Aguinaldo Silva

Avulsive Rivers in the Hydrology of the Pantanal Wetland

This chapter presents and discusses the avulsive nature of the Pantanal rivers and shows how the ever-changing drainage network influences the surface hydrology and ecology. Besides, the systemic portrait here outlined provides new insights concerning the Pantanal hydrodynamics, in its particularities and as a whole system. A simple model of the avulsion process is illustrated, and several realistic examples of the processes leading to river avulsions are shown and discussed. The north-to-south flood-pulse wave due to the presence of bottlenecks is further described in detail. This systemic approach allows identifying that the fluvial “avulsive and bottleneck” dynamics seasonally affects both local and regional ecohydrological processes. Moreover, it shows that avulsive processes are commonplace in Pantanal, and changes in land use, particularly in river headwaters in the highlands, accelerate the avulsions, making the sustainable use of the Pantanal lowland areas difficult.

Methane and Carbon Dioxide Dynamics in the Paraguay River Floodplain (Pantanal) in Episodic Anoxia Events

Worldwide wetlands contribute to the global carbon cycle by emitting about a third of the global methane (CH4) emissions. However, CH4 and carbon dioxide (CO2) dynamics remain poorly understood in the largest tropical wetland on Earth, the Pantanal. In this chapter, we aim to characterize the CH4 and CO2 biogeochemistry in the floodplain of the Paraguay River, near Corumba, during the course of annual anoxia phenomena locally known as dequada. The strong anoxia is associated to the flooding of terrestrial habitats that enhances respiration, dissolved oxygen (DO) consumption, and methanogenesis. The extremely low DO also leads to high fish mortality in the region. CH4 and CO2 concentration in surface waters and diffusive water–air fluxes were measured in the oxbow Tuiuiu Lake and in the Paraguay River main stem in order to identify temporal and spatial patterns. The whole dataset shows that, for instance, dissolved CH4 and diffusive CH4 fluxes increased dramatically during the dequada. In the study area, CH4 emissions can reach 9–85 mg CH4 m−2 h−1 during dequada climax. Riverine anoxic waters steadily penetrate the oxbow Tuiuiu Lake, indicating water inflow from the river main stem, whereas small reminiscent patches of oxbow waters not mixing with anoxic river waters may function as survival refuges to the aquatic wildlife. Clearly, the DO distribution during several dequadas in major rivers of the Pantanal highlights the importance of geomorphology on the biogeochemistry in the riverine floodplains of the Pantanal wetland.

Paleolimnology in the Pantanal: Using Lake Sediments to Track Quaternary Environmental Change in the World’s Largest Tropical Wetland

In spite of its global significance to biodiversity and biogeochemical cycles (e.g., as a methane source and carbon dioxide sink), the Pantanal of western Brazil remains underexplored from the perspective of Quaternary paleoecology, paleogeography, and paleoclimatology. Long in the scientific and cultural shadow cast by the Amazon Basin, recent research using lake sediment cores from different sites across the Pantanal lowlands has provided a glimpse at the sensitivity of this savanna floodplain wetland to climate-driven perturbations in the hydrologic cycle. Understanding the controls and feedbacks associated with this sensitivity is important, as the Pantanal is a critical freshwater resource situated in the headwaters of the immense Rio de la Plata Basin. Published lake sediment archives have adopted a multi-indicator analytical approach, focusing on physical sedimentology, geochemistry, palynology, and siliceous microfossils. Such studies extend in time from the late Pleistocene to the present day, with the greatest emphasis placed on reconstruction of the Holocene environmental history. Several important transitions in effective precipitation have been inferred for the Holocene, which appear to be dominantly linked to variability in insolation and the South American Summer Monsoon system. By contrast, evidence of aridity in the Pantanal during the Last Glacial Maximum suggests that the wetlands also respond in a complex manner to Northern Hemisphere ice volume and that insolation forcing alone fails to fully explain patterns of environmental change. The great diversity of lacustrine ecosystems in the Pantanal warrant additional study and hold the potential to broaden our understanding of the response of tropical wetlands to global change. Such insights will be valuable for conservation planning, resource security, and sustainable management.

Amazon rainforest modulation of water security in the Pantanal wetland

The Pantanal is a large wetland mainly located in Brazil, whose natural resources are important for local, regional and global economies. Many human activities in the region rely on Pantanals ecosystem services including cattle breeding for beef production, professional and touristic fishing, and contemplative tourism. The conservation of natural resources and ecosystems services provided by the Pantanal wetland must consider strategies for water security. We explored precipitation data from 1926 to 2016 provided by a regional network of rain gauge stations managed by the Brazilian Government. A timeseries obtained by dividing the monthly accumulated-rainfall by the number of rainy days indicated a positive trend of the mean rate of rainy days (mm/day) for the studied period in all seasons. We assessed the linkage of Pantanals rainfall patterns with large-scale climate data in South America provided by NOAA/ESRL from 1949 to 2016. Analysis of spatiotemporal correlation maps indicated that, in agreement with previous studies, the Amazon biome plays a significant role in controlling summer rainfall in the Pantanal. Based on these spatiotemporal maps, a multi-linear regression model was built to predict the mean rate of summer rainy days in Pantanal by 2100, relative to the 1961-1990 mean reference. We found that the deforestation of the Amazon rainforest has profound implications for water security and the conservation of Pantanals ecosystem services.