Environ Monit Assess DOI 10.1007/s10661-014-3707-8
Use of multiple indicators to assess the environmental quality of urbanized aquatic surroundings in San Luis, Argentina Mirian R. Calderon & Patricia González & Marta Moglia & Soledad Oliva Gonzáles & Mariana Jofré
Received: 15 July 2013 / Accepted: 5 March 2014 # Springer International Publishing Switzerland 2014
Abstract Urbanization can cause significant changes in the integrity of fluvial ecosystems, which makes it necessary to assess environmental conditions of areas where population growth rates are high. A study of the environmental quality of Chorrillos River (San LuisArgentina) and its tributaries was carried out in order to evaluate the potential effect of an urbanization gradient. Six sites were sampled along the main course and tributaries of the river. Urbanization variables were measured and included to calculate an Urbanization Index. Physical–chemical analyses were performed in water samples to evaluate water quality through the use of a simplified index of water quality (SIWQ). Plants, macroinvertebrates, and amphibians metrics were used to assess the biological state of the studied sites. The Urbanization Index varied significantly between sites M. R. Calderon (*) : M. Moglia : M. Jofré Área de Biología, Departamento de Bioquímica y Ciencias Biológicas, Facultad de Química, Bioquímica y Farmacia, Universidad Nacional de San Luis, San Luis, Argentina e-mail: [email protected] P. González : S. Oliva Gonzáles Área de Química Analítica, Departamento de Química, Facultad de Química, Bioquímica y Farmacia, Universidad Nacional de San Luis, San Luis, Argentina S. Oliva Gonzáles Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina
and was significantly correlated to the SIWQ. However, no significant correlations were found between SIWQ and macroinvertebrates and amphibians variables. Water quality of Chorrillos River and its tributaries is good, but it is affected by anthropic influences as reflected by the declining of SIWQ values. Although biological sampling constitutes an important tool in the assessment of water quality of rivers, in this report biological results were not conclusive. Keywords Urbanization . Environmental conditions . Water quality . River . Bioindicators
Introduction Urbanization is a complex process driven by an increase in human density that causes significant changes in the chemical, physical, and ecological conditions of areas with human development and specifically results in the creation of new land cover and new biotic assemblages (Hamer and McDonnell 2008). Urbanization may cause habitat loss and fragmentation, loss of species diversity, enlargement of impervious surfaces, increase of runoff, and discharges of point or nonpoint source pollution, and it can also promote the establishment of exotic plant and animal species (Faulkner 2004; Longing and Haggard 2010; McKinney 2002, 2006, 2008; Ridley et al. 2005; Sutula and Stein 2003). Therefore, the impacts of urbanization are currently one of the most pervasive causes of natural ecosystem alteration.
Environ Monit Assess
Water chemical quality is the most relevant aspect to measure in order to assess the environmental quality of an aquatic ecosystem. However, the use of biological indicators to evaluate health of aquatic systems represents an important management tool (Zampella et al. 2006). Chemical monitoring cannot provide the sole assessment of the health of an aquatic system, as one of its limitations is that it does not account for many man-induced perturbations, such as flow alterations and habitat perturbation, which impair biological health (Roux et al. 1993). Thus, even when chemical quality monitoring is used, biological monitoring has been recognized as one of the most useful tools in assessing water quality (Muenz et al. 2006). The problems, limitations, and costs of chemical analysis of water, required the inclusion of biological approaches that provide an integrated framework for addressing cumulative and synergistic environmental impacts (Adams and Greeley 2000; Bode and Novak 1995; Metcalfe-Smith 1994; Oscoz et al. 2007; Tercedor 1996). Biological assessments of human and environmental impacts on water quality and aquatic organisms have been used since the early 1900s (Wallace et al. 1996). A bioindicator can be defined as a species or group of species that readily reflects the abiotic or biotic state of an environment and represents the impact of environmental changes on a habitat, community, or ecosystem (Hodkinson and Jackson 2005). A valuable bioindicator provides early warning of natural responses to environmental impacts and allows continuous assessment over a wide range and intensity of stresses, enabling to detect several impacts. It is cost-effective to measure and can be accurately estimated by all personnel involved in the monitoring (Burger 2006; Carignan and Villard 2002). Foremost, a bioindicator must exhibit changes in response to a stressor but not be so sensitive that changes occur when there is no cause for concern (no lasting reproductive, survival, or population effects) (Burger 2006; Carignan and Villard 2002). From all organisms that can be used as bioindicators, macroinvertebrates have often been employed to assess and monitor health in aquatic environments (Canter and Atkinson 2011; Ector and Rimet 2005; Longing and Haggard 2010; Metcalfe-Smith 1994; Muenz et al. 2006; Torralba-Burrial and Ocharan 2007). Macroinvertebrates are considered the most accurate bioindicator as they are resident in aquatic ecosystems during some or all periods of their life histories, and they respond to both short-term episodic events, such as flooding or
toxic discharges, and to longer-term cumulative effects (Stribling et al. 1998). Benthic macroinvertebrates are directly and persistently affected by physical and chemical environmental conditions along streambeds and possess a wide range of sensitivity to pollutants (Longing and Haggard 2010). Another advantage of using macroinvetebrates as bioindicators is that it is possible to calculate quality indices that include metrics such as species richness, as they produce a rapid turnaround of results, and they could be used to assess a wide range of water qualities. Indices also allow the reduction of taxonomic resolution and the use of multiple metrics to calculate water quality values (Resh and Unzicker 1975; Wallace et al. 1996). Amphibians have the highest proportion of species on the verge of extinction among the world’s vertebrates (Stuart et al. 2004). Habitat loss, fragmentation, and degradation, which often result from urbanization, currently impact on the 88 % of threatened amphibians, and they can be considered among the greatest threats to amphibian populations (Hamer and McDonnell 2008). Although their decline may indicate a degradation of environmental health, their role as bioindicators is still under discussion (Muenz et al. 2006; Sewell and Griffiths 2009). Vegetation is directly related to the diversification of the landscape, the regulation of water temperature, the organic material and nutrients input, and it even has the capacity to design microenvironments used by different organisms (Suárez 2002). This is why riparian vegetation composition is a key element in assessing the environmental quality of a river. The province of San Luis, located in central Argentina, is a region with low industrial and agricultural activities. In the central zone of the province, where the capital city of San Luis and the city of Juana Koslay are placed, an acceleration in urban growth has been occurring for the last 10 years. According to the Instituto Nacional de Estadística y Censos (2010), in 2001 the population of Juana Koslay city was 8,689 and the population of the capital city was 162,011. Ten years later, these numbers have risen to 12,467 and 169,947 respectively, which is the equivalent to a 43 % and a 5 % increase. The goal of this study was to assess the environmental conditions of an urban river in the cities of Juana Koslay and San Luis, using physical–chemical analysis of water and benthic macroinvertebrates, anuran amphibians, and riparian vegetation as bioindicators. As the impact of urbanization can be minimized through the early diagnosis of environmental disturbance and health,
Environ Monit Assess
it is crucial to develop this type of study in such vulnerable areas.
Methods
(March 2011). Amphibians were surveyed during two summers (October 2009 to January 2010 and November to December 2010), covering the peak of reproductive activity of the species. Vegetation was surveyed during February and March 2010 and urbanization variables between October 2009 and March 2011.
Study area Urbanization measures The Chorrillos River is located in the Central zone of San Luis, Argentina and has two tributaries, the Cuchi Corral and Las Chacras streams, both regulated systems, whose confluence is located in Juana Koslay city (33° 16′ 59, 32″, 66° 14′ 15, 03″ W). The tributaries and main channel of Chorrillos River run through the semiurbanized areas of Juan Koslay city and urbanized areas of the capital city of San Luis (Fig. 1). After flowing through the city, the river passes through plain areas and, in low-flow periods, its volume decreases considerably, infiltrating into the subsurface about 15 km away from the city of San Luis. The Chorrillos River drains about 42 km southwest of the capital city near Salinas del Bebedero. The Chorrillos River and both of its tributaries do not have big impacts from recreational usage; the urban impacts are more related to pollution load from anthropogenic sources, drainage surface, and domestic wastewater runoff. Six sampling sites along the river and its tributaries were chosen for the study. Two in Las Chacras stream (LCS1 and LCS2), two in Cuchi Corral stream (CCS1 and CCS2), and two in the main course of Chorrillos River (CR1 and CR2) (Fig. 1). LCS1 and CCS1 represented sites with the minor influences of anthropogenic activities; LCS2 and CCS2, located in semiurbanized areas of Juan Koslay city, represented mildly impacted areas; and CR1 and CR2, located in the main course of the river in Juana Koslay city and San Luis capital city, respectively, represented high urban impacts. Sampling regime The sampling strategy was designed to cover a wide range of variables at key sites, which reasonably represented the water quality of the river system, accounting for the tributaries and the drains that may impact downstream water quality (Almeida et al. 2007; Garbagnati et al. 2005). Water samples for physical–chemical analysis and macroinvertebrate samples were collected on high flow periods in 2010 (March 2010) and 2011
To estimate the level of urbanization of each site, the following variables were measured: house density, road density, frequency of domestic animals, urban debris, presence of industries, channelization of the stream, domestic sewage and pipes, road traffic, and noise level, among others. These measures were integrated in an Urbanization Index (Nievas 2011) in order to compare level of urbanization between sites. Road traffic was measured by counting the number of cars and motorcycles traveling along the roads that cross over the river/stream at each site in a period of five minutes. This procedure was performed during the peak of diurnal urban activity (between 12:00 and 13:30) on the same day at all the sites and repeated on seven different working days during the sampling period. Noise levels were measured using a decibel meter DT 805 Sound Level Type II ten times in five minutes. This procedure was performed in coincidence with diurnal road traffic sampling and also during nocturnal amphibian surveys, giving a total of 16 measurements for each site. ANOVA was carried out in order to compare noise level and traffic between sites. Physical–chemical sampling and analytical methods Water samples were taken from two points (a–b) across the river width at all the six sampling sites. Sampling, preservation, and transportation of samples were performed according to Standard Methods for the Examination of Water and Wastewater (APHA 2005). Flow of the streams and the river was calculated by multiplying a cross sectional area by the velocity of water. The cross-sectional area was calculated from measures of width and depth at 30-cm intervals at each cross-stream transect. Water speed was estimated by measuring the time it took a float to travel down an established length on the stream. Water samples were analyzed for 19 variables, including temperature, pH, electrical conductivity (EC), turbidity (Tbd), color (CO), total alkalinity (T-Alk), total
Environ Monit Assess
Fig. 1 Localization of sampling sites at Chorrillos River and tributaries. LCS Las Chacras stream, CCS Cuchi Corral stream, CR Chorrillos River. White dots indicate sampling sites
hardness (T-Hard), dissolved oxygen (DO), 5-day biochemical oxygen demand (BOD), chemical oxygen demand (COD), chloride (Cl−), sulfate (SO42−), nitrate (NO3−), dissolved solids (DS), calcium (Ca2+), magnesium (Mg2+), flouride (F−), organic matter (OM), and total suspended solids (TSS). Water pH, temperature, and EC were measured using a portable meter. All other parameters were determined in the laboratory, following standard protocols (APHA 2005). All the water quality parameters were expressed in milligrams per liter, except pH, and EC (μS cm−1). Analytical quality of data was ensured through careful standardization, procedural blank measurements, spiked and duplicate samples. The ionic charge balance of each sample was within±5 %. Water quality index A simplified index of water quality (SIWQ) (Queralt 1982) was applied. The SIWQ is calculated based on five variables: water temperature, TSS; EC, DO, and COD. For completely contaminated water, this index will be close to 0, whereas for excellent water quality the index will be 100. Biological surveys Vegetation Vegetation was characterized in two plots (100×3 m) positioned adjacent to both sides of the stream in each site. The Zürich-Montpellier (Braun-Blanquet 1928,
1932) method was used to generate phytosociological inventories. Richness of native and exotic vascular plants was recorded, and the tree and herbaceous abundance cover was calculated. The species that could not be identified in the field were taken to the laboratory for taxonomic identification using dichotomous keys.
Amphibians Species richness and relative abundance were estimated from calling and visual encounter surveys. All sites were visited during the same evening-night, ten times through the sampling periods. Anuran calls were recorded for 5 min on each site. The anuran call index proposed by Pillsbury and Miller (2008) was used as an indication of relative abundance, as follows: 0, no individuals of a given species heard; 1, one individual heard; 2, multiple individuals with no overlap in calls; and 3, full chorus. At each site, two encounter survey plots (100×5 m) were installed, one on each side of the stream. After calling registers, observers walked and searched plots at a standard pace using as much time as was needed to examine each area thoroughly. In accordance with NAAMP protocol, surveys were conducted at least 0.5 h after dusk and completed by 01:00 (Weir and Mossman 2005). One-way ANOVA was used to compare maximum monthly call index values between sites. Correlation analysis was employed to evaluate the relationship of richness and call index values (relative abundance) with values of Urbanization Index.
Environ Monit Assess
Macroinvertebrates Benthic macroinvertebrates were sampled during high flow periods in 2010 and 2011, concurrently with water sample collection. Two quantitative samples were collected at each site using a 0.09-m2 area and 300 μm meshed Surber net. Multihabitat samples within the stream channel were composited allowing the comparisons between the different sites. All macroinvertebrate collections were preserved in 70 % ethanol in the field and returned to the laboratory for sorting and identification. All specimens were identified in the laboratory, down to the lower taxonomic level required by the Sierra of San Luis Macroinvertebrates Biotic Index (MBI) (Vallania et al. 1996), which was created to evaluate biological water quality of San Luis rivers using macroinvertebrates as bioindicators. Taxonomic richness and sensibility of taxa are used to calculate the scores of the index, which varies from 4 for extremely contaminated environments to 12 for no contaminated environments. Correlation analysis was performed to analyze the relation between MBI and SIWQ, and MBI and Urbanization Index.
Table 1 Urbanization Index calculated for the sites studied Site
LCS1 CCS1 LCS2 CCS2 CR1 CR2
Urbanization Index 14
14
16
19
22
40
p
Use of multiple indicators to assess the environmental quality of urbanized aquatic surroundings in San Luis, Argentina Mirian R. Calderon & Patricia González & Marta Moglia & Soledad Oliva Gonzáles & Mariana Jofré
Received: 15 July 2013 / Accepted: 5 March 2014 # Springer International Publishing Switzerland 2014
Abstract Urbanization can cause significant changes in the integrity of fluvial ecosystems, which makes it necessary to assess environmental conditions of areas where population growth rates are high. A study of the environmental quality of Chorrillos River (San LuisArgentina) and its tributaries was carried out in order to evaluate the potential effect of an urbanization gradient. Six sites were sampled along the main course and tributaries of the river. Urbanization variables were measured and included to calculate an Urbanization Index. Physical–chemical analyses were performed in water samples to evaluate water quality through the use of a simplified index of water quality (SIWQ). Plants, macroinvertebrates, and amphibians metrics were used to assess the biological state of the studied sites. The Urbanization Index varied significantly between sites M. R. Calderon (*) : M. Moglia : M. Jofré Área de Biología, Departamento de Bioquímica y Ciencias Biológicas, Facultad de Química, Bioquímica y Farmacia, Universidad Nacional de San Luis, San Luis, Argentina e-mail: [email protected] P. González : S. Oliva Gonzáles Área de Química Analítica, Departamento de Química, Facultad de Química, Bioquímica y Farmacia, Universidad Nacional de San Luis, San Luis, Argentina S. Oliva Gonzáles Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina
and was significantly correlated to the SIWQ. However, no significant correlations were found between SIWQ and macroinvertebrates and amphibians variables. Water quality of Chorrillos River and its tributaries is good, but it is affected by anthropic influences as reflected by the declining of SIWQ values. Although biological sampling constitutes an important tool in the assessment of water quality of rivers, in this report biological results were not conclusive. Keywords Urbanization . Environmental conditions . Water quality . River . Bioindicators
Introduction Urbanization is a complex process driven by an increase in human density that causes significant changes in the chemical, physical, and ecological conditions of areas with human development and specifically results in the creation of new land cover and new biotic assemblages (Hamer and McDonnell 2008). Urbanization may cause habitat loss and fragmentation, loss of species diversity, enlargement of impervious surfaces, increase of runoff, and discharges of point or nonpoint source pollution, and it can also promote the establishment of exotic plant and animal species (Faulkner 2004; Longing and Haggard 2010; McKinney 2002, 2006, 2008; Ridley et al. 2005; Sutula and Stein 2003). Therefore, the impacts of urbanization are currently one of the most pervasive causes of natural ecosystem alteration.
Environ Monit Assess
Water chemical quality is the most relevant aspect to measure in order to assess the environmental quality of an aquatic ecosystem. However, the use of biological indicators to evaluate health of aquatic systems represents an important management tool (Zampella et al. 2006). Chemical monitoring cannot provide the sole assessment of the health of an aquatic system, as one of its limitations is that it does not account for many man-induced perturbations, such as flow alterations and habitat perturbation, which impair biological health (Roux et al. 1993). Thus, even when chemical quality monitoring is used, biological monitoring has been recognized as one of the most useful tools in assessing water quality (Muenz et al. 2006). The problems, limitations, and costs of chemical analysis of water, required the inclusion of biological approaches that provide an integrated framework for addressing cumulative and synergistic environmental impacts (Adams and Greeley 2000; Bode and Novak 1995; Metcalfe-Smith 1994; Oscoz et al. 2007; Tercedor 1996). Biological assessments of human and environmental impacts on water quality and aquatic organisms have been used since the early 1900s (Wallace et al. 1996). A bioindicator can be defined as a species or group of species that readily reflects the abiotic or biotic state of an environment and represents the impact of environmental changes on a habitat, community, or ecosystem (Hodkinson and Jackson 2005). A valuable bioindicator provides early warning of natural responses to environmental impacts and allows continuous assessment over a wide range and intensity of stresses, enabling to detect several impacts. It is cost-effective to measure and can be accurately estimated by all personnel involved in the monitoring (Burger 2006; Carignan and Villard 2002). Foremost, a bioindicator must exhibit changes in response to a stressor but not be so sensitive that changes occur when there is no cause for concern (no lasting reproductive, survival, or population effects) (Burger 2006; Carignan and Villard 2002). From all organisms that can be used as bioindicators, macroinvertebrates have often been employed to assess and monitor health in aquatic environments (Canter and Atkinson 2011; Ector and Rimet 2005; Longing and Haggard 2010; Metcalfe-Smith 1994; Muenz et al. 2006; Torralba-Burrial and Ocharan 2007). Macroinvertebrates are considered the most accurate bioindicator as they are resident in aquatic ecosystems during some or all periods of their life histories, and they respond to both short-term episodic events, such as flooding or
toxic discharges, and to longer-term cumulative effects (Stribling et al. 1998). Benthic macroinvertebrates are directly and persistently affected by physical and chemical environmental conditions along streambeds and possess a wide range of sensitivity to pollutants (Longing and Haggard 2010). Another advantage of using macroinvetebrates as bioindicators is that it is possible to calculate quality indices that include metrics such as species richness, as they produce a rapid turnaround of results, and they could be used to assess a wide range of water qualities. Indices also allow the reduction of taxonomic resolution and the use of multiple metrics to calculate water quality values (Resh and Unzicker 1975; Wallace et al. 1996). Amphibians have the highest proportion of species on the verge of extinction among the world’s vertebrates (Stuart et al. 2004). Habitat loss, fragmentation, and degradation, which often result from urbanization, currently impact on the 88 % of threatened amphibians, and they can be considered among the greatest threats to amphibian populations (Hamer and McDonnell 2008). Although their decline may indicate a degradation of environmental health, their role as bioindicators is still under discussion (Muenz et al. 2006; Sewell and Griffiths 2009). Vegetation is directly related to the diversification of the landscape, the regulation of water temperature, the organic material and nutrients input, and it even has the capacity to design microenvironments used by different organisms (Suárez 2002). This is why riparian vegetation composition is a key element in assessing the environmental quality of a river. The province of San Luis, located in central Argentina, is a region with low industrial and agricultural activities. In the central zone of the province, where the capital city of San Luis and the city of Juana Koslay are placed, an acceleration in urban growth has been occurring for the last 10 years. According to the Instituto Nacional de Estadística y Censos (2010), in 2001 the population of Juana Koslay city was 8,689 and the population of the capital city was 162,011. Ten years later, these numbers have risen to 12,467 and 169,947 respectively, which is the equivalent to a 43 % and a 5 % increase. The goal of this study was to assess the environmental conditions of an urban river in the cities of Juana Koslay and San Luis, using physical–chemical analysis of water and benthic macroinvertebrates, anuran amphibians, and riparian vegetation as bioindicators. As the impact of urbanization can be minimized through the early diagnosis of environmental disturbance and health,
Environ Monit Assess
it is crucial to develop this type of study in such vulnerable areas.
Methods
(March 2011). Amphibians were surveyed during two summers (October 2009 to January 2010 and November to December 2010), covering the peak of reproductive activity of the species. Vegetation was surveyed during February and March 2010 and urbanization variables between October 2009 and March 2011.
Study area Urbanization measures The Chorrillos River is located in the Central zone of San Luis, Argentina and has two tributaries, the Cuchi Corral and Las Chacras streams, both regulated systems, whose confluence is located in Juana Koslay city (33° 16′ 59, 32″, 66° 14′ 15, 03″ W). The tributaries and main channel of Chorrillos River run through the semiurbanized areas of Juan Koslay city and urbanized areas of the capital city of San Luis (Fig. 1). After flowing through the city, the river passes through plain areas and, in low-flow periods, its volume decreases considerably, infiltrating into the subsurface about 15 km away from the city of San Luis. The Chorrillos River drains about 42 km southwest of the capital city near Salinas del Bebedero. The Chorrillos River and both of its tributaries do not have big impacts from recreational usage; the urban impacts are more related to pollution load from anthropogenic sources, drainage surface, and domestic wastewater runoff. Six sampling sites along the river and its tributaries were chosen for the study. Two in Las Chacras stream (LCS1 and LCS2), two in Cuchi Corral stream (CCS1 and CCS2), and two in the main course of Chorrillos River (CR1 and CR2) (Fig. 1). LCS1 and CCS1 represented sites with the minor influences of anthropogenic activities; LCS2 and CCS2, located in semiurbanized areas of Juan Koslay city, represented mildly impacted areas; and CR1 and CR2, located in the main course of the river in Juana Koslay city and San Luis capital city, respectively, represented high urban impacts. Sampling regime The sampling strategy was designed to cover a wide range of variables at key sites, which reasonably represented the water quality of the river system, accounting for the tributaries and the drains that may impact downstream water quality (Almeida et al. 2007; Garbagnati et al. 2005). Water samples for physical–chemical analysis and macroinvertebrate samples were collected on high flow periods in 2010 (March 2010) and 2011
To estimate the level of urbanization of each site, the following variables were measured: house density, road density, frequency of domestic animals, urban debris, presence of industries, channelization of the stream, domestic sewage and pipes, road traffic, and noise level, among others. These measures were integrated in an Urbanization Index (Nievas 2011) in order to compare level of urbanization between sites. Road traffic was measured by counting the number of cars and motorcycles traveling along the roads that cross over the river/stream at each site in a period of five minutes. This procedure was performed during the peak of diurnal urban activity (between 12:00 and 13:30) on the same day at all the sites and repeated on seven different working days during the sampling period. Noise levels were measured using a decibel meter DT 805 Sound Level Type II ten times in five minutes. This procedure was performed in coincidence with diurnal road traffic sampling and also during nocturnal amphibian surveys, giving a total of 16 measurements for each site. ANOVA was carried out in order to compare noise level and traffic between sites. Physical–chemical sampling and analytical methods Water samples were taken from two points (a–b) across the river width at all the six sampling sites. Sampling, preservation, and transportation of samples were performed according to Standard Methods for the Examination of Water and Wastewater (APHA 2005). Flow of the streams and the river was calculated by multiplying a cross sectional area by the velocity of water. The cross-sectional area was calculated from measures of width and depth at 30-cm intervals at each cross-stream transect. Water speed was estimated by measuring the time it took a float to travel down an established length on the stream. Water samples were analyzed for 19 variables, including temperature, pH, electrical conductivity (EC), turbidity (Tbd), color (CO), total alkalinity (T-Alk), total
Environ Monit Assess
Fig. 1 Localization of sampling sites at Chorrillos River and tributaries. LCS Las Chacras stream, CCS Cuchi Corral stream, CR Chorrillos River. White dots indicate sampling sites
hardness (T-Hard), dissolved oxygen (DO), 5-day biochemical oxygen demand (BOD), chemical oxygen demand (COD), chloride (Cl−), sulfate (SO42−), nitrate (NO3−), dissolved solids (DS), calcium (Ca2+), magnesium (Mg2+), flouride (F−), organic matter (OM), and total suspended solids (TSS). Water pH, temperature, and EC were measured using a portable meter. All other parameters were determined in the laboratory, following standard protocols (APHA 2005). All the water quality parameters were expressed in milligrams per liter, except pH, and EC (μS cm−1). Analytical quality of data was ensured through careful standardization, procedural blank measurements, spiked and duplicate samples. The ionic charge balance of each sample was within±5 %. Water quality index A simplified index of water quality (SIWQ) (Queralt 1982) was applied. The SIWQ is calculated based on five variables: water temperature, TSS; EC, DO, and COD. For completely contaminated water, this index will be close to 0, whereas for excellent water quality the index will be 100. Biological surveys Vegetation Vegetation was characterized in two plots (100×3 m) positioned adjacent to both sides of the stream in each site. The Zürich-Montpellier (Braun-Blanquet 1928,
1932) method was used to generate phytosociological inventories. Richness of native and exotic vascular plants was recorded, and the tree and herbaceous abundance cover was calculated. The species that could not be identified in the field were taken to the laboratory for taxonomic identification using dichotomous keys.
Amphibians Species richness and relative abundance were estimated from calling and visual encounter surveys. All sites were visited during the same evening-night, ten times through the sampling periods. Anuran calls were recorded for 5 min on each site. The anuran call index proposed by Pillsbury and Miller (2008) was used as an indication of relative abundance, as follows: 0, no individuals of a given species heard; 1, one individual heard; 2, multiple individuals with no overlap in calls; and 3, full chorus. At each site, two encounter survey plots (100×5 m) were installed, one on each side of the stream. After calling registers, observers walked and searched plots at a standard pace using as much time as was needed to examine each area thoroughly. In accordance with NAAMP protocol, surveys were conducted at least 0.5 h after dusk and completed by 01:00 (Weir and Mossman 2005). One-way ANOVA was used to compare maximum monthly call index values between sites. Correlation analysis was employed to evaluate the relationship of richness and call index values (relative abundance) with values of Urbanization Index.
Environ Monit Assess
Macroinvertebrates Benthic macroinvertebrates were sampled during high flow periods in 2010 and 2011, concurrently with water sample collection. Two quantitative samples were collected at each site using a 0.09-m2 area and 300 μm meshed Surber net. Multihabitat samples within the stream channel were composited allowing the comparisons between the different sites. All macroinvertebrate collections were preserved in 70 % ethanol in the field and returned to the laboratory for sorting and identification. All specimens were identified in the laboratory, down to the lower taxonomic level required by the Sierra of San Luis Macroinvertebrates Biotic Index (MBI) (Vallania et al. 1996), which was created to evaluate biological water quality of San Luis rivers using macroinvertebrates as bioindicators. Taxonomic richness and sensibility of taxa are used to calculate the scores of the index, which varies from 4 for extremely contaminated environments to 12 for no contaminated environments. Correlation analysis was performed to analyze the relation between MBI and SIWQ, and MBI and Urbanization Index.
Table 1 Urbanization Index calculated for the sites studied Site
LCS1 CCS1 LCS2 CCS2 CR1 CR2
Urbanization Index 14
14
16
19
22
40
p
