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Concentrations of Three DifferentCarbon Forms in Surface Waters from anAgroforestry Catchment in NorthwestSpainPatricia Sande-Fouz a , José Manuel Mirás-Avalos a , Rosane Da SilvaDias a & Eva Vidal-Vázquez aa Faculty of Sciences, University of A Coruña, Campus A Zapateira, ACoruña, SpainAccepted author version posted online: 24 Oct 2012.Version ofrecord first published: 19 Feb 2013.

To cite this article: Patricia Sande-Fouz , José Manuel Mirás-Avalos , Rosane Da Silva Dias & EvaVidal-Vázquez (2013): Concentrations of Three Different Carbon Forms in Surface Waters from anAgroforestry Catchment in Northwest Spain, Communications in Soil Science and Plant Analysis,44:1-4, 404-414

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Communications in Soil Science and Plant Analysis, 44:404–414, 2013Copyright © Taylor & Francis Group, LLCISSN: 0010-3624 print / 1532-2416 onlineDOI: 10.1080/00103624.2013.742329

Concentrations of Three Different CarbonForms in Surface Waters from an Agroforestry

Catchment in Northwest Spain

PATRICIA SANDE-FOUZ, JOSÉ MANUEL MIRÁS-AVALOS,ROSANE DA SILVA DIAS, AND EVA VIDAL-VÁZQUEZ

Faculty of Sciences, University of A Coruña, Campus A Zapateira, A Coruña,Spain

Carbon (C) levels in waters allow us to assess the risk of pollution of streams andwater bodies. The aim of this study was to assess the temporal changes in the concen-trations of three different carbon forms (total, organic, and inorganic) at the outlet of anagroforestry catchment under Atlantic climate conditions. This research was conductedat Valiñas River catchment in Coruña (NW Spain), a periurban area. Data sets rangefrom March 2007 to December 2009. A total of 205 samples were collected: 57 in 2007,88 in 2008, and 60 in 2009. Carbon forms were determined using a total organic carbonanalyzer. Total carbon values ranged from 7.39 to 7.94 mg L−1, inorganic carbon variedbetween 4.91 and 5.61 mg L−1, and organic carbon varied between 2.03 and 2.84 mgL−1 during the studied years. Significant correlations were observed between the threeconsidered carbon forms during the study period, except that of inorganic and organiccarbon in 2007. The lowest mean values of the three carbon forms were observed inwinter 2007, winter 2009, and autumn 2008, whereas the greatest concentrations wereobserved in autumn 2007, summer 2008, and summer 2009. Year did not affect car-bon concentrations in water; however, season influenced these concentrations, maybebecause of the rainfall distribution.

Keywords Dissolved organic carbon, seasonality, total carbon, water stream

Introduction

Organic matter affects biogeochemical processes, nutrient cycling, biological activity, andchemical transport in aquatic systems. Organic-matter content in waters is typically mea-sured as total organic carbon (TOC) and dissolved organic carbon (DOC), which arefundamental components of the carbon (C) cycle (Niemirycz, Gozdek, and Koska-Maron2006).

The TOC measurements provide information on all organic substances content inwater (Dojlido and Best 1993), whereas DOC is a ubiquitous component of natural waters,operationally defined as any organic compound passing through a 0.45-µm filter (Evans,Monteith, and Cooper 2005). Some TOC concentrations in natural waters have beenreported in the literature: 0.7 mg L−1 in groundwaters, 2 mg L−1 in seas, and around10 mg L−1 in rivers and lakes (Niemirycz, Gozdek, and Koska-Maron 2006).

Address correspondence to Eva Vidal-Vázquez, Faculty of Sciences, University of A Coruña,Campus A Zapateira, 15008 A Coruña, Spain. E-mail: evidal@udc.es

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Carbon Forms in Surface Waters 405

The DOC concentrations in surface waters vary widely, from 1 to 50 mg L−1 (Thurman1985), with the lowest values observed in the oceans, groundwater, and “clearwater” lakesand rivers draining bare rock or thin, organic-poor soils. Elevated DOC concentrations instreams are of concern because abundant DOC complicates and makes for more expensivewater treatment and is a vector for micropollutants such as heavy metals or pesticides(Miskimmin, Rudd, and Kelly 1992).

Increasing DOC concentrations have been reported during the past decades in manystreams from Western and Northern Europe and North America (e.g., Freeman et al. 2001;Evans, Monteith, and Cooper 2005; Worrall and Burt 2007; Morel et al. 2009; Ågren et al.2010). Different hypotheses, including changes in land use and an increase in soil micro-bial activity, have been put forward to explain this trend. These studies pointed out theimportance of describing the C concentration oscillation in waters from different regionsworldwide in order to assess the impact of land use and human activities on surface waterpollution.

Northern and northwestern regions of Spain are rich in freshwater. Catchments locatedin periurban areas of these regions are used for different purposes such as agriculture,forestry, and recreation. Land use affects the DOC concentration in surface waters becauseof leachates from soil erosion (Miranda et al. 2006). Therefore, monitoring concentrationsof TOC and DOC in waters from these regions is of paramount importance to assess thepollution status of streams.

The current study reports data on C concentrations of water from a small headwaterstream in NW Spain over 3 years (2007–2009). It is interesting to observe whether the sametrends as those observed by other researchers (e.g., Freeman et al. 2001; Evans, Monteith,and Cooper 2005; Worrall and Burt 2007; Morel et al. 2009) are also found in an Atlanticarea of Spain. The studied stream is located on a mixed agroforestry catchment that israpidly changing because of its proximity to an urban area. This site was selected becauseit was representative of the main land uses in the province. Moreover, previous studies onphosphorus and other elements (iron, manganese, copper, and zinc) concentrations in thisstream reported interesting results (Sande Fouz, Vidal Vázquez, and Paz González 2006;Sande Fouz et al. 2009). Total, organic, and inorganic C concentrations were monitoredthrough the whole study period, whereas DOC was assessed from 2009 onward. This studyconstitutes a basis for further research on water quality in Atlantic catchments.

Material and Methods

Study Site

The Valiñas River is a small headwater stream located in the province of La Coruña (NWSpain). The surface area of its catchment is 36.3 km2. The soils within this catchmentare mainly loam and sandy-loam textured, formed on granite bedrocks. The Valiñas Riverbasin has been transformed by human activities.

Agriculture is the main land use within this catchment (55% of the surface is cul-tivated) but also forest is present (45% of the surface). The lower part of the Valiñascatchment is dominated by pastures, old orchards, and scattered fields in patches wheremaize is grown. Small villages and buildings are not connected to a public sewer systemand release sewage into the river, which has an impact on water quality. Surface runofffrom village streets, roads, and a recently built highway also impact the water quality ofthis stream. More details of the Valiñas River catchment can be found in Sande-Fouz et al.(2009).

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This catchment was selected because of several reasons: its accessibility, representa-tive land uses of the region, a nearby climatic station (2 km), and the availability of previouswater quality analyses (Antelo Cortizas and Arce Vázquez 1996).

The climate is Atlantic with an annual total rainfall amount of 1171 mm and an averagetemperature of 13.81 ◦C from 1961 to 1992. During the studied years, rainfall varied from763.4 mm in 2007 to 1074.7 mm in 2008, whereas mean annual temperature varied slightlyfrom year to year (13.73 ◦C in 2007 to 13.92 ◦C in 2009).

Sampling and Laboratory Analyses

The study period reported here extended from March 2007 to December 2009. Prior to thestudy, chemical characterization of water from this river was performed (Table 1). Watersamples were collected at the catchment outlet under base and storm flow conditions. Thesampling strategy was a stratified point sampling involving more frequent collections whenflow was high (Kronvang and Bruhn 1996). A total of 205 samples were taken at the outletof the catchment: 57 samples in 2007, 88 in 2008, and 60 in 2009. The difference in thenumber of samples taken each individual year was a consequence of the frequency andintensity of rainfall.

Samples were collected manually using polyethylenethereptale (PET) bottles and wererefrigerated at 4 ◦C as a method for preservation. Total carbon (TC) and TOC weredetermined after a combustion catalytic oxidation followed by nondispersive infrared spec-troscopy (Crompton 2000) using a TOC analyzer (TOC-V CSN, Shimadzu, Tokyo, Japan)(Ming and Takako 2003). Total inorganic carbon (TIC) was obtained from the differ-ence between TC and TOC. In 2009 only, portions of the samples were filtered througha 0.45-µm syringe filter for measurement of dissolved carbon (DC) fractions, namely, DC,

Table 1Main characteristics of the water from Valiñas River

Parameter Units Value

pH — 6.92Electrical conductivity µS cm−1 171.17Suspended solids mg L−1 17.32Total phosphorus µg L−1 72.31Total sedimentary phosphorus µg L−1 43.12Total dissolved phosphorus µg L−1 29.52Nitrate mg L−1 13.84Sodium mg L−1 16.17Magnesium mg L−1 3.94Potassium mg L−1 2.31Calcium mg L−1 7.44Iron µg L−1 34.88Manganese µg L−1 7.97Copper µg L−1 0.80Zinc µg L−1 6.50Silicon mg L−1 5.43Aluminium µg L−1 12.78

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Carbon Forms in Surface Waters 407

dissolved organic C (DOC), and dissolved inorganic C (DIC). After filtration, DC fractionswere determined using the same procedure as for total C fractions.

Statistical Analyses

A statistical characterization of the studied variables was performed, which consistedof calculating the main descriptive statistics and the frequency distribution. Relationsbetween the different C forms were assessed through Pearson’s r correlation coefficient.Analysis of variance (ANOVA) was used for evaluating the effects of the year and theseason on the concentration in waters of the studied C forms; mean separation was madeusing Tukey’s HSD test. The Kolmogorov–Smirnoff test was used for comparing, on ayearly basis, the frequency distributions of the different C forms analyzed. Statisticalanalyses were carried out using R statistical environment (R Development Core Team2010).

Results and Discussion

Total C annual average concentrations were very similar during the 3 years studied, from7.39 mg L−1 in 2009 to 7.94 mg L−1 in 2008 (Table 2). Similarly, TOC annual averageconcentrations differed slightly from year to year, from 2.03 mg L−1 in 2007 to 2.85 mgL−1 in 2008. The TOC decreased from year to year (Table 2). These values were lessthan those reported for other rivers in Europe (Evans, Monteith, and Cooper 2005; Morelet al. 2009). The TOC values registered in the Valiñas River during this study were alwayswithin the range of those reported for natural waters (Niemirycz, Gozdek, and Koska-Maron 2006).

Median values were similar to those of the means (Table 2), and thus frequencydistributions of the three C forms studied can be considered symmetric. This result wasconfirmed by the skewness coefficients.

Coefficients of variation of TC concentrations increased from year to year. In contrast,the coefficient of variation of TOC was lower from one year to the next (Table 2). Thisseems to indicate that TOC concentrations in waters from the Valiñas River were moreconstant during the study period than those of TC, indicating that the source of variationwas the TIC.

The greatest TC values were registered in autumn every year, mainly in October andNovember. They coincided with increases in TOC concentrations (Figure 1). The low-est values were observed in spring, mainly in March and April. The range of variationof the three C forms was similar from year to year. In addition, TIC was the C fractioncontributing most to the TC concentration in waters from the Valiñas River.

However, regarding the C fractions for the different seasons (Table 3), TC values weregreater in summer and autumn. The TIC average concentrations were greater in sum-mer. However, TOC highest concentrations did not show a general trend, being greaterin winter in 2007, spring in 2008, and autumn in 2009 (Table 3). For the whole studyperiod (2007–2009), the greatest TC and TIC values were recorded in summer, whereasthe greatest TOC concentrations were registered in autumn.

Season significantly affected the concentration of TC and TIC in waters for all theyears studied (data not shown). However, TOC concentrations were only affected by sea-son during 2009 (P value < 0.001). Similar results were observed by other authors indifferent rivers (Butturini and Sabater 2000; Evans, Monteith, and Cooper 2005), indi-cating that temperature and rainfall variations among the seasons are important factors

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Table 2Summary statistics for total carbon (TC), total inorganic carbon (TIC), and total organic

carbon (TOC) each studied year (2007–2009); data for total dissolved carbon (DC),dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) for

2009 are also shown

ParameterTC

(mg L−1)TIC

(mg L−1)TOC

(mg L−1)DC

(mg L−1)DIC

(mg L−1)DOC

(mg L−1)

2007Mean 7.64 5.61 2.03Median 7.77 5.42 1.93Standard

deviation1.78 1.70 0.90

Minimum 2.17 0.27 0.45Maximum 11.46 8.68 4.96Coefficient

of variation23.24 30.30 44.46

Skewness −0.37 −0.29 0.88Kurtosis 0.23 0.28 1.46

2008Mean 7.94 5.09 2.85Median 7.73 4.87 2.54Standard

deviation2.19 1.60 1.09

Minimum 2.77 1.47 1.31Maximum 13.73 9.04 6.63Coefficient

of variation27.55 31.35 38.38

Skewness −0.03 0.07 1.69Kurtosis 0.27 0.19 3.29

2009Mean 7.39 4.91 2.48 7.05 4.60 2.45Median 7.46 4.94 2.42 7.06 4.61 2.38Standard

deviation2.45 1.96 0.79 2.36 1.85 0.75

Minimum 0.99 0.10 0.84 0.94 0.10 0.84Maximum 12.00 8.83 4.59 11.40 8.35 4.50Coefficient

of variation33.15 39.83 31.71 33.50 40.30 30.82

Skewness −0.45 −0.23 0.61 −0.48 −0.26 0.54Kurtosis 0.86 0.42 1.44 0.87 0.50 1.38

affecting C concentrations in surface waters. In this study, slight between-year variationswere observed in C concentrations; however, temperature was a climatic factor corre-lated to TC during the study period (r = 0.46, n = 21) as well as DC in 2009 (r =0.81, n = 12). Niemirycz, Gozdek, and Koska-Maron (2006) also observed significantcorrelations between DOC concentrations in surface waters and temperature.

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Carbon Forms in Surface Waters 409

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Figure 1. Temporal evolution of total carbon (TC), total inorganic carbon (TIC), and total organiccarbon (TOC) at the outlet of the Valiñas River catchment during the 3 years studied (2007–2009).

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Table 3Seasonal average concentrations of the different carbon fractions analyzedat the catchment outlet of the Valiñas River during the studied years and

average for the study period

Season 2007 2008 2009 2007–2009

TC (mg L−1)Winter 5.23 8.27 5.88 6.46Spring 6.68 8.07 6.69 7.15Summer 8.39 8.62 9.26 8.76Autumn 9.35 6.29 8.39 8.01

TIC (mg L−1)Winter 3.07 5.36 3.78 4.07Spring 4.66 4.87 4.61 4.71Summer 6.40 6.08 6.62 6.37Autumn 7.33 3.78 5.00 5.37

TOC (mg L−1)Winter 2.16 2.91 2.10 2.39Spring 2.01 3.18 2.08 2.42Summer 1.99 2.54 2.64 2.39Autumn 2.01 2.51 3.38 2.63

y = 0.717x–0.3347 R2

= 0.7879

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Figure 2. Relation between total inorganic carbon (TIC) and total carbon (TC) for the 3 years studied(2007–2009).

Taking into account the whole dataset, from 2007 to 2009, highly significant correla-tions (P < 0.01) were observed between all the C fractions studied (TC, TIC, and TOC).For instance, TC significantly increases with TIC (Figure 2).

Regarding each individual year, highly significant correlations between TC and TICand between TC and TOC were observed. However, the relation between TIC and TOC in2007 proved to be nonsignificant (Table 4).

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Table 4Pearson’s r coefficients for the studied elements

Parameter 2007 2008 2009

TC/TIC 0.866∗ 0.880∗ 0.960∗TC/TOC 0.335∗ 0.718∗ 0.724∗TIC/TOC 0.181ns 0.301+ 0.503∗

Notes. ns, not significant; +, significant at P < 0.05; and ∗, highlysignificant at P < 0.01.

In the DC fractions measured in 2009 were significantly correlated, as well (DC-DIC:r = 0.96; DC-DOC: r = 0.76; DIC-DOC: r = 0.56), indicating a similar origin of thesefractions.

The frequency distribution of the C concentrations in the waters from this river did notdiffer from year to year. The only exception was TOC, which was different in 2007 than inthe other 2 years analyzed (P value < 0.001). These results may indicate a certain temporalstability of the three C forms analyzed in the waters from the Valiñas River.

The dissolved fraction composed the major part of the C measured in the ValiñasRiver waters during 2009 (more than 95% of the TC). From this fraction, DOC consti-tuted 20%. Thus, inorganic C constituted the major part of both TC and DC fractions inwaters.

The DOC concentrations found in this river were similar to those reported by Evans,Monteith, and Cooper (2005) for certain rivers in the United Kingdom, whereas DOCconcentrations reported by these authors for other British rivers and lakes were muchhigher than those observed here, which can be due to inherent differences in water qualitybetween sample sources. Moreover, Morel et al. (2009) found greater DOC values thanthose reported here in the headwater of an agricultural catchment in northwestern Franceafter storm events.

The greatest concentrations were observed in summer for TC and DIC concentra-tions and in autumn for DOC concentrations (Figure 3). However, mean TOC valuesfor the study period showed a stable behavior of this parameter in the Valiñas River(Figure 4).

Some authors (Hinton, Schiff, and English 1997; Butturini and Sabater 2000) foundsignificant increases of DOC concentrations in streams after storm events. In this study,the slight increase of DOC concentrations during autumn may be due to the greater rainfallamounts registered during those months, which may have involved greater leaching andrunoff rates. However, this assumption is not always true, because high rainfall may reducedissolved solids through dilution.

Conclusions

The TOC concentrations in the Valiñas River registered during 3 years were always withinthe range of those reported for natural waters. A certain stability was observed in TOCconcentrations from year to year. The maximum TOC values were characteristic of theautumn period, whereas the minimum ones were usually recorded in spring. This variationmay be attributed to the differences in temperature and rainfall observed in these months.The increase in TC coincided with increases in TOC; however, in this study TIC was themain fraction of TC observed in Valiñas River waters. Moreover, in 2009, DC was the

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Figure 3. Monthly variability of DOC mean concentrations in waters from the Valiñas River in 2009.Black dots indicate the average for each month, whereas boxes and whiskers indicate the mediansand quartiles, respectively.

Figure 4. Monthly variability of TOC mean concentrations in waters from the Valiñas River in theperiod 2007–2009. Black dots indicate the average for each month, whereas boxes and whiskersindicate the medians and quartiles, respectively.

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main fraction of C in waters. These results showed the influence of the seasonality on thedifferent C fractions studied.

Acknowledgments

This work was supported by Spanish Ministry of Science and Innovation (ProjectCGL2009-13700-C02-01/BTE) and by Xunta de Galicia (Projects INCITE08PXIB162169PR and 10MRU162037PR).

References

Ågren, A., M. Haei, S. J. Köhler, K. Bishop, and H. Laudon. 2010. Regulation of stream waterdissolved organic carbon (DOC) concentrations during snowmelt: The role of discharge, winterclimate, and memory effects. Biogeosciences 7:2901–2913.

Antelo Cortizas, J. M., and F. Arce Vázquez. 1996. Características fisicoquímicas das augas super-ficiais. In As augas de Galicia, ed. F. Díaz Fierros, 351–446. Santiago de Compostela, Spain:Consello da Cultura Galega, Xunta de Galicia.

Butturini, A., and F. Sabater. 2000. Seasonal variability of dissolved organic carbon in aMediterranean stream. Biogeochemistry 51:303–321.

Crompton, T. R. 2000. Determination of organic compounds in natural and treated waters. London:E & FN Spon.

Dojlido, J., and G. Best. 1993. Chemistry of water and water pollution. London: Ellis Horwood.Evans, C. D., D. T. Monteith, and D. M. Cooper. 2005. Long-term increases in surface

water dissolved organic carbon: Observations, possible causes, and environmental impacts.Environmental Pollution 137:55–71.

Freeman, C., C. D. Evans, D. T. Monteith, B. Reynolds, and N. Fenner. 2001. Export of organiccarbon from peat soils. Nature 412:785–786.

Hinton, M. J., S. L. Schiff, and M. C. English. 1997. The significance of storms for the con-centration and export of dissolved organic carbon from two Precambrian Shield catchments.Biogeochemistry 36:67–88.

Kronvang, B., and A. J. Bruhn. 1996. Choice of sampling strategy and estimation method for cal-culating nitrogen and phosphorus transport in small lowland streams. Hydrological Processes10:1483–1501.

Ming, C. A., and T. Takako. 2003. High sensitivity total organic carbon analysis (ShimadzuApplication Report AD-0007-TOC). Tokyo: Shimadzu.

Miranda, J., L. M. da Costa, H. A. Ruiz, and R. Einloft. 2006. Chemical composition of soil solu-tion under different land cover and soluble organic carbon in water from small creeks. RevistaBrasileira de Ciência do Solo 30:633–647.

Miskimmin, B. M., J. W. M. Rudd, and C. A. Kelly. 1992. Influence of dissolved organic carbon,pH, and microbial respiration rates on mercury methylation and demethylation in lake water.Canadian Journal of Fisheries and Aquatic Sciences 49:17–22.

Morel, B., P. Durand, A. Jaffrezic, G. Gruau, and J. Molenat. 2009. Sources of dissolved organiccarbon during stormflow in a headwater agricultural catchment. Hydrological Processes23:2888–2901.

Niemirycz, E., J. Gozdek, and D. Koska-Maron. 2006. Variability of organic carbon in water andsediments of the Odra River and its tributaries. Polish Journal of Environmental Studies 15 (4):557–563.

R Development Core Team. 2010. R: A language and environment for statistical computing. Vienna,Austria: R Foundation for Statistical Computing. Available at http://www.R-project.org.

Sande Fouz, P., E. Vidal Vázquez, and A. Paz González. 2006. Heavy-metal losses from anagroforestry catchment. Communications in Soil Science and Plant Analysis 37:2745–2750.

Dow

nloa

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by [

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3

414 P. Sande-Fouz et al.

Sande Fouz, P., J. M. Mirás Avalos, E. Vidal Vázquez, and A. Paz González. 2009. Phosphoruscontents and loads at the outlet of an agroforestry catchment in northwestern Spain.Communications in Soil Science and Plant Analysis 40:660–671.

Thurman, E. M. 1985. Organic geochemistry of natural waters. Dordrecht, the Netherlands: Kluwer.Worrall, F., and T. P. Burt. 2007. Trends in DOC concentration in Great Britain. Journal of Hydrology

346:81–92.

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