Assessing the Impacts of Land Use on Water Quality in the Acacias River Basin, Colombia

Abstract

Surface water resources have played a fundamental role in the development of human societies. Considering that different agricultural and industrial activities are carried out in the Acacias River basin, the main objective of this research was to analyze the influence of land use on the water quality in this area by identifying the main sources that influence river water quality. The methodology consisted of establishing 12 sampling stations with different land uses at three times. The National Sanitation Foundation-Water Quality Index (NSF-WQI) was applied to the obtained water quality evaluation data. The main results showed that the stations associated with urban centers presented a higher concentration in the following variables: fecal coliforms, biochemical oxygen demand (BOD) and phosphates. The principal components analysis revealed a close relation between the parameters of fecal coliforms, phosphates and BOD, and the pollution processes by organic matter, which are probably related to domestic and industrial wastewater discharges, and to detergents in urbanized areas. The parameters with the greatest range of values were total dissolved solids and turbidity. These results coincide with what was observed in the correlation analysis. Finally, nitrates showed higher concentrations at stations 6 and 7, associated with agricultural and industrial influence areas (i.e., oil palm crops in the basin). This study about the Acacias River is, thus, extremely important for the region, and concludes that the river’s self-purifying capacity allows improved water quality in the areas where the predominant land use is not associated with human settlements.

1. Introduction

Globally speaking, there is currently awareness that the deterioration of surface water quality is a considerable issue in river basin management [1,2]. Water resources are essential for human survival [3]. Therefore, the water quality/land use interaction is extremely important because agriculture has been proven to exert pressure on the quality of both groundwater and surface water [4]. In fact, human activities have greatly affected the physico-chemical properties of water quality and the stability of aquatic ecosystems on regional scales, and even on global scales [5]. Processes like the loss of nutrients (nitrogen and phosphorous) intervene through leaching and erosion. This has been especially visible in Europe and North America since the 1950s, and more recently in many other parts of the world [5,6,7,8]. Damo et al. [9] and Selemani et al. [10] stated that water chemistry and, therefore, water quality are governed mainly by natural and human factors. In general, according to Ngoye et al. [11], land-use activities such as industrialization, agriculture and urbanization in river catchments determine not only the amount but also the quality of runoff from rainfall. As a result, the water quality in a river is related to changes in land-use activities, which are aggravated by population pressure [12].

The correlation between water quality and land-use types is evident. Specifically, there is a positive association between cropland and urban areas with pollutants in streams. Furthermore, woodland and grassland are influenced less by human activities and display negative correlations [13,14,15,16]. Similarly, Song et al. [17] investigated land-use effects on water quality across multiple spatial scales in Hangzhou City, China. They detected that the total nitrogen (TN) and total phosphorus (TP) concentrations were closely related to land use. In general terms, industrial, mining and arable land types have relatively high pollution risks compared to other land-use types; in contrast, forests and wetlands are sinks of potential pollutants in water bodies, while riparian vegetation buffer zones usually have a filtering and barrier effect on pollutants [17,18,19].

In particular, surface water sources have played a fundamental role throughout history in the development of human societies, and in such a way that water bodies not only provide the necessary supply for domestic, agricultural and industrial uses, but also play a crucial role in wastewater disposal [20,21]. The complex land use/water quality interaction in hydrographic basins has aroused the scientific community’s interest [14,22], and land use, the expansion of urban areas, population growth and agricultural and industrial activities are the main causes of the changes observed in these basins’ water quality [11,12,13,14,15,16,17,18,19,20,21,22,23]. Likewise, riparian vegetation fragmentation, agricultural expansion, and a lack of territorial planning and control, can reduce water resources quality [24]. Agricultural lands provide nutrients like P and N due to current production practices [25,26]. Meanwhile, urban areas contribute to increased organic loads and also bacteria, such as Escherichia coli and Enterococcus sp. [27,28,29]. In contrast, industrial areas are associated with pollutants, including inorganic compounds like fats, oils and hydrocarbons [30].

The evaluation of the state of aquatic ecosystems incorporates water quality indices (WQIs) as monitoring strategies. These indices, based on physico-chemical and microbiological parameters, allow the evaluation of water characteristics in relation to various uses to facilitate the identification of the degree of impact and the application of mitigation strategies [31,32]. The Acacias River basin plays an important role in the industry, agriculture and forestry of Meta department (Colombia) because intense anthropogenic activities, such as agricultural production, industrial activities and urbanization, have affected this river’s water quality for a long time [20]. Indeed, river water is used for not only irrigation and domestic purposes, but is also used heavily in industry. Therefore, water quality maintenance is essential. In this context, the Acacias River is one of the main tributaries of the upper basin of the Meta River and supplies 136,978 inhabitants in four municipalities on the piedmont. Various productive activities are carried out there that form a mosaic of land uses, including grasslands, oil palm crops, rice production and smaller-scale agriculture, as well as urban centers, industrial activities, tourism and natural spaces [20]. However, it is especially important to note that there is a lack of comprehensive scientific understanding on the state of the rivers and how they respond to land use influences in the Piedmont region of Colombia.

The Acacias River basin plays an important role in urbanization, industry, agriculture and forestry. Based on the hypothesis that spatial variability in water and soil quality should occur due to the type and physico-chemical properties of soils, and taking into account their interactions, this work aimed to analyze the influence of various land-use types on the water quality in the Acacias River basin based on water quality monitoring. This study enhances our understanding of the physicochemical characteristics of rivers across various land uses. It also highlights the limited financial resources available in Colombia to advance scientific research. The present study aims to analyze the relation between land use and water quality in the Acacias River to provide technical tools for the future implementation of a river basin management plan to guide decisions toward sustainable water resource management. Specifically, the main objectives of this study are as follows: (1) to assess the physico-chemical properties of river water; (2) to analyze the spatial and temporal distribution characteristics of the surface water quality in each ecoregion; and (3) to analyze the relations between the different land-use and water quality parameters.

2. Materials and Methods

2.1. Study Area and Sampling Sites

The Acacias River is located in the central-eastern part of Colombia, and ranges from its highest point at 1800 m above sea level (m.a.s.l.). at coordinates 03°58′26.2″ N–073°52′08.1″ W to its lowest point at 200 m.a.s.l. at coordinates 03°52′53.7″ N–073°06′43.7″ W. It is 119.61 km long with a total basin area of 497.87 km². The annual precipitation in this area fluctuates between 2500 mm/year (station 12) and 6000 mm/year (station 1). In the upper basin zone, the flow ranges between 6171.6 and 817.7 L/s, and between 14,191.3 and 2317.6 L/s in its middle zone. The basin is characterized by agricultural, livestock, fishing and industrial activities related to the hydrocarbon sector. These particularities configure a pertinent context in which to analyze the relation between land use and water quality in the Acacias River (Figure 1).

2.2. Land Use on The Basin Scale

There are five land-use types found in the Acacias River basin, which is located at the basin level: agricultural production accounts for 84.8% of the total land area; pastures cover 47,734 hectares and are employed by animals; oil palm cultivation takes up 27,326 hectares; rice cultivation occupies up to 3213 hectares; and other transitional crops are grown on up to 752 hectares. According to these numbers, agriculture is the most important economic activity; 11.5% of the land area comprises natural and seminatural areas, which is equivalent to 10,748 hectares. These regions include natural forests, gallery forests, and secondary or intervened vegetative plants. In all, 1528 hectares of urbanized areas, 68 hectares of industrial zones and 384 hectares of hydrocarbon exploitation sites make up the artificial territories, which account for 2.1% of the total land surface. Finally, the total basin area is covered by water bodies, which include rivers that account for 1169 hectares and wetland areas that account for 175 hectares.

2.3. Water Sampling and Analytical Methods

Twelve sampling stations with different land uses were established (

Table 1. Location and land use of the stations on the Acacias River, Colombia.

Station	Altitude (m.a.s.l.)	Geographical Coordinates		Land Uses
1	744	3°57′35.0″ N	73°49′10.4″ W	Low intervention area
2	523	3°58′15.8″ N	73°46′13.4″ W	Low intervention area
3	496	3°58′47.3″ N	73°44′52.1″ W	Urban area
4	491	3°58′53.1″ N	73°44′38.6″ W	Urban area
5	421	3°57′22.3″ N	73°40′5.7″ W	Agricultural and industrial area
6	412	3°57′16.7″ N	73°39′46.8″ W	Agricultural and industrial area
7	259	3°52′06.4″ N	73°23′25.2″ W	Agricultural areas
8	257	3°51′59.6″ N	73°23′15.0″ W	Agricultural areas
9	245	3°51′52.6″ N	73°18′58.4″ W	Agricultural areas
10	239	3°51′45.8″ N	73°18′40.4″ W	Urban area
11	214	3°52′25.1″ N	73°14′10.6″ W	Agricultural areas
12	200	3°53′12.8″ N	73°06′50.0″ W	Low intervention area

) along the 119.61 km length of the Acacias River. Samples were collected 3 times based on the variable precipitation regime (Figure 2). For water quality monitoring purposes, a rigorous approach was taken. Samples were meticulously collected, and the analysis was carried out in a laboratory. The water sampling process was meticulously followed and involved careful collection. Refined plastic bottles were used for this purpose. Samples were diligently preserved at temperatures below 4 °C until the analytical processes were conducted following standardized procedures.

During water sampling, standard methods were used: the dissolved oxygen (DO) and pH of the water samples were measured in situ using a multiparametric monitoring instrument for water quality (HQ40d, HACH, Loveland, CO, USA). Water samples were then transported to the laboratory and kept at 4 °C for further analyses.

The Acacias River water quality was evaluated by analyzing the physico-chemical parameters to describe the reasons for possible contamination, and then comparing it to international standards, such as the World Health Organization [33].

The physico-chemical parameters were applied following the international reference methods described in the “SM” Standard Methods for the Examination of Water and Wastewater, 23rd edition (2017) by APHA-AWWA-WEF: Dissolved Oxygen (DO, mg L⁻¹), pH (units pH), temperature (°C), biochemical oxygen demand (BOD5, mg L⁻¹), phosphates (PO₄³⁻ mg L⁻¹), total solids (mg L⁻¹), turbidity (NTU) and nitrates (NO₃⁻ mg L⁻¹), and the microbiological ones, such as Fecal Coliforms (MPN 100 m L⁻¹). Quality control assurance was carried out with certified reference reagents (Merck) and triplicates of samples in the laboratory.

2.4. Statistical Analysis

Descriptive statistics were carried out, including the mean, standard deviation, minimum and maximum ranges, and the coefficient of variation. The Kruskal-Wallis test was calculated for the comparison of medians and the Spearman correlation coefficient was applied to verify the association between variables. To graphically represent the association between the evaluated stations and the physico-chemical variables, a principal component analysis (PCA) was performed [34]. The IBM SPSS Statistics version 25 software was used for all analyses [35].

2.5. Water Quality Index

Water quality evaluation methods included physical and chemical indicators. Today biological indicators have gradually increased with a more comprehensive and scientific index system. T rationally quantify the comprehensive state of water quality, a large number of mathematical methods have been successfully applied to water quality evaluations. [3]. These methods have their own characteristics and have solved the comprehensive water quality problem to a certain extent. The WQI of the National Sanitation Foundation (NSF-WQI), proposed by Brown [36], was applied in this study. It is composed of the weighted sum of the subindices of variables: percentage of DO saturation, fecal coliforms, pH, BOD5, temperature (°C), phosphates, nitrates, turbidity and total solids (TS). The general Equation (1) for calculating the index is:

$$NSFWQI=\sum _{i=1}^n{SI}_i{W}_i$$

(1)

• NSF-WQI = National Sanitation Foundation-Water Quality Index
• SI_i = (i) Subscript of each parameter
• W_i = (i) Weighting factor for each subscript

The NSF-WQI aquatic quality ranges are defined in

Table 2. NSF-WQI Water Quality ranges [35,36].

Description	Range	Color
Excellent	91–100
Good	71–90
Medium	51–70
Bad	26–50
Very Bad	0–25

.

3. Results and Discussion

3.1. Water Quality Evaluation

The water quality analysis results of the sampling points are presented in Table 2, including the statistical analysis of the water quality parameters of the 12 river sections. Variations in physico-chemical, and microbiological properties were observed along the Acacias River, as shown in the box plots (Figure 3).

The results showed that the river water physico-chemical parameters varied as follows: fecal coliforms had the widest amplitude, with concentrations that ranged from 2.7 × 10¹ to 2.4 × 10⁶ MPN 100 mL⁻¹. Turbidity had values ranging from 6.17 to 302.00 NTU. BOD₅ exhibited considerable variation, ranging from 0.85 to 13.70 mg O₂ L⁻¹. Phosphates presented moderate variation, ranging from 0.04 to 1.43 mg PO₄^3−· L⁻¹. The total dissolved solids showed variation, ranging from 31.0 to 354.0 mg L⁻¹. For nitrates, the concentrations ranged from 0.06 to 0.47 mg NO₃⁻ L⁻¹. Water temperature presented narrower variability, ranging from 20.52 to 28.20 °C. The pH varied from 5.64 to 6.71 pH units. Finally, DO had the least variability, ranging from 5.56 to 6.85 mg O₂ L⁻¹.

The BOD₅ results showed significant variability, with a CV% of 113.06% and a mean of 3.45 mg O₂ L⁻¹. This value falls within the limits recommended by the World Health Organization [33] for water intended for human consumption, which sets a threshold of 6.0 mg O₂ L⁻¹. However, in urbanized areas, stations 3 and 4 obtained respective mean values of 10.09 and 13.71 mg O₂ L⁻¹. These values could be related to the presence of organic contaminants and untreated domestic waste, which are factors that increase BOD₅ levels [37,38].

According to the guidelines established by [33], the optimal temperature of water for human use ranges between 12 °C and 25 °C. However, in this study, the temperature values along the Acacias River varied between 20.52 °C at station 1 and 28.20 °C at station 10, which exceed the reference value. This increase in temperature is related to proximity to urban areas, the presence of wastewater discharges and changes in forest cover [39,40].

For DO, a mean of 6.55 mg O2 L⁻¹ was obtained, along with a low CV% of 4.92% along the Acacias River. These values are in accordance with the recommendations established by [33] for water intended for human consumption. They also indicate an oxygen concentration level that is adequate to preserve aquatic life [41,42]. DO values of up to 14.5 mg O₂ L⁻¹ are expected in natural waters, but lower DO values in water below the optimum range of 4–6 mg O₂ L⁻¹ is an indication of organic pollution caused by atmospheric dissolution, oxygen-consuming autotrophic processes and heterotrophic activities that consume oxygen in water [43]. The dissolved salts level, the water temperature and the biological processes that take place may dictate the oxygen level detected in a river [44].

The Acacias River is characterized by an acidic tendency, with a mean of 6.38 pH units and a low CV% of 4.93%. These values are associated with the basin’s geology, mainly with the Oxisols typic that provides an acidic pH in water [45,46]. Water with pH < 5.3 reduces minerals and vitamin assimilation. The pH of drinking water strongly affects water temperature, the number of organic compounds and the solubility of toxic metals and, therefore, influences health and body chemistry.

The results for TS showed a CV% of 90.17%. The TS values ranged between 31.0 and 354.0 mg L⁻¹, with the minimum value recorded at station 1, located at the head of the river, and the maximum value at station 12, close to the mouth. The high concentration of TS in this latter station could be related to agricultural activities and a sandy bed, which contributed to a significant impact on the increase in the TS concentration [47,48]. It is worth highlighting that, despite this variability, the TS values remained within the limits recommended by [33]. With turbidity, stations 1, 2, 5, 6, 8 and 10 exhibited values between 2 and 25 NTU, which are higher than the limit suggested by [33]. The highest value was obtained at station 12 with 302 NTU, which is associated with increased sediment due to agricultural activities and urban settlements [49,50]. Phosphates had a maximum value of 1.43 mg PO43-L⁻¹ at station 4, which is close to urban centers. These values could have been influenced by the presence of deficiently treated domestic wastewater discharges. High phosphate levels usually indicate contamination due to inadequately treated industrial discharges and domestic water [51,52,53].

Fecal coliforms showed wide variation from the standard [33]. The maximum value was recorded at station 3, located in the urban area, with a concentration of 2.4 × 10⁶ MPN 100 mL⁻¹. In addition, stations 4, 5, 6, 10 and 11 reported values that exceeded 2000 MPN 100 mL⁻¹. This marked presence of fecal coliforms is related to the insufficiency of wastewater treatment systems and livestock activities in this region, which led to an increase in the concentrations of organic matter and fecal coliforms [29,54,55,56].

For nitrate levels, values were recorded to range between 0.057 and 0.469 mg NO₃- L⁻¹, which fall within the established limits [33]. The minimum value was observed at station 2, located at the head of the river, while the maximum value was for station 6, which corresponds to an area of agricultural and industrial activity.

According to the Kruskal–Wallis test (

Table 3. The descriptive statistics results of the physico-chemical and microbiological parameters.

Parameters	Units	Mean ± SD	Max.	Min.	CV%	[33]
Dissolved Oxygen	mg O2 L−1	6.55 ± 0.32	6.85	5.56	4.92	4.0–6.0
Fecal Coliforms	MPN 100 mL−1	2.7 × 104 * ± 6.81 × 105	2.4 × 106	2.7 × 101	2.52 × 102	0
pH	pH units	6.38 ± 0.31	6.71	5.64	4.93	6.5–8.5
BOD5	mg O2 L−1	3.45 ± 3.91	13.70	0.85	113.06	6.0
Nitrates	mg NO3− L−1	0.18 * ± 0.11	0.47	0.06	60.03	50.0
Phosphates	mg PO43− L−1	0.42 ± 0.43	1.43	0.04	104.03	-
Temperature	°C	25.58 ± 2.10	28.20	20.52	8.22	12–25
Turbidity	NTU	49.87 ± 77.55	302.00	6.17	155.49	1.0
Total Solids	mg L−1	90.48 ± 81.58	354.00	31.00	90.17	500

Note(s): * Significance of the Kruskal–Wallis test p-value < 0.05. Me: mean, Max: maximum, Min: minimum, SD: standard deviation, CV%: coefficient of variation.

), nitrates (0.042 p-value) and fecal coliforms (0.002 p-value) presented significant differences in the stations along the Acacias River. These results were related to land-use changes, where urbanized and agriculturally influenced areas presented higher concentrations of these parameters, while natural areas with low intervention exhibited low values [24].

The Spearman correlation coefficient results (

Table 4. Spearman correlation coefficient (ρ) of the physico-chemical and microbiological parameters.

	DO	F Col.	pH	BOD5	NO3−	PO43−	Temp	Turb	TS
DO	1
F Col.	−0.573	1
pH	−0.077	0.084	1
BOD5	−0.343	0.699 *	−0.224	1
NO3−	0.084	−0.168	0.480	−0.112	1
PO43−	−0.441	0.832 *	0.049	0.685 *	0.070	1
Temp	0.210	−0.203	0.566	−0.329	0.760 *	−0.203	1
Turb	−0.105	−0.266	0.231	−0.392	0.007	−0.434	0.392	1
TS	−0.336	0.112	0.364	−0.252	0.007	−0.126	0.406	0.902 *	1

Note(s): * Correlation is significant at the p < 0.05 level (two-tailed).

) showed a positive correlation between fecal coliforms and phosphates (ρ = 0.832) and BOD₅ (ρ = 0.685), and also between the last two (ρ = 0.685). These relations confirmed the presence of organic matter degradation processes, which favor the proliferation of microorganisms and accelerate the consumption of oxygen dissolved in water. Similarly, the presence of phosphates acts as a food source for bacterial populations [42].

A significant positive correlation appeared between the temperature and nitrate levels (ρ = 0.760). This rise in temperature is associated with anaerobic denitrification processes, which release nitrates into water and cause their concentration to increase [57,58]. A strong correlation was detected between water turbidity and the total dissolved solids concentration (ρ = 0.902). The presence of total dissolved solids can be attributed to an increase in suspended particles in water, a consequence of erosion processes, runoff and the entry of decomposing organic matter [59,60].

3.2. Principal Component Analysis

The PCA explained 84.34% of the total variance with the first three PCs (

Table 5. Principal component analysis of the physico-chemical and microbiological parameters.

Parameters	Components
	PC1	PC2	PC3
DO	−0.706	−0.459	−0.034
F Col	0.753	0.271	−0.023
pH	−0.294	0.677	0.467
BOD5	0.939	0.305	0.07
NO3−	−0.259	0.044	0.804
PO43−	0.924	0.245	0.248
Temp	−0.521	0.517	0.578
Turb	−0.385	0.753	−0.494
TS	−0.338	0.804	−0.46
Total	3.489	2.379	1.723
% variance	38.768	26.431	19.139
% accumulative variance	38.768	65.199	84.339

and Figure 4). PC1 represented 38.76% of the total variance. It revealed a close relation among the parameters of fecal coliforms, phosphates and BOD₅, which indicated contamination processes by organic matter. The parameters of fecal coliforms, phosphates and BOD5 directly indicate that it is associated with domestic and industrial wastewater discharges, which are linked to land use in urbanized areas [61]. PC2 explained 26.43% of the total variance, with total dissolved solids and turbidity being the parameters with the widest variation. These results coincide with those observed in the correlation analysis. PC3 accounted for 19.13% of the total variance and showed that nitrates had the most variation in the Acacias River surface waters; this was probably related to nitrogenous compounds coming from the fertilizers used in agricultural areas (i.e., oil palm crops in the basin) [62,63].

3.3. Water Quality Evaluation Using the Water Quality Index

Both the quality and suitability of the water for drinking purposes in the selected river sections were assessed by determining the WQI. The NSF-WQI index results for the Acacias River showed that, on average 71.01, the water quality fell in the Good category of (Figure 5). The highest water quality values were obtained for stations 8 and 9, which are in agricultural areas, with the lowest values obtained in urban areas at stations 3 and 4.

In addition to natural processes like the interaction of water with the lithogenic structure through which the river flows, including geochemical factors and the chemical river basin composition, anthropogenic processes can intervene and ultimately degrade the surface water quality by making it unsuitable for drinking, industry and agriculture, among other purposes [64,65,66,67,68]. Other research in the Acacias River basin, Colombia, has addressed water quality through biological communities such as phytoperiphyton, highlighting their diversity and bioindicator role [69]. In a study by Vera-Parra [70], the impact of water associated with oil production on the colonization of periphyton algae in the Acacias River was analyzed, and they concluded that these biological communities may be affected by oil activity.

The calculation of the NSF-WQI involved utilizing nine physico-chemical water parameters. The Acacias River’s water quality is classified as Good to Medium for human consumption. These findings indicate that by appropriately treating the water from these rivers, this resource can be used to enhance residents’ living standards.

The situation carries significant consequences for the financial burden associated with treatment. Utilizing the water sourced from the Acacias River for human consumption already involves substantial expenditure. Based on the data in Table 5, there are environmental hazards associated with different land uses that affect the Acacias River’s water quality.

A combination of natural and anthropogenic factors influences water quality. In this manner, numerous researchers have reported that the degradation of water quality in adjacent aquatic systems is influenced by agricultural and urban land uses [13]. The results of this investigation were generally in accordance with the findings of previous research. The water eco-functional regionalization, which was initially proposed by Omernik [71], has been implemented in numerous countries.

Therefore, it may be time to implement it in the region under investigation.

Water is considered a fundamental human right on a global scale because of its crucial role in promoting human well-being. Water- and soil-based systems are the focus of collaborative research within the sustainable development framework. This study into the Acacias River holds significant importance for the region because it demonstrates that the river’s self-purification potential facilitates water quality enhancement across most of its monitoring stations.

4. Conclusions

Globally speaking, it has been widely accepted that there is a relationship between the land use type and water quality. Although the land use–water quality relationship is complex, the obtained results provide a region-based approach to identifying the impact of land-use patterns on the quality of the water that flows through the Acacias River. Wastewater discharges from urban and agro-industrial (oil palm) facilities, as well as runoff from agricultural regions, are the most prominent activities that are related to this effect. Declining water quality was detected at stations 3 and 4. However, the self-purifying capacity of the river developed in the stations with lower environmental pressure. This was made possible by the river’s ability to produce clean water. According to the coliform analyses, fecal contamination was, on the other hand, more prevalent in the regions close to urban settlements and agro-industrial zones. It seems, therefore, that the growth rate of the urban land should be slowed, guaranteeing healthy use. The results of this study suggest that there is a pressing need to establish efficient wastewater treatment systems to contribute to the sustainable management of the water resources in the neighborhood. Additionally, it is of the utmost importance to implement a continuous monitoring program to enable appropriate actions to ensure the long-term viability of this resource in the study area.