This story is part of a special National Geographic News series on global water issues.

Insects—and aquatic bugs in particular—could be key to understanding how the opening of an ambitious new highway connecting Brazil and Peru will affect the Amazon rain forest.

Earlier this year, stretches of the approximately 1,600-mile (2,600-kilometer) long Transoceanic Highway opened to public vehicles for the first time. The east-west passageway stretches from the Atlantic Ocean in Brazil to the Pacific Ocean in Peru via two different branches and cuts through the heart of the Amazon rain forest.

The highway brings with it high economic hopes for the region but also environmental concerns about the impact it will have on the Amazon's plants and animals, many of which are found nowhere else on Earth.

"If you spend any time in rural Peru, you know that a very large percentage of the country is dealing with intense poverty, so it's very difficult to look at a road like that and say don't do it," said Roger Mustalish, president of the Amazon Center for Environmental Education and Research (ACEER).

"But every time you see a road like this going through, it's not long before you see major changes in population migration."

Earlier this year, ACEER launched a project to help document the environmental impacts of building construction, forest clearing, and gold mining (especially illegal gold mining, which leaches toxic mercury) on waterways near the new thoroughfare. ACEER scientists are employing a unique "leaf pack" tool to assess and monitor the health of nearly two dozen streams along a stretch of the highway. (ACEER has received funding from the National Geographic Society.)

The leaf pack consists of a mesh bag that is stuffed with local tree leaves and secured to the bed of a stream. Over the course of several weeks, aquatic insect larvae colonize and feed on the leaves. By looking at the types and abundance of the insects, scientists can get a sense of the health of the stream—and, with luck, the impacts of the road upon the aquatic communities.

This will provide a baseline against which future environmental changes can be measured, ACEER's Mustalish said. "We want to try to not only capture what's going on now but also monitor the rates of change at a given location."

Leaf Pack Citizen Science

The leaf pack was designed by Stroud Water Research Center, based in Pennsylvania. Like the "bucket" device used by the Louisiana Bucket Brigade to monitor air quality, the leaf pack is designed to be easy to use.

In addition to a mesh net, the leaf pack kit also contains high-resolution images of various aquatic insects to aid identification, a magnifying glass, and a simple chart for measuring and cataloguing what is found.

Despite their simplicity, the leaf packs can reveal a surprising amount of information about not only the health of a stream, but also the land surrounding it, Mustalish said.

For example, if a stream contains a high concentration of flies known as midges, then it's a sign that the ecosystem is likely polluted because midges can tolerate low oxygen levels and high levels of silt in the water, which could be due to forest clearing.

The project will focus on three groups, or "orders," of insects: mayflies, stoneflies, and caddisflies. Present nearly everywhere on Earth and almost always found together, these insects have been shown in other studies to be excellent gauges of watershed health, said R. Edward DeWalt, an aquatic entomologist at the University of Illinois at Urbana-Champaign who is not involved in the project.

Stoneflies, in particular, are "probably the most sensitive of all the aquatic insects and very little change needs to take place to eliminate them," DeWalt said.

Getting Into the Field

For the initial phase of the project, ACEER will focus on a 266-mile (428-km) section of the Transoceanic Highway that stretches from the port city of Puerto Maldonado in Peru to the highlands of Cusco, also in Peru. Mustalish said this particular stretch of the highway was chosen because it cuts through an unusually high number of diverse "life zones," including tropical rain forests, cloud forests, and temperate and alpine ecosystems.

"You go through seven ecological life zones, but they're very compacted," Mustalish said. "There's almost no other place on the planet where you can replicate looking at so many life zones. It would be as if you were traveling from the North Pole to the equator."

Monitoring will be done in two phases. The first phase, with 20 monitoring sites, began in March and will conclude in November. Sampling is being conducted roughly every six weeks. The project will break for the rainy season, and resume again in March 2013 with more sites and the aid of non-scientist volunteers from local villages.

"When people find out that their watershed is pristine, they ask how they can keep it that way," Mustalish said. "But when they find out their watershed is being stressed, they want to know why, and what they can do about it."

ACEER has presented data from trial experiments to different villages, with promising results. Mustalish recalled ACEER's field team showing a leaf pack filled with insects to one group of villagers.

"We told them they ought to be really happy that their water quality was so good. Well, they looked at it and said, 'Wait a sec, when we see all those bugs, we think the water is dirty, so we've been taking poisons and putting it in the water to kill them off,'" he said.

DeWalt praised ACEER's decision to involve nonscientists in the project. "It builds a constituency," he said. "When people understand a bit about their environment, they develop an attachment to it and are willing to go to bat for it . . . If you don't have those people involved, the voices are smaller and can be ignored more easily."

Sharing the Learning

Richard Donovan, vice president of sustainable forestry for the Rainforest Alliance, said the leaf packs could help monitor ecosystems in South America, such as the cloud forest near Cusco, that can't be seen by satellites.

"It could be useful there because the other tools we typically use for monitoring deforestation, like remote sensing, just don't give us this kind of data on how the ecosystem is actually responding to large-scale disturbances like roads," Donovan said.

ACEER's Mustalish said the leaf pack results will be made available online at the National Geographic Society's FieldScope global database, which is designed to put scientific data into the hands of citizen scientists worldwide.

Mustalish envisions similar leaf pack studies in Asia and Africa so comparisons between different sites can be made. "If we can create a global network of ecosystem data, then it could be really valuable in looking at everything from the impacts of climate change, land use practices, and population pressures," he said.

Donovan said he hopes efforts will also be made to present the data to government officials so they can incorporate the information into decisions that involve the Transoceanic Highway and its environmental impacts.