water Article
Ecosystemic Assessment of Surface Water Quality in the Virilla River: Towards Sanitation Processes in Costa Rica Leonardo Mena-Rivera 1, *,† ID , Oscar Vásquez-Bolaños 2,† , Cinthya Gómez-Castro 3 , Alicia Fonseca-Sánchez 2 , Abad Rodríguez-Rodríguez 4 and Rolando Sánchez-Gutiérrez 1 1 2
3 4
* †
Water Resources Management Laboratory, School of Chemistry, Universidad Nacional, Heredia 83-3000, Costa Rica;
[email protected] Laboratory of Environmental Hydrology, School of Biological Sciences, Universidad Nacional, Heredia 83-3000, Costa Rica;
[email protected] (O.V.-B.);
[email protected] (A.F.-S.) Empresa de Servicios Públicos de Heredia S.A., Heredia 40301, Costa Rica;
[email protected] Laboratory of Microbial Biotechnology, School of Biological Sciences, Universidad Nacional, Campus Omar Dengo, Heredia 83-3000, Costa Rica;
[email protected] Correspondence:
[email protected]; Tel.: +506-2277-3824 These authors contributed equally to this work.
Received: 14 May 2018; Accepted: 1 June 2018; Published: 26 June 2018
Abstract: Water quality information is essential supporting decision making in water management processes. The lack of information restricts, at some point, the implementation of adequate sanitation, which is still scarce in developing countries. In this study, an ecosystemic water quality assessment was conducted in the Virilla river in Costa Rica, in a section of particular interest for future sanitation development. It included the monitoring of physical, chemical, microbiological and benthic macroinvertebrate parameters from 2014 to 2016. Mutivariate statistics and water quality indexes were used for data interpretation. Results indicated that water quality decreased downstream towards more urbanised areas. Particularly, extreme values of phosphorous, nitrogen and E. coli were found. Sample sites were grouped in two clusters, which were consistent with land use. Benthic macroinverterbrates diversity was predominantly represented by Baetidae, Chironomidae, Leptohyphidae, Hydropsychidae, Simuliidae and Physidae. They were mostly influenced by water temperature, nitrite, ammonium, soluble reactive phosphorous, total solids, alkalinity, nitrate and total suspended solids. Three water quality indexes consistently showed the poor condition of the water body. The overall results indicate that the main sources of pollution in the river are likely to be wastewater discharges. Thus, special efforts should be undertaken regarding its regulation in the country. Keywords: macroinvertebrates; management; monitoring; sanitation; water quality
1. Introduction Rivers are an important source of aquatic biota and water for human development. They provide essential resources for recreation, tourism, human water consumption, agriculture, electricity generation and industry [1,2]. However, riverine systems have been constantly modified by human activities [3], causing the alteration of the hydrological cycle and the degradation of their water quality at both a local or regional scale [4]. Whereas natural processes such as erosion, soil mineralisation and meteorological conditions, eventually impact surface water quality; the major impact on its
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degradation is due to anthropogenic activities such as the excessive use of pesticides and fertilizers, alteration of land use and untreated wastewater discharges from industries and houses [5,6]. Untreated wastewater discharges are the main source of surface water pollution in urban areas [7–10]. They reduce the quality of the water body and stimulate the proliferation of pathogenic organisms that can cause severe diseases concerning public health [11–13]. Its collection, transport, treatment, disposal and reuse are taken into account in the framework of sanitation according to the United Nations and the World Health Organisation. In addition, the provision of adequate treatment for the disposal of urine and human faeces is considered a human right [14,15]. Despite this, there remain countries, in particular developing ones, where access to sanitation is limited [16–18]. Central American countries face substantial challenges regarding water and sanitation. In Costa Rica, for example, 76% of houses use septic tanks and only 22% are connected to sewerage; but only 8.2% of the wastewater is treated before being discharged into the rivers [19]. The effect of this lack of wastewater treatment in the riverine ecosystem could be even worse in areas with accelerated socio-economic development [2]. One of these areas is the Virilla river catchment, which drains the Greater Metropolitan Area (GAM) and receives approximately 67% of the wastewater discharges of the country [15]. The GAM corresponds to only 4% of the Costa Rican territory but its population density is nearly 1200 hab km−2 . It also contains the largest sector of industrial and commercial activities in the country [15]. To reduce the potential impact of these activities in the environment, implementation of new legislation and environmental programs have been undertaken during the last years [19,20]. However, the success of these policies is difficult to estimate, due to the functions overlapping across different institutions and the lack of accurate information about the ecological status of the water bodies [17,19,20]. Notably, information about the surface water bodies is essential regarding control of pollution and the application of mitigation strategies. These networks are useful in providing reliable information to better understand temporal and spatial changes in water quality and supporting integrated water management processes [17,21]. But only a few studies have been reported in the country and water monitoring networks are scarce [22–26]. Water quality in rivers can be estimated using physical and chemical characteristics or macro and micro biological indicators [22,23,27]. The category and number of such indicators are not generally uniform among similar studies and its selection depends on the objectives and financial resources of the monitoring program. This makes difficult the comparison among different studies and different disciplines are rarely integrated together. One approach oriented to simplify this is the water quality index; which takes into account the value of certain parameters in an overall water quality score, through the estimation of a relative weight of each parameter [28,29]. However, there is still uncertainty related to the selection and weight of the parameters. Thus, there is an interest in more holistic approaches, which will provide better and integrative perspectives of the riverine ecosystem status [30]. This study presents results of an holistic integrative approach to surface water quality assessment in the Virilla river catchment in Costa Rica, where sanitation mitigation measures will be developed. Nevertheless, there is not enough background information about the water quality of this area in general. The ecosystemic approach presented here includes physical, chemical, microbiological and benthic macroinvertebrate data; which are interpreted using land use information, multivariate statistics and water quality indexes. This information is useful to better understand the water quality status in the Virilla river catchment; and therefore, to generate evidence-based mitigation strategies in the near future. Finally, this information will provide a surface water quality background in Costa Rica for further implementation of sanitation processes in the country.
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2. Materials and Methods 2.1. Study Area This study was developed in the Virilla river catchment in Costa Rica, between the longitude 84◦ 100 4800 and 84◦ 020 3800 , and the latitude 9◦ 590 3000 and 9◦ 570 2800 (see Figure 1). The Virilla river flows from the north-east Central Volcanic range of the Central Valley in Costa Rica, to the south-west Pacific region; where it confluences with the Grande river and forms the Grande de Tárcoles river. The covered area includes a section of approximately 20 km of the river from the city of San Miguel to San Antonio, both of the Heredia providence. This section is remarkably important because it will be directly impacted by the implementation of a sewage treatment plant in the upcoming years. In this area, the climate is characterised by a dry season (December to March) and rainy season (May to October) regarding April and November as transition months. During the study period, the average monthly precipitation was 148 mm and air temperature ranged from 17.7 ◦ C to 24.8 ◦ C with an average of 21.4 ◦ C. The elevation gradient was 277 m ranging from 1161 m to 884 m. This area is classified as premontane wet forest zone with irregular relief and soils predominantly vertisols. Land use categorisation (56 km2 ) included forest (4.9%), pasture (14.9%), arable (21.0%), industry (11.5%) and urban (47.7%), and it was generated by the photo-interpretation technique in ArcGIS 10.4.1 (ESRI) at scale 1:5000, using the satellite images Quick Bird II at 0.6 m resolution distributed by Digital Globe R in Google Earth Pro . In this section of the river, there are wastewater discharges from real estate activities (e.g., sewage disposal from condos), from manufacturing industries of concrete, cement and food products (e.g., coffee, beverages and food preservatives). 84°9′36″W
84°6′36″W
84°3′36″W
9°58′48″N
9°58′48″N
9°57′54″N
9°57′54″N
84°9′36″W
84°6′36″W
84°3′36″W Nicaragua
Legend Land use classification (%) Forest 4.9 Industry 11.5 Pasture 14.9 Arable 21.0 Urban 47.7
Costa Rica
Original scale 1:45000 1
0
1
2 km
Study area
Panamá
Sampling sites Rivers Virilla river Streets Contour lines every 50 m
Projection: WGS 84
Figure 1. Study area in the Virilla river sub-catchment: including sample sites and land use.
2.2. Sampling and Methods Water samples were collected at eight sample sites, every two months, from October 2014 to March 2016 (n = 71). They were collected using high-density polyethylene and glass bottles previously washed with hydrochloric acid 3% m/v and de-ionised water. Samples were then stored at 4 ◦ C and delivered to the laboratory within 6 h of collection. Microbiological samples were collected in 100 mL sterile vessels and stored separately. All samples were analysed using the procedures of the Standard Methods for the Examination of Water and Wastewater [31]. Temperature, dissolved oxygen (DO), pH and conductivity were determined in situ using a field meter Oakton 300 (Vernon Hills, IL, USA) and a Thermo Orion Star A222 (Chelmsford, MA, R USA). An aliquot of each water sample was filtered through 0.45 µm pore filter (Advantec GC-50) for analysis of total dissolved solids (TDS), total suspended solids (TSS), ammonium, nitrite and
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soluble reactive phosphorous (SRP). Alkalinity was measured by titration using a sulphuric acid standard solution. Total solids (TS), TDS and TSS were determined by gravimetry at 105 ◦ C, 180 ◦ C and 105 ◦ C, respectively. Nephelometry was used to analyse turbidity (Oakton Inst. T100, Vernon Hills, IL, USA). Biochemical oxygen demand (BOD) was determined using the 5-days test and the modified Winkler method. Ammonium was measured using the indophenol blue reaction at 640 nm and nitrite was colorimetric determined at 543 nm. Total phosphorous (TP) and SRP were analysed spectrophotometrically by the stannous chloride method after the application of the persulfate digestion procedure for TP and after filtration for SRP. All spectrophotometric analyses were carried out in a Thermo Aquamate 2000E (Cambridge, UK). Fluoride, chloride, nitrate and sulphate were analysed by ion chromatography (Dionex ICS-5000, Sunnyvale, CA, USA). Finally, total coliform (TC) and Escherichia coli were determined by the multiple tube fermentation technique using the R Fluorocult medium and 24–48 h of incubation at 37 ◦ C. The microbial population was estimated using the table reported by Woomer [32]. The sampling of benthic macroinvertebrate community was undertaken in the water body in safe and accessible sites, on the same day as water sample collection, from February 2015 to March 2016 (n = 49). Sample collection and preservation were achieved according to the methods described by Springer et al. [33]. In brief, composite samples were collected using a D network (500 µm mesh) placed opposite to the water direction flow; while the substrate was gently moved for approximately five minutes in order to collect the maximum amount of macroinvertebrates possible. This procedure was repeated three times in different points around each sample site (e.g., upstream and downstream) for a total of 15 min of effort per site. An initial selection was made in the field where macroinvertebrates were picked live and preserved in ethanol 70% m/v. In addition, samples were stored in plastic bags with ethanol 95% m/v and delivered to the laboratory for a more extensive selection. Macroinvertebrates were processed, classified and quantified as families using a stereoscope according to the taxonomic guidelines established in the Costa Rican surface water legislation [34]. 2.3. Data Analysis Data analysis, including non-parametric survival methods and ordination exploratory analysis, were carried out in R statistical package using NADA and vegan libraries [35–37]. Analysis of data with values below the quantification limit (
