Sanjay Kumar Sundaray Binod Bihari Nayak Dinabandhu Bhatta

Transcription

1 Environ Monit Assess (2009) 155: DOI /s Environmental studies on river water quality with reference to suitability for agricultural purposes: Mahanadi river estuarine system, India a case study Sanjay Kumar Sundaray Binod Bihari Nayak Dinabandhu Bhatta Received: 3 October 2007 / Accepted: 3 June 2008 / Published online: 1 August 2008 Springer Science + Business Media B.V Abstract Hydrochemistry of surface water (ph, specific conductance, total dissolved solids, sulfate, chloride, nitrate, bicarbonate, hardness, calcium, magnesium, sodium, potassium) in the Mahanadi river estuarine system, India was used to assess the quality of water for agricultural purposes. The samples were studied for 31 different stations during six different seasons in the years Chemical data were used for mathematical calculations (SAR, Na%, RSC, potential salinity, permeability index, Kelly s index, magnesium hazard, osmotic pressure and salt index) for better understanding the suitability river water quality for agricultural purposes. The river water is free from nitrate-nitrogen hazard and has much less osmotic pressure and RSC values. Further there is no complete precipitation of calcium and magnesium in the study area. The results S. K. Sundaray (B) Department of Chemistry, S.C.S. (Autonomous) College, Puri , Orissa, India sanjay_sundaray@yahoo.com B. B. Nayak Institute of Minerals and Materials Technology, Bhubaneswar , Orissa, India D. Bhatta Department of Chemistry, Utkal University, Bhubaneswar , Orissa, India revealed that waters of some polluted stations like Sambalpur down (D/s of Sambalpur town) and Kathjodi (Cuttack) down (D/s of Cuttack town) are unsuitable up to some extent, where as it is quite unsuitable in case of estuarine samples during the pre-monsoon and post-monsoon seasons. The results were verified by USSL and Wilcox diagrams, which show all the fresh water zone samples (low-medium salinity with low sodium) of the study area are in the Excellent to good category and are suitable to irrigate all soils for semitolerant and tolerant as well as sensitive crops. Keywords Water quality Mahanadi river Irrigation SAR Na% RSC PI Salt index Kelly s index Introduction Irrigated lands contribute significantly to the world agriculture output and food supply. India is one of the agriculture based countries. Water used for irrigation can vary greatly in quality depending upon the type and quantity of dissolved salts. Salts are present in irrigation water in relatively small but significant amounts. They originate from dissolution or weathering of the rocks and soil, including dissolution of lime, gypsum and other soil minerals. These salts are carried with the water to wherever it is used. In the case of irrigation,

2 228 Environ Monit Assess (2009) 155: the salts are applied with the water and remain behind in the soil as water evaporates or is used by the crop. In irrigated agriculture, the hazard of salt water is a constant threat. Poor quality irrigation water is of concern in arid climatic conditions. Besides affecting crop yield and soil physical conditions, irrigation water quality affects fertility needs, irrigation system performance and longevity and how the water can be applied (Ayers and Westcot 1994). Rivers play an important role in human development and are important natural potential sources of irrigation water. The hydro-chemical characteristics of water determine its usefulness for agricultural, municipal, industrial and domestic water supplies. The suitability of river water for agricultural purposes can be determined by evaluating some physico chemical parameters along with some calculated hydrogeochemical parameters and graphical representations. Study area Geographical setting The Mahanadi River system is the third largest in the peninsula of India and the largest river of the Orissa state. The basin ( Eand N) extends over an area of approximately 141,600 km 2, has a total length of 851 km and an annual runoff of m 3 with a peak discharge of 44,740 m 3 s 1 (Konhauser et al. 1997; Chakrapani and Subramanian 1990; Sundaray et al. 2006). The basin is characterised by a tropical climate with average annual rainfall of 142 cm (NWDA 1981) with 90% occurring during the south-west monsoon. The river begins in the Baster hills of Madhya Pradesh flows over different geological formations of Eastern Ghats and adjacent areas and joins the Bay of Bengal after dividing into different branches in the deltaic area. The main branches of the Mahanadi River meet the Bay of Bengal at Paradip and Nuagarh (Devi estuary; Fig. 1). The tidal estuarine part of the river covers a length of 40 km and has a basin area of 9 km 2. Based on its physical characteristics, the estuary has been characterized as a partially mixed coastal plain estuary. Geology of the basin The basin geology is characterised by the pre- Cambrians of Eastern Ghats consisting of rock types as khondalites, charnockites, leptynites, granites, gneisses, etc., the limestones sandstones and shales of the Gondwanas, and the costal tracts constituted by the recent deltaic alluvium of the river with littoral deposits. The basin lithology consists of granite suite (34% of the basin area), khondalite suite (7%), charnockite suite (15%), limestone, shale of lower gondwana (17%), sandstone, shale of upper gondwana (22%) and coastal alluvium (5%). A part of the richest mineral belt of the sub-continent consisting of Fe ore, coal, lime-stone, dolomite, bauxite, Pb and Cu deposits fall within the basin (Chakrapani and Subramanian 1990). Anthropogenic setup of the area The quantity of water utilized for irrigation is quite large, particularly in comparison to the quantity used for municipal, industrial and other beneficial purposes. Irrigation use accounts for about 87% of the total water use in the basin. The river serves as a major source of water supply for an irrigated area of about 13,590 km 2 area in the basin. Agriculture is the most important economic activity within the basin and agricultural land use constitute the most significant aspects in comparison to the other form of land use. The cultivated area (69,655 km 2 ) of the basin accounts for 49.39% of the total basin area, where 13% of the basin area is cultivated more than once in a year (CPCB 2000). The river receives back the untreated domestic waste water from the cities of Sambalpur, Bauda, Cuttack, Choudwar, Jagatpur and Paradip and effluents from some industries (fertilizer, paper, textile distilleries and others) present in its course (Radhakrishna 2001; Sundaray et al. 2006). It also receives a large amount of agricultural runoff along its course. Human influences are pronounced at three major urban settlements on the banks of the river (Fig. 1), namely Cuttack (population of about 0.50 million), Sambalpur (population of about 0.20 million) and the port city of Paradip (population of about 0.15 million), where the proliferation

3 Environ Monit Assess (2009) 155: Fig. 1 Map showing station locations of industries and sewer discharges are prominent. The details of agricultural land use along with annual irrigation water abstraction and total population of the basin area are presented in Table 1. Literature review and thought process Numerous research projects have been carried out on the role of different urban and industrial effluents on the water quality of the Mahanadi river and estuarine system (Upadhyay 1988; Chakrapani and Subramanian 1990, 1993; Das et al. 1997; Nanda and Tiwari 2001; Radhakrishna 2001; Nayak et al. 2002; Das 2003; Sundaray et al. 2005, 2006), but no study has been carried out on the suitability of the water quality of the Mahanadi river for agricultural purposes. In the present study, the evaluation of the water quality of the Mahanadi river suitability for agricultural purposes has been attempted. Materials and methods Sampling and analytical methods The water samples were collected from 31 stations along the course of the Mahanadi river system Table 1 Agricultural land use characteristics of Mahanadi river basin Characteristics Unit Value Total basin area in km 2 141, Total population of the basin 26,321,362 Cultivated area in the basin area in km 2 69, % of cultivated area to total basin area % Irrigated area in the basin in km 2 13, River water use for agriculture in the basin Mm 3 /year 17, Total river water abstraction (for all purposes) in the basin Mm 3 /year 18, % of river water abstraction to total abstraction in the basin % 95.11

4 230 Environ Monit Assess (2009) 155: Table 2 Water quality parameters with ranges average value in 31 different stations of Mahanadi river systems during six different seasons (both and Sessions) Parameters Pre-monsoon Monsoon Post-monsoon Min Max Mean Std. dev. Min Max Mean Std. dev. Min Max Mean Std. dev. ph EC , , , , , , , ,994.7 TDS , , , , , ,120.8 Cl , , , , , ,418.4 SO NO3-N Hardness , , , Alkalinity Na 9.5 6, , , , K Ca Mg Na% SAR RSC Potnl. sal Mg hazard Kelly s index Permi index Salt index , , , , Osm. press Units: TDS, Cl, SO4,NO3, Hardness, Alkalinity, Na, K, Ca and Mg are in mg/l, RSC is in meq/l, EC is in μ S/cm, Osmotic pressure is in atm

5 Environ Monit Assess (2009) 155: Table 3 Water quality classes for agricultural use of Mahanadi river system during three different seasons each in and sessions Parameters Rate of hazard Water class Repretending samples no. Pre-monsoon Monsoon Post-monsoon ph No problem 1 24, , , , , , and Moderate , and 9.5+ Severe EC < 250 Excellent 1 3,8,10 12,14, 1 3, ,6 19, ,6 22, ,7 15,17 18, 1 3,7 11,13 15,17 19, (μs/cm) , Good 4 7,9,13, ,14 19,26,28 5,20 23,27,30 5,23 4 6,16,19 20,27 4 6,12,16, ,250 Permissible 31 24,31 21,29,30 21,29 2,250 5,000 Unsuitable 20 25, , , ,30,31 TDS < 200 Excellent 1 3,7 14,17 18,28 1 3,7 15,17 19, 1 21, , ,6 19,26,28 1 4,6 19,26,28 (mg/l) 26, Good 4 6,15 16,19, ,16, , ,20,27 5,20, ,500 Permissible 24, ,29, ,500 3,000 Unsuitable 20 25, , , ,29 31 Cl < 4 No problem 1 19, , , , , , (meq/l) 4 10 Moderate 24, 30 24, > 10 Severe 20 25, , , , , 31 NO3-N < 5 No problem (mg/l) 5 30 Moderate > 30 Severe Hardness 0 60 Soft 1 2,7,9,10,12, ,3,9 1 4,6 19,26 1 4,6 19,26,28 (mg/l) Mod. soft 1 3,7 14,17 19,28 1 3,6 19,26,28 3 6,8,11, ,4 8,10 19, , ,20, Hard 4,6,15,16,26,27 4 5, ,29, ,29 20 > 180 Very hard 5,20 25, , , , , ,29 31 Na% < 20 Excellent 8 9,11 12,14,17,26 6, Good 1 4,6 7,10,13,15 16, 1,2 84,7 9,11 19, 1 4,6 19,26,28,29 1 4,6 20, ,6 14,17 19, 1,3,8 15,17,18, , 28 26,28 26, Permissible 5,27 5 5,27, , ,15,16,27 2,4,6,7,16,19,27, Doubtful 20,21,23,25,29, ,25,27,29, , ,30, ,25,29 5,20 25,29 31 > 80 Unsuitable 22,24,31 24,31 24,30,31 SAR < 10 Excellent 1 19, , , , , , Good 20,29 20,29 24,31 24,31 21,29 21, Fair 21,30 21,30 22,23, ,25,30 > 26 Poor 22 25, , ,25,31 24,31 RSC < 1.25 Safe meq/l Permissible > 2.50 Unsuitable

6 232 Environ Monit Assess (2009) 155: starting from Hirakud reservoir to the estuary points i.e. at Paradip and Nuagarh (Fig. 1). Field visits were made during three different seasons viz. Pre-monsoon (February May), Monsoon (June September), Post-monsoon (October January) during the and session. In each season, sampling was carried out three times and samples were collected at three points (1/4, 1/2 and 3/4) across the river width at a depth of cm from the water surface, with the help of country boats. The mean value was taken for the evaluation. The onboard measurements of temperature, ph and conductance were carried out immediately after the collection of the samples. Other parameters such as total dissolved solid (TDS), chloride (Cl ), sulfate (SO 2 4 ), nitrate (NO 3 -N), hardness, alkalinity, sodium (Na), potassium (K), calcium (Ca) and magnesium (Mg) were analysed following standard guidelines and procedures (APHA et al. 1998; Vogel 1961). Each analysis was done in triplicate and the mean value was taken. The analytical data quality was ensured through careful standardization, procedural blank measurements, spiked and duplicate samples. Data treatment and classification methods The parameters such as sodium adsorption ratio, percent sodium, residual sodium carbonate, potential salinity, permeability index, Kelly s index, magnesium ratio, salt index and osmotic pressure were calculated to evaluate the suitability of the water quality for agricultural purposes. Further the results of the analyses were interpreted using various related diagrams, such as USSL diagram and Wilcox diagram. The techniques and methods followed for analysis, calculation and interpretation are those given by Ayers and Westcot (1994), Tiwari and Manzoor (1988a, b), ISI (1974), Durfer and Backer (1964), Wilcox (1948, 1955), Richards (1954), US Salinity Laboratory (1954), Doneen (1954, 1962, 1964), Kelly (1940), Paliwal (1967, 1972), Vogel (1961), APHA et al. (1998). Results and discussion Water quality for irrigation use The suitability of river water samples for irrigation use depends upon the mineral constituent present in the water. The major physico-chemical parameters, which decide the suitability of river water for irrigation, are ph, EC, TDS, hardness, chloride, sulfate, carbonate, bicarbonate, nitrate, sodium, potassium, calcium, magnesium, etc. Silica, iron and boron are usually present in very small amounts and are determined in special circumstances, for example when industrial waste alone is to be used for irrigation (Deo and Ali 1993). The hydrogeochemical parameters of the Mahanadi river estuarine system with minimum, maximum, mean and standard deviation values in 31 different stations during pre-monsoon, monsoon and post-monsoon seasons of both and are incorporated in Table 2. ph The normal ph range for irrigation water is from 6.5 to 8.4. An abnormal value is a warning that the water needs further evaluation. Irrigation water with a ph outside the normal range may cause a nutritional imbalance or may contain a toxic ion. The ph of the samples analyzed was slightly alkaline in nature with an average value (except the Atharbanki station) of 7.46, 7.51 and 7.45 during and 7.34, 7.34 and 7.52 during and for the pre-monsoon, monsoon and post-monsoon season, respectively. The ph value of all water samples (except the Atharbanki station) lies in the range from 6.54 to 8.10, which implies that waters are suitable for irrigation purposes with respect to ph, i.e. there is no alkalinity hazard as shown in Table 3. The very acidic character of Atharbanki creek water (ph 3.66, 5.07, 5.24, 3.23, 4.89 and 4.55), contributed by industries like fertilizer plants (Paradip Phosphate Limited, PPL) at Paradip discharge acidic effluents to the river, which indicates creek water is unsuitable for irrigation and it is in the severe water class (Table 3) with respect to ph (Ayers and Westcot 1994).

7 Environ Monit Assess (2009) 155: Electrical conductance (EC) and total dissolved solids (TDS) Electrical conductivity is the most important parameter in determining the suitability of water for irrigation use. Irrigation using river water can add salt concentration to the soils and a problem occurs if the added salt accumulates to a concentration that is harmful to the crop or landscape. Salinity of river water that is used for irrigation is determined by EC, which is used as a surrogate measure of total dissolved solids (TDS) concentration in water. TDS refer to any minerals, salts, metals, cations or anions dissolved in water. This includes anything present in water other than pure water (H 2 O) molecules and suspended solids. According to Langenegger (1990), the importance of EC is its measure of salinity. The EC for water is expressed as micro siemens per centimeter (μs/cm) and salt concentration is also reported as TDSinmg/l. On the basis of the EC values of the water samples from stations 1 19 and were considered fresh/river water influenced stations, whereas stations and were considered as estuarine characterized/saline influenced stations for pre-monsoon, post-monsoon and some extend for monsoon seasons. In the fresh water zone the EC range was to 729.0, to and to μs/cm, where as in saline water it ranged from 3,119.4 to 26,748.0, to 14,402.5 and to 15,047.3 μs/cm during pre-monsoon, monsoon and post-monsoon season, respectively, for both and similarly in fresh water zones TDS concentrations ranged from 72.7 to mg/l, 61.4 to mg/l and 64.8 to mg/l during pre-monsoon, monsoon and post-monsoon season, respectively, and in case of saline water it ranged from 1,658.0 to 13,845.0, 87.8 to and to 8,627.4 mg/l for the respective three different season during both and investigating periods. Table 3 shows the guidelines for EC and TDS values in waters used for irrigation. On the basis of EC and TDS, water samples (fresh water zone) of the study area come under the excellent to good category (Table 3) for irrigation purposes (Ayers and Westcot 1994). Comparing with ISI (1974) guidelines, irrespective to seasons, the values of EC and TDS for fresh water regions are within the tolerance limit for irrigation (Table 4). However the estuarine water samples (St and St ) were unsuitable for irrigation. Chloride The most common toxicity is from chloride in the irrigation water. Chloride is not adsorbed or held back by soils, therefore it moves readily with the soil-water, is taken up by the crop, moves in the transpiration stream, and accumulates in the leaves. If the chloride concentration in the leaves exceeds the tolerance of the crop, injury symptoms develop such as leaf burn or drying of leaf tissue. Normally, plant injury occurs first at the leaf tips (which is common for chloride toxicity), and progresses from the tip back along the edges as severity increases. Excessive necrosis (dead tissue) is often accompanied by early leaf drop or defoliation (Ayers and Westcot 1994). The concentration of chloride of the Mahanadi river ranged from 9.93 to mg/l during premonsoon, 4.26 to mg/l during monsoon, 6.96 to mg/l during post-monsoon in case of fresh water region and from to 13,151.9 mg/l during pre-monsoon, 27.6 to 4,413.5 mg/l during monsoon, 87.7 to 5,977.8 mg/l during post-monsoon in case of saline water region for both and sampling periods. The C1 content for the fresh water region of the river systems are within the tolerance limit (Table 4) for irrigation (ISI 1974, 600 mg/l). Since the chloride concentration in fresh water samples lie in the range from 0.12 to 2.84 meq/l, hence the fresh water region of the Mahanadi river is free from chloride hazard and it is in the no problem water class for irrigation purposes (Table 3). In the estuarine water zone it is obvious that the concentration of chloride is directly proportional to salinity. Hence all the estuarine stations are in the moderate to severe water class for irrigation purposes with respect to chloride content (Ayers and Westcot 1994).

8 234 Environ Monit Assess (2009) 155: Table 4 Samples of Mahanadi river system, which exceeded tolerance limit (ISI 1974) for agricultural use Parameters Samples nos. (which exceeded tolerance limit) Tolerance limit for agriculture Pre-monsoon Monsoon Post-monsoon Pre-monsoon Monsoon Post-monsoon ph EC 20 25, , , , 31 3,000 Cl 20 25, , , , TDS 20 25, , , , 31 2,100 SO4 1,000 Na% 20 25, , 31 5, 20 25, , 20 25, , , 20 25, Sulfate The source of sulfate ions to water environment is mainly from acid mine drainage. The sulfide minerals viz. pyrides, chalco pyrides, galena, spalerites etc get oxidized to sulfate and are leached out with the mine water. Source of sulfate ions into the river water may be attributed to industrial effluents. Natural waters have few to several thousand mg/l of sulfate (APHA et al. 1998). Anthropogenic sources can contribute up to 40% of the total sulfate of river waters (Friend 1973). A number of crops show sensitivity to very high concentrations of sulfates in the irrigation water, but it is likely that this sensitivity is related to the tendency of high sulfate concentrations to limit the uptake of calcium by plants. This decrease in the uptake of calcium is associated, on the other hand, with relative increases in the absorption of sodium and potassium (Tiwari and Manzoor 1988a). SO 4 content of Mahanadi river water ranged mg/l during pre-monsoon, mg/l during monsoon and mg/l during post-monsoon season for and , and mg/l during the respective three different seasons for the sampling period. The SO 4 content of the Mahanadi river system are within the tolerance limit (Table 4) for irrigation purposes (ISI 1974; 1,000 mg/l). Nitrate Nitrogen is a plant nutrient and stimulates crop growth. Natural soil nitrogen or added fertilizers are the usual sources, but nitrogen in the irrigation water has much the same effect as soil-applied fertilizer nitrogen and an excess will cause problems, just as too much fertilizer would. If excessive quantities are present or applied, production of several commonly grown crops may be upset because of over-stimulation of growth, delayed maturity or poor quality. Sensitive crops may be affected by nitrogen concentrations above 5 mg/l. Most other crops are relatively unaffected until nitrogen exceeds 30 mg/l (Ayers and Westcot 1994).

9 Environ Monit Assess (2009) 155: The nitrate concentration of the study area ranges from 0.19 to 2.62, 0.36 to 3.73 and 0.29 to 2.90 mg/l for and from 0.08 to 2.83, 0.26 to 3.30 and 0.26 to 2.64 mg/l for during pre-monsoon, monsoon and post-monsoon season, respectively. The nitrogen concentration in the form of nitrate is very low varying from 0.08 to 3.73 mg/l, which indicate that Mahanadi river water is free from nitrate-nitrogen hazard (Table 3). Hardness Hardness is the property of water which prevents the lather formation with soap and increases the boiling point of water. Hardness is due to the presence of divalent metallic cations like calcium, magnesium, strontium, ferrous iron and manganese ions. Ferric iron and aluminum ions can also contribute to hardness, but the contribution is normally negligible due to their limited solubility, at the ph value encountered in the Mahanadi River. Hardness in water is also derived from the solution of carbon dioxide released from the bacterial action in soil in percolating water (Sawyer and McCarty 1967). The hardness is commonly classified in terms of degree of hardness as (1) soft (0 to 60 mg/l), (2) moderately hard (60 to 120 mg/l), (3) hard (120 to 180 mg/l) and (4) very hard (>180 mg/l; Durfer and Backer 1964) The Mahanadi river water (fresh water zone) is classified as soft to moderately hard in monsoon ( mg/l) and post-monsoon ( mg/l) seasons. Where as in case of pre-monsoon season it is moderately hard ( mg/l), except some polluted stations like station 5 (215.8 mg/l) and station 27 (195.2 mg/l) which are categorized as hard and this hardness was due to discharge of sewage from the township of Sambalpur and Cuttack, respectively. Mohanta and Patra (2000) opined that addition of sewage, detergents and large scale human use might be the cause of the higher levels of hardness (Jain and Sharma 2002). However estuarine water samples contain very high values of hardness ( ,437.5 mg/l during pre-monsoon, ,575.0 mg/l during monsoon and ,742.2 mg/l during post-monsoon season) in comparison to fresh water systems of the Mahanadi river irrespective of seasons, which revealed that the hardness in the estuarine stations is from saline sources. The data indicate that waters of the fresh zone are suitable (except the polluted stations like St. 5 and St. 27; Sundaray et al. 2006) for irrigation purposes (<180 mg/l; Durfer and Backer 1964), where as estuarine stations are quite unsuitable (Table 3). Sodium Sodium toxicity is not as easily diagnosed as chloride toxicity, but clear cases of the former have been recorded as a result of relatively high sodium concentrations in the water (high Na or SAR). Typical toxicity symptoms are leaf burn, scorch and dead tissue along the outside edges of leaves in contrast to symptoms of chloride toxicity which normally occur initially at the extreme leaf tip. An extended period of time (many days or weeks) is normally required before accumulation reaches toxic concentrations. Symptoms appear first on the older leaves, starting at the outer edges and, as the severity increases, move progressively inward between the veins toward the leaf centre. Sensitive crops include deciduous fruits, nuts, citrus, avocados and beans, but there are many others (Ayers and Westcot 1994). The sodium hazard of irrigation water is usually specified as two sodium related indices named as sodium adsorption ratio (SAR) and sodium percentage (Na %). Sodium adsorption ratio (SAR) Excess sodium in water produces the undesirable effects of changing soil properties and reducing soil permeability (Kelly 1951). High Sodium concentration leads to development of an alkaline soil. The sodium or alkali hazard in the use of water for irrigation is determined by the absolute and relative concentration of cations and is expressed in terms of sodium adsorption ratio (SAR). SAR is a calculated value and an indicator of sodium hazard of water.

10 236 Environ Monit Assess (2009) 155: Sodium adsorption ratio (SAR) has been calculated as follows: Na SAR= Ca+Mg 2 Where: Na, Ca and Mg are in meq/l. There is a significant relationship between SAR values of irrigation water and the extent to which sodium is adsorbed by the soil. High concentrations of sodium in soils affect its physical condition and soil structure resulting in formation of crusts, water-logging, reduced soil aeration, reduced infiltration rate, and reduced soil permeability; excessive concentrations of sodium in soils may also be toxic to certain types of crops. SAR gives a very reliable assessment of water quality of irrigation waters with respect to sodium hazard, since it is more closely related to exchangeable sodium percentages in the soil than the simpler sodium percentage (Tiwari and Manzoor 1988a). Sodium replacing adsorbed calcium and magnesium is a hazard as it causes damage to the soil structure. It becomes compact and impervious. SAR is an important parameter for the determination of the suitability of irrigation water because it is responsible for the sodium hazard (Todd 1980). The waters were classified in relation to irrigation based on the ranges of SAR values (Richards 1954). The SAR value in the Mahanadi river estuarine system ranges from 0.39 to 3.59 in pre-monsoon, 0.40 to 2.51 in monsoon and 0.41 to 3.11 in post-monsoon in case of fresh water samples, where as in estuarine samples its values varied from to 46.56, 0.47 to and 3.64 to for the respective three different seasons during both the and sampling periods. The SAR values are more pronounced in the estuarine region than in the fresh region samples. According to Richard s classification all the samples in the fresh water zone have been classified as excellent for irrigation (Table 3). The water samples in the estuarine area are quite unsuitable for irrigation purposes with respect to SAR values in case of pre-monsoon, post-monsoon and to some extent during monsoon season. Sodium percentage (Na%) Soils containing a large proportion of sodium with carbonate as the predominant anion are termed alkali soils; those with chloride or sulphate as the predominant anion are saline soils. The role of sodium in the classification of river water for irrigation was emphasised because of the fact that sodium reacts with soil and as a result clogging of particles takes place, there by reducing the permeability (Todd 1980; Domenico and Schwartz 1990; Nagaraju et al. 2006). Percent sodium in water is a parameter computed to evaluate the suitability for irrigation (Wilcox 1948; Tiwari and Manzoor 1988a). Na% can be calculated by the following relation, (Na+K) Na% = ( ) 100 Ca+Mg+Na+K Where: Na, K, Ca and Mg are in meq/l. The percent sodium values of the Mahanadi river samples varied from to 82.53, to and to during the pre-monsoon, monsoon and post-monsoon season, respectively, for both and sampling periods. The fresh water samples with exception to some polluted stations like Sambalpur down (St. 5; Down stream of Sambalpur town) and Kathjodi (Cuttack) down (St. 27; Down stream of Cuttack town) are categorized as excellent to good classes with respect to Na % values, where as the polluted stations fall on the permissible category, however the estuarine samples are categorized as doubtful to unsuitable for irrigation purposes. The Na% is higher in the estuarine region than in the fresh region, this is due to the input of sodium from sea water. As per ISI (1974) guidelines, the maximum tolerance limit of Na% for inland surface water used for irrigation is 60. Accordingly all fresh zone waters (except St. 5 and St. 27) of Mahanadi river is suitable for irrigation, where as Na% is higher than 60 in case of polluted stations like Sambalpur down (St. 5; during post-monsoon and ) and Kathjodi (Cuttack) down (St. 27; during pre-monsoon ). This higher value of Na% at station 5 and 27 was due to contribution of sewage discharge from the township of Sambalpur and Cuttack, respectively.

11 Environ Monit Assess (2009) 155: However estuarine zone waters are unsuitable for irrigation. In addition to this, some indices such as residual sodium carbonate (RSC), potential salinity (PS), permeability index (PI), Kelly s index (KI), magnesium hazard (MH), osmotic pressure (OP) and salt index (SI) have been utilize to verify the water quality for irrigation use. Residual sodium carbonate (RSC) When total carbonate levels exceed the total amount of calcium and magnesium, the water quality may be diminished. When the excess carbonate (residual) concentration becomes too high, the carbonates combine with calcium and magnesium to form a solid material (scale) which settles out of the water. The relative abundance of sodium with respect to alkaline earths and boron, and the quantity of bicarbonate and carbonate in excess of alkaline earths also influence the suitability of water for irrigation. This excess is denoted by residual sodium carbonate (RSC) and is determined as suggested by Richards (1954). The water with high RSC has high ph and land irrigated by such waters becomes infertile owing to deposition of sodium carbonate as known from the black colour of the soil (Eaton 1950). Further, continued usage of high residual sodium carbonate waters affects crop yields. RSC is given by the relation RSC = (CO 3 + HCO 3 ) ( Ca + Mg ) According to the US Salinity Laboratory (1954), an RSC value less than 1.25 meq/l is safe for irrigation, a value between 1.25 and 2.5 meq/l is of marginal quality and a value more than 2.5 meq/l is unsuitable for irrigation. In the present study, the waters in both fresh and estuarine samples show RSC values of to 0.28 meq/l in pre-monsoon, to 0.21 meq/l in monsoon and to 0.90 meq/l in post-monsoon seasons during both the and sampling periods. All the samples have RSC values much less than 1.25 meq/l (safe for irrigation), which revealed that all samples are of safe quality categories for irrigation. Further the value of RSC is negative at all sampling sites, indicating that there is no complete precipitation of calcium and magnesium (Tiwari and Manzoor 1988b). Potential salinity (PS) Doneen (1954) pointed out that the suitability of water for irrigation is not dependent on the concentration of soluble salts. Doneen (1962)isof the opinion that the low solubility salts precipitate in the soil and accumulate with each successive irrigation, whereas the concentration of highly soluble salts increases the salinity of the soil. Potential salinity is defined as the chloride concentration plus half of the sulfate concentration. In the fresh water zone potential salinity of the water samples varied from 0.36 to 3.07, 0.14 to 1.90 and 0.32 to 2.28 during pre-monsoon, monsoon and post-monsoon season, respectively, and in the case of saline water it ranged from to , 0.82 to and 2.98 to for the respective three different seasons during both and investigating periods. The PS values are more pronounced in the estuarine region than in the fresh region samples. The huge amount of potential salinity in the estuarine region is due to the presence of chlorides, which are derived from sea source. Permeability index (PI) The soil permeability is affected by long-term use of irrigation water. Sodium, calcium, magnesium and bicarbonate content of the soil influence it. Doneen (1964) evolved a criterion for assessing the suitability of water for irrigation based on a permeability index (P.I.) where PI = Na + [ HCO 3 ] 1/2 ( Ca + Mg + Na ) 100 Accordingly, waters can be classified as Class I, Class II, and Class III. Class I and Class II waters are categorized as good for irrigation with

12 238 Environ Monit Assess (2009) 155: % or more of maximum permeability. Class III waters are unsuitable with 25% of maximum permeability. The permeability index of Mahanadi river water varied in pre-monsoon from to 82.70, in monsoon from to and in postmonsoon from to during both and sampling periods. Accordingly, all the samples fall into the Class I and II category of Doneen s chart. Kelly s index Based on Kelly s index (KI) waters are classified for irrigation. Sodium measured against calcium and magnesium was considered by Kelly (1940) and Paliwal (1967) to calculate this parameter. A Kelly s index of more than one indicates an excess level of sodium in waters. Therefore, waters with a Kelly s index less than one are suitable for irrigation, while those with a ratio more than one are unsuitable. Kelly s index in the present study (except polluted station no. 5 and 27) varied from 0.18 to 0.53, 0.25 to 0.58 and 0.28 to 0.92 in the fresh water zone and ranged from 2.51 to 4.61, 0.23 to 3.65 and 1.74 to 4.03 in the estuarine zone during pre-monsoon, monsoon and post-monsoon season, respectively, for both and sampling periods. Therefore, according to Kelly s index, the water samples in the fresh zone (except St. 5 and 27) are Fig. 2 US Salinity Laboratory classification of Mahanadi river water

13 Environ Monit Assess (2009) 155: suitable for irrigation. However the water samples of polluted stations (St. 5 and 27) along with the estuarine zone are unsuitable for irrigation, as the KI values are more than one in these stations. Magnesium hazard (MH) Generally, calcium and magnesium maintain a state of equilibrium in most waters. In equilibrium more Mg in the water will adversely affect crop yields. Paliwal (1972) introduced an important ratio called index of magnesium hazard (magnesium ratio). Magnesium ratios of more than 50% would adversely affect the crop yield as the soils become more alkaline. The magnesium ratio (MR) values of Mahanadi river systems were reported to be in the range of minimum of 36.10, and and maximum of 87.53, and for pre-monsoon, monsoon and post-monsoon season, respectively, during both and sampling periods. The estuarine samples contain a Mg ratio more than 50%. In the present study the MR values are more pronounced in the estuarine region than in the fresh region samples. These high values in the estuarine region are because of the presence of high magnesium, which are derived from sea source. Osmotic pressure (OP) It is a parameter, related to the conductivity of irrigated water. Due to osmotic effects, the salt concentration interferes with extraction of water by the plants thereby affecting the plant growth. It is indicated that plants wilt permanently under the osmotic pressure of atm (Tiwari and Manzoor 1988b). But in our case, the osmotic pressure is much below this value in all cases (Table 2). The Osmotic pressure in Mahanadi water ranged from 0.07 to 9.63 atm for premonsoon, 0.05 to 5.18 atm for monsoon and 0.04 to 5.42 atm for post-monsoon season during and sampling periods. Salt index (SI) Based on their salt index waters are classified for irrigation. Total sodium, total calcium and calcium Table 5 Classification of water quality of Mahanadi river system in 31 different stations during three different seasons each in and sessions Classification/type Repretending samples no. Pre-monsoon Monsoon Post-monsson USSL classification C1S1 1, 2, 8, 10 12, , , 6 19, 26, , 6 22, , 7 15, 17 18, , 7 11, 13 15, 17 19, C2S1 3 7, 9, 13, 15 19, , 14 19, , 20 23, 27, 30 5, , 16, 19 20, , 12, 16, 20 C3S , 29 21, 29 C3S C4S3 20 C4S , , , , Wilcox classification Excellent to good 1 19, , , , , , Good to permissible Permissible to doubtful 24 24, 31 21, , 29 Doubtful to unsuitable Unsuitable 20 25, , , , 31

14 240 Environ Monit Assess (2009) 155: in CaCO 3 of irrigated water were considered to evaluate salt index. The SI is negative for water to be suitable for irrigation and positive for those unsuitable (Tiwari and Manzoor 1988b; Mishra et al. 2003). The salt index in the Mahanadi water were reported to be in the range of minimum ( 132.9, and 57.47) and maximum of ( 109.1, 65.7 and 33.1) in the fresh water stations, whereas it ranged from (248.4, and 83.0) to (5,280.5, 2,069.0 and 2,357.7) in the estuarine stations for pre-monsoon, monsoon and post-monsoon season, respectively, during both and sampling periods. The salt index of estuarine water samples is very high in comparison to fresh water systems irrespective of seasons; this was due to the input of high salts from the sea water. Therefore according to SI, waters of the fresh zone are suitable for irrigation, where as estuarine stations are quite unsuitable. Graphical methods of representing analyses Most of the graphical methods are designed to simultaneously represent the total dissolved solid concentration and the relative proportions of certain major ionic species (Hem 1989; Guler et al. 2002). Two accepted and widely used graphical methods, such as Wilcox diagrams and US salinity diagrams are adopted in the present study to verify the suitability of water quality of Mahanadi river estuarine system for agricultural purposes. US salinity diagram The US salinity diagram is based on the integrated effect of EC and SAR, in which EC is taken as salinity hazard and SAR is taken as alkalinity hazard. The SAR and EC values of water samples (31 in each season for and ) of the Fig. 3 Wilcox diagram for classification of Mahanadi river water

15 Environ Monit Assess (2009) 155: study area were plotted in the graphical diagram (Fig. 2) of irrigated water (US Salinity Laboratory 1954). Irrespective to the seasons, entire fresh water samples of the Mahanadi river (Table 5) fallinto C1S1 (low salinity with low sodium) and C2S1 (medium salinity with low sodium) categories, which revealed that these water samples can be used to irrigate all soils for semi-tolerant and tolerant as well as sensitive crops. Whereas, most of the estuarine samples (Fig. 2) during pre-monsoon and post-monsoon seasons fall into the C4S4 (very high salinity with very high sodium) category and thus these samples are unsuitable for irrigation. However, in case of monsoon seasons the most of estuarine samples fall into the C1S1 (low salinity with low sodium) and C2S1 (medium salinity with low sodium) categories. Wilcox diagram Percent sodium is plotted against conductivity, which is designated as a Wilcox diagram (Wilcox 1955). The chemical analysis data of all the 181 samples (31 in each seasons for and ) have been plotted on a Wilcox diagram for the three sets of data (Fig. 3) and the results of the same have been summarized in Table 5. Figure 3 indicates that irrespective to the seasons all the samples in the fresh water zone are Excellent to good category for irrigation. As per the Wilcox classification, in case of estuarine samples, all the 18 samples in the pre-monsoon (nine samples each in and ) and 10 samples in the post-monsoon (five each in and ) fall into the category of Unsuitable, where the remaining samples in the post-monsoon fall into Permissible to doubtful and Doubtful to unsuitable categories (Table 5). In case of the monsoon seasons majorities of the samples (12 samples; six each in and ) fall into Excellent to good category. station). The polluted stations (Sundaray et al. 2006) Atharbanki creek (St. 25) is in the severe water class and unsuitable for irrigation with respect to ph (Ayers and Westcot 1994), which is due to the influx of acidic effluents discharged by the fertilizer plants (PPL) at Paradip. On the basis of EC and TDS, fresh water zone samples come under the excellent to good category for irrigation purposes (Ayers and Westcot 1994). Comparing with ISI (1974) guidelines, the present study suggests that the water quality of the fresh water region irrespective to seasons is suitable for irrigation, where as it is quite unsuitable in the case of estuarine stations (St and St ) during the pre-monsoon, and post-monsoon seasons. The data indicate that waters of the fresh zone are free from chloride hazard which are classified as soft to moderately hard type (except the polluted stations like St. 5 and St. 27) and are suitable for irrigation purposes (<180 mg/l; Durfer and Backer 1964). The results revealed that waters of some polluted stations (Sundaray et al. 2006) like Sambalpur down (St. 5) and Kathjodi (Cuttack) down (St. 27) are unsuitable with respect to parameters like Kelly s index and hardness. This is due to the proximity of the effluent discharged from the two major towns namely Sambalpur and Cuttack, respectively. Mahanadi river water is free from nitrate-nitrogen hazard and has lower osmotic pressure and RSC values, which revealed suitability for irrigation. Further the value of RSC is negative at all sampling sites, indicating that there is no complete precipitation of calcium and magnesium (Tiwari and Manzoor 1988b). According to USSL and Wilcox diagrams, all the fresh water zone samples (low-medium salinity with low sodium) of the study area are of Excellent to good category for irrigation and are suitable to irrigate all soils for semi-tolerant and tolerant as well as sensitive crops. Conclusion Like major world rivers, the Mahanadi River is alkaline. There is no alkalinity hazard for irrigation found in the basin (except at Atharbanki Acknowledgements The authors are thankful to Prof. U.N. Dash, head, department of chemistry, Utkal University, Bhubaneswar for providing the necessary facilities. SKS s gratitude due to Dr. P. Mishra, Principal, S. C. S. (Autonomous) College, Puri, for much of his help and encouragement.

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