Aspectos metodológicos y conceptuales para el conocimiento de las áreas anegables del Chaco Oriental

En el Oriente Chaqueño la dinámica del escurrimiento es clave para comprender el funcionamiento del paisaje de la llanura

Sinopsis ecológica y estado actual del Chaco Oriental

The Eastem Chaco landscape comprises the autochthonous flatland basin of the chaquean región. This subtropical area (82,700 km2), where rivers with seasonal regime are frequent, have streams with autumnal floods and dry periods at the end of the winter. The rainfall distribution in these subtropical flatplains is the most important cause of the "continuum” vegetation with the cattail-swamps and mixed-woods in both gradient's ends. This landscape continuity is the same as that of the river basins in the Eastern Chaco. This continuity is given from headwaters to mouth in their bio-physical environments with a widespread water changes in their chemical, physical and biotic features even in spatial and temporal series. Climatic, hydrologic, physiographic, limnologic, vegetation and other features, are discussed and some considerations on the rational management of the ecosystems, are made. The purpose of this paper is to emphasize in the ecological value of the flatland basins as descriptors of the landscape dynamics in a regional limnological approach.The Eastem Chaco landscape comprises the autochthonous flatland basin of the chaquean región. This subtropical area (82,700 km2), where rivers with seasonal regime are frequent, have streams with autumnal floods and dry periods at the end of the winter. The rainfall distribution in these subtropical flatplains is the most important cause of the "continuum” vegetation with the cattail-swamps and mixed-woods in both gradient's ends. This landscape continuity is the same as that of the river basins in the Eastern Chaco. This continuity is given from headwaters to mouth in their bio-physical environments with a widespread water changes in their chemical, physical and biotic features even in spatial and temporal series. Climatic, hydrologic, physiographic, limnologic, vegetation and other features, are discussed and some considerations on the rational management of the ecosystems, are made. The purpose of this paper is to emphasize in the ecological value of the flatland basins as descriptors of the landscape dynamics in a regional limnological approach

Los bosques fluviales del Chaco Oriental: Primera aproximación

The structure and distribution of the gallery forests from the Eastern Chaco and their economical possibilities, are studied. It was analized using the Quarter Method (Cottan and Curtis, 1956) in 316 samples. The entire clear bole, diameters, coverage, stratification, total tree-heights and the present species in each stand, were measured. Transgressive species from river habitats and the Chaco landscapes, were identified. Difameters variability and heights, are characteristic of these irreguiar forests. Differences among the present stands due to many factors, were verified: stripping, presence of animáis, frequence and intensity of floods. This fact less affects the protection function of the margins, but it does with the availability of merchandable lumber resources. The application of management techniques would allow to better the quali and quantitative possibilities of the forest utilization.The structure and distribution of the gallery forests from the Eastern Chaco and their economical possibilities, are studied. It was analized using the Quarter Method (Cottan and Curtis, 1956) in 316 samples. The entire clear bole, diameters, coverage, stratification, total tree-heights and the present species in each stand, were measured. Transgressive species from river habitats and the Chaco landscapes, were identified. Difameters variability and heights, are characteristic of these irreguiar forests. Differences among the present stands due to many factors, were verified: stripping, presence of animáis, frequence and intensity of floods. This fact less affects the protection function of the margins, but it does with the availability of merchandable lumber resources. The application of management techniques would allow to better the quali and quantitative possibilities of the forest utilization

Distribución de las aves en el valle del río Paraná. Relación con el régimen pulsátil y la vegetación

Freshwater birds are important in the floodplains because its role in trophic nets and their influence on distribution of other organisms. In the Parana riverine system alnost four guilds way are identified: 1-Birds feeding while walking; 2-Birds feeding swimning of diving; 3-Birds that see their food flying or from snare for birds; 4-Birds that capture their food on stems and leanes. Therefore, they live in relationships to the landscape units that are also influenced by the water level fluctuation as a macrofactor that determine fast influence on the distribution and abundance of bird communities. The amplitude, frequency, and phase recurrence whithin the hydrological regime conform a key factor for understanding the amplitude of niches, and periodicity patterns of aquatic birds inhabiting on a very open environments where the seasonality are mainly conferred by hydrological pulses.Freshwater birds are important in the floodplains because its role in trophic nets and their influence on distribution of other organisms. In the Parana riverine system alnost four guilds way are identified: 1-Birds feeding while walking; 2-Birds feeding swimning of diving; 3-Birds that see their food flying or from snare for birds; 4-Birds that capture their food on stems and leanes. Therefore, they live in relationships to the landscape units that are also influenced by the water level fluctuation as a macrofactor that determine fast influence on the distribution and abundance of bird communities. The amplitude, frequency, and phase recurrence whithin the hydrological regime conform a key factor for understanding the amplitude of niches, and periodicity patterns of aquatic birds inhabiting on a very open environments where the seasonality are mainly conferred by hydrological pulses

Descomposición de la hojarasca en un bosque nativo y en una plantación de Grevillea robusta del Chaco Oriental

Litter fall and decomposition were simultaneously studied in a mixed natural forest in an adjacent stands of Grevlllea robusta (22 years oíd), near Makalló City (20*07'S; 59*21’W) where annual rainfall mean is 1100 mm with a humid period at the end of summer and a dry period in winter time. Simultaneously, a strong seasonality in the litter fall could be recorded by biweekly sampling operations. The annual fine litter fall was estimated in 6.96 tn/ha/yr in a native forest. The water storage was different in both soil sites as a consequence of a higher density and lower infiltration in Grevillea forest. Thirty litter bags with 10g of dead leaves, and 30 cellulose bagswere placed in each site in order to estímate the organic matter decomposition. Using the Olson equation, we obtained faster valúes in the natural forest: 173 days for haif-life time, compared with Grevillea forest:750 days for haif-life time. Similar trend could be observed in cellulose decomposition: remaining dry weight of 5 % was found at 220 and 968 days in native and Grevlllea forest, respectívety. Compiementary.the actívity of microbiota funtional groups were calculated (as cellulotítis, nitrifiers, and soil algae) demónstrate that the biological actívity in the decomposition procesess is mainly related with two key factors: different litter quality and dfferent water budget in the soil surface. After only two decades of implantad Grevillea forest, the fluxestand ralease of nutrient and organic matter is quite different.Litter fall and decomposition were simultaneously studied in a mixed natural forest in an adjacent stands of Grevlllea robusta (22 years oíd), near Makalló City (20*07'S; 59*21’W) where annual rainfall mean is 1100 mm with a humid period at the end of summer and a dry period in winter time. Simultaneously, a strong seasonality in the litter fall could be recorded by biweekly sampling operations. The annual fine litter fall was estimated in 6.96 tn/ha/yr in a native forest. The water storage was different in both soil sites as a consequence of a higher density and lower infiltration in Grevillea forest. Thirty litter bags with 10g of dead leaves, and 30 cellulose bagswere placed in each site in order to estímate the organic matter decomposition. Using the Olson equation, we obtained faster valúes in the natural forest: 173 days for haif-life time, compared with Grevillea forest:750 days for haif-life time. Similar trend could be observed in cellulose decomposition: remaining dry weight of 5 % was found at 220 and 968 days in native and Grevlllea forest, respectívety. Compiementary.the actívity of microbiota funtional groups were calculated (as cellulotítis, nitrifiers, and soil algae) demónstrate that the biological actívity in the decomposition procesess is mainly related with two key factors: different litter quality and dfferent water budget in the soil surface. After only two decades of implantad Grevillea forest, the fluxestand ralease of nutrient and organic matter is quite different

Atenuación del escurrimiento fluvial por bosques de Tessaria

The flow interference effect of the Tessaria integrifolia forest intwo islands of the Paraná River, located dounstream of the Paraná-Paraguay rivers confluence, was studied. Current velocity, suspended sediments, channel depth, water transparency, tree density, tallness and coverage, were measured in cross sections of the stream. The atenuation of the running water by trees can be assumed as a "biological roughness" of the vegetation. It produce a strong decrease in the grain-size distribution of the islands superficial sediments as concequence of the flow interference. In central areas of the islands occuped by forest with 20-30 ind/m*, current velocity was 10 times lower than similar (depth, slope) Coastal sites without vegetation, while the suspended load resulted lesser than the half. The erodability coefficient decrease proportionally to the square of the current velocity diminishing. Owing to the forest extensión and coverage in rivers of the De la Plata basin, it is advisable to consider their effect during flood periods.The flow interference effect of the Tessaria integrifolia forest intwo islands of the Paraná River, located dounstream of the Paraná-Paraguay rivers confluence, was studied. Current velocity, suspended sediments, channel depth, water transparency, tree density, tallness and coverage, were measured in cross sections of the stream. The atenuation of the running water by trees can be assumed as a "biological roughness" of the vegetation. It produce a strong decrease in the grain-size distribution of the islands superficial sediments as concequence of the flow interference. In central areas of the islands occuped by forest with 20-30 ind/m*, current velocity was 10 times lower than similar (depth, slope) Coastal sites without vegetation, while the suspended load resulted lesser than the half. The erodability coefficient decrease proportionally to the square of the current velocity diminishing. Owing to the forest extensión and coverage in rivers of the De la Plata basin, it is advisable to consider their effect during flood periods

Spatial and temporal variation of fish assemblage associated with aquatic macrophyte patches in the littoral zone of the Ayapel Swamp Complex, Colombia

ABSTRACT: Aim: The purpose of the present study was to examine spatial and temporal variation in fish assemblage structure associated with aquatic macrophytes in the littoral zone of the ASC. Methods: Specimens were caught between January 2008 and February 2009, over four limnimetric moments, using both cast net and seine net. Data on the temperature, electrical conductivity, pH and dissolved oxygen was recorded for the characterization of the water mass in the sites. Results: A total of 34,151 specimens from 44 species were collected. The most abundant species were Eigenmannia virescens, Astyanax caucanus, Astyanax fasciatus, Roeboides dayi and Cyphocharax magdalenae, which together accounted for more than 75% of the sample. Temporal and spatial comparisons showed variation in the environmental conditions and highlighted the existence of heterogeneous abiotic conditions (p0.05) regarding the fish assemblage structure. The multivariate analysis showed no significant relationship between existing environmental conditions and the fish assemblage (p=0.04). The analysis also showed the absence of a relationship between the fish assemblage and environmental variables with respect to the flood pulse and sampling sites (p>0.05). Conclusion: The uniformity of the fish communities that inhabit aquatic macrophyte patches in the littoral region of the ASC may be related to the availability of suitable habitat in structural terms, that probably supports a more abundant and varied wildlife

Changes in vegetation composition and structure following livestock exclusion in a temperate fluvial wetland

Questions: Responses of wetland systems to grazing can be highly variable with both positive or negative responses. However, the sustainable use of wetlands for grazing will depend on the management implemented and the resilience of each type of them. In this context, we addressed the question: will the vegetation in the studied wetland be able to recover its structural and functional parameters in the short term after livestock exclusion?. Location: Temperate fluvial wetlands in the middle Delta of the Paraná River, Argentina, South America. Methods: We evaluated the effect of cattle ranching on vegetation composition and diversity by determining changes in species richness and evenness, biomass (green and dry vegetative, and reproductive biomass), and litter content. We also analyzed the changes in biomass of weeds and of species according to their forage quality, toxicity, and growth form. We applied a randomized block design (by topographic position) with repeated measures over time, using livestock exclusion as treatment. Results: After 16 months, livestock exclusion affected vegetation species richness, but did not have a significant effect on diversity due to a slightly compensatory effect of evenness. Species composition differed markedly among treatments over time. There was an increase in dry and green vegetative biomass and litter content after eight months of exclusion, while changes in reproductive biomass occurred later. The increase in these variables was closely related to changes in biomass of species with erect habit and good forage quality. Conclusions: Livestock exclusion increased the forage value for the studied wetland by the development of natural palatable species typical of these environments. This shift in species composition promoted a higher production in biomass in the ungrazed areas. This suggests a remarkable recovery of the structural and functional parameters of the vegetation communities in the short term (two years).Fil: Magnano, Andrea Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Provincia de Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Universidad Nacional de Cuyo. Instituto Argentino de Investigaciones de las Zonas Áridas; ArgentinaFil: Krug, Cecilia Pamela. Universidad Nacional de San Martín. Instituto de Investigación e Ingeniería Ambiental. - Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigación e Ingeniería Ambiental; ArgentinaFil: Casa, Valeria. Universidad Nacional de San Martín. Instituto de Investigación e Ingeniería Ambiental. - Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigación e Ingeniería Ambiental; ArgentinaFil: Quintana, Ruben Dario. Universidad Nacional de San Martín. Instituto de Investigación e Ingeniería Ambiental. - Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigación e Ingeniería Ambiental; Argentin

Feeding spectra and activity of the freshwater crab Trichodactylus kensleyi (Decapoda: Brachyura: Trichodactylidae) at La Plata basin

Background: In inland water systems, it is important to characterize the trophic links in order to identify the ‘trophic species’ and, from the studies of functional diversity, understand the dynamics of matter and energy in these environments. The aim of this study is to analyze the natural diet of Trichodactylus kensleyi of subtropical rainforest streams and corroborate the temporal variation in the trophic activity during day hours. Results: A total of 15 major taxonomic groups were recognized in gut contents. The index of relative importance identified the following main prey items in decreasing order of importance: vegetal remains, oligochaetes, chironomid larvae, and algae. A significant difference was found in the amount of full stomachs during day hours showing a less trophic activity at midday and afternoon. The index of relative importance values evidenced the consumption of different prey according to day moments. Results of the gut content indicate that T. kensleyi is an omnivorous crab like other trichodactylid species. Opportunistic behavior is revealed by the ingestion of organisms abundant in streams such as oligochaetes and chironomid larvae. The consumption of allochthonous plant debris shows the importance of this crab as shredder in subtropical streams. However, the effective assimilation of plant matter is yet unknown in trichodactylid crabs. Conclusions: This research provides knowledge that complements previous studies about trophic relationships of trichodactylid crabs and supported the importance of T. kensleyi in the transference of energy and matter from benthic community and riparian sources to superior trophic levels using both macro- and microfauna.Fil: Williner, Verónica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; Argentina. Universidad Nacional del Litoral. Facultad de Humanidades y Ciencias; ArgentinaFil: de Azevedo Carvalho, Debora. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; ArgentinaFil: Collins, Pablo Agustin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; Argentina. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas; Argentin

Commercial fisheries in a mega unregulated floodplain river: assessment of the most favourable hydrological conditions for its preservation

This paper deals with the hydrological variability effects on the primary commercial fish species inhabiting the main channel and the floodplain of the large Paraná River in its middle reaches in Argentina. Analysing more than eight decades (1935–2016) of information on the most frequent and abundant commercial species in conjunction with hydrological levels and temperature, our results show that spring–summer floods of a certain magnitude (c. 6 m) and durations (> 80 days) are crucial for sustaining commercial fisheries. Moreover, the frequency of these floods was modulated by the decadal climatic fluctuations that have occurred over the past 100 years in the Paraná Basin. An insight into the probable incidence of some anthropogenic influences is also provided.Fil: Rabuffetti, Ana Pia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; ArgentinaFil: Espínola, Luis Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; ArgentinaFil: Abrial, Elie. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; ArgentinaFil: Amsler, Mario Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; ArgentinaFil: Blettler, Martin Cesar Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; ArgentinaFil: Eurich, María Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; ArgentinaFil: Eberle Folmer, Eliana Gisel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; Argentin