In recent years many reports have identified agricultural non-point source pollution as the leading source of water quality impacts to rivers and lakes. The impact of agricultural practices on groundwater quality is of particular concern. This concern is heightened by the fact that a majority of the population of the state receives their drinking water supply from private wells. Most of these wells are shallow and are vulnerable to water pollution, especially from nitrate (Bhumbla, 2001). For example in west Virginia, contamination of surface and groundwater by non-point sources is of great concern. West Virginia is a water rich state and rivers originating in this state drain into the Chesapeake Bay and into the Gulf of Mexico (Bhumbla, 2001).
Nitrates and nitrites occur normally in nature from the breakdown of ammonia
in the nitrogen life cycle. Nitrates in nature cause plant and algae growth
that may affect the balance of water-based ecosystems. Nitrate is found in fertilizers
and animal waste. Rain tends to wash fertilizers containing nitrates into nearby
natural water systems and ground water. Groundwater used as drinking water that
contains nitrogen represents a hazard to babies. Many die every year as a result
from Blue Baby Syndrome (www.ScienceFairCenter.com).
Nitrates cause sudden death when animals ingest large amounts, as in fertilizer.
Nitrates are not really very toxic, but are converted to nitrite. Nitrates are
converted to ammonia and made into protein. If this conversion does not occur
fast enough, nitrite is absorbed and converts hemoglobin to methemoglobin. The
ferrous ion(+2) is converted to the ferric(+3) form. Methemoglobin can no longer
carry oxygen, so the blood is a dark chocolate color and the animal suffers
anoxia (Smith, 2006).
Excessive level of nitrate in drinking water and fresh vegetables when is converted to nitrate in the digestive system of human and animal interferes with the oxygen-carrying capacity of blood and caused a condition known as methamoglobinamia. Also continuous consumption of vegetable and drinking water with high level of nitrate content may react with nitrosamines to form N-Nitrose, which, are potent carcinogens in human and animals (Malakuti, 2000).
Agricultural activities in Slovenia are described and results of calculation of nitrogen and phosphorus balance in the catchment areas of the water bodies presented. The analyses show that hydro-morphological and chemical pressures from point pressures and diffused pollution from agriculture are the main reasons for the non-attainment of environmental objectives. Though consumption of mineral fertilizers and plant nutrients in Slovenia has reached more or less steady state in the last years, the quantities are still too high to reduce the risk to water environment (Globevnik et al., 2006).
Even thought the ratios between N, P and K uptake by plants is about 10: 1: 10, the fertilizer recommendation in Iran do not follow this ratio (Malakuti, 1999). Also, the application time is not synchronized with plant uptake. Consequently, the highly dissolved nitrate has been leached from the soil into ground water. In addition the accumulation of nitrate in vegetables such as Spinach, lettuce has causes in human and animals (Malakuti, 1999).
The denitrification and nitrate uptake by plants and microbes reduce the nitrate concentration in soil solution. In USA the permissible nitrate concentration for drinking water is 40 mg L-1 and higher concentrations may cause methamoglobinamia (Dabiri, 1996).
One month after nitrogen fertilizer application, the nitrate concentration in ground water increased, which shows nitrate leaching and transportations to ground water (Bhatt, 1997). Investigation of seasonal nitrate concentration shows that 97 kg ha-1 in spring and summer and 199 kg ha-1 in fall and winter have been leached and entered into ground water (Bruckler et al., 1997). Investigation of nitrate concentration (Edmunds and Gaye, 1997) in 8200 well-water in highly intensive agricultural showed that nitrate concentration is higher than permissible value 10 mg L-1. Ninety percent of well-waters in Michigan State were contaminated with nitrate (Clift et al., 2001). In the paddy fields in northern Iran and southern of city of Tehran the high nitrate concentration is due to excessive application of nitrate fertilizer (Malakuti, 1999). In central Iran, in city of Yazd, in the vicinity of the Steel complex in Esfahan province the well water nitrate concentration were higher than permissible level (Rahmani, 2003).
In this study the nitrate concentration in water in Ardestan area in 2005 will be examine.
MATERIALS AND METHODS
This research did in 2005 in Ardestan area, located 100 km north of city of Esfahan in central part of Iran.
In the first phase from 86 agricultural districts in Ardestan county 10 agricultural
districts was selected (Table 1). In each district 3 to 4
well waters were seasonally (times of sampling were in spring, summer, fall
and winter in 2005) sampled. The water samples were immediately placed in an
icebox and carried to the laboratory for standard analysis. The pH and EC were
measured by a portable field EC and pH meters. The NO3-N was determined
with automated hydrazide reduction method (APHA, 1995) and Total Dissolved Solid
(TDS) was measured in the laboratory (a well-mixed sample is filtered through
a standard glass fiber filter and the filtrate is evaporated to dryness in a
weighted dish and dried to constant weight at 180°C.
||The selected studied districts
The increase in dish weight represents the total dissolved solids (APHA, 1995).
The results were compared with the permissible level for irrigation and drinking
RESULTS AND DISCUSSION
Table 2 shows the range and mean of pH, EC, TDS and NO3-N in water samples of different districts and seasons. In water samples of different districts the highest pH was in spring (40% of districts) and summer (60% of districts) and lowest was in winter and fall. For EC and TDS the highest value was in fall (40% of districts) and winter (60% of districts) and lowest was in spring and summer. In other words the districts of 1, 4, 5, 6, 8 and 9 had the highest EC and TDS in winter and the districts of 2, 3, 7 and 10 had the highest EC and TDS in fall. In water samples of different districts the highest NO3-N was, in districts of 2, 3, 4, 9 and 10 in fall, in districts of 6 and 7 in winter, in district of 8 in spring and in district of 1 in summer. In other words 50, 20, 10 and 10% of districts had the highest NO3-N in fall, winter, spring and summer, respectively.
Table 3 shows the mean pH values in the various selected districts. The pH ranges from 6.73 to 7.01. The permissible pH values are from 6.5 to 8.4 or 6.0 to 8.5 (IEPA, 1994; EPA/ROC, 1989). Therefore, the pH value is not a limiting factor in the well-water.
Table 3 shows the mean Electrical Conductivity (EC). The lowest and the highest EC was recorded from Amiran (4.4 dS m-1) and Charmill (7.7 dS m-1), respectively. The ECs of all of the well water are higher than the recommended non-limiting values (EPA/ROC, 1989; Ayers and Westcot, 1985) for irrigation. The salt tolerance crop and cultivars should be planting and irrigation management such as leaching fraction be applied to minimize the crop yield reduction due to salinity. It is suggest that the Agricultural management office recommend planting suitable salt resistance crop and genotypes, to minimize the effect of saline irrigation water on crop yield.
In addition recommend irrigation practices to minimize salt load to ground water, while controlling root zone salinity. The total dissolved solid is ranging from 2900 to 4990 mg L-1. Table 3 shows the total dissolved solid is higher than permissible values (EPA/ROC, 1989; Ayers and Westcot, 1985) for irrigation utilization. The permissible level is 2000 mg L-1 and is 450 mg L-1 for long-term irrigation application without any limitations.
The TDS Value in the Decreasing Order Are:
Charmil>Telk-Abad>Kachurastagh2>Zavareh2 and Zavareh1>Hosien-Abad
Table 3 shows the mean concentration of NO3-N in the well water. The mean NO3-N and considering the permissible concentration level (Ayers and Westcot, 1985) the mean concentration of well water in Kachurastagh 1 and 2, Zavareh 1 and 2, Telk-Abad and Charmil is higher than 5 mg L-1 and has low to medium limitation for agricultural land irrigations.
||The range and mean of some characteristics of water samples
in the selected districts with time of sampling
||The range and mean of some characteristics of water samples
in the selected districts in 2005
The NO3-N values in the decreasing order are:
Kachurastagh 2, Charmil>Telk-abad>Kachurastagh1>Zavareh1>Zavareh2>Amiran>Rigestan>
According to the results Najaf-Abad and Kachurastagh 2 have the lowest and highest value NO3-N concentration in well-water, respectively. For irrigation, wells water in Najaf-Abad and Hosein-Abad areas do not have and in other areas have low to moderate limitation, respectively.
The results of pH analysis indicate that pH of wells water is in the normal and permissible range and has no limitation for irrigation of agricultural land.
The comparisons of the well-water EC values with the maximum permissible values for irrigation water (Ayers and Westcot, 1985) shows that EC of all well-water are higher than maximum permissible values for irrigation. From the 10 studied districts the well-water in the Amiran and Charmil had the highest and lowest EC value, respectively.
Application of best management practices for reducing soil salinity and cultivation of salt tolerance plants is necessary.
The TDS of wells water in every district are higher than maximum permissible level (2000 mg L-1) and according to Ayers and Westcot (1985) have limitation for land irrigation.
The highest nitrate concentrations were measured in summer and fall seasons, which may be the results of soil nitrogen fertilizer application and leaching from the upper soil profile in the previous seasons and transportation into ground water.
For irrigation, wells water in Najaf-Abad and Hosein-Abad areas do not have and in other areas have low to moderate limitation.
Due to negative balance of ground water resource due to excessive pumping, water resource planning and implementation is recommended. Uncontrolled and excessive ground water pumping put more pressure on local water resources and brings about water crisis especially in dry years.
The establishment and expansion of industries with high water demand is not feasible. Assessment of water demand for establishment of new and expansion of current industries should be considered.
Ground water pollution especially in arid regions is a serious treat. The ground water in many of the studied areas is the sources of drinking water. It is recommended to study the prevention and reduction methods for chemical loads into ground water by reducing and timing of fertilizer application and sound irrigation managements.
The high Nitrate concentration in ground water in some studied districts is due the over application of chemical nitrogen fertilizer in agricultural lands.