Climate crisis and human action are leading the Pantanal to imbalance

With 150 thousand square kilometers, the Pantanal occupies an area equivalent to 1.8% of the national territory, extending across the states of Mato Grosso and Mato Grosso do Sul. A mix of open fields, savannahs and forests, the macro-region is home to the largest floodplain on the planet and makes up, together with the Chaco region, located further south, a complex of wetlands with great biodiversity, which provides ecosystem and cultural services for the Brazil, Bolivia and Paraguay.

But, like the Amazon Forest and the Cerrado, the Pantanal has been strongly pressured by the expansion of agriculture. And, in recent years, it has been the scene of an unprecedented number of fires – most of them caused by human action, with the aim of increasing arable areas and pastures.

A new study, which seeks to account for the complexity of the natural processes that occur in the Pantanal and that have become even more complex in recent years due to the global climate crisis and human action, was published in the Journal of South American Earth Sciences by two veterans in the scientific research in the region: Ivan Bergier and Mario Luis Assine.

Bergier, a researcher at Embrapa Pantanal, in Corumbá (MS), has been studying the region for 15 years, and Assine, a professor at the São Paulo State University (Unesp) in Rio Claro, for over 30 years.

“In this new study, we’ve divided the Pantanal into sections, which we call functional compartments, to show how these areas behave differently depending on hydrology: areas that dry faster, areas that only receive rainwater, areas that combine rainwater and rivers. And how this natural and recurrent process is now being strongly affected by global warming and by human action in the surroundings and inside the Pantanal itself”, Assine tells Agência FAPESP.

According to the article, the intensity of rainfall in summer and the number of dry days in autumn-winter have consistently increased, making it possible to predict an increase in river discharge and sediment load in the rainy seasons and the occurrence of water deficits in the dry seasons. “Such a scenario indicates extreme drought cycles in all self-related functional landforms, particularly in wolves. [pronuncia-se ‘lóbos’] depositional deposits that depend exclusively on rainwater, while extremes of rainfall intensity at the headwaters of rivers can amplify the risks of large-scale avulsions in active lobes of river megafans”, summarizes the text.

To understand the meanings of expressions such as “self-similar reliefs”, “abandoned wolves”, “active wolves” and “river megafans”, it is necessary to know a little more about the geomorphological peculiarities of the Pantanal.

There is the mistaken idea that the Pantanal is a homogeneous structure, formed by swamps. But it’s not like that. “The Pantanal is an extensive area subject to flooding, due to a series of geological features of the landscape. It is a morphological depression, a sedimentary basin, subject to years of greater flooding and years of less flooding, associated with periods of greater or lesser precipitation. It’s not low just because there was erosion. It’s also low due to tectonic lowering, with earthquakes that still occur in the area. I’ve already called the Pantanal a geological gift”, informs Assine.

This geological history created a vast expanse of extremely flat land, with an average altitude of just 100 meters. And this plain is very susceptible to what happens in the surroundings, both in the eastern part, in the Maracaju Plateau, associated with the Cerrado vegetation, and in the northern part, in the Parecis Plateau, already in the transition to the Amazon Forest. The rivers that descend from the highlands and bring sediment to the plain are very different from the usual ones. They are not rivers confined in valleys. But rivers that open, branch and distribute their waters through many smaller rivers or streams, which form descending fan-like structures. As they are vast, these structures are called “megafans” by Bergier and Assine.

“The megafans are avulsive, nomadic river systems that constantly change their position. As a result, the Pantanal is a changing landscape and very susceptible to any human interference”, underlines Assine.

“These megafan structures are self-similar, or better said, self-affine. They are similar shapes that are repeated at various scales. In our study, we sought to understand how these shapes originate and how they are repeated. There are several megafans within the plain. of all is the Taquari River, which has a greater fluvial discharge, spreading more sediments on the plain and taking over the space. But much smaller rivers, such as the one called Negro, exhibit similar megafans. So, the Pantanal was formed, along of millions of years, in the context of this competition between rivers, which is related to the amount of sediments generated in the plateaus, and which produced the functionalities observed today, with active wolves, where the waters of the rivers spread, and abandoned wolves, for where the waters no longer flow”, explains Bergier (see the graphic representation of this complex system in the figure below).

The Paraguay River is the final outlet, which captures all the water that does not evaporate or seep underground. As the southern portion of the Pantanal is still a little lower than the northern portion, there is an altitude gradient that causes the Paraguay River to flow slowly southward, towards the La Plata basin.

“There is a huge collection of water from the surroundings, of water that comes from the plateaus, and the exit is made difficult by three bottlenecks that Paraguay presents along its course in the Pantanal. In our work, we show how these three bottlenecks limit the flow of water, slow down the flow and cause flooding in the southern part. The flow is so slow that, in the Nabilek area in the southern part, the biggest floods occur only four to five months after the periods of greatest precipitation. It is a sui generis thing”, account Sign up.

In this way, the Pantanal works as a large water reservoir. If it rains a lot, the amount of water that enters the system, in the plain, is much greater than the water that leaves the rivers. This water then accumulates, raising the general water table in the area, which is flooded. But, if there is a year of little rain, the water starts to decrease. Another thing, also peculiar, is that the Pantanal is in a region of water deficit. Evapotranspiration is greater than precipitation. Thus, water is also lost to the atmosphere. As a result, a situation is created in which the general water table, which is the surface water level, becomes increasingly lower. And the ponds and rivers begin to dry up.

This rise and fall, which is already complicated in itself, becomes, of course, more complicated in the context of the global climate crisis, which tends to exacerbate all extreme events, whether rains or droughts. It is even more complicated when human action, whether deforesting the savannah areas of the adjacent plateaus, or promoting fires and deforestation in the interior of the Pantanal itself, puts the entire system under strong pressure.

accelerated changes

Bergier and Assine worked with hydrology to understand how the variations in precipitation cycles arranged in series through indicators of the fluvial discharge of the Paraguay River, which is the river that captures all the water, condition the periods of lesser or greater drought in the Pantanal. , thus making it possible to predict which areas will suffer the most.

The highest areas are, of course, those where the water table drops the fastest. They are the ones that dry before and are more subject to fires and other complications. The wolf active today is the one that distributes sand on the plain. But, as has been said, there are wolves that were active in the past and today are abandoned by the river. They may also harbor areas of dry grass that are more susceptible to burning.

“The wolves distribute the sand, the sediments, and this clogs the channel until it reaches a critical state, which the swamps call ‘breaking into the banks’. The river then overflows and spreads out to later rebuild another With each multi-annual flood cycle, the river rebuilds itself, reshaping the landscape. Therefore, there are patches of vegetation that were once gallery forests and are no longer. of critical states, in which from a certain threshold the system changes abruptly, to conjecture how the Pantanal landscape resulted from these non-linearities. And how it can evolve from now on”, comments Bergier.

The Pantanal is generally thought of as one of six Brazilian biomes (alongside the Amazon Forest, Cerrado, Caatinga, Pampa and Atlantic Forest). But the biome idea is associated with vegetation. And it’s not just that. The Pantanal is, above all, this peculiar geological entity, which divides, creates spaces and transforms itself all the time. For example, 30 years ago, the Taquari descended to a place called Porto da Manga. Today, its mouth is located tens of kilometers to the north.

“These changes are natural. On a long time scale, such events are recurrent. But anthropic interference causes all processes to be accelerated, affecting not only the environment, but economic activity itself, such as livestock, which is the in the region. This, along with climate change, which is another accelerating factor”, underlines Bergier.

With all these aspects taken into account, the study proposes six pillars that should guide a sustainable governance model in the Pantanal. First, consider that self-related functional landforms are ultimately associated with predominant types of ecosystem services. Second, that these forms evolve over time and that subtle environmental changes can substantially alter the nature, quality and quantity of ecosystem services provided. Third, that changes and alterations become drastic in magnitude whenever river discharge and sediment load balance depart from the river critical state.

Fourth, that climate change combined with unsustainable land use practices push the system away from critical states at shorter temporal scales and at larger spatial scales. Fifth, that eco-hydrology tools combined with integrated crop-livestock-forest systems can mitigate human impacts on river discharge and sediment load balance, while contributing positively to atmospheric carbon sequestration. Sixth, and finally, that external factors, such as climate change, influence the formation and evolution of functional landforms in the Pantanal on a large scale. Other external factors such as tectonics may also play a role and deserve further investigation.

The study in question was supported by FAPESP through the project “Paleohydrological changes, chronology of events and sedimentary dynamics in the Quaternary of the Pantanal Basin”, conducted by Assine.

The article Functional fluvial landforms of the Pantanal: Hydrologic trends and responses to climate changes can be accessed here.