The Cordillera Blanca is the most glacierized area in the tropics, but in the last 30 years the region has lost over 25 percent of its glacier area. A consequence of this glacier retreat has been higher concentrations of heavy metals downstream, which have created serious water contamination issues for indigenous communities living nearby the shrinking glaciers. A recent study led by Alexandre Guittard, Michel Baraër, Jeffrey M. McKenzie and others provided a comprehensive assessment of the extent of trace-metal contamination across the Rio Santa basin, one of the largest and most important rivers in the Cordillera Blanca range.
About 300 miles northeast of the capital city of Lima, the glacier-fed Santa river is located in the Ancash Region of Peru, flowing north between the glacierized Blanca and the non-glacierized Negra mountain ranges, winding west through the Cañon del Pato before discharging into the Pacific Ocean. Since the 1940s, the region has experienced population growth and increased economic activities, greatly intensifying water demand.
“For two decades we have been hearing about shrinking mountain glaciers and the impacts on downstream water supplies. But the vast majority of the research in glacierized basins so far has been on the quantity of water coming out of the glaciers, not the quality of that water,” environmental historian Mark Carey, one of the authors of the study, explained to GlacierHub. “Studies must also take seriously the issues of intensifying water contamination and risk levels for communities living downstream from shrinking glaciers.”
But how does glacier retreat result in trace metal contamination? Essentially, there are two opposing theories, according to lead author Michel Baraër. The first theory is that glacier retreat uncovers bedrock rich in pyrite that oxidizes when uncovered, acidifying the water and facilitating the release of trace metals in water, he told GlacierHub.
The second theory deals with glacier retreat and its impact on the physical weathering of the bedrock, which decreases in intensity. “There are therefore less fresh particles released in water bodies and therefore less trace metals,” he said. To break down the two theories, the authors pinpoint anthropogenic sources (i.e. active mining) to be a major source of the trace metal contamination. Thus, even if the two theories counteract one another, scientists consider the anthropogenic influence of industrial mining, as noted throughout the study, to be a much stronger contributor to the water contamination.
According to the study, “the findings indicate that contamination levels in some areas of the watershed could potentially represent a threat to the health of humans or ecosystems.” Water quality has been a major issue in recent years, and the contamination of arsenic and manganese as found could have devastating health and ecological impacts on the quality of life in the Rio Santa basin.
Even if mining activities are shut down, contamination would continue to be problematic under climate change if the first theory— that glacier retreat exacerbates the oxidation process— outweighs the second that states it slows the release. There is already concern about another health risk: disease-causing organisms that may be lying dormant in ice. They might become more active as they thaw. If that is the case, communities and scientists must keep a careful eye on receding glaciers across the world to see what health impacts may arise when the ice melts.