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Low-order streams and riparian wetlands are important contributors to the drainage network in the landscape. However, there has been little research into the nature of these ecosystems in Brazil. Our estimates show that riparian wetlands of low-order streams and other small associated wetlands cover at least 25% of the forested part of the Amazon basin and about 10% of the Cerrado region. Information on the semi-arid Caatinga is lacking, but ~ 3% of the area may be occupied by riparian wetlands and other small wetland types, many of which are periodically dry. Riparian vegetation includes a very large richness in tree species. The amount and species richness of herbaceous plants depend on light availability. In-streams of the semi-arid region of Brazil, hydrophytes are restricted by unpredictable flash floods and periodic drought. Aquatic food webs are largely based on the organic matter produced by the riparian vegetation. Large-scale agriculture and cattle ranching pose a serious threat to riparian wetlands, their biodiversity, and their function as a buffer in the hydrological cycle of the landscape. A nation-wide screening program would provide a more detailed picture and allow the elaboration of a national conservation and restoration program for the Brazilian riparia.

Made available in DSpace on 2021-06-25T10:22:58Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-05-01 Fundação de Amparo à Pesquisa do Estado do Amazonas Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) The Balbina hydropower dam in the Central Amazon basin, established in the Uatumã River in the 1980s, is emblematic for its socio-environmental disaster. Its environmental impacts go far beyond the reservoir and dam, however, affecting the floodplain forests (igapó) in the downstream area (dam shadow), which have been assessed using a transdisciplinary research approach, synthesized in this review. Floodplain tree species are adapted to a regular and predictable flood pulse, with high- and low-water periods occurring during the year. This was severely affected by the operation of the Balbina dam, which caused the suppression of both the aquatic phase at higher floodplain elevations and the terrestrial phase at lower floodplain elevations (termed the ‘sandwich effect’). During the period of construction and reservoir fill, large-scale mortality already occurred in the floodplains of the dam shadow as a result of reduced stream flow, in synergy with severe drought conditions induced by El Niño events, causing hydraulic failure and making floodplains vulnerable to wildfires. During the operational period of the dam, permanent flooding conditions at low topographical elevations resulted in massive tree mortality. So far, 12% of the igapó forests have died along a downstream river stretch of more than 125 km. As a result of flood suppression at the highest elevations, an encroachment of secondary tree species from upland (terra firme) forests occurred. More than 35 years after the implementation of the Balbina dam, the downstream impacts caused massive losses of macrohabitats, ecosystem services, and diversity of flood-adapted tree species, probably cascading down to the entire food web, which must be considered in conservation management. These findings are discussed critically, emphasizing the urgent need for the Brazilian environmental regulatory agencies to incorporate downstream impacts in the environmental assessments of several dam projects planned for the Amazon region. Grupo de Pesquisa Ecologia Monitoramento e uso Sustentável de Áreas Úmidas (MAUA) Instituto Nacional de Pesquisas da Amazônia (INPA) Institute of Geography and Geoecology Department of Wetland Ecology Karlsruhe Institute for Technology (KIT) Programa de Pós-graduação em Botânica Instituto Nacional de Pesquisas da Amazônia (INPA) Programa de Pós-graduação em Ecologia Instituto Nacional de Pesquisas da Amazônia (INPA) Programa de Pós-graduação em Clima e Ambiente Instituto Nacional de Pesquisas da Amazônia (INPA)/Universidade do Estado do Amazonas (UEA) Programa de Pós-graduação em Biologia de Água Doce e Pesca Interior Instituto Nacional de Pesquisas da Amazônia (INPA) Instituto de Ciências Biológicas Departamento de Ecologia Universidade de Brasília (UnB) Department of Biogeochemical Processes Max-Planck-Institute for Biogeochemistry Universidade Estadual Paulista (UNESP) Instituto de Geociências e Ciências Exatas Naturalis Biodiversity Center Systems Ecology Vrije Universiteit Amsterdam Instituto Nacional de Pesquisas da Amazônia (INPA) Laboratório de Ecofisiologia e Evolução Molecular (LEEM) Instituto Nacional de Ciência e Tecnologia em Adaptações da Biota Aquática da Amazônia (ADAPTA) Instituto Nacional de Ciência e Tecnologia em Áreas Úmidas (INAU) Universidade Federal de Mato Grosso (UFMT) Programa de Pós-graduação em Ciência Ambiental (PROCAM) Universidade de São Paulo (USP) Centro de Formação em Ciências Agroflorestais Universidade Federal do Sul da Bahia (UFSB) Faculty of Natural Sciences University of Stirling Núcleo de Estudos e Pesquisas Ambientais (NEPAM) Universidade Estadual de Campinas (UNICAMP) Universidade Estadual Paulista (UNESP) Instituto de Geociências e Ciências Exatas Fundação de Amparo à Pesquisa do Estado do Amazonas: 062.1187/2017 CNPq: 403792/2012-6 CNPq: 441462/2017-0 CNPq: 441498/2017-5 CNPq: 441590/2016-0 CNPq: 457893/2013-3 CNPq: 465540/2014-7 CAPES: Finance Code 001 Fundação de Amparo à Pesquisa do Estado do Amazonas: FIXAM 017/2914

The large flood pulse of the Amazon basin is a principal driver of environmental heterogeneity with important implications for ecosystem function and the assembly of natural communities. Understanding species ecological response to the flood pulse is thus a key question with implications for theories of species coexistence, resource management, and conservation. Yet these remain largely undescribed for most species, and in particular for trees. The large flood pulse and high tree diversity of the Negro River floodplain makes it an ideal system to begin filling this knowledge gap. We merged historical hydrologic data with 41 forest inventories under variable flooding conditions distributed across the Negro River basin, comprising a total area of 34 ha, to (i) assess the importance of flood duration as a driver of compositional variation, (ii) model the response curve shapes of 111 of the most frequent tree species in function of flood duration, and (iii) derive their niche properties (optima and tolerance). We found that flood duration is a strong driver of compositional turnover, although the majority site-to-site variation in forest composition still remains unexplained. About 73% of species responded to the flood duration gradient, exhibiting a diversity of shapes, but most frequently skewed. About 29% of species were clearly favored by flood durations >120 days year–1, and 44% of species favored by shorter floods. The median niche breadth was 85 flood days year–1, corresponding to approximately 30% of the flood duration gradient. A significant subset of species (27%) did not respond to flooding, but rather exhibited wide tolerance to the flood gradient. The response models provided here offer valuable information regarding tree species differential capacity to grow, survive, and regenerate along an ecologically important gradient and are spatially valid for the Amazon Negro basin. These attributes make them an appealing tool with wide applicability for field and experimental studies in the region, as well as for vegetation monitoring and simulation models of floodplain forest change in the face of hydrologic alteration.

Building bridges between environmental and political agendas is essential nowadays in face of the increasing human pressure on natural environments, including wetlands. Wetlands provide critical ecosystem services for humanity and can generate a considerable direct or indirect income to the local communities. To meet many of the sustainable development goals, we need to move our trajectory from the current environmental destructive development to a wiser wetland use. The current article contain a proposed agenda for the Pantanal aiming the improvement of public policy for conservation in the Pantanal, one of the largest, most diverse, and continuous inland wetland in the world. We suggest and discuss a list of 11 essential interfaces between science, policy, and development in region linked to the proposed agenda. We believe that a functional science network can booster the collaborative capability to generate creative ideas and solutions to address the big challenges faced by the Pantanal wetland. Made available in DSpace on 2019-09-27T00:39:34Z (GMT). No. of bitstreams: 1 SustainabilityAgenda2019.pdf: 7046678 bytes, checksum: 95e607f5662246d9f5e01cf9b656b030 (MD5) Previous issue date: 2019

Knowledge about the distribution and diversity of wetlands has become an essential tool for environmental management and policy-making. Yet, while recent estimates indicate that 27% of the area of Colombia is covered by wetlands and despite a number of regional studies, information about the diversity of wetlands nationally is scarce. In response, we present a national wetland classification system that is based on an ecological approach, from the perspective of wetland scientists, and which builds upon the assumptions underlying the flood pulse concept and hydrogeomorphic approach. Thus, the approach and structure of the Brazilian wetland classification system are used, with geomorphological adjustments made according to Colombia’s topography. The classification is hierarchical, multi-scale, functional, and organized according to four levels (system, macroregion, subsystem, and class), with the wetland diversity of Colombia represented nationally by 89 macrohabitats across marine-coastal, inland, and anthropogenic systems. The primary purpose of this classification is to provide integrated and organized information on the distribution and diversity of Colombian wetlands that will serve as a baseline for transparent environmental policy-making.

The Pantanal is subjected to a monomodal and predictable flood pulse of low amplitude which is the main driver of ecological processes and patterns of biodiversity in one of the largest wetlands in the world. Nevertheless, little is known about how the plant communities of this wetland respond to predicted climate changes. In this paper, we used tree-ring analyses of Vochysia divergens Pohl (Vochysiaceae), a light-demanding pioneer species that occurs in periodically or short-term flooded areas in the Cerrado and Pantanal. We evaluated the influence of precipitation and water level on the growth rates of this species, where it occurs, to determine how local climatic variables (precipitation and water level) influence tree growth and how a large-scale climatic driver in the tropical eastern Pacific (El Niño events) could affect both tree growth and local climate in the northern region of the Pantanal. The indexed tree-ring chronology of eight individuals had a significant relationship with annual precipitation (r = 0.22). Interannual variations of the water level did not affect tree growth. Sea surface temperature anomalies of the El Niño 1 + 2 region lead to decreased precipitation in the northern region of the Pantanal, resulting in decreased diameter increments of V. divergens. Our results demonstrated the dendrochronological potential of V. divergens for analyzing climate–growth relationships for developing climate-sensitive proxies for reconstructing past climatic conditions. © 2018, Botanical Society of Sao Paulo.

International audience; Question: The encroachment of woody species has been globally reported over much of arid and semi-arid biomes, and has been associated with a decrease in cover and number of herbaceous species. How does the encroachment of a woody shrub affect herbaceous community structure and species composition in grasslands of a wetland ecosystem? Location: Seasonally flooded grasslands in a Neotropical Hyperseasonal Savanna, the Pantanal wetland, Brazil. Methods: We investigated the effect of the encroaching plant Combretum laxum on a herbaceous community from seasonally flooded grasslands in the Pantanal wetland using 29 vegetation samples representing encroachment at different spatio-temporal stages. The point quadrat method was used to acquire vegetation data, as plant cover, species richness (S) and Shannon-Wiener diversity index (H'). We evaluated the existence of stages of encroachment related to differences in vegetation structure and species composition using non-metric multidimensional scaling ordination and analysis of similarity. The response of the herbaceous community to shrub advance was analysed using linear and quadratic polynomial regression models. Model fitness was tested using the ACI. Results: The advance of the woody encroaching plant C. laxum over the seasonally flooded grassland occurs in three stages: grassland stage, shrub islands stage and shrubland stage. The initial advance of C. laxum over the grassland, represented by the shrub islands stage was correlated to an increase in species richness and a decrease in important native forage grasses. Critical changes in the herbaceous community were observed when the encroaching plant covered > 30% of the periodically flooded grassland, when the richness of herbaceous species dropped from 22 to four. Conclusions: Woody encroachment causes impoverishment and simplification of the herbaceous community. The shift from a grass-to a shrub-dominated state is related to the reduction in important grassland-obligate species, forage resources for herbivore livestock and wild animals, affecting the ecological dynamics and the economy of rangelands. Conservation of these grassland ecosystems depends on rangeland management practices guided by scientific knowledge on the causes and consequences of plant community changes.

Ocorrem na Bacia do Rio Bento Gomes (MT), às margens do Pantanal Mato-grossense, cerca de sessenta garimpos de ouro, onde o mercúrio é utilizado de forma intensiva nos processos de produção, através da formação de amálgamas que facilitam a aglutinação de partículas finas. A queima do amálgama nem sempre é feita em sistemas fechados de recuperação, havendo, portanto, perda de vapor para a atmosfera. Este estudo traz resultados de análises de mercúrio total nos cabelos de quatro grupos de voluntários que vivem em Poconé (MT), e faz uma caracterização geral do ambiente no que se refere à presença do metal na água e no sedimento do Rio Bento Gomes. Um equipamento de detecção por fluorescência foi usado para a determinação das concentrações, e os resultados indicam que os valores são mais baixos do que os de outras populações de áreas de garimpo no Brasil. Indicam também que a via ocupacional parece ser a mais eficiente rota potencial de contaminação da população por mercúrio. There are some 60 gold-mining sites in the Bento Gomes River basin (Mato Grosso), at the border of the Mato Grosso Pantanal (Swamp), where mercury is used to agglutinate fine gold particles through amalgamation. During burning of the amalgam to release the gold, mercury vapor is lost to the atmosphere, since closed systems for mercury recovery are not always used. This study shows the results of total mercury analysis in hair from four volunteer groups living in Poconé, Mato Grosso, and presents a general environmental description pertaining to the presence of mercury in water and sediments from the Bento Gomes River. Atomic fluorescence was used for measuring mercury concentrations. The results were lower than for other populations from gold-mining areas in Brazil.

The exact size of the wetland area of South America is not known but may comprise as much as 20% of the sub-continent, with river floodplains and intermittent interfluvial wetlands as the most prominent types. A few wetland areas have been well studied, whereas little is known about others, including some that are very large. Despite the fact that most South American countries have signed the Ramsar convention, efforts to elaborate basic data have been insufficient, thereby hindering the formulation of a wetland-friendly policy allowing the sustainable management of these areas. Until now, the low population density in many wetland areas has provided a high level of protection; however, the pressure on wetland integrity is increasing, mainly as a result of land reclamation for agriculture and animal ranching, infrastructure building, pollution, mining activities, and the construction of hydroelectric power plants. The Intergovernmental Panel on Climate Change has predicted increasing temperatures, accelerated melting of the glaciers in Patagonia and the Andes, a rise in sea level of 20–60 cm, and an increase in extreme multiannual and short-term climate events (El Nin˜o and La Nin˜a, heavy rains and droughts, heat waves). Precipitation may decrease slightly near the Caribbean coast as well as over large parts of Brazil, Chile, and Patagonia, but increase in Colombia, Ecuador, and Peru, around the equator, and in southeastern South America. Of even greater impact may be a change in rainfall distribution, with precipitation increasing during the rainy season and decreasing during the dry season. There is no doubt that the predicted changes in global climate will strongly affect South American wetlands, mainly those with a low hydrologic buffer capacity. However, for the coming decades, wetland destruction by wetland-unfriendly development planning will by far outweigh the negative impacts of global climate change. South American governments must bear in mind that there are many benefits that wetlands bring about for the landscape and biodiversity as well as for humans. While water availability will be the key problem for the continent’s cities and agroindustries, intact wetlands can play a major role in storing water, buffering river and stream discharges, and recharging subterranean aquifers.

Water chemistry provides important parameters for the study of river ecology and management options of rivers and connected wetlands. Sioli, in the 1950s, established three water types (whitewater, blackwater and clearwater) for explaining limnological characteristics of the large Amazonian rivers, and related the physico-chemical parameters of these water types with the geological properties of their basins; a landscape ecology approach. Today, an increasing amount of hydrochemical data indicate that the chemical composition of Amazonian water bodies varies much more than assumed by Sioli. Nonetheless, due to its simplicity for describing the natural physico-chemical variability of Amazonian rivers, his classification is still valid. Our analysis, based in literature and field work, allowed to distinguish well among the three classical water types and to provide new preliminary insights about the limnological classification of Amazonian rivers in order to subsidize the sustainable management of water resources and wetlands. © 2014 WIT Press.

The Amazonian wetlands cover a vast area subject to a monomodal flood pulse with an annual amplitude averaging 10 m, which defines an aquatic phase and a terrestrial phase of great biological importance. According to the geological origin and the catchment areas, the physical and chemical properties of the wetland will vary, being defined two major groups, the varzeas and the igapos. Although aquatic herbaceous plants do occur in the two types, higher species richness and densities are typical of the varzeas where aquatic herbaceous species, particularly C4 plants may exhibit high biomass values and net primary production - NPP about three times these of the floodplain forest. The aquatic herbaceous plants are very important in the carbon and nutrient budgets of the varzea, since through their decomposition they promote the enrichment of the aquatic system and associated floodplains, both during the aquatic and terrestrial phases of the hydrologic cycle. The major threats to herbaceous aquatic plants are related to the modification and contamination of the habitats owing to their use in economic activities as cattle and buffalo ranching and agriculture. Degradation improves the susceptibility of these systems to fire especially during the terrestrial phase, resulting in economic losses and further degradation of floodplains. Recently oil spills linked to the petroliferous activities in the region are of major concern demanding further and urgent evaluation.

This paper delivers a conceptual framework for the ecological functioning and biodiversity patterns of lakes that is based on the floodpulse concept (FPC). The specific characteristics of rivers and lakes considering water-level fluctuations are compared, with respect to catchment linkages, temporal patterns, and hydraulic forces of flooding and drawdown. The influences of floodpulses on element cycles, biodiversity, and adaptations of lake biota are analyzed, and the importance of multi-annual flooding cycles is highlighted. The degree by which these water-level fluctuations influence lake ecosystems strongly depends on lake morphology, where shallow lakes or those with large shallow margins are the most sensitive. Although floodpulses play a major role for ecosystem services such as lake management and climate change mitigation schemes, this issue is only scarcely dealt with. Tenets of the extended FPC for lakes are formulated in order to overcome this problem.

The aquatic invertebrates of Amazonian floodplains can be divided into three large communities: the zooplankton, the benthos and the perizoon. Most studies deal with zooplankton, concentrating on taxonomic aspects and on community structure during the hydrological cycle.

When the first Europeans came to the Amazon they were deeply impressed by the rich wildlife along the river. Cristobal de Acuna, who participated in the Amazon expedition of the Portuguese General Pedro Teixeira in 1637–1638, reported the great abundance of river turtles, which the natives caught for food and stored alive behind fences. Caimans had been so frequent that they were crowded at low water level in the remaining lakes in the floodplain. The exploitation of the large stocks of manatees and turtles became economically important activities. At the end of the last century, Verissimo (1895) criticised the irresponsible fishing and hunting practises and predicted the extinction of the turtles, the manatee, and the giant osteoglossid fish Pirarucu (Arapaima gigas). After World War II, the hides of caimans became of interest for tanneries and the populations were greatly reduced in a few decades.

Structure and function of an ecosystem are determined to a large extent by its trophic dynamics (Lindeman 1942). Organic material produced by primary producers is processed by a suite of consumer and decomposer populations, the species composition and size of which depends upon the amount, quality and availability of the organic material (Boyd and Goodyear 1971). In Amazonian floodplains large amounts of non-woody biomass are available for primary consumers. Herbaceous plant communities produce up to 100 t ha−1 year−1 dry matter in the varzea. The floodplain forest of the varzea provides up to 13.6 t ha−1 year−1 leaf litter and that of the igapo up to 6.7 t ha−1 year−1 (Chaps. 8, 11). However, only a very small fraction is utilized by herbivorous animals.

The different water colors of Amazonian rivers are documented in the river names e.g., Rio Negro (black river), Rio Branco (white river), Rio Claro (clear river), Rio Verde (green river), and indicate differences in water quality. Sioli (1950) related water color to specific conditions in the catchment areas and recognized three main water types based on water color, load of suspended solids, pH, and load of dissolved minerals, indicated by the specific conductance.

Floodplains are wetlands which oscillate between terrestrial and aquatic phases. This makes them alternately suitable for aquatic and terrestrial organisms, but makes utilization by humans difficult. For this reason, the extensive floodplains of Europe and North America were largely eliminated or strongly modified early on by human activities. For example, flood control measures by Tulla brought about extensive changes in the large floodplain of the upper Rhine valley in the middle of the last century (Kunz 1975) long before the study of limnology was established. Therefore, floodplains were neglected by limnologists and terrestrial ecologists for a long time (Bayley 1980; Junk 1980).

The contribution of termites to the global methane budget has been controversely discussed in the last decade. We measured methane emissions from nests of wood-feeding termite species (Nasutitermes spp.) of primary and secondary forests of Amazonia. The methane emission rates from single termite nests varied in a broad range between 0.01 and 9.4 mg CH4 hour−1 nest−1 (average = 2.0 ± 2.4 mg CH4 hour−1 nest−1), as termite colonies vary considerably in size (biomass). Consequently, data given as methane emission per nest are unsuitable for interspecific comparison. In seek for an appropriate unit the methane flux was related to the biomass of the termites dwelling in the nest. On this basis, the variation between the methane emissions of the nests was far lower (0.4 – 4.9 μg hour−1 g termites−1). Biomass-related methane emission rates averaged 3.0 ± 1.3 μg hour−1 g termites−1, which means that Amazonian termites release significantly (at p = 0.01%) more methane than species from other regions. By extrapolating these emission rates to the estimated global biomass of termites we calculated a total emission of 26 Tg CH4 year−1, which represents about 5 % of the annual methane flux from all sources to the world atmosphere. Termites are unlikely to contribute essentially to the global budget of the “greenhouse gas” methane.

In Amazonian floodplains the trees are exposed to extreme flooding of up to 230 days a year. Waterlogging of the roots and stems affects growth and metabolic activity of the trees. An increased leaf fall in the aquatic period and annual increment rings in the wood indicate periodical growth reductions. The present study aims at documenting seasonal changes of metabolism and vitality of adult trees in the annual cycle as expressed by changes of leaf nitrogen content. Leaves of six tree species common in floodplains in Central Amazonia and typical representants of different growth strategies were collected every month between May 1994 and June 1995 in the vicinity of Manaus, Brazil. Mean leaf nitrogen content varied between 1.3% and 3.2% in the non-flooded trees. Three species showed significantly lower Ν content in the flooded period (p=0.05, 0.001, 0.001), the difference ranging 20-25% lower than in the non-flooded period. Two species showed no significant difference while Nectandra amazonum showed 32% more Ν in the flooded season (p=0.001). Leaf nitrogen content was generally high when new leaves were flushed (in the flooded period) and decreased continuously thereafter in all species. Three species showed an additional peak of nitrogen during the first month of the terrestrial phase, in leaves which had flushed earlier, indicating that flooding may disturb nitrogen uptake.

Ao longo do trecho entre Cuiabá-Porto Velho-Manaus (cerca de 2300 km) foram tomadas 46 amostras de água de igarapés e rios, e analisadas quanto aos seguintes parâmetros químicospH, condutividade elétrica, Ca, Mg, Sr, Ba, Na, K. Mn, Fe, Al, Cu, Zn, org. C tot., P tot., Kjeldahl N. Paralelamente, foi anotada a ocorrência de macrófitas aquáticas. A análise dos resultados, em combinação com as informações existentes sobre a geologia da região mostra a relação intensiva entre as águas e a geologia de suas áreas de captação respectivas. Enquanto os rios e igarapés que drenam para o rio Paraguai, são ricos em eletrólitos e alcalinos, todos os igarapés que drenam para o rio Amazonas têm que ser considerados como pobre em eletrólitos e na maioria como ácidos. Todavia, também nas águas pobres em eletrólitos, podem ser observadas diferenças nítidas em dependência da área de captação. Como extremamente pobre do ponto de vista químico, podem ser consideradas as águas da Formação Parecis no Mato Grosso com uma condutividade elétrica de cerca de 3-6 μS.cm-1. Quimicamente mais ricas, no entanto muito heterogêneo, são as águas do embasamento indiviso, enquanto as águas dos sedimentos terciários da Série de Barreiras são muito pobres em eletrólitos (10-20 μS.cm-1). Não entram nessa classificação as águas dos rios Solimões e Madeira, relativamente ricas em eletrólitos, as quais são caracterizadas do ponto de vista químico pela região andina e pré-andina. As diferenças entre as águas, descritas pela condutividade elétrica, refletem-se em grande parte nas concentrações das substâncias analisadas. Exceções são Cu, Zn, Al e C org. A ocorrência de macrófitas aquáticas todavia pode ser ligada somente em limites com as concentrações de eletrólitos na água. Nos igarapés química e extremamente pobres da Formação Parecis. existe uma flora submersa luxuosa, que não ocorre nos igarapés quimicamente parecidos da Série de Barreiras. Neste contexto, está sendo discutida a importância da luz como fator limitante. Fourty-six rivers and creeks intersected by the 2,300 km long Cuiabá-Porto Velho-Manaus road in north-central Brazil were sampled and analyzed for pH, electric conductivity, contents of Ca, Mg, Ba, Na, K, Mn, Fe, Al, Cu, Zn, organic-C, total P and Kjeldahl-N. The occurrence of aquatic macrophytes was recorded. The results show a close relationship between the chemistry of the waters and the geology of the respective catchments. The waters of creeks draining towards the Rio Paraguai are rich in electrolytes and alkaline in nature, while waters flowing towards the Amazon are generally acidic and poor in electrolytes. Significant differences between the electrolyte-poor waters are seen. Waters from the creeks within the Parecis Formation of Mato Grosso are chemically extremely poor (μS around 3). Chemically richer, but very heterogeneous are the waters from the Archaic rock regions, while waters from regions of the Tertiary Barreiras sediments (μS around 10) are very low in electrolytes. The relatively electrolyterich waters of the Rio Madeira and Solimões do not fit into the classification, since their chemical composition is due to geochemical influence in the pre-Andean area. The above-mentioned differences are again reflected by the data on the concentrations of the elements analyzed, except for Cu, Zn, Al, organic-C and Kjeldahl-N. The occurrence and distribution of aquatic macrophytes cannot be correlated with the electrolyte content of the waters. The extremely poor waters of the Parecis-Formation sustain a rather luxurious flora of submerged species which is absent in the chemically similar waters of the Barreiras sediments The role of light as a limiting factor in this case is discussed.