During 2008, under a region-wide drought, there were a large number of simultaneous fires in the Paraná River Delta region: the most affected vegetation was in marshes dominated by Schoenoplectus californicus (C.A.Mey.) Soják or Cyperus giganteus Vahl. The objective of this paper was to study fire severity in terms of fire effect on vegetation cover and soil properties, and the recovery of those properties after one growing season, using optical remote sensing techniques and fieldwork data. To this aim, we performed unsupervised classification of Landsat TM imagery and conducted vegetation censuses and soil sampling in November 2008 and May 2009. Our results show that we could identify three fire severity classes: low severity, medium severity, and high severity. These classes are characterized by a remnant vegetation cover of approximately 75 %, 25 %, and 5 %, respectively, and a diminution of soil organic carbon and nitrogen of 66 % and 59 % in the case of medium severity and high severity. Fire had almost no effect over pH and a slight effect on electrical conductivity. After one growing season, vegetation recovery is dependent on fire severity and hydrological condition, while soil properties did not show signs of recovery. This is one of the first studies of fire effects and recovery on fluvial herbaceous wetlands.

Wetland ecosystems have a high carbon storage potential as a result of high primary productivity and low decomposition rates dictated by water saturation. In the herbaceous wetlands of the Parana Ŕiver Delta, drainage and afforestation with poplars represents one of the dominant land uses. We explored the effects of these interventions on the volume and carbon storage of the young sedimentary soils of the region. At three sites we identified paired stands occupying similar landscape positions and soil types but subject to natural flooding and covered by natural herbaceous communities or drainage and flood control by dikes and covered by poplar plantations established 12, 17 and 19 years ago. Soil sampling at these sites revealed a reduction of the litter compartment (-86 %) and decreasing volume and porosity of its underlying mineral layer (0-10 cm in the wetland reduced to 0-4 cm in the plantation). Our comparisons of carbon storage accounted for these volumetric shifts by using accumulated mineral mass rather than depth as a reference, showing that tree plantations gained in the mineral soil (22 Mg C ha -1 ) almost as much as what they lost in the litter. These gains were particularly large at intermediate depths (4-43 cm in the plantations) were soil porosity remained unaffected and C was raised by 64 % explained by (1) the pulse of inputs from overlaying litter and organic layers subject to rapid decomposition and mobilization after drainage and (2) root colonization, since tree plantations had 75 % of their fine root biomass at these intermediate soil depths, whereas roots in the wetlands did not explore the mineral soil profile and were completely confined to the organic layer. A neutral C balance following wetland drainage and afforestation resulted from the opposing effects of aeration, favoring decomposition in the organic layer, root colonization and organic matter stabilization, favoring its accumulation in the mineral soil.

Manuscrito recibido el 14 de junio de 2016. Aceptado, tras revisión, el 15 de septiembre de 2016. ResumenSe realizó una exploración inicial sobre medidas de adaptación implementadas frente a Eventos Hidrometeorológicos Extremos (EHE) en zonas rurales, extraídas de sitios seleccionados en Argentina, Brasil, Chile, Colombia y Ecuador; el primer desafío encontrado fue la definición de EHE; puesto que la misma cambia si se la enfoca desde el punto de vista meteorológico o hidrológico; además, no existe acuerdo en la definición de valores límites para caracterizar estos eventos dentro de la región; finalmente, en muchos de los sitios donde se realizó este estudio no existen registros lo suficientemente largos y confiables para poder cuantificar los EHE; en consecuencia se decidió utilizar una definición "empírica" de EHE, dejando que sean los actores sociales que vivieron la experiencia los que determinen cuando ocurrió un evento de esa naturaleza. A pesar de las diferencias en la vulnerabilidad y los impactos sobre los paisajes rurales de cada sitio, las evidencias sugieren que la gestión integrada de los paisajes a nivel comunitario permite a los productores agrícolas adoptar medidas de adaptación a su debido tiempo y preparar a las comunidades rurales para enfrentarse y responder ante la ocurrencia de EHE. Entre las lecciones aprendidas más importantes se identificaron: La demanda de una adecuada transferencia de información relacionada a EHE; la necesidad de promoción del capital social; la importancia de tener un Estado desempeñando un rol proactivo; la relevancia de tener una prensa que oriente y no escandalice; y la necesidad de contar con mecanismos óptimos para estimación de costos.Palabras claves: evento ENOS, cambio climático, adaptación.

Nitrogen (N) and phosphorus (P) are the most limiting nutrients in natural freshwater wetlands. Flooded marshes dominate in the freshwater wetlands of the Lower Paraná River floodplain (Argentina). The leaf N and P concentration and the N:P ratios were assessed as a first approach to evaluate the nature of nutrient limitation. A total of 96 sites and 131 dominant plant populations (belonging to 50 herbaceous macrophyte species) were sampled in medium hydrometric level conditions. The interspecific variability of leaf nutrients was higher than the intraspecific variability. Foliar N ranged from 0.5% to 5.3%, while foliar P ranged from 0.1% to 0.5%. Leaf N:P was 9.3 ± 4.3 (mean ± standard deviation), suggesting N-limitation for most of the plant populations –under the assumption of the validity of the critical N:P thresholds previously proposed (N:P < 10 for N limitation, N:P > 20 for P limitation). Neither the leaf nutrients nor the N:P were affected by the flooding frequency, hydrometric water level, or wetland landscape unit/subunit location. The species identity accounted for most of the leaf nutrient and N:P variability, followed by the sampling date for P and N:P levels. This study provides a baseline on the nature of nutrient limitation, mainly by N, in plants of the Lower Paraná River floodplain. Future surveys or experiments could address the variations of leaf nutrients and nutrient limitation in contrasting hydrological conditions.