In the Andes Mountains today, water managers are using both ancient and modern approaches to improve supplies of this vital resource. Novel methods, including those based on Indigenous knowledge, are needed to help meet the challenges of population growth and a warming climate.
I’ve been interested in water supply issues for decades, starting in my teens when I began whitewater kayaking in California rivers. Those years, during the 1960s and 70s, were when an era of large dam construction (primarily by the U.S. Army Corps of Engineers and the U.S. Bureau of Reclamation) was ending, with tremendous controversy around growth, water rights and environmental protection issues. Ultimately, the conflicts sparked around large dam construction led to increased support for river conservation in California and throughout the United States.
Recent publicity about two distinct water-related situations in the Peruvian Andes captured my interest. The first is the concerning development of melting glaciers exposing rocks that contain heavy metals, which allows toxic substances to leach into water supplies. In one mountain village, a low-tech, nature-based system is being used to improve the local water quality. The second is where workers are restoring an ancient Andean water management system to enhance groundwater storage and supplement water supplies for the expanding population of Lima, the capital city of Peru. In both cases, simple approaches are based on traditional knowledge; they could be implemented and used widely to advantage. Indigenous people of the past and present have a wealth of knowledge about their landscapes.
Cordillera Blanca, Ancash, Peru (Wikimedia)
Glaciers, Rocks, and Runoff
Around our planet, glaciers are melting rapidly. In the high Andes Mountains, among the consequences is an alarming increase in acid runoff, turning stream, lake and river water into sickly colors, with a chemistry and hue typically associated with mining wastewater. Specifically, when rocks containing abundant iron are uncovered, meltwater and precipitation washing over the rocks trigger chemical reactions to form iron hydroxide and corrosive sulfuric acid. Known as acid rock drainage, it is a problem that is getting worse—not only in the Andes, but globally in many regions where glaciers are melting.
The Andes Mountains are renowned for extensive metals deposits, the products of millions of years of powerful tectonic activity. Acid rock drainage is a growing dilemma in the Cordillera Blanca of northern Peru—a spectacular region where I’ve had the opportunity to hike. Pure water has a neutral pH of 7, but at least one lake tested in the Cordillera Blanca, picturesque Lake Shallap (below), now has a pH of 4, approaching the acidity of vinegar. Levels of lead, manganese, iron, and zinc are also extremely high. Satellite images and modeling by scientists show at least 60 lakes in the Cordillera Blanca that are likely to be highly acidic. One scientist describes the problem as a time bomb for people and their ecosystems in the highlands.
Laguna Shallap, Cordillera Blanca, Peru (Wikimedia)
Highly acidic water is unfit for human consumption and agricultural use. The utility company that provides water for the city of Huaraz, a major city within the Cordillera Blanca, is building a multi-million-dollar treatment plant to process acidified waters with heavy metals. However, significantly less help from authorities is available to mountain communities. But in one rural area, the village of Canrey Chico, a low-tech approach is being used to help reduce the heavy metals from the local river water. Workers have planted native reeds in a series of tightly coiled, meandering canals, directing river water through them for a six-and-a-half-day journey. The plants are full of sulfur-hungry bacteria and act as natural water filters that reduce the metal content of the water, raising pH levels. It is a low-tech approach that works.
The growing acid rock drainage situation is critical and increasing in severity. Expanding the simple but effective plant-filter technique into rural highland communities that can’t afford large-scale projects, but could effectively manage an inexpensive system, offers a path to cleaner water for mountain people.
Tracing Ancient Channels Across the Landscape
For millennia, societies have flourished in arid coastal areas along the western flank of the Andes Mountains. Now, expanding populations are facing critical water shortages—especially in rapidly growing cities like Lima, Peru. Innovative approaches are needed to help increase water supplies. These include a traditional, nature-based water management system, currently being restored in the highlands above Lima to help stabilize and augment water supplies for the city,
Over one thousand years ago, long before the Incas flourished, ancient Andean societies constructed a series of small reservoirs and water-carrying canals known as amunas. Today, traces of the amunas are being carefully mapped and construction crews are digging out the soil filling the ancient canals and reinforcing the rockwork walls. Mile after mile of these stone-lined canals along hillslopes capture rainy season runoff and guide it to spongy areas where it slowly seeps into the soil, replenishing groundwater and turning aquifers into natural reservoirs. During dry months, the water is slowly released into lakes and rivers.
A system of amunas totaling around 32 miles has been rebuilt over the past several years. Researchers have placed tracer dyes into the repaired canals, and the dyes show that captured water can extend river flows into the dry season by five months or more. By restoring or protecting wetlands, grasslands and forests, land managers are also increasing the landscape’s ability to absorb and retain water.
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Engineering-heavy water management systems such as dams and aqueducts will always have a major place in ensuring clean water supplies for domestic and agricultural use. Nonetheless, management methods employed by Indigenous people—sometimes for thousands of years—can also be effective. We can benefit from the wisdom of people who live on the land.
Andean Caracara (Phalcoboenus megalopterus) flying in the Cordillera Blanca, Peru (Wikimedia)
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Nice piece, Roseanne. I remember you successfully battling to save Walnut Creek in front of Las Lomas back in 1969 (?). The launch of an acclaimed career in conservation!
Thanks, Steve – good memory! And oh my — that was a long time ago — but yes, definitely at the start of my interest in water conservation!
Really fun piece, Roseanne. We find that the hydrothermal systems of recently (or currently) active volcanoes tends to concentrate dissolved metals. Many gold mines are associated with old volcanic hydrothermal systems. Acidic water is also associated with similar systems, though more with currently active volcanoes. My guess is that sulfur is likely volcanic in origin.
The other source for heavy metals are the thermal vents found on the ocean floors at mid-oceanic ridges. These are formed right at the spreading center, operate for a while and die off as the location moves away from the magma source. Over time, tectonics does what tectonics does and they end up as mountains tens of millions of years (or longer) after they were active.
Glaciers are great for scouring mountains and moving the debris downhill and downstream.
Found Laguna Shallap via Google Maps. Best I can tell, it is a long way N of the currently active volcanic front in Peru (last 10,000 years). Don’t know about the older ones.
Neat article. Much new to consider. Cheers –
Great info – thank you!