Glacier Retreat and Trace-Metal Contamination in Peru

The Cordillera Blanca, the largest glacial area in the tropics (Source: Richard Doker/Flickr).

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.

Part of the glacier runoff from the Cordillera Blanca that feeds the Rio Santa (Source: Esmée Winnubst/Flickr).

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.

This map demonstrates the breakdown of trace-metal contamination across the Rio Santa Basin (Source: Guittard et al.).

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.

Glacier Past Unveiled Through Sediments

Svalbard: Ny Ålesund. Note: this lake was not part of the study. Courtesy of James Stringer/Flickr
Svalbard: Ny Ålesund. Note: this lake was not part of the study. Courtesy of James Stringer/Flickr

Researchers have long used preserved sediment layers in glaciers as time records to understand the climate of the past. But now, researchers, publishing in Quaternary Science Reviews, have used lake sediments in glacier-fed Lake Hajeren in Svalbard to recreate glacier variability during the Holocene period.

The sediments, which were deposited over millennia, have been undisturbed, allowing researchers to develop a continuous and full record of glaciers as early as 11,700 calibrated Before Present (BP). The dates were calculated using radiocarbon calibration, meaning that the dates have been compared to other radiocarbon samples. Atmospheric carbon varies over time, so it does not necessarily correspond to the current Gregorian calendar. By comparing different radiocarbon samples, researchers hope to develop a more accurate dating system.

The researchers’ complete record revealed a number of new findings about the advance and presence of the Svalbard glacier. Sediments in Lake Hajeren indicated that between 3380 and 3230 cal BP there was a glacier advance that lasted more than 100 years. The glacier advance had never before been recorded.

Researchers also noted that during the deglaciation period before 11,300 cal BP, glaciers in Svalbard remained, and that between 7.4 and 6.7 thousand cal BP, glaciers disappeared. It wasn’t until 4250 cal BP that glacier reformation began. The variability in glacier presence and formation can be attributed to pulses from the melting Laurentide Ice Sheet, episodes of cooling in the Atlantic and reduced isolation during summers.

“These findings highlight the climate-sensitivity of the small glaciers studied, which rapidly responded to climate shifts,” the authors wrote.

Their research contributes to a body of work looking to better understand the driving forces behind climate variability in the Arctic, the region most affected by climate change. The Arctic also has a disproportional impact on the global climate compared to other parts of the world.

Arctic response to climate change can also be used to develop climate models that estimate the impacts of global warming.

“The rapid response of the small Hajeren glaciers improves our understanding of climate variability on Svalbard, suggesting that the Holocene was punctuated by major centennial-scale perturbations,” the authors concluded. “As such, this study underlines the value of glacier-fed lake sediments in contextualizing Arctic climate dynamics.”