Environ Monit Assess (2015) 187:323 DOI 10.1007/s10661-015-4549-8
Changes in the dissolved organic matter leaching from soil under severe temperature and N-deposition Hang Vo-Minh Nguyen & Jung Hyun Choi
Received: 8 July 2014 / Accepted: 21 April 2015 # Springer International Publishing Switzerland 2015
Abstract In this study, we conducted growth chamber experiments using three types of soil (wetland, rice paddy, and forest) under the conditions of a severe increase in the temperature and N-deposition in order to investigate how extreme weather influences the characteristics of the dissolved organic matter (DOM) leaching from different soil types. This leachate controls the quantity and quality of DOM in surface water systems. After 5 months of incubation, the dissolved organic carbon (DOC) concentrations decreased in the range of 21.1 to 88.9 %, while the specific UV absorption (SUVA) values increased substantially in the range of 19.9 to 319.9 % for all of the samples. Higher increases in the SUVA values were observed at higher temperatures, whereas the opposite trend was observed for samples with N-addition. The parallel factor analysis (PARAFAC) results showed that four fluorescence components: terrestrial humic-like (component 1 (C1)), microbial humic-like (component 2 (C2)), protein-like (component 3 (C3)), and anthropogenic humic-like (component 4 (C4)) constituted the fluorescence matrices of soil samples. During the experiment, labile DOM from the soils was consumed and transformed into resistant aromatic carbon structures and less biodegradable components via microbial processes. The principle component analysis (PCA) results indicated that severe temperatures and N-deposition could enhance the H. V.0.05, ANOVA). During the experiment, higher percentages of the terrestrial humic-like component (%C1) were observed for the forest soil in chamber 2 than in chamber 1, while the opposite trend was demonstrated for the rice paddy soil (Fig. 4a). In addition, the microbial humic-like component (%C2) also exhibited higher values in chamber 2 than in chamber 1 (Fig. 4b). Both the protein-like (%C3) and the anthropogenic humic-like (%C4) components exhibited higher values in the samples from chamber 2 without N-addition (Fig. 4c, d). With Naddition, all of the wetland samples and forest samples presented lower values of C4 in chamber 2 than in chamber 1 (Fig. 4d).
At the end of the experiment, the %C1 and %C2 values slightly decreased from 1 to 14 %, while the %C3 and %C4 values increased from 1 to 35 % for the rice paddy (Fig. 4). The samples from the wetland in chamber 2 also exhibited higher values of the terrestrial and microbial humic-like components (%C1, %C2) after 5 months of incubation, while lower trends were observed for the samples from chamber 1. The percentage values of the protein-like component (%C3) for the wetland in chamber 2 (2W, 2WN) decreased after incubation, due to the higher temperature. An increase in the anthropogenic humic-like component (%C4) was only observed for the wetland soil from chamber 2 without N-addition (2W). The leachate from the forest soils exhibited an increase in the %C1 for samples 1FN and 2F and higher values of %C2 for 1F, 1FN, and 2F after 5 months of incubation. In addition, the %C3 values
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Fig. 4 Score of the PARAFAC components a C1, b C2, c C3, and d C4 from all of the soil leachate samples
decreased for all of the samples of the forest soils except for 2FN.
For samples with N-addition, both the %C1 and %C2 values of the samples were higher than those of the
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samples without N-addition in both of the chambers. However, the various trends of the %C3 and %C4 due to the N-addition conditions were not observed in this study.
Discussion The concentration of the DOC values leaching from almost all of the pots decreased during the 5 months of incubation. The decrease in the DOC during incubation could be explained by the consumption of labile DOC via microbial processes (Hur et al. 2009; Xu et al. 2012). The concentrations of the DOC from the pots in chamber 2 were higher than those in chamber 1, indicating that a 10 °C higher temperature (chamber 2) led to an increase in soil respiration, which strongly affected the increase in the DOC leaching (McDowell and Likens 1988; Andersson et al. 1994; Christ and David 1996). However, the ranges of the DOC were influenced more by the type of soil than by the chamber conditions. The leachate from the forest soil showed the highest reduction compared to those of the wetland and rice paddy soil. The positive and negative effects of the N-addition on the DOM concentration have been discussed by several researchers. For instance, Aber (1992) and Mo et al. (2008) stated that N-addition leads to a reduction in the DOC by decreasing the production and increasing the consumption of DOC. However, Fog (1998) and Guggenberger (1994) demonstrated that the Ndeposition resulted in an increase in the DOC from recalcitrant organic carbon, due to the reduced lignolytic activity of the white-rot fungi and simulated biological activity. Our results with the increased DOC values in the N-addition are in agreement with the reports of Fog (1998) and Guggenberger (1994). The increase in the SUVA demonstrates the high concentration of aromatic compounds since SUVA values are known to have a positive correlation with the aromatic carbon content of DOM (Weishaar et al. 2003). Similar results were reported in previous studies. For example, Kalbitz et al. (2003b) demonstrated that the UV absorptions of soil samples incubated in the dark at 20 °C increased during a 90-day period. Saadi et al. (2006) and Hur and Cho (2012) also reported an increase in the SUVA values (above 50 %) by the transformation from labile DOM to refractory DOM. The increased SUVA values could be explained by the
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preferential utilization of non-aromatic moieties by the microorganisms, the microbial transformation of the labile compounds to aromatic carbon structures, or a combination of these processes (Hur et al. 2009). Since the SUVA value can be increased by the microbial decomposition of DOM, higher SUVA values may indicate higher rates of humification, more resistant aromatic humic matter, and lower biodegradability of the DOM (Laor and Avnimelech 2002; Saadi et al. 2006). The results of this study showed that the SUVA values in chamber 2 were higher than those in chamber 1 for all of the samples without N-addition. The increase in SUVA values was highest for the forest soil compared to those of the wetland and rice paddy soil. The forest soil was known to have a higher component of leaf litter, while the wetland soil differed primarily in terms of organic matter due to the abundance of submerged plants. Leaf litter has a higher degradation rate than other parts of plants (i.e., culm) due to the reduced proportions of recalcitrant components, such as celluloses and lignins (Dinka et al. 2004). From the results of the DOC and SUVA measurements, it was determined that higher temperatures strongly affected the production of aromatic compounds due to the increase in the microbial degradation, while N-additions primarily led to an increase in the DOC production. The increase in the HIX can be determined by the microbial changes in the fluorescent components related to longer wavelengths and/or structural modification (Ishii and Boyer 2012). Previous studies presented that HIX increased after 28–30 days of incubation (Kalbitz et al. 2003b; Zhao et al. 2008; Hur and Cho 2012). Since the range of HIX values from the wetland was lower than the ranges from the rice paddy and forest, the wetland was associated with the enrichment of lesscondensed aromatic structures and/or less conjugation of the aliphatic chains than those in the rice paddy and forest (Fuentes et al. 2006). Despite the lack of increase in the HIX from two pots (1W and 2FN) during the incubation and the unclear trend of the wetland under conditions of N-addition and non-N-addition, HIX is still a useful index for investigating the degree of DOM biodegradation. The PARAFAC results showed that four fluorescence components (i.e., terrestrial humic-like (C1), microbial humic-like (C2), protein-like (C3), and anthropogenic humic-like (C4)) constituted the fluorescence matrices of all of the soil samples during the incubation. From the shorter emission of C2, called Bblue shifting,^ it can be
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interpreted that the C2 contained less-conjugated and less-condensed structures than the C1 (Stedmon et al. 2003). The blue shifting of the fluorescence spectra represented a lower degree of humification with the Fig. 5 a Factor loading plot for the measured properties of the first two principal components and b factor scores plot for each sample as the first two principal components
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decomposition of the condensed aromatic moieties of the DOM samples (Coble 1996; Fuentes et al. 2006). Component 3 (C3) identified as a protein-like component indicated that the origin of the fluorophore group
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was related to a microbial-derived amino acid or protein substance (Coble 1996). Component 4 (C4) was associated with an anthropogenic humic fluorophore from agricultural land due to the spreading of animal waste as fertilizer (Stedmon and Markager 2005b). From the data, it was observed that the rice paddy and forest soils dominantly contained terrestrial humic-like and microbial humic-like compounds due to the high percentage of C1 and C2, while most of the wetland samples presented a dominance of C3 and C4. Thus, protein-like and anthropogenic humic fluorophore components of leachate from wetland soil could be strongly affected by the outflow of the watershed which is relatively populated and industrialized. The PCA analysis was conducted using the seven parameters such as DOC, SUVA, HIX, %C1, %C2, %C3, and %C4. The first two principal components explained approximately 70.73 % of the variance (Fig. 5). The correlations between the first two components and the measured parameters were predicted in a loading plot (Fig. 5a). The first component (PC1) explained approximately 53.2 % of the variance and was positively related to %C1, %C2, and HIX. The PC2 was related to %C3, DOC, and SUVA. The second component (PC2) accounted for 17.5 % of the total variance and was positively correlated with the DOC value. The wetland soils were positioned in an opposite direction to the rice paddy and forest soil samples for the PC1 in the score plot (Fig. 5b). These distributions indicate that the leachate from the wetland soil was associated with the protein-like component, while the leachate from the forest and rice paddy soils was related to the humic-like compounds during the experiment. For the PC1, the positive loading of the forest soils in chamber 2 was higher than that of the forest soil in chamber 1 due to the higher temperature. The distribution of the score plot also indicated the high contributions of the %C1 and %C2 for all of the samples in the N-addition conditions. For the PC2, the positive distribution of the score loading for 1FN, 1FN1, 2F1, and 2FN2 exhibited higher values of DOC and lower SUVA values than the other samples. The loadings of the soil leachate from the pots in chamber 2 had a stronger negative distribution with the PC2 than the loadings of those in chamber 1, indicating the higher contribution of aromatic compounds for samples in chamber 2. The C1 and C2 were the dominant compounds in the rice paddy and forest soils, while the C3 and C4 were the main constituents of the wetland soil.
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Conclusions In this study, we conducted growth chamber experiments using three types of soil (wetland, rice paddy, and forest) under conditions of increased temperature and N-addition in order to investigate how an extreme increase in the temperature and N-deposition influences the characteristics of the DOM leaching from different soil types, thereby controlling the quantity and quality of the DOM in the surface water systems. After 5 months of incubation, the DOC concentrations leaching from almost all of the samples decreased by 21.1 to 88.9 %, while the SUVA values substantially increased from 19.9 to 319.9 % for all of the samples. Higher increases in the SUVA values were observed over time under conditions of higher temperatures, whereas decreases were observed for samples with N-addition. During the incubation, the range of HIX values from the wetland (0.4–2.2) was lower than those of the rice paddy (0.9–7.2) and forest (0.5–4.7), indicating that the wetland was associated with the enrichment of lesscondensed aromatic structures and/or less conjugation of the aliphatic chains compared to the rice paddy and forest. The PARAFAC results showed that four fluorescence components (i.e., terrestrial humic-like (C1), microbial humic-like (C2), protein-like (C3), and anthropogenic humic-like (C4)) constituted the fluorescence matrices of all of the soil samples during the incubation. The C2 was present in higher percentages in chamber 2 than in chamber 1 for all of the samples, except for RN and FN. For the N-addition, both the %C1 and %C2 values of most of the samples exhibited higher values than those without N-addition in both of the chambers. The PCA results revealed that 70.7 % of the variance in the DOM distribution could be explained by humic-like and protein-like components (PC1) and the contribution of aromatic carbon compounds (PC2). From the score plot, the C1 and C2 were the dominant compounds in the rice paddy and forest soils, while the C3 and C4 were the main constituents of the wetland soil. The summation result of the PCA showed that higher temperatures enhanced the contribution of aromatic compounds and N-addition was associated with the contents of the humic-like components in the soil samples. The increase of aromatic compounds and the humiclike components in soil leachates could lead to the increase of recalcitrant DOM in surface water. The recalcitrant DOM is a precursor of disinfection (e.g., chlorine) by-products (DBPs) such as trihalomethanes
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(THMs) and haloacetonitriles (HANs), and the level of DOM is of particular concern in the surface water system used for drinking water. In addition, there is substantial evidence that DBPs may have a negative impact on human health (e.g., mutagen and carcinogen), which makes that the recalcitrant DOM is a serious challenge for drinking water supply. The results of this study provide insight into the characteristics of DOM responding to various scenarios of climate change, cultivating practices, and water resource management. Acknowledgments This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIP) (No. 2009-0083527).
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Changes in the dissolved organic matter leaching from soil under severe temperature and N-deposition Hang Vo-Minh Nguyen & Jung Hyun Choi
Received: 8 July 2014 / Accepted: 21 April 2015 # Springer International Publishing Switzerland 2015
Abstract In this study, we conducted growth chamber experiments using three types of soil (wetland, rice paddy, and forest) under the conditions of a severe increase in the temperature and N-deposition in order to investigate how extreme weather influences the characteristics of the dissolved organic matter (DOM) leaching from different soil types. This leachate controls the quantity and quality of DOM in surface water systems. After 5 months of incubation, the dissolved organic carbon (DOC) concentrations decreased in the range of 21.1 to 88.9 %, while the specific UV absorption (SUVA) values increased substantially in the range of 19.9 to 319.9 % for all of the samples. Higher increases in the SUVA values were observed at higher temperatures, whereas the opposite trend was observed for samples with N-addition. The parallel factor analysis (PARAFAC) results showed that four fluorescence components: terrestrial humic-like (component 1 (C1)), microbial humic-like (component 2 (C2)), protein-like (component 3 (C3)), and anthropogenic humic-like (component 4 (C4)) constituted the fluorescence matrices of soil samples. During the experiment, labile DOM from the soils was consumed and transformed into resistant aromatic carbon structures and less biodegradable components via microbial processes. The principle component analysis (PCA) results indicated that severe temperatures and N-deposition could enhance the H. V.0.05, ANOVA). During the experiment, higher percentages of the terrestrial humic-like component (%C1) were observed for the forest soil in chamber 2 than in chamber 1, while the opposite trend was demonstrated for the rice paddy soil (Fig. 4a). In addition, the microbial humic-like component (%C2) also exhibited higher values in chamber 2 than in chamber 1 (Fig. 4b). Both the protein-like (%C3) and the anthropogenic humic-like (%C4) components exhibited higher values in the samples from chamber 2 without N-addition (Fig. 4c, d). With Naddition, all of the wetland samples and forest samples presented lower values of C4 in chamber 2 than in chamber 1 (Fig. 4d).
At the end of the experiment, the %C1 and %C2 values slightly decreased from 1 to 14 %, while the %C3 and %C4 values increased from 1 to 35 % for the rice paddy (Fig. 4). The samples from the wetland in chamber 2 also exhibited higher values of the terrestrial and microbial humic-like components (%C1, %C2) after 5 months of incubation, while lower trends were observed for the samples from chamber 1. The percentage values of the protein-like component (%C3) for the wetland in chamber 2 (2W, 2WN) decreased after incubation, due to the higher temperature. An increase in the anthropogenic humic-like component (%C4) was only observed for the wetland soil from chamber 2 without N-addition (2W). The leachate from the forest soils exhibited an increase in the %C1 for samples 1FN and 2F and higher values of %C2 for 1F, 1FN, and 2F after 5 months of incubation. In addition, the %C3 values
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Fig. 4 Score of the PARAFAC components a C1, b C2, c C3, and d C4 from all of the soil leachate samples
decreased for all of the samples of the forest soils except for 2FN.
For samples with N-addition, both the %C1 and %C2 values of the samples were higher than those of the
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samples without N-addition in both of the chambers. However, the various trends of the %C3 and %C4 due to the N-addition conditions were not observed in this study.
Discussion The concentration of the DOC values leaching from almost all of the pots decreased during the 5 months of incubation. The decrease in the DOC during incubation could be explained by the consumption of labile DOC via microbial processes (Hur et al. 2009; Xu et al. 2012). The concentrations of the DOC from the pots in chamber 2 were higher than those in chamber 1, indicating that a 10 °C higher temperature (chamber 2) led to an increase in soil respiration, which strongly affected the increase in the DOC leaching (McDowell and Likens 1988; Andersson et al. 1994; Christ and David 1996). However, the ranges of the DOC were influenced more by the type of soil than by the chamber conditions. The leachate from the forest soil showed the highest reduction compared to those of the wetland and rice paddy soil. The positive and negative effects of the N-addition on the DOM concentration have been discussed by several researchers. For instance, Aber (1992) and Mo et al. (2008) stated that N-addition leads to a reduction in the DOC by decreasing the production and increasing the consumption of DOC. However, Fog (1998) and Guggenberger (1994) demonstrated that the Ndeposition resulted in an increase in the DOC from recalcitrant organic carbon, due to the reduced lignolytic activity of the white-rot fungi and simulated biological activity. Our results with the increased DOC values in the N-addition are in agreement with the reports of Fog (1998) and Guggenberger (1994). The increase in the SUVA demonstrates the high concentration of aromatic compounds since SUVA values are known to have a positive correlation with the aromatic carbon content of DOM (Weishaar et al. 2003). Similar results were reported in previous studies. For example, Kalbitz et al. (2003b) demonstrated that the UV absorptions of soil samples incubated in the dark at 20 °C increased during a 90-day period. Saadi et al. (2006) and Hur and Cho (2012) also reported an increase in the SUVA values (above 50 %) by the transformation from labile DOM to refractory DOM. The increased SUVA values could be explained by the
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preferential utilization of non-aromatic moieties by the microorganisms, the microbial transformation of the labile compounds to aromatic carbon structures, or a combination of these processes (Hur et al. 2009). Since the SUVA value can be increased by the microbial decomposition of DOM, higher SUVA values may indicate higher rates of humification, more resistant aromatic humic matter, and lower biodegradability of the DOM (Laor and Avnimelech 2002; Saadi et al. 2006). The results of this study showed that the SUVA values in chamber 2 were higher than those in chamber 1 for all of the samples without N-addition. The increase in SUVA values was highest for the forest soil compared to those of the wetland and rice paddy soil. The forest soil was known to have a higher component of leaf litter, while the wetland soil differed primarily in terms of organic matter due to the abundance of submerged plants. Leaf litter has a higher degradation rate than other parts of plants (i.e., culm) due to the reduced proportions of recalcitrant components, such as celluloses and lignins (Dinka et al. 2004). From the results of the DOC and SUVA measurements, it was determined that higher temperatures strongly affected the production of aromatic compounds due to the increase in the microbial degradation, while N-additions primarily led to an increase in the DOC production. The increase in the HIX can be determined by the microbial changes in the fluorescent components related to longer wavelengths and/or structural modification (Ishii and Boyer 2012). Previous studies presented that HIX increased after 28–30 days of incubation (Kalbitz et al. 2003b; Zhao et al. 2008; Hur and Cho 2012). Since the range of HIX values from the wetland was lower than the ranges from the rice paddy and forest, the wetland was associated with the enrichment of lesscondensed aromatic structures and/or less conjugation of the aliphatic chains than those in the rice paddy and forest (Fuentes et al. 2006). Despite the lack of increase in the HIX from two pots (1W and 2FN) during the incubation and the unclear trend of the wetland under conditions of N-addition and non-N-addition, HIX is still a useful index for investigating the degree of DOM biodegradation. The PARAFAC results showed that four fluorescence components (i.e., terrestrial humic-like (C1), microbial humic-like (C2), protein-like (C3), and anthropogenic humic-like (C4)) constituted the fluorescence matrices of all of the soil samples during the incubation. From the shorter emission of C2, called Bblue shifting,^ it can be
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interpreted that the C2 contained less-conjugated and less-condensed structures than the C1 (Stedmon et al. 2003). The blue shifting of the fluorescence spectra represented a lower degree of humification with the Fig. 5 a Factor loading plot for the measured properties of the first two principal components and b factor scores plot for each sample as the first two principal components
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decomposition of the condensed aromatic moieties of the DOM samples (Coble 1996; Fuentes et al. 2006). Component 3 (C3) identified as a protein-like component indicated that the origin of the fluorophore group
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was related to a microbial-derived amino acid or protein substance (Coble 1996). Component 4 (C4) was associated with an anthropogenic humic fluorophore from agricultural land due to the spreading of animal waste as fertilizer (Stedmon and Markager 2005b). From the data, it was observed that the rice paddy and forest soils dominantly contained terrestrial humic-like and microbial humic-like compounds due to the high percentage of C1 and C2, while most of the wetland samples presented a dominance of C3 and C4. Thus, protein-like and anthropogenic humic fluorophore components of leachate from wetland soil could be strongly affected by the outflow of the watershed which is relatively populated and industrialized. The PCA analysis was conducted using the seven parameters such as DOC, SUVA, HIX, %C1, %C2, %C3, and %C4. The first two principal components explained approximately 70.73 % of the variance (Fig. 5). The correlations between the first two components and the measured parameters were predicted in a loading plot (Fig. 5a). The first component (PC1) explained approximately 53.2 % of the variance and was positively related to %C1, %C2, and HIX. The PC2 was related to %C3, DOC, and SUVA. The second component (PC2) accounted for 17.5 % of the total variance and was positively correlated with the DOC value. The wetland soils were positioned in an opposite direction to the rice paddy and forest soil samples for the PC1 in the score plot (Fig. 5b). These distributions indicate that the leachate from the wetland soil was associated with the protein-like component, while the leachate from the forest and rice paddy soils was related to the humic-like compounds during the experiment. For the PC1, the positive loading of the forest soils in chamber 2 was higher than that of the forest soil in chamber 1 due to the higher temperature. The distribution of the score plot also indicated the high contributions of the %C1 and %C2 for all of the samples in the N-addition conditions. For the PC2, the positive distribution of the score loading for 1FN, 1FN1, 2F1, and 2FN2 exhibited higher values of DOC and lower SUVA values than the other samples. The loadings of the soil leachate from the pots in chamber 2 had a stronger negative distribution with the PC2 than the loadings of those in chamber 1, indicating the higher contribution of aromatic compounds for samples in chamber 2. The C1 and C2 were the dominant compounds in the rice paddy and forest soils, while the C3 and C4 were the main constituents of the wetland soil.
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Conclusions In this study, we conducted growth chamber experiments using three types of soil (wetland, rice paddy, and forest) under conditions of increased temperature and N-addition in order to investigate how an extreme increase in the temperature and N-deposition influences the characteristics of the DOM leaching from different soil types, thereby controlling the quantity and quality of the DOM in the surface water systems. After 5 months of incubation, the DOC concentrations leaching from almost all of the samples decreased by 21.1 to 88.9 %, while the SUVA values substantially increased from 19.9 to 319.9 % for all of the samples. Higher increases in the SUVA values were observed over time under conditions of higher temperatures, whereas decreases were observed for samples with N-addition. During the incubation, the range of HIX values from the wetland (0.4–2.2) was lower than those of the rice paddy (0.9–7.2) and forest (0.5–4.7), indicating that the wetland was associated with the enrichment of lesscondensed aromatic structures and/or less conjugation of the aliphatic chains compared to the rice paddy and forest. The PARAFAC results showed that four fluorescence components (i.e., terrestrial humic-like (C1), microbial humic-like (C2), protein-like (C3), and anthropogenic humic-like (C4)) constituted the fluorescence matrices of all of the soil samples during the incubation. The C2 was present in higher percentages in chamber 2 than in chamber 1 for all of the samples, except for RN and FN. For the N-addition, both the %C1 and %C2 values of most of the samples exhibited higher values than those without N-addition in both of the chambers. The PCA results revealed that 70.7 % of the variance in the DOM distribution could be explained by humic-like and protein-like components (PC1) and the contribution of aromatic carbon compounds (PC2). From the score plot, the C1 and C2 were the dominant compounds in the rice paddy and forest soils, while the C3 and C4 were the main constituents of the wetland soil. The summation result of the PCA showed that higher temperatures enhanced the contribution of aromatic compounds and N-addition was associated with the contents of the humic-like components in the soil samples. The increase of aromatic compounds and the humiclike components in soil leachates could lead to the increase of recalcitrant DOM in surface water. The recalcitrant DOM is a precursor of disinfection (e.g., chlorine) by-products (DBPs) such as trihalomethanes
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(THMs) and haloacetonitriles (HANs), and the level of DOM is of particular concern in the surface water system used for drinking water. In addition, there is substantial evidence that DBPs may have a negative impact on human health (e.g., mutagen and carcinogen), which makes that the recalcitrant DOM is a serious challenge for drinking water supply. The results of this study provide insight into the characteristics of DOM responding to various scenarios of climate change, cultivating practices, and water resource management. Acknowledgments This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIP) (No. 2009-0083527).
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