Natural wetlands in protected areas as a key to water quality resilience

doi:10.21203/rs.3.rs-2693979/v1

Wetlands are buffers for terrestrial runoff with the essential service of water purification. Despite its importance, they are experiencing degradation due to the combined effect of climate change and poor land-use practices. Studies of natural wetlands in Paraguay are scarce. We assessed wetland water quality conditions using pH, turbidity, total phosphorus (TP), and bacterial indicators of 12 natural wetlands located in protected areas (PW) or in the border of agricultural lands (AW) in the Paraguayan side of the watershed of Parana River. AW presented acidic pH values (x̄=5.5). We registered higher TP values in AW (x̄=0.14 mg/L) compared to PW (x̄=0.06 mg/L). For turbidity AW presented higher and variable values (x̄=425 NTU) than PW (x̄=34 NTU). In connected wetlands as the nutrient flows through the wetlands system to the reservoir concentration decreased 70% (0.1 to 0.03 mg/L) and the turbidity decreased from 112 to 42,6 NTU. This study observed a high degree of variability of bacterial indicators in water and sediment. The counts of coliforms in water and sediment samples were in the order E.Coli>Total coliforms>Fecal Coliforms. Long term contamination by organophosphorus and carbamate pesticides was pointed by the positive results in 100% of the sediment samples. As far as we can conclude wetlands has a key function in ecosystem function, health and preserving the water quality that enters to the reservoir, and protected PW presented better water quality conditions in terms of TP, turbidity, and bacterial indicators.

natural-wetland

Paraguay

Parana-River

physicochemical

bacterial indicators

phosphorus

turbidity

pH

Total phosphorus in water decreases by 70 %, and turbidity reduces by 62% in connected wetlands as long as the water flows through the wetlands system to the reservoir.
Natural wetlands have an essential role in sediment buffering.
Agricultural wetlands presented acidic pH values in water and sediment compared to the wetlands in forest areas.
The bacterial counts were highly variable, and E.coli is proposed to be a good bioindicator in water and sediment samples.

Wetlands are ecosystems found in almost all parts of the world. Being on the transition between terrestrial and aquatic ecosystems, they are buffers for terrestrial runoff. Due to their environmental importance, sometimes they are referred to as "kidneys of the landscape." With a wide variety of hydrologic conditions, wetlands are distinguished by the presence of shallow water with unique soil conditions characterized by standing water, poorly aeration and/or water-saturated soil, and the occurrence of organisms capable of exploiting specific environmental conditions (Mitsch, William J, Gosselink, 2015; Peralta et al., 2014).

One of the essential wetland services is water purification, which is accomplished through physical and biochemical processes that reduce excess nutrient concentrations and microbial pathogens loads derived from human activities (Clairmont et al., 2021; Watson et al., 1990). Wetlands are believed to be a key factor in water storage, stabilizing water supplies, mitigating effects of floods and drought, protecting shorelines, cleaning polluted waters by bioremediation, and recharging groundwater aquifers that result in improvements to downstream water quality (Henrichs et al., 2007; Mitsch, William J, Gosselink, 2015; Scholz & Hedmark, n.d.).

Natural wetlands are under high anthropogenic pressure worldwide, experiencing degradation due to the combined effect of climate change and poor land-use practices, drainage, and freshwater abstraction (Brunet & Westbrook, 2012; Cochrane & Laurance, 2008; Dalu et al., 2022). As wetlands represent buffer zones between rivers and adjacent terrestrial systems, excess of nutrient input and accumulation results in eutrophication negatively affecting wetland integrity and function (Dalu et al., 2017; Mitsch, William J, Gosselink, 2015). As a result, more than 50% of the wetlands worldwide have been lost in the last decades, and the trend is that existing wetlands continue to be endangered (Brunet & Westbrook, 2012; Hong et al., 2020; Zedler & Kercher, 2005).

Although their widely accepted ecological importance and growing risk, natural wetlands in the Latin American region, specifically Paraguay, are poorly studied (Iriondo, 2004, Kopcow et al. 2017). In this scenario, an important indicator in the 2030 Agenda for Sustainable Development commits countries to the Sustainable Goal of Development SGD 6.6, to protect and restore water ecosystems. Wetlands and connected ecosystems such as aquifers, lakes, and rivers play a crucial role in the water cycle (UN-Water, 2018). They are fundamental for good environmental water quality and aquatic ecosystem health.

Itaipu Binacional is the result of a partnership between the governments of Brazil and Paraguay. The plant is located at the Paraná River, the border between the two countries. The company maintains ten protected areas and a reservoir protection strip in Brazil and Paraguay, Paraguayan territory holds eight Natural Reserves (Tati Yupi, Pikyry, Itabo, Yvyty Rokái, Limoy, Pozuelo and Carapã) and a Binational Biological Refuge Mbaracayú. These protected areas present a wide variety of ecosystems, including wetlands with a variety of vegetation assemblages, volume, and water characteristics. As far as the right bank is concerned, the eight protected areas hold essential wetlands for general biota whose aquatic-palustrine plants richness are currently being the focus of various studies related to biodiversity (Itaipu-Binacional, 2018).

Climate information shows that the area has a total annual rainfall of 1,800 mm and an average annual temperature of 21.7°C. The summer months are characterized by high temperatures and high air humidity, which favors the formation of poorly organized storm systems, which produce rains of short duration and almost daily frequency. The average values of precipitation in the summer are of the order of 180 mm. The maximum precipitation peak of the year takes place in October, with a value of 224 mm. About temperature, in the summer a mass of warm and humid air prevails over the analyzed region, coming from more tropical latitudes, which is transported by the Low-Level Jet (LLJ) from the Amazon to the La Plata Basin ((Vera et al., n.d.; Victória Weykamp & Ambrizzi, n.d.)).

The study of natural wetlands in protected areas provides important pre-degradation information on the factors that govern ecosystem functioning and productivity, with the goal of providing important information for management and quantification of the ecosystem services of these systems elsewhere in the future (Dalu et al., 2021; Sims et al., 2013). Additionally, the sites of study are located in protected areas and agricultural land in heavy cropped watersheds, the presence of pesticides and excess of nutrients are suspected to endanger these ecosystems.

Consequently, more information on water and sediment chemistry and the microbiology of these systems is desirable. To improve that knowledge, 12 wetlands in two groups according to the surrounding main land use, six agricultural and 6 in protected areas in the Paraguayan side of Parana River basin, have been investigated. The main aims of this study were to gain insight into 1) the physicochemical composition of water and surface sediments, including nutrients and pesticides, and 2) the microbiological composition of water and surface sediments focusing on coliforms and Pseudomonas spp.

2.1 Study area and sampling sites

The twenty investigated wetlands are located in eight protected areas on the Paraná river watershed near Itaipu Dam reservoir in Paraguay. The main characteristics of the sampling sites are summarized in Table. 1. Detailed information and georeferenced data are available in Supplementary Table S1.

Table 1. The twelve study wetlands, including some of their characteristics

Study area	Wetland ID	Type (FWS/OBS- 1979)	Sediment type	Reservoir connection	Land use
Itabo	IT_12	palustrine	hydric	no	agricultural
	IT_14	palustrine	hydric	no	agricultural
	IT_15	lacustrine	nonhydric	yes	protected area
Yvyty Rokái	YR_16	lacustrine	hydric	yes	agricultural
	YR_17	lacustrine	hydric	yes	agricultural
	YR_18	lacustrine	hydric	yes	agricultural
Limoy	LI_20	palustrine	hydric	no	agricultural
	LI_21	lacustrine	hydric	yes	protected area
	LI_22	lacustrine	hydric	yes	protected area
Mbaracayu	MB_34	palustrine	hydric	no	protected area
	MB_35	lacustrine	hydric	yes	protected area
	MB_36	palustrine	hydric	no	protected area

2.2 Sampling and preparation of surface water and sediments

Duplicate samples of surface water and sediments were collected from the 12 wetlands (details in Table 1). In each site, surface water was sampled from the wetland center and five surrounding equidistant points, ranging from about 10 m from shore, depending on wetland size and accessibility. Composite surface water samples were obtained by collecting 100 mL in the same points and then combined in a 500 mL sterile bag for each wetland. In the same way and after water collection, sediments were sampled from the same points by obtaining equal amounts of sediment (approx. 80 mL) with an Ekman grab (Wildco, USA) or plastic spoon from the superficial 10 cm at each location, placed in a plastic tray and then mixed and combined in a composite sample of 500 mL sample in a sterile bag for each wetland (McMurry et al., 2016; Shelton et al., 1994). Samples were stored in an ice cooler and delivered to the laboratory within a day. Before sample analysis, all sediment samples were homogenized, quartered, and subsampled for the required testing procedure.

2.3 pH and turbidity

Water characterization of the wetlands was performed following (Rice & Baird, 2017). First, water turbidity in NTU units was determined by measuring subsamples in 15 mL glass vials in a turbidimeter (2100Q01 HACH, USA) according to 180.1 USEPA Method (James O’Dell, 1993). Next, a pH/ATC triode combination electrode (ORION STAR A 214 Thermo Scientific, USA) was used to determine pH. On the other hand, for sediment samples, according to AFNOR NFX31-103 (Pansu & Gautheyrou, 2006), 20g of the quartered sample was weighed and added 50 mL of distilled water, then was homogenized, and placed in an orbital shaker (IKA KS 3000 ic control), at 80 rpm and room temperature for 60 min, then transferred to 50 mL plastic centrifuge tubes, centrifuged OHAUS Frontier TM 5706 for 5000 rpm for 5 min. Finally, the pH was measured from the supernatant.

2.4 Mineral hydric sediment determination

The determination of whether a sediment sample was a hydric sediment was done by determining sample color. Sediment colors were determined by visually comparing a soil sample to colored chips of the standard Munsell Soil Color Charts (Geological Society of America, USA). Three attributes, hue, value, and chroma, describe the possible colors in the chart. Each sediment sample to be classified as a hydric was considered a chroma of 2 or less. Therefore, samples with low chromas indicated hydric sediments, and those that contained bright reds, browns, yellows, or oranges were deemed nonhydric (Mitsch, William J, Gosselink, 2015).

2.5 Total Phosphorus (TP) in water

Total phosphorus was determined in water samples by digestion with K₂S₂O₈ (Biopack, AR) (Valderrama, 1981) and subsequent analysis of the resulting orthophosphate by colorimetry, ascorbic acid method APHA Method 4500-P E (Rice & Baird, 2017).

All glassware used for analysis was previously acid washed with 20% HCl solution and rinsed with type I distilled water. Initially, 50 ml of the water sample was introduced into 100 mL bottles, and 6.7 mL of the oxidation reagent was added. The oxidant compounds were of 50 g of potassium persulfate p.a., 30 g of boric acid p.a. (Biopack, AR) dissolved with 350 mL of 1 M sodium hydroxide (Biopack, AR) and made up to 1000 mL with distilled water. The mixture of water and oxidizing reagent was then introduced into an autoclave for 30 min and then were cooled to a flask, and 1.5 ml of the combined reagent was added APHA Method, 4500-P E (Rice & Baird, 2017). The molybdenum blue color development time is considered within the following 10 minutes. Then, the sample's absorbance was measured at 880 nm (GENESYS 10S Thermo Scientific, USA).

2.6 Bacterial culturing in water and sediment

Water and sediment sampling took place for the quantification of the following bacterial indicators: Total Coliforms (TC), Fecal Coliforms (FC), Escherichia coli (EC), Heterotrophic bacteria (HB), and Pseudomonas spp. (PS). The microbiological quantification of bacteria was assessed by the membrane filter technique for members of the coliform group APHA Method 9222 (Rice & Baird, 2017), using nitrocellulose membranes with 0.45 μm pore size and 47 mm diameter (Millipore, USA).

For water samples, dilutions of 500 μL, 1 mL, and 10 mL of each sample were filtered, followed by plating on culture media, and the volume of 1mL was chosen considering the suggested colony counts according to APHA 9222 (Rice & Baird, 2017), for sediment samples were carried a pretreatment according to the methodology of Young et al. (2016) and Craig et al. (2002) (Craig et al., 2002; Seo et al., 2016). An amount of 25 g of sediment was placed in sterile glass flasks containing 75 mL of 0.1 % peptone water ( 3M, USA), then placed in an orbital shaker for 15 minutes at 250 rpm, centrifuged at 3000 rpm for 15 min, and the supernatant was separated, filtered by a membrane filtration method and followed the same procedure as water samples. Water and sediment samples were cultured in Petri dishes with mEndo (BD Difco, USA) medium for CT, mFC agar (BD Difco, USA) for CF, Brilliance EC chromogenic agar (Oxoid, UK) for EC, Cetrimide Agar (Condalab, Spain) for Pseudomonas spp, and AQHC Petrifilm (3M, USA) for heterotrophic organisms. To determine the concentration of heterotrophic bacteria, a dehydrated film medium slide was used for water and sediment samples where 500 μL of the sample was diluted in 500 μL of sterile distilled water to a final volume of 1 mL hydrate the plates. Finally, TC, EC, and heterotrophic bacteria were incubated at 37ºC while FC at 45ºC and Pseudomonas spp. at room temperature. The colony counts were registered following APHA 9222 (Rice & Baird, 2017)and the manufacturer's instructions.

2.7 Organophosphorus and carbamate pesticides in water and sediment

Organophosphate/Carbamate was determined using the Abraxis Organophosphate/Carbamate ELISA kit (Eurofins, USA). The qualitative determination of organophosphates and carbamates in water and sediment samples was made by a qualitative colorimetric assay based on a modification of the inhibition of the enzyme Acetyl Cholinesterase (ACh-E). Ach-E hydrolyzes acetylthiocholine (ATC) which reacts with 5,5’-Dithio-bis (2-Nitrobenzoic acid) [DTNB] to produce a yellow color which was read at 405 nm. Therefore, if OP or Carbamate pesticides were present in a sample, they inhibit ACh-E.

Sediments samples were quartered, and 15g was extracted with NaH₂PO₄ 0.1 M placed for agitation for 15 min and then centrifugation at 3500 rpm for 10 min (Peruzzo et al., 2008). The extraction step was repeated twice with the solid residue (pellet). Supernatant extracts were filtered through 0.45 mm 0.45 μm pore size, 47 mm diameter, (Millipore, USA) membrane, and the determination was carried with de eluate.

2.8 Statistical analysis

The distribution of the data was determined using the Shapiro Wilks test. According to the distribution, the t paired test or Kruskall-Wallis was used to determine whether significant differences existed in pH, TP, and turbidity. Calculations were performed using PAST® software (Hammer et al., 2001).

As shown in Table 2 and Figs. 2. a and 2. b, water pH values according to land uses surrounding the natural wetlands in this study were significatively different (t=-2.48; p = 0.03125). For sediment samples, considering that pH represents the value of pH of a solution in equilibrium with the sediment (Pansu & Gautheyrou, 2006), the observed difference was not significant (t=-2.47; p = 0.06). However, the agricultural wetlands presented more acidic pH values (mean pH values of water and sediment of 5.59 and 5.58, respectively); than the wetlands in protected or forest areas; sediment pH values were neutral or circumneutral (Table 2), in accordance with the pH values registered in water samples (mean pH values of water and sediment of 6.72 and 5.99, respectively).

Table 2

Water and sediment physicochemical parameters of the studied wetlands. The values are expressed in mean ± SD. TP: Total Phosphorus
Wetland	pH water			pH sediments			Turbidity (NTU)			TP (mg/L)
IT-12	5,89	±	0,01	5,18	±	0,09	112	±	7,0	0,1	±	0,01
IT-14	5,99	±	0,01	5,67	±	0,02	> 1000			0,05	±	0,01
IT-15	6,87	±	0,00	5,38	±	0,01	42,6	±	0,5	0,03	±	0,01
YR-16	5,56	±	0,01	5,72	±	0,28	> 1000			0,11	±	0,01
YR-17	6,44	±	0,01	5,38	±	0,00	26,0	±	0,4	0,04	±	0,01
YR-18	7,01	±	0,01	5,35	±	0,35	123	±	2,6	0,07	±	0,01
LI-20	4,92	±	0,02	6,53	±	0,10	290	±	5,2	0,46	±	0,01
LI-21	6,08	±	0,02	6,16	±	0,15	18,8	±	2,4	0,09	±	0,01
LI-22	7,28	±	0,07	5,96	±	0,04	12,0	±	0,5	0,05	±	0,01
MB-34	6,68	±	0,09	6,70	±	0,15	88,5	±	1,8	0,06	±	0,01
MB-35	7,03	±	0,10	6,49	±	0,00	27,8	±	0,6	0,09	±	0,01
MB-36	6,44	±	0,06	6,48	±	0,01	17,1	±	0,2	0,05	±	0,01

The acidic trend observed in agricultural wetlands may affect phosphorus concentration; in this study, P solubility seems to increase in acidic medium (Table 2); we observed higher TP values in agricultural wetlands, with a mean of 0.14 mg/L compared to wetlands located in protected areas with a mean of 0.06 mg/L. In addition, water TP concentrations were higher than 0.1 mg/L in LI-22, and YR-16 with 0.46 and 0.11 mg/L, respectively, both surrounded by agricultural land uses (Fig. 2.d).

Water turbidity (Fig. 2. c) also presented significant differences between both groups (H = 5.78, p = 0.016), and samples from agricultural wetlands presented higher and variable values (mean 425 NTU) than wetlands in protected areas (mean 34 NTU). This observation makes it possible to hypothesize that the wetlands in this study have an essential role in sediment buffering, reducing the amount of suspended sediments entering the reservoir.

The highest TP value was 0.46 mg/L, recorded in the agricultural wetland LI-20, a value ten times over the regional regulatory limit of 0.05 mg/L in Paraguay and Brazil (CONAMA, 2005; SEAM, 2002). This wetland located on the border of the Limoy protected area has no physical connection with LI-21 and LI-22 and considering the distance from the wetlands to the reservoir, as we go inside the protected area (Fig. 1. c), the TP concentration decreases almost ten times from 0.46; to 0.09 and finally to 0.05 mg/L, respectively.

TP in water decreases in connected wetlands as long as the nutrient flows through the wetlands system to the reservoir. The lowest TP concentration of 0.03 mg/L was observed in IT-15, a natural lacustrine wetland in Itabo protected area connected to an agricultural wetland IT-12 located 3.24 km upstream. From IT-12 (0.1 mg/L) to IT-15 (0.03 mg/L) the TP concentration decreased 70% and the turbidity decreased from 112 to 42,6 NTU (Table 2, Fig. 3). For bacterial indicators in water, in IT-15, was recorded high densities of total and fecal coliforms with no growth of E.coli and Pseudomonas spp. This lets us propose that as the wetland system improves its water quality in terms of TP and turbidity, the bacterial indicators Pseudomonas spp. and E.coli decrease, shifting to the dominance of TC and FC bacteria (Table 3, Fig. 4).

Increased TP level have been used has an indicator of fecal coliform proliferation in wetland waters in North Carolina, USA (Chudoba et al., 2013; Toothman et al., n.d.), in this study the wetlands IT-12, YR-16 and LI-20 presented TP values > 0.1 mg/mL with low densities of FC bacteria of 200 to 600 CFU/100ml. At the same time, it is important to consider that TC and FC counts may be hindered by heterotrophic bacteria in plate counts (Amanidaz et al., 2015).

Heterotrophic bacteria (HB) count in all samples was too high to count per plate, even with dilutions of 0.1 mL. This does not allow for obtaining quantitative data but permits estimating the high amounts of HB in all samples. This may explain the low counts registered for TC and FC in this study, as organisms like Pseudomonas and Flavobacterium in counts over 1,000 CFU/mL interfere with coliform on mEndo medium, hindering coliform detection (Amanidaz et al., 2015).

In natural wetlands of this study and contrary to the findings of Clairmont et al. (2021) in wetland mesocosms, we do not observe positive correlation between TP concentrations and EC bacteria counts. No significant regression was found between sediment TP and either bacterial indicator in combined group data by land use or for any individual site. According to these results, sediment bacteria are not likely to be P limited and this could be due the influence TP in sediment and the TP recycling across the sediment–water interface.

Considering all data, regardless of the type of sample and sampling sites, the number of bacterial indicators fluctuated largely. Contrary to the expected, considering E.coli bacteria as a part of the FC group, the counts of coliforms in water and sediment samples, in general, were in the order EC > TC > FC (Table 3 and Fig. 5). The difference between agricultural and protected area wetlands for the density of E.coli and Pseudomonas spp. were not significant. This would compromise their use as indicators of fecal contamination, as other studies suggested since they have been found in pristine natural subtropical environments (Desmarais et al., 2002; Fish & Pettibone, 1995) and the evidence that E. coli survive and persist for longer times associated with algae and fungi in freshwater, soil, and sediments (Byappanahalli et al., 2006; Ksoll et al., 2007; Power et al., 2005; Solo-Gabriele et al., 2000).

Table 3

Microbiological indicators count of water and sediments of the studied wetlands. The values are expressed in CFU/100 mL. No growing colony is represented as < 1.
Wetland		Compartment	Total Coliforms	Fecal Coliforms	Escherichia coli	Pseudomonas spp.
IT-12		water	< 1	200	450	80
		sediment	1,300	< 1	< 1	10,700
IT-14		water	400	< 1	400	< 1
		sediment	600	60	< 1	< 1
IT-15		water	200	1,000	< 1	< 1
		sediment	20	260	30	< 1
YR-16		water	3,400	600	25	< 1
		sediment	30	0	40	160
YR-17		water	21,000	200	100	< 1
		sediment	400	40	< 1	1,660
YR-18		water	200	300	20,000	20,000
		sediment	320	< 1	< 1	< 1
LI-20		water	900	600	600	210
		sediment	11,600	5,300	100	19,800
LI-21	water		< 1	600	2,900	< 1
	sediment		12,800	< 1	20,000	340
LI-22	water		400	180	140	230
	sediment		23,000	60	20,000	20,000
MB-34	water		600	4,800	6,200	2,000
	sediment		660	< 1	< 1	20,000
MB-35	water		< 1	9,600	15,000	4,200
	sediment		< 1	400	20,000	1,700
MB-36	water		1,900	1,400	2,000	1,720
	sediment		1,100	200	600	20

Comparing bacterial counts in water and sediment (Fig. 5), we observed higher FC counts in water with a mean of 3,729 CFU/100mL and sediment samples with 1,993 CFU/100mL. This suggests that in wetland water samples, the decay rates of FC were lower compared to sediments, contrary to the observations for general freshwater systems (Craig et al., 2004). For Pseudomonas spp. we found higher counts in sediment with violet, green and orange colonies in cetrimide agar, with a mean of 6,198 CFU/100mL; on the other hand, in water samples, the colonies were mainly green with a mean of 2,370 CFU/mL.

Finally, the analysis of presence of the group of organophosphorus and carbamate pesticides in water and sediment samples, evidenced the absence of pesticides in water samples and the presence in the 100% sediment samples in both groups of wetlands. As sediment reflects pesticide long term contamination, (Peris et al., 2022), it is possible that wetlands in agricultural and protected areas in this study were under chronic pressure of pesticides.

In this study, we assessed wetland water quality conditions using pH, turbidity, total phosphorus, and bacterial indicators of 12 natural wetlands located in protected areas or in the border of cropped lands in the Paraguayan side of the watershed od Parana River, next to the Itaipu dam binational reservoir shared between Paraguay and Brazil.

The agricultural wetlands presented more acidic pH values (mean pH values of water and sediment of 5.59 and 5.58, respectively); than the wetlands in protected or forest areas; sediment pH values were neutral or circumneutral. This acidic trend in agricultural wetlands may affect phosphorus concentration as P solubility as we registered higher TP values in agricultural wetlands, with a mean of 0.14 mg/L compared to wetlands located in protected areas with a mean of 0.06 mg/L. In addition, water TP concentrations were higher than 0.1 mg/L in LI-22, and YR-16 with 0.46 and 0.11 mg/L, respectively, both surrounded by agricultural land uses.

Considering water turbidity values, we propose that wetlands in protected areas have an essential role in sediment buffering, reducing the amount of suspended sediments entering the reservoir. Agricultural wetlands presented higher and variable values (mean 425 NTU) than wetlands in protected areas (mean 34 NTU). Also, TP in water decreases in connected wetlands as long as the nutrient flows through the wetlands system to the reservoir; from IT-12 (0.1 mg/L) to IT-15 (0.03 mg/L) the TP concentration decreased 70% and the turbidity decreased from 112 to 42,6 NTU.

This study observed a high degree of variability of bacterial indicators in natural wetlands investigated. The counts of coliforms in water and sediment samples, in general, were in the order EC > TC > FC. At the same time, it is important to consider that TC and FC counts may be hindered by heterotrophic bacteria in plate counts (Amanidaz et al., 2015). High variability between water and sediment samples was observed probably due to multiple contributing factors, including patchy distribution of bacterial organisms in sediments and difficulty in dissociating bacteria from sediment particles (Anderson et al., 2005). In addition, responses to wetland type (lacustrine and palustrine) and surrounding land use (agricultural and protected area) varied within and between bacterial indicator groups. This compromise their use as indicators of fecal contamination, as other studies suggested since they have been found in pristine natural subtropical environments (Desmarais et al., 2002; Fish & Pettibone, 1995). These results show the difficulties encountered in finding the utility of common water bacterial indicators to a dynamic, varied wetland ecosystem.

Long term contamination by organophosphorus and carbamate pesticides was pointed by the positive results in 100% of the sediment samples in both groups of wetlands.

Summarizing, natural wetlands in protected areas presented lowest values of TP, turbidity and circumneutral pH values, bacterial indicators varied widely, and it is necessary to stablish a long monitoring program to adopt adequate bacterial indicators for this dynamic ecosystem. As far as we can conclude based on the results, natural wetlands have a key function in ecosystem function, health, preserving the quality of water that enters to the reservoir. Protected areas also have a great impact as wetlands presents better water quality conditions in terms of TP, turbidity, and bacterial indicators.

Acknowledgments

We thank Carlos José Flores and Rubén Caballero, from the Environment Superintendency and Protected areas Division of Itaipu Binacional – for supporting and promoting research in the Paraguayan side of Itaipu Reservoir to HydroGIS Environmental Consulting through the person of Gustavo Bareiro for geoprocessing the data, designing the maps and conducting sampling planning.

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Financing This research was supported by the Water and Sediments laboratory of the Reservoir Division of Itaipu Binacional.

Competing Interests The authors have no relevant financial or non-financial interests to disclose.

Author contributions GSB and LIG analyzed data, designed research, and wrote the manuscript. AV, KM, RC, and GV conducted experiments. GSB, LIG, SMG, and PS analyzed data and revised the manuscript. FN and LM designed and conducted sampling and revised the manuscript. GB geo-processed the data and designed the maps. ACG revised the manuscript.

Data Availability All data generated or analyzed during this study are included in this publication.

Ethical Approval Not applicable

Table S1 not available with this version.

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Graphical abstract

Natural wetlands in protected areas as a key to water quality resilience

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Abstract

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Highlights

1. Introduction

2. Materials And Methods

3. Results And Discussion

4. Conclusions

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Acknowledgments

References

Additional Declarations

Supplementary Files

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