Tendencias y respuestas de la fenología de la superficie terrestre a la variabilidad climática en la Pampa Argentina

Comprender la interacción entre los procesos de la superficie terrestre y la atmósfera es fundamental para predecir los efectos del cambio climático futuro sobre el funcionamiento de los ecosistemas y la dinámica del carbono. Los objetivos de este trabajo fueron analizar las tendencias en métricas de la fenología de la superficie terrestre derivadas de sensores remotos, y revelar su relación con la precipitación y el fenómeno ENSO en la región pampeana de Argentina. A partir de una serie temporal de imágenes del Índice de Vegetación de Diferencia Normalizada (NDVI) de MODIS para el período 2000-2014, se obtuvo para la región pampeana de Argentina el inicio de la estación de crecimiento (SOS), la integral anual del NDVI (i-NDVI, estimador lineal de la productividad anual), el tiempo del máximo anual del NDVI (t-MAX) y el rango relativo anual de NDVI (RREL, estimador de la estacionalidad). Posteriormente, se analizaron las relaciones espaciales y temporales con el Índice Multivariado del ENSO (MEI) y la precipitación. Los resultados mostraron una tendencia negativa en la productividad anual en un 53,6% del área de estudio asociado a zonas de pastizales naturales y semi-naturales, mientras que un 40,3% de la Pampa Argentina mostró una tendencia positiva significativa en la estacionalidad de las ganancias de carbono. Este estudio también revela que la variabilidad climática tiene un impacto significativo en la fenología de la superficie terrestre de la región pampeana, aunque este impacto es heterogéneo. SOS y t-MAX mostraron una correlación negativa significativa con la precipitación, lo que indica una ocurrencia más temprana. El 23,6% y 28,4% del área de estudio mostró una correlación positiva de la productividad anual con el MEI y la precipitación, respectivamente, asociado a pastizales (en el primer caso) y sobre pastizales y áreas agrícolas en el segundo caso. La variabilidad climática no explicó la variabilidad en la estacionalidad de la fenología. Las relaciones encontradas entre las métricas de la fenología de la superficie terrestre y la variabilidad climática podrían ser importantes para la implementación de estrategias para el manejo de los recursos naturales.Understanding the interaction between land surface and atmosphere processes is fundamental for predicting the effects of future climate change on ecosystem functioning and carbon dynamics. The objectives of this work were to analyze the trends in land surface phenology (LSP) metrics from remote sensing data, and to reveal their relationship with precipitation and ENSO phenomenon in the Argentina Pampas. Using a time series of MODIS Normalized Difference Vegetation Index (NDVI) data from 2000 to 2014, the start of the growing season (SOS), the annual integral of NDVI (i-NDVI, linear estimator of annual productivity), the timing of the annual maximum NDVI (t-MAX) and the annual relative range of NDVI (RREL, estimator of seasonality) were obtained for the Argentina Pampas. Then, spatial and temporal relationships with the Multivariate ENSO Index (MEI) and precipitation were analyzed. Results showed a negative trend in annual productivity over a 53.6% of the study area associated to natural and semi-natural grassland under cattle grazing, whereas a 40.3% of Argentina Pampas showed a significant positive trend in seasonality of carbon gains. The study also reveals that climate variability has a significant impact on land surface phenology in Argentina Pampas, although the impact is heterogeneous. SOS and t-MAX showed a significant negative correlation with the precipitation indicating an earlier occurrence. 23.6% and 28.4% of the study area showed a positive correlation of the annual productivity with MEI and precipitation, respectively, associated to rangelands (in the first case) and to both rangeland and croplands, in the second case. Climate variability did not explain the seasonal variability of phenology. The relationships found between LSP metrics and climate variability could be important for implementation of strategies for natural resource management.Fil: Lara, Bruno Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil; Argentina. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Agronomía. Departamento Ciencias Básicas Agronómicas y Biológicas. Laboratorio de Investigación y Servicios en Teledetección de Azul; ArgentinaFil: Gandini, M.. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Agronomía. Departamento Ciencias Básicas Agronómicas y Biológicas. Laboratorio de Investigación y Servicios en Teledetección de Azul; ArgentinaFil: Gantes, P.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Universidad Nacional de Luján. Instituto de Ecología y Desarrollo Sustentable; ArgentinaFil: Matteucci, Silvia Diana. Universidad de Buenos Aires. Facultad de Arquitectura y Urbanismo. Grupo de Ecología del Paisaje y Medio Ambiente; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

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

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.Facultad de Ciencias Naturales y Muse

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

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.Facultad de Ciencias Naturales y Muse

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

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.Facultad de Ciencias Naturales y Muse

Descomposición de macrófitas en el arroyo Las Flores (Buenos Aires)

The macrophytes contribute significantly to the autochthonous primary production of the streams of the Buenos Aires province. Their biomass is partly exported, mainly during floods, and partly incorporated to the detritus pathway of the water bodies. The aim of this study is to determine the losses in weight and nitrogen along the process of decomposition of Lemna gibba and Ceratophyllum demersum, two of the dominant species in the Las Flores stream. A total of 40 bags with 4 g (fresh weight) of L. gibba and 10 g of C. demersum were set in two sites of the stream. Periodically, 4 samples of each species were redrawn, and the dry weight and total nitrogen concentration were determined. L. gibba lost 50% of its weight in 4 days, from then on and until the end of the incubation period (50 days) the weight kept approximately constant, fitted to a Hill’s function with a maximum rate of 0.158 day-1. The weight of C. demersum was almost stable until day 44, and at the end of the following 42 days it was observed that it had lost 62% of its initial weight, with a constant rate of k = 0.0203 day-1. In L. gibba essay, nitrogen concentration lowered from 3.4% to 2.4% in the first 48 hours, thus representing a 52% loss of the total nitrogen content of the plant. For C. demersum, nitrogen concentration decayed from 4.1% until 3.2%; by the end of the sampling, the total nitrogen content had reduced to 33.5% of the initial value. The results indicate that, given the quickness of the decomposition and nutrient release, an important part of the production can be incorporated to the material cycles of the stream before the plants are washed downstream during floods.Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) - Instituto de Limnología "Dr. Raul A. Ringuelet" (ILPLA

Descomposición de macrófitas en el arroyo Las Flores (Buenos Aires)

The macrophytes contribute significantly to the autochthonous primary production of the streams of the Buenos Aires province. Their biomass is partly exported, mainly during floods, and partly incorporated to the detritus pathway of the water bodies. The aim of this study is to determine the losses in weight and nitrogen along the process of decomposition of Lemna gibba and Ceratophyllum demersum, two of the dominant species in the Las Flores stream. A total of 40 bags with 4 g (fresh weight) of L. gibba and 10 g of C. demersum were set in two sites of the stream. Periodically, 4 samples of each species were redrawn, and the dry weight and total nitrogen concentration were determined. L. gibba lost 50% of its weight in 4 days, from then on and until the end of the incubation period (50 days) the weight kept approximately constant, fitted to a Hill’s function with a maximum rate of 0.158 day-1. The weight of C. demersum was almost stable until day 44, and at the end of the following 42 days it was observed that it had lost 62% of its initial weight, with a constant rate of k = 0.0203 day-1. In L. gibba essay, nitrogen concentration lowered from 3.4% to 2.4% in the first 48 hours, thus representing a 52% loss of the total nitrogen content of the plant. For C. demersum, nitrogen concentration decayed from 4.1% until 3.2%; by the end of the sampling, the total nitrogen content had reduced to 33.5% of the initial value. The results indicate that, given the quickness of the decomposition and nutrient release, an important part of the production can be incorporated to the material cycles of the stream before the plants are washed downstream during floods.Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) - Instituto de Limnología "Dr. Raul A. Ringuelet" (ILPLA

Descomposición de macrófitas en el arroyo Las Flores (Buenos Aires)

The macrophytes contribute significantly to the autochthonous primary production of the streams of the Buenos Aires province. Their biomass is partly exported, mainly during floods, and partly incorporated to the detritus pathway of the water bodies. The aim of this study is to determine the losses in weight and nitrogen along the process of decomposition of Lemna gibba and Ceratophyllum demersum, two of the dominant species in the Las Flores stream. A total of 40 bags with 4 g (fresh weight) of L. gibba and 10 g of C. demersum were set in two sites of the stream. Periodically, 4 samples of each species were redrawn, and the dry weight and total nitrogen concentration were determined. L. gibba lost 50% of its weight in 4 days, from then on and until the end of the incubation period (50 days) the weight kept approximately constant, fitted to a Hill’s function with a maximum rate of 0.158 day-1. The weight of C. demersum was almost stable until day 44, and at the end of the following 42 days it was observed that it had lost 62% of its initial weight, with a constant rate of k = 0.0203 day-1. In L. gibba essay, nitrogen concentration lowered from 3.4% to 2.4% in the first 48 hours, thus representing a 52% loss of the total nitrogen content of the plant. For C. demersum, nitrogen concentration decayed from 4.1% until 3.2%; by the end of the sampling, the total nitrogen content had reduced to 33.5% of the initial value. The results indicate that, given the quickness of the decomposition and nutrient release, an important part of the production can be incorporated to the material cycles of the stream before the plants are washed downstream during floods.Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) - Instituto de Limnología "Dr. Raul A. Ringuelet" (ILPLA

Valoración de la calidad de ribera en un arroyo pampeano y su relación con las comunidades de macrófitas y peces

An Index of Riparian Quality was applied to a Pampean stream with moderate human impact (Las Flores stream, Luján river basin) to evaluate its degree of conservation. Aquatic macrophyte cover and diversity were also registered in 12 different reaches along the stream to analyze its relationship with the riparian index. In addition, the richness and diversity of the fish community were registered in two reaches with contrasting use of riparian zones and channel morphology. The results of the survey indicate that conservation of the riparian zones is difficult in the stream due to the increase of farming activities, the development of cropland near the margins, the invasion of an alien tree Gleditsia triacanthos (acacio negro) and the development of urban zones. Alteration of the riparian zone also modified the structure of the macrophyte communities and could be associated with a reduction in the richness and diversity of the fish community. We consider that the needs for conservation and recuperation of the riparian zones must be transmitted to the land owners. Activities should be coordinated to maintain the water quality and habitat diversity in order to enhance the basin health.Instituto de Limnología "Raúl A. Ringuelet

Valoración de la calidad de ribera en un arroyo pampeano y su relación con las comunidades de macrófitas y peces

An Index of Riparian Quality was applied to a Pampean stream with moderate human impact (Las Flores stream, Luján river basin) to evaluate its degree of conservation. Aquatic macrophyte cover and diversity were also registered in 12 different reaches along the stream to analyze its relationship with the riparian index. In addition, the richness and diversity of the fish community were registered in two reaches with contrasting use of riparian zones and channel morphology. The results of the survey indicate that conservation of the riparian zones is difficult in the stream due to the increase of farming activities, the development of cropland near the margins, the invasion of an alien tree Gleditsia triacanthos (acacio negro) and the development of urban zones. Alteration of the riparian zone also modified the structure of the macrophyte communities and could be associated with a reduction in the richness and diversity of the fish community. We consider that the needs for conservation and recuperation of the riparian zones must be transmitted to the land owners. Activities should be coordinated to maintain the water quality and habitat diversity in order to enhance the basin health.Instituto de Limnología "Raúl A. Ringuelet

Trayectoria del ensamble de especies leñosas de la ribera del río Luján a cinco años de su desmonte.

El desmonte y el perfilado de la ribera del río Luján se realiza para acelerar el traslado del agua durante las crecidas. En dos sitios ribereños de la cuenca del río Luján (desmontados en 2014 y con desmonte planificado para 2020) se establecieron parcelas sobre dos transectos situados a 0 y a 10m de la orilla del río. En cada una de éstas se determinó el número de individuos de cada especie. Las distribuciones de abundancias relativas de especies de los distintos años se linealizaron y sólo fueron significativamente diferentes (ANOVA) las pendientes del año inmediatamente posterior al desmonte (2015). Al realizar un análisis de similitudes (ANOSIM) se distingue también la comunidad hallada antes del desmonte (2014) donde la especie dominante no era acacia negra sino arce. Se concluye que estas intervenciones facilitan el avance de la acacia negra en desmedro de las otras especies que constituyen el bosque ribereño en el río Luján