- Microbial communities are important indicators of ecological degradation in the tropics, often reflecting levels of disturbance and contamination of rivers and streams.
- To monitor the ecological status of various waterways in central Panama, researchers from the Smithsonian Tropical Research Institute (STRI) assessed the impact of various land uses, such as livestock grazing and secondary forest. , on microbial diversity and community structure.
- According to the researchers, in less than a decade, reforested land allows bacterial communities to recover, highlighting the importance of reforestation for overall ecosystem recovery.
Scientists have long identified a link between animal production and deforestation, with extensive research showing the detrimental effect of agricultural activities on natural resources. However, little is known about the impact of these practices on water microbial communities – the tiny organisms that maintain water quality by cycling nutrients and energy.
A new study published in Scientific reports by researchers at the Smithsonian Tropical Research Institute (STRI) focused on this: the specific impact of different land uses, such as livestock pasture and secondary forest, on bacterial communities in the water column of four rivers in central Panama.
The results reveal key insights into nature’s ability to recover from harsh environmental changes, such as land degradation and deforestation, which are largely a consequence of human-related agricultural practices. According to the researchers, reforestation of land can restore many aspects of water quality, allowing bacterial communities to thrive again, which directly benefits both human health and the environment.
“Microbes are the biological engines that change the world,” Bob Hilderbrand, associate professor at the University of Maryland Environmental Science Center, who was not involved in the study, told Mongabay. “They may be particularly important for removing excess nutrients, such as pollutants, and even for breaking down toxic pollutants.”
Assessing the ecological conditions of freshwater streams, in particular by identifying the distribution and diversity of microbes, helps researchers identify the impact of human activities on the environment and can therefore help governments and policy makers in informing policies and practices.
“Since microbes in the water column tend to reflect the surrounding uplands, the results suggest that the land is recovering in much more than a vegetative manner, which is encouraging from a recovery and sustainability perspective. ecosystem restoration,” said Hilderbrand.
The project was a collaboration with Agua Salud, an initiative that aims to understand the drivers and consequences of environmental change. The data was collected at the Agua Salud project site, an area managed by STRI.
The researchers studied streams surrounded by four types of land use: mature forest, secondary forest, silvopasture and traditional cattle grazing. A mature forest, also called primary forest or old-growth forest, is an intact forest, containing little or no traces of human activity, while a secondary forest is a forest that has been disturbed in some way. , but who was able to recover. and push back. Silvograzing, on the other hand, is a practice that incorporates trees into pastures used for crop production, often in a mutually beneficial way. This differs from cattle pasture, which is land used exclusively for the grazing of domestic livestock.
In the streams that cross each type of terrain, the researchers took weekly water samples for more than two years to measure different aspects of water quality, as well as to extract and sequence bacterial DNA. .
According to Kristin Saltonstall, co-author of the study and researcher at STRI, the main objective was “to understand how different land uses and reforestation treatments impact the hydrological environment and improve ecosystem services”.
Saltonstall and his colleagues found high bacterial diversity in streams surrounded by mature and secondary forests. Streams surrounded by traditional cattle pastures, on the other hand, had much lower diversity, highlighting the negative influence of cattle ranching on water quality and bacterial communities.
“When waterways are polluted or surrounding landscapes are degraded, microbial communities move on, risking their ability to help maintain natural processes and often allowing harmful bacteria to thrive,” Saltonstall said.
Study reveals huge benefits by allowing forests to regrow on abandoned farmland, finding that bacterial communities in waterways can recover and thrive in as little as a decade when livestock are removed from the region.
“Our results indicate that the presence of livestock in the watershed can decrease bacterial diversity,” said Megan Lindmark, researcher at STRI and co-author of the study. However, “our results also indicate that streams in restored secondary forests have similar bacterial communities and diversity to those in mature forests, indicating the importance of reforestation,” she said.
Clamping down on livestock production would be a huge feat requiring a major international effort – a hugely complex process, as demonstrated by negotiations by IUCN members and leaders at the COP26 climate summit in United Nations in Glasgow.
Instead, researchers are advocating for alternative solutions that both restore and maintain ecosystems, while leaving room for the land to be used for food production.
“The study illustrates the direct benefits to stream water quality of transitioning from conventional livestock grazing to silvopastoral systems, particularly if livestock are prevented from congregating in streams during dry season,” said Robin Chazdon, a professor at the University of the Sunshine Coast, Australia, who was not affiliated with the study.
Streams surrounded by silvopastures, consisting of deliberately planted trees over traditional cattle pastures, showed significant seasonal variation. During wet months, bacterial diversity was similar to that found in forested streams, exhibiting higher diversity than during dry months in which bacterial communities closely resembled those in livestock pastures.
The findings of the STRI study further underscore the importance of natural forest regeneration and targeted management, such as maintaining and restoring riparian corridors, on aquatic microbiomes and water quality in tropical landscapes. In other words, riparian corridors, which are the communities of trees and plants that grow near watercourses, are essential to the ecology of watercourses.
“The results of this research underscore the importance of conserving and restoring riparian forest buffers to effectively balance agriculture and ecosystem services,” Hillary Brumberg, an environmental scientist from the University of Colorado in Boulder who did not participate in the study.
“All waterways have strong communities of bacteria, which probably do a lot of things, like breaking down organic matter and recycling nutrients,” Saltonstall said. “Streams lined with mature and young secondary forests showed little change over time and seasonal changes, suggesting that these communities are stable and resilient to environmental changes.”
In agricultural settings, however, protecting waterways with forest corridors and fencing can help improve ecosystem services and improve water quality and overall bacterial diversity, especially during the rainy season. .
“Nature’s ability to recover is remarkable, in that a river community can return to something resembling the natural community within a few years, even after decades of impact from cattle ranching,” said Saltonstall.
“It gives hope and helps point the way to addressing some of our human-made environmental challenges.”
Quote: Chavarria, KA, Saltonstall, K., Vinda, J., Batista, J., Lindmark, M., Stallard, RF and Hall, JS (2021). Land use influences bacterial stream communities in tropical lowland watersheds. Scientific reports, 11(1). doi:10.1038/s41598-021-01193-7
Banner image by Rhett Butler/Mongabay.
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