Interactive comment on “ Response of dissolved and particulate organic carbon and nitrogen in runoff to monsoon storm events in two watersheds of different tree species composition ”

General comments The manuscript presented very useful information on forms and flows of carbon and nitrogen in an upland fluvial system. The planning and coverage of sampling and parameters are good. The results will improve our understanding of material flows in terrestrial fluvial systems based on nature of tree types and water flows. The results deserve to be published but not in the present form. The basic problem is with the presentation and the way they dealt with scientific and technical issues. I


Introduction
Forested watersheds play an important role for human wellbeing in that they are often used as source areas for drinking water basins.As much of the dissolved organic matter (DOM) in aquatic systems originates from soil derived organic matter, the export of terrestrial carbon (C) and nitrogen (N) into aquatic environments is a primary link between these systems Biogeosciences Discuss., doi:10.5194/bg-2016Discuss., doi:10.5194/bg- -92, 2016 Manuscript under review for journal Biogeosciences Published: 13 May 2016 c Author(s) 2016.CC-BY 3.0 License.(Bauer and Bianchi, 2011;Bianchi, 2011;Camino-Serrano et al., 2014;Canham et al., 2012).The export of terrestrial C and N occurs in the form of dissolved and particulate organic carbon and nitrogen (DOC, DON, POC, PON).Particulate organic matter can be operationally classified into fine (0.1 to 63 µm) and coarse (63 µm to 2 mm) fractions (Richey, 2005).The export of POC was in some cases the major C export in stream (Dhillon and Inamdar, 2013;Jung et al., 2012;Kim et al., 2010;Lloret et al., 2013).On the contrary, DOC was reported as the dominant organic C form in a temperate headwater catchment (Johnson et al., 2006), a tropical rainforest catchment (Bass et al., 2011) and for several large tropical watersheds such as Amazon, Orinoco, Parana and Mengong (Lloret et al., 2013).
In regions with seasonally large differences in precipitation, most of the annual organic C export from forested watershed to steams is driven by heavy storm events with cyclones and hurricane (Dhillon and Inamdar, 2013;Lloret et al., 2013).Such conditions are pronounced in the Korean peninsula in which the monsoon season (Jeong et al., 2012;Kim et al., 2010), represented 52% and 83% of the annual DOC and POC runoff fluxes.During storm events, a change in hydrological flow paths in watersheds has been often observed from deeper to upper soil layers (Bass et al., 2011;Sanderman et al., 2009;Singh et al., 2014).Surface flow-inducing storm events can alter the fluxes and concentrations of DOC and POC in runoff by shifting preferential flows through macropores, surface runoff and lateral flow (Katsuyama and Ohte, 2002;Kim et al., 2010;McGlynn and McDonnell, 2003).
DON was the major form of N in runoff from pristine forested watersheds (Alvarez-Cobelas et al., 2008;Frank et al., 2000;Kaushal and Lewis, 2003;Pellerin et al., 2006;Yates and Johnes, 2013).Only few data are available on the partitioning of DON and PON fluxes in runoff from forested watersheds (Inamdar et al., 2015).The question remains open, if organic N in runoff -either dissolved or particulate -from forested watersheds behaves similar to organic C or not.Some studies reported that concentrations of DON and DOC correlated strongly (von Schiller et al., 2015), but also their weak relationships were found (Singh et al., 2015).
Tree species might influence the export of dissolved organic matter from forested watersheds.DOM from coniferous litter generally comprises more refractory (e.g.hydrophobic acid, lignin) and aromatic compounds, and a relatively larger proportion of high molecular weight compounds than DOM from deciduous litter.It is also more acidic than DOM from deciduous litter (Don and Kalbitz, 2005;Hansson et al., 2011;Kiikkilä et al., 2013).Moreover, higher DOC and DON concentrations were found in oak, beech and silver birch forest floors compared to Norway spruce, Douglas-fir and Scots pine (Smolander and Kitunen, 2011;Trum et al., 2011).
As a result of global warming, heavy storm events have occurred more frequently and became stronger in recent decades (IPCC, 2013).Furthermore, forest management, namely the selection of tree species, might influence the export of organic matter from forested watersheds.The influence of both drivers should be known in order to better understand the link between terrestrial and aquatic ecosystems and to support an efficient downstream water quality management.The goal of this study was thus to investigate the influence of tree species and heavy storm events on the fluxes of dissolved and particulate forms of C and N from a mixed coniferous/deciduous and a deciduous forested watershed.To do so, a measuring campaign was conducted in South Korea during the 2013 monsoon season.Discuss., doi:10.5194/bg-2016Discuss., doi:10.5194/bg- -92, 2016 Manuscript under review for journal Biogeosciences Published: 13 May 2016 c Author(s) 2016.CC-BY 3.0 License.

Study area and site
The Lake Soyang basin area (Figure 1) is located in the upstream region of the Han River, which is the main source of drinking water for about 23 million citizens of South Korea (Lee et al., 2013;Park et al., 2010).Annual air temperature ranges from 10 to 15 o C with -6 o C in January and 26 o C in August.Annual precipitation ranges from 1200 to 1500 mm and the summer monsoon usually accounts for 50 to 60% of the annual precipitation (Korean meteorological administration).
Korean mountainous forests are mostly composed of broadleaved forests representing 47% of the total forested area (coniferous forest 38%, mixed forest 12%) and most of the broadleaved forests of South Korea are distributed within the Gangwon province (Korea forest research institute, 2013).
The mixed coniferous/deciduous forested watershed (mixed watershed) (Figure 1) is located in Seohwa, the Gangwon province (Lat. 38.206828 N, Long. 128.185719 W, 368 to 682 m above sea level).The area of the mixed watershed (Table 1) is 15.6 ha with 6.1 ha of coniferous forest (39%) and 9.5 ha of deciduous forest (61%).Two research plots as one in the The deciduous forested watershed (deciduous watershed) (Figure 1) is located in Haean, the Gangwon province (Lat. 38.251532, N 128.11991Long.W, 586 to 1005 m above sea level).The area of the deciduous watershed (Table 1) is 39 ha and is covered by various deciduous species.A research plot as deciduous plot (DD plot) was established in this watershed.

Water sampling
Bulk precipitation samplers (n=2) were installed at each watershed in an open area located ~100 m from the plots.
Throughfall collectors (n=5) were equipped with filters to prevent large particles from entering.Forest floor leachate was collected beneath the organic layer along the slope side using zero tension lysimeters (n=5) of 185 cm 2 made of acrylic Biogeosciences Discuss., doi:10.5194/bg-2016-92,2016 Manuscript under review for journal Biogeosciences Published: 13 May 2016 c Author(s) 2016.CC-BY 3.0 License.material.Soil solution was collected at a depth of ~50 cm with suction lysimeters (n=5) made of ceramic cups.The suction of suction lysimeters was maintained through manual pumping with syringe after taking samples.
Before storm events in June 2013, throughfall, forest floor leachate and soil solution were collected at about weekly intervals, and runoff samples were collected 3 times per week.During storm events in July 2013, throughfall, forest floor leachate and soil solution were collected after each storm event, and runoff samples were collected every 1 or 2 h in the weir at the two watersheds using automatic collectors (6712 Portable Sampler, Teledyne Isco Inc., Lincoln, NE, USA).Discharge at the outlet of the watersheds was measured by a v-notch weir.During routine runoff sampling, water quality parameters including water temperature, pH and electrical conductivity were measured in situ.Water samples were cooled at 4 o C and then were filtered (see 2.4) within 2 days after sampling.Filtered solution samples were frozen for 1 month until further analysis of water quality and quantity.
Meteorological data at the study area were used from the weather station of the Korean meteorological administration.

Soil sampling
The total stock of the Oi and Oe+Oa layers was collected at each plot in a 20 × 20 cm frame for 10 replicates.Mineral soil samples were collected from 3 pits at each plot in 10 cm depth layers down to 50 cm depth.In case of the DD plot, the sampling of mineral soil was not possible more than 40 cm depth due to massive rock.Before the analyses, soil samples were air-dried and crushed to pass through a 2 mm sieve.Soil pH was measured from a solution of a soil to solution (0.01 M CaCl 2 ) ratio of 1:2.5 after shaking for 2 hours.Total C and N contents were analyzed using an elemental analyzer (vario MAX CN, Elemental, Germany).Soil texture was determined by sedimentation.

Fluxes of C and N in runoff
Before storm events in June 2013, the fluxes of DOC were calculated on a weekly basis by multiplying the DOC weekly mean concentration in runoff by the weekly mean discharge.The concentrations of DON, NO 3 -N, POC and PON in runoff were partly below the detection limit.Thus, the detected minimum concentrations were applied to the calculation of their export fluxes as 0.03 mg DON L -1 , 0.5 mg NO 3 -N L -1 , 0.003 mg POC L -1 , 0.0003 mg PON L -1 .During the period of storm events in July 2013, the fluxes of DOC, DON, NO 3 -N, POC and PON in runoff were computed at 1 or 2 h intervals by multiplying the measured concentrations with corresponding discharge.The storm events during monsoon season were identified from the start to the end of precipitation with more than a day interval between each storm event.

Statistic for origin of DOM and POM
The normality of data was tested with the Shapiro-Wilk Test.When the normality was passed as the p value less than 0.05, the Holm-Sidak Test was used for both pairwise comparisons and comparisons versus a control group.When the normality

Chemical analyses
After filtration through a pre-rinsed cellulose acetate membrane filter (0.45 μm, Whatman), the concentrations of DOC and dissolved total nitrogen (DTN) in water samples were measured by a total organic carbon analyzer (Shimadzu V-series, TOC-CPH).DON concentration was calculated as the difference between total nitrogen and mineral-N (NO 3 -+ NH 4 + ).
Nitrate and ammonium concentrations were measured by flow injection (MLE Dresden, FIA-LAB).
In this study, the POC and PON fraction is defined as the size class 0.7 μm to 1 mm.Samples were filtered through a 1 mm mesh to remove larger particulate materials and then finally filtered through a pre-rinsed 0.7 μm pore size glass filter (GF/F, Whatman).Before using the glass filters, the filters were pre-combusted at 450°C to remove any organic material.The residues of particulate material on the GF/F filters were analysed for POC and PON after drying at 65°C using an elemental analyser (Carlo Erba1108, Milano, Italy) coupled to a ConFlo III interface and an isotope ratio mass spectrometer (Finnigan MAT, Bremen, Germany).
The absorption spectra of DOM were obtained at wavelengths from 200 to 600 nm using a UV-visible spectrophotometer (HACH, DR5000).Specific ultraviolet absorbance (SUVA 280 ) values were determined by UV absorbance at 280 nm divided by the DOC concentrations and multiplied by 100.
For fluorescence excitation-emission matrices, fluorescence intensities were recorded with a luminescence spectrometer (LS-50B, Perkin-Elmer) following the method of Baker (2001), Chen et al. (2007), and Hur and Cho (2012).Excitation and emission slits were both adjusted to 10 nm.DOM samples were diluted under the ultraviolet absorbance of 0.1 at 280 nm to avoid inner-filter correction, and then were adjusted to pH 3.0 for the fluorescence measurements.The fluorescence intensities of all samples were normalized to units of quinine sulfate equivalents.The humification index (HIXem) was calculated by dividing the emission intensity from 435 to 480 nm region by intensity from 300 to 345 nm (Zsolnay et al., 1999).Fluorescence characteristics of water samples were interpreted as fulvic-like fluorescence (FLF), humic-like fluorescence (HLF) and protein-like fluorescence (PLF) (Fellman et al., 2010;Singh et al., 2014).
After filtration (0.45 μm, Whatman) and freeze-drying of water samples, 13 C and 15 N isotope abundances of DOC and DTN were measured using an elemental analyzer (Carlo Erba1108, Milano, Italy) coupled to a ConFlo III interface and an isotope ratio mass spectrometer (Finnigan MAT, Bremen, Germany).

Soil and hydrological characteristics
The structures of the organic layers at the MC, MD and DD plots are similar, representing a moder-like organic layer, with distinct Oi-layers and less distinct Oe and Oa-layers, but the depth of O-layer in the MC plot (ca. 3 cm) was thinner than in The average discharge was much less before storm events in June 2013, 0.03 mm h -1 at the mixed watershed and 0.06 mm h -1 at the deciduous watershed (data not shown) compared to during storm events in July 2013.During storm events, the hydrological characteristics were similar at both watersheds (Table 2).In the study period, the highest precipitation coincided with the maximum precipitation intensity, the highest precipitation intensity and the maximum discharge at the mixed watershed and at the deciduous watershed on July 14 th , 2013.

Concentrations of carbon and nitrogen in runoff during storm events
The increase of the DOC concentrations in runoff with discharge was steeper at the deciduous watershed (e.g.1.9 to 6.9 mg C L -1 on July 8 th , 2013) than at the mixed watershed (e.g.1.0 to 3.7 mg C L -1 on July 8 th , 2013) (Figure 2a).In contrast, the DON concentrations in runoff from both watersheds were independent of discharge (Figure 2b).The highest concentrations of DOC and DON in runoff were observed during the earlier storm events (Table 2).The NH 4 -N concentrations were at any time negligible (< 0.05 mg N L -1 ).
During storm events, the concentrations of POC and PON in runoff increased steeply and instantly after a threshold on July 8 th and July 14 th , 2013 (Figure 2d, 2e).For example, at the mixed watershed, an increase of POC was observed up to 10.7 mg C L -1 at the largest discharge of 9 mm h -1 (Figure 2d, Table 2).At the deciduous watershed, the POC concentration in runoff increased to 8.6 mg C L -1 at the first large storm event with 3 mm h -1 discharge.The following more intense storms did result in lower POC concentrations.The pattern of POC concentration coincided with those of PON (r=0.99).
The runoff DOC concentrations in response to discharge had a clockwise hysteretic loop with higher concentrations on the rising than on the falling limb (Figure 2a).No hysteretic loops were observed for DON, POC and PON (Figure 2b, 2d, 2e).
The DOC/DON ratio in runoff ranged from 5 to 60 (Figure 2c).DON concentrations lower than 0.05 mg N L -1 were not considered for calculation of DOC/DON ratios.In response to increased discharge, the DOC/DON ratio were stable at the mixed watershed, while there was a tendency for increasing DOC/DON ratios with discharge at the deciduous watershed.On the contrary, there was no response of the POC/PON ratio to discharge.Unlike to DOC/DON ratio, the POC/PON ratio ranged narrowly from 10 to 20 at both watersheds (Figure 2f) with an average of 12 at the mixed and 13 at the deciduous watershed.

Fluxes of carbon and nitrogen
The fluxes of DOC, DON and NO 3 -N in runoff were linearly correlated to discharge at both watersheds (Figure 3).The fluxes of DOC and NO 3 -N increased with a much steeper slope at the deciduous and at the mixed watershed, respectively.The cumulative C and N fluxes from both watersheds were in the order; DOC > POC and NO 3 -N > DON > PON (Table 3).
The DOC fluxes as the dominant C flux form contributed 75% and 92% of the total organic C flux at the mixed and the deciduous watersheds, respectively.The cumulative fluxes of DOC and DON were higher at the deciduous watershed (16 kg C ha -1 and 0.5 kg N ha -1 ) than at the mixed watershed (6.7 kg C ha -1 and 0.26 kg N ha -1 ).The cumulative fluxes of POC and PON were small at both watersheds with only minor differences.Before storm events in June 2013, POC and PON were almost not exported at both watersheds.However, the cumulative fluxes of POC and PON increased extremely during heavy storm events in July 2013.NO 3 -N fluxes as the dominant N flux form represented 93% and 82% of the total N flux at the mixed and the deciduous watershed, respectively.The cumulative fluxes of NO 3 -N was about twice as high (5.2N ha -1 yr -1 ) at the mixed watershed than at the deciduous watershed (2.9 N ha -1 yr -1 ).

Chemical properties of DOM and POM in runoff
The chemical properties of DOM changed with increased discharge at the deciduous watershed, while no significant changes were observed at the mixed watershed (Figure 4).At the deciduous watershed, SUVA 280 and HIXem increased with increased discharge, while PLF/FLF, PLF/HLF, δ 13 C DOC and δ 15 N DTN decreased.
At the mixed watershed, the ranges of the DOC/DON ratio, SUVA 280 and HIXem in runoff were similar to those in throughfall and soil solution, while PLF/FLF in runoff corresponded more to those in forest floor percolates (Figure 5).In contrast at the deciduous watershed, these parameters were all closely related to the quality of forest floor leachates as being likely a mixture of forest floor leachates and soil solution.Comparing between plots, the distributions of the DOM quality parameters at the MC and MD plot were similar in throughfall and forest floor leachates, but they were different in soil solution.These parameters at the MD and DD plot were similarly distributed in throughfall, forest floor leachates and soil solutions.
The range of the POC/PON ratio in runoff was similar to that of the POC/PON ratio of upper and deeper mineral soil layers at both watersheds (Figure 6).The same holds for the δ 13 C POC values.The δ 15 N PON in runoff had a huge variation, with averages being larger than those of the forest floor, but less than those of the mineral soil.watershed-specific biogeochemical responses to four heavy rainfall events of the monsoon season at both watersheds.The four events represented a substantial proportion of the annual precipitation in the region.While the number of events was rather low, consistent patterns emerged from this rare opportunity to examine concurrent changes in elemental composition and isotopic ratios during intense rainfall events.The increase of DOC concentrations and fluxes in runoff induced by heavy storm events and increasing discharge is consistent with the findings of previous studies (Dhillon and Inamdar, 2013;Jeong et al., 2012;Johnson et al., 2006;Lloret et al., 2013).In our study, the response to discharge and the cumulative fluxes of DOC in runoff were much larger at the deciduous than at the mixed watershed.Only few studies compared different tree species effects on DOC exports (mixed coniferous and deciduous vs. deciduous).Similar to our results larger annual DOC fluxes at a deciduous forested catchment than at a mixed catchment were reported (Amiotte-Suchet et al., 2007).
The different response of DOM quality parameters in runoff to discharge between the two watersheds, such as the large response of runoff DOC concentration to discharge (Figure 2a) and the significant change in runoff DOC quality parameters (Figure 4) at the deciduous watershed, are likely due to shifting of hydrological flow paths at the deciduous watershed.Also, the distribution of DOC quality parameters in runoff between forest floor leachates and soil solution at the deciduous watershed (Figure 5) indicated that a larger proportion of the DOC in runoff results from forest floor leachates at the deciduous while this proportion was less at the mixed watershed.Previous studies have reported that positive relationships between discharge and DOM concentrations in runoff point to changing hydrologic flow paths from deeper soil to upper soil layers and forest floors at high discharge (Aitkenhead-Peterson et al., 2005;Bass et al., 2011;Sanderman et al., 2009).As the similar watershed characteristics (slope and soil textures) and the precipitation regime at both watersheds, the differences between the watersheds are likely due to the tree species effects on the infiltration of precipitation water into the soil and on the mobilization of DOM.The tree species effect became obvious although the proportion of coniferous tree species was only 39% of the watershed area.Several processes might be involved to explain the tree species effect: i) In the deciduous litter layer the leaves are overlapping and are partly impermeable which may cause more surface near flow than in coniferous litter layers with large pore spaces in between needles.In general, ii) the relatively higher level of hydrophobicity of coniferous forest floors compared to deciduous forest floors (Butzen et al., 2014) can result in less DOC release from coniferous forest floors.Moreover, iii) the mobilization of DOC in soils depends on throughfall chemistry (Kalbitz et al., 2000).Throughfall at the MC plot was more acidic (pH 4.7±0.4)and had a higher ionic strength (15.9±11.3µS cm -1 ) than at the DD plot (pH 6.1±0.2,10.3±6.3 µS cm -1 ) and the MD plot (pH 5.8±0.4,9.0±6.3µS cm -1 ).Acidity and ionic strength are negatively related to DOC release from soils (Clark et al., 2011;Michalzik et al., 2001;Moldan et al., 2012).Lastly, iv) in stream generation of DOC from litter might be involved (Johnson et al., 2006) if more leaf than needle litter enters the stream.

Organic and inorganic nitrogen in runoff
The patterns of DOC/DON ratios in response to discharge were also different at the two watersheds (Figure 2c).Large DOC/DON ratios at high discharge at the deciduous watershed resulted from the positive response of DOC concentration and the independent response of DON concentration to discharge.No significant changes in DOC/DON ratios at the coniferous watershed were due to the relatively small increase in DOC concentration and the stable DON concentration.The changing response of the DOC/DON ratio at the deciduous watershed again points to a larger proportion of near surface flow to runoff at high discharge because the DOC/DON ratio of the forest floor leachates was larger than those of the soil solution.
At both watersheds, NO 3 -N was the dominant form of total N flux in runoff (Table 3).Several studies have reported that DON accounted for the dominant fraction of N in undisturbed forested watersheds (Alvarez-Cobelas et al., 2008;Frank et al., 2000;Kaushal and Lewis, 2003;Pellerin et al., 2006).Substantial fluxes of NO 3 -N and the dominance of NO 3 -N over DON in runoff are likely due to a certain degree of N-saturation (N supply > N demand) of these forested watersheds (Aber et al., 1998;Compton et al., 2003).Hence, the finding of the dominant NO 3 -N of total N flux implies that the N deposition in the area seems quite high (estimated between 24-51 kg N ha -1 yr -1 , Berger et al., 2013).In July 2013, the cumulative N flux in throughfall was however similar at the both watersheds (data not shown).Hence, the differences in N deposition between the two watersheds unlikely explain higher NO 3 -N fluxes in runoff at the mixed than at the deciduous watershed (Table 3).
The C/N ratio of the forest floor was found to be a good indicator of NO 3 -N release with increasing fluxes at low C/N ratios (Borken and Matzner, 2004;MacDonald et al., 2002).However, the C/N ratio of the organic layer at the mixed watershed (20-28) was higher than at the deciduous watershed (19-21), which does not agree with the findings of MacDonald et al.
( 2002).Overall, it seems that a larger N uptake by the deciduous trees at the deciduous watershed could explain the differences in NO 3 -N fluxes.

Particulate organic matter in runoff
The cumulative fluxes of POC and PON during the study period were much less than those of the dissolved elements and did not differ significantly between the watersheds.POC and PON fluxes exceed their dissolved fractions only for short time during heavy storm events with more than 100 mm precipitation.The small proportion of particulate fluxes in our study seems to be caused by the relatively moderate precipitation events during the study period.Previous studies in the nearby region considered 100 mm precipitation as a threshold that would induced large POC fluxes (Jeong et al., 2012;Jung et al., 2012).The POC/PON ratios in runoff as well as the δ 13 C POC and δ 15 N PON were similar to those of the mineral soil and different to those of the forest floor.This indicates that the particulate matter originated from the erosion of mineral soil along the stream benches.Higher annual POC fluxes than DOC fluxes were observed in some mountainous forested watersheds (Kao and Liu, 1997;Kim et al., 2010;Lloret et al., 2013), which does not agree with our finding and some other studies (Dhillon and Inamdar, 2013;Inamdar et al., 2011;Jeong et al., 2012).The differences in findings may be related to the topography of forested watersheds because steeper slopes induce higher fluxes of POC (Hilton et al., 2012;Janeau et al., 2014;Jung et al., 2012).

Conclusions
Our study emphasized the role of vegetation cover and site-specific flowpaths for the storm-induced export of C and N in DOM and POM with runoff from forested watersheds.Our results suggest that changes in the precipitation regime, as more severe monsoon storms as predicted in the future, will increase the export of dissolved and particulate organic matter from these watersheds, with the magnitude of storm responses depending on both element/phase and the composition of tree species.The proportion of coniferous tree species at the mixed watershed was sufficient to induce less DOC fluxes and larger NO 3 -N fluxes with runoff as compared to the deciduous watershed.Differences in the flow paths between the watersheds are seen as the major trigger for the differences in runoff with a larger proportion of near surface flow at the deciduous watershed.A larger proportion of coniferous forests in the forested watersheds of this region will likely lead to less inputs of organic carbon and larger inputs of inorganic nitrogen to the receiving surface water bodies..

Mi
coniferous part (MC plot) and the other one in the deciduous part (MD plot) were established.The slope of the mixed watershed as obtained from a digital elevation model ranges from 4.0 to 41° with an average of 28°.The lower part of the mixed watershed is dominated by coniferous species, including Larix kaempferi (Lamb.)Carr.(Japanese larch) and Pinus densiflora Siebold & Zucc.(Japanese red pine).The upper part of the mixed watershed is dominated by deciduous species, such as Juglans mandshurica Maxim.(Manchurian walnut), Acer pictum subsp.mono (Maxim.)H.Ohashi (Mono maple), Quercus dentata Thunb.(Daimyo oak), Tilia amurensis Kom.(Lime tree) and Ulmus davidiana var.japonica (Rehder) Nakai (Japanese elm).
Biogeosciences Discuss., doi:10.5194/bg-2016-92,2016 Manuscript under review for journal Biogeosciences Published: 13 May 2016 c Author(s) 2016.CC-BY 3.0 License.test failed, the Dunn's Test was used for all pairwise comparisons and comparisons against a control group with rank-based-ANOVA.
Biogeosciences Discuss., doi:10.5194/bg-2016-92,2016 Manuscript under review for journal Biogeosciences Published: 13 May 2016 c Author(s) 2016.CC-BY 3.0 License.Only when discharge exceeded a certain discharge threshold, POC and PON fluxes increased in a non-linear response.Before reaching the discharge threshold, the POC fluxes were much lower than the DOC fluxes.At a single peak flow event on July 14 th 2013, the POC fluxes at the mixed watershed were 5 times greater than the DOC fluxes.The same trend was found for PON and DON fluxes.At the deciduous watershed, only one event caused slightly larger POC than DOC fluxes during the study period.
response of DOC to increased discharge at the mixed and the deciduous watershed Simultaneous analyses of C and N concentrations and isotopic ratios in both DOM and POM allowed us to characterize BiogeosciencesDiscuss., doi:10.5194/bg-2016Discuss., doi:10.5194/bg--92, 2016     Manuscript under review for journal Biogeosciences Published: 13 May 2016 c Author(s) 2016.CC-BY 3.0 License.
-Hee Lee carried out the experimental work and data evaluation and prepared the manuscript with contribution from all co-authors Egbert Matzner and Ji-Hyung Park contributed to the design of this study, to data evaluation, interpretation of results and writing of the manuscript Jean-Lionel Payeur-Poirier supported the field work and provided the discharge data Acknowledgements This study was accomplished within the framework of the International Research Training Group TERRECO (GRK 1565/1) and funded by the German Research Foundation (Deutsche Forschungsgemeinschaft; DFG) at the University of Bayreuth and the Korean Research Foundation (KRF) at Kangwon National University.We acknowledge the BayCEER Laboratory of Isotope Biogeochemistry for the isotope abundance analysis and the Central Analytical Department of BayCEER for inorganic-N measurement at the University of Bayreuth.We are grateful to other TERRECO colleagues for the comprehensive support and to Uwe Hell for the sampler installation of soil solution.We also appreciate the international collaboration with Bomchul Kim, Youngsoon Choi and Jaesung Eum from Kangwon National University (Chuncheon) and with Jin Hur and Bomi Lee from Sejong University (Seoul).Biogeosciences Discuss., doi:10.5194/bg-2016-92,2016 Manuscript under review for journal Biogeosciences Published: 13 May 2016 c Author(s) 2016.CC-BY 3.0 License.

Figure 1 :
Figure 1: Location and tree species composition of the two studied forested watersheds.Lake Soyang map was modified from Jung et al. (2015).

Figure 2 :
Figure 2: Concentrations of a) dissolved organic carbon (DOC) and b) nitrogen (DON), d) particulate organic carbon (POC) and e) nitrogen (PON) and the ratios of c) DOC/DON and f) POC/PON in runoff with discharge during monsoon storm events.Doted, solid and dashed lines correspond to the storm event of July 8 th 2013, July 11 th 2013 and July 14 th 2013, respectively.

Figure 3 :
Figure 3: Fluxes of carbon (dissolved organic carbon (DOC) and particulate organic carbon (POC) and nitrogen (dissolved organic nitrogen (DON), and particulate organic nitrogen (PON) and nitrate (NO 3 -N) in runoff with discharge during monsoon storm events.

Figure 6 :
Figure 6: Range of particulate organic carbon and nitrogen ratio (POC/PON ratio), δ 13 C and δ 15 N in runoff, Oi, Oe+Oa, upper soil (0-10 cm depth) and deeper soil (40-50 cm depth at the MC and MD plot, 30-40 cm depth at the DD plot).Box plots display minimum, lower quartile, median, upper quartile, maximum and outliers.Different alphabet letters indicate the significant difference between groups.5