Estimation of Nitrate Leaching in Groundwater in an Agriculturally Used Area in the State Karnataka, India, Using Existing Model and GIS
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Available online at www.sciencedirect.com ScienceDirect Aquatic Procedia 4 ( 2015 ) 1047 – 1053 INTERNATIONAL CONFERENCE ON WATER RESOURCES, COASTAL AND OCEAN ENGINEERING (ICWRCOE 2015) Estimation of Nitrate Leaching in Groundwater in an Agriculturally Used Area in the State Karnataka, India, Using Existing Model and GIS a * b c Vinod P. N , Chandramouli P. N , Manfred Koch * aDayanandaSagar College of Engineering, Bangalore-560078 b National Institute of Engineering, Mysore-570008 cUniversity of Kassel, Kassel, Germany-34125. [email protected],[email protected],[email protected] Abstract Water pollution is one of the biggest environmental problems and nitrate is among the most common and widespread pollutants in groundwater. There has been an increasing demand for fresh water in the last two decades due to a progressive increase in population. In addition, people face serious water shortages, because groundwater has been used faster than it is naturally replenished.At the same time an increasing amount of wastes and chemicals causes contamination of water resources, especially of groundwater. Although the movement of groundwater through the aquifer has often the effect of removing a lot of impurities from the water by filtering it through the porous rocks, so that groundwater is generally much cleaner than surface water, there are many contaminants which are not easily degraded in the subsurface. Such is the case for nitrate which is impounded into the groundwater by agricultural activities, namely fertilizers and livestock manure. Since nitrate is soluble and negatively charged, it has high mobility and is thus easily leached from the unsaturated zone. In this research work, an attempt has been made to estimate nitrate leaching to groundwater at six different places around the village of Srirangapatnataluk where organic manure and inorganic fertilizers, together with irrigation water and cesspools are the major sources of nitrate in the area. Existing models and Arc-GIS have been used for the analysis. The results indicate that, except for Belagola village, the groundwater nitrate concentrations underneath the irrigated lands are still within the permissible limit, which means that the water of these villages can be used for both drinking and irrigation purposes. The average leached nitrate amounts in the sampled areas supplied from irrigated land have been estimated to range between 51.23 and 74.93 kg/ha/year. For the groundwater nitrate concentrations underneath the cesspools, the results of the analysis show that they are all within the permissible limit, except for * Corresponding author. E-mail address: [email protected] 2214-241X © 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of organizing committee of ICWRCOE 2015 doi: 10.1016/j.aqpro.2015.02.132 1048 P.N. Vinod et al. / Aquatic Procedia 4 ( 2015 ) 1047 – 1053 the villages of Karekura and Bommuragrahara. Nitrate leaching amounts supplied from the cesspools lie between 87.81 and 381.96 kg/year. The reasons for this wide margin are likely losses due to denitrification and volatilisation processes. ©© 20152015 The The Authors. Authors. Published Published by byElsevier Elsevier B.V. B.V. This is an open access article under the CC BY-NC-ND license (Peerhttp://creativecommons.org/licenses/by-nc-nd/4.0/-review under responsibility of organizing committee). of ICWRCOE 2015. Peer-review under responsibility of organizing committee of ICWRCOE 2015 Keywords: Ground water pollution; nitrate leaching; Arc GIS; Karnataka,; India 1. Introduction Groundwater is the water under the earth’s surface that flows freely through tiny pores and cracks in rocks and soilscalled aquifers and that can be pumped from wells. Groundwater contamination by anthropological activities and/or infiltration of polluted surface waters has become an ubiquitous problem in many aquifers across the world in recent decades (Gustafson 1993, Fetter 1999).Sources of groundwater contamination are widespread and include accidental spills, landfills, storage tanks, pipelines, agricultural activities, and many other sources. These sources are often classified into two groups, point sources or non-point sources. Dealing with the latter has become a particular challenge in groundwater remediation, as non-point sources act on a much wider scale than point sources. One major representative of non-point sources is diffuse pollution from agricultural activities and livestock (Rail, 1989). One major chemical involved in this kind of groundwater contamination is nitrate which poses a significant health risk above some critical threshold concentration (Kross et al. 1993). Agricultural activities are in fact the main sources of high nitrate concentrations not only in groundwaterbut also in superficial water courses in many regions of the world(Forman et al.1985, Zhang et al. 1996).The origins of the nitrates are either chemical fertilizers or manure from livestock. The problem of nitrate groundwater pollution has really been aggravated over the last decades, due to more intensive agriculture and the introduction of high yield crops which has raised the use of fertilizers and so increased nitrate concentrations in groundwater. Successful groundwater pollution prevention means that potential contaminants must be controlled so that they cannot infiltrate into the groundwater system. For evaluating and possibly preventing nitrate contamination,it is important to understand the various physical, chemical and biological processes that control the transport and fate of this pollutant in the subsurface (Fetter, 1999). The most important physical process involved in possible nitrate contamination is leaching into groundwater by rain or irrigation water infiltrating through the soil down to the groundwater table.With regard to the chemical and biological processes that transform nitrogen to its various chemical derivatives, as described mainly by the nitrogen cycle (Galloway et al., 2004), and that may be either benevolent or toxic in groundwater, these are theoretically well known, but are difficult to evaluate in real subsurface environments.For example, nitrogen applied through fertilizers or manure is converted into nitrate by bacteria living in the soil. The nitrate that is not taken up by the crops, immobilized by bacteria into soil organic matter or converted to atmospheric gases by de-nitrification can leach from the root zone and possibly end up in groundwater leading to the pollutions problems as mentioned. 2. Study region and data collection For the purpose of the study, i.e. the estimation of nitrate leaching into groundwater, a fieldwork was carried out in the study region (Figures 1 and 2) which consisted in the collection of soil samples from the agricultural land and groundwater samples from all wells used for irrigation. The nitrate level was measured for two different depths (0- 100 mm, 400-500 mm). More specifically, for each agricultural land, 5 to 6 soil samples were taken at various depths and mixed to get the average nitrate content in the soil. Samples were also taken from the numerous cesspools dispersed across the agricultural lands. Table 1 shows the measured nitrate contents of the collected samples in the study areas for ground water, soil before cultivation (SBC) and the cesspools. P.N. Vinod et al. / Aquatic Procedia 4 ( 2015 ) 1047 – 1053 1049 Fig.1: Map of sampling area Fig.2: DEM (left) and stream network (right) of study area Table 1.Nitrate content in the groundwater, soil before cultivation and cesspools Location NO3in GW (mg/l)NO3-conc in SBC NO3-conc in cesspools (mg/l) (kg of NO3/kg of soil) (mg/l) PALAHALLI 42.45 3.2×10-6 29.23 HOSAHALLI 12.92 4.5×10-6 28.29 KAREKURA 6.69 3.6×10-6 61.63 BRAMHAPURA 21.16 2.8×10-6 39.23 B AGRAHARA 28.70 4.7×10-6 57.67 BELAGOLA 24.70 4.1×10-6 40.60 1050 P.N. Vinod et al. / Aquatic Procedia 4 ( 2015 ) 1047 – 1053 Rainfall data were available from three daily weather stations (Srirangapatna). In congruence with the sampling periodwhich lasted from January 2012 to December 2012 rainfall during this year was taken into account for the leaching model. The rainfall in the study area falls in the monsoon months of May, June, July, August, September, and October. To compute the areal rainfall from the gauge recordings, the Thiessen polygon method was used which, according to Ward and Robinson(2000), is better than using the mean of the gauge measurement, because it allows for a non-uniform distribution of rainfall gauges by assigning weights to the rainfall depths corresponding to the areas of the surrounding Thiessen polygon. The amount of nitrate (kg/ha) supplied by the rainfall was calculated from the following equation. NO3(R) =NO3 (CR) × R (kg/ha) (1) 100 where CR is the concentration of NO3 in rainwater (mg /l), and R is the rainfall (mm) 3. Modelling Model is defined as any tool that is ableto represent an approximation of a real field situation. The use of groundwater flow models is nowadays prevalent in the field of environmental science. Models have been applied to investigate a wide variety of hydro-geologic conditions. More recently, groundwater models are being applied to predict the transport of contaminants for risk evaluation. In general, models are conceptual descriptions or approximations that describe physical systems using mathematical equations; they are not exact descriptions of physical systems or processes. By mathematically representing a simplified version of a hydro-geological system, reasonable alternative scenarios can be predicted, tested, and compared. The applicability or usefulness of a model depends on how closely the mathematical equations approximate the physical system being modelled.Since the models are developed on the basis of a certain set of measurements, their applicability to areas with other conditions may be restricted. In this study, the amount of nitrate leaching to the groundwater was calculated by using a mathematical model.