Depósitos marinos de la Formación Chuy (pleistoceno tardío) y reajustes isostáticos en el área de la Laguna de Rocha (Uruguay)

The Chuy Formation is characterized by up to 135 m of an alternation of green pelites and fine to coarse sandstones with sparse invertebrate fossils. The marine deposits are interbedded with continental, loessic deposits of the Libertad Formation and overlain by the Dolores Formation, made up of mudstones with calcareous concretions. The results of the radiocarbon dating showed calibrated ages of 13.9±0.2, 41.5±1.9 and 50±3 ka BP on bioclasts of marine fossils at an elevation (above sea level, asl) of -2.8, -6.13 and -8 m respectively. Such ages and elevations are in disagreement with the sea-level evolution inferred for the Late Pleistocene. Two possible explanations are: (a) the ages represent minimum ages and deposition took place during the last interglacial at 115-130 ka (Marine Isotope Stage MIS 5e), or (b) they represent depositional ages but the area experimented large isostatic readjustments during and after the last glaciation. Several lines of evidence suggest a Late Pleistocene age for the upper Chuy Formation, including the δ18O curve obtained from invertebrate shells, which shows large secular variations consistent with MIS 1 to 7. The proposed scenario envisages significant subsidence between 50-20 ka due to the far-field effects of glacial load in the Andes/Patagonia. At 20 ka the eustatic regression outpaced subsidence, leading to continentalization of the Laguna de Rocha area. Marine conditions returned at 15 ka and into the Holocene, except for continental deposits (Dolores Formation) at ca. 11-10 ka (Younger Dryas). An uplift of 115 m took place between 15 and 9 ka in the area, which is interpreted as post-glacial rebound. In the Holocene, moderate subsidence was further recorded. A regional trend is observed, with uplift of marine deposits increasing towards the W-SW, which is consistent with an explanation as post-glacial isostatic rebound.La Formación Chuy se caracteriza por hasta 135 m de una alternancia de pelitas verdes y areniscas finas a gruesas con fósiles de invertebrados marinos. Los depósitos marinos están intercalados con depósitos loéssicos continentales de la Formación Libertad y sobreyacidos por la Formación Dolores, con lodolitas con concreciones calcáreas. Los resultados de dataciones radiocarbónicas mostraron edades calibradas de 13900±200, 41500±1900 y 50000±3000 años AP, para bioclastos de fósiles marinos a una cota sobre el nivel medio del mar (NMM) de -2,8, -6,13 y -8 m, respectivamente. Estas edades y cotas están en desacuerdo con la evolución del nivel medio del mar aceptada para el Pleistoceno tardío. Dos posibles explicaciones son: (a) las edades representan edades mínimas y la depositación tuvo lugar durante el último interglacial (115-130 ka; MIS 5e), o (b) representan edades de depositación, pero el área experimentó grandes reajustes isostáticos durante y después de la última glaciación. Varias líneas de evidencia favorecen una edad Pleistoceno tardío para la Formación Chuy superior, incluyendo la curva de δ18O obtenida para conchillas de invertebrados, que muestra grandes variaciones seculares consistentes con los estadios MIS 1 a MIS 7. El escenario propuesto prevé un hundimiento significativo entre 50-20 ka debido a los efectos lejanos de la carga glacial en los Andes/Patagonia. A los 20 ka, la regresión eustática superó al hundimiento, lo que llevó a la continentalización en el área de Laguna de Rocha. Las condiciones marinas regresaron a los 15 ka y durante el Holoceno, excepto por depósitos continentales (Formación Dolores) en 11-10 ka (Younger Dryas). Se produjo un levantamiento de unos 115 m entre 15 y 9 ka en la zona, lo que se interpreta como un rebote post-glacial. En el Holoceno, se registra nuevamente un hundimiento moderado. Se observa una tendencia regional, con un aumento de los depósitos marinos hacia el W-SW, lo que es consistente con un rebote isostático post-glacial

Coastal Wetlands: an integrated ecosystem approach

Coastal Wetlands, Second Edition: An Integrated and Ecosystem Approach provides an understanding of the functioning of coastal ecosystems and the ecological services that they provide. As coastal wetlands are under a great deal of pressure from the dual forces of rising sea levels and the intervention of human populations, both along the estuary and in the river catchment, this book covers important issues, such as the destruction or degradation of wetlands from land reclamation and infrastructures, impacts from the discharge of pollutants, changes in river flows and sediment supplies, land clearing, and dam operations

Implicancias de la Variabilidad Físico-Biológica y la Aplicación de Normas Legislativas Sobre el Recurso Pesquero en la Zona Costera del Sur de la Provincia de Buenos Aires, Argentina

Las condiciones hidrográficas y climatológicas de las aguas costeras son el principal factor a tener en cuenta cuando se analiza la abundancia de las especies ictícolas. Además se deben considerar las leyes de protección pesquera, como las vedas y las limitaciones en permisos de pesca. El Rincón, localizado en el sur de la Provincia de Buenos Aires (Argentina) es un área costera compleja por las diferentes interacciones que se evidencian entre el continente y el mar y principalmente a través de la susceptibilidad del sistema a la variabilidad climática (eventos el Niño). En el presente estudio se analizan los desembarques pesqueros anuales en el periodo 2002-2010 en la zona de El Rincón asociado con las variaciones físico ambientales del medio marino y las normas legislativas pesqueras de la zona. Como conclusión se infiere que las condiciones Niño benefician la abundancia de ciertas especies, mientras que el evento Niña beneficia el desarrollo de otras

Caracterización de médanos parabólicos de la región pampeana oriental, centro oeste de la provincia de Buenos Aires (Argentina).

 La región pampeana, especialmente la provincia de Buenos Aires, se caracteriza por la presencia de paisajes eólicos que, si bien responden a eventos producidos en el Cuaternario Superior, en la actualidad son reactivados por la actividad agropecuaria. El objetivo de este trabajo se centra en la detección y delimitación de un campo de médanos parabólicos parcialmente reactivados, ubicados en el centro oeste de dicha provincia, que si bien han sido mencionados en la literatura, no han sido objeto de estudio detallado. Mediante la generación de un Modelo Digital de Elevaciones (MDE) a partir de imágenes SRTM (Shuttle Radar Topography Mission) se ha detectado un campo con un total de 254 médanos parabólicos que ocupan 20.200 km2, ubicados entre los 120 y 90 msnm. Los mismos presentan una dirección general SW-NE, con anchos que varían entre 2 y 5 km y alturas entre 2 y 6 m. Aplicando la herramienta Distancia Vertical al Curso (Vertical Distance to Channel Network, VDCN) del Software SAGA GIS 2.1.2 y una clasificación automática no supervisada en ArcGIS 10.1, se lograron discriminar los médanos de la planicie circundante. A partir de muestras de sedimento de un médano testigo ubicado en la localidad de 30 de Agosto (Buenos Aires), se establecieron claras diferencias en la granulometría en distintos sectores del mismo. La ubicación de estos médanos es clave en la configuración del escurrimiento y, en consecuencia, este paisaje arenoso tiene un rol importante en la configuración del espacio del área de estudio ya que se forman lagunas intermedanales someras cuyo desarrollo depende de las precipitaciones locales

A preliminary analysis of flat-gravel transport over a sandy beach, Pehuén Co, Argentina

Pehuén Co Beach, on the southwest coast of the Buenos Aires Province (Argentina), provides an example of an heterogeneous (mixed sand-gravel) sediment beach with gravels of the most diverse size and origin. Over 40% of the pebbles are carbonate flat gravels. Field observations included beach profiles, measurements of wave generated currents with an acoustic currentmeter (ADV), videos of 5 x 5 m grid located on the swash zone during inundation from a nearby tower. Video films where rectified and analyzed using PIV and wavelets. Based on the results, we demonstrated that flat gravels can be easily transported upbeach distances in excess of 5 m in about 1.5 h. This period corresponds to the high tide situation and covering the steepest beachface segment. Wave conditions during the experiment corresponded to low breaker height and short periods, but by no means they could be considered as storm waves demonstrating that gravels can be transported even by saltation during fair weather conditions

Engaging stakeholders across a socio-environmentally diverse network of water research sites in North and South America

Maintaining and restoring freshwater ecosystem services in the face of local and global change requires adaptive research that effectively engages stakeholders. However, there is a lack of understanding and consensus in the research community regarding where, when, and which stakeholders should be engaged and what kind of researcher should do the engaging (e.g., physical, ecological, or social scientists). This paper explores stakeholder engagement across a developing network of aquatic research sites in North and South America with wide ranging cultural norms, social values, resource management paradigms, and eco-physical conditions. With seven sites in six countries, we found different degrees of engagement were explained by differences in the interests of the stakeholders given the history and perceived urgency of water resource problems as well as differences in the capacities of the site teams to effectively engage given their expertise and resources. We categorized engagement activities and applied Hurlbert and Gupta's split ladder of participation to better understand site differences and distill lessons learned for planning comparative socio-hydrological research and systematic evaluations of the effectiveness of stakeholder engagement approaches. We recommend research networks practice deliberate engagement of stakeholders that adaptively accounts for variations and changes in local socio-hydrologic conditions. This, in turn, requires further efforts to foster the development of well-integrated research teams that attract and retain researchers from multiple social science disciplines and enable training on effective engagement strategies for diverse conditions

Can scenario-planning support community-based natural resource management? Experiences from three countries in latin america

Community Based Natural Resource Management (CBNRM) is a concept critical to managing socio-ecological systems, but whose implementation needs strengthening. Scenario-planning is one approach that may offer benefits relevant to CBNRM, but whose potential is not yet well understood. We therefore designed, trialled and evaluated a scenario-planning method intended to support CBNRM at three cases, located in Colombia, Mexico and Argentina. Implementing scenario-planning was judged as worthwhile in all three cases, although aspects of it could be challenging to facilitate. The benefits generated were relevant to strengthening CBNRM: encouraging the participation of local people and using their knowledge; enhanced consideration and adaption of future change; and supporting the development of systems thinking. Tracing exactly when and how these benefits arise is challenging, but two elements of the method seemed particularly useful. Firstly, using a systematic approach to discuss how drivers of change may affect local socio-ecological systems helped to foster systems thinking and identify connections between issues. Secondly, explicitly focusing on how to use and respond to scenarios helped identify specific practical activities ('response options') that would support CBNRM despite the pressures of future change. Discussions about response options also highlighted the need for support by other actors (e.g. policy groups): this raises the question of when and how other actors and other sources of knowledge should be involved in scenario-planning, so as to encourage their buy-in to actions identified by the process. We suggest other CBNRM initiatives may benefit from adapting and applying scenario-planning. However, these initiatives should be carefully monitored since further research is required to understand how and when scenario-planning methods may produce benefits, and their strengths and weaknesses versus other methods

Calidad y aprovechamiento del agua de la Laguna Unamuno (Buenos Aires, Argentina)

Una de las características más destacadas de la geomorfología de la provincia de Buenos Aires es la presencia de un número muy grande de lagunas, de tamaños y formas diversas, con una distribución aparentemente caótica. Muchas de ellas han ocupado tierras potencialmente productivas. La laguna Unamuno se halla localizada en la cuenca del arroyo Napostá Chico (1320 km2), en la región pampeana argentina. El objetivo del trabajo es el estudio de la calidad del agua de la laguna y el análisis de las posibilidades de aprovechamiento del recurso hídrico. Se recopilaron datos edafológicos y meteorológicos, se midieron parámetros físicos y se analizaron muestras de agua en superfi cie y profundidad. La calidad del agua es evaluada desde las perspectivas biológica, química y física