Natural Resources Research, Vol. 20, No. 1, March 2011 ( 2010) DOI: 10.1007/s11053-010-9131-z

Hydrogeochemistry of Groundwater and Its Suitability for Drinking and Agricultural Use in Nahavand, Western Iran Mohsen Jalali1,2 Received 11 March 2010; accepted 2 December 2010 Published online: 23 December 2010

Groundwater is the major source of drinking water in Nahavand city. However, the groundwater quality at the agricultural areas has been deteriorating in recent years. Ground water quality monitoring is a tool which provides important information for water management and sustainable development of the water resources in Nahavand. Hydrochemical investigations were carried out in an agricultural area in Nahavand, western Iran, to assess chemical composition of groundwater. In this study, 64 representative groundwater samples were collected from different irrigation wells and analyzed for pH, electrical conductivity, major ions, and nitrate. The results of the chemical analysis of the groundwater showed that concentrations of ions vary widely and the most prevalent water type is Ca–Mg–HCO3, followed by other water types: Ca–HCO3, Ca–Na–HCO3, and Na–Cl, which is in relation with their interactions with the geological formations of the basin, dissolution of feldspars and chloride and bicarbonate minerals, and anthropogenic activities. Thirty-seven percent of the water samples showed nitrate (NO3) concentrations above the human affected value (13 mg L1). The phosphorous (P) concentration in groundwater was between 0.11 and 0.90 mg L1, with an average value of 0.30 mg L1, with all of the samples over 0.05 mg L1. The most dominant class C2-S1 (76.5%) was found in the studied area, indicating that sodicity is very low and salinity is medium, and that these waters are suitable for irrigation in almost all soils. Agronomic practices, such as cultivation, cropping, and irrigation water management may decrease the average NO3 concentration in water draining from the soil zone. KEY WORDS: Chemical composition, groundwater, hydrochemistry, agricultural activities.

resources is being increasingly degraded as a consequence of its intensified anthropogenic exploitation (Causape´ and others, 2004). Studies have demonstrated that groundwater quality has deteriorated noticeably in many countries during the past few years (Pacheco and Cabrera, 1997; Jeong, 2001; Elhatip and others, 2003; Lee and others, 2003; Rajmohan and Elango, 2005; Jalali, 2007b, 2009). Contamination by different pollutants, mainly due to the intense agricultural and urban development, has placed the whole environment at greater risk (Jalali, 2006). The quality of groundwater in agricultural area is sensitive to the contaminations

INTRODUCTION Groundwater is the primary source of water for human consumption, as well as for agriculture and industrial uses in many regions all over the world. Groundwater quality is controlled by both the natural and human activities (Kouras, Katsoyiannis, and Voutsa, 2007). The quality of world water 1

Department of Soil Science, College of Agriculture, Bu-Ali Sina University, Hamedan, Iran. 2 To whom correspondence should be addressed; e-mail: [email protected].

65 1520-7439/11/0300-0065/0  2010 International Association for Mathematical Geology

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66 originated from the agricultural chemical. A few earlier studies have reported the occurrence of high levels of nitrate (Jalali, 2005; Jalali, 2011) and salinity (Jalali, 2007b, c) in the Hamedan province. The highest salt concentrations have been measured in Tajarak, Hamedan, western Iran from saltaffected soils, reaching values as high as four times the lower limit for poor irrigation water (generally electrical conductivity EC 2.5 dS m1). Salinity of groundwater from non-saline areas are much lower (EC<1.0 dS m1). Nitrate concentrations as high as 250 mg L1 (five times the nitrate limit of 50 mg L1 set by WHO) have been recorded in shallow aquifers located in intensive agricultural areas of Hamedan (Jalali, 2005). Groundwaters in mountainous areas do rarely reach 50 mg L1, but their nitrate concentrations can be still one order of magnitude higher than those present in uncontaminated waters (Jalali, 2006). The quality of groundwater is an important criterion to decide the water for irrigation activities and various parameters such as sodium percentage (% Na+), sodium adsorption ratio (SAR), residual sodium carbonate (RSC), and Ca2+/Mg2+ ratio have been used to assess the suitability of water for irrigation purposes by several researchers (Kumar and others, 2007; Jalali, 2007c; Nagarajan and others, 2010; Reddy and Kumar, 2010). Groundwater is the major source of drinking water in Nahavand city. However, the groundwater quality at the agricultural areas has been deteriorating in recent years. The pollution of groundwater in Nahavand is of particular concern because of the proximity of the region to environmentally sensitive areas and the large number of people in city and rural areas relying on groundwaters for drinking. The water quality of groundwater in the Nahavand area is likely be affected with the increase in groundwater extraction, changes in land use pattern, the expansion of irrigation in arid and semi-arid areas, and its inefficient use and socioeconomic condition in the recent years. Ground water quality monitoring is a tool which provides important information for water management and sustainable development of the water resources in Nahavand. Increased knowledge of geochemical processes that control groundwater chemical composition in arid and semi-arid regions could lead to improved understanding of hydrochemical systems and minimization of negative effects in such areas. Such improved understanding can contribute to effective management and utilization of the groundwater

resource by clarifying relations among groundwater quality and quantifying any future quality changes. Despite the importance of groundwater in Iran, little is known about the natural phenomena that govern the chemical composition of groundwater or anthropogenic factors that presently affect them.

MATERIALS AND METHODS Study Area The water reservoirs of this region has made it a suitable settling for humans even from pre-historical time. Today, this town gets it water from the groundwater and river. It is located south of Hamedan. The study area (Nahavand, Hamedan, western Iran) lies between longitudes 4753¢ and 4832¢E and latitudes 3400¢ and 3426¢N, with a mean altitude of 1880 m.a.s.l. The area studied occupies about 1660 km2 (Fig. 1). The climate of the study area is considered to be semi-arid, the annual average precipitation being approximately 416 mm. Rainfall occurs from October to May, with a maximum during January and February every year. The precipitation in the study area is irregular annual distribution. The mean annual temperatures varies between 5.78 and 20.55C, the mean annual value being 13.48C, and the annual potential evaporation far exceeds the annual rainfall with a mean annual amount of approximately (estimated from 1975 to 2001) 1783 mm (Sabziparvar, 2003). Basement rocks in the Nahavand area consist of marmorized limestone being sandy in part, limestone, limestone with subordinate volcanics, and plio-pleistocene conglomerate. The study area covers different land use types including agriculture, gardens, and uncultivated soils (Fig. 2a). The most important economic activity of the area is agriculture, with the chief crops being garlic (Allium sativum), potato (Solanum tubersum), and wheat (Triticum aestivum L.). Soils in the studied area are mostly calcareous, and dominant soil textures are clay loam, loam, sandy loam, and silty clay (Fig. 2b).

Water Analysis Water samples for chemical analysis were obtained in 2005 from the 64 wells shown in Figure 1. Samples were collected in polyethylene bottles. These bottles had been rinsed with distilled water

Hydrogeochemistry of Groundwater and Its Suitability

67

Figure 1. Study area showing location of wells sampled for groundwater analysis.

before sampling. Samples were collected after a pumping time of about 30 min. The samples were adequately labeled, and preserved in the refrigerator until they were taken to the laboratory for measurement. Samples were analyzed in the laboratory for the major ions (Na+, K+, Ca2+, Mg2+, SO42, Cl,

HCO3, CO32, and NO3), pH, and EC. The determinations were made within 48 h after collection. Calcium, Mg2+, Cl, and HCO3 were determined by titration. Sodium and K+ were measured by flame photometry, SO42 by spectrophotometric turbidimetry, and NO3 by colorimetry with an

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68 UV–Vis spectrophotometer (Rowell, 1994). Care was taken to see that the HCO3 and Ca2+ ions were analyzed within 24 h of sampling. Dissolved P was measured by the Murphey and Riley (1962) method. Total dissolved solids (TDS) were computed by multiplying the EC (dS m1) by a factor of 640. The residual sodium carbonate was calculated as follows:   RSC ¼ ðCO3  þ HCO3  Þ  Ca2þ þ Mg2þ ð1Þ Sodium content expressed in terms of sodium percentage or soluble sodium percentage is defined as

%Na ¼ 

Ca

2þ

ðNaþ Þ   100 þ Mg2þ þ Kþ þ Naþ

ð2Þ

The SAR which indicates the effect of relative cation concentration on Na+ accumulation in the soil was calculated as follows: Naþ ffi SAR ¼ qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2þ

ð3Þ

Ca þMg2þ 2

The ionic symbols indicate concentrations of the ions in the water in meq L1. Total hardness (TH) of groundwater was calculated using following equation (Sawyer, McCarty, and Parkin, 2003):   TH as mg CaCO3 L1   ð4Þ ¼ Ca2þ þ Mg2þ meq L1  50 The statistical software package MINITAB (version 13.1, Minitab Inc.) was employed for the calculations. Surfer package (version 8.0) was used to analyze the spatial structure of the data and to develop the contour maps using point kriging. The GW chart program was used to draw piper diagram.

RESULTS AND DISCUSSION Major Ion Chemistry

Figure 2. Study area showing (a) different land use and (b) soil type. C = clay, CL = clay loam, L = loam, SaL = sandy loam, SiCL = silty clay (Anonymous, 2006).

In Table 1, the major ion chemistry of groundwater from Nahavand is summarized showing minimum, maximum, mean, and standard deviation. Sodium, Ca2+, Mg2+, and K+ concentrations (on the basis of meq L1) represent on an average to 44.9, 29.7, 24.3, and 1.5% of all the cations, respectively, and the order of abundance is Na+>Ca2+>Mg2+> K+. The order of anion abundance is HCO3> Cl>NO3>SO42, contributing on an average (meq L1), respectively, 53.3, 41.4, 4, and 1.4% to the total anions. The EC indicates the amount of material dissolved in water (Rowell, 1994) and its values ranges from 0.254 to 1.73 dS m1 with a mean of 0.629 dS m1. The recommended value of EC for the potable water is 0.250 dS m1 (WHO, 1993). Thus, the EC of the most samples are higher than

Table 1. Chemical Compositions (Major Elements) in the Well Water Samples

Mean Max Min Sd

Ca2+

Mg2+

K+

Na+

Cl

Alkanity

NO3

SO42

EC

pH

TDS

%Na

SAR

RSC

Ca2+/Mg2+

1.62 3.20 0.10 0.65

1.58 5.75 0.20 1.32

0.07 1.15 0.01 0.16

3.01 10.43 0.21 2.06

2.71 10.00 0.50 1.95

3.53 9.30 1.00 2.03

0.25 1.02 0.06 0.20

0.08 0.77 0.00 0.14

0.629 1.734 0.239 0.271

7.68 8.33 6.20 0.38

402.80 1109.76 152.77 173.33

44.5 82.1 7.3 16.6

2.42 7.70 0.19 1.57

0.33 6.45 3.35 2.10

1.92 16.00 0.02 2.22

Concentrations are expressed in meq L1, TDS in mg L1, EC in dS m1

Hydrogeochemistry of Groundwater and Its Suitability the maximum permissible limit. Chloride ion induces a salty taste to water. The limit for domestic purposes is fixed at 250 mg L1. In this study, except in two water samples, Cl content are well within the maximum permissible limit. The WHO (1993) guiding limits for SO42 is 400 mg L1. All of the water samples are within the maximum permissible limit. Most of the Ca2+, Mg2+, and Na+ contents in groundwater samples are also well within the permissible limits. Hardness of water depends mainly upon the amounts of divalent metallic cations of which Ca2+ and Mg2+ are more abundant in groundwater. The hardness values in water samples range from 62 to 317, the average being 160 mg L1 CaCO3. The most recommended limit of total hardness is 80–100 mg L1 CaCO3 (Freeze and Cherry, 1979). Groundwater exceeding the limit of 300 mg L1 CaCO3 is considered to be very hard (Sawyer, McCarty, and Parkin, 2003). The results indicate that only two water samples fall in the very hard water category. Total dissolved solids ranges from 153 to 1062 with an average of 403 mg L1. The recommended value of TDS for potable water is 1000 mg L1. Thus, the TDS (except the two samples) of water samples are mainly well within the maximum permissible limit (WHO, 1993). The average pH is 7.7, the maximum is 8.2, and minimum 6.4, indicating that the pH of water samples is well within the desirable limit (7.0–8.5) (WHO, 1993).

Hydrochemical Facies Based on dominant cations and anions, six water types (Fig. 3) were found for water samples: Ca–Mg–HCO3, Ca–Na–HCO3, Ca–HCO3, Na–Cl, Na–HCO3, and Ca–Cl. The Ca–Mg–HCO3, Ca–Na– HCO3, Ca–HCO3, and Na–Cl, respectively, represent 44, 17, 17, and 16% of the total number of the water samples analyzed, while Na–HCO3 and Ca–Cl, respectively, represent 5% and 1% of the total number of the water samples analyzed. A better understanding of the behavior and origin of cations and anions in groundwater could be attained by means of correlation analysis among ions. The results of the correlation analysis are presented in Table 2. Statistical analyses indicate positive correlation between some pairs of parameters. There was no relation between HCO3 and Ca2+ and Mg2+ and correlation coefficients are not significant (Table 2), but there was strong positive correlation

69

Figure 3. Piper diagram for the groundwater of the studied area.

between HCO3 and Na+ (r = 0.79), indicating that NaCO3 mineral can be a source of Na+. Bicarbonate, formed by neutralization of CO2, originated either by adsorption from the atmosphere or from the decomposition of organic matter in the recharge area. Weathering of silicates in the sediments of the study area also releases HCO3 into groundwater. The relationship between Na+ plus K+ and HCO3 is well described by the 1:1 relation (r = 0.80), indicating dissolution of Na- and K-feldspars. A parallel enrichment in Na+ and Cl indicates dissolution of chloride salts or reconcentration processes by evaporation (Sami, 1992). There is a high correlation (r = 0.66) between Mg2+ and Cl and significant correlation (r = 0.35) between Na+ and Cl, indicating that Mg2+ and Na+ in these samples mostly result from dissolution of magnesium and sodium chloride minerals. The cation exchange between Ca2+ or Mg2+ and Na+ may also explain the excess Na+ concentration. There was no significant correlation between SO42 and other cations.

Phosphorous Concentration in Groundwater Since maximum allowed P groundwater contents have not been established in Iran, a value of 0.05 mg L1, as suggested by USEPA (1992) for incoming water to surface water bodies, was used to evaluate the effect of P groundwater concentrations

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70 Table 2. The Matrix Correlation Among the Chemical Constituents for the Groundwater Samples

Ca2+ Mg2+ K+ Na+ HCO3 Cl NO3 SO42 P

Ca2+

Mg2+

K+

Na+

HCO3

Cl

NO3

SO42

1.0 0.53** 0.12 0.08 0.12 0.03 0.24 0.07 0.14

1.0 0.06 0.29* 0.16 0.66** 0.04 0.09 0.11

1.0 0.01 0.10 0.01 0.05 0.06 0.16

1.0 0.79 0.35** 0.36** 0.06 0.11

1.0 0.17 0.35** 0.10 0.15

1.0 0.00 0.08 0.03

1.0 0.02 0.29*

1.0 0.10

* Correlations significant at p = 0.05; ** Correlations significant at p = 0.01

34.4 0.75

20

34.35 0.65

Degree

Percent

34.3

0.55

34.25

0.45

34.2

0.35

34.15

0.25

10

0.15

34.1

0.05

48.05

48.1

48.15

48.2

48.25

48.3

48.35

48.4

Degree

0 0.0

0.1 0.2

0.3

0.4

0.5 0.6

0.7

0.8

0.9 1.0

Figure 5. Distribution of P (mg L1) in the groundwater of Nahavand area.

P (mg/1) Figure 4. Frequency distributions for P in the groundwater.

in the study area. The P concentration in groundwater was between 0.11 and 0.90 mg L1, with an average value of 0.30 mg L1, in all of the samples over 0.05 mg L1. The frequency distribution (Fig. 4) indicates that 61% of the samples contain P in the range 0.10–0.20 mg L1. The distribution of P concentration is positively skewed (1.19). The lines of equal P concentrations are shown in Figure 5. High P concentrations mainly occurred in three areas: north, northeast, and center. Phosphorus fertilization in amounts exceeding crop needs have resulted in the accumulation of available P in the surface horizon of the most Iranian soils (Jalali, 2007a). In the studied area of intensive crop production, continual P applications as P fertilizer and farmyard manure have been used at levels exceeding crop requirements. Jalali (2007a) compared the amounts of P added to the soil with the crop P uptake in several crops in the Hamedan province. The amounts of P added to the soil for several crops

varied from 31 to 42 kg ha1 and crop P uptake varied from 4.3 to 18.6 kg ha1, resulting in 14–59% of P-fertilizer applied being taken by the crop (Jalali, 2007a), indicating that the P input is higher than the P requirement. Phosphorous fertilizer is used annually, and plant uptake and microbial immobilization cannot remove the entire P from the solution. Long-term fertilization of coarse- to medium-textured soils could increase downward P mobility (Mozaffari and Sims, 1994; Zhang, Mackenzie, and Liang, 1995). Although it is likely that several P minerals are present in the soil in addition to Ca–P minerals, the high concentration of Ca2+ (Ca2+ concentration ranges from 2 to 64 with an average of 32.4 mg L1) in the groundwater and the low solubility of P minerals suggest that Ca–P minerals are most likely present (Hansen and Strawn, 2003), and this also suggested that the most water samples were oversaturated with respect to hydroxyapatite (Jalali, 2009), indicating that this mineral is most likely controlling P concentration in groundwater.

Hydrogeochemistry of Groundwater and Its Suitability

71

40

34.4

62 34.35

Degree

Percent

52

34.3

30

42 34.25

32 34.2

20

22

34.15

12 34.1

2

10

48.05

48.1

48.15

48.2

48.25

48.3

48.35

48.4

Degree

Figure 7. Distribution of NO3 (mg L1) in the groundwater of Nahavand area.

0 0

10

20

30

40

50

60

70

Nitrate (mg/l) Figure 6. Frequency distributions for NO3 in the groundwater.

Nitrate Concentration in Groundwater In Figure 6, the result of water analysis for NO3 concentration are shown as frequency distribution. Nitrate concentrations in the well samples varied from 3.8 to 63.5 with an average value of 15.2 mg L1. The distribution of NO3 concentration is positively skewed (2.26) which is more than that of P. The skewed frequency distribution of NO3 concentration of groundwater suggests the presence of both point and non-point sources of pollution. In comparison with the WHOs drinking water guideline (1993) of 50 mg L1 for NO3, a total of three wells (5%) showed higher concentrations (Fig. 6). In 83% of the samples (53), NO3 concentration was low (<20 mg L1) and NO3 concentration in 17% of the samples (11) were in the range of 20–50 mg L1. High NO3 concentrations mainly occurred in the east part of the study area (Fig. 7). Soil texture in the east part of the studied area consists mainly of loam and sandy loam (Fig. 2). The application of N fertilizers to sandy soils with low clay content and small buffer capacity, in which NO3 does not interact strongly with the soil matrix, results in localized increases in NO3 concentration in the soil solution; subsequently, NO3 is leached by rainfall or irrigation water. Groundwater with NO3 concentration exceeding the threshold of 13 mg L1 NO3 is considered to be contaminated because of human activities (the

so-called human affected value; Burkart and Kolpin, 1993; Eckhardt and Stackelberg, 1995). Thirty-seven percent of the water samples showed NO3 concentrations above the human affected value. It is well known that P, NO3, SO42, Na+, and Cl ions are mostly derived from agricultural fertilizers, animal waste, and municipal and industrial sewage. There are positive correlations between NO3 and Na+ (0.36) and HCO3 (0.35), and negative correlation between NO3 and P (r = 0.29). In Iran, the application of N-fertilizers (200–300 kg ha1 yr1; Jalali, 2005) is higher than those of other countries, such as England (128 kg ha1 yr1; Petry and others, 2002) and the USA (27.5 kg ha1 yr1; Nolan, 2001). A large amount of N fertilizer and an inadequate management of N fertilization coupled with a low irrigation efficiency (about 50%) are mainly responsible for the NO3 concentrations in groundwaters (Jalali, 2005). As further NO3 moves through the soil profile with percolating water, it can be expected that the number of wells that has concentration above recommended guidelines be increased in future.

Water Classification The water quality evaluation in the area of study is carried out to determine their suitability for agricultural purposes. The SAR, percent of Na+, RSC, and Ca2+/Mg2+ ratio were used to assess the suitability of water for irrigation purposes. Sodium concentration is important when evaluating the suitability of groundwater for irrigation. High concentrations of Na+ are not preferred in water

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72

Ca2+/Mg2+ ratio less than 1, and thus can be classified as unsuitable for irrigation.

30 C1-S4

C3-S4

C2-S4

C4-S4

26 22 C1-S3

C2-S3 C3-S3

SAR

18

CONCLUSIONS

14 C4-S3

C1-S2 C2-S2

C3-S2

10

C4-S2

6 2 -2 0

C1-S1

C3-S1 C2S1

500

C4-S1

1000

1500

2000

2500

3000

3500

4000

4500

5000

EC (µmhos cm -1)

Figure 8. Diagram of sodium adsorption ratio and salinity for the classification of groundwater for irrigation purposes.

because of Na+ adsorption onto the soil cation exchange sites, causing soil aggregates to disperse, reducing its permeability. The SAR which indicates the effect of relative cation concentration on Na+ accumulation in the soil is used for evaluating sodicity of irrigation water. The percent of Na+ ranged from 7.3 to 82.1 and the calculated SAR ranged from 0.20 to 7.7. The calculated value of RSC indicated that most of the values (81%) were within the limit of suitability, and only 19% of values were found above the limits (2.5). In order to identify the availability of waters for irrigation use, the Wilcox Classification diagram (1955) has been used (Fig. 8). This graph is based on the EC and SAR. According to this graph, water classes of water samples are C1-S1 (12.5%), C2-S1 (76.5%), and C3-S1 (11%). Only salinity in C3-S1 classes is high. In C2-S1 classes, salinity is medium. Water can be used if a moderate amount of leaching occurs. In respect of Na+, water can be used for irrigation on almost all the soils with little danger of the development of Na+. Therefore, in general most of the water from this aquifer is good for irrigation. Calcium and Mg2+ do not behave equally in the soil system and high concentrations of Mg2+ are not preferred in water because of Mg2+ adsorption onto the soil cation exchange sites, causing soil aggregates to disperse and deteriorate soil structure particularly when waters are Na+ dominated and highly saline. In a Mg2+-dominated water (ratio of Ca2+/Mg2+<1) or a Mg2+ soil (soil–water ratio of Ca2+/Mg2+<1), the potential effect of Na+ may be increased, and adversely affect soil quality. In other words, a given SAR value will show slightly more damage if the Ca2+/Mg2+ ratio is less than 1. Results of this study showed that 31% of the water samples have

In the areas of intensive crop production, continual N and P applications and farmyard manure have been made at levels exceeding crop requirement. As a result, surface soil accumulations of N and P have occurred to such an extent that loss of them in surface runoff and a high risk for N and P transfer into groundwater in concentrations exceeding the groundwater quality standard has become a priority management concern. The chemical analyses of groundwater samples from Nahavand area indicated that some groundwater is typically contaminated with P and NO3 originating from chemical fertilizers. Nitrate proved to have unacceptable concentrations where 37% of water samples have shown NO3 concentrations above human affected value (13 mg L1). The most dominant class C2-S1 (76.5%) was found in the studied area. In this class, sodicity is very low and salinity is medium, indicating that these waters are suitable for irrigation in almost all the soils with less danger of the development of Na+ and salinity problems. To maintain yield increase and minimise NO3 pollution of the groundwater, best management practices concerning N fertilizer use should be applied and excessive fertilizer application prevented. Optimizing management practices for the use of water and N fertilizers in agriculture is a possible means of avoiding, or at least minimizing, environmental contamination by NO3. Fertilizer application should be done in the spring and summer, and the number of applications should be at least two, although a higher frequency is preferred. The results of P concentration in groundwater could be used to identify areas where management approaches, such as the P applied and the crop type planted, could be adjusted relative to the different types of soils, and geology and topography.

ACKNOWLEDGMENTS Two anonymous reviewers made valuable comments on the manuscript. The author gratefully expresses his gratitude for their thoughtful and thorough reviews.

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