Comparative implications of tobacco and non-tobacco crop farming on aquatic ecosystems: a multi-index evaluation of irrigation suitability and pollution risks Open Access

Water, especially freshwater, is an essential and abundant natural resource for all living organisms, including plants, animals, humans, and other life forms (FAO & AWC 2023; Rai et al. 2024). Water has played an important role in maintaining the human race, socio-economic advancement, and ecosystem resilience since the beginning of life on Earth (Islam et al. 2016; Sharma et al. 2025). The agricultural sector is the largest consumer of water for irrigation, using 70% of the world's freshwater; in developing countries like Bangladesh, this percentage is much higher, reaching 95% (Roy et al. 2015). As an irrigated agricultural economy country, Bangladesh depends on an adequate water supply, of which 80.60% comes from groundwater and 19.40% from surface water. In Bangladesh, approximately 5,049,785 ha of land is irrigated, requiring quality water to support crop growth and yield (Vyas & Jethoo 2015). Surface water is typically the main source of irrigation for farmers because it is readily available and cost-effective. However, it is threatened by factors such as quality degradation, pollution, and overuse during dry periods (Islam et al. 2016). Agriculture plays a major role in water pollution, and its pollution surpasses urban and industrial sources (Evans et al. 2018; FAO 2018). Since the beginning of the 20th century, agriculture has become both a cause and a victim of water pollution. Agricultural pollution is caused by excessive use of agrochemicals (fertilizers and pesticides), poor post-harvest management, and inefficient irrigation systems (Roy et al. 2024b; Zia et al. 2013). These traditional agrarian practices release large amounts of nutrients, salts, organic matter, pesticides, sediments, heavy metals, pathogens, and other emerging pollutants into nearby waters through leaching, runoff, erosion, and atmospheric deposition (FAO 2018), leading to significant degradation of surface water quality for irrigation (FAO 2013; Monira et al. 2024). Two separate studies demonstrated that agriculture accounts for 37% of surface water pollution in the Philippines and 38% in the European Union (FAO 2017). FAO (2013) revealed that agriculture is North America's single largest source of surface water pollution. About 30–50% of crop production depends on commercial fertilizers, and to feed a growing population, about 200 MT of chemical fertilizers (NPK) are used worldwide annually in agriculture. In Bangladesh, excessive chemical fertilizers are commonly used to increase commercial yields, patronized by the government, with an average use of 320.9 kg/ha, which is significantly higher than India (121.4), China (301.5), Britain (287.5), and the USA (160.8) (Savci 2012). Excessive chemical fertilizers are often not fully utilized by crops, thereby entering water bodies (Corradini et al. 2015), which degrade surface water quality, pollute water sources, harming aquatic ecosystems, endangering wildlife, and threatening human health (Liu et al. 2020; Roy & Mostafa 2024). FAO (2013) reported that this pollution is responsible for almost half of the world's surface water quality, and about 66% of all Chinese lakes have undergone eutrophication to hyper-eutrophication. Several studies showed that agriculture is the main source of pollution in surface waters, contributing 81% of N, 93% of N, and 50% of chemical oxygen demand (COD) in China, compared to only 10–16% from industry (Cui et al. 2020; Zhang et al. 2020); it also contributes to 60–65% of N, 60% of P, and 60% of K pollution in Vietnam and 7.6% of pesticide pollution in Thailand (FAO 2018). The total area under tobacco cultivation in Bangladesh was 40,634 ha, and the total production was 92,327 tons in FY 2021–22. It is the 6th major cash earner but the second top export crop of Bangladesh, ranking 14th in acreage and 12th for production in the world (Roy et al. 2024a). Tobacco cultivation uses a large amount of chemical fertilizers (1,594 kg/ha), which is 2.02, 2.48, and 1.48 times more than boro rice, wheat, and winter maize, respectively (Roy et al. 2024b). Therefore, tobacco cultivation pollutes water more than other crops. Despite this situation, the issue of water pollution from agriculture has not received much attention in the world, including in Bangladesh (Evans et al. 2018).

Water quality is crucial for establishing a successful irrigation system in agriculture, and it should be regularly monitored and evaluated for the suitability of irrigation water (Shill et al. 2019). Poor irrigation water quality directly affects the quality of soil and the crops that are cultivated there, as well as significantly contributing to surface water pollution (Sappa et al. 2015). All irrigation water contains mineral salts, but their concentration and composition vary from location to location (Ayers & Westcot 1985). The suitability of irrigation water depends on its mineral content. Various water quality index (WQI) techniques have been established worldwide to assess IWQ for improved crop growth and production, as no single model can fully assess water quality (Islam & Mostafa 2022). Plants and agricultural soil are physically and chemically impacted by excessive dissolved ions in irrigation water, which lowers their productivity (Liu et al. 2020). Physical stress reduces the osmotic stress in plant cells and chemical stress disrupts plant metabolism (Bai et al. 2019). Therefore, pH, alkalinity, sodium adsorption ratio (SAR), cation ratio of soil structural stability (CROSS_Opt), soluble sodium percentage (SSP), residual sodium bicarbonate (RSBC), permeability index (PI), Kelly's ratio (KR), magnesium adsorption ratio (MAR), salt index (SI), dry residue (RS), osmotic potential (OP_π), electrical conductivity (EC), total dissolved solids (TDS), total hardness (TH), HMs, and some specific ions are commonly used to assess the suitability of drinking and irrigation water (Islam et al. 2017; Wagh et al. 2018; Elsayed et al. 2020; Ali Rahmani et al. 2024; Thapa et al. 2024). The USA Salinity Laboratory diagram (USSL 1954) and the Wilcox diagram (1955) are also commonly used to interpret irrigation water suitability (Roy et al. 2015; Sharma et al. 2025). However, the impact of irrigation water on soil and plants depends on various factors, including climate, soil texture, soil organic matter, crop type, management practices, and irrigation systems. Recently, many studies have been conducted worldwide, including in Bangladesh, to evaluate the suitability of ground and river water for irrigation; a comprehensive assessment of salinity risk, permeability risk, specific ion toxicity, miscellaneous effects, and HM contamination is also found in the literature but their numbers are very few (Goher et al. 2014; Roy et al. 2015; Islam et al. 2016, 2017; Wagh et al. 2018; Elsayed et al. 2020; Zakir et al. 2020; Yousif & Chabuk 2023). However, no researcher in the world, including Bangladesh, has evaluated the suitability of pond water near crop farms for irrigation by considering both major physico-chemical parameters and HM. Additionally, no one has assessed the impact of tobacco cultivation on surface water suitability for irrigation compared to non-tobacco crops. A comprehensive study was conducted on surface water within the tobacco and non-tobacco crop-growing areas using multiple indexing tools of irrigation water suitability, water health, and HM pollution. The findings of this study will offer farmers valuable insights into the effects of tobacco and non-tobacco crop cultivation on the quality of water bodies used for irrigation. This information can assist them in implementing risk-reduction strategies to support the sustainable management of surface water resources. In addition, by understanding the devastating implications of tobacco cultivation on surface water, policymakers of the country may be encouraged to shift tobacco farmers to more profitable crops in the future.

Laboratory data were compiled into a master sheet and analyzed using Statistical Package for the Social Sciences (SPSS) software (version 20) and Microsoft Excel 2016 for statistical evaluation of various water parameters.

No single method can effectively assess the surface water suitability for irrigation. The following methods were considered for the evaluation of IWQ, where all input values of SAR, CROSS_Opt, SSP, KR, MAR, RSBC, and PI were considered in mEq/L. Pearson's bivariate correlation matrix (t_0.05 = 2.571 at 5 df) was also performed to compare the differences between BCS and ACS for both fields.

• a) Richards in 1954 proposed that the SAR can be expressed using Equation (2) and stated that SAR values <9 mEq/L are generally suitable for irrigation (Ali Rahmani et al. 2024).

  

  (2)
• b) SAR is the standard for predicting the potential impact of irrigation water on soil permeability and structural hazard (USSL 1954; Ayers & Westcot 1985). Ca²⁺ and Mg²⁺ are known to support good soil structure, while K⁺, though less dispersive than Na⁺, has a stronger dispersive effect than Ca²⁺ and Mg²⁺. However, K⁺ is excluded from the SAR equation. To address this, Smith et al. (2014) introduced CROSS_Opt, a modified indexing technique to more accurately predict infiltration hazards as Equation (3), and applicable to all irrigation waters (FAO & AWC 2023; Thapa et al. 2024).

  

  (3)
• c) Wilcox in 1948 defined the SSP using Equation (4) and indicated that SSP values <20% signify excellent for irrigation water (Roy et al. 2015).

  

  (4)
• d) KR, introduced in 1963 and calculated using Equation (5), indicates that values >1 are unsuitable for irrigation (Wagh et al. 2018).

  

  (5)
• e) The MAR, or magnesium hazard, was calculated by Todd in 1980 using Equation (6), with MAR values >50% deemed unsuitable for irrigation (Wagh et al. 2018).

  

  (6)
• f) The RSBC, defined by USSL (1954) in Equation (7), considers values <1.25 mEq/L as low alkalinity, typically suitable for irrigation (Roy et al. 2015).

  

  (7)
• g) Doneen in 1964 defined the PI in Equation (8), with classifications as follows: >90 = excellent, 90–75 = good, 75–30 = fair, and <30 = unsuitable for irrigation (Islam & Mostafa 2022).

  

  (8)
• h) Dry residue (RS), expressed in Equation (9) by Bai et al. (2019), is measured in μS/cm. RS values >525 mg/L are considered incompatible for irrigation.

  

  (9)
• i) OP_π, calculated using Equation (10) with values in μS/cm, is considered unsuitable for irrigation when OP_π > 0.27 atm (Bai et al. 2019).

  

  (10)
• j) The SI, calculated using Equation (11), predicts salt and sodium hazards to soil and plants, with all ions measured in mg/L. A positive SI value is unsuitable for irrigation (El-Defan et al. 2016).

  

  (11)

The excessive use of pesticides, fertilizers, and other agrochemicals in agriculture often results in toxic runoff with rain or irrigation water, contaminating nearby water bodies.

Water salinity, measured by TDS and EC_W, is a key factor affecting crop productivity. Dissolved salts reduce the soil's osmotic potential, impacting both crop yield and soil physical properties (USSL 1954; El-Defan et al. 2016; Islam & Mostafa 2022; FAO 2023). TDS measures dissolved ions directly, while EC_W measures them indirectly using an electrode. Since plants only absorb fresh water, higher EC_W significantly reduces the water available to plants. For example, water with an EC_W of 1 μS/cm contains about 1.74 pounds of salt per acre-foot (Ayers & Westcot 1985). The results showed that during BCS, the EC_W and TDS values were (571.17 ± 119.65 μS/cm) and (360.00 ± 74.19 mg/L) for TF water, and (861.17 ± 424.02 μS/cm) and (597.00 ± 350.03 mg/L) for NTF water. During ACR, EC_W increased by 42.72%, reaching (815.17 ± 49.20 μS/cm) for TF water, and by 5.84%, reaching (911.50 ± 360.18 μS/cm) for NTF water. TDS increased by 46.18%, reaching (526.25 ± 27.85 mg/L) in TF water, while it remained almost unchanged in NTF water at (590.75 ± 238.21 mg/L). Islam & Mostafa (2022) found similar values for Bangladeshi pond water: 685.31 μS/cm for EC_W and 402.54 mg/L for TDS. However, all values were well below the maximum permissible limit (MPL) for IWQ set by FAO (2023) and SWQ by BEPR (2023) (Table 1). According to irrigation water criteria, EC_W (μS/cm) < 700 and TDS (mg/L) < 450 represent excellent or freshwater; EC_W = (700–1,500) and TDS = (450–900) represent good water; EC_W = (1,500–3,000) and TDS = (900–2,000) refers to doubtful water; and EC_W > 3,000 and TDS > 2,000 indicate water unsuitable for irrigation (Roy et al. 2015; El-Defan et al. 2016; Islam & Mostafa 2022). The US salinity hazard diagram (1954) in Figure 4(a) shows that all values fall within the S₁ (very low salinity) category. Statistical analysis of salinity hazards shows that TF water was classified as Grade A (non-saline) during BCS, but it significantly deteriorated to Grade B (slightly saline) during ACS (as 5.39 > t_0.05). In contrast, the water quality of NTF remained unchanged at Grade B (slightly saline) with no significant difference (as 0.81 < t_0.05). High EC_W and TDS reduce crop productivity by causing physical drought, as plants struggle to compete with ions in the soil solution, leading to wilting (osmotic effect) even when the soil is wet. Soluble salts in irrigation water can also burn leaf tissue (toxic effect) when applied to foliage. Increased salinity can corrode machinery, cause nutrient imbalances (especially Ca²⁺, ⁠, and K⁺), reduce chlorophyll, disrupt metabolic processes such as respiration and photosynthesis, delay germination, and stunt growth by affecting cell division and elongation (FAO & AWC 2023). Conversely, increasing soil salt levels to a threshold level improves soil aeration, root growth, and root penetration. Halophytes thrive in saline conditions and can enhance the quality of some crops, such as higher sugar content in carrots, higher soluble solids in tomatoes and melons, better grain quality in wheat, and improved freezing tolerance in citrus. However, most crop plants are glycophytes and cannot tolerate the stress caused by high salinity hazards (FAO & AWC 2023). Though the impact of salt stress depends not only on its intensity but also on the crop species, age, and other factors like drought, extreme temperatures, flooding, poor soil conditions, nutrient deficiencies, and pests or diseases (FAO & AWC 2023). Results show tobacco cultivation raises the salinity risk for nearby surface water, potentially stressing sensitive plants and causing moderate soil leaching. This may be due to rainwater runoff carrying extra minerals from tobacco fields (TFs) into nearby water bodies, along with seasonal variations, increasing EC_w and TDS values. In contrast, non-tobacco crops have no statistically significant impact on surface water salinity risk, as they use less chemical fertilizers and pesticides compared to tobacco farming (Roy et al. 2024b).

The high Ca²⁺ and Mg²⁺ levels, along with low Na⁺ concentrations, ensured excellent water quality with minimal sodium hazards during BCS for both TF and NTF waters. The average Ca²⁺ levels were 32 mg/L in Bangladeshi surface water, but 124 mg/L in Kushtia water (Islam & Mostafa 2022). Surprisingly, during ACS, sodium hazards decreased compared to BCS for both fields, with SAR, CROSS_Opt, SSP, KR, and SI values improving by 12.39, 0.18, 23.05, 28.01, and 46.91 for TF water, and by −7.39, 21.50%, 4.12, 6.20, and 27.95% for NTF water, respectively (Figure 3). The reduction in sodium hazards was due to a greater increase in Ca²⁺ (mg/L) levels (49.00 ± 7.24 to 70.67 ± 8.26 for TF and 59.83 ± 27.41 to 76.33 ± 22.99 for NTF) compared to Na⁺ (15.72 ± 1.25 to 16.68 ± 0.99 for TF and 17.99 ± 2.46 to 21.94 ± 6.94 for NTF) (Table 1). This rise in Ca²⁺ may result from gypsum fertilizer (CaSO₄.2H₂O, 23% Ca²⁺) leaching into nearby surface waters. However, statistical analysis revealed that the reduction in sodium hazards was significant for TF water (SAR = 2.59, SSP = 3.05, KR = 3.43, and SI = 5.32, all >t₀.₀₅ = 2.571). For NTF water, improvements were not significant (SAR = 0.72, CROSS_Opt = 2.14, SSP = 0.41, and KR = 0.53, all <t₀.₀₅), except for SI (3.72 > t₀.₀₅). Thus, it can be inferred that tobacco cultivation reduces the risk of sodium in the surrounding surface water for irrigation, while non-tobacco crops have no statistically significant effect.

Irrigation water pH within an acceptable range is generally not harmful to plant growth. However, extreme pH levels can cause nutrient imbalances, increase equipment corrosion, and enhance potential sodium hazards due to high concentrations of major anions such as ⁠, Cl⁻, and (Ayers & Westcot 1985; Roy et al. 2015). High pH of irrigation water can significantly affect crop production, cause salt precipitation, affect the efficiency of coagulation and flocculation processes, and reduce the effectiveness of pesticides (FAO & AWC 2023). The study revealed that the pH value of the area remained within the normal range (6.0–8.5) but was slightly alkaline (FAO 2023). It increased slightly from (7.67 ± 0.63) to (7.77 ± 0.34) in TF but decreased slightly from (7.81 ± 0.37) to (7.72 ± 0.43) in NTF (Table 1). Statistical analysis showed that this slight increase in pH for TF water and decrease for NTF water were not significant (0.76 for TF and 0.73 for NTF, all <t₀.₀₅), suggesting that cultivation of tobacco or non-tobacco crops does not significantly affect the pH of surrounding irrigation water.

The water's pH below 8.5 suggests a lack of carbonate ions (FAO 2023), so only RSBC, not residual sodium carbonate, was used to assess alkalinity hazards, with an ideal RSBC value of <1.15 mEq/L for irrigation suitability (El-Defan et al. 2016). Irrigation water with RSBC >2.5 mEq/L can clog soil pores with salts, restricting water and air movement (Sudhakar & Narsimha 2013). Alkaline water raises soil pH, causing ⁠, Ca²⁺, Mg²⁺, and Fe^2/3+ deficiencies and creating an imbalanced system by precipitating Ca²⁺ and Mg²⁺ that reduces salinity hazards but raises sodium hazards to levels higher than those indicated by the SAR (FAO & AWC 2023). Figure 3(f) shows RSBC values (mEq/L) during BCS as −0.83 for TF and −1.28 for NTF, which decreased to −1.62 (94.20%) for TF and −1.71 (33.26%) for NTF during ACS, i.e., all water samples were slightly alkaline for both fields during BCS and further improved after the harvest season. This was due to the higher increase of Ca²⁺ (44.22% for TF, 27.58% for NTF) compared to Na⁺ (6.11% for TF, 21.96% for NTF). This may be due to fertilizers, particularly urea, TSP, and DAP, runoff from fields during rainfall or irrigation, which may acidify soil, promote limestone dissolution, enhance algae growth, and contribute to organic matter decomposition, all of which increase bicarbonate levels in nearby surface water by altering pH and facilitating reactions with atmospheric CO₂. Statistical analysis revealed that the improvement in alkalinity was significant for TF water (2.70 > t_0.05) but not for NTF water (1.60 < t_0.05). Therefore, tobacco farming significantly improves water alkalinity, while non-tobacco crops have no significant effect on nearby surface water alkalinity.

Magnesium content is crucial for irrigation water suitability, as a high MAR >50% can increase soil alkalinity, degrade physical properties, and reduce crop yield (El-Defan et al. 2016; Islam et al. 2017; Wagh et al. 2018; Islam & Mostafa 2022). Figure 3(d) shows that during BCS, MAR (%) values in TF ranged from 16.72 to 36.84, averaging 24.76, and increased by 5.08% during ACS. In NTF during BCS, MAR values ranged from 18.38 to 32.70, averaging 26.02, but decreased by 14.31% during ACS. However, all MAR values remained within the ideal range (<50%), indicating suitability for irrigation. This slight fluctuation in MAR is likely due to natural processes, as no Mg-containing fertilizers were used in the fields. Statistical analysis shows that MAR fluctuations in both fields were insignificant (0.32 for TF and 1.09 for NTF, both <t_0.05). Therefore, it suggests that tobacco and non-tobacco cultivation have no significant impacts on magnesium hazards.

The PI evaluates irrigation water suitability, influenced by high Na⁺, Ca²⁺, Mg²⁺, and alkalinity levels. Excess Na⁺ causes soil de-flocculation, sealing pores, and reducing air and water flow, especially in clay-rich soils (FAO & AWC 2023). Figure 3(g) shows a decrease in PI values from 57.21 to 45.59% for TF and from 51.35 to 46.50% for NTF. According to the PI classification, all values fall within the ‘poor’ irrigation suitability range (30–75%). Wilcox's (1955) irrigation suitability diagrams showed water quality in both fields during BCS ranged from excellent to acceptable, with no classification changes during ACS (Figure 4(b)). This may be due to increased ion from fertilizer runoff such as urea, triple super phosphate (TSP), and di-ammonium phosphate (DAP), soil acidification, limestone dissolution, organic matter decomposition, and atmospheric CO₂. Statistical analysis showed a significant deterioration in PI for TF water (4.83 > t_0.05), but not for NTF water (2.37 < t_0.05). Therefore, tobacco farming likely has a significant negative impact on surface water permeability, while non-tobacco crops do not.

Dry residue index (RS) and osmotic potential (OP_π) are key indicators of irrigation water suitability, with higher RS and OP_π reflecting greater mineralization and less compatibility with irrigation. The higher the salinity of the soil solution, the greater the osmotic pressure, making it harder for roots to absorb water. For proper plant growth, RS should be <525 mg/L and OP_π < 0.27 atm (Bai et al. 2019; FAO & AWC 2023). Figure 3(h) shows that RS increased beyond the threshold (525 mg/L), from 399.82 to 570.62 for TF (42.72%) and from 602.82 to 638.05 for NTF (5.84%), making the water unsuitable for irrigation. Similarly, the OP_π (atm) values became unsuitable for irrigation (OP_π > 0.27) in ACS, rising from 0.21 to 0.29 for TF (38.10%) and from 0.31 to 0.33 for NTF (6.45%). This may be due to mineral runoff from farms, which raises EC and TDS levels in surface water during ACS. Statistical analysis of RS and OP_π reveals that tobacco cultivation has a significant negative impact on surface water around farms because RS (5.39) > t_0.05 and OP_π (5.32) > t_0.05. In contrast, non-tobacco crop cultivation has no significant effect, as RS (0.81) and OP_π (0.71) are both <t_0.05.

High ion concentrations, particularly Na⁺, can cause nutrient deficiencies (e.g., Ca²⁺, ⁠, and K⁺), leading to crop injuries and disorders like blossom-end rot in tomato, melon, and pepper, soft-nose in mango, and cracking in apple, ultimately reducing crop yield and quality (FAO & AWC 2023). Although K⁺ is an essential plant macro-nutrient, high concentrations of K⁺ in irrigation water can negatively affect soil permeability, physical properties, and plant nutrition, and can cause plant toxicity (Islam & Mostafa 2022). The concentration of K⁺ increased from 0.40 ± 0.63 to 0.62 ± 0.53 for TF (142.50%) and 0.97 ± 0.67 to 0.97 ± 0.57 for NTF (56.45%) (Table 1) but remained below the IWQ standard (2 mg/L, FAO 2023), likely due to runoff from muriate of potash (MOP, 50% K) and sulfate of potash (SOP, 28% K) fertilizers. However, statistical analysis shows that tobacco cultivation significantly impacts surface water around farms (t = 4.03 > t_0.05), while non-tobacco crops have no significant effect (t = 2.09 < t_0.05). Chloride (Cl⁻) is essential in low concentrations but can be toxic to crops like onion, bean, strawberry, avocado, and citrus at levels >140 mg/L (Roy et al. 2015; Islam et al. 2016, 2017; Elsayed et al. 2020), causing leaf burn and reducing uptake (FAO & AWC 2023). It does not affect the soil's physical properties, as the soil particles do not absorb it (FAO 2023). Sulfate is less harmful than chloride (Cl⁻) since only half contributes to salinity as Na₂SO₄ or MgSO₄, with the rest precipitating as CaSO₄ (El-Defan et al. 2016). However, high concentrations (>192 mg/L) can interfere with other nutrient uptake (Roy et al. 2015). Table 1 shows that and Cl⁻ levels in both BCS and ACS remain within the MPL of IWQ (FAO 2023) and SWQ standards (BEPR 2023). Statistical analysis revealed that non-tobacco crops had no significant effect on (1.70 < t_0.05) or Cl⁻ (1.20 < t_0.05), while tobacco cultivation significantly affected Cl⁻ (3.41 > t_0.05) but not (1.97 < t_0.05), likely due to increased EC in TF during ACS (El-Defan et al. 2016). Water suitability for irrigation can also be assessed by potential salinity (PS), calculated as (Cl⁻ + ½ mE/L). El-Defan et al. (2016) state that PS values of 3–7 mE/L are suitable for low permeability soils, while 3–15 mE/L values are appropriate for medium permeability soils. PS analysis shows the values increased (decreased suitably for irrigation) from 1.48 to 2.03 for TF (37.01%) and 2.14 to 2.73 for NTF (27.79%), but the change was statistically insignificant, as 2.27 (TF) and 2.09 (NTF) are both <t_0.05. Thus, the water of both fields remains suitable for irrigation on all types of soil.

Nutrient pollution, mainly from nitrogen (NO₃-N) and phosphorus (PO₄-P), stimulates excessive plant growth, weakens stalks resulting in severe lodging, delays maturity or poor quality, and causes eutrophication, oxygen depletion, and harmful algal blooms (FAO 2023). Table 1 shows that in BCS, NO₃-N and PO₄-P values were below the MPL standards of IWQ (FAO 2023) and SWQ (BEPR 2023). But ACS, NO₃-N (mg/L) increased from (4.39 ± 1.45) to (10.19 ± 2.80) for TF and from (3.14 ± 1.89) to (7.57 ± 4.99) for NTF; while PO₄-P (mg/L) increased from (0.89 ± 0.90) to (2.26 ± 0.85) for TF and from (0.72 ± 0.63) to (1.65 ± 0.56). Tobacco cultivation caused 1.31 times more NO₃-N and 1.47 times more PO₄-P pollution, exceeding MPL standards only in TF during ACS. FAO (2013) estimated surface water pollution from fertilizers using delivery coefficients of 0.75% for N and 0.34% for P. Tobacco cultivation (205 kg N, 134 kg P/ha) releases 1.54 kg N and 0.46 kg P per ha, while non-tobacco crops (rice, wheat, maize; 148 kg N, 74 kg P/ha) (Roy et al. 2024a) releases 1.12 kg N and 0.25 kg P per ha to surrounding surface water. Statistical analysis indicates that both tobacco and non-tobacco cultivation negatively affect surface water suitability for irrigation, increasing NO₃-N (4.81 for TF and 2.96 for NTF, >t_0.05) and PO₄-P (10.93 for TF and 5.54 for NTF, > t_0.05).

Many potentially toxic elements are usually present in low amounts in soil and water. While trace amounts of Fe, Mn, Zn, Cu, and Ni are beneficial to plants (FAO 2023), elements like As, Pb, Cd, and Cr are non-essential and highly toxic to plants, animals, and humans. These harmful metals can enter ecosystems through agrochemicals, particularly phosphate fertilizers and pesticides (Rodriguez-Eugenio et al. 2018). Cr poses less risk to humans due to its low solubility, strong soil retention, and low plant uptake. Pb is strongly adsorbed by soil colloids, and although absorbed by plant roots, its low translocation rate makes it relatively less harmful to higher organisms. In contrast, Cd and As are highly toxic due to their availability, mobility, photo-toxicity to plants like beans, beets, and turnips, and potential for bioaccumulation in edible plant parts (FAO 2023). Table 1 shows that the concentrations (mg/L) of nine analyzed HM increased in ACS compared to BCS. However, only Pb (0.119 ± 0.162), Cd (0.021 ± 0.009), and Ni (0.242 ± 0.111) in TF, and only Cd (0.015 ± 0.005) in NTF, exceeded the MPL for IWQ (FAO 2023) and SWQ (BEPR 2023). Sharma et al. (2025) reported a similar trend. Statistical analysis revealed significant increases in As (3.75), Pb (2.77), Cd (5.24), Cr (4.02), and Ni (3.34) in TF, and Zn (7.01), Cu (4.58), As (3.59), Cr (6.13), and Ni (9.24) in NTF, with values exceeding t₀.₀₅ at 5 df (2.571). This may result from surface runoff into nearby waters, driven by excessive HM-containing agrochemical application, including pesticides, DAP, TSP, and SOP fertilizers. Based on the exceeded MPL and t-test analysis, it can be inferred that tobacco cultivation significantly increases Pb, Cd, and Ni levels in the surrounding surface water, while non-tobacco crop cultivation has no significant impact on HM concentration.

Turbidity and TSS are key indicators of irrigation water quality, reflecting the presence of solid particles, organic matter, plankton, and potential pathogen vectors (FAO 2013). Turbidity (NTU) and TSS (mg/L) pollution increased significantly in both field waters. From Table 1, turbidity rose from 18.14 ± 13.25 to 69.12 ± 33.71 in TF (269%) and from 17.88 ± 18.72 to 57.89 ± 52.77 in NTF (224%). Similarly, TSS increased from 91.99 ± 13.31 to 121.83 ± 9.60 in TF (132.44%) and from 89.27 ± 17.14 to 114.17 ± 18.27 in NTF (27.89%). Both turbidity and TSS levels in ACS exceeded the MPL standard for IWQ (FAO 2023) and SWQ (BEPR 2023), likely due to algal blooms from nutrient and organic matter enrichment, along with fine plant particles (<200 μm) entering surface water via runoff. Statistical analysis shows that both tobacco and non-tobacco cultivation significantly and negatively impacted turbidity (TF: 3.14, NTF: 2.62 > t₀.₀₅) and TSS (TF: 4.68, NTF: 4.22 > t₀.₀₅) in surrounding surface water. COD levels (mg/L) exceeded the MPL (100 mg/L) for SWQ (BEPR 2023) across all samples: TF BCS (144.67 ± 29.00), TF ACS (218.33 ± 50.33), NTF BCS (146.67 ± 45.30), and NTF ACS (206.11 ± 66.00) (Table 1), attributed to increased organic matter and HM in surface water. Statistical analysis revealed that tobacco and non-tobacco cultivation have a significant negative effect on COD (TF: 7.01 and NTF: 5.79, both are >t₀.₀₅). According to FAO (2013), COD in irrigation water does not directly affect plants and soil. A report displayed that agriculture contributes 24–52% N, 22–90% P, and 28% COD pollution in the Chinese river basins (FAO 2023). DO in irrigation water is crucial for crop production (Wang et al. 2023). Low DO levels create oxygen stress, affect seed germination, reduce root biomass production, impair nutrient absorption, and inhibit plant growth (Wang et al. 2023). DO levels in farm surface water decreased significantly during ACS compared to BCS for both TF (4.43 ± 0.47 to 3.03 ± 0.52) and NTF (5.48 ± 0.90 to 3.95 ± 1.05), falling below the MPL for SWQ (BEPR 2023). This decline is likely due to algal blooms driven by nutrient and organic matter enrichment. Statistical analysis shows that tobacco (6.58 > t₀.₀₅) and non-tobacco crop cultivation (3.88 > t₀.₀₅) significantly negatively affect DO levels in nearby surface water.

Interestingly, WHI values declined drastically during ACS to 0.176 (very poor, grade-E) for TF (79.44%) and 0.368 (poor, grade-D) for NTF (44.32%), indicating significant water health degradation due to crop cultivation. However, the deterioration rate for TF was 2.32 times higher than NTF, as the erosion rates for most water parameters were greater in TF than in NTF (Table 1). Among MDS, caused the most degradation in TF, followed by Mg, Ni, Fe, K, Zn, and pH, while TH led degradation in NTF, followed by ⁠, Zn, temperature, and Mn (Figure 7(b)). Surface water in both fields was suitable for irrigation use and aquatic life during BCS but ACS became inconsistent, with tobacco cultivation contributing more significantly to water health deterioration than NTF.

HM contamination in surface water was assessed using the HPI and HEI for both TF and NTF, as these widely-used indexing techniques help identify and quantify pollution trends (Goher et al. 2014; Saleh et al. 2018; Islam & Mostafa 2024; Rai et al. 2024). The HPI values for both fields were similar, indicating good water quality during BCS. However, it deteriorated in ACS: 88.88 (suitable) to 170.89 (unsuitable) for TF (108.92%) and 85.80 (suitable for irrigation) to 120.05 (unsuitable for irrigation) for NTF (39.92%) (Table 4). During BCS, 16.67% of samples were excellent, 50% good, and 33.33% poor in both fields. However, during ACS, this changed to 16.67% good, 50% poor, and 33.33% very poor for TF water, while 33.33% were good and 66.67% poor for NTF. The order of HM contributing to HPI degradation for both waters was Cd > Pb/Cr > Ni > As > Cu > Mn > Zn > Fe. The HEI values were similar and less contaminated (A-grade) during BCS for both fields. However, during ACS, the HEI value increased by 86.30% for TF (from 3.74 to 6.97, low pollution) and 43.63% for NTF (from 3.85 to 5.53, low pollution). The order of heavy metals contributing to HEI degradation was Cd > Ni > Pb > Cr > Mn > Cu > Fe > As > Zn for TF, and Cd > Cr > Ni > Pb > Mn > Cu > Fe > As > Zn for NTF. Both HPI and HEI analyses showed that Mn, Cu, Fe, As, and Zn had minimal (<5%) impact on surface water quality. The main pollutants driving HPI and HEI degradation in both fields were Cd, Ni, Pb, and Cr, likely entering surface water through rainwater runoff from excessive use of chemical fertilizers like TSP, DAP, SOP, and HM-containing pesticides (FAO 2013). Sharma et al. (2025) previously identified heavy metals, such as Cd, Cr, Ni, and Pb, as the key factors influencing the WQI. This section infers that both tobacco and non-tobacco crop cultivation significantly impact HM pollution in the surrounding surface water, although the intensity remains minimal in both fields.

The IR tool assessed the ER of TF and NTF, showing low and similar risks during BCS (39.61 for TF, 40.85 for NTF). However, risks increased by 110.12 and 42.58% during ACS, reaching moderate levels for TF (83.24) and low levels for NTF (58.25), indicating tobacco cultivation poses 2.51 times higher potential environmental risk than NTF (Table 4). The decreasing order of parameters contributing to ER generation for both fields was Cd > Ni > Pb > As > Cr > Cu > Zn. However, the main contributors were Cd, Ni, and Pb, while As, Cr, Cu, and Zn had negligible impacts (<5%). These risks likely arise from the overuse of chemical fertilizers (TSP, DAP, and SOP) and HM-containing pesticides (FAO 2013). This section concludes that both tobacco and non-tobacco crop cultivation pose potential environmental risks in surrounding surface water, with a medium risk for TF and a low risk for NTF.

Balanced agrochemical use in TF and NTF, raising pond banks to prevent leaching, runoff, and irrigation return, as well as adopting good management practices can reduce risks when using pond water for irrigation purposes such as (i) selecting suitable crops for irrigation (e.g., amaranth and halophytes; with avoiding rice, wheat, vegetables, vines, and trees), (ii) using appropriate irrigation methods (avoiding sprinkler), (iii) timing of irrigation (e.g., avoiding vegetative and early reproductive stages but encouraging germination and flowering to harvesting stages), (iv) improving soil structure with lime and organic matter, and (v) supplementing Ca²⁺ deficiency with gypsum (FAO & AWC 2023). Since TF requires more fertilizers and pesticides than NTF (Roy et al. 2024b), its contribution to surface water pollution is higher.

This study offers valuable insights into the differing impacts of tobacco and non-tobacco crop farming on surrounding aquatic ecosystems. The results exposed that out of 27 assessed water quality parameters, turbidity, TSS, DO, COD, NO₃-N, PO₄-P, Pb, Cd, and Ni in TF water exceeded safe limits, especially during the ACS. Irrigation water suitability indices confirmed that TF improves sodium-related hazards (SAR, SSP, KR, and SI) and alkalinity (RSBC) hazards, while considerably worsening salinity (EC_w, TDS), PI, OP_π, RS, nutrient pollution, and miscellaneous hazards, with insignificant impact on water pH, MAR, CROSS_Opt, PS, and ⁠. Conversely, NTF showed minimal influence on most indices, except for SI, nutrient pollution (NO₃-N, PO₄-P), and miscellaneous hazards. TF released higher nitrogen (1.54 kg N/ha) and phosphorus (0.46 kg P/ha) into adjacent water bodies than NTF crops like rice, wheat, and maize (1.12 kg N and 0.25 kg P per ha). Diagrams (USSL, Wilcox, and Piper) demonstrated consistent water types (Ca–Mg–HCO₃) and permeability levels between BCS and ACS, indicating water type remained stable even as pollution increased. The WQI declined from good to very poor, while the WHI dropped from excellent to very poor for TF and from good to poor for NTF. Heavy metal indices (HPI and HEI) showed minimal pollution during BCS, but significant increases during ACS, by 108.92% for TF and 39.92% for NTF, while the IR followed a similar trend, rising 110.12% in TF and 42.58% in NTF, with Cd, Ni, and Pb as the main contributors. Excessive agrochemical use in tobacco farming accelerates the degradation of nearby aquatic systems, making irrigation water increasingly unsuitable and threatening long-term water sustainability. The findings emphasize the need for sustainable practices, such as balanced agrochemical use, improved field management, and conversion to less polluting crops, to mitigate water risks. These insights can support both farmers and policymakers in promoting environmentally sustainable agriculture. Future research should extend to evaluating the broader ecological impacts of these farming systems on aquatic biodiversity and ecosystem functioning.

The authors gratefully acknowledge the farmers of Bheramara and Daulatpur upazilas for allowing water sample collection from their fields, and thank the Department of Agricultural Extension (DAE), Kushtia, for their valuable information, support, and cooperation.

A.R. contributed in research design, sample collection and analysis, data analysis, table and graph creation, drafting the initial manuscript, and editing. M.G.M. assisted with research design, manuscript revisions and editing, cover page preparation, and final manuscript submission.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.