Número 30

Biología Acuática | Número 30: Trabajos completos del VII Congreso de Ecología y Manejo de Ecosistemas Acuáticos Pampeanos (Río Cuarto, 2013)

2026-03-18T18:42:41Z

Edicion de revista VII Congreso de Ecología y Manejo de Ecosistemas Acuáticos Pampeanos (EMEAP) (Río Cuarto, Córdoba, 19 y 20 de septiembre de 2013); Biología Acuática; no. 30 Con mucho agrado ponemos a disposición de la comunidad científica, los artículos completos de los trabajos presentados en el VII Congreso de Ecología y Manejo de Ecosistemas Acuáticos Pampeanos (EMEAP 7), que se realizó el 19 y 20 de septiembre de 2013 organizado por las cátedras de Acuicultura y Ecología de la Facultad de Agronomía y Veterinaria de la Universidad Nacional de Río Cuarto (Argentina). En este evento, que contó con la asistencia de unos ciento sesenta investigadores y alumnos, se expusieron ciento dieciséis trabajos representando a veintiséis universidades e institutos de las provincias de Buenos Aires, La Pampa, Córdoba, San Luis, Corrientes, Entre Ríos y Salta.

En memoria de Víctor H. Conzonno

2019-04-06T20:02:47Z

Contribucion a revista VII Congreso de Ecología y Manejo de Ecosistemas Acuáticos Pampeanos (EMEAP) (Río Cuarto, Córdoba, 19 y 20 de septiembre de 2013); Biología Acuática; no. 30 Víctor H. Conzonno falleció el 3 de febrero de 2014. Cursó sus estudios universitarios en la Facultad de Ciencias Exactas y Naturales de la Universidad de Buenos Aires (UBA), de donde egresó como Licenciado y posteriormente como Doctor en Ciencias Químicas (1996). Su tesis se basó en “Sustancias húmicas solubles presentes en ambientes acuáticos” e inició de esta manera el estudio de la importancia de los ácidos húmicos en los cuerpos de agua pampeanos en nuestro país, siendo un pionero en la temática.

Biotransferencia de flúor de agua a diferentes tejidos de pejerrey (Odontotesthes bonariensis)

2019-04-06T20:03:32Z

Articulo VII Congreso de Ecología y Manejo de Ecosistemas Acuáticos Pampeanos (EMEAP) (Río Cuarto, Córdoba, 19 y 20 de septiembre de 2013); Biología Acuática; no. 30 The presence of fluorine (F), toxic trace element, has relevance in the trophic chain because it can biotrasfer to different levels. It can come from water as food, being chronic ingestion harmful to human beings. Fluorine was found in different water bodies of southwest of Buenos Aires. Chasicó Lake has the highest fluorine concentration. This water body is the most important for commercial and recreational fishing silverside (Odontesthes bonariensis) of the area. The aim of this paper is to analyze the biotransfer of F from water to different silverside tissues in Chasicó Lake. Fish organs were subjected to an alkaline digestion. Fluorine was determined using a fluoride ion selective electrode. F concentrations were 6,4-8,5 mg/L in water and in fish tissues were in gonads: 4,2 to 69,4 μg/g , in liver: 7,1 to 75,3 μg/g , in gills: 49,1 to 110,1 μg/g , in vertebrae: 70,2 to 457,9 μg/g and in muscle: 5,1 to 86,8 μg/g . The concentrations found in muscle were higher than the maximum limit allowable for human consumption, according to CAA (1,5 μg/g). Whereas silverside is a native fish of major commercial importance in Buenos Aires Province, it is important to perform studies on the fluorine concentration to ensure quality for human consumption.

La vegetación de ribera como indicadora de calidad ambiental en ríos serranos de la provincia de San Luis (Argentina)

2019-04-06T20:03:24Z

Articulo VII Congreso de Ecología y Manejo de Ecosistemas Acuáticos Pampeanos (EMEAP) (Río Cuarto, Córdoba, 19 y 20 de septiembre de 2013); Biología Acuática; no. 30 The quality of the rivers can be analyzed using the characteristics of the vegetation of its banks. Nowadays, these habitats are being degraded at an accelerated rate by human disturbance. The aim of this study was to use the riparian vegetation of three rivers of the Sierra de San Luis (Argentina) as an indicator of the quality of aquatic environments. Fourteen phytosociological inventories were conducted in randomly selected sites on the banks of Potrero, El Volcán and El Trapiche rivers. In addition to the inventories, an anthropization index was calculated and a total of 23 alterations were identified. Each of these were assigned a value 0 (zero), 1 (low), 2 (medium) and 3 (high). These values were summed up to obtain a final score for each site. The results indicated that areas with higher anthropization possess a higher richness and coverage of invasive plants species, which are characteristic of disturbed sites. The site with the highest human disturbance was located on the banks of river El Volcán, while the lowest value was found in Potrero river. It can be inferred that invasive plants and the riparian communities’ characteristics are good indicators of the environmental quality of these rivers.

Estudio del fitoplancton aguas arriba y aguas abajo del embalse Casa de Piedra, río Colorado (La Pampa, Argentina)

2019-04-06T20:03:20Z

Articulo VII Congreso de Ecología y Manejo de Ecosistemas Acuáticos Pampeanos (EMEAP) (Río Cuarto, Córdoba, 19 y 20 de septiembre de 2013); Biología Acuática; no. 30 In order to study the phytoplankton composition of the Colorado river, seasonal samples were taken during the period between May 2010 and April 2011. The study area is a natural border basin of the provinces of La Pampa and Río Negro and a transitional basin of Patagonia Argentina without records of previous studies. Selected sampling points are located upstream and downstream of the dam reservoir Casa de Piedra. In this study are presented preliminary results of phytoplankton composition analized in emplaced sites at 38º01’58”S-67º52’90”W to 288 msnm and 38°14’55’’ S-67º11’49’’W to 232 msnm. Samples were collected with plankton net of 20 μm mesh size and physicochemical variables were recorded simultaneously. Phytoplankton samples were observed in vivo and then fixed in 4% formalin and embedded in the herbarium of the SRFA UNLPam. As a result of the qualitative study so far hundred forty-one taxa were reported, of which twenty-nine belong to Cyanophyceae, fourty five to Chlorophyceae and fifty five to Bacillariophyceae. The index of similarity of Bray Curtis with S= 48 separates the sampled sites. The greatest similarity is between summer and autumn of 2011 with S = 66.66. Among the common species of Bacillariophyceae, with Aulacoseira granulata var. angustissima, Melosira varians, Fragilaria crotonensis, Cocconeis placentula var. euglypta, Epithemia sorex, Nitzschia sigma, N. sigmoidea and Cymatopleura solea were the highest percentage of occurrence at the study sites. Our results represent a great advance in the knowledge and distribution of algae in this region of the country.

Evaluación de la capacidad de auto-depuración de un arroyo urbano y el uso de macrófitas nativas como estrategia de restauración

2019-04-06T20:03:15Z

Articulo VII Congreso de Ecología y Manejo de Ecosistemas Acuáticos Pampeanos (EMEAP) (Río Cuarto, Córdoba, 19 y 20 de septiembre de 2013); Biología Acuática; no. 30 Environmental degradation is one of the most serious problems in the metropolitan area of Buenos Aires, especially water pollution. The main aim of this work was to study mechanisms of self-purifying of a segment of San Francisco stream (located in Almirante Brown district), evaluating it in situ capacity of self-purifying downstream of a tubing and, in addition, by static bioassays in a greenhouse with native macrophytes. A stream section of 1500m was sampled twice during autumn 2013. The stream was generally hypoxic throughout the section (DO<2 mg/l), presenting low velocity (0.084 ± 0.008 m/s), moderate organic load (COD=72 ± 3 mg/l), high dissolved inorganic nitrogen (9.2 ± 0.9 mg/l) mostly as ammonium, and high levels of coliforms (7600 ± 700 cfu/ml). There was no increase in the dissolved oxigen and no decrese in the nutrients and COD along the section, suggesting that the self-purifying process for this parameters, along this section and this time of this year was negligible. Almost complete removal of ammonium (90-95%) and nitrites was observed in the bioassays. Based on our results, the present condition of the stream may be modified by increasing water oxygenation and macrophytes biomass, among others strategies. It is planned to incorporate the analysis of seasonal effects and complementary bioassays with macrophytes minimizing the algal growth.

Composición taxonómica y variación estacional del zooplancton del embalse Piedras Moras (Córdoba, Argentina)

2019-04-06T20:03:10Z

Articulo VII Congreso de Ecología y Manejo de Ecosistemas Acuáticos Pampeanos (EMEAP) (Río Cuarto, Córdoba, 19 y 20 de septiembre de 2013); Biología Acuática; no. 30 Reservoirs are water bodies relatively similar to natural lakes, differing in aspects such as the longitudinal gradient of certain environmental and biotic factors. In the mountainous region of Córdoba there are more than 15000 ha of reservoirs. Although aspects of these reservoirs have been studied, the zooplankton has generally not received much attention. The aim of this study was to determine the composition and seasonal variation of the zooplankton of Piedras Moras reservoir, a multipurpose reservoir built on the Ctalamochita River, in which this community had not been previously studied. Seasonal samples were taken (November 2009 - September 2010) at three sites. The richness was 20 taxa and the highest diversity was recorded in the center of the reservoir. The typical association of the center-northwest of the country reservoirs was found. The crustaceans Notodiaptomus incompositus, Metacyclops mendocinus, Ceriodaphnia dubia y Bosmina longirostris were recorded in the majority of the samples and, although they were the more frequent rotifers, Brachionus plicatilis, B. dimidiatus, B. caudatus and Polyarthra sp. were found less frequently. In the center, cladocerans were dominant in the summer and autumn, and copepods were dominant in the spring and winter. Though longitudinal zonation was found, this was based only on information from the summer period.

Dieta de Pseudocorynopoma doriae (Characiformes: characidae) en el arroyo La Choza, Buenos Aires, Argentina

2019-04-06T20:03:05Z

Articulo VII Congreso de Ecología y Manejo de Ecosistemas Acuáticos Pampeanos (EMEAP) (Río Cuarto, Córdoba, 19 y 20 de septiembre de 2013); Biología Acuática; no. 30 In this paper the objective is to characterize the Pseudocorynopoma doriae diet of the La Choza stream, assessing the relative importance of the contribution of the terrestrial environment to it and compare it with mesopotamian lotic environments. In all environments studied this species presented an invertivorous feeding. In the case of La Choza stream, comparison of diet between sampling dates showed a low degree of similarity, nevertheless the food items were all related to the surface film of water. Latter also is found in mesopotamian streams. When comparing the results of the percentage composition of the diet of P.doriae, it has shown that in mesopotamian environments diet is dominated by allochthonous insects while in the case of La Choza, dominance is shared with autochthonous items.

Variación estacional de la comunidad microfitoplanctónica del curso medio del río Colorado (La Pampa, Argentina)

2019-04-06T20:03:02Z

Articulo VII Congreso de Ecología y Manejo de Ecosistemas Acuáticos Pampeanos (EMEAP) (Río Cuarto, Córdoba, 19 y 20 de septiembre de 2013); Biología Acuática; no. 30 We analyzed the seasonal variation of the phycoflora in the Colorado River alluvium with the aim of expanding knowledge of algal biodiversity in lotic environments of the province of La Pampa. The study area is located in the middle basin of the Colorado River (38º 49’ S and 64º 59’ W), Lihue Calel, which is the natural limit between La Pampa and Río Negro provinces. The site is located 122 meters above sea level with a channel width of 113 m. Samples were collected according to the standard methodology for lotic environments during autumn 2010 - autumn 2011. Physicochemical parameters were measured in situ. Water temperature ranged from 3.4 to 24°C for winter and summer respectively. The pH ranged between 8.1 and 8.6, the conductivity varied between 938 and 1950 μS cm-1 and the flow velocity ranged between 0.5 and 0.9 m sec-1. Phytoplankton samples were deposited in the Herbarium SRFA (UNLPam). 163 taxa were identified mostly belonging to Bacillariophyceae (42%). Chlorophyceae contributed 36%, while 17% Cyanobacteria, Euglenophyceae, Dinophyceae, Rhodophyceae and Xanthophyceae were found as companions taxa. The similarity of biodiversity in the alluvial section of the Colorado River is almost 70% as observed in the dendrogram resulting from the application of the Bray Curtis index, and grouped according to a seasonal sampling sequence.

Efecto de la invasión de acacia negra (Gleditsia triacanthos L.) sobre arroyos pampeanos

2021-03-24T19:19:43Z

Articulo VII Congreso de Ecología y Manejo de Ecosistemas Acuáticos Pampeanos (EMEAP) (Río Cuarto, Córdoba, 19 y 20 de septiembre de 2013); Biología Acuática; no. 30 Pampean fluvial ecosystems of low order usually lack of riparian vegetation. In recent years the invasion of honey locust (Gleditsia triacanthos L.) has caused changes in landscape composition. The aim of this study was to evaluate the effect of honey locust invasion on pampean streams. Three reaches with different degree of invasion were selected and compared with three control reaches with no canopy. In order to evaluate the effect of invasion, nutrients (soluble reactive phosphorus, ammonium and nitrates), biomass of producers (seston, macrophytes, periphyton and phytobenthos) and net production in each reach were determined. Significant differences were observed for all of variables estimated between reaches with and without canopy, but not in all cases. The amount of variables with significant differences between both reaches rises following a gradient of increasing invasion levels. Furthermore, differences are more pronounced with increasing percentage of honey locust coverage on the stream. We conclude that sustained invasion of honey locust modifies the concentration of nutrients in water, the biomass of some communities and the production of these communities. This effect could be avoided with early management of the invasion of honey locust.

Crecimiento de juveniles de pejerrey (Odontotesthes bonaeriensis) bajo diferentes condiciones de cultivo

2019-04-06T20:02:57Z

Articulo VII Congreso de Ecología y Manejo de Ecosistemas Acuáticos Pampeanos (EMEAP) (Río Cuarto, Córdoba, 19 y 20 de septiembre de 2013); Biología Acuática; no. 30 The aim of this work was to analyze the growth and survival of Odontesthes bonariensis juveniles using different densities and culture conditions. One assay (E1) was carried out with individuals from 67 to 295 day-old, with a density of 217.2 ind/m3 in a 20 m3 tank. Water salinity varied between 12 and 15 g/L and an open water circulation system was used. The other assay (E2) was carried out with individuals from 43 to 182 day-old, with a density of 121.2 ind/m3 in a 100 m3 previously fertilized pond. Water salinity varied between 4 and 5 g/L and partial water exchanges were made. At the end of E1, the TL and W mean were 191.25 mm and 53.85 g respectively. Besides the survival rate was 88.2% and the production was 96,438 kg/hectare after 228 days of rearing. This result, was the highest recorded in Argentina. At the end of E2, the TL and W mean were 132.5 mm ±10.9 and 19.74 g respectively. In this case the survival rate was 73.34% and production was 17,463 kg./hectare/139 days of rearing. Although a higher density was used in E1 growth and survival were not affected because of the utilization of water circulation and a high salinity. In both assays, the mean weight and the survival rates obtained were superior to others recorded by different authors. In the case of the productions achieved, they were one order higher than all the previously reported in Argentina using different cultures systems.

Evaluación de modelos de crecimiento de diferentes condiciones de cultivo de pejerrey (Odontotesthes bonariensis)

2020-05-07T00:47:59Z

Articulo VII Congreso de Ecología y Manejo de Ecosistemas Acuáticos Pampeanos (EMEAP) (Río Cuarto, Córdoba, 19 y 20 de septiembre de 2013); Biología Acuática; no. 30 The pejerrey is one of the most important temperate native freshwater species of Argentina. Its culture is mainly done intensively and in recent years is being developed in floating cages in several Pampean lakes under semi-intensive and extensive conditions. To evaluate the growth of fish under different culture methodologies several models are used, most of which are based on the specific growth rate (SGR). The objective of this study is to compare how the SGR of pejerrey responds under different culture methods and generate a theoretical model to predict the growth that the species can reach. To carry out the models a data base was made with the available data of intensive, extensive and semi-intensive culture, to which an exponential and polynomial models were adjusted by the method of least squares and then the expected growth was simulated using the model that better fits. From the results it was observed that the polynomial model presented the best fit to different methods of culture. In all cases the models reflected the seasonality in the growth rates exhibited by the species, where SGR was lowest in winter and highest in spring. The growth simulation models also show that the semi-intensive culture could produce greater weight than other methods. Under these conditions, fish obtain zooplankton from the environment incorporating essential elements from its natural food source. This suggests that it is possible to improve the sizes of fish by using techniques that also incorporate natural food or its equivalent in the composition of the artificial diets.

Ecología trófica del pejerrey (Odontotesthes bonariensis) en la laguna del Venado y Alsina, dos ambientes del sistema Encadenadas del Oeste, prov. de Buenos Aires

2021-03-24T19:06:07Z

Articulo VII Congreso de Ecología y Manejo de Ecosistemas Acuáticos Pampeanos (EMEAP) (Río Cuarto, Córdoba, 19 y 20 de septiembre de 2013); Biología Acuática; no. 30 The aim of the present study was to analyze the feeding of the silverside Odontesthes bonariensis in the Venado and Alsina lake. which are part of the Encadenadas del Oeste lake system. The stomach content of 206 individuals was analyzed. Total length ranged from 93 to 585 mm. The vacuity index (VI) and repletion index (RI) were estimated by season and site. Index of Relative Importance (IRI) for each food category and the trophic level (TL) of pejerrey were calculated by site. The diet of the silverside was composed of 68 prey items, most of which were occasional preys. Copepods and cladocerans were the main prey items in the diet in both lagoons. Copepods were the most important item in Venado lagoon and cladocerans were so in Alsina lagoon. The micro crustaceans were the main prey item for both size classes, however their %IRI decreased in the larger fish (95% IRI for the 93-299 mm Tl size class and 63% IRI for the 300-585 mm Tl size class). Silverside TL estimated for each lagoon (TL= 3) characterizes it as secondary consumer.

Estudio limnológico de Laguna Blanca Chica (Olavarría, provincia de Buenos Aires) durante un período de sequía

2019-04-06T20:02:27Z

Articulo VII Congreso de Ecología y Manejo de Ecosistemas Acuáticos Pampeanos (EMEAP) (Río Cuarto, Córdoba, 19 y 20 de septiembre de 2013); Biología Acuática; no. 30 The aquatic ecosystems of the Pampean plains usually have highly variable dynamics which affects the abundance of fish resources. We analyzed Blanca Chica shallow lake located in the central region of the province of Buenos Aires. It has neither tributaries nor effluents. It hosts sport fishing, water sports without engine, and its surroundings are used for recreation. Here we report the effects of drought in the structure and functioning of the shallow lake, with emphasis on the fish community. Limnological and ichthyologic analyses were carried out in 2007, 2008, 2011 (year characterized by extreme regional dry period) and 2014. In 2007 the phytoplankton was dominated by Botryococcus braunii. Pejerrey (Odontesthes bonariensis) was dominant in the fish samples, but showing an important decrease in numbers and biomass. Catch per unit effort (CPUE) was low and showed poor fish quality with high taeniasis. In 2008, zooplankton improved both in quality and quantity and became the basis of pejerrey`s diet, which effectively increased its abundance and its biomass, with fish in the 1- and 2-year class. In 2011 the conductivity, chlorophyll-a, chlorides, sodium, ammonium and sulfates were one order of magnitude above historical values. The extreme limnological conditions and notorious area reduction triggered a total absence of fish. The 2014 campaign showed that the shallow lake level had increased from 1,5 to 2 m. However, no fish were detected; the absence may be explained by the lake’s isolation and natural massive mortality occurred.

La comunidad algal epilítica en hábitat de rabión en un arroyo serrano

2021-03-24T19:41:19Z

Articulo VII Congreso de Ecología y Manejo de Ecosistemas Acuáticos Pampeanos (EMEAP) (Río Cuarto, Córdoba, 19 y 20 de septiembre de 2013); Biología Acuática; no. 30 In flowing water habitats areas of turbulent erosion, oxygenated waters and heterogeneity can be distinguished, which are called riffles. The objective of this study was to determine the composition and structure of the epilithic algal community in riffle habitat of Arroyo Achiras (Córdoba, Argentina). Two sampling sites were selected along the longitudinal gradient, one in mountainous zone (A) and another one in piedmont (B). In 2005 and 2006 epilithic samples were collected during periods of low and high waters and physico-chemical and hydraulic variables were measured. At each site algal abundance and frequency were determined. Similarity index, taxonomic richness, species diversity (Shannon) and evenness were calculated. Differences between both zones were analyzed by two-way ANOVAs. A total of 175 taxa were determined. The greatest similarity (67%) was observed between high and low water hydrological periods at site B. Ochrophyta dominated over the other algal divisions. The highest algal density was recorded at site B during the period of low water. Significant differences between sites and hydrological periods were observed in all biological parameters, except for abundance.

Estructura y dinámica del fitoepifiton en cuerpos de agua temporarios del Cinturón Hortícola Platense

2019-12-17T18:43:45Z

Articulo VII Congreso de Ecología y Manejo de Ecosistemas Acuáticos Pampeanos (EMEAP) (Río Cuarto, Córdoba, 19 y 20 de septiembre de 2013); Biología Acuática; no. 30 The horticultural belt of La Plata is a complex framework of lands with a marked urban influence. The unregulated use of agrochemicals is one of the most important sources of superficial and underground water contamination producing drastic changes in the biodiversity of natural communities. The shallowness of the temporary waters favors the macrophyte growth which, in turn, allows the colonization of the phytoepiphyton. Four samplings were carried out during spring 2011 and summer 2012 in four adjacent temporary waters of different agroecosystems, three of them with agricultural activity (site over 5 meters crops, CUL1 and CUL2; site within 5 meters of crops: CUL3) and one, taken as reference (REF), with livestock activity. Seven species of macrophytes were sampled, two submerged and 5 emergent. 88 phytoepiphytic species were recorded, being clorophytes and diatoms the dominant groups. The submerged macrophytes presented a higher mean abundance than the emergent ones in all the sampling sites. Oedogonium species were dominant in all temporary waters. L. peploides showed the highest total specific richness while S. californicus presented the highest mean diversity specific. The highest phytoepiphyton mean abundance was recorded in CUL1 while the least phytoepiphytic density was found in REF. Nygaard index shows that the four temporary waters are meso to eutrophic. The conductivity was the most significant factor in the distribution of diatoms species in temporary waters.

Cambios en la características limnológicas del embalse Río Tercero por efecto de la invasión de Limnoperma fortunei (Bivalvia: Mytilidae)

2019-04-06T04:06:50Z

Articulo VII Congreso de Ecología y Manejo de Ecosistemas Acuáticos Pampeanos (EMEAP) (Río Cuarto, Córdoba, 19 y 20 de septiembre de 2013); Biología Acuática; no. 30 Since its introduction in South America around 1990, the freshwater Asian mussel Limnoperna fortunei has been shown to strongly interact with several components of the local biota, sometimes producing significant changes at the ecosystem-wide scale. The “golden mussel” is present prior to 2000 in Río Tercero reservoir, Córdoba, Argentina, most probably introduced overland by a fouled recreational or fishing boat from the Paraná River. Since 2003 massive growth on submerged solid structures (piles, moorings, boat hulls) was strongly noticeably. Data collected regularly since 1996 showed changes in several water-column properties after the invasion. From 2004 on, water transparency increased, and suspended matter, chlorophyll a, and primary production decreased significantly, with stronger changes occurring in the area with highest mussel densities. On the basis of diver collected bottom samples taken in a 2006 survey, it has been estimated that the 47 km2 reservoir hosts around 45 billion mussels, distributed mainly on solid surfaces, in waters less than 10m depth. At these densities, a volume equivalent to that of this water body can potentially be filtered by the bivalves every 2-3 days. The present survey addresses the question whether Limnoperna impact on the ecosystem is measurable.

Caracterización limnológica y fauna de peces de la laguna La Helvecia (Córdoba, Argentina)

2026-03-18T18:40:20Z

Articulo VII Congreso de Ecología y Manejo de Ecosistemas Acuáticos Pampeanos (EMEAP) (Río Cuarto, Córdoba, 19 y 20 de septiembre de 2013); Biología Acuática; no. 30 La Helvecia shallow lake (33°25’16’’S, 62°53’26’’W, 90 ha) is one of the few permanent aquatic environments that still exist in the “Bañados del Saladillo” (Córdoba, Argentina). During November 2011, a study of fish and limnological characterization was performed. Different active and passive gears were used and water quality variables were measured. Average values pH, oxygen concentration, temperature and water transparency (Secchi disk) were 8.63, 9.05 mg/L, 23.8 °C and 39 cm respectively. The shallow lake was classified as “turbid” type. The water was hypohaline (4.74 g/L), sulfated sodium chlorinated and very hard (298 ppm CaCO3). The macrozooplankton abundance was 240,850 org/m3. A total of nine species of fish, belonging to five orders and seven families were captured. Odontesthes bonariensis was the most abundant species (78.6%), while Cyprinus carpio was the species with most biomass (41.4%). Zooplankton (Cladocera and Copepdoda) was the main food of O. bonariensis. The principal finding was the presence of Parapimelodus valenciennis. The gradual and permanent changes that have occurred in the landscape of the region, with higher intensities of land use, may have been the main causes of the transformation of La Helvecia lake from clear to turbid, which favored the recreational fishery.

Efectos de la exclusión de ganado sobre la calidad ambiental de un arroyo pampeano

2021-03-24T18:51:17Z

Articulo VII Congreso de Ecología y Manejo de Ecosistemas Acuáticos Pampeanos (EMEAP) (Río Cuarto, Córdoba, 19 y 20 de septiembre de 2013); Biología Acuática; no. 30 For two years, records of channel morphology and quality of the bank on a section of a stream were made because the cattle farming have been excluded at a section of 500 meters of long near the bank and 10 meters at each bank. There were registered also changes in the aquatic vegetation and some physico-chemical parameters. Fish sampling was conducted annually to observe species presence and their relative abundance. It was detected a rapid improvement in the quality of banks and an increase of the richness of fishes in each sample. Contrary to expectations macrophyte richness was reduced and morphological heterogeneity of the channel is not increased. However, the stream ceased to be interrupted and started having more water in the entire stretch. This was as a result of reshaping the banks. Although this register should be validated with future surveys, the results suggest that the recovery of the banks is very fast and the runway and the fish colonization are staggered. Despite this, there was a clear recovery at the studied reach, with the exclusion of cattle in the area as the unique management practice.

Efecto del ganado sobre la estructura de la vegetación en las riberas de un arroyo pampeano

2019-04-06T04:06:38Z

Articulo VII Congreso de Ecología y Manejo de Ecosistemas Acuáticos Pampeanos (EMEAP) (Río Cuarto, Córdoba, 19 y 20 de septiembre de 2013); Biología Acuática; no. 30 Livestock is a main perturbation for the riparian zones of streams in the Buenos Aires province. Our goal is to compare the vegetation’s and soil’s characteristics of two almost contiguous reaches of the Nutrias stream, an affluent to the Reconquista river. One reach has been closed to cattle for 2 years, and the other -500m downstream- has kept livestock along the whole period. For each stream margin, six 10m transects were sampled for species cover and 3 soil samples were drawn for organic matter, phosphorus, pH, conductivity and apparent density determination. The vegetation’s canopy hight, cover, and the amphibious macrophytes’ abundance were higher in the closed reach; instead, species number was higher in the reach opened to cattle. Eleocharis bonariensis (19%), Paspalum distichum (17%) y Cynodon dactylon (15%) were dominant within the closure, while the exotic grass C. dactylon dominated (63%) in the grazed reach. Regarding the soil variables, a PCA distinguishes the two reaches in the first component (35% of the total variance), and the two margins of the closed reach are separated along the 2nd axis (25%). This separation of the reaches and the margins is consistent with the ordination analysis (NMDS) performed among the species. In this case study, the observed changes in the community structure after two years of closure may enhance the riparian zone’s capability to regulate the exchanges between land and watercourse.