Streams that have strong connections to shallow groundwater flowpaths exhibit a higher level of microbial diversity and are more effective at preventing the entry and transport of toxic metals, which are often byproducts of upstream mining. These streams are also better at detoxifying metals that are already present.
However, the researchers of this study, which was published in Applied and Environmental Microbiology, discovered that when contaminants from mining activities enter a stream, they diminish the filtration capacity of this reactive zone. This is due to the inflow of acidic, metal-rich abandoned mine drainage, which creates an iron-rich mineral barrier that blocks the entry of stream water into the streambed, where filtration takes place.
This barrier reduces the diversity of microorganisms living in the streambed, and the types of microorganisms that thrive under these conditions convert metals dissolved in the water to minerals that further clog the stream channel, limiting the exchange of nutrients between the stream and the groundwater below it.
“This finding is significant because the lack of exchange between the stream and groundwater also prevents the stream from naturally filtering out toxic metals,” said corresponding author Beth Hoagland, Ph.D., a geochemist at S.S. Papadopulos & Associates, Inc., Rockville, Md. “Metals such as aluminum and copper accumulated in this stream to levels that are harmful to aquatic species.”
The research was carried out in two streams in the San Juan mountains of southwestern Colorado, an area that experienced extensive mining from the late 1800s to the present day. The region is now a U.S. Environmental Protection Agency Superfund site known as the Bonita Peak Mining District.
2024-02-23 10:00:05
Post from phys.org