)and electric conductivity (EC) with a portable instrument(pHcond 340i WTW Weilheim Germany) DischargeQ

[l sminus1] was computed based on stream velocity and the cross-sectional area of the stream bed Triplicates of grabbed wa-ter samples were filled in 100 ml low-density polyethylene-bottles at each waypoint on each sampling day One bottlewas stored cold for immediate analyses whilst two bottleswere frozen for later analyses at the laboratory of the Justus-Liebig-Universitat Gieszligen

Samples were filtered and analysed at Aarhus Univer-sity within 24 h NOminus

3 and ammonium (NH+4 ) concentra-

tions were measured with a field photometer (Spectroquantreg

Multy Merck Darmstadt Germany) and converted to corre-sponding NOminus3 -N and NH+

4 -N concentrations pH was mea-sured with the same portable instrument as EC Samples thatwere stored frozen were later filtered with a 045 microm filter andanalysed for DOC and TDN with a liquiTOC analyser (Ele-mentar Analysensysteme GmbH Hanau Germany) based onhigh temperature oxidation

DON was finally computed as the difference betweenTDN and DIN Because measured NH+

4 concentrations wereoften under the detection limit of 002 mg lminus1 (63 of

Fig 2 Soil type distribution over the Bjerringbro study area withstream network delineated subcatchments and selected samplingsite numbers along the stream (based on the soil type map fromDalgaard et al 2002)

measurements) or just above (lt 005 mg lminus1 in 93 of mea-surements) DIN was assumed to be equivalent to NOminus

3 -Nconcentrations Specific loads [g haminus1 dminus1] of NOminus

3 -N DONand DOC were calculated by multiplying concentrations withdaily specific discharge They refer to yields (loads or themass of nutrient exported) per unit of area and allow com-paring losses from catchments of different size

23 Statistical analysis

To determine significant spatial and temporal differences ofC and N solutes t-tests between different stream sections andsampling periods at a 5 level were carried out Further-more Pearson correlation coefficients were calculated be-tween the three components (NOminus

3 -N DON DOC) for con-centrations and specific loads to check for inter-dependenceof solute dynamics

To investigate the influence of land use and soils on streamchemistry multivariate regression analyses were made withthe ldquobackwardsrdquo method using SPSS 1501 (2006) (Job-son 1991) defining measured stream chemistry at each way-point as dependent variables The independent variables werethe areal fraction of contributing area covered by croplandthe portions covered by coarse clayey sandy soils and por-tion covered and by organic soils two GIS-derived land-scape characteristics (mean slope and mean topographic wet-ness index (TWI) of each sub-basin) and the sampling pe-riod (April August September) TWI (Wilson and Gallant2000) is a measure of topographic control on hydrologicalprocesses that considers the local upslope catchment areaand its slope It was calculated with the spatial analyst tool-box of ArcGIS 93 as TWI = ln(As tanβ) with As beingthe specific catchment area andβ the slope gradient Weonly report coefficient of determinations (R2) and standard-ised beta coefficients as we focus on the relative importance

wwwbiogeosciencesnet945132012 Biogeosciences 9 4513ndash4525 2012


Table 1Upstream area with related land use and soil type in the top layer calculated with ArcGIS Point numbers correspond to Figs 1 2and 3

UpstreamCropland Pasture Forest Wetland

Coarse Coarse FineOrganic

Point area[] [] [] []

clayey sand sandy clay clayey sand[]

[ha] [] [] []

01 1530 720 141 19 01 597 81 186 6406 2271 665 216 13 02 402 55 411 7211 2632 683 200 17 11 359 220 131 27520 5592 723 195 10 06 228 366 125 15921 8090 709 197 10 04 270 282 217 13024 8427 700 203 13 04 260 274 239 129

Fig 3 Elevation model (2times 2 m based on the airborne laser-scanning by Hansen 2004) with locations of sampling points alongthe three stream sections with corresponding subcatchments Nu-meric labels indicate the number of the sampling point

of independent variables rather than predicting dependentvariables To exclude multicollinearity and autocorrelationof residuals both tolerance and Durbin-Watson coefficientswere checked Multicollinearity can be expected with a tol-erance value smaller than 01 (Jobson 1991) None of theregression coefficients had tolerance values below this levelFor the Durbin-Watson coefficient values below 1 or above3 point to strong autocorrelation Durbin-Watson coefficientsof all regression analyses varied between 1 and 15 indi-cating a moderate positive autocorrelation of residuals Thisis often observed when time series are analysed In partic-ular snapshot sampling is very sensitive to autocorrelationas waypoints are located in vicinity to each other and con-centrations measured upstream are likely to impact condi-tions downstream However as we used the regression analy-ses for identifying relevant independent variables rather thanpredicting dependent variables we assume to observe the ba-sic conditions of regression analyses

3 Results

Precipitation during the sampling period varied within thespan of long-term trends Whilst April was substantially drierthan usual with only 11 mm (minus71 ) precipitation instead ofa long-term monthly mean of 38 mm July and August sawmore rainfall than usual with 90 mm (+40 ) and 82 mm(+28 ) respectively in relation to a mean of 64 mm forboth months September was drier than usual with 45 mm(minus33 ) instead of its monthly mean of 67 mm

Measured EC and pH are presented in Table 2 Mean ECranged from 351 to 418 microS cmminus1 and mean pH values from72 to 77 in accordance with typically observed values inDanish streams (National Environmental Research Institute2006)

Discharge of up to 100 l sminus1 in the northern stream waslow in comparison to the southern branch The dischargefrom the source of the southern stream towards the catchmentoutlet (including the converged part) increased from 21 l sminus1

to 254 l sminus1 for the southern stream part and from 168 l sminus1

to 376 l sminus1 for the converged part Mean runoff during thesampling period is given in Table 2 for all three stream sec-tions

As shown in Fig 4a NOminus3 -N concentrations ranged from04 to 113 mg N lminus1 for all three stream sections MeanwhileDON concentrations (Fig 4c) showed the highest values inthe northern stream betweenlt 001 and 43 mg N lminus1 On thecontrary DOC concentrations (Fig 4e) were lowest in thenorthern part with concentrations from 59 to 115 mg C lminus1

Figure 4b d and f show the corresponding loads of thethree stream solutes The northern branch detected highestloads of NOminus

3 -N with up to 485 g N haminus1 dminus1 as well as high-est DON loads of up to 160 g N haminus1 dminus1 Along with ob-served DOC concentrations loads were higher in the south-ern stream with up to 591 g C haminus1 dminus1

Distinct differences in concentrations between stream sec-tions could be observed from the measurements As shown inFig 4a the northern part always showed significantly higherNOminus

3 -N concentrations than the other streams Furthermorethe same stream section also depicted higher DON concen-trations than the two other ones in August and September



Table 2 Mean values of pH EC and discharge (Q) for April August and September for the northern stream southern stream and afterconvergence

pH [ndash] EC [micro S cmminus1] Q [l sminus1]

April August September April August September April August September

Northern part 74ax 72ax 73ax 351ax 407bx 405bx 58ax 60ax 53ax

Southern part 75ax 74by 74abx 402ay 418ax 405by 147ay 100by 107aby

Converged part 77ay 76az 76by 367axy 409ax 413bz 319az 209bz 265cz

abc indicate significant differences between April August and September measurementsxyz indicate significant differences between northern part southern part andconverged part

Regarding DOC concentrations significantly higher val-ues were measured in the southern stream for all threemonths In the northern stream the high NOminus

3 -N concen-trations remained stable throughout the complete samplingperiod whereas DON concentrations increased significantlybetween April and September (Fig 4c) Similarly DOC con-centrations were significantly lower in April than in Augustand September

Considering losses DON loads were significantly lowerin April than in August and September whereas NOminus

3 -N andDOC loads remained stable in the northern part over the ob-servation periods

In the southern stream section the NOminus

3 -N concentra-tions were significantly higher in April in comparison to thelatter sampling periods DON concentrations and losses inthis stream section increased significantly between April andthe end of summer DOC concentrations were significantlyhigher in September than in April and August FurthermoreNOminus

3 -N loads were significantly higher in April than in Au-gust and September Significant differences in DOC loadswere found for all three months in the southern part

The converged stream part showed significantly risingNOminus

3 -N loads from August to September Furthermore DOCloads declined significantly from April to August whereasno significant differences were found between August andSeptember All measured concentrations and DON loadsshowed no significant differences between the three samplingperiods

The drains sampled were all located in the southern sub-catchment as in the northern sections no such drains couldbe found NOminus3 -N concentrations in April (sim 2 mg N lminus1)

were higher than in August (sim 05 mg N lminus1) and declinedin September to concentrations around 15 mg N lminus1 (Fig 6)Groundwater well concentrations were in the range of drainsMeanwhile DON and DOC showed neither significant tem-poral nor spatial differences throughout the sampling peri-ods apart from single drains peaking in concentration duringthe third snapshot sampling in April and the first one in Au-gust Multivariate regression analyses demonstrated a signif-icant influence of organic and sandy soils on stream chem-istry NOminus

3 -N concentrations and loads are negatively corre-lated with the occurrence of organic soils while sandy soils

Fig 4Boxplots of measured NOminus3 -N (a andb) DON (c andd) andDOC (e andf) concentrations and loads for the northern southernand converged part Each group of three boxes corresponds to val-ues measured in April August and September respectively Mark-ers indicate quartiles In cases where most of the measured valueswere under detection limits remaining single values are shown withcrosses Letters a b and c above markers indicate significant differ-ences between the mean values of April August and Septemberwhereas letters x y and z denote significant differences betweenthe three stream branches referring to one sampling period Coloursindicate the compared groups of either date or stream section

showed positive correlations indicated by standardized betacoefficients ofminus055 andminus057 for organic soils and 048and 045 for coarse clayey sand respectively (Table 3) ForDON we found positive correlations with both the samplingdate and the portion of contributing area covered by sandysoils The sampling period had the most significant influenceon DON concentrations and loads with beta coefficients of047 and 038 respectively DOC concentrations showed apositive correlation with organic soils while DOC loads pos-itively correlated with arable cropland The distribution oforganic soils seemed to have the most important influence onDOC concentrations as illustrated by a high beta coefficientof 070 The two topographical indicators (mean TWI andmean slope) had the lowest beta values probably due to theuniformly gentle topography



Table 3CorrectedR2 and standardized beta coefficients of multivariate regression analyses (ns = not significant TWI = topographic wet-ness index)

R2 SoilSoil Land use

Samplingcorrected (Organic)

(Coarse (Arable Dischargeperiod

Slope TWIclayey sand) Cropland)

NOminus

3 -N 098 minus055 048 minus018 minus007 minus005 ns minus002[mg N lminus1]DON 047 minus024 025 minus017 ns 047 ns ns[mg N lminus1]DOC 068 070 ns ns 029 017minus028 ns[mg N lminus1]NOminus

3 -N 087 minus057 045 ns ns minus022 015 minus008[g N haminus1 dminus1]DON 042 minus025 037 ns ns 038 ns ns[g N haminus1 dminus1]DOC 025 ns minus018 036 ns minus018 ns ns[g N haminus1 dminus1]

Furthermore correlation coefficients were calculated forconcentrations and loads to determine relations between thethree solutes We found NOminus3 -N and DON to exhibit a rel-ative strong correlation with respect to concentrations andloads with coefficients of 047 and 057 respectively On theother hand DON and DOC were poorly correlated with cor-responding coefficients ofminus017 and 006 for concentrationsand loads respectively Whilst concentrations of DOC andNOminus

3 -N depicted the highest correlation ofminus076 this rela-tion was not evident for loads (minus005)

4 Discussion

41 Nitrate

In the Danish stream Tyrebaeligkken water analyses showed aquite heterogeneous distribution of NOminus

3 -N concentrationsand fluxes between the three stream sections In the northernpart they were significantly higher than in the southern parteven though the land use distribution according to Table 1apparently did not vary much On average NOminus

3 -N concen-trations measured in the southern part represented about 15 of the concentrations measured on the same day in the north-ern part However as mentioned in Sect 21 detailed infor-mation about site-specific management practices (Dalgaardet al 2012 Cellier et al 2011) showed relatively larger ar-eas with extensive grazing (and thereby lower N fertiliser andmanure input) in the northern part which also included morewet meadows compared to the more steep terrain along thesouthern stream branch Despite this higher NOminus

3 -N concen-trations were exhibited in the northern branch during summer2009 As pointed out in many studies (Bohlke and Denver1995 Ruiz et al 2002a Worrall and Burt 2001) soils areable to store N leading to poor correlations between N losses

from agricultural soils and headwater quality ConsequentlyN leaching is affected by past land use and management prac-tices (Hansen et al 2011 2012) which varied a lot in thisarea during the past 300 yr (Caspersen and Fritzboslashger 2002)but a further study of this aspect was out the scope of thepresent study Furthermore the NOminus

3 stored in soils can bereleased into sub-surface and groundwater after some timeNutrients are mobilised by mineralisation processes duringthe growing season when high rates of microbial activity areobserved (Bohlke and Denver 1995 Bohlke 2002 Schn-abel et al 1993) NOminus3 leached to shallow groundwater maybe steadily released through time periods of a year or more(Martin et al 2004 Molenat et al 2002 Ruiz et al 2002b)As shown by Schiff et al (2002) NOminus3 concentrations can betraced back to groundwater charges and might give a correctbasis to explain the almost constant NOminus

3 -N concentrationsmeasured at sampling point 1 over the whole sampling pe-riod

Meanwhile C concentrations measured in the southernpart were significantly lower in August and September thanin April This was also seen in the concentrations of thedrainage outlets found in the southern subcatchment Thelack of rainfall in April may have led to a concentrationeffect (Poor and McDonnell 2007) as concentrations mea-sured during wetter periods of August and September werealmost two times lower (Fig 4) In the described study areaSchelde et al (2012) measured nitrous oxide (N2O) emis-sions during the study period 2007 to 2009 N2O emissionswere found to be higher during periods with moist soil sug-gesting higher denitrification rates and therefore lower inputrates of NOminus

3 with the water draining through soil and intostream water An intensive field campaign was carried out inApril 2009 when N2O emissions were found to be relativelylow due to dry weather conditions (Schelde et al 2012)



leading to the assumption that denitrification rates were lowin April Low denitrification rates in spring 2009 might ex-plain higher NOminus3 concentrations in the southern stream dur-ing August and September 2009 Nevertheless along withthe general shallow groundwater table depth of 04 m ob-served by Schelde et al (2012) denitrification is likely toplay a dominating factor for N losses in the area

Regression analyses showed that NOminus

3 -N concentrationsand loads significantly depended on soil properties Organicsoils in the upstream area obtained beta coefficients ofminus055for all three months despite their low proportion of the studyarea As summarized in Table 1 there are more organic soilsin the contributing area of the southern catchment than inthe northern catchment These soil properties imply a partialimmobilization of NOminus

3 (Randall and Mulla 2001 Schiff etal 2002) and therefore lower concentrations in stream wa-ter In the same area with organic soils along the southernbranch Schelde et al (2012) observed that ammonia wasmore abundant than NOminus3 in the organic soils and they foundemissions of nitrous oxide to be relatively low at the riparianorganic soils On the other hand high positive correlations(087) between NOminus3 -N concentrations and soil propertieswere observed for coarse clayey sand that is predominant inthe northern branch contributing area The sandy nature im-plies a faster drainage of water and nutrients through the soiland a better aeration that favours mineralization and slowsdown denitrification (Scheffer and Schachtschabel 2002)Therefore and in correspondence with earlier Danish stud-ies (Kronvang et al 2008 Hansen et al 2012) sandy soilsmay be the explanation for the higher NOminus

3 concentrations inthe northern stream water

According to the statistical analyses arable cropland (ieexcl grasslands) had a low influence (beta =minus019) on NOminus

3 -N concentrations and loads There was a very similar distri-bution of land use over the respective contributing areas ofthe different sampled points This might be the reason whyregression analyses did not assign a higher influence to crop-land Usually rivers that flow through agricultural land trans-port much greater NOminus3 loads in comparison to rivers flowingthrough forested land (Randall and Mulla 2001) This con-tributes to the idea that agricultural practices have the great-est impact on NOminus3 losses However according to Keeneyand DeLuca (1993) the fertilizer N addition is not the impor-tant N contributor to streams The major part of NOminus

3 sup-plies rather arises from agricultural practices that enhancedmineralization leading to soluble N that can be rapidly trans-ported to the aquatic environment through tile drains Thesepractices lead to higher losses of NOminus

3 in agricultural dom-inated areas Maybe the higher NOminus

3 concentrations in thenorthern part can be explained by tile drains from the moreflat and thereby larger areas of drained agricultural uplandsin this area as compared to the southern part but this couldnot be confirmed by the present study A more elaborateddiscussion of the hydrology in the area can be found in Dahl

et al (2004) who also discuss the potential effect of cleangroundwater from buried valleys which may affect the NOminus

3concentration in the stream but no systematic difference be-tween the northern and the southern branch of Tyrebaeligkkenwas found Furthermore according to Randall (1998) NOminus

3losses are also greatly affected by dry and wet climatic cy-cles This might explain the low influence of land use and thehigher influence of soil properties on NOminus

3 concentrations inour study

42 Dissolved organic nitrogen (DON)

DON was found to be an important part of dissolved Nlosses from soils with concentrations as well as loads in-creasing through the sampling period Statistical analyses de-rived significant differences between the northern and south-ern stream part for August and September (Fig 4) Multiplestudies have shown that DON accounts for a significant frac-tion of N losses to streams of pristine or forested catchments(Campbell et al 2000 Hedin et al 1995 Lajtha et al 1995Neff et al 2003) Mean April concentrations for the north-ern and southern stream part were 01 mg lminus1 with 85 ofthem being less than 001 mg lminus1 (Fig 4) As DON drainsthrough soils the duration and amount of drainage water areimportant factors and DON losses depend on rainfall events(Hedin et al 1995) Even if there is much DON found in thesoil the driving factor that transports the nutrient to surfacewater may be missing (Hedin et al 1995 van Kessel et al2009) The total precipitation in the Bjerringbro area in Aprilwas very low which may explain the low DON values duringthis period

In the review of van Kessel et al (2009) it was found thatthe average loss of DON in diverse agricultural systems withmostly light textured soils accounts for 26 of total solubleN (mostly NOminus

3 and DON) We found average contributionsof 12 to 412 in the various study periods and an overallaverage of 17 of DON to TDN throughout the entire study(Fig 5) This is somewhat lower than the typical contribu-tion of DON to TDN in more pristine freshwater ecosystems(Willett et al 2004) Goodale et al (2000) found an aver-age of 54 of DON in total N exports in forested landscapeswith corresponding mean DON losses of 07 kg haminus1 yrminus1Willett et al (2004) described a contribution of 40plusmn 2 ofDON to total N in soil solution of Histosols and Spodosolsnotably under grazed grassland and forested land in Walesand Scotland Besides Mattsson et al (2009) found an aver-aging proportion of organic N of 21 in Danish catchmentsthat were dominated by agricultural land The study pointsout a mean DON concentration of 11 mg N lminus1 Siemensand Kaupenjohann (2002) described median DON concen-trations of 04 to 23 mg N lminus1 for leaching losses of an agri-cultural site in northwestern Germany and concluded thatDON contributes significantly to N losses from agriculturalsoils Considering these findings together with our resultswe conclude that DON can contribute substantially to the



Fig 5 Contribution () of DON (dark grey) and DIN (light grey)to total dissolved nitrogen losses for every stream section and everysampling period

total N budget even under highly intensive land use systemssuch as those of the Bjerringbro landscape

DON exports in our study ranged fromlt 001 g haminus1 dminus1

to 160 g haminus1 dminus1 and were mostly in the range of observedvalues reported in other studies However little is known onthe role of DON in the N cycle in agricultural soils (Murphyet al 2000) and flow path dynamics (Willett et al 2004)Therefore the connection between the organic N pool in soiland the in-stream DON export is not well understood Gener-ally DON does not vary as much as inorganic N with biolog-ical activity soil fertility or season Campbell et al (2000)and Goodale et al (2000) found that DON actually variedlittle throughout a year This statement is not compatiblewith the increasing values from April to September that weobserved In fact multivariate regression analyses pointedout that sampling time had the highest influence on DONconcentrations and loads Corresponding beta coefficients of051 for DON concentrations and 055 for loads reflect theincreasing values described above Neff et al (2002) pointedout that DON can enter ecosystems through precipitationDifferent forms of DON are found in the atmosphere andhave the potential to be washed out and flushed into soilsand water Dust might also play an important role as wellas components emitted from surrounding agricultural fields(Neff et al 2002) Wet N deposition can contain between25 and 50 of DON but direct inputs to freshwater ecosys-tems are very low (Antia et al 1991 McHale et al 2000)Neff et al (2002) also observed that the organic componentsof N found in rain are often labile fractions and very reac-tive Due to quick transformations the reactive N compo-nents in the atmosphere might therefore be more importantfor local emissions (Neff et al 2002) and hence contribute

Fig 6 Measured NO3-N DON and DOC concentrations [mg lminus1]analysed in drains (T ) and groundwater wells (GW) during the ninesnap shot samplings The given numbers of the drains refer to theprevious in-stream sampling point letters indicate the position ofeach drain between two points (A first B second C third)

less to freshwater It is difficult to estimate to what extentthese components contribute to surface water input but theyshould not be forgotten as a possible path for DON Thatis why the ongoing rainfall in July (897 mm) and August(818 mm) might have an influence on the DON concentra-tions and fluxes at our landscape The significant contrast tothe drier month of April also highlights the importance of thesampling period and heterogeneities in weather conditionsin the regression

Regression analyses showed a significant influence ofcoarse clayey sand on DON concentrations and loads In gen-eral DON can be affected by biotic factors like the pro-duction of organic matter and abiotic factors like soil tex-ture that is responsible for sorption of organic components(Neff et al 2000) On the other hand DON losses did notseem to be strongly linked to traditional biotic mechanismsas described for inorganic N (Campbell et al 2000 Hedinet al 1995 Willett et al 2004) Beta coefficients of 039and 024 for concentrations and loads respectively may give



an idea about the influence of soil texture on DON lossesinto streams As shown in Fig 4 DON and NOminus

3 -N concen-trations and loads were higher in the sand-dominated north-ern stream part consistent with previous studies (Neff et al2003) For DON concentrations similarly to NOminus

3 -N regres-sion analyses assigned negative beta coefficient values forland use (minus017) and organic soils (minus024) Moreover corre-lations between NOminus3 -N and DON concentrations and loadslink the behaviour of the two studied N components

43 Dissolved organic carbon (DOC)

Similarly to the other chemical species studied measuredDOC concentrations and corresponding loads were signifi-cantly different between the stream sections In contrast toNOminus

3 concentrations DOC values were lower in the northernstream section Concentrations increased from April to Au-gust in the northern stream section whereas values rose sig-nificantly in September in the southern one (Fig 4) Theseobservations suggest an increasing trend during the growingseason which was also observed by Dawson et al (2002)and Aitkenhead et al (1999) These studies reported in-creasing concentrations in Scottish landscapes from June toNovember and from May to June respectively The earlyautumn is considered to be the time of maximum DOC ex-port (Cooper et al 2007 Grieve 1984 Worrall et al 2004)The rising trend can result from increasing soil temperatureand moisture which are driving factors for decompositionMoore (2003) measured DOC concentrations ranging from10 to 30 mg C lminus1 in a boreal landscape with generally in-creasing values throughout summer Sand-Jensen and Ped-ersen (2005) reported DOC concentrations between 47 and183 mg C lminus1 in northern Zealand Denmark for differentsites (agriculture forest urban) Mattson et al (2009) founda mean DOC concentration of 72 mg lminus1 while considering10 Danish streams throughout a year Generally the concen-trations measured in our study were consistent with theseprevious results

Due to the same organic matter origin and similar organiccomponents DON is often closely linked to the C cycle(Campbell et al 2000 Cooper et al 2007 Ghani et al2007 Goodale et al 2000 van Kessel et al 2009 Wil-lett et al 2004) Accordingly it is assumed that DON andDOC should be equally influenced by soil type or land useHowever we hardly saw any correlations between DOC andDON Organic soil occurrence explained only little of ob-served DON concentrations and loads (Table 3) whereas ahighly significant influence of organic soils on DOC concen-trations was found The dependency of DOC concentrationson organic soils has been already described by Aitkenheadet al (1999) Accordingly Dawson et al (2008) concludedthat the export rate of DOC depends on the carbon soil pooland therefore the organic fraction They suggested the pos-sibility of assessing mean stream water concentrations fromC pools in soils Organic soils contain a high proportion of

degradable organic matter that can be eventually released bydifferent physicochemical processes into streams (Kennedyet al 1996) These observations coincide with the results ofour study where we find a higher proportion of organic soilsin the southern stream part along with higher DOC concen-trations and loads

Results indicated a significant influence of discharge onDOC concentrations shown also in many other studies(Cooper et al 2007 Grieve 1994 Hope et al 1994 Worrallet al 2002) Cooper et al (2007) and Worrall et al (2002)described the importance of the amount of water flowingthrough soils and its transit time for flushing C out of soilsSoil properties can reduce the dissolution of C into surfacewaters through sorption on the one hand (Aitkenhead et al1999 Cooper et al 2007 Kennedy et al 1996) but a fasterdrainage might limit the ability for adsorption on the otherRewetting through rain and storm events seems to play animportant role on the release of carbon During these eventsquick discharge components such as surface and sub-surfacerunoff rapidly transport C laterally reducing time for micro-biological degradation in the upper soil horizons (Cooper etal 2007) and releasing dissolved organic matter into streamwater We assume that the water input by precipitation thatinfluences the in-stream runoff is a driving factor for DOCexports to stream thus explaining the observed correlationbetween DOC and discharge Nevertheless one has to care-fully consider the discharge data obtained with the handheldflow meter and the uncertainty introduced by the evaluationof the cross-section in the transformation of velocity data tovolumes

Interestingly organic soils have opposite influences on in-stream concentrations of DOC and DON With concentra-tions higher in the southern than in the northern stream DOCconcentrations are positively correlated with the percentagearea corresponding to organic soils Conversely organic soilshave a negative effect on DON concentrations as a result ofmore adsorption or faster degradation Actually adsorptionof dissolved organic matter depends on molecular weightacidic group and aromatic structure (Kaiser and Zech 2000)The adsorption of DOC and DON also depends on their re-spective concentrations in the draining water (Lilienfein etal 2004) According to Lilienfein et al (2004) at low initialconcentrations in soil solution the soil releases potentiallymore dissolved organic matter (DOM) than at higher concen-trations for which it is more likely to retain these substancesMeanwhile Lilienfein et al (2004) also state that adsorptionmechanisms of both species are controlled by similar fac-tors Nevertheless in other studies that compare the behaviourof these two DOM components conclusions are drawn thatthe tendencies for adsorption and degradation probably dif-fer between DOC and DON (Michalzik and Matzner 1999Kalbitz et al 2000) It is worth noting that DON has differ-ent characteristics in these controlled laboratory experimentsthan in field studies (Michalzik and Matzner 1999) Boththese previous studies and our current results may indicate



the existence of at least two different pools of organic matterwith heterogeneous composition in the organic soils How-ever this would require further field investigations to be con-firmed or refuted

5 Conclusions

In spite of the homogeneous distribution of cropland in thearea C and N concentrations and loads were significantlydifferent between the different sampled stream parts We sug-gest that differences in soil properties are the strongest factorexplaining this heterogeneity As shown by the multiple re-gression analyses the distribution of organic soils seemed tohave high impact on stream chemistry especially for DOCexports Furthermore dominating sandy soils in the northernpart involved a better drainage leading to higher losses of Ncomponents than in the southern part notably for DON Theland use distribution also had a significant influence on in-stream chemistry but to a weaker extent Additionally DONcontributed up to 81 to the TDN losses during the wetterperiods of August and September and might therefore play animportant role in the N budget in intensively managed agri-cultural landscapes Meanwhile the little knowledge on therole of DON in the N cycle in agricultural soils and flow pathdynamics hampers our efforts to connect observed streamwater chemistry with agricultural practices and soil proper-ties and there is a clear need to investigate these aspects infurther studies Some discussion points that could not be an-swered at the time the study was conducted remain Samplingefforts were mostly undertaken in the frame of a punctualfield work campaign and we acknowledged that they mightnot provide a definitive view of in-stream nutrient dynamics

AcknowledgementsThe authors would like to thank the Ni-troEurope IP for providing financial support We would like tothank further the University of Aarhus for providing laboratoriesand working instrumentation and the possibility of working inthe study area of Bjerringbro Further the Viborg Kommune forproviding datasets and landowners for allowing us to work on theirland Finally we thank all the involved people for helping withanalyses laboratory instrumentation and data preparation at AarhusUniversity (AU-Foulum) and the Institute for Landscape Ecologyand Resources Management (ILR) Justus-Liebig-UniversitatGieszligen

Edited by U Skiba

References

Aitkenhead J A Hope D and Billett M F The relationshipbetween dissolved organic carbon in stream water and soil or-ganic carbon pools at different spatial scales Hydrol Process13 1289ndash1302 1999

Antia N J Harrison P J and Oliveira L The role of dis-solved organic nitrogen in phytoplankton nutrition cell biologyand ecology Phycologia 30 1ndash89doi102216i0031-8884-30-1-11 1991

Bohlke J-K Groundwater recharge and agricultural contamina-tion Hydrogeol J 10 153ndash179doi101007s10040-001-0183-3 2002

Bohlke J K and Denver J M Combined Use of GroundwaterDating Chemical and Isotopic Analyses to Resolve the Historyand Fate of Nitrate Contamination in Two Agricultural Water-sheds Atlantic Coastal Plain Maryland Water Resour Res 312319ndash2339doi10102995WR01584 1995

Campbell J L Hornbeck J W McDowell W H Buso D CShanley J B and Likens G E Dissolved organic nitrogen bud-gets for upland forested ecosystems in New England Biogeo-chemistry 49 123ndash142 2000

Caspersen O and Fritzboslashger B Long-term landscape dynamics ndasha 300 years case study from Denmark Danish Journal of Geog-raphy 3 13ndash26 2002

Cellier P Durand P Hutchings N Dragosits U Theobald MDrouet J L Oenema O Bleeker A Breuer L Dalgaard TDuretz S Kros H Loubet B Olesen J E Merot P Vi-aud V de Vries W and Sutton M A Nitrogen flows andfate in rural landscapes in The European Nitrogen AssessmentSources Effects and Policy Perspectives edited by Sutton MA Howard C M Erisman J W Billen G Bleeker A Gren-nfelt P van Griensven H Grizzetti B Cambridge CambridgeUniversity Press 229ndash248 2011

Cooper R Thoss V and Watson H Factors influencing the re-lease of dissolved organic carbon and dissolved forms of nitro-gen from a small upland headwater during autumn runoff eventsHydrol Process 21 622ndash633doi101002hyp6261 2007

Dahl M Rasmussen P Joslashrgensen L F Erntsen V Platen-Hallermund F and Pedersen S S The effect of alternativeland use on nitrate content in groundwater and surface watersndash illustrated by scenario studies DJF report no 110 (Markbrug)Foulum Denmark 59ndash70 2004

Dalgaard T Rygnestad H Jensen J D and Larsen P E Meth-ods to map and simulate agricultural activity at the landscapescale Danish Journal of Geography 3 29ndash39 2002

Dalgaard T Hutchings N Dragosits U Olesen J E KjeldsenC Drouet J L and Cellier P Effects of farm heterogeneityand methods for upscaling on modelled nitrogen losses in agri-cultural landscapes Environ Poll 159 3183ndash3192 2011a

Dalgaard T Olesen J E Petersen S O Petersen B MJoslashrgensen U Kristensen T Hutchings N Gyldenkaeligrne Sand Hermansen J E Developments in greenhouse gas emis-sions and net energy use in Danish agriculture ndash How to achievesubstantial CO2 reductions Environ Poll 159 3193ndash32032011b

Dalgaard T Bienkowski J F Bleeker A Drouet J L DurandP Dragosits U Frumau A Hutchings N J Kedziora AMagliulo V Olesen J E Theobald M R Maury O Akkal



N and Cellier P Farm nitrogen balances in six European agri-cultural landscapes ndash a method for farming system assessmentemission hotspot identification and mitigation measure evalua-tion Biogeosciences Discuss 9 8859ndash8904doi105194bgd-9-8859-2012 2012

Dawson J J C Billett M F Neal C and Hill S A compar-ison of particulate dissolved and gaseous carbon in two con-trasting upland streams in the UK J Hydrol 257 226ndash246doi101016S0022-1694(01)00545-5 2002

Dawson J J C Soulsby C Tetzlaff D Hrachowitz M DunnS M and Malcolm I A Influence of hydrology and season-ality on DOC exports from three contrasting upland catchmentsBiogeochemistry 90 93ndash113doi101007s10533-008-9234-32008

Durand P Breuer L Johnes P J Billen G Butturini A PinayG van Grinsven H Garnier J Rivett M Reay D S CurtisC Siemens J Maberly S Kaste O Humborg C Loeb Rde Klein J Hejzlar J Skoulikidis N Kortelainen P LepistoA and Wright R Nitrogen processes in aquatic ecosystems inThe European Nitrogen Assessment Sources Effects and PolicyPerspectives edited by Sutton M A Howard C M ErismanJ W Billen G Bleeker A Grennfelt P van Griensven Hand Grizzetti B Cambridge Cambridge University Press 124ndash146 2011

Edwards A C Creasey J and Cresser M S Factors in-fluencing nitrogen inputs and outputs in two Scottish uplandcatchments Soil Use Manage 1 83ndash88doi101111j1475-27431985tb00664x 1985

EMEP status report 12012 ldquoTransboundary acidification eutroph-ication and ground level ozone in Europe in 2010rdquo Joint MSC-W amp CCC amp CEIP Report ISSN 1504-6192 181 pp avail-able at httpemepintpublreports2012statusreport1 2012pdf last access 12 November 2012

Ghani A Dexter M Carran R A and Theobald P WDissolved organic nitrogen and carbon in pastoral soils theNew Zealand experience European J Soil Sci 58 832ndash843doi101111j1365-2389200600873x 2007

Goodale C L Aber J D and McDowell W H The long-termeffects of disturbance on organic and inorganic nitrogen export inthe White Mountains New Hampshire Ecosystems 3 433ndash4502000

Grayson R B Gippel C J Finlayson B L and Hart B TCatchment-wide impacts on water quality the use of ldquosnap-shotrdquo sampling during stable flow J Hydrol 199 121ndash134doi101016S0022-1694(96)03275-1 1997

Grieve I C Concentrations and annual loading of dissolved or-ganic matter in a small moorland stream Freshwater Biol 14533ndash537doi101111j1365-24271984tb00173x 1984

Grieve I C Dissolved organic carbon dynamics in two streamsdraining forested catchments at Loch ard Scotland Hydrol Pro-cess 8 457ndash464doi101002hyp3360080508 1994

Hansen B Thorling L Dalgaard T and Erlandsen M Trend re-versal of nitrate in Danish groundwater ndash a reflection of agricul-tural practices and nitrogen surpluses since 1950 Environ SciTechnol 45 228ndash234 2011

Hansen B Dalgaard T Thorling L Soslashrensen B and Erland-sen M Regional analysis of groundwater nitrate concentrationsand trends in Denmark in regard to agricultural influence Bio-geosciences 9 3277ndash3286doi105194bg-9-3277-2012 2012

Hansen J Land Use and Landscape development Perspectivesfor nature agriculture environment and management ExtentedSummary DJF report no 110 (markbrug) Foulum Denmark15ndash29 2004

Hedin L O Armesto J J and Johnson A H Patterns of nutrientloss from unpolluted old-growth temperate forests evaluation ofbiogeochemical theory Ecology 76 493ndash509 1995

Holl A Andersen E Rygnestad H Dalgaard T Soslashrensen EM and Nilsson K Scenario analyses for cultural landscape de-velopment Danish Journal of Geography 3 1ndash12 2002

Hope D Billett M F and Cresser M S A review of the exportof carbon in river water Fluxes and processes Environ Poll 84301ndash324doi1010160269-7491(94)90142-2 1994

Hutchings N J Dalgaard T Rasmussen B M Hansen J FDahl M Jorgensen L F Ernstsen V von Platen-HallermundF and Pedersen S S Watershed nitrogen modelling in Con-trolling Nitrogen Flows and Losses edited by Hatch D JChadwick D R Jarvis S C and Roker J A WageningenAcademic Publishers ISBN 90-7699-984-34 47ndash53 2004

Jobson J D Applied Multivariate Data Analysis Regression andExperimental Design Springer 1991

Kaiser K and Zech W Sorption of dissolved organic nitrogen byacid subsoil horizons and individual mineral phases Eur J SoilSci 51 403ndash411doi101046j1365-2389200000320x 2000

Kalbitz K Solinger S Park J H Michalzik B and Matzner EControls on the dynamics of dissolved organic matter in soils areview Soil Sci 165 277ndash304 2000

Keeney D R and DeLuca T H Des Moines River nitrate in re-lation to watershed agricultural practices 1945 versus 1980s JEnviron Qual 22 267ndash272 1993

Kennedy J Billett M F Duthie D Fraser A R and HarrisonA F Organic matter retention in an upland humic podzol theeffects of pH and solute type Eur J Soil Sci 47 615ndash625doi101111j1365-23891996tb01860x 1996

Kronvang B Jeppesen E Conley D J Soslashndergaard M LarsenS E Ovesen N B and Carstensen J Nutrient pressuresand ecological responses to nutrient loading reductions in Dan-ish streams lakes and coastal waters J Hydrol 304 274ndash288doi101016jjhydrol200407035 2005

Kronvang B Andersen H E Boslashrgesen C Dalgaard T LarsenS E Boslashgestrand J and Blicher-Mathiasen G Effects of pol-icy measures implemented in Denmark on nitrogen pollutionof the aquatic environment Environ Sci Pol 11 144ndash152doi101016jenvsci200710007 2008

Lajtha K Seely B and Valiela I Retention and leaching lossesof atmospherically-derived nitrogen in the aggrading coastalwatershed of Waquoit Bay MA Biogeochemistry 28 33ndash54doi101007BF02178060 1995

Lilienfein J Bridgham S D Qualls R G and Uselman S MAdsorption of dissolved organic carbon and nitrogen in soils of aweathering chronosequence Soil Sci Soc Am J 68 292ndash3052004

Martin C Aquilina L Gascuel-Odoux C Molenat J FaucheuxM and Ruiz L Seasonal and interannual variations of nitrateand chloride in stream waters related to spatial and temporal pat-terns of groundwater concentrations in agricultural catchmentsHydrol Process 18 1237ndash1254doi101002hyp1395 2004

Mattsson T Kortelainen P Laubel A Evans D Pujo-Pay MRaike A and Conan P Export of dissolved organic matter in



relation to land use along a European climatic gradient Sci TotalEnviron 407 1967ndash1976doi101016jscitotenv2008110142009

McHale M R Mitchell M J McDonnell J J and Cirmo C PNitrogen solutes in an Adirondack forested watershed Impor-tance of dissolved organic nitrogen Biogeochemistry 48 165ndash184doi101023A1006121828108 2000

Michalzik B and Matzner E Dynamics of dissolved organicnitrogen and carbon in a Central European Norway spruceecosystem Eur J Soil Sci 50 579ndash590doi101046j1365-2389199900267x 1999

Molenat J Durand P Gascuel-Odoux C Davy P and GruauG Mechanisms of Nitrate Transfer from Soil to Stream in anAgricultural Watershed of French Brittany Water Air Soil Poll133 161ndash183 2002

Moore T R Dissolved organic carbon in a northern boreal land-scape Global Biogeochem Cy 17 1ndash8 2003

Murphy D V Macdonald A J Stockdale E A GouldingK W T Fortune S Gaunt J L Poulton P R Wake-field J A Webster C P and Wilmer W S Soluble organicnitrogen in agricultural soils Biol Fert Soils 30 374ndash387doi101007s003740050018 2000

Nasholm T Kielland K and Ganeteg U Uptake of organic ni-trogen by plants New Phytol 182 31-48doi101111j1469-8137200802751x 2009

National Environmental Research Institute Denmark Running Wa-ters ndash Historical development and restoration of lowland Dan-ish streams Copenhagen available athttpwww2dmudk1viden2Publikationer3OvrigerapporterRWwebpdf (last ac-cess 12 November 2012) 2006

Neff J C Hobbie S E and Vitousek P M Nutrient and min-eralogical control on dissolved organic C N and P fluxes andstoichiometry in Hawaiian soils Biogeochemistry 51 283ndash3022000

Neff J C Holland E A Dentener F J McDowell W H andRussell K M The origin composition and rates of organic ni-trogen deposition A missing piece of the nitrogen cycle Bio-geochemistry 57 99ndash136 2002

Neff J C Chapin III F S and Vitousek P M Breaks in thecycle dissolved organic nitrogen in terrestrial ecosystems FrontEcol Environ 1 205ndash211 2003

Perakis S S Nutrient limitation hydrology and water-shed nitrogen loss Hydrol Process 16 3507ndash3511doi101002hyp5078 2002

PlanteInfo available at httpwwwplanteinfodkVejret2008indexaspitemid=649ampappl=0amp sessionid=DTzWYlw9M52amp server=17223173222amp port=5007amppi menu=1ampFuzz=719(last access 30 May 2011) 2011

Poor C J and McDonnell J J The effects of landuse on stream nitrate dynamics J Hydrol 332 54ndash68doi101016jjhydrol200606022 2007

Randall G W Implications of dry and wet cycles on nitrate lossto subsurface tile drainage in Proc 7th Annu Drainage SympOrlando FL 8ndash10 March 1998 Drainage in the 21st CenturyAmerican Society of Agricultural Engineers St Joseph MI 53ndash60 1998

Randall G W and Mulla D J Nitrate Nitrogen in Surface Watersas Influenced by Climatic Conditions and Agricultural PracticesJ Environ Qual 30 337ndash344 2001

Ruiz L Abiven S Durand P Martin C Vertes F and Beau-jouan V Effect on nitrate concentration in stream water ofagricultural practices in small catchments in Brittany I An-nual nitrogen budgets Hydrol Earth Syst Sci 6 497ndash506doi105194hess-6-497-2002 2002a

Ruiz L Abiven S Martin C Durand P Beaujouan V andMolenat J Effect on nitrate concentration in stream water ofagricultural practices in small catchments in Brittany II Tempo-ral variations and mixing processes Hydrol Earth Syst Sci 6507ndash514doi105194hess-6-507-2002 2002b

Sand-Jensen K and Pedersen N L Differences in tempera-ture organic carbon and oxygen consumption among lowlandstreams Freshwater Biol 50 1927ndash1937doi101111j1365-2427200501436x 2005

Scheffer F and Schachtschabel P Lehrbuch der BodenkundeSpektrum Akademischer Verlag GmbH 2002

Schelde K Cellier P Bertolini T Dalgaard T Weidinger TTheobald M R and Olesen J E Spatial and temporal vari-ability of nitrous oxide emissions in a mixed farming landscapeof Denmark Biogeosciences 9 2989ndash3002doi105194bg-9-2989-2012 2012

Schiff S L Devito K J Elgood R J McCrindle P M Spoel-stra J and Dillon P Two adjacent forested catchments Dra-matically different NOminus3 export Water Resour Res 38 1292doi1010292000WR000170 2002

Schnabel R R Urban J B and Gburek W J Hydrologic con-trols in nitrate sulfate and chloride concentrations J EnvironQual 22 589ndash596 1993

Siemens J and Kaupenjohann M Contribution of dis-solved organic nitrogen to N leaching from four Germanagricultural soils J Plant Nutr Soil Sc 165 675ndash681doi101002jpln200290002 2002

SPSS Inc Systat for Windows Version 1501 SPSS Inc ChicagoIL USA 2006

Steenvoorden J H A M Claessen F and Willems J Agricul-tural effects on ground and surface waters research at the edge ofscience and society IAHS-AISH P Publication no 273 71 pp2002

Vagstad N Stalnacke P Andersen H-E Deelstra J JansonsV Kyllmar K Loigu E Rekolainen S and Tumas R Re-gional variations in diffuse nitrogen losses from agriculture inthe Nordic and Baltic regions Hydrol Earth Syst Sci 8 651ndash662doi105194hess-8-651-2004 2004

van Breemen N Nitrogen cycle Natural organic tendency Nature415 381ndash382doi101038415381a 2002

van Kessel C Clough T and van Groenigen J W DissolvedOrganic Nitrogen An Overlooked Pathway of Nitrogen Lossfrom Agricultural Systems J Environ Qual 38 393ndash401doi102134jeq20080277 2009

Vitousek P M Aber J D Howarth R W Likens G E Mat-son P A Schindler D W Schlesinger W H and TilmanD G Human alteration of the global nitrogen cycle sourcesand consequences Ecol Appl 7 737ndash750doi1018901051-0761(1997)007[0737HAOTGN]20CO2 1997

Willett V B Reynolds B A Stevens P A Ormerod S J andJones D L Dissolved organic nitrogen regulation in freshwa-ters J Environ Qual 33 201ndash209 2004

Wilson J P and Gallant J C Terrain analysis principles and ap-plications John Wiley and Sons 2000



Worrall F and Burt T P Inter-annual controls on nitrate ex-port from an agricultural catchment ndash how much land-usechange is safe J Hydrol 243 228ndash241doi101016S0022-1694(00)00411-X 2001

Worrall F Burt T P Jaeban R Y Warburton J and SheddenR Release of dissolved organic carbon from upland peat Hy-drol Process 16 3487ndash3504doi101002hyp1111 2002

Worrall F Harriman R Evans C D Watts C D Adamson JNeal C Tipping E Burt T Grieve I Monteith D Naden PS Nisbet T Reynolds B and Stevens P Trends in DissolvedOrganic Carbon in UK Rivers and Lakes Biogeochemistry 70369ndash402doi101007s10533-004-8131-7 2004



texture or organic content play an important role on N lossesRecently researchers have put more emphasis on studyingthe contribution of dissolved organic nitrogen (DON) to theN balance of landscapes (Mattson et al 2009 Cooper et al2007 Ghani et al 2007 van Kessel et al 2009 Neff et al2003 2002) Hedin et al (1995) found that organic N repre-sents a large part of the total N losses from forest ecosystemswhich was also described in other studies (van Breemen2002 Cooper et al 2007 van Kessel et al 2009 Neff etal 2003 2002) It was also found that DON can be used asN source by many plant species (Nasholm et al 2009) andtherefore could also play a substantial role in N flows of agri-cultural systems

Cooper et al (2007) pointed out that the release of DON(and DOC) is ldquostrongly influenced by a wide range of hydro-meteorological factorsrdquo As DON includes labile and recal-citrant compounds (Neff et al 2003) and has different reten-tion times in soil and water corresponding losses can sub-stantially vary between different watersheds Therefore thereis a need to better understand the fundamental role of DONin agricultural systems (Ghani et al 2007 van Kessel et al2009) and in the global N cycle (see review by Durand et al2011) including its preferential flow pathways and biologi-cal degradation mechanisms (Perakis 2002)

In this study we focused on the N and carbon (C) fluxesin the Tyrebaeligkken stream (Denmark) and the influence ofland use and soil properties on stream chemistry Agricul-ture represents a large sector of Danish economy due toa suitable climate and relatively good soils Manure is themain fertiliser source for agricultural production (Dalgaardet al 2011b) and represents more than 80 of the N sourcein Danish streams lakes and coastal waters (Kronvang etal 2005 2008 National Environmental Research Institute2006) We investigated the fractions of dissolved inorganicnitrogen (DIN) and DON within total dissolved nitrogen(TDN) concentrations and fluxes in the stream water respec-tively As DON is linked to DOC by often sharing the sameorigin of organic matter DOC values were also studied Themain concern of this investigation concentrated on answeringtwo questions

1 What is the relative influence on stream chemistry ofland use and soil properties

2 How big is the contribution of DON to TDN losses fromagriculture-dominated land

In order to unravel the impact of soil properties and land useon in-stream chemistry measurements of different C and Nsolutes with a high spatial and temporal resolution are re-quired Furthermore to get a general overview on seasonaltrends in effects of nutrient export flushing rainfall eventsneed to be excluded Therefore in our study we performedldquosnapshotrdquo sampling campaigns during stable flow condi-tions (Grayson et al 1997)

2 Materials and methods

21 Study area

The study site is located south of Bjerringbro in centralJutland Denmark Two streams run through the investi-gated area from the east towards north-west (Fig 1 Hutch-ings et al 2004) They converge to form the Tyrebaeligkkenstream that ultimately reaches the Gudena River approxi-mately 3 km downstream of the studied area The total catch-ment area is 8427 ha and outlet coordinates are 5635prime14primeprime Nand 965prime09primeprime E According to the available 2times 2 m DEMdigitised for the NitroEurope project (Dalgaard et al 2012Hansen 2004) elevation ranges from 25 to 58 m asl andtopography is gentle with a mean slope of 37 althoughlocal maximum reaches 214 The mean annual rainfall inthe area is about 712 mm with a corresponding mean evapo-transpiration of 555 mm per year Mean annual temperatureis 77C (PlanteInfo 2011)

As presented in Fig 1 three river parts were analysed thenorthern branch (sampling points 1 to 6) the southern branch(points 11 to 20) and the downstream converged part (points21 to 24) As summarised in Table 1 and depicted in Fig 1land use is dominated by 90 of intensive farming primar-ily arable cropland in rotation (70 ) Pasture is the secondmost frequent land cover (20 ) totally dominating the landuse along the stream (Cellier et al 2011) The average fer-tilisation in the area is 80 kg N haminus1 yrminus1 in the form of live-stock manure (equal amounts of pig and cattle slurry) and74 kg N haminus1 yrminus1 in the form of synthetic fertilisers with amodelled average NOminus3 leaching equal to 58 kg N haminus1 yrminus1

(Dalgaard et al 2011a) correlating to the typical croppingand management practices in this part of Denmark (moraineplateaus with arable land dominated by winter wheat cere-als and with permanent grassland on the lowland organicsoils Dalgaard et al 2012 Holl et al 2002) Accordingto Dalgaard et al (2012) atmospheric N deposition for theBjerringbro area derived from EMEP (2012) was around12 kg haminus1 yrminus1 adding another 8 of total N input whichdoes not significantly change the overall N budget The fourdominant soil textures are coarse sandy clay (27 ) coarseclayey sand (26 ) fine clayey sand (24 ) and 13 withsoil organic matter predominant (Table 1) As illustrated inFig 2 (Dalgaard et al 2002) organic soils are mostly foundnear streams The northern part is dominated by coarse andfine clayey sands whilst coarse sandy clay dominates thesouthern part (Fig 2)

22 Sample collection and analyses

A total of nine snapshot sampling campaigns (Grayson etal 1997) were carried out in 2009 Sampling periods cor-responded to stable flow conditions in April (20th 24thand 27th) August (4th 11th 13th) and September (10th17th and 25th) Twenty different locations at an approximate




























[ha] [] [] []

01 1530 720 141 19 01 597 81 186 6406 2271 665 216 13 02 402 55 411 7211 2632 683 200 17 11 359 220 131 27520 5592 723 195 10 06 228 366 125 15921 8090 709 197 10 04 270 282 217 13024 8427 700 203 13 04 260 274 239 129



3 Results









































NOminus





4 Discussion

41 Nitrate






















































5 Conclusions



Edited by U Skiba

References















































































































[ha] [] [] []

01 1530 720 141 19 01 597 81 186 6406 2271 665 216 13 02 402 55 411 7211 2632 683 200 17 11 359 220 131 27520 5592 723 195 10 06 228 366 125 15921 8090 709 197 10 04 270 282 217 13024 8427 700 203 13 04 260 274 239 129



3 Results









































NOminus





4 Discussion

41 Nitrate






















































5 Conclusions



Edited by U Skiba

References



























































































[ha] [] [] []

01 1530 720 141 19 01 597 81 186 6406 2271 665 216 13 02 402 55 411 7211 2632 683 200 17 11 359 220 131 27520 5592 723 195 10 06 228 366 125 15921 8090 709 197 10 04 270 282 217 13024 8427 700 203 13 04 260 274 239 129



3 Results









































NOminus





4 Discussion

41 Nitrate






















































5 Conclusions



Edited by U Skiba

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NOminus





4 Discussion

41 Nitrate






















































5 Conclusions



Edited by U Skiba

References



























































































NOminus





4 Discussion

41 Nitrate






















































5 Conclusions



Edited by U Skiba

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5 Conclusions



Edited by U Skiba

References












































































































5 Conclusions



Edited by U Skiba

References



































































































5 Conclusions



Edited by U Skiba

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5 Conclusions



Edited by U Skiba

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Documents

Spatial distribution of soils determines export of nitrogen and …pure.au.dk/portal/files/52809829/Wohlfart_2012.pdf · · 2013-02-26tions were measured with a ﬁeld photometer