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INTRODUCTION

Groundwater is one of the planet’s most crucial freshwater resources, serving as a lifeline for human survival, economic growth, and environmental sustainability. Globally, it plays a vital role in agriculture, industry, and domestic water supply, providing essential freshwater to both rural and urban populations [1-2]. With the growing demands of agriculture, driven by population growth and intensified irrigation practices, the pressure on groundwater resources has surged, leading to both quantitative depletion and quality degradation. Agriculture alone accounts for approximately 65% of global water use, with industry and power generation consuming 25%, and domestic purposes accounting for the remaining 10% [3-4]. The quality of groundwater is influenced by both natural geochemical processes, such as mineral weathering, dissolution, precipitation, and ion exchange, as well as various anthropogenic activities. These human-induced factors include agricultural runoff, sewage discharge, mining, and industrial waste [5-7]. In regions with irregular monsoon patterns, growing urbanization, and extensive agricultural activities, the demand for sufficient, high-quality groundwater has become even more critical. Groundwater chemistry is primarily shaped by the surrounding lithology, flow dynamics, geochemical reactions, residence time, and the solubility of minerals. However, human activities—especially in agriculture—significantly alter the natural recharge of groundwater [8]. Excessive irrigation and leakage from sewage systems have exacerbated groundwater contamination . Agricultural practices, in particular, contribute to increasing salinity and elevated nutrient concentrations, notably nitrates, phosphates, and potassium, in groundwater supplies.

Nutrient pollution from agriculture, such as the leaching of fertilizers, is one of the major threats to groundwater quality. This is evident in the growing instances of salinization and nitrate contamination, which have been documented globally. Nutrients in groundwater serve as critical indicators for assessing the impact of agricultural activities on the shallow subsurface environment . High concentrations of nitrates in groundwater—often above permissible limits for drinking water—pose significant risks to human health and environmental stability [9-10]. Furthermore, long-term use of fertilizers in agricultural fields contributes to groundwater pollution, which manifests as elevated nutrient levels and salinity, the presence of nutrients, particularly nitrates, phosphates, and potassium, in groundwater is closely tied to agricultural activities. Sustainable water management practices are essential to preserve groundwater quality and ensure its availability for future generations.

Fertilizers are widely used to enhance the availability of essential nutrients—nitrogen, phosphorus, and potassium—to plants. Of these nutrients, nitrate is the most readily leached into groundwater due to its high solubility, mobility, and persistence under aerobic conditions. In contrast, potassium and phosphate are less frequently found at elevated concentrations in groundwater [11]. This is primarily because potassium and phosphate are often present in smaller quantities in fertilizer mixes, and phosphate tends to be adsorbed by clay particles in the soil, reducing its mobility. However, when potassium chloride (KCl) is used in fertilizers, there may also be an associated increase in chloride concentrations in groundwater [12-14]. Agricultural and domestic activities contribute significantly to nutrient loading in groundwater. Unlike major ions, which are less impacted by human activities, nutrients like nitrates, phosphates, and potassium are directly influenced by agricultural practices such as fertilization and irrigation. These practices can result in two main impacts on groundwater: (i) salinization of soil and groundwater beneath the agricultural fields, especially in arid regions due to high evapotranspiration, and (ii) elevated nitrate concentrations from fertilizer leaching   . In arid and semi-arid regions, irrigation can exacerbate salinity in the root zone. To prevent salinization, farmers often apply excess water, which can leach salts and nutrients, such as nitrates, down to the groundwater  .

Excessive fertilization introduces long-term risks to groundwater quality by increasing the likelihood of nitrate, phosphate, and pesticide leaching. Nitrate contamination, in particular, is a well-documented consequence of agricultural activities on a regional scale  . While phosphorus and potassium are less mobile, agricultural runoff can still contribute to their elevated concentrations in both surface and groundwater [15-16]. Many studies indicate that over-fertilization does not enhance crop yields but instead increases nutrient loads, specifically nitrogen and phosphorus, in both surface and groundwater, posing environmental hazards. The present study focuses on understanding the nutrient chemistry of groundwater in agricultural regions and evaluates the spatial and seasonal variations of groundwater quality in the Medchal-Malkajgiri District of Telangana State, India. This region is heavily dependent on agriculture, with irrigated lands dominating the landscape. Groundwater serves as the primary source of water for both agricultural and domestic purposes, making its quality critical for the well-being of the local population.

Study Area

The study area (Fig.1.) covers the selected areas i.e.  Lalgadi Malakpet, Thurkapally, Muraharipally, Kolthur, Sampambole, Peta, Vaagunuthi, Gangadharpally, Anna Sagar, Ksheera Sagar and Zapthi Singaipally of Medchal-Malkajgiri district of Telangana State, India.  The average annual highest temperature in Medchal-Malkajgiri is 40.0°C (104.0°F), and the May 24^th, 2024 is the hottest day on average. The average annual lowest temperature in Medchal-Malkajgiri is 13.8°C (56.8°F), and the December 24^th, 2023 is the coldest day on average. It receives an average annual rainfall of 900.9 mm. Rainfall is the major source of for groundwater recharge.

Patterns of Land use and Agricultural Activity

The agricultural lands dominate the study area, where groundwater serves as the sole source of irrigation. The agricultural calendar is divided into two main cropping seasons. The primary season, known as Kharif, spans from July to October and is characterized by the cultivation of paddy as the major crop. During the second cropping season, from November to March, farmers grow a variety of crops including paddy, vegetables such as spinach, bottle gourd, tomato, bitter gourd, and cauliflower, as well as pulses. To sustain the agricultural productivity of these crops, local farmers rely heavily on chemical fertilizers. The most commonly applied fertilizers in the region for paddy cultivation include Urea, NPK complex fertilizers, Diammonium phosphate ((NH4)2HPO4), Zinc Sulphate (ZnSO4), and Muriate of Potash (KCl). The recommended application rate of nitrogen (N) fertilizers for paddy is 120 kg N/ha, while for other crops like vegetables and pulses, the recommended nitrogen application ranges between 40 to 100 kg N/ha, depending on the specific crop requirements. This extensive use of fertilizers, particularly nitrogen-rich compounds, poses potential risks of nutrient leaching into the groundwater. Given the reliance on groundwater for both irrigation and domestic use, the excessive use of fertilizers increases the likelihood of nitrate contamination, which could affect the overall water quality in the region. Monitoring nutrient levels in groundwater is essential to managing the potential environmental impact of agricultural activities and ensuring sustainable water use.

Materials and Methodology

Total Forty (40) samples were collected from bore wells in the study area from agricultural fields and residential areas. Samples were collected (Table. 1) during December (Post-Monsoon) – 2023 and May (Pre-Monsoon) – 2024 in 1 litre PVC bottles. The collected groundwater samples were analysed in the laboratory for agricultural nutrients such as Nitrates (N), Phosphates (P), Potassium (K) and other physico-chemical parameters such as pH and Electrical Conductivity (EC), Total Dissolved Solids (TDS), Total Hardness (TH), Total Alkalinity (TA), Carbonates (CO₃^2-), Bicarbonates (HCO₃^–), Calcium (Ca²⁺), Magnesium (Mg²⁺), Sodium (Na⁺), Fluoride (F^–), Chloride (Cl^–) and Sulphate (SO₄^2-) as per the Standard Methods for Examination of Water and Wastewater [16]. Obtained results were compared with Indian Standards – Drinking Water Specification (IS 10500:2012) of Bureau of Indian Standards [17].

The verification of analytical accuracy for the concentrations of major ions (expressed in meq/L) was cross-checked using the charge-balance error (CBE) method, ensuring that the error remained within the acceptable limit of ±5% . The CBE was calculated using the following equation:

Results and Discussion

The analytical results of NPK and other physico-chemical parameters are presented in Table 2 & Table 3, during pre-monsoon and post-monsoon season respectively. The results compared with BIS 2012 are presented in Table 4 & Table 5, during pre-monsoon and post-monsoon seasons respectively.

Table 2: Analytical results of NPK and other Physico-Chemical Parameters (Pre-Monsoon)

(Note: All the parameters expressed in mg/L, except EC in µS/cm, No units for pH)

Nitrates (NO^3-)

Nitrate is a significant contributor to groundwater pollution resulting from agricultural activities. Nitrates primarily originate from nitrogenous fertilizers, organic manure, and waste from humans and animals. Due to its high mobility in groundwater, nitrate is not easily adsorbed or precipitated on aquifer solids . According to BIS 2012 standards, the acceptable limit for NO^3- – N in drinking water is 45 mg/L. In the current study, nitrate concentrations during the pre-monsoon season ranged from 4 mg/L to 38 mg/L, with an average of 13.5 mg/L. All groundwater samples were found to be within the BIS 2012 acceptable limit. However, during the post-monsoon season, nitrate concentrations increased, ranging from 9 mg/L to 63 mg/L, with an average of 31 mg/L. Five samples (25%), namely S2, S3, S11, S13, and S14, exhibited concentrations exceeding the BIS 2012 acceptable limit for drinking water. This increase is attributed to the percolation of nitrates into the groundwater during rainfall [16-19].

The risk of nitrate pollution in groundwater depends on both the nitrogen load and the vulnerability of the aquifer . Nitrate leaching from agricultural areas, especially from the application of agrochemicals, is a major source of contamination. In the study area, the application of 500 kg/ha of fertilizer leads to excess nitrate in groundwater, with a spatial impact extending up to 2.0 km from bore wells  . Other potential sources of nitrate contamination include effluent discharge from intensive livestock units, leachate from manure storage, leaking slurry pits, and the spreading of slurry or manure as organic fertilizer, all of which can contribute to groundwater pollution .

Phosphates (PO₄^3-)

Phosphates are common constituents of agricultural fertilizers, manure, and organic wastes. In the present study PO₄^3- valuesranged from 0.001 mg/L to 0.087 mg/L with an average of 0.018 mg/L and 0.001 mg/L to 0.091 mg/L with an average of 0.026 mg/L during pre-monsoon and post-monsoon seasons respectively. All the samples are within the acceptable limit of 0.1 mg/L [20-24].

Potassium (K⁺)

In the present study K^+- valuesranged from 1.4 mg/L to 6.3 mg/L with an average of 3.4 mg/L and 1.4 mg/L to 4.6 mg/L with an average of 2.8 mg/L during pre-monsoon and post-monsoon seasons respectively. The BIS 2012 acceptable limit is 10 mg/L. All the samples are within the acceptable limit.

Physico-Chemical Parameters

In this study, the pH of groundwater samples ranged from 7.9 to 8.3, with an average of 8.1 during the pre-monsoon season, and from 8.1 to 8.4, with an average of 8.3, during the post-monsoon season. The BIS acceptable pH limit for drinking water is 6.5–8.5, and all the groundwater samples fell within this range. Electrical Conductivity (EC) values ranged from 352 µS/cm to 1331 µS/cm, with an average of 842 µS/cm during pre-monsoon, and from 278 µS/cm to 1359 µS/cm, with an average of 862 µS/cm during post-monsoon. All samples were within the BIS acceptable limit of 1500 µS/cm.

Total Dissolved Solids (TDS) ranged from 226 mg/L to 852 mg/L, with an average of 539 mg/L during the pre-monsoon season, and from 178 mg/L to 870 mg/L, with an average of 551 mg/L during post-monsoon. The BIS acceptable limit for TDS is 500 mg/L, with 65% of samples during pre-monsoon and 75% during post-monsoon exceeding this limit. TDS is an indicator of groundwater salinity, influenced by both natural and anthropogenic factors such as weathering, rock–water interaction, household, industrial, and irrigational activities. Total Hardness (TH) ranged from 129 mg/L to 306 mg/L, with an average of 225 mg/L during pre-monsoon, and from 83 mg/L to 365 mg/L, with an average of 256 mg/L during post-monsoon. The BIS acceptable limit for TH is 200 mg/L, with 70% of samples in both seasons exceeding this limit. Total Alkalinity (TA) ranged from 86 mg/L to 314 mg/L, with an average of 228 mg/L during pre-monsoon, and from 88 mg/L to 311 mg/L, with an average of 226 mg/L during post-monsoon. TA values exceeded the BIS limit of 200 mg/L in 80% of samples during pre-monsoon and 65% during post-monsoon.

Sodium (Na⁺) concentrations ranged from 33 mg/L to 181 mg/L, with an average of 114 mg/L during pre-monsoon, and from 39 mg/L to 196 mg/L, with an average of 115 mg/L during post-monsoon, with all samples within the BIS acceptable limit of 200 mg/L. Calcium (Ca²⁺) concentrations ranged from 27 mg/L to 93 mg/L, with an average of 65 mg/L during pre-monsoon, and from 25 mg/L to 91 mg/L, with an average of 71 mg/L during post-monsoon. About 20% of samples during pre-monsoon and 45% during post-monsoon exceeded the BIS acceptable limit of 75 mg/L. Magnesium (Mg²⁺) concentrations ranged from 5.0 mg/L to 29 mg/L, with an average of 15 mg/L during pre-monsoon, and from 5.0 mg/L to 49 mg/L, with an average of 19 mg/L during post-monsoon. About 15% of the samples exceeded the BIS acceptable limit of 30 mg/L during the post-monsoon season. Carbonate (CO32-) concentrations ranged from 5.0 mg/L to 25 mg/L, with an average of 16 mg/L during pre-monsoon, and from 5.0 mg/L to 20 mg/L, with an average of 9.0 mg/L during post-monsoon. Bicarbonate (HCO^3-) concentrations ranged from 71 mg/L to 304 mg/L, with an average of 212 mg/L during pre-monsoon, and from 78 mg/L to 291 mg/L, with an average of 218 mg/L during post-monsoon. HCO3- values exceeded the BIS acceptable limit of 200 mg/L in 65% of samples during both seasons.

The fluoride (F-) values ranged from 0.14 mg/L to 0.3 mg/L, with an average of 0.21 mg/L during the pre-monsoon season, and from 0.14 mg/L to 0.37 mg/L, averaging 0.25 mg/L in the post-monsoon season. All samples remained within the acceptable limit of 1.0 mg/L set by the Bureau of Indian Standards (BIS) for both seasons. Chloride (Cl-) values varied from 87 mg/L to 329 mg/L, averaging 198 mg/L in the pre-monsoon season, and from 72 mg/L to 390 mg/L during the post-monsoon season. The BIS acceptable limit for Cl- is 250 mg/L, with 20% of samples exceeding this limit in both seasons. The elevated Cl- concentrations are attributed to the disposal of agrochemicals and domestic wastewater into groundwater sources. Sulfate (SO₄^^2-) values ranged from 13 mg/L to 93 mg/L, with an average of 26 mg/L during the pre-monsoon season, and from 6.0 mg/L to 125 mg/L, averaging 29 mg/L in the post-monsoon season. All samples were within the acceptable limit of 200 mg/L set by the BIS for both seasons.

CONCLUSION

The present study aims to assess the influence of agricultural activities on groundwater quality. A total of 40 groundwater samples were collected from bore wells in selected areas of the Medchal-Malkajgiri district, Telangana, India, during both the pre-monsoon and post-monsoon seasons. The samples were analyzed for nitrogen (N), phosphorus (P), potassium (K), and other physico-chemical parameters to evaluate nutrient concentrations and their spatial and seasonal variations in the groundwater of the study area. The results indicate that agricultural practices, including the application of fertilizers, soil mineralization processes, and irrigation return flow, significantly influence the concentrations of NPK nutrients and other major ions in the region’s groundwater. Spatially the nitrate levels are higher in the groundwater samples which collected from the bore wells of agricultural fields than the groundwater samples collected from the bore wells of residential areas. Seasonal variation studies reflected that the concentration of nitrate were double in post-monsoon. The concentration of salinity parameters such as EC, TDS and Cl^– also increased during post-monsoon season. It is clearly indicating that the percolation of nitrates and other ions during rains of monsoon season reaches to the groundwater and values are higher in post-monsoon season. The study recommends that ongoing efforts be made to educate farmers on the optimal use of fertilizers in relation to crop requirements and irrigation schedules. This approach is essential for preserving the groundwater quality in the study area.

Acknowledgements

The authors wish to acknowledge the Coordinator and faculty members of Department of Environmental Science, University College of Science, Osmania University for providing research opportunity.

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