Drones in the Service of Sustainability: Tracking Soil Moisture in the Peruvian Andes

Amid the tropical Andes of Peru lies the Cordillera Blanca mountains, home to more tropical glaciers than anywhere else on Earth. This range provides water to some 95 million people. Rising temperatures over the last several decades, however, mean its once abundant glaciers are vanishing rapidly. That’s impacting the water supply of downstream communities, which are becoming increasingly dependent on soil moisture.

In an innovative study published in the journal Remote Sensing of Environment, researchers used drones to obtain high-resolution images of the valleys left behind as Cordillera Blanca’s glaciers recede. As the drones pass over these “proglacial valleys,” they can produce highly accurate maps of the soil moisture within the fields, rivers, wetlands, and meadows below.

Historically there has been “very little understanding” of how water circulates in areas like proglacial valleys, Jorge Recharte, director of the Andes program at the Mountain Institute, told GlacierHub.

The study’s lead author, Oliver Wigmore of the University of Colorado, Boulder, said his team’s findings help to improve understanding of proglacial hydrology. “This data … is providing unique insights into the patterns and processes that move and store water within these dynamic proglacial environments,” he said.

A view of Huandoy, the second-tallest peak in the Cordillera Blanca, at sunrise. Just beneath it is the Llanganuco Valley, which was surveyed in the study. (Source: cookierace/Flickr)

This study is the first to apply drone images to the temperature vegetation dryness index (TVDI) method. TVDI demonstrates the relationship between land surface temperature and normalized difference vegetation index (NDVI), which measures an area’s greenness, or density of vegetation, which can then be used to determine soil moisture.

Anais Zimmer, a Ph.D candidate in the department of geography and the environment at the University of Texas, Austin, said the study offered “excellent outcomes on surface and subsurface hydrological processes that could be used at a broader scale and applied to many other sub-disciplines to understand the functioning and the future of alpine ecosystem services.”

The researchers found that soil moisture varied drastically over very short distances. “The unique, high-resolution multispectral drone imagery that we collected has provided an unprecedented snapshot of the spatial variability of surface soil moisture within these systems,” said Wigmore.

high elevation drone on GlacierHub
A photo of one of the drones used to conduct this study. (Source: Wigmore, et al.)

Drones are essentially the third generation of technology to be used in scientific research. First were direct measurements, which cannot be accurately generalized over such a variable area. Then came remote sensing using satellites, which provides averaged data over larger areas, but would likely miss any important variability happening on a smaller scale. For this study, researchers used two types of drone-mounted cameras: one to measure greenness, an indicator of plant health, and a second to record temperature.

“[The images] provide excellent tools to establish comparisons between valleys, depending on land use changes and climatic factors,” Zimmer said. 

Wigmore and his team conducted their survey in two proglacial valleys in the Cordillera Blanca that were markedly different from each other in terms of precipitation level, glacier extent, land cover, and land use. The researchers found that soil moisture variability across the Cordillera Blanca’s proglacial valleys can be attributed to three criteria: distance from local water supplies; the type and abundance of vegetation; and soil disturbance such as animal grazing.

“We have found that the proglacial valleys in Cordillera Blanca often have substantial groundwater reservoirs that regulate dry season stream flow by storing and gradually releasing wet season precipitation and glacial meltwater,” said Wigmore. He added that knowing the groundwater storage capacity of these valleys could help minimize negative impacts of meltwater decline on downstream communities.

Cordillera Blanca Laguna 69 on GlacierHub
A view of a glacier in the Cordillera Blanca from the Laguna 69, one one of the most famous hikes in Peru. (Source: Esmée Winnubst)/Flickr)

“Research in these high landscapes is key to planning for both local impacts in the short term and whole-watershed impacts in the long term,” Recharte said.

Zimmer emphasized the need for enhanced monitoring, modeling, and case studies that might help to better predict the impact of climate change in mountain communities.

Around the world, many glaciers have already reached peak discharge, which threatens the freshwater supplies of downstream communities. The study by Wigmore and his team not only provides an unprecedented look into the hydrology of proglacial valleys, it also provides a glimmer of hope that not all is lost, at least for now. Their results document the enormous water-storage potential that lies beneath the surface of proglacial valleys, but also highlights the extreme vulnerability of these ecosystems.

Read more on GlacierHub:

Hindu Kush Himalaya Assessment Outlines Potentially Dire Impacts of Climate Change

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A Survey of the UNESCO Andean Glacier Water Atlas

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Roundup: Glacier-Fed Lakes, Remote Sensing, and Glacial Succession

Roundup: Glacier-Fed Lakes, Remote Sensing, and Soil

 

Global Warming and Glacier-Fed Lakes

From Freshwater Biology: “Climate warming is accelerating the retreat of glaciers, and recently, many ‘new’ glacial turbid lakes have been created. In the course of time, the loss of the hydrological connectivity to a glacier causes, however, changes in their water turbidity (cloudiness) and turns these ecosystems into clear ones. To understand potential differences in the food-web structure between glacier-fed turbid and clear alpine lakes, we sampled ciliates (single-celled animals bearing ciliates), phyto-, bacterio- and zooplankton in one clear and one glacial turbid alpine lake, and measured key physicochemical parameters. In particular, we focused on the ciliate community and the potential drivers for their abundance distribution.”

Learn more about how global warming affects lakes here:

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A glacier-fed lake (Source: Rodrigo Soldon/Creative Commons).

 

Glacier Remote Sensing Using Sentinel-2

From Remote Sensing: “Mapping of glacier extents from automated classification of optical satellite images has become a major application of the freely available images from Landsat. A widely applied method is based on segmented ratio images from a red and shortwave infrared band. With the now available data from Sentinel-2 (S2) and Landsat 8 (L8) there is high potential to further extend the existing time series (starting with Landsat 4/5 in 1982) and to considerably improve over previous capabilities, thanks to increased spatial resolution and dynamic range, a wider swath width and more frequent coverage.”

Read more about remote sensing here:

Test region 1 in the Kunlun Mountains in northern Tibet using a S2A image from 18 November 2015 (Source: Remote Sensing).
Test region 1 in Tibet using a S2A image from 2015 (Source: Remote Sensing).

 

The Impact of Soil During Glacial Succession

From Journal of Ecology: “Plant–soil interactions are temporally dynamic in ways that are important for the development of plant communities. Yet, during primary succession [colonization of plant life in a deglaciated landscape], the degree to which changing soil characteristics (e.g. increasing nutrient availabilities) and developing communities of soil biota influence plant growth and species turnover is not well understood. We conducted a two-phase glasshouse experiment with two native plant species and soils collected from three ages (early, mid- and late succession) of an actively developing glacial chronosequence ranging from approximately 5 to <100 years in age.”

Learn more about the impact of soil during glacier succession here:

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A photo of Lyman Glacier with different plants growing on its face (Source: Marshmallow/ Creative Commons).

 

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Worms Contribute to Soil Ecology After Glacier Retreat

Nematodes under a microscope, courtesy of snickclunk/flickr.
Nematodes under a microscope, courtesy of snickclunk/flickr.

The rock, gravel, sand and fine particles that are trapped under glaciers for millennia undergo major changes as glaciers retreat. Once they are exposed to the atmosphere, they are colonized by a variety of organisms and develop soils. They shift from having relatively few species of bacteria to developing more complex ecosystems.

Studying nematodes — or roundworms — communities in these soils can provide insight into the stages of ecosystem development as the worms respond differently to vegetative changes from grasslands to forested areas, a recent study from the Chinese Academy of Sciences found. The types of nematodes found in soil can also give insights about soil health, the authors found.

Though they may not look very impressive, nematodes are complex creatures. More than 25,000 species have been identified and have been known to adapt to a large variety of environments — from terrestrial to watery ecosystems, from salty to fresh habitats, and from northern to southern longitudes.

Collecting samples in glacier forelands (source: LTERNET)
Collecting samples in glacier forelands (source: LTERNET)

The Hailuogou Glacier on the southeastern Tibetan Plateau in China has retreated 1.8 kilometers in the 20th century, according to glaciologist Mauri Pelto. Because of the glacier’s rapid retreat, researchers from the Chinese Academy of Sciences were able to observe 120 years of plant regeneration in seven different stages. In phase one–the first 3 years after soil is initially exposed–mosses, small plants and grasses begin to grow. During phases two, three and four, or years 3 through 40, grasses eventually become replaced by shrubs and low trees. In phases five, six and seven, from 40 to 120 years after exposure, mature forests develop. Samples of these phases were taken from seven different sites and analysed for pH balance, phosphorus and nitrogen content. Nematodes were extracted from the samples.

The researchers found that while all these changes were occurring above ground, dynamic changes were also occurring beneath the surface. As the soils first developed, levels of soil phosphorous increased, and fungi-eating nematodes were dominant. In later stages, these nematodes were replaced with bacteria-eating nematodes; this shift is likely a response to the improvement of soil quality.

Hailuogou Glacier, courtesy of Mykle Hoban/Flickr.
Hailuogou Glacier, courtesy of Mykle Hoban/Flickr.

But by the seventh phase, soil health began to decrease, and the researchers noticed the return of fungi-eating nematodes, species that survive well in poor soil conditions. Nutrient availability at this later phase began decreasing, suggesting that the ecosystem was entering a retrogressive phase.

“Further research should be conducted to determine the most efficient approach to integrate plant succession, nutrient availability, and soil bacterial and invertebrate community dynamics into models of ecosystem development and succession,” the researchers concluded. “These models would be helpful for prediction and management of nutrient limitation during long-term soil development.” It will be interesting to see whether the patterns of changing nematode populations in the glacier forelands in China are similar to those in other areas. It will also be of importance to framing climate change policy, since the expansion of vegetation in areas formerly covered by glaciers has the potential to sequester carbon dioxide.

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