The Amazon Basin: A Vast Wetland
The Amazon Basin is the most extensive and diverse freshwater wetland in the world. Amazonian waters range from small glacier-fed streams in the high Andes above 4,000 m to the largest river in the world flanked by floodplain lakes, flooded forests, and floating herbaceous communities. Much of its high biodiversity is linked to the extensive flooded forests where aquatic and arboreal life converge during the long annual floods. Even at the end of its course, the Amazon River provides freshwater to a vast estuary, ultimately pushing Atlantic waters offshore.
Map based on “Hess et al. 2003. Dual-season mapping of wetland inundation and vegetation for the central Amazon basin” (Remote Sensing and Environment 87: 404-428). Wetlands of the Amazon Basin. Wildlife Conservation Society, 2015.
Although it was once thought that the Amazon was primarily a vast forest, the area now recognized as wetlands has increased with the advent of satellite imagery and, depending on how wetlands are defined, as much as 800,000 km2, 14% of the lowland Basin, could potentially be classified as wetlands. Some areas dominated by wetlands exceed 50,000 km2, such as the palm swamps in the Marañón and Ucayali basins of Peru and the Llanos de Mojos savannas of eastern Bolivia in the Madeira Basin.
Although the Amazon River floodplains account for less than 2% of the Amazon Basin surface, they nevertheless represent a disproportional 12% of the Basin’s wetlands. During the highest river levels, approximately 85,000 km2 of the Amazon River floodplains are flooded. During the lowest water levels, floodplain area decreases by about 45% and consists mostly of permanent channels and lakes. The Llanos de Mojos savannas in Eastern Bolivia represent the single largest wetland (92,000 km2) in the Amazon Basin. Other large contiguous wetlands include Bananal Island between the Tocantins and Araguaia rivers (59,000 km2) and the Roraima plains through which the Branco River flows in northern Brazil (16,000 km2).
In general, wetlands are recognized as fragile ecosystems and, thus, in need of special and specific conservation action. However, such action has been slow to materialize across the Amazon Basin. In the last 3-4 decades, conservation efforts have largely centered on combating upland deforestation, with the unintended consequence of failing to integrate upland and wetland management efforts. A lack of widely recognized and used terms for wetlands in both Spanish and Portuguese also hinders their conceptualization. It should be noted that the integrity of wetlands depends on the health of surrounding forests and uplands. Uplands and wetlands should be considered together to preserve ecosystem functions.
Wetland Definitions
The first step to conserving a wetland is to define it. There are many definitions of a wetland, usually revolving around what the researcher is interested in. Hydrologists and ecologists usually emphasize flooding as the main distinguishing feature; botanists focus on vegetation as a clear indicator of certain wetland types; and soil scientists center their definitions on soil properties. Although the word “wetland” is commonly used in English and generally understood by the public, its equivalents in Spanish (humedal) and Portuguese (paisagens aquáticas or áreas húmidas) are more ambiguous and rarely understood by the public.
Scientists often emphasize the need to standardize definitions, but this has rarely, if ever, happened at international or national levels. Different countries and jurisdictions tend to prioritize the wetland types found within their own borders. The danger of endless debate about what a wetland is can also hinder the development of wetland policy, such as, for instance, when the wetland definition does not include rivers, which many classifications do not.
Flooded savanna with wetland forests in eastern Bolivia. Department – Country: El Beni – Bolivia. Basin: Madeira, main basin Mamoré. Photographer: Luiz Claudio Marigo.
All Amazonian countries are signatories to the Ramsar Convention on Wetlands (RCW), whose principal premise is the importance and fragility of wetlands. The RCW adopts a deliberately broad definition:
“Wetlands are areas where water is the primary factor controlling the environment and the associated plant and animal life. They occur where the water table is at or near the surface of the land, or where the land is covered by water”.
This definition is general enough to include everything that is aquatic and leaves more specific definitions to local areas where some combination of local, scientific, and legal frameworks may be required to advance wetland conservation. Academics are usually the main group, suggesting that unifying definitions are necessary, principally because doing so would theoretically facilitate the classification of wetlands over large areas, especially in academic disciplines such as limnology or botany. Examples of definitions that favor the presence of plants include:
“A wetland is an ecosystem that arises when inundation by water produces soils dominated by anaerobic processes and forces the biota, particularly rooted plants, to exhibit adaptions to tolerate flooding.” (Paul A. Keddy, Wetland Ecology: Principles and Conservation)
In the United States the complexity of defining wetlands legally can be seen by the diverse definitions that the federal government and each state use. A couple of examples suffice to illustrate this complexity:
“Wetland is a generic term for all the different kinds of wet habitats–implying that it is land that is wet for some period of time, but not necessarily permanently wet.” (United States Geological Survey – USGS)
“Wetlands are lands transitional between terrestrial and aquatic systems where the water table is usually at or near the surface or the land is covered by shallow water. For purposes of this classification, wetlands must have one or more of the following three attributes: (1) at least periodically, the land supports predominantly hydrophytes (plants specifically adapted to live in wetlands); (2) the substrate is predominantly undrained hydric (wetland) soil; and (3) the substrate is non-soil and is saturated with water or covered by shallow water at some time during the growing season of each year”. (The U.S. Fish and Wildlife Service)
The definitions adopted by different political entities can have important implications in terms of wetland regulations. By keeping the general definition of wetland broad, we can further specify specific conditions in regulations relevant to jurisdictions and other factors, while at the same time being inclusive enough in terms of protection of wetlands as a whole.