CASCADA - Toxin or Treat?

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The most sensitive glaciers to climate warming in the 21st century are situated in tropical mountain regions, and thus, serve as valuable sentinels of climate change. Most attention to date has focused on the quantity of meltwater released from these glaciers, because of the impact on global sea level and water security. The concurrent changes in water quality are much more poorly constrained, but have implications for drinking water, agriculture and industry. Peru holds 71% of all tropical glaciers, all of which have undergone high rates of mass loss and retreat in the last two decades. However, certain rivers fed by glacial meltwater are becoming acidic, with concentrations of metals often above World Health Organisation standards. This is thought due to the exposure of metal-rich (sulphidic) rocks in retreating glacier forefields, which release sulphuric acid and metals once oxidised - this acidity can no longer be neutralized by the intense chemical weathering which takes place beneath glaciers. The overarching hypothesis that CASCADA will test is that glaciated catchments in the Cordillera Blanca are evolving along a trajectory from pristine conditions, where glacial runoff is an important nutrient source for downstream ecosystems ("treat"), to those in which the same runoff is toxic to ecosystems and human health ("toxin"). CASCADA unites Peruvian experts in water resources, glaciology and ecology with UK geochemists, glaciologists and technologists to investigate and generate solutions to the cascading impacts of glacier retreat on water quality in Cordillera Blanca rivers. It employs cutting edge in situ monitoring technologies to capture first time data on the year-round quality of Cordillera Blanca rivers and to develop and test a novel wetland management model to remediate rivers with high metal toxicity. A strong partnership with local water users' committees under a citizen science scheme and the formation of an engagement board with governmental institutions and local communities will ensure capacity building and the transfer of technology for integrated wetland management and water quality reporting. Thus, CASCADA provides the transformative process understanding required to deliver a step jump in our ability to predict water quality evolution in deglaciating terrains and to develop effective solutions to toxic catchments.