Their results show that nitric and sulfuric acid levels in the Green Lakes Valley region of Niwot Ridge have generally decreased over the past 30 years, especially since the mid-2000s. The findings, which suggest that alpine regions across the Mountain West may be recovering, are published in the Journal of Geophysical Research: Biogeosciences.

This is good news for the wildlife and wildflowers of Rocky Mountain National Park to the north of Niwot Ridge, which depend on limited levels of acidity in the water and soil to thrive. Colorado’s Rocky Mountains are also the source of a lot of water for people living in the Mountain West, and the integrity of these ecosystems influences both the quantity and the quality of this water.

“It looks like we’re doing the right thing. By controlling vehicle emissions, some of these really special places that make Colorado unique are going back to what they used to be,” said Jason Neff, co-author on the paper and director of the Sustainability Innovation Lab at Colorado (SILC).

Almost every area in the world, including Colorado’s Rocky Mountains, has been affected in the past 200 years by increased acidic nutrients, like nitrogen, contained in rain and snow. Nitrogen oxides, like nitrate, are produced primarily from vehicles and energy production. Ammonium is a main ingredient in common agricultural fertilizers.

Nitrogen is a fundamental nutrient required in ecosystems. But when nitrogen levels increase too much, this changed soil and water chemistry can make it difficult for native plants to thrive or even survive — leading to a cascade of negative consequences.

In the summer, the sun heats up the Eastern flanks of the Front Range, causing the warmer air to rise — bringing nitrogen from cars, industry and agriculture with it. As this air cools, it forms clouds over the Rocky Mountains and falls back down as afternoon thunderstorms — depositing contaminants, explained Neff.

In the 1970s, so-called “acid rain” hit East Coast ecosystems much harder than the Mountain West, famously wiping out fish populations and killing trees across large swaths of upstate New York. But scientists are still working to understand how increased levels of acidic nutrients affect the alpine region and how long these ecosystems take to recover.

To fill this gap of knowledge, the researchers analyzed data from 1984 to 2017 on atmospheric deposition and stream water chemistry from the Mountain Research Station, a research facility of the Institute of Arctic and Alpine Research (INSTAAR) and CU Boulder located on Niwot Ridge. They found that around the early 2000s, levels of nitric and sulfuric acid stopped increasing in the Green Lakes Valley. In the mid-2000s they started decreasing.

Their findings were not all good news, however. Levels of ammonium from fertilizer have more than doubled in rainfall in this area between 1984 and 2017, indicating a need to continue monitoring this agricultural chemical and its effects on the mountain ecosystem.

From field work to statistics

This work builds on decades of field work by Colorado researchers at CU Boulder and beyond.

Niwot Ridge is one of 28 Long Term Ecological Research (LTER) Network sites in the U.S., funded by the National Science Foundation. Its 4 square miles stretch from the Continental Divide down to the subalpine forest, 25 miles northwest of Boulder. Researchers at CU Boulder, as well as Colorado State University and the United States Geological Survey, have been collecting data here since the mid-1970s, hiking through snow, sleet and rain to get it.

In the 80s, 90s and 2000s they worked to bring attention to increasing acidification in Colorado mountain ecosystems as a need for pollution regulation in the Front Range.

This new research was made possible by these dedicated scientists, stresses Neff.

“We used water quality modeling and statistical approaches to analyze the long-term datasets that Niwot researchers have been collecting for decades,” said Eve-Lyn Hinckley, a co-author on the paper and fellow of INSTAAR. “The data are available for anyone to download. Our modeling approaches allowed us to evaluate the patterns they hold in a rigorous way.”

Since 1990, Bill Bowman, director of the Mountain Research Station and a professor of ecology and evolutionary biology, has been looking into how nutrients like nitrogen affect plants in mountain ecosystems. He’s found that alpine environments are unique in how they respond to these nutrients.

“It’s a system that is adapted to low nutrients, as well as a harsh climate and a very short growing season — and frost in the middle of the season. These are very slow growing plants. And they just simply can’t respond to the addition of more nitrogen into the system,” said Bowman, also a fellow in INSTAAR.

He has also found that these ecosystems recover quite slowly, even after acidic elements like nitrogen are no longer being added. But like Neff, who completed his undergraduate honors thesis with Bowman in 1993 using Niwot Ridge data, he sees this research as encouraging.

Even if it’s slow going, they said, these results show that the ecosystem has a chance to recover.

“We still have air quality issues in the Front Range. But even with those air quality issues, this research shows that regulating vehicle and power plant emissions is having a big impact,” said Neff.

Additional authors on this paper include lead author John Crawford of the Institute of Arctic and Alpine Research (INSTAAR) and CU Boulder.

About a decade ago, a group of neurons known as “time cells” was discovered in rats. These cells appear to play a unique role in recording when events take place, allowing the brain to correctly mark the order of what happens in an episodic memory.

Located in the brain’s hippocampus, these cells show a characteristic activity pattern while the animals are encoding and recalling events, explains Bradley Lega, M.D., associate professor of neurological surgery at UTSW and senior author of the PNAS study. By firing in a reproducible sequence, they allow the brain to organize when events happen, Lega says. The timing of their firing is controlled by 5 Hz brain waves, called theta oscillations, in a process known as precession.

Lega investigated whether humans also have time cells by using a memory task that makes strong demands on time-related information. Lega and his colleagues recruited volunteers from the Epilepsy Monitoring Unit at UT Southwestern’s Peter O’Donnell Jr. Brain Institute, where epilepsy patients stay for several days before surgery to remove damaged parts of their brains that spark seizures. Electrodes implanted in these patients’ brains help their surgeons precisely identify the seizure foci and also provide valuable information on the brain’s inner workings, Lega says.

While recording electrical activity from the hippocampus in 27 volunteers’ brains, the researchers had them do “free recall” tasks that involved reading a list of 12 words for 30 seconds, doing a short math problem to distract them from rehearsing the lists, and then recalling as many words from the list as possible for the next 30 seconds. This task requires associating each word with a segment of time (the list it was on), which allowed Lega and his team to look for time cells. What the team found was exciting: Not only did they identify a robust population of time cells, but the firing of these cells predicted how well individuals were able to link words together in time (a phenomenon called temporal clustering). Finally, these cells appear to exhibit phase precession in humans, as predicted.

“For years scientists have proposed that time cells are like the glue that holds together memories of events in our lives,” according to Lega. “This finding specifically supports that idea in an elegant way.”

In the second study in Science, Brad Pfeiffer, Ph.D., assistant professor of neuroscience, led a team investigating place cells — a population of hippocampal cells in both animals and humans that records where events occur. Researchers have long known that as animals travel a path they’ve been on before, neurons encoding different locations along the path will fire in sequence much like time cells fire in the order of temporal events, Pfeiffer explains. In addition, while rats are actively exploring an environment, place cells are further organized into “mini-sequences” that represent a virtual sweep of locations ahead of the rat. These radar-like sweeps happen roughly 8-10 times per second and are thought to be a brain mechanism for predicting immediately upcoming events or outcomes.

Prior to this study, it was known that when rats stopped running, place cells would often reactivate in long sequences that appeared to replay the rat’s prior experience in the reverse. While these “reverse replay” events were known to be important for memory formation, it was unclear how the hippocampus was able to produce such sequences. Indeed, considerable work had indicated that experience should strengthen forward, “look ahead” sequences but weaken reverse replay events.

To determine how these backward and forward memories work together, Pfeiffer and his colleagues placed electrodes in the hippocampi of rats, then allowed them to explore two different places: a square arena and a long, straight track. To encourage them to move through these spaces, they placed wells with chocolate milk at various places. They then analyzed the animals’ place cell activity to see how it corresponded to their locations.

Particular neurons fired as the rats wandered through these spaces, encoding information on place. These same neurons fired in the same sequence as the rats retraced their paths, and periodically fired in reverse as they completed different legs of their journeys. However, taking a closer look at the data, the researchers found something new: As the rats moved through these spaces, their neurons not only exhibited forward, predictive mini-sequences, but also backward, retrospective mini-sequences. The forward and backward sequences alternated with each other, each taking only a few dozen milliseconds to complete.

“While these animals were moving forward, their brains were constantly switching between expecting what would happen next and recalling what just happened, all within fraction-of-a-second timeframes,” Pfeiffer says.

Pfeiffer and his team are currently studying what inputs these cells are receiving from other parts of the brain that cause them to act in these forward or reverse patterns. In theory, he says, it might be possible to hijack this system to help the brain recall where an event happened with more fidelity. Similarly, adds Lega, stimulation techniques might eventually be able to mimic the precise patterning of time cells to help people more accurately remember temporal sequences of events. Further studies with “In the past few decades, there’s been an explosion in new findings about memory,” he adds. “The distance between fundamental discoveries in animals and how they can help people is becoming much shorter now.”

“While the commercialization of highly efficient fuel-cell electric vehicles has successfully begun,” said Yu Seung Kim, project leader at Los Alamos, “further technological innovations are needed for the next-generation fuel cell platform evolving towards heavy-duty vehicle applications. One of the technical challenges of current fuel cells is the heat rejection from the exothermic electrochemical reactions of fuel cells.

“We had been struggling to improve the performance of high-temperature membrane fuel cells after we had developed an ion-pair coordinated membrane in 2016,” said Kim. “The ion-pair polymers are good for membrane use, but the high content of phosphoric acid dopants caused electrode poisoning and acid flooding when we used the polymer as an electrode binder.”

In current fuel cells, the heat rejection requirement is met by operating the fuel cell at a high cell voltage. To achieve an efficient fuel-cell powered engine, the operating temperature of fuel cell stacks must increase at least to the engine coolant temperature (100 C).

“We believed that phosphonated polymers would be a good alternative, but previous materials could not be implemented because of undesirable anhydride formation at fuel cell operating temperatures. So we have focused on preparing phosphonated polymers that do not undergo the anhydride formation. Kerres’ team at the University of Stuttgart was able to prepare such materials by introducing fluorine moiety into the polymer. It is exciting that we have now both membrane and ionomeric binder for high-temperature fuel cells,” said Kim.

Ten years ago, Atanasov and Kerres developed a new synthesis for a phosphonated poly(pentafluorostyrene) which consisted of the steps i) polymerization of pentafluorostyrene via radical emulsion polymerization and ii) phosphonation of this polymer by a nucleophilic phosphonation reaction. Surprisingly, this polymer showed a good proton conductivity being higher than Nafion in the temperature range >100°C, and an unexpected excellent chemical and thermal stability of >300°C.

Atanasov and Kerres shared their development with Kim at Los Alamos, whose team in turn developed high-temperature fuel cells to use with the phosphonated polymers. With the integration of membrane electrode assembly with LANL’s ion-pair coordinated membrane (Lee et al. Nature Energy, 1, 16120, 2016), the fuel cells employing the phosphonated polymer exhibited an excellent power density (1.13 W cm-2 under H2/O2 conditions with > 500 h stability at 160 C).

What’s next? “Reaching over 1 W cm-2 power density is a critical milestone that tells us this technology may successfully go to commercialization” said Kim. Currently, the technology is pursuing commercialization through the Department of Energy’s ARPA-E and the Hydrogen and Fuel Cell Technologies Office within the Energy Efficiency and Renewable Energy Office (EERE).

Story Source:

Materials provided by DOE/Los Alamos National Laboratory. Note: Content may be edited for style and length.