The Tonle Sap is the largest wetland in South-east Asia and the heart of the largest inland fishery in the world. Its unique flood pulse system and annual flow reversal is a hotspot for biodiversity and productivity, as well as an essential habitat for many endangered fishes and birds. Despite predicted changes to the wetland's hydrology due to climate change and hydropower development in the Mekong, the consequent impacts on the fauna of the lake are poorly understood. A spatial modelling framework was developed to simulate the impact of potential scenarios of change using relationships between fauna and biophysical characteristics. Potential impacts on 61 animal species with documented nutritional, conservation or ecological value were examined. A large number of species rely on gallery forest to provide important habitats for their life history, yet this area is likely to be highly impacted by permanent inundation. There is a strong synchronicity between life histories and the flood pulse; consequently continued hydrological disruptions will have a significant impact on ecosystem dynamics, imposing further challenges to conservation. Protecting areas that may become suitable for gallery forests and shrublands under a modified flood regime will be crucial to management planning and the maintenance of a diverse and healthy ecosystem.

The Pantanal is the world's largest tropical wetland and a biodiversity hotspot, yet its response to Quaternary environmental change is unclear. To address this problem, sediment cores from shallow lakes connected to the Upper Paraguay River (PR) were analyzed and radiocarbon dated to track changes in sedimentary environments. Stratal relations, detrital particle size, multiple biogeochemical indicators, and sponge spicules suggest fluctuating lake-level lowstand conditions between ~ 11,000 and 5300 cal yr BP, punctuated by sporadic and in some cases erosive flood flows. A hiatus has been recorded from ~ 5300 to 2600 cal yr BP, spurred by confinement of the PR within its channel during an episode of profound regional drought. Sustained PR flooding caused a transgression after ~ 2600 cal yr BP, with lake-level highstand conditions appearing during the Little Ice Age. Holocene PR flood pulse dynamics are best explained by variability in effective precipitation, likely driven by insolation and tropical sea-surface temperature gradients. Our results provide novel support for hypotheses on: (1) stratigraphic discontinuity of floodplain sedimentary archives; (2) late Holocene methane flux from Southern Hemisphere wetlands; and (3) pre-colonial indigenous ceramics traditions in western Brazil.

In contrast to rivers, the effects of water level fluctuations on the biota are severely understudied in lakes. Lake Constance has a naturally pulsing hydrograph with average amplitudes of 1.4 m between winter drought and summer flood seasons (annual flood pulse (AFP)). Additionally, heavy rainstorms in summer have the potential to create short-term summer flood pulses (SFP). The flood pulse concept for lakes predicts that littoral organisms should be adapted to the regularly occurring AFP, i.e. taking advantage of benefits such as an influx of food sources and low predator pressure, though these organisms will not possess adaptations for the SFP. To test this hypothesis, we studied the aquatic invertebrate assemblages colonizing the gravel sediments of Lake Constance, the AFP in spring and a dramatic SFP event consisting of a one meter rise of water level in 24 h. Here, we introduce the term ‘hypolacustric interstitial’ for lakes analog to the hyporheic zone of running water ecosystems. Our results confirm the hypothesis of contrasting effects of a regular AFP and a random SFP indicating that the AFP enhances the productivity and biodiversity of the littoral zone with benthic invertebrates displaying an array of adaptations enabling them to survive. The littoral zones of lakes deliver important ecosystem services by regulating flood effects, producing biomass and supporting biodiversity. To maintain and foster these services, the maintenance or reintroduction of natural water level fluctuations and the conservation of the habitat structures of the hypolacustric interstitial are urgently needed.

Animal populations have a certain synchronization between their fluctuations and the environmental factors which have adirect influence on density, sex ratio and recruitment. Trichodactylus borellianus is a common freshwater crab of theTrichodactylidae family, originary from South America. This crab is omnivorous and grazes upon the littoral communities. Thepresent study is the first analysis of the natural distribution and population dynamics of freshwater crabs in La Plata Basin(Argentina) and their relationship with certain abiotic and biotic parameters. It was carried out in three environments (riverinezone of streams and river) of the Paraná River floodplain. Crab populations were sampled monthly from August 2001 to October2002. The mean crab abundance among the study sites was significantly different, being lower in samples from the environmentsurrounding the principal channel of the Paraná River. Crab density showed two peaks: the highest occurred during late winterand early spring, and the lowest during late summer. Males were only more abundant in late winter and spring. In spring, summerand autumn, the population showed a contagious distribution. The population displayed a regular arrangement in winter.From mid-spring to mid-autumn juveniles were very frequent whereas adults predominated the rest of the year. Total crab numberin the stream nearest to the main channel varied according to the level and temperature of the river. In the other sites, locatedfurther from the main channel of the Paraná River, crab numbers and vegetation biomass showed a more similar arrangementwith a higher correlation.