Planetary Exploration Begins at Home

This Special Paper from the Geological Society of America provides a great overview of the science, training, and planning related to planetary exploration for students, educators, researchers, and geology enthusiasts. As we learn about the solar system we can better understand our own planet Earth. -  The Geological Society of America
This Special Paper from the Geological Society of America provides a great overview of the science, training, and planning related to planetary exploration for students, educators, researchers, and geology enthusiasts. As we learn about the solar system we can better understand our own planet Earth. – The Geological Society of America

Where on Earth is it like Mars? How were the Apollo astronauts trained to be geologists on the Moon? Are volcanoes on Earth just like the ones on other planets? The exploration of our solar system begins in our own backyard. Discoveries on other planetary bodies cannot always be easily explained. Therefore, geologic sites on this planet are used to better understand the extraterrestrial worlds we explore with humans, robots, and satellites.

‘Analogs for Planetary Exploration’ is a compilation of historical accounts of astronaut geology training, overviews of planetary geology research on Mars, educational field guides to analog sites, plus concepts for future human missions to the Moon. The volume includes contributions by Apollo 17 Astronaut Harrison H. Schmitt, Farouk El-Baz, Ronald Greeley, and David A. Williams.

This Special Paper provides a great overview of the science, training, and planning related to planetary exploration for students, educators, researchers, and geology enthusiasts. After all, as we learn about the solar system we can better understand our own planet Earth.

First ever direct measurement of the Earth’s rotation

The Earth wobbles. Like a spinning top touched in mid-spin, its rotational axis fluctuates in relation to space. This is partly caused by gravitation from the sun and the moon. At the same time, the Earth’s rotational axis constantly changes relative to the Earth’s surface. On the one hand, this is caused by variation in atmospheric pressure, ocean loading and wind. These elements combine in an effect known as the Chandler wobble to create polar motion. Named after the scientist who discovered it, this phenomenon has a period of around 435 days. On the other hand, an event known as the “annual wobble” causes the rotational axis to move over a period of a year. This is due to the Earth’s elliptical orbit around the sun. These two effects cause the Earth’s axis to migrate irregularly along a circular path with a radius of up to six meters.

Capturing these movements is crucial to create a reliable coordinate system that can feed navigation systems or project trajectory paths in space travel. “Locating a point to the exact centimeter for global positioning is an extremely dynamic process – after all, at our latitude, we are moving at around 350 meters to the east per second,” explains Prof. Karl Ulrich Schreiber who directed the project in TUM’s Research Section Satellite Geodesy. The orientation of the Earth’s axis relative to space and its rotational velocity are currently established in a complicated process that involves 30 radio telescopes around the globe. Every Monday and Thursday, eight to twelve of these telescopes alternately measure the direction between Earth and specific quasars. Scientists assume that these galaxy nuclei never change their position and can therefore be used as reference points. The geodetic observatory Wettzell, which is run by TUM and Germany’s Federal Agency for Cartography (BKG), is also part of this process.

In the mid-1990s, scientists of TUM and BKG joined forces with researchers at New Zealand’s University of Canterbury to develop a simpler method that would be capable of continuously tracking the Chandler wobble and annual wobble. “We also wanted to develop an alternative that would enable us to eliminate any systematic errors,” continues Schreiber. “After all, there was always a possibility that the reference points in space were not actually stationary.” The scientists had the idea of building a ring laser similar to ones used in aircraft guidance systems – only millions of times more exact. “At the time, we were almost laughed off. Hardly anyone thought that our project was feasible,” says Schreiber.

Yet at the end of the 1990s, work on the world’s most stable ring laser got underway at the Wettzell observatory. The installation comprises two counter-rotating laser beams that travel around a square path with mirrors in the corners, which form a closed beam path (hence the name ring laser). When the assembly rotates, the co-rotating light has farther to travel than the counter-rotating light. The beams adjust their wavelengths, causing the optical frequency to change. The scientists can use this difference to calculate the rotational velocity the instrumentation experiences. In Wettzell, it is the Earth that rotates, not the ring laser. To ensure that only the Earth’s rotation influences the laser beams, the four-by-four-meter assembly is anchored in a solid concrete pillar, which extends six meters down into the solid rock of the Earth’s crust.

The Earth’s rotation affects light in different ways, depending on the laser’s location. “If we were at one of the poles, the Earth and the laser’s rotational axes would be in complete synch and their rotational velocity would map 1:1,” details Schreiber. “At the equator, however, the light beam wouldn’t even notice that the Earth is turning.” The scientists therefore have to factor in the position of the Wettzell laser at the 49th degree of latitude. Any change in the Earth’s rotational axis is reflected in the indicators for rotational velocity. The light’s behavior therefore reveals shifts in the Earth’s axis.

“The principle is simple,” adds Schreiber. “The biggest challenge was ensuring that the laser remains stable enough for us to measure the weak geophysical signal without interference – especially over a period of several months.” In other words, the scientists had to eliminate any changes in frequency that do not come from the Earth’s rotation. These include environmental factors such as atmospheric pressure and temperature. They relied predominantly on a ceramic glass plate and a pressurized cabin to achieve this. The researchers mounted the ring laser on a nine-ton Zerodur base plate, also using Zerodur for the supporting beams. They chose Zerodur as it is extremely resistant to changes in temperature. The installation is housed in a pressurized cabin, which registers changes in atmospheric pressure and temperature (12 degrees) and automatically compensates for these. The scientists sunk the lab five meters below ground level to keep these kinds of ambient influences to a minimum. It is insulated from above with layers of Styrodur and clay, and topped by a four-meter high mound of Earth. Scientists have to pass through a twenty-meter tunnel with five cold storage doors and a lock to get to the laser.

Under these conditions, the researchers have succeeded in corroborating the Chandler and annual wobble measurements based on the data captured by radio telescopes. They now aim to make the apparatus more accurate, enabling them to determine changes in the Earth’s rotational axis over a single day. The scientists also plan to make the ring laser capable of continuous operation so that it can run for a period of years without any deviations. “In simple terms,” concludes Schreiber, “in future, we want to be able to just pop down into the basement and find out how fast the Earth is accurately turning right now.”

Landmark discovery has magnetic appeal for scientists

A fundamental problem that has puzzled generations of scientists has finally been solved after more than 70 years.

An international team of scientists has discovered a subtle electronic effect in magnetite – the most magnetic of all naturally occurring minerals – causes a dramatic change to how this material conducts electricity at very low temperatures.

The discovery gives new insight into the mineral in which mankind discovered magnetism, and it may enable magnetite and similar materials to be exploited in new ways.

The research, published in Nature, was led by the University of Edinburgh in collaboration with the European Synchrotron Radiation Facility (ESRF) in Grenoble, France, where the experiments were conducted.

The magnetic properties of magnetite have been known for more than 2000 years and gave rise to the original concepts of magnets and magnetism. The mineral has also formed the basis for decades of research into magnetic recording and information storage materials.

In 1939, Dutch scientist Evert Verwey discovered that the electrical conductivity of magnetite decreases abruptly and dramatically at low temperatures. At about 125 Kelvin, or minus 150 degrees Celsius, the metallic mineral turns into an insulator. Despite many efforts, until now the reason for this transition has been debated and remained controversial.

When the team of scientists fired an intense X-ray beam at a tiny crystal of magnetite at very low temperatures, they were able to understand the subtle rearrangement of the mineral’s chemical structure. Electrons are being trapped within groups of three iron atoms where they can no longer transport an electrical current.

Dr Jon Wright of the ESRF said: “Our main challenge was to obtain a perfect crystal, which meant using one that was tiny, just half the diameter of a human hair. Then we needed to observe subtle changes in this microscopic sample as we lowered the temperature. In Europe, this is only possible at the ESRF, thanks to the extremely high energy of its synchrotron X-rays.”

Professor Paul Attfield, of the University of Edinburgh, said: “We have solved a fundamental problem in understanding the original magnetic material, upon which everything we know about magnetism is built. This vital insight into how magnetite is constructed and how it behaves will help in the development of future electronic and magnetic technologies.”

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The research was funded by the Science and Technology Facilities Council, the Engineering and Physical Sciences Research Council, and the Leverhulme Trust.

Glacial tap is open but the water will run dry

Glaciers are retreating at an unexpectedly fast rate according to research done in Peru’s Cordillera Blanca by McGill doctoral student Michel Baraer. They are currently shrinking by about one per cent a year, and that percentage is increasing steadily, according to his calculations.

But despite this accelerated glacial shrinking, for the first time, the volume of water draining from the glacier into the Rio Santa in Northern Peru has started to decrease significantly. Baraer, and collaborators Prof. Bryan Mark, at the Ohio State University, and Prof. Jeffrey McKenzie, at McGill, calculate that water levels during the dry season could decrease by as much as 30 per cent lower than they are currently. “When a glacier starts to retreat, at some point you reach a plateau and from this point onwards, you have a decrease in the discharge of melt water from the glacier,” explained Baraer.

“Where scientists once believed that they had 10 to 20 years to adapt to reduced runoff, that time is now up,” said Baraer. “For almost all the watersheds we have studied, we have good evidence that we have passed peak water.” This means that the millions of people in the region who depend on the water for electricity, agriculture and drinking water could soon face serious problems because of reduced water supplies.

In hot water: Ice Age findings forecast problems

The first comprehensive study of changes in the oxygenation of oceans at the end of the last Ice Age (between about 10 to 20,000 years ago) has implications for the future of our oceans under global warming. The study, which was co-authored by Eric Galbraith, of McGill’s Department of Earth & Planetary Sciences, looked at marine sediment and found that that the dissolved oxygen concentrations in large parts of the oceans changed dramatically during the relatively slow natural climate changes at the end of the last Ice Age. This was at a time when the temperature of surface water around the globe increased by approximately 2 °C over a period of 10,000 years. A similar rise in temperature will result from human emissions of heat-trapping gases within the next 100 years, if emissions are not curbed, giving cause for concern.

Most of the animals living in the ocean, from herring to tuna, shrimp to zooplankton, rely on dissolved oxygen to breathe. The amount of oxygen that seawater can soak up from the atmosphere depends on the water temperature at the sea surface. As temperatures at the surface increase, the dissolved oxygen supply below the surface gets used up more quickly. Currently, in about 15 per cent of the oceans – in areas referred to as dead zones – dissolved oxygen concentrations are so low that fish have a hard time breathing at all. The findings from the study show that these dead zones increased significantly at the end of the last Ice Age.

“Given how complex the ocean is, it’s been hard to predict how climate change will alter the amount of dissolved oxygen in water. As a result of this research, we can now say unequivocally that the oxygen content of the ocean is sensitive to climate change, confirming the general cause for concern.”</

Ironing out the details of the Earth’s core

This shows the vibrational spectrum of iron, the most abundant element in Earth's core, at 171 gigapascals. By squeezing iron between two diamond anvils (inset), Caltech researchers reproduced the pressures found in Earth's core. -  Caitlin A. Murphy
This shows the vibrational spectrum of iron, the most abundant element in Earth’s core, at 171 gigapascals. By squeezing iron between two diamond anvils (inset), Caltech researchers reproduced the pressures found in Earth’s core. – Caitlin A. Murphy

Identifying the composition of the earth’s core is key to understanding how our planet formed and the current behavior of its interior. While it has been known for many years that iron is the main element in the core, many questions have remained about just how iron behaves under the conditions found deep in the earth. Now, a team led by mineral-physics researchers at the California Institute of Technology (Caltech) has honed in on those behaviors by conducting extremely high-pressure experiments on the element.

“Pinpointing the properties of iron is the gold standard-or I guess ‘iron standard’-for how the core behaves,” says Jennifer Jackson, assistant professor of mineral physics at Caltech and coauthor of the study, which appears in the December 20 issue of Geophysical Research Letters. “That is where most discussions about the deep interior of the earth begin. The temperature distribution, the formation of the planet-it all goes back to the core.”

To learn more about how iron behaves under the extreme conditions that exist in the earth’s core, the team used diamond anvil cells (DAC) to compress tiny samples of the element. The DACs use two small diamonds to squeeze the iron, reproducing the types of pressures felt in the earth’s core. These particular samples were pressurized to 171 Gigapascals, which is 1.7 million times the pressure we feel on the surface of the earth.

To complete the experiments, the team took the DACs to the Advanced Photon Source at Argonne National Laboratory in Illinois, where they were able to use powerful X-rays to measure the vibrational density of states of compressed iron. This information allows the researchers to determine how quickly sound waves move through iron and compare the results to seismic observations of the core.

“The vibrational properties that we were able to measure at extraordinarily high pressures are unprecedented,” says Jackson. “These pressures exist in the earth’s outer core, and are very difficult to reproduce experimentally.”

Caitlin Murphy, a graduate student in Jackson’s group and first author of the paper, says the group was happy to find that their data set on the vibrational properties of iron evolved smoothly over a very wide pressure range, suggesting that their pressure-dependent analysis was robust, and that iron did not encounter any phase changes over this pressure range. To help achieve these successful measurements at high pressures, the group used some innovative techniques to keep the iron from thinning out in the DACs, such as preparing an insert to stabilize the sample chamber during compression. Additionally, they measured the volume of the compressed iron sample in situ and hydrostatically loaded the iron sample with neon into the sample chamber.

“These techniques allowed us to get the very high statistical quality we wanted in a reasonable amount of time, thus allowing us to obtain accurate vibrational properties of compressed iron, such as its Grüneisen parameter,” says Jackson. “The Grüneisen parameter of a material describes how its total energy changes with compression and informs us on how iron may behave in the earth’s core. It is an extremely difficult quantity to measure accurately.”

The team was also able to get a closer estimate of the melting point of iron from their experiments-which they report to be around 5800 Kelvin at the boundary between the earth’s solid inner core and liquid outer core. This information, combined with the other vibrational properties they found, gives the group important clues for estimating the amount of light elements, or impurities, in the core. By comparing the density of iron at the relevant pressure and temperature conditions with seismic observations of the core’s density, they found that iron is 5.5 percent more dense than the solid inner core at this boundary.

“With our new data on iron, we can discuss several aspects of the earth’s core with more certainty and narrow down the amount of light elements that may be needed to help power the geodynamo-the process responsible for maintaining the earth’s magnetic field, which originates in the core,” says Jackson.

According to Murphy, the next step is to perform similar experiments alloying iron with nickel and various light elements to determine how the density and, in particular, the vibrational properties of pure iron are affected. In turn, they will be able to evaluate the amount of light elements that produce a closer match to seismic observations of the core.

“There are a few candidate light elements for the core that everyone is always talking about-sulfur, silicon, oxygen, carbon, and hydrogen, for instance,” says Murphy. “Silicon and oxygen are a few of the more popular, but they have not been studied in this great of detail yet. So that’s where we will begin to expand our study.”

A new kind of metal in the deep Earth

The crushing pressures and intense temperatures in Earth’s deep interior squeeze atoms and electrons so closely together that they interact very differently. With depth materials change. New experiments and supercomputer computations discovered that iron oxide undergoes a new kind of transition under deep Earth conditions. Iron oxide, FeO, is a component of the second most abundant mineral at Earth’s lower mantle, ferropericlase. The finding, published in an upcoming issue of Physical Review Letters, could alter our understanding of deep Earth dynamics and the behavior of the protective magnetic field, which shields our planet from harmful cosmic rays.

Ferropericlase contains both magnesium and iron oxide. To imitate the extreme conditions in the lab, the team including coauthor Ronald Cohen of Carnegie’s Geophysical Laboratory, studied the electrical conductivity of iron oxide to pressures and temperatures up to 1.4 million times atmospheric pressure and 4000°F-on par with conditions at the core-mantle boundary. They also used a new computational method that uses only fundamental physics to model the complex many-body interactions among electrons. The theory and experiments both predict a new kind of metallization in FeO.

Compounds typically undergo structural, chemical, electronic, and other changes under these extremes. Contrary to previous thought, the iron oxide went from an insulating (non-electrical conducting) state to become a highly conducting metal at 690,000 atmospheres and 3000°F, but without a change to its structure. Previous studies had assumed that metallization in FeO was associated with a change in its crystal structure. This result means that iron oxide can be both an insulator and a metal depending on temperature and pressure conditions.

“At high temperatures, the atoms in iron oxide crystals are arranged with the same structure as common table salt, NaCl,” explained Cohen. “Just like table salt, FeO at ambient conditions is a good insulator-it does not conduct electricity. Older measurements showed metallization in FeO at high pressures and temperatures, but it was thought that a new crystal structure formed. Our new results show, instead, that FeO metallizes without any change in structure and that combined temperature and pressure are required. Furthermore, our theory shows that the way the electrons behave to make it metallic is different from other materials that become metallic.”

“The results imply that iron oxide is conducting in the whole range of its stability in Earth’s lower mantle.” Cohen continues, “The metallic phase will enhance the electromagnetic interaction between the liquid core and lower mantle. This has implications for Earth’s magnetic field, which is generated in the outer core. It will change the way the magnetic field is propagated to Earth’s surface, because it provides magnetomechanical coupling between the Earth’s mantle and core.”

“The fact that one mineral has properties that differ so completely-depending on its composition and where it is within the Earth-is a major discovery,” concluded Geophysical Laboratory director Russell Hemley.

Mercury releases into the atmosphere from ancient to modern times

In pursuit of riches and energy over the last 5,000 years, humans have released into the environment 385,000 tons of mercury, the source of numerous health concerns, according to a new study that challenges the idea that releases of the metal are on the decline. The report appears in ACS’ journal Environmental Science & Technology.

David Streets and colleagues explain that humans put mercury into the atmosphere by burning fossil fuels and through mining and industrial processes. Mercury is present in coal and the ores used to extract gold and silver. Much information exists about recent releases of mercury, but there is little information on releases in the past. To find out how much impact people have had over the centuries, the scientists reconstructed human additions of mercury to the atmosphere using historical data and computer models.

Their research shows that mercury emissions peaked during the North American gold and silver rushes in the late 1800s, but after a decline in the middle of the 20th century, are quickly rising again thanks mostly to a surge in coal use. They report that Asia has overtaken Europe and America as the largest contributor of mercury. Recent data suggest that mercury concentrations in the atmosphere are declining, and this is not consistent with their conclusion of increasing emissions. Changing atmospheric conditions may be partly responsible, but more work is also needed to understand the fate of large amounts of mercury in discarded products like batteries and thermometers. The researchers predict mercury released from mining and fuel may take as many as 2,000 years to exit the environment and be reincorporated into rocks and minerals in the Earth.

Industry, regulators should take ‘system safety’ approach to offshore drilling in aftermath of Deepwater Horizon accident, says new report

To reduce the risk of another accident as catastrophic as the Deepwater Horizon explosion and oil spill, a new report from the National Academy of Engineering and National Research Council says, companies involved in offshore drilling should take a “system safety” approach to anticipating and managing possible dangers at every level of operation — from ensuring the integrity of wells to designing blowout preventers that function “under all foreseeable conditions.” In addition, an enhanced regulatory approach should combine strong industry safety goals with mandatory oversight at critical points during drilling operations.

The report says the lack of effective safety management among the companies involved in the Macondo Well-Deepwater Horizon disaster is evident in the multiple flawed decisions that led to the blowout and explosion, which killed 11 workers and produced the biggest accidental oil spill in U.S. history. Regulators also failed to exercise effective oversight.

“The need to maintain domestic sources of oil is great, but so is the need to protect the lives of those who work in the offshore drilling industry as well as protect the viability of the Gulf of Mexico region,” said Donald C. Winter, former secretary of the Navy, professor of engineering practice at the University of Michigan, and chair of the committee that wrote the report. “Industry and regulators need to include a factual assessment of all the risks in deepwater drilling operations in their decisions and make the overall safety of the many complex systems involved a top priority.”

Despite challenging geological conditions, alternative techniques and processes were available that could have been used to prepare the exploratory Macondo well safely for “temporary abandonment” — sealing it until the necessary infrastructure could be installed to support hydrocarbon production, the report says. In addition, several signs of an impending blowout were missed by management and crew, resulting in a failure to take action in a timely manner. And despite numerous past warnings of potential failures of blowout preventer (BOP) systems, both industry and regulators had a “misplaced trust” in the ability of these systems to act as fail-safe mechanisms in the event of a well blowout.

BOP systems commonly in use — including the system used by the Deepwater Horizon — are neither designed nor tested to operate in the dynamic conditions that occurred during the accident. BOP systems should be redesigned, rigorously tested, and maintained to operate reliably, the report says. Proper training in the use of these systems in the event of an emergency is also essential. And while BOP systems are being improved, industry should ensure timely access to demonstrated capping and containment systems that can be rapidly deployed during a future blowout.

Operating companies should have ultimate responsibility and accountability for well integrity, the report says, because only they possess the ability to view all aspects of well design and operation. The drilling contractor should be held responsible and accountable for the operation and safety of the offshore equipment. Both industry and regulators should significantly expand the formal education and training of personnel engaged in offshore drilling to ensure that they can properly implement system safety. Guidelines should be established so that well designs incorporate protection against the various credible risks associated with the drilling and abandonment process. In addition, cemented and mechanical barriers designed to contain the flow of hydrocarbons in wells should be tested to make sure they are effective, and those tests should be subject to independent, near real-time review by a competent authority.

The U.S. Department of the Interior’s recent establishment of a Safety and Environmental Management Systems (SEMS) program — which requires companies to demonstrate procedures for meeting explicit goals related to health, safety, and environmental protection — is a “good first step” toward an enhanced regulatory approach. Regulators should identify and enforce safety-critical points that warrant explicit regulatory review and approval before operations can proceed.

Offshore drilling operations are currently governed by a number of agencies, sometimes with overlapping authorities. The U.S. should make a single government agency responsible for integrating system safety for all offshore drilling activities. Reporting of safety-related incidents should be improved to enable anonymous input, and corporations should investigate all such reports and disseminate lessons learned to personnel and the industry as a whole.

New study documents cumulative impact of mountaintop mining

Increased salinity and concentrations of trace elements in one West Virginia watershed have been tied directly to multiple surface coal mines upstream by a detailed new survey of stream chemistry. The Duke University team that conducted the study said it provides new evidence of the cumulative effects multiple mountaintop mining permits can have in a river network.

“Our analysis of water samples from 23 sites along West Virginia’s Upper Mud River and its tributaries shows that salinity and trace element concentrations, including selenium, increased at a rate directly proportional to the cumulative amount of surface mining in the watershed,” said Duke researcher Ty Lindberg. “We found a strong linear correlation.”

Changes in water quality due to the increased salinity in the Upper Mud from mine runoff also were found to be “exceptionally persistent,” Lindberg said. “Mines reclaimed almost two decades ago are continuing to release effluents with salinity similar to active mines in the region.”

The Duke team’s study appears this week in the peer-reviewed online Early Edition of the Proceedings of the National Academy of Sciences.

In mountaintop mining, companies use explosives and heavy machinery to clear away surface rocks and extract shallow deposits of high-quality coal below. The companies typically dispose of the waste rock in adjacent valleys, where it buries existing headwater streams.

To assess the cumulative impact of the more than 100 permitted discharge outlets draining approximately 28 square kilometers of active and reclaimed mountaintop coal mines in the Upper Mud watershed, the Duke researchers collected 152 sets of samples from 23 sites – including two sites upstream of any active or reclaimed surface mines – between May and December 2010. They sampled for electrical conductivity, a measure of salinity and for concentrations of major ions and trace elements derived from coal or its matrix rock.

All conductivity measurements taken downstream of mine discharge outlets exceeded levels known to be harmful to aquatic life, said Richard Di Giulio, professor of environmental toxicology. At the two sampling sites upstream of any mines, conductivity levels were within an acceptable range. Concentrations of selenium, a known fish toxin, followed a similar trend, Di Giulio said. The researchers also observed deformities typical of selenium exposure in fish collected from downstream waters.

“As eight separate mining-impacted tributaries flowed into the Upper Mud, conductivity and concentrations of selenium, sulfate, magnesium and other inorganic solutes increased proportionately,” said Avner Vengosh, professor of geochemistry and water quality. “Nearly 90 percent of the variation in trace elements and salinity could be explained by the amount of upstream surface mining.”

The Upper Mud flows through sparsely populated sections of Boone and Lincoln counties in southern West Virginia as a headwater stream until reaching its impoundment in the Mud River reservoir 25 kilometers downstream. For about 10 kilometers, the river passes through the Hobet 21 surface mining complex, which has been active since the 1970s and is among the largest in the Appalachian coalfields region.

The Duke team selected the Upper Mud watershed for their field survey because water-quality impacts from other potential sources are largely absent. Historically, surface rather than underground mining has been the dominant form of coal extraction in the Upper Mud’s river basin, and there are very few people now living within the Hobet mine’s permitted boundary. This helped to minimize other factors that might account for changes in water quality.

“This is a remarkably clean dataset and that’s why it’s so powerful,” said Emily Bernhardt, associate professor of biogeochemistry. “We see these incredibly strong patterns, which previously have not been well established.”

Past studies have shown that individual
mines profoundly impact stream water quality, biological community structure and ecosystem function immediately downstream of valley fills, but empirical data on the cumulative impacts of multiple mining operations on larger downstream rivers has been lacking, she said.

“Individual permitting decisions are typically made without consideration of the extent of historic mining impacts already occurring within a watershed,” Bernhardt said. “Our survey helps fill that gap.”

Duke PhD students Raven Bier and Brittany Merola and postdoctoral researcher Ashley Helton co-authored the study.