DIAGNOSIS OF WATER QUALITY IN AN URBAN WETLAND

Purpose: The objective was to evaluate the water quality based on physical and chemical parameters in different quadrants of an urban wetland and correlate variables that may show possible natural and anthropogenic polluting sources. Theoretical framework: Wetlands are essential ecosystems for the maintenance of ecological balance, biodiversity of organisms, and water reserves. Studies on water quality in urban wetlands are important for understanding their preservation level, elucidating the need for possible conservationist actions. Method/design/approach: The wetland area was divided into four quadrants; water samples were collected for analysis of physical and chemical. When possible, the results were compared with the limits established by the CONAMA Resolution 357/2005 (class 1), which deals with surface waters, and with the literature. Results and conclusion: The Quadrant 3, which presented riparian forest, invasive species, and high deposition of solid waste, showed a greater degree of environmental impact. Changes in several physical and chemical parameters indicate that the impairment of water quality in the evaluated wetland is mainly due to the anthropogenic action of the surrounding population. Research implications: The analysis of wetland water quality as an indicator of socio-environmental actions can be implemented and stimulate public power actions, ensuring its preservation.


INTRODUCTION
Water is an essential natural resource for the survival of all living organisms. It is important for maintaining the climate on the planet and is necessary for most means of production. Its availability is essential for the maintenance of life on the planet, not only in quantity, but also in quality (Siqueira, Aprile, & Miguéis, 2012;Fikri, Fauzi, & Firmansyah, 2023).
Availability of good quality water is essential for economic development, quality of life of human populations, and sustainability of nutrient cycling on the planet (Tundisi, 2003). However, the term "water quality" is not directly linked to absolute or close to absolute degree of purity; it is closer to the concept of "natural", i.e., water is found in rivers, lakes, and springs before human contact (Sardinha et al., 2008;Copetti et al., 2022). 3 The growing demographic and industrial expansions brought a serious consequence: the compromising of waters of rivers, lakes, and reservoirs (Petry et al., 2016;Aragão, Pereira & Silva, 2022). Water quality had human interference in a concentrated (dumping of sewage) and diffused (use of pesticides) ways, both contributing to increase the concentration of organic and inorganic substances in the water (Alves et al., 2008;Grieco et al., 2017).
Studies on multiple uses of water resources are control and evaluation instruments for the development and improvement of techniques for the use, treatment, and recovery of water sources. They also provide information on the water status, qualitative and quantitative trends of natural resources, and effects of human activities and natural factors on the environment, contributing to the planning, control, and recovery of environments and development of environmental policies (Alves et al., 2008;Daranco et al., 2020;Bartá et al., 2021).
Brazil is a country of continental dimensions; thus, it has advantages regarding availability of natural resources, mainly water resources. Proper use of these resources demands investigations that point out areas of aquatic ecosystems that need preservation (Batalha et al., 2014). Wetlands in the south of Brazil, are among the country's aquatic ecosystems that requires special attention. About 20% of the area of Brazil is covered by this ecosystem, which has distinct characteristics (Cunha, Piedade & Junk, 2015). Natural wetlands are sources of benefits for society; they are among the most productive ecosystems on the world and have a high biological diversity, which make them important areas for biodiversity conservation programs (Van Vuuren & Roy 1993).
Wetlands are habitats for several species of aquatic birds, mammals, and other animals (Diegues, 2002;Leal, 1995). In addition, they are important refuges for animals and have the ecological function of filtering water (Baptista, 2007). Aquatic plants found in these ecosystems can be used for purification of water bodies as collectors of pollutants and heavy metals and retention of excess nutrients from artificial fertilization for rice and other crops (Museu de Ciências Naturais, 2019). Baptista (2007) reports the need for more adequate characterization of these environments and recommended further studies, as wetlands are among the ecosystems most affected by hydrological and anthropogenic changes.
Water quality parameters are widely used in studies to characterize liquids from pluvial, industrial, fluvial, domestic, or others sources. These parameters express the result of natural phenomena and/or direct or indirect human action on the water (Von Sperling 2005).
The progressive population growth in dichotomy with biodiversity increasingly generates the need for studies that indicate the quality of wetland waters. Studies on preservation or recovery of urban wetlands contribute to the maintenance of biodiversity and water bodies and provides information for basic and higher education. Thus, the objective of the present study was to evaluate the water quality, based on physical and chemical parameters, in different quadrants of an urban wetland and correlate variables that may show possible natural and anthropogenic polluting sources.

MATERIALS AND METHODS
The study was focused on an urban wetland (Figure 1) in the municipality of Ijui, RS,Brazil (53º55'36.84"W and 28º22'29.25"S). This water body qualifies as class 1 freshwater according to the Resolution 357/2005 of the Brazilian National Council for the Environment (CONAMA), which provides classification criteria and environmental guidelines for classification of water bodies and establishes conditions and standards for discharge of effluents.
The urban wetland, which has 2.5 hectares, was divided into four quadrants, based on the characteristics of its surroundings. Three water samples were collected in each quadrant on January 21, 2020, from the edge to the center of the wetland, in all quadrants (Figure 1), at a depth of 30 cm and preserved in bottles provided by the Laboratory of Waters and Ecotoxicology of the Federal University of Fronteira Sul (UFFS), Cerro Largo campus. Data from the meteorological station of the Regional Institute of Rural Development (IRDeR/UNIJUÍ) showed an accumulated rainfall depth of 92.4 mm from January to the date of collections, with no rainfall events in the four days before sample collections. Water analyses were carried out according to the methodology described in the Standard Methods for the Examination of Water and Wastewater (Apha, 2005). The parameters pH, electrical conductivity, water temperature, and dissolved oxygen were measured at the collection site, using a Multiparameter Probe YSI Professional Plus ® . Then, the samples were packed on ice and sent to the Water and Ecotoxicology Laboratory of the UFFS, Cerro Largo campus. The parameters analyzed in the laboratory were: absorbance (Evolution 201 UV-VisSpectrophotometer ® ), apparent color (Del Lab ® Colorimeter), settleable solids (Imhoff Cone), biochemical oxygen demand (BOD5) (BOD T Hach® Evolution 201 UV-VisSpectrophotometer), chemical oxygen demand (COD) (Digestor Block Evolution 201 UV-VisSpectrophotometer), and nitrate (NO3) (Evolution 201 UV-VisSpectrophotometer).
The analysis of the quadrants was carried out based on results obtained through descriptive statistics using mean ± standard deviation of 0.5 (Cruz, 2016). Then, Pearson's correlation was performed for each group of physical and chemical parameters to analyze the magnitude and correlations between variables at 5% error probability level. Additionally, the results were compared, when possible, with the CONAMA Resolution 357/2005 to strengthen the analysis and discussion. The water spring near the wetland (Figure 1) was also considered as a standard for comparison between quadrants. Table 1 shows the means of the physical parameters of water quality for the different wetland quadrants analyzed as mean ± standard deviation of 0.5 (SD). Higher means were found in quadrants 3 (presence of riparian forest and high deposition of solid waste) and 4 (riparian forest and lower deposition of solid waste). However, the results of absorbance found in quadrants 1 (under occupation by animals) and 2 (under domestic occupation on the edge) were practically null. Absorbance refers to the capacity to absorb light and may have greater or lesser transmittance. A higher absorbance indicates a lower transmittance, denoting low capacity for the incident light to pass through a solution. It raised the hypothesis that quadrants 3 and 4 possibly have higher suspended solids contents or even substances that can change the water color. However, the analysis of apparent color and settleable solids showed that the raised hypothesis was confirmed only for quadrant 3. Quadrant 4 showed higher electrical conductivity, indicating a greater number of free ions. The results of physical parameters found for the spring were significantly lower than those found for the different quadrants, showing a water with better conditions. Biochemical oxygen demand (BOD) and chemical oxygen demand (COD) in quadrant 3 presented values with standard deviation greater than 0.5 above the mean, confirmed by the lowest dissolved oxygen concentration found in this quadrant. These results partially explain those found for physical parameters. A higher nitrate concentration was found in quadrant 1, indicating the presence of older pollution in this location, which is consistent with the last state of oxidation of nitrogenous compounds. Moreover, a high BOD was found in the spring, indicating contamination of this water source, despite presenting values well above the limits established by the CONAMA resolution 357/2005. 6 Reference ** Up to 3 mg L -1 -10 mg L -1 6 to 9 Minimum 6 mg L -1 AB: absorbance; AC: apparent color; SS: settleable solids; WT: water temperature; EC: electrical conductivity; BOD: biochemical oxygen demand; COD: chemical oxygen demand; NO3: nitrate; pH: hydrogen potential; DO: dissolved oxygen (mg L-1); Quadrant 1: erosion and occupation by horses and railway; Quadrant 2: irregular domestic occupation and railway; Quadrant 3: riparian forest along its entire area and high deposition of solid waste; Quadrant 4: riparian forest in part of its extension and medium deposition of solid waste; *Not described in the CONAMA Resolution 357/2005; **Reference: CONAMA Resolution 357/2005. Source: Prepared by the authors (2023).

RESULTS AND DISCUSSIONS
The most significant results for apparent color and settleable solids were found in quadrant 3. The highest values were based on the mean + 0.5 SD. In general, the analysis of physical parameters showed a greater degree of environmental impact on quadrant 3. This condition allows for different analyses, and one of them confirms that the presence of riparian forest is not always synonymous of absence of environmental impact and good water quality. The significant means found for apparent color and settleable solids indicate changes in water quality in this microhabitat. According to the description of the quadrants, the statistical analysis confirmed the evaluation carried out in loco, i.e., considering the topography and deposition of solid waste in the place, particles are transported to the wetland edge, resulting in significant apparent color and concentration of settleable solids. Solids can damage aquatic ecosystems by sedimentation from the edges, which affects the metabolism of organisms and even fish spawning (Alves et al., 2019).
However, quadrant 1 presented the lowest apparent color and concentration of settleable solids, which was initially not expected, considering that part of this quadrant presented erosion and occupation of the bank by horses. The volume of eroded soil sediments and horse excrements was probably not high enough to cause significant changes in these parameters. Another possibility is a water upwelling, which would dissipate part of the sediments. Alves et al. (2008) reported that changes in color of a water body originate from industrial and domestic wastes. Fiore, Bardini, & Novaes (2017) attribute the presence of color in natural waters to the decomposition of organic matter from plants and animals and the presence of natural metallic ions, such as iron and manganese. The presence of color in waters can suppress photosynthetic processes and significantly alter water bodies. Domestic waste, soil particles, plant residues, and urban wastes that are carried by rain enter the wetlands.
Electrical conductivity is another important parameter to determine water quality, although it is not found in the CONAMA Resolution 357/2005. Low electrical conductivities were found in all quadrants (from 29.55 to 37.90 μS cm -1 ,), indicating that the wetland water may be drinkable, as it is within the limits considered good in the literature: from 10 to 100 μS cm -1 (Von Sperling, 2007). However, environments polluted by domestic or industrial sewage can reach up to 1000 μS cm -1 (Piratoba et al., 2017). Solutions containing inorganic compounds are considered good in electrolytes. Molecules of organic compounds, however, do not dissociate in aqueous solutions and are, therefore, very poor conductors (Siqueira & Schimdt, 2018). Siqueira & Schmidt (2018) confirm that wetlands are subjected to pollution of organic origin.
The means of chemical parameters of water quality (Table 1) confirms the impact on quadrant 3. BOD and COD had values higher than the mean, whereas dissolved oxygen was below the mean and the limit established by the CONAMA Resolution 357/2005. The results of these parameters reinforce those found for physical parameters. Therefore, the entry of sediments into quadrant 3 due to its topography and the flow of water to it significantly affected these parameters. Moreover, its strip of riparian forest is probably insufficient to retain sediments, and the water flow probably is high enough to cause runoff in the forest, as observed in loco.
The correlation analysis for physical parameters (Table 2) showed a high positive correlation between apparent color and settleable solids, i.e., an increase in one increases the other. This correlation can contribute to improve these parameters by actions that promote better water quality when compared to actions for recovery and control. No correlation was found for the other parameters, indicating absence of dependence and the need for different specific actions to improve them.

Source: Prepared by the authors (2023).
The correlation analysis for chemical parameters (Table 2) showed that nitrate had a a negative correlation with pH and a positive correlation with dissolved oxygen (DO). A low pH facilitates the nitrification process, in which nitrogenous compounds entering the system are converted into gaseous ammonia, which is then converted into ionized ammonia, which is converted into nitrite by the action of nitrifying bacteria and, subsequently, into nitrate; however, the alkalinity of the water promotes the mortality of nitrifying bacteria. Although not expected, a positive correlation was found between nitrate and DO, which raises the hypothesis that nitrate may be used as a nutrient by algae that produce oxygen, which is dissolved in the water body. The correlation between DO and most variables is one of the most relevant results of this analysis. The negative correlation of DO with COD and BOD confirms the correlation trend between these parameters. It also confirms the higher consumption of oxygen for degradation of organic matter, leading to a decreased available oxygen. Von Sperling (2005) reported that decreases in DO concentrations are connected to BOD and, therefore, to COD.
Based on the negative correlation between BOD and DO, the wetland sites with presence of organic matter tend to have lower availability of oxygen in the water, as observed in quadrant 3. Under low DO and high organic matter concentrations, microorganisms can use oxygen to stabilize organic compounds, in general, from effluent discharges at some specific points along the water body (Von Sperling, 2014). Petry et al. (2016) also found a negative correlation between DO and BOD in a study carried out in the Luiz Rau stream, Rio dos Sinos River Basin, RS, Brazil.
BOD is an indicator of presence of biodegradable organic substances in water bodies, such as decomposing plants, animal materials, organic chemicals, and rainwater runoff (Santiago, Jesus, & Santos, 2016;Petry et al., 2016). Rainwater runoff probably is the main factor for the changes found in BOD, COD, and DO in quadrant 3, which is the quadrant that receives most rainwater due to the land slope, which allows the drainage of almost all the nearby water to the wetland. Carvalho et al. (2016) evaluated the Ribeirao São João stream, in Porto Nacional, TO, Brazil; they found DO concentrations between 4.8 and 5.30 mg L -1 and attributed these results to discharges of organic matter from the urban area. They also reported that decreases in DO concentrations are usually connected to pollution of water sources by domestic effluent, with increases in BOD as the dissolved oxygen decreases. Barcelos et al. (2017) found decrease in DO concentration in one sampling point in the Sucuri stream, in Caçu, GO, Brazil, due to the entry of materials from agricultural areas, which contributed to increases in phosphate load. Similar result was found by Toledo & Nicolella (2002) in a watershed subjected to agricultural and urban uses in Guaira, SP, Brazil.
A study on water quality in the urban perimeter of Riachao do Jacuipe, BA, Brazil, showed DO concentrations outside the limits of the CONAMA Resolution 357/2005, which was attributed to anthropogenic actions, such as release of raw effluents and solid waste into the water body studied (Santiago, Jesus & Santos, 2016).
Visually, quadrant 2 was the most impacted, which was expected to be confirmed by the analyses of physical and chemical parameters; however, the results did not confirm the visual observations. It may indicate the existence of a self-purification process by the action of microorganisms and some macrophyte species, as this wetland site receives untreated domestic sewage; the inflow of water from the spring may also be an important factor for these results. According to Paula (2011), the existence of a self-purification process does not mean that the water is the same as its initial conditions, but that the ecosystem can reach an equilibrium without presenting environmental problems.
Absorbance (AB) showed a negative correlation with nitrate and DO, but a positive correlation with COD (Table 3). Thus, the greater presence of nitrate in the aquatic environment probably hindered the understanding of the low absorbance, indicating that the nitrogen might being used by organisms that depend on this compound. The negative correlation between nitrogen and dissolved oxygen also supports this interpretation. However, the positive correlation between absorbance and COD indicates the presence of organic matter in the system. Apparent color (AC) and settleable solids (SS) showed a positive correlation with COD and an inverse correlation with DO, which were expected. Regarding the effects of water temperature on pH, the hypothesis raised is that the water temperature conditions and the release of gases alter the hydrogen concentration.
The positive correlation between COD and the physical parameters AB, AC, and SS is explained by the high organic matter contents in the degradation process, which results in high SS concentrations. Consequently, AC also presents high indexes, as its measurement is based on the presence of organic and inorganic colloidal solids. Similar results were found for AB, as the presence of organic matter allows for greater absorption of light energy due to the presence of colloidal residues. -0.20 *: Significant at 5% probability of error; AB: absorbance (u.a); AC: apparent color (uH); SS: settleable solids (mL L -1 ); WT: water temperature (ºC); EC: electrical conductivity (µS cm -1 ); BOD: biochemical oxygen demand (mg L -1 ); COD: chemical oxygen demand (mg L -1 ); NO3: nitrate (mg L -1 ); pH: hydrogen potential (scale); DO: dissolved oxygen (mg L -1 ). Source: Prepared by the authors (2023). (2007), the determination of AB under UV light 254 nm is an alternative to obtain a fast estimate of organic matter contents in untreated or treated water samples. Differing from COD, DO showed a negative correlation with AB, AC, and SS, as organic matter stabilization requires high consumption of DO.

According to Lage Filho & Andrade Júnior
The negative correlation found between SS and DO shows that organic matter contents affect DO concentrations. Significant decreases in DO can be caused by discharges of organic origin and/or high temperatures, which can decrease O2 solubility in water (Fiorucci & Benedetti Filho, 2005).
Organic particles carried by rains promote metabolic processes due to use of organic matter by microorganisms, resulting in decreases in DO concentrations (Von Sperling, 2014). These environmental parameters are connected to organic pollution. Branco (1986( apud Peres et al., 2008 found that high values for such water parameters are due to high pollution and erosion. It explains the high BOD and COD and the very low DO concentrations found. DO concentrations lower than that established by the CONAMA Resolution 357/2005 (at least 6 mg L -1 ) indicate environmental impact, which was found for all quadrants evaluated (4.30 to 5.35 mg L -1 ). These results reinforce that quadrant 3 presented the highest pollution level.
SS is the parameter used to indicate the presence of organic matter; it is connected to AC and AB: the higher the SS concentration, the higher the AC and AB. Organic matter degradation involves the use of oxygen, leading to decreases in its concentrations. According to Vasconcelos, Pavanin & Pavanin (2012), bacteria use oxygen for their respiration processes during the organic matter stabilization, which may decrease its concentrations in the medium. The correlation between AC and suspended solids contents can be explained by the determination of water color, which is carried out by light reflection and refraction on dissolved or suspended materials. Many of these associations indicate unnatural processes, such as disposal of sanitary and industrial effluents from urban and agricultural activities.
The highest SS was found in quadrant 3, which can be explained by its topography, which channels waste from the nearby urbanization into the wetland during the rainy season and presents ditches opened for installation of domestic sewage pipes, which have been in process for several months. Libânio (2016) reported that organic compounds that color natural waters are basically from the decomposition of plant organic matter and metabolism of microorganisms in the soil, or even from anthropogenic activities, such as discharges of domestic and industrial effluents and runoff from urban roads and plowed soils. Water apparent color is connected to the degree of reduction in light intensity passing through it; this reduction is caused by the absorption of part of the electromagnetic radiation due to the presence of dissolved solids, mainly organic and inorganic colloidal materials (Vasconcelos, Pavanin & Pavanin, 2012).
According to Von Sperling (2005), pH affects the distribution of several chemical compounds in free and ionized forms and the solubility of substances and defines the toxicity potential of several elements. Variations in pH in natural waters are usually due to consumption or production of carbon dioxide (CO2) by photosynthetic organisms and respiration and fermentation processes of all organisms in the water body, producing weak organic acids.
The negative correlation between water temperature and pH is due to the water capacity to solubilize gases, as lower temperatures represent greater oxygen availability in the environment. Additionally, some temperature variations alter the toxicity of some chemical components in aquatic environments (Simoneli, Jungles & Döll, 2017). The effects of pH and temperature can be observed in the distribution of dissolved substances in rivers and lakes, mainly in lakes, which present pronounced pH gradients: high pH in the surface due to photosynthetic activity (carbonic acid absorption → increase in pH), and lower levels in the bottom due to predominance of respiratory processes (release of carbon dioxide → decrease in pH) (Brasil, 2021).
The CONAMA Resolution 357/2005 does not determine limits for water temperature, but studies indicate that temperatures close to 20 °C are ideal for freshwater bodies. In addition to gases, water can dissolve chemical substances that are important for determining water quality. The solubility of these substances is connected to the pH of the medium and, usually, the solubility increases as the pH decreases. Increases in temperature also favors the solubility of several chemical substances (Brasil, 2021).
BOD, COD, DO, SS, and AC were the most significant parameters to indicate the water quality in the wetland evaluated. Considering the results found for these parameters, quadrant 3 is the most impacted by anthropogenic action. A high SS concentration was found, indicating presence of organic matter and other sediments; and the processes resulting from the organic matter degradation changed the other parameters, which indicates that they are significantly correlated.

FINAL CONSIDERATIONS
The results indicated that the entire wetland presents signs of environmental degradation. The analyses of physical and chemical parameters confirmed the initial hypothesis that the wetland undergoes human interference. Additionally, the results indicate, in general, signs of organic pollution.
The results also show pollution of the wetland waters due to the land use and occupation in its surroundings. Quadrant 3 was the most impacted by anthropogenic action; it presented parameters with values outside (above or below) the limits established by the Resolution 357/2005 of the Brazilian National Council for the Environment (CONAMA) for Class 1 freshwaters.
The high biochemical oxygen demand and low dissolved oxygen concentrations found in quadrant 3 indicate a greater availability of organic matter, which can lead to complete depletion of oxygen in the water and compromise the aquatic life in the wetland, causing loss of its functionality in the environment.
The statistical analysis showed significant variations in the parameters analyzed. The use of multivariate analysis allowed the connection of the impacts observed in the surroundings of the wetland with the results of the analysis of its waters.
The diagnosis carried out in the present study makes it possible to recommend the development and application of a recovery plan for the wetland to restore its water quality. Conservation actions need to be applied around the wetland to protect the biodiversity of this ecosystem.
In view of these findings, the continuity of researches and monitoring for this water body are essential to encourage effective actions by government authorities to interrupt the degradation process, ensuring water quality and preservation of the entire wetland.