identification of groundwater recharge and nitrate ...

Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering), Vol. 68, No. 4, I_199-I_204, 2012.

IDENTIFICATION OF GROUNDWATER RECHARGE AND NITRATE POLLUTION IN THE KANEGAWA ALLUVIAL FAN OF THE KOFU BASIN, JAPAN, USING STABLE ISOTOPES AND IONS Yureana WIJAYANTI1, Takashi NAKAMURA2, Kei NISHIDA3, Eiji HARAMOTO4 and Yasushi SAKAMOTO5 1Student member of JSCE, Ph.D Student, Interdisciplinary Graduate School of Medicine and Engineering, Univ. of

Yamanashi (4-3-11 Takeda, Kofu, Yamanashi 400-8511, Japan)

2Project Assistant Professor, International Research Center for River Basin Environment (ICRE), Univ.of Yamanashi

(4-3-11 Takeda, Kofu, Yamanashi 400-8511, Japan)

3Associate Professor, Interdisciplinary Graduate School of Medicine and Engineering, Univ. of Yamanashi


4Assistant Professor, Interdisciplinary Graduate School of Medicine and Engineering, Univ. of Yamanashi


5Member of JSCE, Professor, Interdisciplinary Graduate School of Medicine and Engineering, Univ. of Yamanashi


Major ions and stable isotopic measurements were utilized in order to investigate the groundwater recharge and nitrate pollutant transformation of shallow alluvial groundwater aquifer. The spatial distribution and multivariate analysis of ions, combined with stable isotope analysis were performed. The result showed that precipitation contributed to the whole year groundwater recharge. Pollutants were transported from the land surface through an infiltration of precipitation. Sources of nitrate are from ammonium fertilizer, manure and septic waste. According to the ion and isotope characteristics, both denitrification and mixing process could take place. The statistical correlation and cluster analysis coupled by spatial analysis approach, based on isotope and ion data could be utilized for a quick assessment of groundwater recharge and nitrate pollution dynamics in an alluvial fan. Key Words: water isotope, nitrogen isotope, major ions, groundwater, river water, correlation and cluster analysis

gain more understanding of the transformation process and transport of pollutant. Comparison of isotope behavior under different land use has also been performed5). These researches were performed using data from boring wells where the hydraulic head or groundwater levels are accessible, so that the flow path and aquifer information were deduced. However, for some areas or regions, it is not possible to construct the bore holes for monitoring wells due to technical or nontechnical limitations. In such case, the only access to get the groundwater data is from an existing inhabitant’s well, which rarely has a reliable hydraulic head information. Moreover, recently the water quality monitoring data has shown that there are some groundwater pollutions in the Kanegawa alluvial fan of the Kofu basin, Japan. The origin of a pollutant is not clear, and it is suspected as a result of nitrate pollutant leaching from agriculture area. In addition, the decreasing of nitrate concentration

1. INTRODUCTION In the past decades, a large amount of groundwater pollution surveys on trace element have been carried out at different scales and there were many studies reported in the scientific literatures1),2),3). Stable isotopes had been utilized to trace pollutant transport in groundwater research because it did not react with the soil as it transported or diffused from land to groundwater. A major advantage of environmental isotopes is that the input function or the ‘injection of tracer’ into the hydrological system is provided by nature. Therefore, environmental isotopes can be used on different scales for local, regional and even global studies4). Moreover, the stable isotope technique is an effective approach to identify the sources, fate and transport of pollutants, because certain contaminant sources have characteristic or distinctive isotopic compositions. Spatial and temporal approaches also have been conducted to

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from 1996 to 2010 was also observed in the groundwater despite of a relatively constant agricultural practice 6). Hence, this study was conducted in the Kanegawa alluvial fan, to evaluate the nitrate pollutant dynamics by utilizing the groundwater samples from the existing wells. In order to understand the nitrate transport from land to groundwater, the hydro-geological process occurred in study area must be also evaluated. Therefore, major ions, water (2H(H2O) and 18  O(H2O)) and Nitrogen (15N(NO3-) and 18O(NO3-)) isotopes were be used to identify nitrate pollution transformation in the groundwater. The main objectives of this study are: (1) to determine and quantify groundwater recharge pattern of seasonal variation; (2) to obtain spatial distribution of major ions in the ground water; (3) to identify major sources that may contaminate the shallow groundwater; and (4) to identify mixing and denitrification process of groundwater using ions and nitrogen isotope data.

The average annual precipitation is 1160 mm recorded over 75-year period from 1936 - 2010. Rainy period precipitation occurs from June to October (Fig.2), which can be considered also as summer season. This rainy period accounts for about 63% of the total annual rain. Geological formations consist of quartz-diorite soil type and acid plutonic rock formed by a volcanic activity of Miocene Epoch. The soil contains gravel and small particles (from Miocene Epoch).

3. METHODS Groundwater samples were collected directly from the eleven wells (GW2-GW12) that equipped with a submersible pump and stored in plastic bottles on ice. The river water samples were also collected from six sampling points at the Fuefuki (R1), Tekawa (R5 and R7) and Kanegawa (R2,R3 and R4) River. The sampling locations are shown in Fig.1. The samples of alluvial groundwater were collected for this study during two sampling campaigns in December 2010 and June 2011 to investigate the effect of fertilizer application occurring in fall and summer on groundwater quality. Cations (Na+, K+, Ca2+, and Mg2+) and anions (Cl-, SO42- and NO3-) of all samples were analyzed using ion chromatography (DIONEX ICS-1100). The isotope samples were analyzed at the International Research Center for River Basin Environment, University of Yamanashi, Kofu, Japan. D or 2H and 18O values of H2O were analyzed using ratio mass spectrometer (Piccaro IRMS). D and 18O values are measured versus the internationally accepted standard V-SMOW. The errors range of analysis was within ±0.05‰ for 18O and ±0.5‰ for D. Meanwhile, 15N and 18O values of NO3 were analyzed using the denitrifier technique9). The N and O isotope ratios were measured on the produced N2O using ratio mass spectrometer (GCIRMS). The 15N values are reported relative to atmospheric nitrogen and 18O values relative to standard mean ocean water (V-SMOW), respectively. Analytical errors for the analysis of 15N and 18O values were about ±0.2‰ and ±0.5‰, respectively. The proposed methodology is combining isotope and ion data in order to explain processes occurring in groundwater system using restricted data sets. The tools for analyzing ions data were statistical methods applying correlation analysis and cluster analysis. Spatial analysis and statistical analysis were carried out with ArcGIS ver.10 and SPSS ver.13, respectively.

2. STUDY AREA The Kanegawa alluvial fan has been a setting for a field-scale research area on alluvial fan groundwater pollution, such as: groundwater pollution by volatile chlorinated hydrocarbon7) and ion concentration and flow direction estimation using statistical analysis8). It is a small (14.2 km2) rural area with a heterogeneous land use of residence and agriculture, located at eastern of the Kofu basin in the Yamanashi prefecture of Japan. Mountainous area, the Fuefuki River, the Tekawa River and the Kanegawa River are the boundaries of the study area located at the east, west, south and north side, respectively (Fig.1).

Fig.1 Study area of the Kanegawa alluvial fan, Kofu basin, Yamanashi prefecture, Japan

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than in rainy period (June to October), that showed a distinct seasonal variation in the dexcess values (Fig.2). Another approach was using the LMWLs of study area. The 18O and D values during rainy and dry period were plotted. As a result, two different local meteoric water lines were drawn to describe isotopic data for two different periods: D=7.618O+4.48 for rainy period precipitation and D=7.318O+4.83 for dry period precipitation (Fig.3a). Such seasonal isotopic differences reflect differences in the local climate of the Kofu basin. Furthermore, the water isotope values of river water and groundwater (ranged from -9.8 to 10.8‰ and -7.7 to -11.6‰ for 18O, respectively, and -69.1 to -74.8‰ and -47.8 to -79.6‰ for D, respectively) were fell between the rainy and dry local meteoric water line (Fig.3b). This indicated that the river and groundwater source was the mixture of precipitation of two seasons. Thus it appeared, based on the d-excess values and LMWLs analysis, that seasonal variation affected the groundwater recharge. Secondly, to quantify the relative contribution of rainy and dry period precipitation to the groundwater recharge, the d-excess values was again being utilized, using a mass-balance equation : dGroundwater = Xdrainy period + (1-X)ddry period (1)

4. RESULTS AND DISCUSSIONS

200 180 160 140 120 100 80 60 40 20 0

precipitation

J

F

M A M

J

J

18 16 14 12 10 8 6 4 2 0

d-excess

A

S

O

N

d-excess (‰)

Precipitation (mm)

(1) D and 18O-H2O of precipitation, river water and groundwater. The isotopic composition of precipitation was acquired from a study by Nakamura10). The precipitation data was collected every month during 2006 at the Hirose, Oyasiki and Hikawa rain stations, in the upland area of the study area (±24 km, ±12 km, and ±3.5 km, respectively). The observed values of  18O and D ranged from -6.5 to -15.8‰ and -41.9 to -113.1 ‰, respectively. Firstly, to detect the seasonal variation of groundwater recharge, two approaches were applied, using the d-excess values and the local meteoric water lines (LMWLs) 11) 12). The d-excess value, which is the excess of deuterium relative to the relationship between 18O and D, is calculated by the equation d=D-818O. The d values ranged from 5.3 to 17.7‰. It was generally higher in dry period (November to May)

D

Month

where dGroundwater is an average d-excess value of groundwater; drainy period and ddry period are the precipitation weighted average d-excess value of rainy and dry period, respectively; X and (1-X) are the fraction of rainy and dry period precipitation, respectively. The mass-balance analysis on isotope showed that those groundwaters are composed of average approximately 60% from rainy period precipitation and 40% from dry period precipitation. It can be inferred that a substantial amount of rainy period precipitation in Kofu recharged the groundwater in the study area. Moreover, this proportion is nearly the same as the proportion of rainy and dry period precipitation amount (75-years of Kofu), about 63% occurrence (during June-October). This implies that isotopic composition of groundwater nearly equals the mean weighted annual isotopic composition of precipitation, and that there was thus no seasonal bias of recharge and evapotranspiration effect may be minimal. This hypothesis is also consistent with the comparison result between the mean d-excess values of the precipitation and the groundwater for 9.7‰ and 9.8‰, respectively. Small

Fig.2 The monthly average precipitation amount during the 75-year period of the Kofu basin and the d-excess of precipitation during year of 2006.

(a)

(b) Fig.3 (a) The local meteoric water lines (LMWLs) were obtained with a linear equation. (b) D versus 18O plot of precipitation, groundwater and river water.

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difference of the mean d-excess value between them indicates a very low evapotranspiration effect occurrence, where most of the rainwater directly infiltrates to the groundwater during precipitation event. This condition might be due to relatively high permeable volcanic rocks and thin soils. This reason is consistent with the research reported by Lee et al12).

straw) both applied in this area, with a trend of increasing utilization of organic fertilizer 15). It might thus be the cause of manure source observed in most wells. Another approach using ions were conducted to complement the nitrogen source identification, as the relationship among ions can provide information about the origin of sources 16). The Pearson correlation coefficients were calculated and the results were shown in Table 1. Anions NO3-N, SO42- and cations Ca2+ and Mg2+ showed strong correlations (r2= 0.91, at 0.01 significance level) indicating that they originated from the same sources. Material such as Ca2+, NO3-N and Mg2+ may be derived from chemical fertilizers and manure such as NH4NO3, (NH4)2SO4, Ca(NO3)2, (Ca, Mg)CO3, and KCl. At this point, both nitrogen isotope and ions analysis showed consistent result that suggested chemical and organic fertilizer (manure) as the nitrogen source in groundwater. Nevertheless, the proportion of nitrogen sources contributed to the groundwater, could not be assessed. The spatial analysis was developed to identify the ions distribution in the groundwater. It showed the highest and the lowest concentration of both NO3-N and SO42- was located at the centered lower part of the alluvial fan and the riverside location of the Kanegawa River, respectively (Fig.5). This high concentration may be due to the over fertilization on orchard agricultural fields causing high concentration of nitrate, and sulfate. The low NO3-N and SO42- concentration might be due to infiltration of water from the river to the groundwater.

(2) Nitrogen isotope and spatial distribution of ions The NO3-N concentration in the Kanegawa alluvial fan groundwater ranges between 0.92 and 6.86 mg/L, below the 10 mg/L limit (Drinking water standard value in Japan). Nevertheless, understanding the nitrate sources and behaviors in groundwater is an important issue for preventing the water quality decline and promoting long-term water resource preservation. Nitrogen isotope ratios have recently been used to identify sources of nitrate and to determine the occurrence of denitrification13), with comparisons to the possible source material such as polluted precipitation, leaching of nitrous fertilizers, manure and septic waste. Kendall et al.14) concluded that ammonium fertilizers have distinctive 15N-NO3 values ranging from -10.0‰ up to +5.0‰. Manure and septic waste have higher values than ammonium fertilizer and a wider range of compositions (generally +2 ‰ up to 30‰). Meanwhile, ammonium fertilizer, manure and septic waste altogether have 18O values of NO3 ranging from -15.0‰ up to +15.0‰14). The 15N and 18O values of NO3 from samples were ranging from 4.83 ‰ up to 7.9‰ and from -1.5‰ to -3.9‰, respectively. These values were compared with the above possible source materials of Kendall et al.14) as shown in Fig.4. The groundwater samples are ranged under the category of overlapping sources of ammonium fertilizer, manure and septic. It is noteworthy that chemical and organic fertilizer (manure or paddy

Table 1 Correlation of ions in groundwater and river water. +

+

2+

2+

-

Na K Mg Ca Cl + Na 1 + K 0.384 1 2+ Mg 0.715* 0.32 1 2+ Ca 0.696* 0.28 0.914* 1 * 0 Cl 0.844* 0.40 0.726* 0.802* 1 * 0 * NO3- 0.737* 0.36 0.949* 0.888* 0.682* * 5 * * 2 SO 0.616* 0.27 0.844* 0.890* 0.567* N4 * 5 * * * ** - Correlation at *the 0.01 level (2-tailed). * is significant 7 * * Correlation is significant at the 0.05 level (2-tailed).

(a) NO3-N (mg/L)

NO3-N

SO4

1 0.826* *

1

2

-

(b) SO42- (mg/L)

Fig.5 NO3-N and SO42- concentration contours (black lines), river boundaries (green lines) & streams (purple lines).

Fig.4 15N-NO3- vs. 18O-NO3- values for groundwater samples.

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(3) Combined river water mixing and denitrification effect on groundwater nitrogen. The NO3-N and SO42- concentration contours inferred the occurrence of river water mixing in groundwater at the riverside location. The reduction of NO3-N concentrations in these locations not only due to the mixing with river water but could also caused by the occurrence of denitrification process 17). In order to check this hypothesis, the correlation between Nitratenitrogen isotope and log of nitrate concentration was used to identify denitrification occurrence in groundwater18),19). The 15N-NO3 values of groundwater and river water ranged from 6.40‰ to 7.99‰, and 4.3‰ to 6.9‰, respectively. However, it was difficult to recognize the denitrification process along the groundwater pathway, due to the absence of the flow direction information. Therefore, a statistical analysis of ions was conducted to identify the spatial similarity and dissimilarity among groundwater and river water. The cluster analysis was applied based on major ions of Na+, Mg2+, SO42- and Ca2+. Clustering had effectively groups the groundwater samples according to their chemical characteristics20). The combination of cluster was based on the dissimilarity defined by Euclidean distance and the nearest neighbor method. The result of grouping was described by dendrogram (Fig.6a). It grouped all sampling locations into two statistically significant clusters of groundwater characteristics. There was an interesting finding, that the group 1 consists of both groundwater and river water despite of a wide range of gaps (±129 m to ±1053 m) between the well locations and the Kanegawa River in a perpendicular direction. Hence, group 1 was classified into two sub-groups of ‘mixing’ and ‘denitrification’; and group 2 was considered as ‘no denitrification’. These groups labeled regarded as the mechanisms that were deduced by nitrogen concentration. Then, within the group of ‘denitrification’, the denitrification process was examined by using the correlation between nitrate isotope and log nitrate concentration (Fig.6b). Bottcher et al.18) verified that the denitrification process, which follow the rule of the Rayleigh fractionation, results in a linear relationship. Thus, the regression line was obtained within the group of ‘denitrification’ (straight-line box, Fig.6b). As the denitrification occurred along the groundwater flow, the direction of the regression line should follow the flow direction. Arrows were positioned in Fig.6c to show the assumed groundwater flow direction among the wells of the group of ‘denitri-

mixing

GROUP 1 denitrification

GROUP 2

No denitrification

(a) 8.5 GW7

8.0

GW2

7.5

15N(‰)

7.0

R5

6.5

GW10 GW5

R1

GW11

GW3

GW6 GW12 GW4

6.0 R7

5.5

GW9

R2

5.0 R3

4.5

GW8

ground water

R4

river

4.0 0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

ln NO3 (mg/L)

(b)

(c) Fig.6 (a) The group of ‘mixing’ (dashed-line box), ‘denitrification’ (straight-line box) and ‘no denitrification’ (dot-dashed line box) labeled in the dendrogram. (b) The relationship between 15N-NO3 and the log of NO3 concentration. (c) The groundwater flow direction within the group of ‘denitrification’.

fication’. Then, by combining the Rayleigh linear equation and well location map, the denitrification was identify within the group of ‘denitrification’. Hence, it can be inferred that the denitrification may occur from G11 to G2, G4 to G6, and G5 to G10. However, further study within the group of ‘no denitrification’ should be performed to evaluate the occurrence of the nitrification process.

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7) Sakamoto,Y., Nakamura,F., Kazama,F. : Characteristic of groundwater pollution by volatile chlorinated hydrocarbon on alluvial fan and its multivariate analysis, Annual Journal of Hydraulic Engineering, Vol.39,Feb., 1995. 8) Sakamoto, Y., Nishida,K. : The relation between the results of principal component analysis for groundwater ion concentrations and groundwater flow direction, Annual Journal of Hydraulic Engineering, Vol.44,Feb., 2000. 9) Casciotti, K. L., Sigman,D. M., Hastings,G. M., Bohlke,J. K. ,and Hilkert,A. : Measurement of the Oxygen Isotopic Composition of Nitrate in Seawater and Freshwater Using the Denitrifier Method, Analytical Chemistry., Vol. 74, pp. 4905-4912, 2002. 10) Nakamura, T., Kazama, Futaba. : Nitrate Loading during a Strom Event in River Lovated in Aluvial Fan Area-Use of Water 18O, Journal of Japan Society on Water Environment., Vol.33,No.2,pp.11-16, 2010. (in Japanese language) 11) Mandal. A.K., Zhang .J ,Asai. K. : Stable isotopic and geochemical data for inferring sources of recharge and groundwater flow on the volcanic island of Rishiri, Japan, Applied Geochemistry., Vol. 26, pp.1741-1751, 2011. 12) Lee. K, S, Wenner. D.B., Lee. I. : Using H- and Oisotopic data for estimating the relative contributions of rainy and dry season precipitation to groundwater: example from Cheju, Island, Korea, Journal of Hydrology., Vol.222, pp.65-74, 1999. 13) Mohamed,A.A., Terao,H., Suzuki,R., Babiker, I.S. ,Ohta,K., Kaori,K., Kato,K. : Natural denitrification in the Kakamigahara groundwater basin, Gifu prefecture, central Japan, The Science of the Total Environment., Vol.307, pp.191–201, 2003. 14) Kendall,C., Elliot.,M., Wankel,S.D. : Chapter 12. Tracing anthropogenic inputs of nitrogen to ecosystems, Stable isotopes in ecology & environmental science, Blackwell publishing., pp.375-449, 2007. 15) Ota, T. : Use of Long-term soil monitoring Database for management of arable Land in Japan, Technical bulletin of Food & Fertilizer Technology Center; http://www.agnet.org/library/tb/179/, 2010. 16) Kaown, D., Koh, D. C. , Mayer, B., Lee, K. K. : Identification of nitrate and sulfate sources in groundwater using dual stable isotope approaches for an agricultural area with different land use (Chuncheon, mid-eastern Korea), Agriculture, Ecosystems and Environment., Vol. 132, pp. 223-231, 2009. 17) Fukada.T, Hiscocka K.M., Dennis.P.F., Grischek.T. : A dual isotope approach to identify denitrification in groundwater at a river-bank infiltration site, Water Research., Vol.37, pp.3070-3078, 2003. 18) Bottcher. J., strebel. O., Voerkelius. S and Schmidt.L.H. : Using isotope fractionation of nitrate-nitrogen and nitrate oxygen for evaluation of microbial denitrification in a sandy aquifer, Journal of Hydrology., Vol.114, pp.413424, 1990. 19) Chen.J., Taniguchi.M., Liu.G., Miyaoka.K., Onodera.S., Tokunaga.T., Fukushima.Y. Nitrate pollution of groundwater in the Yellow River delta, China. Hydrogeology Journal., Vol.15, pp.1605–1614, 2007 20) Chae. G. T., Kim. K., Yun. S. T., Kim. K. H., Kim. S. O., Choi. B. Y., Kim. H. S., Rhee. C. W. : Hydrogeochemistry of alluvial groundwaters in an agricultural area: an implication for groundwater contamination susceptibility, Chemosphere., Vol.55,pp. 369–378, 2004. (Received September 30, 2011)

5. CONCLUSIONS Major ions and stable isotopic measurements were used to examine the groundwater recharge and nitrate pollution of shallow alluvial groundwater aquifer. The result of examination is the following: a. There was no significant difference between mean d-excess of rain water, and ground water. It indicates evapotranspiration effect on isotope is minimal in the Kanegawa alluvial fan that might due to permeable and thin soils. The dexcess of rain water and LMWLs analysis indicated that precipitation during the whole year contributes to groundwater recharge. b. The nitrogen isotopes and ions correlation interpretation concluded that nitrate pollution source may be derived from chemical fertilizers, manure and septic waste. Three different groups of nitrogen transformation process take place in the groundwater of study area, which are mixing of river water, denitrification and no denitrification process. The above results shown that the groundwater clustering based on major ions combined with nitrogen nitrate isotope (15N-NO3) values could be applied to perform a quick assessment of nitrogen cycle in groundwater. ACKNOWLEDGEMENT: The authors sincerely acknowledge Global COE program of University of Yamanashi for supporting this study. REFERENCES 1) Mengis, M.,Schiff, S.L., Harris, M., English, M.C., Aravena, R., Elfood, R.J., Maclean, A. : Multiple geochemical and isotopic approaches for assessing ground water NO3- elimination in a riparian zone, Ground Water., Vol.37,No.3, pp.448-457, 1999. 2) Karr,J.D., Showers, W.J., Gilliam,W.J.,Andres,S. : Tracing nitrate transport and environmental impact from intensive swine farming using delta nitrogen-15, Journal of Environmental Quality., Vol. 30, pp.1163-1175, 2001. 3) Dunn,S.M., Vinogradoff , S. I., Thornton G. J. P., Bacon J. R., Graham M. C. and Farmer J.G. : Quantifying hydrological budgets and pathways in a small upland catchment using a combined modelling and tracer approach, Hydrol. Process., Vol.20, pp.3049–3068, 2006. 4) Leibundgut. C., Maloszewski. P., Kulls. C., Tracers in hydrology, A John Wiley & Sons, Ltd., Publication, pp.14, 2009. 5) Choi,W.J., Han, G.H. , Lee,S.M. ,Lee,G.T. ,Yoon,K.S. , Choi, S.M., Ro, H.M. : Impact of land-use types on nitrate concentration and Nitrogen-15 isotope in unconfined groundwater in rural areas of Korea, Agriculture, Ecosystems and Environment.,Vol.120, pp.259–268, 2007. 6) Suzuki, S. : Improvement of groundwater quality from nitrate pollution in Kofu Basin, Graduates Thesis, University of Yamanashi, Kofu, Japan, pp.34, 2010. (in Japanese Language)

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