Abundance and diversity of black flies ( Diptera : Simuliidae ) in rivers of the Andean Eastern Hills of Bogotá ( Colombia ) , and its relationship with water stream physicochemical variables

Black flies are abundant benthic organisms in well-oxygenated running water and are considered effective bioindicators of water quality. Information on the ecology of these organisms at the species level is important, since up to now information has mainly been available on a family level. The aim of this study was to evaluate the composition of black flies and their relationships to a group of physical and chemical factors in four small rivers of the Eastern Hills around Bogotá, Colombia. These headwaters are protected by the Empresa de Acueducto y Alcantarillado de Bogotá. Black fly larvae and pupae were collected during four sampling periods during the dry season to the early rainy season of 2012. Multivariate methods were used to determine the presence of each species in relation to dissolved oxygen, nitrates, pH, temperature, and water velocity. PCA ordination revealed a physicochemical environment with a tendency towards a certain homogeneity in the four rivers studied. The DCA ordination confirmed that in La Vieja River the G. ortizi complex dominated while S. muiscorum was dominant in the other three rivers. Similarly, according to the NMDS, the composition of black flies in Arzobispo and Chorro de Padilla rivers was similar, while that of El Delirio and La Vieja rivers were different, especially in this last river. The rivers had low species richness (four species and one species complex). Simulium muiscorum was negatively correlated with dissolved oxygen, temperature and current velocity while S. ignescens was associated with slightly more oxygenated waters and S. furcilatum with faster currents. The low species diversity and richness for the four rivers is consistent with previous reports of low Neotropical diversity of black flies. Results showed that simuliid species could possibly be good indicators of the environmental conditions of Eastern Hills rivers around Bogotá.


Introduction
Simuliids, known generally as "black flies" in English and "jejenes" in Spanish, are widely distributed in streams and rivers worldwide from sea level to altitudes of 5 000 m (Coscarón & Coscarón-Arias 1995, Adler et al. 2004, Adler & Crosskey 2017).A total of 2 204 extant species of black flies are known to science (Adler & Crosskey 2017) of which 74 have been recorded in Colombia (Moncada-Álvarez et al. 2017).Black flies are often the dominant form of secondary productivity in boreal lotic ecosystems (Malmqvist et al. 2004, Currie & Adler 2008).Due to their activity as filter feeders, these aquatic dipterans play a fundamental role in the transfer of energy from fine p articulate o rganic m atter t o p redators, r epresented by other macroinvertebrates and fish.They also are important in the supply of larger particles via their feces to a broad spectrum of deposit-feeding detritivores (Wallace & Webster 1996).Simuliid larvae typically are associated with well-oxygenated waters, although certain species can be found at low concentrations of dissolved oxygen (Welch & Tindell 1992).Consequently, the immature stages can be useful bioindicators of water quality (Martínez & Portillo 1999, Carle et al. 2015).However, few ecological studies of black flies have addressed taxonomic resolution to the species level (McCreadie & Adler 2008), and this has hindered a more accurate use of these organisms as bioindicators.
Most ecological studies of black flies have been conducted in Nearctic and Palearctic regions (Figueiró & Gil-Azevedo 2010, Figueiró et al. 2014).In the Neotropical region, ecological studies have mostly been carried out in Brazil, especially at low elevations (Hamada & McCreadie 1999, Hamada et al. 2002, McCreadie et al. 2005, Figueiró et al. 2006, 2008, 2012, Landeiro et al. 2009, Dos Santos et al. 2010, Couceiro et al. 2014, Docile et al. 2015), with some studies in Venezuela (Grillet & Barrera 1997).In Ecuadorian highland Andean streams the simuliids are one of the four most abundant families during both the wet and dry season (Jacobsen et al. 1997, Jacobsen & Encalada 1998), and one of the most abundant groups when riparian coverings are forests and pastures (Iñiguez-Armijos et al. 2016).These studies and other published on macroinvertebrates in Neotropical high mountain rivers only refer to the simuliids as a family without sufficient ecological information on the species.
In Colombia most simuliid literature is taxonomic (Adler & Crosskey 2017).Early ecological notes were recorded for Colombian black fly s pecies in the Sierra Nevada de Santa Marta (Lewis & Lee-Potter 1964).Bueno et al. (1979) published some ecological annotations for Simulium (Hemicnetha) muiscorium.An analysis of historical ecology of the Central and Eastern Cordilleras in Colombia revealed an elevational species gradient in which the lower areas correspond to the oldest regions with the most primitive species (Muñoz & Miranda-Esquivel 1997).Reports of the presence and abundance of black flies in the Fucha River (a stream of the Eastern Hills of Bogotá) were based on limited environmental observations (Restrepo & Rincón 2009), while a few ecological notes were presented for oviposition behavior of Simulium dinellii (Mantilla et al. 2015).Some studies have addressed the medical importance of simuliids as vectors of onchocerciasis in Colombia (Tidwell et al. 1980, Corredor et al. 1998), the transmission of which is currently eradicated from Colombia (WHO 2013).Other reports have dealt with the role of these dipterans in bird diseases (Lotta et al. 2016).
Simuliid species of the temperate zones, as well as species from lower elevations in Neotropical regions are different from those reported in the Colombian Andean region (Moncada-Álvarez et al. 2017).Therefore, one would expect that on a species level, ecological responses of high mountain river taxa in Colombia are different.A study of bioindication in Brazil showed that Simuliidae species were present in streams with intermediate urban pollution impacts, but absent in heavily impacted sites (Docile et al. 2015).These authors suggested that some species were associated with more pristine breeding sites, while others might be good bioindicators of moderately impacted streams.However, the Brazilian species are different from those found in Colombian waters, so it is necessary to study the native Colombian black fly fauna to know their responses to environmental variables.
The majority of the watercourses in the upper basin of the Bogotá River are used for agricultural, domestic, and industrial purposes.The Arzobispo, Chorro de Padilla (also known as San Francisco), La Vieja, and El Delirio (also known as La Osa) rivers have their upriver areas protected by the Empresa de Acueducto y Alcantarillado de Bogotá (EAAB), and these rivers eventually feed into the Bogotá River.Since, small, highland streams and rivers can influence limnological processes in lower reaches of the Andean basins (Allan et al. 2006), a long-term biomonitoring and environmental assessment of these watercourses is required to account for the impact imposed by anthropic practices.Given the potential value of black flies as bioindicators of water quality, knowledge about their biodiversity and relative abundance could facilitate the conservation of riverine ecosystems, essential for the maintenance of the urban lotic environment and water reserves for cities like Bogotá.Therefore, in the present study the relationship between water stream physical and chemical factors and the presence of black fly species was investigated in four streams of the Bogotá River watershed.This allows to explore the capability of simuliids as indicators of water quality.

Study area
The study area lies within the watershed of the Bogotá River, which has four sub-basins: Teusacá, Juan Amarillo (Salitre), Fucha, and Tunjuelito.The streams and rivers of these sub-basins run through the Eastern Hills around Bogotá before entering the urban area, which lies in an extensive, high montane valley at about 2 600 m above sea level.Sampling sites were in three rivers of the Juan Amarillo river basin-Arzobispo, Chorro de Padilla (San Francisco), and La Vieja-and one river of the Fucha river Basin-El Delirio (La Osa) (Fig. 1).The list of environmental features of each sampled river is presented in Table .1.

Sampling
Each river was sampled four times, twice during the rainy season (March and April) and twice during the beginning of the dry season (May and June) in 2012.A total of 16 samples per river were taken during the study.In each river a sampling section of 30 m including a combination of pools and riffles was randomly established.The same sampling section of each river was visited during the dry and rainy seasons.In each of these sections two people collected simuliid immature states during two hours of effort for a total of four hours per sampling.Abundance data were reported as number of individuals captured during these four hours.Forceps were used to manually collect simulliid larvae and pupae from available substrates (stones, rocks, pieces of wood, leaves, cloths, plastics) along the established sampling section of each river.No adults were collected because they were absent during the sampling periods.Specimens were fixed in 70 % alcohol and transported to the Medical Entomology Laboratory at Universidad Nacional de Colombia (LEMUN) for identification using taxonomic keys by Muñoz et al. (1984), Muñoz & Coscarón (1999), Hamada & Grillet (2001), Shelley et al. (2004), andCoscarón &Coscarón-Arias (2007).Species identification was completed shortly after collection.The following physicochemical variables were measured in situ with a water sample from the stream surface: water temperature and pH were recorded with a potentiometer Schott R HandyLab; and nitrates and dissolved oxygen were assessed with Aqua-Merck R kits.In addition, water velocity was determined following the floating-object method reported by Hauer & Lamberti (2007).

Data analysis
The following ecological indices were calculated: the Shannon-Weaver diversity (natural logarithm), Simpson dominance, and Pielou's equitability (i.e.evenness) indices.To examine the differences of the physical, chemical and biotic variables between the rivers, the nonparametric variance analysis of Kruskal-Wallis was applied to the data.Subsequently, post-hoc pairwise comparisons, based on the Tukey-Kramer test, were performed to establish the set of data that produced the differences.A principal component analysis (PCA) was then performed to inspect the relation among physicochemical variables coupled to a detrended correspondence analysis (DCA) to explore the spatial-temporal organization of species.Two nonmetric multidimensional scaling (NMDS) analyses were performed, one for species and another for environmental variables.For all these ordination procedures, data were square root-transformed due to small sample sizes and to reduce statistical biases.Non-parametric Spearman correlations were calculated to examine the statistical relationship between abiotic factors and taxon abundance using data of the 16 sampling cases.The similarity of the sampling sites was determined based on simuliid composition, using a Bray-Curtis similarity cluster analysis.All statistical analyses were conducted with the PAST program, version 3.18 (Hammer et al. 2001), and species accumulation curves were computed with the EstimateS program (Colwell & Elsensohn 2014), using the nonparametric estimators Chao1 (abundance) and Chao2 (incidence).
Simulium muiscorum was the most abundant taxon in all rivers (68.6 % of the total relative abundance) excluding La Vieja, where it was absent in all sampled months but May.Gigantodax cervicornis was the least abundant species (0.13 %) and was found only in La Vieja in June (Fig. 2).According to the Kruskal-Wallis analysis the abundances of S. muiscorum and the G. ortizi complex were significantly different between rivers (H = 10.3, p = 0.02, H = 9.7, p = 0.02).The Tukey-Kramer test indicated that La Vieja River was the stream that accounted for this difference.There were no significant differences in the abundances of simuliid species between climatic seasons (H = 1.9, p = 0.2).
The obtained species accumulation curves, based on 16 samples and 5 taxa, were asymptotic for the Chao 1 and 2 estimators (Fig. 3), showing that all species of black flies present probably were collected.Thus, the estimators suggested that the sampling program had 100 % efficiency, both in numbers of individuals of each taxon (Chao 1) and as species richness (Chao 2).

Species number
Chao 1 Chao 2 a slightly faster water velocity.El Delirio had the lowest pH and nitrates.
Abiotic variables had values with no significant differences between the rivers, but during the dry period temperature was statistically higher (H = 5.1, p = 0.02) (11.5 • C in dryness vs. 10.4 • C in rains) and water velocity faster (H = 6.1, p = 0.01) (1.65 m s −1 in dryness vs. 1.07 m s −1 in rains).
PCA analysis on abiotic variables showed that principal component (PC) axis 1 explained 41.98 % of the total variability and PC axis 2 explained 27.53 % (Fig. 4).The cumulative explanation for the two components was near 70 % of all variation among physicochemical data.The PC axis 1 was associated mainly with pH and dissolved oxygen and the PC axis 2 with nitrates.Arzobispo river in May and June was related with stream velocity and temperature, parameters that had high scores with axis 1 (0.41 and 0.46, respectively).Oxygen and pH were associated with El Delirio river in June (scores with axis 1: 0.55 and 0.57 respectively) and nitrates with La Vieja and Chorro de Padilla rivers in May (score with axis 2: 0.6).The other sites and samples did not show a clear relation with the physicochemical variables.The DCA (Fig. 5) with a high eigenvalue of 0.532 on the first axis and a minor value of 0.147 on the second axis, indicated that La Vieja was characterized by the presence of the G. ortizi complex and that Arzobispo and Chorro de Padilla shared a predominance of S. muiscorum.The NMDS analysis for species with a stress value of 0.08, indicated that the composition of black flies in Arzobispo and Chorro de Padilla was similar (Fig. 6A).In contrast, the simuliid fauna of La Vieja was distinct, and in El Delirio simuliids also showed some degree of segregation (except in June).The NMDS analysis for environmental variables (with a stress value of 0.03) split data into two groups.
One such group encompassed all April samplings with a handful of samplings across sites and months (Fig. 6B, right hand side cluster  The abundance of S. muiscorum was negatively correlated with dissolved oxygen (r = −0.6,p = 0.02, n = 16), suggesting an increase in abundance in less oxygenated waters.In contrast, S. ignescens abundance correlated positively with oxygen (r = 0.6, p = 0.02, n = 16); S. ignescens tended to be slightly more abundant in more oxygenated waters.S. muiscorum also correlated negatively both with temperature (r = −0.5, p = 0.04, n = 16) and stream velocity (r = −0.6,p = 0.02, n = 16).Abundance of S. furcilatum was directly correlated with stream velocity (r = 0.5, p = 0.04, n = 16), but the correlation between abundance of the entire simuliid community and water velocity was negative (r = −0.8,p < 0.05, n = 16).The mean species number per river on each sampling date was 1.8 -2.5.The low equitability (< 0.5) of the sampled rivers confirmed the dominance of some taxa (S. muiscorum and G. ortizi complex) over others.Shannon-Weaver diversity index had in general low values and was highest in El Delirio (0.86 nats) and lowest in Chorro de Padilla (0.14 nats) (Fig. 7A).In El Delirio, Simpson's dominance index was low, and equitability was high, whereas in La Vieja, the converse was observed (Figs.7B and 7C).

Discussion
Ecological studies of black flies in much of the Neotropical Region are scarce, often addressing these dipterans at the family level and occasionally at the genus level (Prat et al. 2009).Ecological responses, however, are typically species-specific or even population-specific.The family Simuliidae is well known for its cryptic species (Adler et al. 2010, Conflitti et al. 2015).The inability to reliably distinguish nominal species of the G. ortizi complex potentially limits not only high values of diversity, but also it limits the possibility of establishing the responses of each species to environmental variations.We suggest the capture of adults or raising pupae to improve taxonomic identification.Other tools, such as molecular and cytogenetic techniques, and obtaining pharate adults should be used to correctly identify the species from the G. ortizi complex.
The rivers of the Eastern Hills of Bogotá have few simuliid species (a total of 5), with Simulium species being more abundant in the central (Arzobispo) and southern (Chorro de Padilla, El Delirio) rivers, and the Gigantodax species predominating to the north (La Vieja river).Also, a low number of simuliid taxa ( 7) have been recorded in watercourses of the municipality of La Calera (Muñoz et al. 1984) et al. 2005).This lower number of species in the rivers of the Eastern Hills around Bogotá may be due mainly to the fact that the G. ortizi complex includes at least three cryptic species.It is probable that once the taxonomic difficulties of this complex are solved the species richness in the area will increase.
Dissolved oxygen, pH, and temperature are physicochemical parameters to which aquatic organisms are sensitive (Roldán & Ramírez 2008).Changes in these parameters in the four rivers of this study are mainly influenced by climatic variation.No industrial pollutants or household wastes are released into these rivers.Rain, however, can carry eroded sediments into the rivers, increasing substances such as nitrates (Roldán & Ramírez 2008).The high prevalence of Gigantodax in La Vieja could indicate that species of this taxon have some preference for the slightly more acidic waters of this river.This assumption, however, requires further testing, both in the field and in the laboratory.Also, it is likely that the characteristics of the substrate in La Vieja (cobbles and boulders) favor the establishment of species of this genus.This hypothesis, like the previous assumption, should be studied in future research.
Given the appropriate range of physicochemical factors, biotic factors (e.g., competition) and stochastic factors can also influence species assemblage at a given site (McCreadie et al. 1997).One of the factors influencing black fly diversity is elevation, which is associated with temperature (Srisuka et al. 2015, Ya'cob et al. 2016).The maximum difference in elevation among sampling sites was only 266 m, and it was coupled to a temperature difference of ca. 2 • C.This tem ples in May and June, dur when waters were slightly perature difference was able to differentiate sam ing the transition from the rainy to the dry season, warmer (as the Kruskal-Wallis analysis seems to confirm).
Water velocity influences the abundance of Diptera in Andean rivers (Donato 2008), and often it is correlated with simuliid distribution at various spatial scales (Orth & Maughan 1983, Morin et al. 1986, McCreadie & Colbo 1993).Although stream velocity was uniform across the rivers in this study (Table 2), the differences reflected in the standard deviation were sufficient to cause a reduction in the abundance of the total simuliid community when stream velocity was higher.Remarkably, S. furcilatum seemed to prefer swifter waters, which means that a greater speed seems to favor its abundance.Either way, water velocity can have an important effect on the abundance of these dipterans.S. muiscorum, which predominated in three of the four rivers (Chorro de Padilla, Arzobispo, and El Delirio), tends to have a clumped larval distribution.The individuals' aggregations might allow the larvae to optimize filtering of particulate matter when water velocity increases (Eymann 1991), and perhaps a clumped population offers some protection from predators.However, the negative relationship between the total simuliid abundance and water velocity could mean that not all species are favored by the increase in water velocity.The influence of other physical and chemical variables was weak or not correlated with species abundance, perhaps due to the moderate degree of uniformity in the environmental conditions of all rivers.As previously mentioned, temporal variations in environmental conditions were restricted to temperature and stream velocity and did not significantly influence short-term faunal composition or species distribution.
Diversity indices were low.This is partly due to cryptic speciation in the Simuliidae (Adler et al. 2010;Conflitti et al. 2015).An example of this phenomenon is the G. ortizii complex, which could include three species of this genus in the studied rivers.Another reason for the low diversity values is that only Simuliid taxa were considered.The inclusion of other invertebrate groups would have increased diversity index values.All sampled streams had low equitability (that is, the distribution of individuals between populations was uneven), a clear indication of the trend of dominance of some taxa (mainly S. muiscorum).Research on the Simuliidae by Dos Santos et al. (2010) shows that the dominance in a given region (like the Guaravera river, Paraná State, Brazil) is common.In that basin the authors observed that some simuliids species were much more dominant than others.The Simpson index for El Delirio revealed that in this river species predominance was lowest and at the same time, it was the river with greater equitability, possibly because this is a second-order river (Table .1), namely, with contributions from other streams, that could favor a slightly greater diversity.When observing the physicochemical variables of this river (Table 2), it is feasible to think that its colder, more uniform temperatures (from May-June), more oxygenated and nitrate-low environment could lead to a richer and more diverse assemblage of black flies.Furthermore, it can be hypothesized that the greater richness and diversity observed in El Delirio river is also a reflection of the intense competition for niches and habitats taking place in this river, and this prevents dominance of a single species.
The four rivers are geographically close to one another, and all are located in the same cool temperature zone, with similar elevation, flow, and slope.The rivers in the southern and central sectors of the study area (Arzobispo, In conclusion, the results of this study show that the species of simuliids in the rivers of the Eastern Hills around Bogotá can be potential indicators of the environmental conditions of these lotic ecosystems.In this way, the presence of different black fly taxa of could indicate t he conditions of each river.The present study is preliminary and exploratory, so it would be necessary in future studies to increase the number of river ecosystems and deepen the biota-environmental relationships, including many more variables, especially relating to those of sanitation, such as coliform bacteria, chemical and biological oxygen demands, phosphorus and electrical conductivity, among others. Abundancia y diversidad de moscas negras (Diptera: Simuliidae) en ríos de los Cerros Orientales Andinos de Bogotá (Colombia), y su relación con variables fisicoquímicas de las corrientes de agua Resumen.Las moscas negras son organismos bénticos abundantes en corrientes de agua bien oxigenadas y se consideran bioindicadores efectivos de la calidad de agua.La información sobre la ecología de estos organismos a nivel de especie es importante, ya que hasta el momento, ha estado disponible principalmente solo a nivel de familia.El objetivo de este estudio fue evaluar la composición de moscas negras y sus relaciones con un grupo de factores físicos y químicos en cuatro ríos pequeños de los Cerros Orientales alrededor de Bogotá, Colombia.Estos nacimientos están protegidos por la Empresa de Acueducto y Alcantarillado de Bogotá, Colombia.Se colectaron larvas y pupas de moscas negras a lo largo de cuatro períodos de muestreo, desde la estación seca hasta la estación lluviosa de 2012.Se utilizaron métodos multivariados para determinar la presencia de cada especie en relación con: oxígeno disuelto, nitratos, pH, temperatura y velocidad del agua.La ordenación por PCA reveló un ambiente fisicoquímico con tendencia hacia la homogeneidad en los cuatro ríos estudiados.La ordenación por DCA confirmó que en el río La Vieja dominó el complejo G. ortizi, mientras que S. muiscorum fue dominante en los otros tres.De igual forma de acuerdo con el análisis NMDS, la composición de moscas negras en los ríos Arzobispo y Chorro de Padilla fue similar, mientras que en los ríos El Delirio y La Vieja fue diferente, especialmente en este último.Los ríos presentaron baja riqueza de especies (cuatro especies y un complejo de especies).Simulium muiscorum se correlacionó negativamente con el oxígeno disuelto, temperatura y velocidad de la corriente, mientras que S. ignescens estuvo asociado con aguas ligeramente más oxigendas y S. furcilatum, con corrientes más rápidas.La baja diversidad y riqueza para los cuatro ríos es consistente con reportes previos de baja diversidad neotropical de moscas negras.Los resultados muestran que las especies de simúlidos podrían ser buenos indicadores de las condiciones ambientales de los ríos de los Cerros Orientales de Bogotá.

Ligia I Moncada
Biologist from the Universidad Nacional de Colombia, with a Master's Degree in Microbiology from the same university.She has extensive experience in taxonomy and cytogenetics of Simuliids and other insect vectors of diseases.She is a professor of medical entomology and medical parasitology at the Faculty of Medicine of the Universidad Nacional de Colombia.

Peter H Adler
Biologist from Washington & Lee University, with a Master's degree in Zoology from Pennsylvania State University and a doctorate in Entomology from the same university.He works in ecology of medically important insects, vectors, and pathogens.He is also a world expert in ecology, cytogenetics, and systematics of black flies, and professor and researcher at Clemson University.

Figure 1 .
Figure 1.Location of the sampling points in the rivers studied in the Eastern Hills of the city of Bogotá.

Figure 2 .
Figure 2. Logarithm of the abundance of simuliids (individuals .h −1 ) collected in four rivers of the Andean Eastern Hills around Bogotá, Colombia (March, April, May and June of 2012).

Figure 3 .
Figure 3. Species accumulation curves for simuliids in four rivers of the Andean Eastern Hills around Bogotá, Colombia, 2012.

Figure 4 .
Figure 4. PCA biplot of the physicochemical data for four rivers in the Andean Eastern Hills around Bogotá, Colombia, in 2012.

Figure 5 .Figure 6 .
Figure 5. DCA analysis of samples from four rivers in the Andean Eastern Hills around Bogotá, Colombia, in 2012, based on species abundance.

Figure 8 .
Figure 8. Cluster of similarity (Bray-Curtis index) for four rivers in the Andean Eastern Hills around Bogotá, Colombia, in 2012, based on the composition of the simuliid species.
Palabras clave: bioindicadores; moscas negras; macroinvertebrados; rios; qualidade da água.Alexandra Buitrago-GuacanemeDegree in Biology from the Universidad Distrital Francisco José de Caldas of Bogotá, Colombia.Her studies focus on macroinvertebrates of high mountain rivers.She is currently a doctoral fellow of CONICET at the Institute of Neotropical Biodiversity in Tucumán, Argentina, where she develops research on the distribution patterns of the species of this group, which is vulnerable to climate change.Aura Sotelo-LondoñoDegree in Biology from the Universidad Distrital Francisco José de Caldas of Bogotá, Colombia.She has been a student of the Master's Degree in Infections and Health in the Tropics of the Faculty of Medicine at the Universidad Nacional de Colombia, where she participated in research on taxonomic and ecological aspects of the blackflies.Gabriel A Pinilla-AgudeloBiologist graduated from the Universidad Nacional de Colombia with a Master's Degree in Biology Line Ecology from the same university and a Doctorate in Biology from the Universidad del Valle.He is currently a professor of ecology and limnology at the Universidad Nacional de Colombia, where he develops research on continental aquatic ecosystems.Alexander García-GarcíaDegree in Biology from the Universidad Distrital Francisco José de Caldas of Bogotá, Colombia.Magister in Entomology of the Universidad Nacional de Colombia and professor of the Biology program at the Universidad Distrital Francisco José de Caldas.Currently he is doing postgraduate studies in taxonomy.

Table 1 .
General characteristics of the sites in the rivers studied at the Eastern Hills of the Andes around Bogotá, Colombia, 2012.

Table 2 .
Means (and standard deviations in parentheses) of the measurements of physical and chemical variables of the studied rivers in the Andean Eastern Hills around Bogotá, Colombia (March, April, May and June of 2012) (n = 4 for each variable in each river).