IMPACT OF IRRIGATED AGRICULTURE ON GROUNDWATER QUALITY IN & AROUND ROORKEE, INDIA

Abstract

In general, the present work aims to study the impact of irrigated agriculture on the groundwater quality of the Roorkee town and its surrounding areas. Approximately one-half to two-thirds ofthe water applied for irrigation ofcrops is consumed by evapotranspiration and the remainder, termed irrigation return flow, drains to surface channels or joins the underlying groundwater (Todd, 1980). Irrigation increases the salinity of irrigation return flow from three to ten times that ofthe applied water (Jenke, 1974). Hence, the resulting deep percolation water not only contains the salts that were present in the irrigation water, but also fertilizer and pesticide residues that are a potential source ofcontamination ofthe underlying groundwater. Many authors have discussed the impact of irrigation return-flows on groundwater. Kakar (1981) studied the ground water pollution by nitrate in southern and southwestern Haryana. He found nitrate levels exceeding 500 mg/1 at several places. Handa (1987) studied the nitrate content of groundwater in India. This study revealed that in unconfmed aquifers, the nitrate content at times in quite high. Cohen (1990) discussed the pesticides in groundwater. He described how to design the study of pesticides in groundwater. Jones (1990) discussed the pesticides in groundwater, with especial emphasis on the conducting of field research studies. He described the design of research site and monitoring of unsaturated and saturated zones. Ehteshami et al. (1992) developed a methodology for identifying hazardous pesticides/site combinations threatening ground water contamination. This method employed application of hydrogeological screening model (DRASTIC) along with a one-dimensional pesticide transport model (CMLS). Briggins and Moerman (1995) collected samples from 102 farm wells in the most intensively farmed region in Nova Scotia, Canada. Samples were analyzed for pesticides and nitrate. None of the study wells contained pesticide concentrations above maximum acceptable concentrations for Canadian drinking water. In addition, many authors have discussed the environmental fate of pesticides and fertilizers on soil. Gohnson and Lavy (1994) conducted studies to examine the dissipation characteristics in field studies of four commonly used pesticides. Agnihotri et al. (1996) monitored the residues of insecticides in soil and subsoil of the Ganga River at Farrukhabad (India). Organochlorine insecticides i.e. HCH, DDT, aldrin, dieldrin, endosulfan and heptachlor, and organophosphorus insecticides i.e. malathion and monocrotophos were detected in the soil samples. Munster et al. (1995) conducted a field study to monitorthe fate of aldicarb in a poorly drained soil in the North Carolina coastal plain. Aldicarb degraded to nontoxic compounds with a half-life of approximately 7 days. Guzzella et al. (1996) investigated the migration of pesticide residues from agricultural soil to groundwater in the three sampling sites in the Northern Italy and cultivated with maize crop. The GC analyses of soil samples allowed the description of vertical distribution of pesticides residues in the soil profile. Ritter et al. (1996) studied the movement and degradation of Atrazine, Simazine, Cyanazine, Triazines, alachlor, and Metolachlor in sandy soils at Delaware, near Georgetown. They detected atrazine and simazine more frequently in the groundwater than metolachlor and cyanazine. On the other hand, many authors have discussed the Conceptual methods for predicting pesticides and fertilizers fate. Bennett (1990) evaluated the fate of pesticides in water and sediment. He described the concepts for predicting pesticide fate. He discussed the experimental methods for studying pesticide fate. Arora and McTernan (1994) prepared input data files for the PRZM code for the determination of the probabilities of pesticide leaching. They plotted the running mean and standard deviation of these individual simulations to identify the adequacy of the database. Khakural et al. (1995) tested the LEACHP model for predicting atrazine movement in three Minnesota soils. LEACHP was predicted depth of peak atrazine concentration in the soil profile accurately in all three soils. Main objectives of this research work were to delineate occurrence and distribution of pesticide and fertilizer residues in shallow groundwater and soils on one hand and investigating the persistence of pesticide commonly used in the study area on the other. In addition, the relationship between the degree of vulnerability of the shallow surficial aquifer, if any, in relation to their hydrogeochemical characteristics was also studied. The study area is a part of the Indo-Gangetic alluvial plain consisting of recent unconsolidated fluviatile sediments that comprising sand, silt, clay and kankar. The investigated area locates between latitude 29° 47; and 29° 57;N and longitude 77° 46; and 77° 511 EThe study area lies in the Roorkee Tehsil, Hardwar District, Uttaranchal State, India. The investigated area covers about 150 sq. km. Two surface water bodies are located in the study area. First one is the river Solani which is a tributary of the river Ganga and second one is the Upper Ganga Canal. The Experimental Research Farm in the Department of Hydrology, IIT, Roorkee was selected to conduct controlled experiments for measuring the impact of the application of the most common pesticide on groundwater and soil in a farm size. In the study area, the sole source of drinking water supply is groundwater and the economy is mainly agricultural based. In the agricultural areas, application of pesticides and fertilizers by the farmers in the agricultural fields is very common to improve or protect the crops. As a result, the irrigation return-flows can carry the pesticides and fertilizers residues either to drains or to groundwater. The possibility is that the irrigation return-flows percolating the unsaturated zone may cause contamination of the groundwater quality by the residues ofthe pesticides and fertilizers. The hydrogeology ofthe unconfined aquifer in the study area has been studied. The effect of the application of pesticides and fertilizers in the agricultural fields ofthe study area on the groundwater quality was investigated. After conducting extensive field monitoring in the study area followed by laboratory analyses of collected soil and groundwater samples. The occurrence and distribution of the pesticides and fertilizers residues in the groundwater of the study area was assessed and the risk evaluation was carried out employing existing method. In addition, the persistence of most common pesticides in the study area was studied and simulated employing PRZM3 model. Following findings have been observed: In the northern part ofthe study area, the groundwater flow direction was observed to be towards the southeastern direction. Whereas, in the southern portion, the groundwater flow direction was generally observed towards southeast. Arise in the groundwater table levels was detected in the post-monsoon season measurements. The groundwater levels were observed to fall in the pre-monsoon season measurements. The total recharge for groundwater aquifer in the study area during monsoon and non-monsoon seasons was assessed as 6691.24 ha mand 8818.06 ha mrespectively. The storage increase in the monsoon and non-monsoon seasons was evaluated as 4873.82 ha m and 3365.78ha m respectively. The status of groundwater development was reflected as 47% only meaning that the area could be categorized as Safe. The recharge from irrigation return flow during monsoon and non-monsoon seasons in the study area was assessed 469.36 ha m and 1656.68 ha m respectively. TDS values were observed to slightly decrease in general in the post-monsoon groundwater samples in comparison with the pre-monsoon groundwater samples. Non significant variations were mostly observed during five seasonal periods. Based on Hem in classification (1970), groundwater of the unconfined aquifer in the present study area could be classified as Fresh due to their TDS values lower than 1000 mg/L. The impact of the application of synthetic nitrogenous fertilizers, manure and compost was apparently clear in this case. Further, one more source viz. land accumulation of organic nitrogenous matter (coming from municipal and industrial solid waste and effluents) also emerged as important in this regard as the southeastern part of the study area exhibits relatively high urban - industrial development. However, the nitrate content in the groundwater of the study area was observed to be less than 45 mg NO3/L (maximum permissible drinking water limit in the Indian Standards. Therefore, the pollution by nitrates because of the application of the fertilizers, manure and compost etc. could be stated as insignificant. All of the investigated groundwater samples in the study area we observed to be suitable for drinking purposes. In the soil and groundwater, the OCP values were observed to increase in general in the post-monsoon period, in comparison with the pre-monsoon period. On the contrary, the OPP values were observed to slightly decrease in general in the post-monsoon period in comparison with the pre-monsoon period. The total concentration of pesticides of the groundwater samples in the study area was found to exceed the permissible limits of the drinking water standards in all sampling sites in the four seasonal periods except for Tansipur (S8) in pre-Monsoon, 2000. The findings revealed that there is a serious groundwater pollution hazard by the application of pesticides in and around Roorkee area. Based on the General DRASTIC index, the most central and southeastern portions, especially around Nagla Imarti (W19), Roorkee town (VV10), Khanjarpur (W12) and Sheikhpuri (W9) were displayed as the most vulnerable. On the basis of the Agricultural DRASTIC index, Five sites were identified and ranked as most vulnerable, which were located in the northern, southern and central portions of the study area at Saliar Salahpur (W5), Sheikhpuri (VV9), Roorkee (W10), Khanjarpur (W12) and Nagla Imarti (W19). Groundwater Ubiquity Score (GUS) values range between -5.52 (Minimum) for DDT and 2.45 (Maximum) for Dimethoate pesticide. According to GUS classification, the most commonly applied pesticides in the study area could be classified into 4 classes from a total of 6 classes as available in the GUS classification. Only Dimethoate pesticide could be found in the Transition region between high & low leaching potential (Category B). All other pesticides were found nonleachers. IV Dimethoate was applied by using foliar-spray technique on the wheat cultivation at a dose of0.4 kg/ha in one cultivation season. Dimethoate got rapidly dissipated in soil with a halflife of 7 days. The dissipation of Dimethoate was maximum in the first week after application after which it slowed down. Dimethoate could be considered as a non-persistent pesticide because it degraded to half the original concentration in less than 30 days. Further, Dimethoate could not be detected in the groundwater samples collected from five observation wells in the DOH farm for 6 months after application. Employing the PRZM3 model, dissipation rate of Dimethoate was simulated. The model also predicted the half-life of Dimethoate as 7 days in soil. The dissipation rate of Dimethoate was predicted during 1year directly after application on the soil. The predicted results showed an increasing loss of Dimethoate in soil with time, within one year after application. The vertical transport of Dimethoate in soil matrix ofthe crop-root zone was physically monitored in the field and also simulated employing PRZM3 model. Agood match between the measured and predicted values was generally been observed. This revealed that PRZM3 simulation model performed well in simulating the persistence of Dimethoate with the lapse of time in addition to the variations ofDimethoate content with depth.