Hydrogeochemical characteristics of coastal groundwater in ...
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JOURNAL OF COASTAL SCIENCES Journal homepage: www.jcsonline.co.nr
ISSN: 2348 – 6740
Volume 2 Issue No. 2 - 2015
Pages 1-11
Hydrogeochemical characteristics of coastal groundwater in Nagapattinam and Karaikal aquifers꞉ implications for saline intrusion and agricultural suitability S. Gopinath1, K. Srinivasamoorthy1*, K. Saravanan1, R. Prakash1, C.S. Suma1, Faizal Khan1, D. Senthilnathan1, V.S. Sarma2, Padmavathi Devi3 1Department
of Earth Sciences, Pondicherry University, Puducherry – 605 014, India Geophysical Research Institute, Uppal Road, Hyderabad – 500007, India 3Department of Geophysics, Andhra University, Visakhapatnam – 530 003, India Centre for Geotechnology, Manonmaniam Sundaranar University, Tirunelveli, Tamil Nadu 627 012, India 2National
ABSTRACT
Hydrogeochemical analyses were conducted in coastal groundwater of Nagapattinam and Karaikkal regions, to recognize saline water intrusion and suitability of groundwater for domestic and agricultural purposes. The geology of the region is mainly of sandstone, clay, alluvium, and sandy soils of Quaternary age. A total of 122 groundwater samples were analyzed for 14 different water quality parameters and the result indicates higher concentrations of ions like Cl (5060mgL-1), Na (1950 mgL-1), and HCO3 (587 mgL-1). The dominant cations observed in the groundwater samples follow the order Na+>Ca2+>Mg2+>K+, and the anions as Cl-> HCO3- >SO2-4>NO3->H4SiO4>PO4->I and F-. Influence of saline water intrusion was noted along the eastern parts of the study area. The dominant hydrochemical facies observed for the groundwater samples were Na +Cl-, Ca2+HCO3-, Na+HCO3- and mixed Ca2+Mg2+Cl-. Gibbs plot suggests domination of rock water interaction and evaporation processes influencing the water chemistry. Sodium adsorption ratio and sodium percentage designate majority of samples not suitable for irrigation and domestic utility. The residual sodium carbonate indicates chances of prolonged usage of groundwater will affect the crop yield. The Chloro Alkaline Index isolates higher ratio of Cl->Na+–K+, indicating the effect of salt water intrusion. The Permeability Index suggests water to be moderate to good for irrigation purposes. *Corresponding author, E-mail address: [email protected] Phone: +91 9443824902, © 2015 – Journal of Coastal Sciences. All rights reserved
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Received 18 July 2015 Accepted 10 August 2015 Available online 18 August 2015
Keywords Coastal groundwater Hydrochemical facies Saline intrusion Irrigation utility Nagapattinam and Karaikal aquifers
1. Introduction ail.com water demand Groundwater is crucial for resolving fresh worldwide to fulfill urban, agricultural, industrial and environmental requirements. The coastal aquifers of the world are exposed to severe seawater intrusion several kilometers inland (Pulido-Bosch et al. 1999; Trabelsi et al. 2007; Sherif et al. 2012; Gopinath et al. 2015). The problem of groundwater salinization is the result of uncritical and unexpected groundwater exploitation for fulfilling the rising freshwater essentials of coastal regions, as more than two third of the world’s people live in these areas (Singh 2014). Saline intrusion is one among the major sources for groundwater salinization, since mixing of minor quantity (2–3%) of ocean water turns the groundwater unfit for all the utilities (Abd-Elhamid and Javadi 2011). Seawater intrusion to the aquifers may be direct, but can also involve a range of complex geochemical processes like, inter-aquifer mixing, mobilization of brines, water–rock interaction and anthropogenic contamination (Vengosh et al. 2005). Numerous studies have quantified saline water intrusion and anthropogenic contamination effects on groundwater composition worldwide. Groundwater quality degradation due to saline water intrusion along with wind
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driven sea spray and marine aerosols in a coastal region of Apulia was reported by Polemio et al. (2006). Srinivasmoorthy et al. (2011) isolated sources of saline water intrusion in a coastal region of Cuddalore district, Tamilnadu, India using major ion chemistry. SubbaRao et al. (2002) distinguished saline intrusion as an influencing factor for the inferior quality of groundwater in Guntur, Andhra Pradesh, India. Jing et al. (2014) used zonal modeling approach to segregate inferior groundwater quality in Yinchuan, China. Jeevanandam et al. (2007) attempted for hydrochemistry and quality assessment of groundwater in Ponniyar river basin, south India using major ion chemistry and isolated water quality zones. Groundwater quality assessment and utility has been attempted by Mohan et al. (2000) in Naini industrial area, Uttar Pradesh, India by geochemical facies and isolated zones unsuitable for drinking purposes. Numerous authors have reported about the groundwater quality status in different parts of the globe (Barbash and Gillion 1998; Elango et al. 2003; Srinivasa Rao et al. 1997; SubbaRao et al. 1998; Srinivasamoorthy et al. 2011; Vasanthavigar et al. 2010; Zhao et al. 2011; SubbaRao et al. 2012; Bohlke 2002; Jalali and Kolahchi ORIGINAL
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2008; Gopinath et al. 2014, 2015). In the present study an attempt 2.2. Geology has been made in the coastal region of Tamilnadu and Pondicherry to The geology of the area (Figure 1) covers sedimentary isolate groundwater quality with reference to sea water intrusion formations representing quaternary age. Majority of the study area is and allied activities. occupied by alluvial plain deposits along the western parts of the study and Fluviomarine deltaic plain deposits at the central parts of the study area and marine coastal plain deposits along the eastern 2. Study area parts of the study area. The litho units identified are sand stones, The study area Nagapattinam and Karaikal coastal region with sandy clays, unconsolidated sands; clay bound sand and mottled rapidly developing industrial and urban areas is situated in the clays. (Gopinath et al. 2015). southeast coast of Tamil Nadu, India between latitudes 10°85’ and 11°40’N and longitudes 79°01’ and 80°01’E with a total geographical spread of 1000 km2.
Fig. 1. Geology map of the Nagapattinam and karaikkal district of Tamil Nadu, India
2.1. Climate and rainfall The area enjoys humid and tropical climate with hot summers, significant to slight winters and sensible to heavy rainfall. The normal annual rainfall over the area is 1230 mm. Temperature ranges between 40.6 to 19.3° C with piercing fall in night temperatures during monsoon season. The relative moisture ranges from 70 – 77% and it is high during October to November (CGWB 2008). 2
2.3. Geomorphology The geomorphological features reveal major parts of the study area (63%) covered by flood basin followed by point bar, channel bar and palaeochannel type of deposits. A total of 22% of the study area is dominated by marine coastal plains, tidal flats, salt marsh and mangrove swamps. Remaining 15% of the study area is dominated by flood plain deposits. The complete area is a peneplain with a ORIGINAL
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gentle slope towards east and southeast. The maximum elevation is which falls under overexploited stage (CGWB 2008). Groundwater in about 21 m above mean sea level in the west. (Gopinath et al. 2014). the litho units occurs under water table, semi-confined and confined conditions. The main aquifer systems isolated are i) Lower Miocene 2.4. Irrigation practices deeper aquifers between depths 10 to 55 m and ii) Pliocene – Agriculture is the main occupation of which 70 % of the total Quaternary shallow aquifers at depths between 5 to 35 m. The population depends on it. The other occupations are fishing and Transmissivity of the aquifers ranges between 11 to 1202 m2/day aquaculture. The crops sown are paddy, blackgram, greengram, and the storativity ranges between 4.81 x 10-1 to 4.40x10-10. sugarcane, groundnut, cotton, gingelly, sunflower and chillies (DSHN Groundwater in shallow aquifers are in hydraulic assembly with the 2008). sea and hence susceptible to saline intrusion (CGWB 2008). Groundwater withdrawn for domestic and other utilities are from 2.5. Land use land cover dug tube and driven wells segregated whole study area. Majority (70%) of the study area is covered by agriculture land followed by built up land and waste land targeting 12% and 6% of 2.7. Anthropogenic events the study areas. Built up lands were evenly distributed throughout The main industrial activities isolated were petrochemicals, the study area and waste lands were confined to the coastal tracts fertilizers, caustic soda, poly vinyl chlorine resin manufacturing and water bodies were noted to be sparsely distributed throughout industries and small scale industries like aquaculture, farmhouse and the study area (Figure 2). salt production were also noted in the study area. The northern part
Fig. 2 Land use patterns observed in the study area
of the area is mainly occupied by municipal and industrial activities and the southern and eastern parts by intensive agricultural, salt pan 2.6. Hydrogeology Groundwater is the major source of all utilities with net and aquaculture activities. The climate, soil and abundant brine groundwater availability of 11346.29 (M.Cu.M) but with a gross draft water favours salt production, hence salt pans are the second of 15144.43 (M.Cu.M) resulting in 100% groundwater development dominant activity in the study area. 3 ORIGINAL
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3. Methodology Groundwater samples were collected during two different seasons, South West Monsoon (SWM) and Summer (SUM) seasons from dug wells utilized for rural water using standard sampling procedures (APHA 1995). The depth of the wells ranged between 15 to 30 m. Locations were identified by global positioning system (GARMIN 76CSx) and later imported to GIS platform. Groundwater samples were collected in high density polyethylene bottles prewashed with 1 N hydrochloric acid followed by distilled water and then cleaned two to three times prior sampling using sampling water. Groundwater samples were collected from bore wells after 10 minutes of draining and shifted to laboratory for further analysis and retained at 5 C ̊ . The samples were filtered using 0.45 m cellulose membrane earlier analysis. Groundwater samples for cation were acidified with ultrapure hydrochloric acid in the laboratory. Measurements for pH and EC were made using a handheld multi parameter probe (HANNA–H198130). Bicarbonate by titration using 1 N diluted sulphuric acid method; Chloride by AgNO 3 titration, sulphate, silica and phosphate by UV–Vis double beam spectrophotometer (SL-164, Elico). Calcium and magnesium were analyzed by titration, sodium and potassium by flame photometer (CL-220, Elico). Analytical grade chemicals were used all through the study without more purification. To make all reagents and calibration standards, double distilled water was used. The total cation (Tz+) and total anion (Tz-) balance (Freeze and Cherry 1979) ranged between ±1 to ±10 %. 3.1 Groundwater quality map Spatial EC were prepared for two different seasons (SWM and SUM) adopting the inverse distance weighted (IDW) interpolation technique using Arcview Ver. 9.3. The IDW is a method to interpolate data spatially to appraise the local difference in values between the measurements (Gopinath et al. 2014).
4. Results and discussion
4.1. Groundwater Chemistry The summary of hydrochemical parameters are presented in Table 1. The pH of the groundwater indicates water slightly acidic to alkaline with ranges between 6.0 to 8.40 and 6.33 to 8.87 and with averages of 7.39 and 7.54 during SWM and SUM seasons respectively. The slight alkaline nature of groundwater is probably attributed to anthropogenic activities and seawater intrusion. The EC value ranges from 251.5 to 5,355.8 μScm-1, and 370 to 12,430 μScm-1, with averages of 2008.11 μScm-1and 911.1 μScm-1 during SWM and SUM respectively. The large variation in EC is mainly attributed to distinct processes such as saline sources, mineral dissolution, and influx of pollutants from anthropogenic activities (Gopinath et al. 2015). The spatial distribution (Figure 3) of EC exhibits majority (85%) of samples as potable and (15%) as non-potable during SWM. During SUM (70 %) of the groundwater samples are potable and (30%) are non potable. EC exposed growing movement along the groundwater flow path specifying leaching of subsidiary salts and fertilizers resulting in contamination of groundwater (Förstner and Wittman 1981). Lower EC is noted along the western parts of the study area due to the influence of water flow in river Cauvery. The Total Dissolved Solids (TDS) ranges between 329.9 to 8368 mgL-1 and 200.0 to 6220 mgL-1 with averages of 1423.0 and 996.2 mgL-1 during SWM and SUM seasons respectively. The classification of TDS has been attempted using the standards proposed by Freeze 4
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and Cherry (1979). A total of 77 % and 80 % of samples represent fresh water noted to be distributed along the north eastern and central parts of the study area. The remaining samples (33 % and 20 %) represent brackish nature of water distributed along the eastern parts of the study area during both the seasons. The variation in TDS is essentially ascribed to activities like seepage wastes, industries, dispensary waste and saline water intrusion. The dominant cations observed in the groundwater samples follow the order Na+>Ca2+>Mg2+>K+, and the anions as Cl-> HCO3>SO42->NO3->H4SiO4>PO4->I and F during both the seasons. In general domination of cations is observed in the water chemistry. The calcium in groundwater varied from 10.0 to 416.0 mgL -1 and 26.0 to 198.0 mgL-1 with averages 76.2 and 77.6 during SWM and SUM seasons. Magnesium ranged between 26. 0 to198.0 mgL-1 and 4.9 to 411.0 mgL-1 with averages of 49.6 and 40.2 mgL-1 for both the seasons. The desirable limit of calcium and magnesium are 75.0 mgL-1 and 30.0 mgL-1(WHO 2011 and BIS 1991). A total of 31 % and 41 % of the samples exceed the permissible limit of calcium and 55.7% and 60% of the samples exceeds the permissible limit of magnesium during SWM and SUM seasons respectively. The sources of calcium and magnesium in groundwater might be from leaching of calcium and magnesium bearing rock-forming silicates and gypsum dissolution (Krishna Kumar et al. 2014). The Na+ and K+ concentration ranges between 57.0 to 1950.0 mgL-1 during SWM and 2.0 to 218.0 mgL-1 during SUM, with averages of 298.5 and 40.58 mgL-1 respectively. A total of 52% and 54 % of samples during both the seasons record higher values of Na + in comparison with WHO (2011) and BIS (1991) standards. For potassium a total of 39% and 60 % of the samples exceeded the prescribed standard limit during both the seasons. Higher sodium in groundwater is mainly due to Na+ released from silicate weathering (Meyback 1987) and might also due to saline intrusion (Gopinath et al. 2014 and 2015). Higher Potassium in groundwater is confined to agricultural locations indicating the leaching from fertilizer and the role of agricultural return flow. The bicarbonate in groundwater ranges between 26.4 to 567.0 mgL-1 and 103.0 to 587.0 mgL-1 with averages of 320.0 and 302.3 mgL-1 during SWM and SUM. A total of 4% and 12% of samples during SWM and SUM exceed the prescribed standards of (WHO 2011). The bicarbonate ions controls the alkalinity of groundwater and possibly derived from weathering of silicate rocks, dissolution of carbonate from atmospheric and soil CO 2 gas (Jeong 2001; Krishna Kumar et al. 2011). Chloride occurs naturally in all types of water and the desirable limit for chloride in drinking water ranges from 200.0 to 250.0 mgL-1 as per the standards. Chloride in groundwater samples during SWM ranges between 67.0 to 5060.0 mgL-1 with an average of 544.6 mgL-1 and during SUM it ranges between 890.0 to 2478.0 mgL-1with average 680.4mgL-1. A total of 42 % and 63% of groundwater samples during SWM and SUM exceed the desirable limit. Weathering and dissolution of salt deposits, seawater incursion and agricultural return flow control the occurrence of chloride in groundwater (Jeevanandam et al. 2012). Sulfate content ranges from 1.5 to 430.0 mgL-1 with average of 53.6 mgL-1; and 4.5 to 367.0 mgL-1 with average of 62.8 mgL-1 during SWM and SUM respectively. About 99 % of the samples fall below the permissible limit of (200.0 mg/l) when compared with standards. Fewer samples (2%) exceed the desirable limit. Higher sulphate in groundwater might be due to leaching from unprocessed industrial, domestic waste and their sewages materials and marine sources (Baruah et al. 2008; Jeevanandam et al. 2012; SubbaRao et al. 1998). ORIGINAL
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6.0
8.40
7.3
0.5
6.33
8.87
7.54
1435
200
TDS Ca Mg Na K Cl HCO3 SO4 H4SiO4 PO4 Iodide F NO3
251.5
5355.8
911.1
918.8
10.00
416
76.2
392.9 4.90
8368 411
1423 49.6
77.6
36.28
65.00
1330
387.5
89.0
2478
680.4
4.50
367
62.8
72.2
931.6
1.5
430
53.6
3.0
98
0.1
9.8
0.0
0.9
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3.5 145.0
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31.8 3.60 1.27 0.31 44.9
30
198
544.6 320.0
50
26.00
5060 567
500
80.6
67.0 26.4
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2550.1
361.7
40.5
1266.3
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298.5
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BIS 1991 6.5-8.5
12430
1950
2.0
0.53
WHO 2011 6.5-8.5
370
57.0
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50.67
12.00 5.00
120.3
103.0
20.2
6.50
77.6 3.0 0.9 0.2
34.1
6220 99
418 587 66
0.10
12.8
0.11
1.2
0.19 2.67
2.3
103.0
996.2 40.2 80.9
302.3 18.6 0.1 0.5 0.4
44.0
20.71
500 75
-
75
359.6
200
713.2
250
250
66.1
250
200
-
-
105.6 133.5 11.0 1.7 0.4 0.2
23.1
30
500 -
1
45
-
45
Table 1. Minimum, Maximum, Average and Standard deviation of physico-chemical parameters and major ions of groundwater samples (n = 61) (WHO 2011) and (BIS 1991).
The highest SO42- was noted along the eastern parts of the study area near to the coast indicating marine sources. Nitrate in groundwater ranges between 2.0 to145.0 mgL -1with an average of 44.9 mgL-1 and 2.6 to 103.0 mgL-1 with an average of 44.0 mgL-1 during both the seasons respectively. The permissible limit for nitrate in groundwater (WHO 2011) is 45mgL-1. A total of 39% and 37 % of the samples during SWM and SUM exceed the standard desirable limits. Higher concentrations during both the seasons were observed along the western and central parts of the study area where domination of agricultural activities were noted. Ammonium present in the soil zone is transferred to nitrate by the nitrification process in the presence of oxygen as per the equation noted below. 2O2+NH4+=NO3-+H2O
The potential sources of nitrates are aqua farms, animal wastes, septic tank outflows in the urban area. Nitrate leaching is enriched by high infiltration of soil layer and low runoff (Krishna Kumar et al. 2014). The presence of high nitrate in the drinking water increases the incidence of stomach cancer and other potential hazards to babies and pregnant women (Srinivasa Rao 2006). The phosphate in groundwater during SWM ranged between 26 Poor 0 RSC 2.5 Bad 25 Total hardness as CaCO3- (mg/l) 300 Very Hard 23 Table 2 Classification of groundwater based on drinking and agricultural utilities
48 10 1 2 47 1 13 6 5 19 31
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During SWM 19%, 9%, 19%, 46% and 4 % of the samples represents excellent, good, permissible, doubtful and unsuitable categories and during SUM 18%, 15%, 16 %, 37% and 14% of the samples represent excellent, good, permissible, doubtful and unsuitable for irrigation utilities. Majority of the samples 50 % and 51 % during both the seasons represents groundwater in doubtful and unsuitable category due to the excess sodium ions that get displaced by Ca 2+ and Mg2+ ions when absorbed by clay particles. This exchange reduces permeability and causes soil with poor internal drainage. So, air circulation is restricted and soil becomes hard (Gaofeng et al. 2010) and generally unfit for irrigation. 4.2.3. Total hardness The hardness of the water are mainly due to the total concentration of Ca2+ and Mg2+ ions represented in mgL-1 equivalent to CaCO3-. Hardness can be Temporary or permanent. Temporary hardness is essentially due to the presence of calcium carbonate and is removed by boiling the water. Presence of calcium, magnesium chlorides and sulfates is responsible for permanent hardness and can be treated with ion exchange process. Hard water is unfit for domestic purposes. Stiffness of water limits its utility for industrial purposes; initiating scaling of containers, boilers and irrigation tubing may source health harms to humans, such as kidney failure (WHO 2011). Total hardness is determined by substituting the concentration of Ca2+ and Mg2+ in mgL-1 (Todd 1980) as expressed below by equation: Total hardness = 2.497 / (Ca2+) + 4.115 (Mg2+)
Where the concentrations are reported in meq/L -1 Classification of water based on hardness (Sawyer and McCarthy 1967) is described in (Table 2). Total hardness for the groundwater samples varied between 150.0 and 300.0 mgL-1 with 67 % and 81 % of samples representing hard to very hard water category. Rest of the samples during both the seasons fall under moderate or soft water category. The causes of high TH in the study area might be the dissolution of Ca2+ and Mg2+ions from the aquifer matrix and or due to effluents released from bleaching might increase the hardness of water.
4.2.4. Sodium Adsorption Ratio (SAR) The sodium/alkali hazard is typically expressed as sodium adsorption ratio (SAR). This index quantifies the proportion of sodium (Na+) to calcium (Ca2+) and magnesium (Mg2+) ions in a sample.Sodium hazard of irrigation water can be well assumed by knowing SAR .The SAR values for groundwater samples are calculated by using the following equation (Richards 1954):
SAR
Na
Ca 2 Mg 2 2
Where the concentrations are reported in meq/L -1. As per Richards (1954) classification (Table 2) a total of 98 % and 95% of the samples fall in excellent and good category and 2% and 5% fall in fair and poor category during SWM and SUM seasons (Table 2). Good category water can be used for irrigation with little danger of harmful levels of exchangeable sodium. Sustained exposure of soil to high SAR groundwater can render large expanses of land not suitable for agriculture (Younger and Casey 2003). SAR is found to be higher in 98 % and 95 % of samples during both SWM and SUM 8
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season indicating leaching and dissolution of salts during precipitation infiltrates into the aquifer matrix (Vasanthavigar et al. 2012). 4.2.5. Residual Sodium Carbonate (RSC) Residual sodium carbonate (RSC) is mainly due to water having high absorption capacity of bicarbonate, which in turn precipitates calcium and magnesium and raises sodium. RSC is calculated by the following equation (Eaton 1950). RSC = (CO3-+ HCO3-) – (Ca2++ Mg2+)
Where the concentrations are reported in meq/L -1. According to Richards (1954) water comprising more than 2.5 meqL-1 of RSC is not suitable for irrigation, whereas those having 1.25–2.5 and less than 1.25 meq/l are slightly suitable and safe for irrigation purposes. From the RSC values (Table 2), 54 % and 77% of the samples fall in safe and 40 % and 21 % of the samples in bad zones during both the seasons. Deprived agricultural returns and localized material are partially due to this reason. Long usage of this water will affect crop yield.
4.2.6. Index of Base Exchange (IBE) Groundwater quality gets altered when it passes through the aquifer matrix. Hence, it is essential to identify the reactions taking place between the groundwater and the aquifer along its flow path. Schoeller (1965) proposed two indices to measure “Index of Base Exchange”(IBE), namely Chloro-Alkaline Index (CAI-1 and CAI-II), during rock–water interaction using the formula: CAI - I =[Cl- - (Na++K+)]/Cl-
CAI - II = [Cl- - Na+ + K+)] / (SO2-4 + HCO3- + CO3- + NO3-)
All ionic concentrations are expressed in meq/L -1. Clay minerals are called “permutolites” since they absorb and exchange their cations with cations present in water. When there is an exchange of Na++K+ of the water with the Mg2++Ca2+ of the rock, the exchange is direct and both of the ratios are positive, indicating base exchange (chloro-alkaline equilibrium), whereas if the exchange is reversible, i.e., Mg2++Ca2+ of the rock is exchanging with Na ++K+ of water, it is known as reverse exchange and both of them are negative, indicating chloro-alkaline disequilibrium. The CAI (both CAI-I and -II) of the groundwater from the study area points exchange between Na + and K+ in rock with Mg2+ or Ca2+ in groundwater. From the samples a total of 54% and 45% represent exchange between Na+ and K+ in groundwater with Mg2+ or Ca2+ in rock during both the seasons and a total of 42 % and 57% of the samples exhibit reverse ion exchange during both the seasons in this study area. 4.2.7. Permeability index (PI) The permeability of soil is affected by long-term use of irrigation water and is influenced by sodium, calcium, magnesium and bicarbonate contents in soil. Doneen (1964) has evolved a criterion for assessing the suitability of water for irrigation based on PI. It is calculated by using the formula; where all the ions are expressed in meqL-1.
PI
Na HCO3
(Ca 2 Mg 2 Na )
100
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PI ranges from 3.0 to108.0 meqL-1 and 4.0 to 94.0 meqL-1 during water fit for plants having good salt tolerance but unsuitable for SWM and SUM (Figure 6). Permitting to PI values, the groundwater irrigation in soils with restricted drainage (Mohan et al. 2000). samples fall in class I and class II during both the seasons indicating A total of 8 % of the samples fall in C3S2 category during both the water to be moderate to good for irrigation purposes. seasons, indicating water having high salinity and medium sodicity. High salinity, medium sodicity water cannot be used on fine-grained soils with controlled drainage (Srinivasamoorthy et al. 2011). This is because limited flow is likely to result in the accumulation of salts in the root zones of crops, leading to salinity and soil clogging calamity. Representations is also noted in C3S3 and C3S4 category indicating samples not suitable for irrigation utility due to very high salinity and sodium hazards which affects the plant growing.
5. Conclusions
Fig. 6 Classification of irrigation water for soils of medium permeability SWM and SUM
4.2.8. USSL plot The classification of groundwater for salinity hazard is plotted in USSL (1954) diagram (Figure 7). Majority of water samples during SWM falls in C3S1, C2S1 and C2S2, C3S2 zones and during SWM, samples clusters in C3S1, C2S1 and C3S2, C3S3 zones. In SWM (22 %) and SUM (24 %) samples falls in C3S1 zone indicating high salinity and low sodium water, which can be used for irrigation in almost all types of soil with little danger of exchangeable sodium (Kumar et al. 2007). Representations are also noted in C2S1 category indicating
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The study area is underlined by sedimentary formations of Quaternary ages. The dominant cations observed in the groundwater samples follow the order Na+>Ca2+>Mg2+>K+, and the anions follow the order of Cl-> HCO3- >SO2-4>NO3->H4SiO4>PO4->I- and F- during both the seasons. In general, cation dominates the water chemistry of the study area. The chemical composition of the groundwater is controlled by mixing of seawater, ion-exchange reactions, dissolution processes and anthropogenic inputs. The chemistry of groundwater samples indicate Na+, K+ and Cl- are mainly derived from irrigation return flow and anthropogenic activities in inland and seawater intrusion in coastal areas. The calcium and magnesium ions in groundwater are possibly derived from leaching of calcium and magnesium bearing rock-forming silicates and gypsum dissolution. Nearly 42 % and 63% of groundwater samples during SWM and SUM exceed the desirable limit of chloride ions when compared with WHO and BIS standards. The dominated hydrochemical facies are Ca 2+– Mg2+–Cl- and Na+–Cl- types suggesting carbonate, silicate weathering and seawater intrusion influencing major ion chemistry in the study area. The Na+–HCO3- and Ca2+–Na+–HCO3- facies observed is due to irrigation return flow and anthropogenic activities. Irrigation water classification on the basis of SAR indicates groundwater quality of the study area is moderate to low salinity. The RSC values indicate prolonged usage of groundwater will affect the crop yield. The
Fig. 7 Suitability of irrigation water: USSL (1954) diagram during a) SWM and b) SUM ORIGINAL
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contamination of groundwater from Lower Ponnaiyar Basin, Cuddalore positive values of chloro-alkaline indices indicate cation–anion District, Tamil Nadu, India. Environmental Earth Sciences 67(3), 867–887. exchange and the negative values indicate that host rocks are the primary sources of dissolved ions in the groundwater. As per the PI Jeong, C.H., 2001. Effects of land use and urbanization on hydrochemistry and contamination of groundwater from Taejon area, Korea. Journal of values, the groundwater of the study area is moderate to good for Hydrology 253, 194–210. irrigation purposes. According to the overall assessment of the study Jing, X., Yang, Ho., Cao, Y., Wang, W., 2014. Identification of indicators of area, groundwater quality was found to be useful for drinking and groundwater quality formation process using a zoning model. Journal of irrigation purposes. Hydrology 514, 30–40.
Acknowledgements
This research was funded by Grants Commission (UGC) India (Grant No. 41-1036/2012 (SR) Dated. 1.7.2012) through major research proposal. The first author also acknowledges the UGC, India for granting project Fellow (PF) position.
References
Abd-Elhamid, H.F., Javadi, A.A., 2011. A density-dependant finite element model for analysis of saltwater intrusion in coastal aquifers, Journal of Hydrology 401(3-4), 259-271. APHA, 1995. Standard methods for the examination of water and wastewater (19th ed, p. 1467). Washington, DC. Baruah, M., Bhattacharyya, K.G., Patgiri, A.D., 2008. Water quality ofshallow groundwater of core city area of Guwahati. In:Proceedings of sixteenth national symposium on environment, Haryana, India. pp 101–106. BIS, 1991. Indian Standard drinking water specification (1st rev). pp 1–8. Bohlke, J.K., 2002. Groundwater recharge and agricultural contamination. Hydrogeology Journal 10, 153–179. CGWB, 2008. District groundwater brochure Nagapattinam district, Tamil Nadu. Technical Report Series, 1–21. District Statistical hand book of Nagapattinam (DSHN)., 2008. Technical Report Series, 1-25. Doneen, L.D.,1964. Notes on water quality in Agriculture. Published as a Water Science and Engineering. Paper 4001, Department of Water Sciences and Engineering, University of California. Eaton, F.M., 1950. Significance of carbonates in irrigation waters. Soil Sciences 69, 123–133. Elango, L., Kannan, R., Senthil Kumar, M., 2003. Major ion chemistry and identification of hydrogeochemical processes of groundwater in a part of Kancheepuram District, Tamil Nadu, India. Environmental Geosciences 10(4), 157–166. Förstner, U., Wittman, G.T.W., 1981. Metal pollution in aquatic Environment. Springer verlag Berlin, Heidesberg, New York, pp 336. Freeze, R.A., Cherry, J.A., 1979. Groundwater. Englewood Cliffs, NJ: Prentice Hall (p. 604). Gaofeng, Z., Yonghong, S., Chunlin, H., Qi, F., Zhiguang, L., 2010. Hydrogeochemical processes in the groundwater environment of Heihe River Basin, northwest China. Environmental Earth Sciences 60, 139-153 Gibbs, R.J., 1970. Mechanisms controlling world water chemistry. Sciences J170, 795–840. Gopinath, S., Srinivasamoorthy, K., 2015. Application of Geophysical and hydrogeochemical tracers to investigate salinisation sources in Nagapatinam and Karaikal Coastal Aquifers, South India. Aquatic Procedia 4, 65–71. Gopinath, S., Srinivasamoorthy, K., Prakash,R., 2014. Hydrochemical investigations for identification of groundwater salinization sources in Nagapattinam and Karaikal regions, Southern India. Journal of EnviroGeoChimica Acta 1(2), 153-160. Jalali, M., Kolahchi, Z., 2008. Groundwater quality in an irrigated, agricultural area of northern Malayer, western Iran. Nutrient Cycling in Agroecosystems 80, 95–105. Jeevanandam, M., Kannan, M., Srinivasalu, S., Rammohan, V., 2007. Hydrogeochemistry and Groundwater Quality Assessment of Lower Part of the Ponnaiyar River Basin, Cuddalore District, South India. Environmental Monitoring Assessment 132, 263–274. Jeevanandam, M., Nagarajan, R., Manikandan, M., Senthilkumar, M., Srinivasalu, S., Prasanna, M.V., 2012. Hydrogeochemistry and microbial
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Kabata-Pendias, A., Pendias, H., 1984. Fluorine In: Trace elements in soil and plants. Boca Raton, Florida, CRC Press, pp: 209-215. Krishna Kumar, S., Bharani, R., Magesh, N.S., Godson, P.S., Chandrasekar, N., 2014. Hydrogeochemistry and groundwater quality appraisal of part of south Chennai coastal aquifers, Tamil Nadu, India using WQI and fuzzy logic method. Applied Water Sciences 4, 341–350. Krishna Kumar, S., Chandrasekar, N., Seralathan, P., Godson, P.S., Magesh, N.S., 2011. Hydrogeochemical study of shallow carbonate aquifers, Rameswaram Island, India. Environmental Monitoring and Assessment 184 (7), 4127– 4139. Kumar, M., Ramanathan, A.L., Rao, M.S., Kumar, B., 2007. Identification and evaluation of hydrogeochemical process in the groundwater environment of Delhi, India. Environmental Geology 50, 1025-1039. Meyback, M., 1987. Global chemical weathering of surficial rocks estimated from river dissolved loads. American Journal of Science 287, 401–428. Mohan, R., Singh, A.K., Tripathi, J.K., Choudhry, G.C., 2000. Hydrochemistry and quality assessment of ground water in Naini industrial area Allahabad District, Uttar Pradesh. Journal of the Geological Society of India 55, 77–89. Piper, A.M., 1944. A graphic procedure in the geochemical interpretation of water analyses. Transaction in American Geophysical Union 25, 914–923. Polemio, M., Dragone, V., Limoni, P.P., 2006. Salt contamination in Apulian aquifer: Spatial and time trend. In Proceedings of 1st SWIM-SWICA (19th Salt Water Intrusion Meeting–3rd Salt Water Intrusion in Coastal Aquifers, Cagliari. Pulido-Bosch, A., Tahiri, A., Vallejos, A., 1999. Hydrogeochemical characteristics of processes in the Temara aquifer in northwestern Morocco. Water Air and Soil Pollution 114 (3–4), 323–337. Richards, L.A., 1954. Diagnosis and improvement of saline and alkali soils. USDA handbook, Vol. 160.60 pp. Sawyer, C.N., McCarthy, P.L., 1967. Chemistry for sanitary engineers, 2nd edition. McGraw-Hill, New York. Schoeller, H., 1965. Qualitative evaluation of groundwater resources. In: Methods and techniques of groundwater investigations and development. UNESCO, 54–83 pp. Sherif, M., Sefelnasr, A., Javadi, A., 2012. Incorporating the concept of equivalent freshwater head in successive horizontal simulations of seawater intrusion in the Nile Delta aquifer, Egypt, Journal of Hydrology 464-465, 186-198. Singh, A., 2014. Groundwater resources management through the applications of simulation modeling: a review. Science of the Total Environment 499, 414-423. Song, S.H., Lee, J.Y., Park, N., 2007. Use of vertical electrical soundings to delineate seawater intrusion in a coastal area of Byunsan, Korea. Environmental Geology 52, 1207−1219. Srinivasa Rao, N., 2006. Iron, Manganese, Fluoride and Nitrate levels in ground water of East Godavri District, Andhra Pradesh. The Indian Geographical Journal 685-686. Srinivasa Rao, Y., Reddy, T.V.K., Nayudu, P.T., 1997. Groundwater quality in the Niva River basin, Chitoor district, Andhra Pradesh, India. Environmental Geology 32(1), 56–63. Srinivasagowd, S., 2005. Assessment of groundwater quality for drinking and irrigation purposes: a case study of Peddavanka watershed, Anantapur District, Andhra Pradesh, India. Environmental Geology 48, 702-712. Srinivasamoorthy, K. Vasanthavigar, M. Vijayaraghavan, K. Sarathidasan, J., Gopinath, S., 2013. Hydrochemistry of groundwater in a coastal region of Cuddalore district, Tamilnadu, India: implication for quality assessment. Arabian Journal of Geosciences 6, 441-454. Srinivasamoorthy, K., Nandha Kumar, C., Vasanthavigar, M., Vijayaraghavan, K., Rajiv Gandhi, R., Chidambaram, S., Anandhan, P., Manivannan, R, Vasudevan, S., 2011. Groundwater quality assessment from a hardrock terrain, Salem district of Tamilnadu, India. Arabian Journal of Geosciences. 4, 91–102. ORIGINAL
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SubbaRao, N., GurunadhaRao, V.V.S., Gupta, C.P., 1998. Groundwater pollution due to discharge of industrial effluents in Venkatapuram area, Visakhapatnam, Andhra Pradesh, India. Environmental Geology 33(4), 289– 294. SubbaRao, N., PrakasaRao, J., Devadas, J.D., SrinivasaRao, K.V., Krishna, C., NagamalleswaraRao, B., 2002. Hydrogeochemistry and groundwater quality in a developing urban environment of a semi-arid region, Guntur, Andhra Pradesh. Journal of the Geological Society of India 59, 159–166. SubbaRao, N., Surya Rao, P., Venktram Reddy, G., Nagamani, M., Vidyasagar, G., Satyanarayana, N.L.V., 2012. Chemical characteristics of groundwater and assessment of groundwater quality in Varaha River Basin, Visakhapatnam District, Andhra Pradesh, India. Environmental Monitoring and Assessment 184, 5189–5214. Todd, D.K., 1980. Groundwater hydrology. Wiley, New York. Trabelsi, R., Zairi, M., Dhia, H.B., 2007. Groundwater salinization of the Sfax superficial aquifer, Tunisia. Hydrogeology Journal 15(7), 1341–1355. USSL, 1954. Diagnosis and improvement of salinity and alkaline soil. USDA Hand Book no. 60. Vasanthavigar, M., Srinivasamoorthy, K., Prasanna, M.V., 2012. Evaluation of groundwater suitability for domestic, irrigational, and industrial purposes: a case study from Thirumanimuttar river basin, Tamilnadu, India. Environmental Monitoring Assessment 184,405–420. Vasanthavigar, M., Srinivasamoorthy, K., Vijayaragavan, K., Rajiv Ganthi, R., 2010. Application of water quality index for groundwater quality assessment: Thirumanimuttar subbasin Tamilnadu, India. Environmental Monitoring and Assessment 171, 595–609. Vengosh, A., Kloppmann, W., Marei, A., Livshitz, Y., Gutierrez, A., Banna, M., Guerrot, C., Pankratov, I., Raanan, H., 2005. Sources of salinity and boron in the Gaza strip: natural contaminant flow in the southern Mediterranean coastal aquifer. Water Resource Research 41, W01013. DOI: 10.1029/2004WR003344. WHO, 2011. Guidelines for drinking-water quality, 4th edn. World Health Organization, Geneva. Wilcox , L.V., 1955. Classification and use of irrigation waters.U.S. Department of Agriculture Circular 969. Department of Agriculture,Washington, DC, 19 pp Zhao, J., Guo, F., Lei, K., Yanwu, L., 2011. Multivariate analysis of surface water quality in the Three Gorges area of China and implications for water management. Journal of Environmental Sciences 23(9), 1460–1471.
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JOURNAL OF COASTAL SCIENCES Journal homepage: www.jcsonline.co.nr
ISSN: 2348 – 6740
Volume 2 Issue No. 2 - 2015
Pages 1-11
Hydrogeochemical characteristics of coastal groundwater in Nagapattinam and Karaikal aquifers꞉ implications for saline intrusion and agricultural suitability S. Gopinath1, K. Srinivasamoorthy1*, K. Saravanan1, R. Prakash1, C.S. Suma1, Faizal Khan1, D. Senthilnathan1, V.S. Sarma2, Padmavathi Devi3 1Department
of Earth Sciences, Pondicherry University, Puducherry – 605 014, India Geophysical Research Institute, Uppal Road, Hyderabad – 500007, India 3Department of Geophysics, Andhra University, Visakhapatnam – 530 003, India Centre for Geotechnology, Manonmaniam Sundaranar University, Tirunelveli, Tamil Nadu 627 012, India 2National
ABSTRACT
Hydrogeochemical analyses were conducted in coastal groundwater of Nagapattinam and Karaikkal regions, to recognize saline water intrusion and suitability of groundwater for domestic and agricultural purposes. The geology of the region is mainly of sandstone, clay, alluvium, and sandy soils of Quaternary age. A total of 122 groundwater samples were analyzed for 14 different water quality parameters and the result indicates higher concentrations of ions like Cl (5060mgL-1), Na (1950 mgL-1), and HCO3 (587 mgL-1). The dominant cations observed in the groundwater samples follow the order Na+>Ca2+>Mg2+>K+, and the anions as Cl-> HCO3- >SO2-4>NO3->H4SiO4>PO4->I and F-. Influence of saline water intrusion was noted along the eastern parts of the study area. The dominant hydrochemical facies observed for the groundwater samples were Na +Cl-, Ca2+HCO3-, Na+HCO3- and mixed Ca2+Mg2+Cl-. Gibbs plot suggests domination of rock water interaction and evaporation processes influencing the water chemistry. Sodium adsorption ratio and sodium percentage designate majority of samples not suitable for irrigation and domestic utility. The residual sodium carbonate indicates chances of prolonged usage of groundwater will affect the crop yield. The Chloro Alkaline Index isolates higher ratio of Cl->Na+–K+, indicating the effect of salt water intrusion. The Permeability Index suggests water to be moderate to good for irrigation purposes. *Corresponding author, E-mail address: [email protected] Phone: +91 9443824902, © 2015 – Journal of Coastal Sciences. All rights reserved
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Received 18 July 2015 Accepted 10 August 2015 Available online 18 August 2015
Keywords Coastal groundwater Hydrochemical facies Saline intrusion Irrigation utility Nagapattinam and Karaikal aquifers
1. Introduction ail.com water demand Groundwater is crucial for resolving fresh worldwide to fulfill urban, agricultural, industrial and environmental requirements. The coastal aquifers of the world are exposed to severe seawater intrusion several kilometers inland (Pulido-Bosch et al. 1999; Trabelsi et al. 2007; Sherif et al. 2012; Gopinath et al. 2015). The problem of groundwater salinization is the result of uncritical and unexpected groundwater exploitation for fulfilling the rising freshwater essentials of coastal regions, as more than two third of the world’s people live in these areas (Singh 2014). Saline intrusion is one among the major sources for groundwater salinization, since mixing of minor quantity (2–3%) of ocean water turns the groundwater unfit for all the utilities (Abd-Elhamid and Javadi 2011). Seawater intrusion to the aquifers may be direct, but can also involve a range of complex geochemical processes like, inter-aquifer mixing, mobilization of brines, water–rock interaction and anthropogenic contamination (Vengosh et al. 2005). Numerous studies have quantified saline water intrusion and anthropogenic contamination effects on groundwater composition worldwide. Groundwater quality degradation due to saline water intrusion along with wind
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driven sea spray and marine aerosols in a coastal region of Apulia was reported by Polemio et al. (2006). Srinivasmoorthy et al. (2011) isolated sources of saline water intrusion in a coastal region of Cuddalore district, Tamilnadu, India using major ion chemistry. SubbaRao et al. (2002) distinguished saline intrusion as an influencing factor for the inferior quality of groundwater in Guntur, Andhra Pradesh, India. Jing et al. (2014) used zonal modeling approach to segregate inferior groundwater quality in Yinchuan, China. Jeevanandam et al. (2007) attempted for hydrochemistry and quality assessment of groundwater in Ponniyar river basin, south India using major ion chemistry and isolated water quality zones. Groundwater quality assessment and utility has been attempted by Mohan et al. (2000) in Naini industrial area, Uttar Pradesh, India by geochemical facies and isolated zones unsuitable for drinking purposes. Numerous authors have reported about the groundwater quality status in different parts of the globe (Barbash and Gillion 1998; Elango et al. 2003; Srinivasa Rao et al. 1997; SubbaRao et al. 1998; Srinivasamoorthy et al. 2011; Vasanthavigar et al. 2010; Zhao et al. 2011; SubbaRao et al. 2012; Bohlke 2002; Jalali and Kolahchi ORIGINAL
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2008; Gopinath et al. 2014, 2015). In the present study an attempt 2.2. Geology has been made in the coastal region of Tamilnadu and Pondicherry to The geology of the area (Figure 1) covers sedimentary isolate groundwater quality with reference to sea water intrusion formations representing quaternary age. Majority of the study area is and allied activities. occupied by alluvial plain deposits along the western parts of the study and Fluviomarine deltaic plain deposits at the central parts of the study area and marine coastal plain deposits along the eastern 2. Study area parts of the study area. The litho units identified are sand stones, The study area Nagapattinam and Karaikal coastal region with sandy clays, unconsolidated sands; clay bound sand and mottled rapidly developing industrial and urban areas is situated in the clays. (Gopinath et al. 2015). southeast coast of Tamil Nadu, India between latitudes 10°85’ and 11°40’N and longitudes 79°01’ and 80°01’E with a total geographical spread of 1000 km2.
Fig. 1. Geology map of the Nagapattinam and karaikkal district of Tamil Nadu, India
2.1. Climate and rainfall The area enjoys humid and tropical climate with hot summers, significant to slight winters and sensible to heavy rainfall. The normal annual rainfall over the area is 1230 mm. Temperature ranges between 40.6 to 19.3° C with piercing fall in night temperatures during monsoon season. The relative moisture ranges from 70 – 77% and it is high during October to November (CGWB 2008). 2
2.3. Geomorphology The geomorphological features reveal major parts of the study area (63%) covered by flood basin followed by point bar, channel bar and palaeochannel type of deposits. A total of 22% of the study area is dominated by marine coastal plains, tidal flats, salt marsh and mangrove swamps. Remaining 15% of the study area is dominated by flood plain deposits. The complete area is a peneplain with a ORIGINAL
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gentle slope towards east and southeast. The maximum elevation is which falls under overexploited stage (CGWB 2008). Groundwater in about 21 m above mean sea level in the west. (Gopinath et al. 2014). the litho units occurs under water table, semi-confined and confined conditions. The main aquifer systems isolated are i) Lower Miocene 2.4. Irrigation practices deeper aquifers between depths 10 to 55 m and ii) Pliocene – Agriculture is the main occupation of which 70 % of the total Quaternary shallow aquifers at depths between 5 to 35 m. The population depends on it. The other occupations are fishing and Transmissivity of the aquifers ranges between 11 to 1202 m2/day aquaculture. The crops sown are paddy, blackgram, greengram, and the storativity ranges between 4.81 x 10-1 to 4.40x10-10. sugarcane, groundnut, cotton, gingelly, sunflower and chillies (DSHN Groundwater in shallow aquifers are in hydraulic assembly with the 2008). sea and hence susceptible to saline intrusion (CGWB 2008). Groundwater withdrawn for domestic and other utilities are from 2.5. Land use land cover dug tube and driven wells segregated whole study area. Majority (70%) of the study area is covered by agriculture land followed by built up land and waste land targeting 12% and 6% of 2.7. Anthropogenic events the study areas. Built up lands were evenly distributed throughout The main industrial activities isolated were petrochemicals, the study area and waste lands were confined to the coastal tracts fertilizers, caustic soda, poly vinyl chlorine resin manufacturing and water bodies were noted to be sparsely distributed throughout industries and small scale industries like aquaculture, farmhouse and the study area (Figure 2). salt production were also noted in the study area. The northern part
Fig. 2 Land use patterns observed in the study area
of the area is mainly occupied by municipal and industrial activities and the southern and eastern parts by intensive agricultural, salt pan 2.6. Hydrogeology Groundwater is the major source of all utilities with net and aquaculture activities. The climate, soil and abundant brine groundwater availability of 11346.29 (M.Cu.M) but with a gross draft water favours salt production, hence salt pans are the second of 15144.43 (M.Cu.M) resulting in 100% groundwater development dominant activity in the study area. 3 ORIGINAL
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3. Methodology Groundwater samples were collected during two different seasons, South West Monsoon (SWM) and Summer (SUM) seasons from dug wells utilized for rural water using standard sampling procedures (APHA 1995). The depth of the wells ranged between 15 to 30 m. Locations were identified by global positioning system (GARMIN 76CSx) and later imported to GIS platform. Groundwater samples were collected in high density polyethylene bottles prewashed with 1 N hydrochloric acid followed by distilled water and then cleaned two to three times prior sampling using sampling water. Groundwater samples were collected from bore wells after 10 minutes of draining and shifted to laboratory for further analysis and retained at 5 C ̊ . The samples were filtered using 0.45 m cellulose membrane earlier analysis. Groundwater samples for cation were acidified with ultrapure hydrochloric acid in the laboratory. Measurements for pH and EC were made using a handheld multi parameter probe (HANNA–H198130). Bicarbonate by titration using 1 N diluted sulphuric acid method; Chloride by AgNO 3 titration, sulphate, silica and phosphate by UV–Vis double beam spectrophotometer (SL-164, Elico). Calcium and magnesium were analyzed by titration, sodium and potassium by flame photometer (CL-220, Elico). Analytical grade chemicals were used all through the study without more purification. To make all reagents and calibration standards, double distilled water was used. The total cation (Tz+) and total anion (Tz-) balance (Freeze and Cherry 1979) ranged between ±1 to ±10 %. 3.1 Groundwater quality map Spatial EC were prepared for two different seasons (SWM and SUM) adopting the inverse distance weighted (IDW) interpolation technique using Arcview Ver. 9.3. The IDW is a method to interpolate data spatially to appraise the local difference in values between the measurements (Gopinath et al. 2014).
4. Results and discussion
4.1. Groundwater Chemistry The summary of hydrochemical parameters are presented in Table 1. The pH of the groundwater indicates water slightly acidic to alkaline with ranges between 6.0 to 8.40 and 6.33 to 8.87 and with averages of 7.39 and 7.54 during SWM and SUM seasons respectively. The slight alkaline nature of groundwater is probably attributed to anthropogenic activities and seawater intrusion. The EC value ranges from 251.5 to 5,355.8 μScm-1, and 370 to 12,430 μScm-1, with averages of 2008.11 μScm-1and 911.1 μScm-1 during SWM and SUM respectively. The large variation in EC is mainly attributed to distinct processes such as saline sources, mineral dissolution, and influx of pollutants from anthropogenic activities (Gopinath et al. 2015). The spatial distribution (Figure 3) of EC exhibits majority (85%) of samples as potable and (15%) as non-potable during SWM. During SUM (70 %) of the groundwater samples are potable and (30%) are non potable. EC exposed growing movement along the groundwater flow path specifying leaching of subsidiary salts and fertilizers resulting in contamination of groundwater (Förstner and Wittman 1981). Lower EC is noted along the western parts of the study area due to the influence of water flow in river Cauvery. The Total Dissolved Solids (TDS) ranges between 329.9 to 8368 mgL-1 and 200.0 to 6220 mgL-1 with averages of 1423.0 and 996.2 mgL-1 during SWM and SUM seasons respectively. The classification of TDS has been attempted using the standards proposed by Freeze 4
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and Cherry (1979). A total of 77 % and 80 % of samples represent fresh water noted to be distributed along the north eastern and central parts of the study area. The remaining samples (33 % and 20 %) represent brackish nature of water distributed along the eastern parts of the study area during both the seasons. The variation in TDS is essentially ascribed to activities like seepage wastes, industries, dispensary waste and saline water intrusion. The dominant cations observed in the groundwater samples follow the order Na+>Ca2+>Mg2+>K+, and the anions as Cl-> HCO3>SO42->NO3->H4SiO4>PO4->I and F during both the seasons. In general domination of cations is observed in the water chemistry. The calcium in groundwater varied from 10.0 to 416.0 mgL -1 and 26.0 to 198.0 mgL-1 with averages 76.2 and 77.6 during SWM and SUM seasons. Magnesium ranged between 26. 0 to198.0 mgL-1 and 4.9 to 411.0 mgL-1 with averages of 49.6 and 40.2 mgL-1 for both the seasons. The desirable limit of calcium and magnesium are 75.0 mgL-1 and 30.0 mgL-1(WHO 2011 and BIS 1991). A total of 31 % and 41 % of the samples exceed the permissible limit of calcium and 55.7% and 60% of the samples exceeds the permissible limit of magnesium during SWM and SUM seasons respectively. The sources of calcium and magnesium in groundwater might be from leaching of calcium and magnesium bearing rock-forming silicates and gypsum dissolution (Krishna Kumar et al. 2014). The Na+ and K+ concentration ranges between 57.0 to 1950.0 mgL-1 during SWM and 2.0 to 218.0 mgL-1 during SUM, with averages of 298.5 and 40.58 mgL-1 respectively. A total of 52% and 54 % of samples during both the seasons record higher values of Na + in comparison with WHO (2011) and BIS (1991) standards. For potassium a total of 39% and 60 % of the samples exceeded the prescribed standard limit during both the seasons. Higher sodium in groundwater is mainly due to Na+ released from silicate weathering (Meyback 1987) and might also due to saline intrusion (Gopinath et al. 2014 and 2015). Higher Potassium in groundwater is confined to agricultural locations indicating the leaching from fertilizer and the role of agricultural return flow. The bicarbonate in groundwater ranges between 26.4 to 567.0 mgL-1 and 103.0 to 587.0 mgL-1 with averages of 320.0 and 302.3 mgL-1 during SWM and SUM. A total of 4% and 12% of samples during SWM and SUM exceed the prescribed standards of (WHO 2011). The bicarbonate ions controls the alkalinity of groundwater and possibly derived from weathering of silicate rocks, dissolution of carbonate from atmospheric and soil CO 2 gas (Jeong 2001; Krishna Kumar et al. 2011). Chloride occurs naturally in all types of water and the desirable limit for chloride in drinking water ranges from 200.0 to 250.0 mgL-1 as per the standards. Chloride in groundwater samples during SWM ranges between 67.0 to 5060.0 mgL-1 with an average of 544.6 mgL-1 and during SUM it ranges between 890.0 to 2478.0 mgL-1with average 680.4mgL-1. A total of 42 % and 63% of groundwater samples during SWM and SUM exceed the desirable limit. Weathering and dissolution of salt deposits, seawater incursion and agricultural return flow control the occurrence of chloride in groundwater (Jeevanandam et al. 2012). Sulfate content ranges from 1.5 to 430.0 mgL-1 with average of 53.6 mgL-1; and 4.5 to 367.0 mgL-1 with average of 62.8 mgL-1 during SWM and SUM respectively. About 99 % of the samples fall below the permissible limit of (200.0 mg/l) when compared with standards. Fewer samples (2%) exceed the desirable limit. Higher sulphate in groundwater might be due to leaching from unprocessed industrial, domestic waste and their sewages materials and marine sources (Baruah et al. 2008; Jeevanandam et al. 2012; SubbaRao et al. 1998). ORIGINAL
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6.0
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7.3
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6.33
8.87
7.54
1435
200
TDS Ca Mg Na K Cl HCO3 SO4 H4SiO4 PO4 Iodide F NO3
251.5
5355.8
911.1
918.8
10.00
416
76.2
392.9 4.90
8368 411
1423 49.6
77.6
36.28
65.00
1330
387.5
89.0
2478
680.4
4.50
367
62.8
72.2
931.6
1.5
430
53.6
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98
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9.8
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0.9
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3.5 145.0
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31.8 3.60 1.27 0.31 44.9
30
198
544.6 320.0
50
26.00
5060 567
500
80.6
67.0 26.4
500
2550.1
361.7
40.5
1266.3
2008.1
298.5
218
BIS 1991 6.5-8.5
12430
1950
2.0
0.53
WHO 2011 6.5-8.5
370
57.0
2.0
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50.67
12.00 5.00
120.3
103.0
20.2
6.50
77.6 3.0 0.9 0.2
34.1
6220 99
418 587 66
0.10
12.8
0.11
1.2
0.19 2.67
2.3
103.0
996.2 40.2 80.9
302.3 18.6 0.1 0.5 0.4
44.0
20.71
500 75
-
75
359.6
200
713.2
250
250
66.1
250
200
-
-
105.6 133.5 11.0 1.7 0.4 0.2
23.1
30
500 -
1
45
-
45
Table 1. Minimum, Maximum, Average and Standard deviation of physico-chemical parameters and major ions of groundwater samples (n = 61) (WHO 2011) and (BIS 1991).
The highest SO42- was noted along the eastern parts of the study area near to the coast indicating marine sources. Nitrate in groundwater ranges between 2.0 to145.0 mgL -1with an average of 44.9 mgL-1 and 2.6 to 103.0 mgL-1 with an average of 44.0 mgL-1 during both the seasons respectively. The permissible limit for nitrate in groundwater (WHO 2011) is 45mgL-1. A total of 39% and 37 % of the samples during SWM and SUM exceed the standard desirable limits. Higher concentrations during both the seasons were observed along the western and central parts of the study area where domination of agricultural activities were noted. Ammonium present in the soil zone is transferred to nitrate by the nitrification process in the presence of oxygen as per the equation noted below. 2O2+NH4+=NO3-+H2O
The potential sources of nitrates are aqua farms, animal wastes, septic tank outflows in the urban area. Nitrate leaching is enriched by high infiltration of soil layer and low runoff (Krishna Kumar et al. 2014). The presence of high nitrate in the drinking water increases the incidence of stomach cancer and other potential hazards to babies and pregnant women (Srinivasa Rao 2006). The phosphate in groundwater during SWM ranged between 26 Poor 0 RSC 2.5 Bad 25 Total hardness as CaCO3- (mg/l) 300 Very Hard 23 Table 2 Classification of groundwater based on drinking and agricultural utilities
48 10 1 2 47 1 13 6 5 19 31
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During SWM 19%, 9%, 19%, 46% and 4 % of the samples represents excellent, good, permissible, doubtful and unsuitable categories and during SUM 18%, 15%, 16 %, 37% and 14% of the samples represent excellent, good, permissible, doubtful and unsuitable for irrigation utilities. Majority of the samples 50 % and 51 % during both the seasons represents groundwater in doubtful and unsuitable category due to the excess sodium ions that get displaced by Ca 2+ and Mg2+ ions when absorbed by clay particles. This exchange reduces permeability and causes soil with poor internal drainage. So, air circulation is restricted and soil becomes hard (Gaofeng et al. 2010) and generally unfit for irrigation. 4.2.3. Total hardness The hardness of the water are mainly due to the total concentration of Ca2+ and Mg2+ ions represented in mgL-1 equivalent to CaCO3-. Hardness can be Temporary or permanent. Temporary hardness is essentially due to the presence of calcium carbonate and is removed by boiling the water. Presence of calcium, magnesium chlorides and sulfates is responsible for permanent hardness and can be treated with ion exchange process. Hard water is unfit for domestic purposes. Stiffness of water limits its utility for industrial purposes; initiating scaling of containers, boilers and irrigation tubing may source health harms to humans, such as kidney failure (WHO 2011). Total hardness is determined by substituting the concentration of Ca2+ and Mg2+ in mgL-1 (Todd 1980) as expressed below by equation: Total hardness = 2.497 / (Ca2+) + 4.115 (Mg2+)
Where the concentrations are reported in meq/L -1 Classification of water based on hardness (Sawyer and McCarthy 1967) is described in (Table 2). Total hardness for the groundwater samples varied between 150.0 and 300.0 mgL-1 with 67 % and 81 % of samples representing hard to very hard water category. Rest of the samples during both the seasons fall under moderate or soft water category. The causes of high TH in the study area might be the dissolution of Ca2+ and Mg2+ions from the aquifer matrix and or due to effluents released from bleaching might increase the hardness of water.
4.2.4. Sodium Adsorption Ratio (SAR) The sodium/alkali hazard is typically expressed as sodium adsorption ratio (SAR). This index quantifies the proportion of sodium (Na+) to calcium (Ca2+) and magnesium (Mg2+) ions in a sample.Sodium hazard of irrigation water can be well assumed by knowing SAR .The SAR values for groundwater samples are calculated by using the following equation (Richards 1954):
SAR
Na
Ca 2 Mg 2 2
Where the concentrations are reported in meq/L -1. As per Richards (1954) classification (Table 2) a total of 98 % and 95% of the samples fall in excellent and good category and 2% and 5% fall in fair and poor category during SWM and SUM seasons (Table 2). Good category water can be used for irrigation with little danger of harmful levels of exchangeable sodium. Sustained exposure of soil to high SAR groundwater can render large expanses of land not suitable for agriculture (Younger and Casey 2003). SAR is found to be higher in 98 % and 95 % of samples during both SWM and SUM 8
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season indicating leaching and dissolution of salts during precipitation infiltrates into the aquifer matrix (Vasanthavigar et al. 2012). 4.2.5. Residual Sodium Carbonate (RSC) Residual sodium carbonate (RSC) is mainly due to water having high absorption capacity of bicarbonate, which in turn precipitates calcium and magnesium and raises sodium. RSC is calculated by the following equation (Eaton 1950). RSC = (CO3-+ HCO3-) – (Ca2++ Mg2+)
Where the concentrations are reported in meq/L -1. According to Richards (1954) water comprising more than 2.5 meqL-1 of RSC is not suitable for irrigation, whereas those having 1.25–2.5 and less than 1.25 meq/l are slightly suitable and safe for irrigation purposes. From the RSC values (Table 2), 54 % and 77% of the samples fall in safe and 40 % and 21 % of the samples in bad zones during both the seasons. Deprived agricultural returns and localized material are partially due to this reason. Long usage of this water will affect crop yield.
4.2.6. Index of Base Exchange (IBE) Groundwater quality gets altered when it passes through the aquifer matrix. Hence, it is essential to identify the reactions taking place between the groundwater and the aquifer along its flow path. Schoeller (1965) proposed two indices to measure “Index of Base Exchange”(IBE), namely Chloro-Alkaline Index (CAI-1 and CAI-II), during rock–water interaction using the formula: CAI - I =[Cl- - (Na++K+)]/Cl-
CAI - II = [Cl- - Na+ + K+)] / (SO2-4 + HCO3- + CO3- + NO3-)
All ionic concentrations are expressed in meq/L -1. Clay minerals are called “permutolites” since they absorb and exchange their cations with cations present in water. When there is an exchange of Na++K+ of the water with the Mg2++Ca2+ of the rock, the exchange is direct and both of the ratios are positive, indicating base exchange (chloro-alkaline equilibrium), whereas if the exchange is reversible, i.e., Mg2++Ca2+ of the rock is exchanging with Na ++K+ of water, it is known as reverse exchange and both of them are negative, indicating chloro-alkaline disequilibrium. The CAI (both CAI-I and -II) of the groundwater from the study area points exchange between Na + and K+ in rock with Mg2+ or Ca2+ in groundwater. From the samples a total of 54% and 45% represent exchange between Na+ and K+ in groundwater with Mg2+ or Ca2+ in rock during both the seasons and a total of 42 % and 57% of the samples exhibit reverse ion exchange during both the seasons in this study area. 4.2.7. Permeability index (PI) The permeability of soil is affected by long-term use of irrigation water and is influenced by sodium, calcium, magnesium and bicarbonate contents in soil. Doneen (1964) has evolved a criterion for assessing the suitability of water for irrigation based on PI. It is calculated by using the formula; where all the ions are expressed in meqL-1.
PI
Na HCO3
(Ca 2 Mg 2 Na )
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PI ranges from 3.0 to108.0 meqL-1 and 4.0 to 94.0 meqL-1 during water fit for plants having good salt tolerance but unsuitable for SWM and SUM (Figure 6). Permitting to PI values, the groundwater irrigation in soils with restricted drainage (Mohan et al. 2000). samples fall in class I and class II during both the seasons indicating A total of 8 % of the samples fall in C3S2 category during both the water to be moderate to good for irrigation purposes. seasons, indicating water having high salinity and medium sodicity. High salinity, medium sodicity water cannot be used on fine-grained soils with controlled drainage (Srinivasamoorthy et al. 2011). This is because limited flow is likely to result in the accumulation of salts in the root zones of crops, leading to salinity and soil clogging calamity. Representations is also noted in C3S3 and C3S4 category indicating samples not suitable for irrigation utility due to very high salinity and sodium hazards which affects the plant growing.
5. Conclusions
Fig. 6 Classification of irrigation water for soils of medium permeability SWM and SUM
4.2.8. USSL plot The classification of groundwater for salinity hazard is plotted in USSL (1954) diagram (Figure 7). Majority of water samples during SWM falls in C3S1, C2S1 and C2S2, C3S2 zones and during SWM, samples clusters in C3S1, C2S1 and C3S2, C3S3 zones. In SWM (22 %) and SUM (24 %) samples falls in C3S1 zone indicating high salinity and low sodium water, which can be used for irrigation in almost all types of soil with little danger of exchangeable sodium (Kumar et al. 2007). Representations are also noted in C2S1 category indicating
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The study area is underlined by sedimentary formations of Quaternary ages. The dominant cations observed in the groundwater samples follow the order Na+>Ca2+>Mg2+>K+, and the anions follow the order of Cl-> HCO3- >SO2-4>NO3->H4SiO4>PO4->I- and F- during both the seasons. In general, cation dominates the water chemistry of the study area. The chemical composition of the groundwater is controlled by mixing of seawater, ion-exchange reactions, dissolution processes and anthropogenic inputs. The chemistry of groundwater samples indicate Na+, K+ and Cl- are mainly derived from irrigation return flow and anthropogenic activities in inland and seawater intrusion in coastal areas. The calcium and magnesium ions in groundwater are possibly derived from leaching of calcium and magnesium bearing rock-forming silicates and gypsum dissolution. Nearly 42 % and 63% of groundwater samples during SWM and SUM exceed the desirable limit of chloride ions when compared with WHO and BIS standards. The dominated hydrochemical facies are Ca 2+– Mg2+–Cl- and Na+–Cl- types suggesting carbonate, silicate weathering and seawater intrusion influencing major ion chemistry in the study area. The Na+–HCO3- and Ca2+–Na+–HCO3- facies observed is due to irrigation return flow and anthropogenic activities. Irrigation water classification on the basis of SAR indicates groundwater quality of the study area is moderate to low salinity. The RSC values indicate prolonged usage of groundwater will affect the crop yield. The
Fig. 7 Suitability of irrigation water: USSL (1954) diagram during a) SWM and b) SUM ORIGINAL
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contamination of groundwater from Lower Ponnaiyar Basin, Cuddalore positive values of chloro-alkaline indices indicate cation–anion District, Tamil Nadu, India. Environmental Earth Sciences 67(3), 867–887. exchange and the negative values indicate that host rocks are the primary sources of dissolved ions in the groundwater. As per the PI Jeong, C.H., 2001. Effects of land use and urbanization on hydrochemistry and contamination of groundwater from Taejon area, Korea. Journal of values, the groundwater of the study area is moderate to good for Hydrology 253, 194–210. irrigation purposes. According to the overall assessment of the study Jing, X., Yang, Ho., Cao, Y., Wang, W., 2014. Identification of indicators of area, groundwater quality was found to be useful for drinking and groundwater quality formation process using a zoning model. Journal of irrigation purposes. Hydrology 514, 30–40.
Acknowledgements
This research was funded by Grants Commission (UGC) India (Grant No. 41-1036/2012 (SR) Dated. 1.7.2012) through major research proposal. The first author also acknowledges the UGC, India for granting project Fellow (PF) position.
References
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