The Paraná River, in South America, with an extension of around 5,000km and running through Brazil, Paraguay, and Argentina, is second in length within the subregion, and it has a significant economic relevance, in terms of livelihoods for fishermen, trade of goods and generation of hydroelectric power. The delta of the Paraná River is a set of wetlands that supply water, food, storage of greenhouse gases, transportation, and leisure, among other benefits.

Amid the COVID-19 pandemic and during much of 2020, this territory had to withstand fires that affected more than 17% of its surface, causing severe socio-environmental impacts. Due to alterations fire generates in these ecosystems, it is challenging to reverse such damages in the short, medium, and long term. One of the components that undergo substantial modifications is the soil since its natural functions are affected, and the environment is inevitably affected.

In this scenario, the Environmental Observatory of the National University of Rosario, a UNAI member institution in Argentina that serves as the SDG Hub for Goal 13: Climate Action, is carrying out long-term monitoring of the impact and recovery of the wetlands after these fires. For this purpose, a transdisciplinary team was created consisting of different research groups from across the university. 

According to the report The 2019-2021 extreme drought episode in La Plata Basin jointly issued among others, by the United Nations World Meteorological Organization, with inputs from this institution of higher education, warned that “because of the great amount of dry biomass in the soil and the use of burning as a practice associated with human activities, fires have flourished along the extensive corridor of Paraná River wetlands.”

Using a high-precision GPS and a wide range of specific techniques, 24 sites affected by fires of different severity were surveyed. Soil samples were extracted and analyzed in the laboratory, and the degree of soil compaction was measured and recorded. It is worth mentioning that island soils are sediment that the river brings and deposits over time, so they are very fragile against the aggression of fire. 

One of the effects of fires is that they burn part of the organic matter, a vital factor that determines acidity, porosity, level of nutrients, and biological activity. Porosity is lost as water infiltration becomes altered. In addition, water cannot be stored, thus making soil aeration difficult. Both limitations work against the complex web of bioactivity in the soil. Thus, the soil does not “work” properly and loses its ability to hold its biodiversity. 

Nutrients are also lost and, with this, fertility decreases too. Losing, for instance, nitrogen and phosphorus means having fewer resources with which to recover. Other effects are the variations in the minerals of the soil, transforming the internal balance. The more severe the fire, the greater soil thickness it will be affected. From the first survey conducted by the research team, negative impacts were observed that affected soil’s health sustainability.

Burnt soils have become more compact, and more than 60% of phosphorus was lost, generating a decrease in fertility and in the balance with other elements that take part in the nutrition of local vegetation. A highly relevant impact was the decrease in carbon storage, estimating a loss of carbon dioxide equivalent to 16 tons per hectare. Together with the one released by the burned vegetation, this greenhouse gas went up into the atmosphere. 

In this way, both the soils and the vegetation of the wetlands lost their role as sinks. A sink is a system or process by which gases from the atmosphere are extracted and stored, which helps to counter climate change. “It is clear that the effect of the fires has been important,” said Sergio Montico, a lead researcher. “The biodiversity of the wetlands is at risk, and there is hardly any more margin for this aggression to persist,” he alerted.