Water quality evaluation by WQI and ICOs for the rivers of Joya de los Sachas and Francisco de Orellana

Highlights

Introduction

Freshwater quality today is an important concern of the habitats, as they are exposed to pollution originating from natural and anthropogenic sources (Singh et al. 2020), including agricultural and industrial agents (Aristizabal-Tique et al. 2024), namely, agricultural runoff and untreated sewage (Kumar & Mishra 2024). Agriculture pollutes waters through the often-excessive application of fertilizers, composts, and pesticides, as well as by animal farming activities, incorrect irrigation practices, deforestation, and aquaculture (Anh et al. 2023). Among industrial discharges, one should primarily mention industrial waste. Also, one cannot neglect the increasing quantity of household garbage.

Natural causes may play an unwanted role, like biodegradation of plant and animal parts in clear water (Bhosale et al. 2023), and natural events, which trigger erosion processes, such as siltation arising from riverbank erosion (Wu et al. 2024). Therefore, aquatic ecosystems are exposed to threats. One should emphasize that these ecosystems are the most valuable and at the same time the most vulnerable habitats in the world (Ribeiro et al. 2021).

Humankind is confronted with the severe problem of scarcity of fresh water in rivers and lakes, which are exposed to pollutants produced by anthropic activities (Gleick & Cooley 2021). Water quality relates to different uses therefore, it is important to collect quantitative information on the concentrations of organic, inorganic (Teunen et al. 2021), radiological (Asaduzzaman et al. 2022), and microbiological parameters of water (Anggun et al. 2024).

Based on the above theoretical assessment, the authors have identified several factors that affect inadequate water management in Ecuador. Among them, one should mention the scarcity of biophysical information, the absence of planning in agro-productive and industrial activities, the shortage of rural development agencies, and the sectionally organized governments.

According to data from the National Institute of Statistics and Censuses (INEC) of Ecuador in 2020 a total of 5.2 million hectares were allocated to agricultural activities in the country. Such a large agricultural area demands an extensive use of agrochemicals. Because of bad practices, one uses an excessive quantity of pesticides. The latter constitutes a major pollutant; pesticides spread because of runoff and erosion severely affecting water quality. Beyond doubt, this endangers the cleanliness of surface water, human health, and the environment. The agricultural activities in the Joya de los Sachas area have intensified considerably over the years 2008-2015 owing to the drop in oil prices and the utilization of large native forest areas. Another identified problem is hydrocarbon activity, like in Block 60 where oil spills occurred. 58% of the oil spills happened in the parishes of San Carlos, and 42% in the parish Unión Milagreña, where four private companies and one public company function. These are environmental management companies, which handle hazardous wastes of the oil industry. Therefore, rivers are highly polluted.

As reported in previous studies, several toxic metals are present in the Basura, including Cu, Cd, Ni, and Pb; Estero INIAP contains Cu, Ni, Pb, and TPH; Yanayacu has Cu, Ni, and Pb; Blanco identified the presence of TPH, while copper (Cu) was found in Sacha also known as the Quinchayacu River. There are significant problems of water pollution in the parishes Unión Milagreña with 66.2%, San Sebastián del Coca with 56.5%, and Enokanqui with 47.6% of the total available water (Rocha-Gutiérrez et al. 2015; Lorenzo et al. 2016).

The main reason for establishing a monitoring program is to check the physical, chemical, and biological parameters of rivers in the project area, and to rate, whether they represent a climate-smart production system. Also, one aims to determine synergies between mitigation, adaptation, and food security measures implemented since 2017 by the Causana Yachay Group. To establish such synergies, one should document that they meet requirements for agricultural use, conservation of aquatic life, and recreation (Asaduzzaman et al. 2022).

To assess water quality, representative indicators should be considered, which enable a comprehensive analysis of the state of rivers (Torres et al. 2010). A widely used tool is the ICA water quality index (WQI) which identifies the quality trends by considering physicochemical, biological, and non-aquatic aspects. One evaluated the quality of river waters via mathematical models that revealed the approximate quality parameters at points where the water was monitored from October 2019 to February 2020. Models were used to simulate the dynamics of pollutants and compare different rivers. In addition, the natural variables of aquatic ecosystems (Gleick & Cooley 2021, Torres et al. 2010, Morin-Crini et al. 2022) were tracked over time.

Methods

Calculation and analysis of WQI, ICAUCA, ICOMO, ICOSUS, ICOPH, and ICOMI quality indices

The WQI measure was used to evaluate water quality. First, the parameters were selected and then a mathematical equation was developed (see Eq. 1). The WQI value varied from 0 to 10, where “0” represented the lowest quality and “10” the highest. Value ranges were assigned to the obtained WQIs (Miranda et al. 2016). Hence, WQI of 9.0-10.0 means excellent water quality, 7.0-9.0 represents good water quality, the 5.0-7.0 range corresponds to regularly contaminated waters, 2.5-5.0 is highly contaminated water, while 0.0-2.5 relates to an oversaturation of contaminants when the water resource is practically dead (see Table 1). All experimental data and the related calculations are available in the Dryad repository (Lowy 2024).

Figure 1. Sacha River, Basura River, Areas A and B; monitoring points (purple, blue, and green flags).

Source: The authors’ ellaboration based on Google Maps.

Table 1. WQI values for river water classification.

Characteristics	WQI value	Assessment
River water resource in its natural state	9.0-10.0	Excellent water quality
Mildly contaminated river water	7.0 – 9.0	Water of good quality
Regularly contaminated water resource	5.0 – 7.0	Regularly contaminated – reasonable quality
Contaminated water resource	2.5 – 5.0	Highly contaminated – water of poor quality
Dead river water resource	0.0 – 2.5	River water oversaturated with contaminants

Therefore, the selected parameters are grouped according to the organic load (BOD₅)_, recovery effect (expressed as dissolved oxygen, DO), fecal coliforms (FC), and aesthetic aspects (ST, turbidity) as dependent variables, while nutrients NO₃^- and PO₄^3- are considered independent variables (Koch et al. 2023). The WQI factor weights are based on the importance of each parameter for human health, the environment, and the organoleptic properties of the water. For the variables in Eq. 2, the weighting factors commonly used for comparison are the following: a = 1, b = 1.7, c = 1.5, d = 1.6, e = 1, f = 1, g = 1.2, and h = 1.

(1)

$$\mathrm{IQA}=\mathrm{a}\left({\mathrm{DBO}}_5\right)+\mathrm{b}\left(\mathrm{OD}\right)+\mathrm{c}\left(\mathrm{CF}\right)+\mathrm{d}(\mathrm{ST}\bullet \text{Turbidity})+\mathrm{e}\left({\mathrm{NO}}_3^{-}\right)+\mathrm{f}\left({\mathrm{PO}}_4^{3-}\right)+\mathrm{g}\left(\mathrm{pH}\right)+\mathrm{h}\left({\mathrm{T}}^0\right)$$

(2)

$$\mathrm{a}+\mathrm{b}+\mathrm{c}+\mathrm{d}+\mathrm{e}+\mathrm{f}+\mathrm{g}+\mathrm{h}=10$$

To calculate the pollution rate based on the performed monitoring, six pollution indices (ICOs) shall be used: the mineralization pollution index (ICOMI), which in its turn considers 3 parameters (conductivity, hardness, and alkalinity), the organic matter contamination index (ICOMO), BOD_5, total coliforms, percent of dissolved oxygen in water (%DO), suspended solids contamination (ICOSUS), total phosphorus contamination (ICOTRO), and the pH pollution index (ICOpH). The latter parameter is based on the pH and the temperature pollution index (ICOTEMP), i.e., the temperature of the receiving body and the pouring (Lorenzo et al. 2016, Gil-Marín et al. 2018). Also used is the ICAUCA index, a water quality index adapted from the WQI NSF, Dinius, CETESB, and ICOSUS indices (Torres et al. 2010). ICAUCA considers the chemical, physical, and microbiological parameters, including %DO, Fecal coliforms, Turbidity, BOD₅, Total solids, pH, Total phosphorus, and Total nitrogen for the weighting of each parameter of ICAUCA. The weightings of all these parameters are listed in Table 2, developed for tropical rivers.

Table 2. The weighting of ICAUCA parameters.

Parameters	Weighting (Wi), %
Percent of dissolved oxygen (DO)	21
Fecal coliforms (FC)	16
Biochemical oxygen demand after 5 days (DBO5)	15
Turbidity of water	7
Total solids content	7
pH of river water	8
Total phosphorus content	8
Total Nitrogen content	8
Suspended solids in water	5
Color of river water	5

The obtained values were compared with those listed in Table 3, the latter corresponding to the water quality classification according to the ICAUCA value. Several equations shall be used for the calculation of pollution indices: ICOMI, which represents the average value of the three chosen variables, all being defined in the range from 0 to 1, where zero “0” indicates very-low contamination, while values close to the unity “1” correspond to very high contamination (see Eq. 3).

Table 3. Water quality classification by ICAUCA value.

ICAUCA value	Overall rating of river water quality
0-20	Poor quality water
20-35	Inadequate quality water
35-50	Acceptable quality water
50-80	Good quality water
80–100	Optimal quality water

When the conductivity values are greater than 210 μS cm⁻¹, the conductivity index takes the value I_COND = 1; for hardness values that exceed 110 ppm, the hardness index will be I_HARD = 1. For a hardness less than 30 ppm, the hardness index is I_HARD = 0. When the alkalinity is equal to or greater than 250 ppm, the alkalinity index value becomes I_ALK = 1, and for lower alkalinity, one has I_ALK = 0 (Asaduzzaman et al. 2022, Trikoilidou et al. 2017).

For Equation 4 to calculate ICOMO, the values greater than BOD of 30 g m⁻³ correspond to a biochemical oxygen demand index I_BOD = 1; if BOD is less than 2 g m⁻³, I_BOD = 0.

When the total coliforms are greater than 20,000 NMP.100 cm⁻³ the I_{TOT COL} = 1, while in case the total coliforms are less than 500 NMP.100 cm⁻³, I_{TOT COL} = 0. If the percent of oxygen is greater than 100%, then I_O% = 0. Therefore, in chaotic systems, percent-saturations greater than 100% indicate re-aeration of water resources; in lentic systems, this reflects the eutrophication problem (Gil-Marín et al. 2018).

The ICOSUS calculation was performed according to Eq. 5. One considers that suspended solids greater than 340 g m⁻³ correspond to ICOSUS = 1, while suspended solids less than 10 g m⁻³ are assigned an ICOSUS = 0.

For the ICOTRO calculations, values between 0 and 1 are determined, where the total phosphorus concentration defines the oligotrophic <0.01 g m⁻³, mesotrophic 0.01–0.02 g m⁻³, eutrophic 0.02–1 g m⁻³, and hypereutrophic >1 g m⁻³ waters.

(3)

$$\text{ICOMI}=\frac{1}{3}({\mathrm{I}}_{\text{COND}}+{\mathrm{I}}_{\text{HARD}}+{\mathrm{I}}_{\mathrm{ALK}})$$

where: I_COND is the conductivity index, I_HARD – is the hardness index, and I_ALK – is the alkalinity index.

(4)

$$\text{ICOMI}=\frac{1}{3}({\mathrm{I}}_{\mathrm{BOD}}+{\mathrm{I}}_{\mathrm{TOT}\mathrm{COL}}+{\mathrm{I}}_{\%\mathrm{O}})$$

where: I_BOD is the biochemical oxygen demand index, I_{TOT COL} – total coliforms index, and I_%O – the percent oxygen index.

ICOpH calculations were performed based on Eq. 6, where contamination values of 0 and 1 are assigned to the low and high limits of the pH scale (Mokhtar et al. 2021). When Eq. 7 was used for the calculation of ICOTEMP, at a temperature difference (ΔT) less than 2.5 °C, the ICOTEMP value was 0, and when ΔT was greater than 15.0 °C the assigned ICOTEMP value was equal to the unity.

(5)

$$\text{ICOSUS}=-0.02+0.003\bullet (\text{suspended solids},\mathrm{g}{\mathrm{m}}^{-3})$$

(6)

$$\text{ICOpH}=\frac{{\mathrm{e}}^{-31.08}+3.45\bullet \mathrm{pH}}{1+{\mathrm{e}}^{-31.08+3.45\bullet \mathrm{pH}}}$$

(7)

$$\text{ICOTEMP}=-0.49+1.27\bullet log({\mathrm{T}}_{\mathrm{DCH}}^0+{\mathrm{T}}_{\mathrm{RB}}^0)$$

where: ${\mathrm{T}}_{\mathrm{DCH}}^0$ is the temperature of discharge and ${\mathrm{T}}_{\mathrm{RB}}^0$ – the temperature of the receiving body.

Results and Discussion

In total 16 parameters were monitored to calculate contamination rates for the analyzed samples. These parameters were ICOMO, ICOSUS, ICOPH, ICOTRO, and ICOMI, the latter being derived from values of conductivity, hardness, and alkalinity (see Table 4).

The Sacha, Basura, Coca, Huamayacu, Jivino Rojo, Jivino Negro, and Blanco Chico rivers presented low ICOMI values, except for the Jivino Negro River, which has a greater value (this parameter is related to hardness). The ICOMO pollution rate with values as high as 0.292 can be explained by correlating the rate of trophic contamination with the rate of contamination by organic matter already present in the river. A phenomenon of eutrophication originating from the high phosphorus content was revealed. The analysis concluded that because of this phenomenon, the amount of organic matter in the water increased the biological demand for oxygen, generating an oxygen shortage in the environment. Therefore, the excess nutrients and organic matter deteriorate water quality, as revealed in Figure 2a; Figure 2b shows the quantification of phosphorus in the water samples. Figure 2c documents how fecal coliforms were analyzed, while Figure 2d is a picture taken during NO₃^- and PO₄^3- measurements.

Figure 2. Composite picture with 4 connected panels – a, b, c, and d.

a. Jivino Negro River eutrophic quality, b. Total P determination in the laboratory, c. Determination of fecal coliforms, d. Determination of NO₃^- and PO₄^3-.

The ICOpH values, on the 0-1 to 1-0 scale (Quality-Pollution), were determined for the Sacha, Coca, Basura, Huamayacu, Jivino Rojo, Jivino Negro, and Blanco Chico rivers. On the scale established for this parameter (Ramos-Pacheco et al. 2023) they all present low ICOpH values, which reveals that the water quality of these rivers is not altered. This means that no corrosion problems are expected in the pipes. Nonetheless, pH adjustment is needed because of the coagulant used in the flocculation-coagulation stage. Doing so will enable efficient water purification. The ICOSUS parameter, which indicates the suspended solid contamination rates of the Sacha, Coca, Basura, Huamayacu, Red Jivino, Black Jivino, and Blanco Chico rivers arise from a low half-basin, as displayed in Figure 3a. The phosphorus concentration in water affects the Hash Pollution Index (ICOTRO) shown in Figure 3b.

Figure 3. a. The ICOSUS Index; b. The ICOTRO Index.

Therefore, the Sacha, Red Jivino, Black Jivino, Coca, and Basura rivers are of eutrophic quality, a phenomenon caused by an excessive concentration of dissolved or suspended nutrients in the water. Plants and organisms are abundant; upon dying they deplete the water quality. By contrast, mesotrophic quality presents a certain abundance of nitrogen and phosphorus. Nevertheless, Huamayacu and Blanco Chico rivers remain of desirable quality.

Wastewater discharges, solid waste, and uncontrolled spills of hydrocarbons are likely responsible for pollution. From the comparison of ICOs pollution rates, one assigns the Sacha River the value of 0.292, the highest relative to the other rivers investigated in this study; it corresponds to an elevated degree of pollution. Increased BOD values reveal the presence of a large load of organic pollutants, which can originate from household, agricultural, industrial, or soil erosion waste. Likewise, the Sacha River has an ICOSUS value of 0.16, the highest of the rivers examined here. It causes problems when it enters through the pipes of the water purification system; fortunately, it does not pose any health issues, not affecting the daily activities of people.

The water quality of the Sacha, Basura, and Coca Rivers, characterized by the water quality index, WQI, assesses high contamination, the Huamayacu, Jivino Rojo, Jivino Negro, and Blanco Chico rivers being regularly contaminated (Koch et al. 2023). The identified problems are related to the hydrocarbon activity of Block 60, where several oil spills happened. Examples include accidental oil spills, which occurred in the parishes of San Carlos and Unión Milagreña (reported above). In these places 4 private companies and one public company operate, all being environmental managers, which handle the hazardous waste in the oil industry (Table 5).

The results reported in this paper document water quality when remarkable anthropic activity and a strong incidence of contamination are present. The observed chemical, microbiological, and physical parameters show local variations at certain points in the aquatic systems. Wastewater discharges, solid waste, and uncontrolled spills of hydrocarbons (oils) are likely responsible for the contamination of these rivers. The comparison of ICOs pollution rates reveals that Sacha River has an ICO = 0.292, which is the highest of the investigated rivers. This value corresponds to an advanced degree of pollution since increased values of BOD indicate a strong load of organic pollutants. Likewise, the Sacha River has an ICOSUS value of 0.16, the most elevated of all the examined rivers. Nonetheless, it does not pose problems in water treatment, and it does not affect the health or the daily activities of people who get in touch with the water.

The pollution problem of the Sacha, Basura, and Coca rivers is severe and constitutes a concern, as according to our WQI results, these rivers are significantly contaminated. The pollution was mainly caused by the hydrocarbons-related activity in Block 60, where oil spills were reported. It is alarming that most oil spills occurred in the San Carlos parish and in the Unión Milagreña parish. This demonstrates that the environmental management of companies in this area is not effective, therefore, these companies cause severe damage to the water quality of nearby rivers. In April 2000, shortly after the timeframe of the water quality monitoring reported in this paper, a major oil spill occurred in the Ecuadorian Amazon, which severely polluted the Coca River. It affected the area over the entire year, posing serious health problems to the indigenous Kichwa (Flores & Josefsen Hermann 2020). This harsh event demands for urgent measures taken by the authorities in charge to control and prevent pollution in this area. Oil companies must comply with environmental standards and be held accountable for the harm caused to the ecosystem. Furthermore, it is essential to strengthen surveillance and to monitor oil-related activities to prevent new spills and environmental damage. It is also important to involve and motivate the community in protecting the rivers and to encourage local people to report polluting activities. The health of people and the ecosystem depends largely on water quality, so it is vital to reverse environmental decay, and to act for securing a beneficial and safe environment. As revealed by WQI values, the investigated Ecuadorian rivers are polluted. Basura River contains Cu, Cd, Ni, and Pb; Estero INIAP has Cu, Ni, Pb, and TPH; pollutants of Yanayacu River are Cu, Ni, and Pb; Blanco contains TPH, while Sacha or Quinchaya has toxic Cu. The water in the parishes is also contaminated: Unión Milagreña parish with 66.2%, San Sebastián del Coca with 56.5% and Enokanqui with 47.6% of the total water available in natural surface water sources (Rocha-Gutiérrez et al. 2015; Lorenzo et al. 2016).

Conclusions

Sampling and 4-point analysis were carried out on the experimental farms. Seven points in specific settlements, 5 points in the Sacha River, and 5 points in the Basura River, which correspond to the sampling points, identified with the names of the owners and belonged to the Sacha, Huamayacu, Jivino Rojo, Jivino Negro, Coca, and Garbage rivers. From October 2019 to February 2020, 6 rivers in the Joya de los Sacha Canton and 1 river in the Francisco de Orellana Canton were examined.

The ICO pollution rate of Sacha River was found 0.292. This is the highest value among the investigated rivers, and corresponds to a significant degree of pollution, since increased BOD indicates a strong load of organic pollutants originating from household, agricultural, industrial, and soil erosion waste. Likewise, the Sacha River has an ICOSUS value of 0.16, the most elevated of the examined rivers. This poses corrosion problems, when water enters the pipes for water treatment, as the moving solid particles act as abrasives, wearing down the metal surface of the pipes, weakening the pipe wall, and making it more susceptible to chemical corrosion. Fortunately, it does not pose health problem and does not affect the daily activities of people, who get in contact with the water.

The pollution index study represents an easy-to-understand quantitative assessment, which conveys important information of water quality and pollution. An advantage of this method is that it integrates and correlates essential parameters via straightforward equations. Among the considered parameters one finds water hardness, total coliforms, and the total amount of phosphorus present in water. After completing the calculations, one can effortlessly interpret the process, since the values from 0 to 1 provide a good estimate of the other indices.

The water quality was described quantitatively by the water quality index (WQI) and yielded the following classification: (i) the Sacha, Basura and Coca rivers are highly contaminated, while (ii) the Huamayacu, Jivino Rojo, Jivino Negro, and Blanco Chico are regularly contaminated. Importantly, the authors seek to provide incentive, support, and continuity to similar studies, since they provide useful data to improve the general environmental conditions of the province of Orellana. These findings can also promote and generate new legislation that would serve to regulate all company activities in the area. Results reported here also recommend good practices for farmers, who dispense bodies of water. Such streams can yield minimum amounts allowed for the content of potentially harmful substances over the dumping and, in general, can stimulate the dissemination of the results obtained in such studies.

Ethics statement of the authors

The research reported in this manuscript did not involve human participants and no animals were used.

Our manuscript adheres to the reporting standards: the submitted manuscript is accurate and objective. The authors have written an entirely original research article, and the work and/or words of others have been appropriately cited or quoted. No permissions were needed. Proper acknowledgment of the work of others was given, all information contained in the manuscript is cited properly. No privately obtained information was used or reported. No forms of plagiarism are present in the submitted manuscript. No information obtained in the course of confidential services was used. Neither this paper, nor its topic have been submitted for consideration in another journal. Authorship is limited to exclusively the four named authors who have contributed to the conception, design, execution, or interpretation of the reported study. No other experts have contributed to the article.

Comprehensive data availability statement: all data collected and processed in this paper are available in the following repository.