Producing clean water at a lower cost could be on the horizon after researchers from The University of Texas at Austin and Penn State solved a complex problem that has baffled scientists for decades, until now.
Desalination membranes remove salt and other chemicals from water, a process critical to the health of society, cleaning billions of gallons of water for agriculture, energy production and drinking. The idea seems simple — push salty water through and clean water comes out the other side — but it contains complex intricacies that scientists are still trying to understand.
The research team, in partnership with DuPont Water Solutions, solved an important aspect of this mystery, opening the door to reduce costs of clean water production. The researchers determined desalination membranes are inconsistent in density and mass distribution, which can hold back their performance. Uniform density at the nanoscale is the key to increasing how much clean water these membranes can create.
“Reverse osmosis membranes are widely used for cleaning water, but there’s still a lot we don’t know about them,” said Manish Kumar, an associate professor in the Department of Civil, Architectural and Environmental Engineering at UT Austin, who co-led the research. “We couldn’t really say how water moves through them, so all the improvements over the past 40 years have essentially been done in the dark.”
The findings were published today in Science.
The paper documents an increase in efficiency in the membranes tested by 30%-40%, meaning they can clean more water while using significantly less energy. That could lead to increased access to clean water and lower water bills for individual homes and large users alike.
Reverse osmosis membranes work by applying pressure to the salty feed solution on one side. The minerals stay there while the water passes through. Although more efficient than non-membrane desalination processes, it still takes a large amount of energy, the researchers said, and improving the efficiency of the membranes could reduce that burden.
“Fresh water management is becoming a crucial challenge throughout the world,” said Enrique Gomez, a professor of chemical engineering at Penn State who co-led the research. “Shortages, droughts — with increasing severe weather patterns, it is expected this problem will become even more significant. It’s critically important to have clean water availability, especially in low-resource areas.”
The National Science Foundation and DuPont, which makes numerous desalination products, funded the research. The seeds were planted when DuPont researchers found that thicker membranes were actually proving to be more permeable. This came as a surprise because the conventional knowledge was that thickness reduces how much water could flow through the membranes.
The team connected with Dow Water Solutions, which is now a part of DuPont, in 2015 at a “water summit” Kumar organized, and they were eager to solve this mystery. The research team, which also includes researchers from Iowa State University, developed 3D reconstructions of the nanoscale membrane structure using state-of-the-art electron microscopes at the Materials Characterization Lab of Penn State. They modeled the path water takes through these membranes to predict how efficiently water could be cleaned based on structure. Greg Foss of the Texas Advanced Computing Center helped visualize these simulations, and most of the calculations were performed on Stampede2, TACC’s supercomputer.make a difference: sponsored opportunity
Tyler E. Culp et al. Nanoscale control of internal inhomogeneity enhances water transport in desalination membranes. Science, Jan 1st, 2021 DOI: 10.1126/science.abb8518
FOR MORE INFORMATION: University of Texas at Austin. “Desalination breakthrough could lead to cheaper water filtration.” ScienceDaily. ScienceDaily, 31 December 2020. <www.sciencedaily.com/releases/2020/12/201231141511.htm>.
While global sea levels are rising due to the climate crisis and threatening near-coastal infrastructures, higher temperatures in other areas are having exactly the opposite effect. The water levels are falling and also causing massive problems. Although the consequences are equally serious, however, declining water levels are receiving less attention according to Matthias Prange, Thomas Wilke of the Justus Liebig University in Gießen, and Frank P. Wesselingh of the University of Utrecht and the Naturalis Biodiversity Center Leiden (the Netherlands).
“The Caspian Sea can be viewed as representative of many other lakes in the world. Many people are not even aware that an inland lake is dramatically shrinking due to climate change, as our models indicate,” says Matthias Prange. The report of the Intergovernmental Panel on Climate Change (IPCC) also failed to mention lakes, and disregarded the social, political and economic consequences of global warming on the affected regions. “This has to change. We need more studies and a better understanding of the consequences of global warming in this region.” The goal must be to raise awareness of the consequences of climate change for inland seas and lakes so that appropriate strategies can be developed, including approaches for other large lakes and regions facing similar challenges.
Because of its size (it is the largest lake in the world) and because of its relatively high salinity of about one per cent, which is about one-third of the salt concentration in the oceans, the Caspian has been named a ‘Sea’. Its largest inflow is the Volga River and it has no natural connection to the ocean. The water level is determined by the proportional influences of inflow, precipitation and evaporation. Global warming is causing increased evaporation, which results in a declining water level.
The Caspian Sea is an important regional water reservoir and, despite its salt content, a biological and commercial center. It is bounded by Kazakhstan, Turkmenistan, Iran, Azerbaijan and Russia. Depending on the degree of global warming in the future, the water level could fall by 9 to 18 meters during this century. “This would affect not only the biodiversity, various species, and habitats that would disappear. The economies of all the bordering countries would be impacted, including harbors, fisheries and fish farming.” For this reason, the authors argue that in the future the Caspian Sea should be used as an example in scientific research to assess the vulnerability of certain regions to falling water levels. Because no nation can solve the resulting conflicts alone, they propose a global task force to develop and coordinate strategies. The article suggests that “international climate funds” could offer a possibility for financing projects and adaptation measures if changes in the lake level are attributed to climate change.make a difference: sponsored opportunity
Matthias Prange, Thomas Wilke, Frank P. Wesselingh. The other side of sea level change. Communications Earth & Environment, 2020; 1 (1) DOI: 10.1038/s43247-020-00075-6
FOR MORE INFORMATION: gMARUM – Center for Marine Environmental Sciences, University of Bremen. “Climate crisis is causing lakes to shrink.” ScienceDaily. ScienceDaily, 23 December 2020. <www.sciencedaily.com/releases/2020/12/201223091540.htm>.
New Columbia Engineering study — first to investigate the long-term effect of soil moisture-atmosphere feedbacks in drylands — finds that soil moisture exerts a negative feedback on surface water availability in drylands, offsetting some of the expected decline
New York, NY — January 4, 2021 — Scientists have thought that global warming will increase the availability of surface water — freshwater resources generated by precipitation minus evapotranspiration — in wet regions, and decrease water availability in dry regions. This expectation is based primarily on atmospheric thermodynamic processes. As air temperatures rise, more water evaporates into the air from the ocean and land. Because warmer air can hold more water vapor than dry air, a more humid atmosphere is expected to amplify the existing pattern of water availability, causing the “dry-get-drier, and wet-get-wetter” atmospheric responses to global warming.
A Columbia Engineering team led by Pierre Gentine, Maurice Ewing and J. Lamar Worzel professor of earth and environmental engineering and affiliated with the Earth Institute, wondered why coupled climate model predictions do not project significant “dry-get-drier” responses over drylands, tropical and temperate areas with an aridity index of less than 0.65, even when researchers use the high emissions global warming scenario. Sha Zhou, a postdoctoral fellow at Lamont-Doherty Earth Observatory and the Earth Institute who studies land-atmosphere interactions and the global water cycle, thought that soil moisture-atmosphere feedbacks might play an important part in future predictions of water availability in drylands.
The new study, published today by Nature Climate Change, is the first to show the importance of long-term soil moisture changes and associated soil moisture-atmosphere feedbacks in these predictions. The researchers identified a long-term soil moisture regulation of atmospheric circulation and moisture transport that largely ameliorates the potential decline of future water availability in drylands, beyond that expected in the absence of soil moisture feedbacks.
“These feedbacks play a more significant role than realized in long-term surface water changes,” says Zhou. “As soil moisture variations negatively impact water availability, this negative feedback could also partially reduce warming-driven increases in the magnitudes and frequencies of extreme high and extreme low hydroclimatic events, such as droughts and floods. Without the negative feedback, we may experience more frequent and more extreme droughts and floods.”
The team combined a unique, idealized multi-model land-atmosphere coupling experiment with a novel statistical approach they developed for the study. They then applied the algorithm on observations to examine the critical role of soil moisture-atmosphere feedbacks in future water availability changes over drylands, and to investigate the thermodynamic and dynamic mechanisms underpinning future water availability changes due to these feedbacks.
They found, in response to global warming, strong declines in surface water availability (precipitation minus evaporation, P-E) in dry regions over oceans, but only slight P-E declines over drylands. Zhou suspected that this phenomenon is associated with land-atmosphere processes. “Over drylands, soil moisture is projected to decline substantially under climate change,” she explains. “Changes in soil moisture would further impact atmospheric processes and the water cycle.”
Global warming is expected to reduce water availability and hence soil moisture in drylands. But this new study found that the drying of soil moisture actually negatively feeds back onto water availability — declining soil moisture reduces evapotranspiration and evaporative cooling, and enhances surface warming in drylands relative to wet regions and the ocean. The land-ocean warming contrast strengthens the air pressure differences between ocean and land, driving greater wind blowing and water vapor transport from the ocean to land.
“Our work finds that soil moisture predictions and associated atmosphere feedbacks are highly variable and model dependent,” says Gentine. “This study underscores the urgent need to improve future soil moisture predictions and accurately represent soil moisture-atmosphere feedbacks in models, which are critical to providing reliable predictions of dryland water availability for better water resources management.”make a difference: sponsored opportunity
Sha Zhou, A. Park Williams, Benjamin R. Lintner, Alexis M. Berg, Yao Zhang, Trevor F. Keenan, Benjamin I. Cook, Stefan Hagemann, Sonia I. Seneviratne & Pierre Gentine. Soil moisture–atmosphere feedbacks mitigate declining water availability in drylands. Nature Climate Change, 2021 DOI: 10.1038/s41558-020-00945-z
New Columbia Engineering study — first to investigate the long-term effect of soil moisture-atmosphere feedbacks in drylands — finds that soil moisture exerts a negative feedback on surface water availability in drylands, offsetting some of the expected decline
New York, NY — January 4, 2021 — Scientists have thought that global warming will increase the availability of surface water — freshwater resources generated by precipitation minus evapotranspiration — in wet regions, and decrease water availability in dry regions. This expectation is based primarily on atmospheric thermodynamic processes. As air temperatures rise, more water evaporates into the air from the ocean and land. Because warmer air can hold more water vapor than dry air, a more humid atmosphere is expected to amplify the existing pattern of water availability, causing the “dry-get-drier, and wet-get-wetter” atmospheric responses to global warming.
A Columbia Engineering team led by Pierre Gentine, Maurice Ewing and J. Lamar Worzel professor of earth and environmental engineering and affiliated with the Earth Institute, wondered why coupled climate model predictions do not project significant “dry-get-drier” responses over drylands, tropical and temperate areas with an aridity index of less than 0.65, even when researchers use the high emissions global warming scenario. Sha Zhou, a postdoctoral fellow at Lamont-Doherty Earth Observatory and the Earth Institute who studies land-atmosphere interactions and the global water cycle, thought that soil moisture-atmosphere feedbacks might play an important part in future predictions of water availability in drylands.
The new study, published today by Nature Climate Change, is the first to show the importance of long-term soil moisture changes and associated soil moisture-atmosphere feedbacks in these predictions. The researchers identified a long-term soil moisture regulation of atmospheric circulation and moisture transport that largely ameliorates the potential decline of future water availability in drylands, beyond that expected in the absence of soil moisture feedbacks.
“These feedbacks play a more significant role than realized in long-term surface water changes,” says Zhou. “As soil moisture variations negatively impact water availability, this negative feedback could also partially reduce warming-driven increases in the magnitudes and frequencies of extreme high and extreme low hydroclimatic events, such as droughts and floods. Without the negative feedback, we may experience more frequent and more extreme droughts and floods.”
The team combined a unique, idealized multi-model land-atmosphere coupling experiment with a novel statistical approach they developed for the study. They then applied the algorithm on observations to examine the critical role of soil moisture-atmosphere feedbacks in future water availability changes over drylands, and to investigate the thermodynamic and dynamic mechanisms underpinning future water availability changes due to these feedbacks.
They found, in response to global warming, strong declines in surface water availability (precipitation minus evaporation, P-E) in dry regions over oceans, but only slight P-E declines over drylands. Zhou suspected that this phenomenon is associated with land-atmosphere processes. “Over drylands, soil moisture is projected to decline substantially under climate change,” she explains. “Changes in soil moisture would further impact atmospheric processes and the water cycle.”
Global warming is expected to reduce water availability and hence soil moisture in drylands. But this new study found that the drying of soil moisture actually negatively feeds back onto water availability — declining soil moisture reduces evapotranspiration and evaporative cooling, and enhances surface warming in drylands relative to wet regions and the ocean. The land-ocean warming contrast strengthens the air pressure differences between ocean and land, driving greater wind blowing and water vapor transport from the ocean to land.
“Our work finds that soil moisture predictions and associated atmosphere feedbacks are highly variable and model dependent,” says Gentine. “This study underscores the urgent need to improve future soil moisture predictions and accurately represent soil moisture-atmosphere feedbacks in models, which are critical to providing reliable predictions of dryland water availability for better water resources management.”make a difference: sponsored opportunity
Sha Zhou, A. Park Williams, Benjamin R. Lintner, Alexis M. Berg, Yao Zhang, Trevor F. Keenan, Benjamin I. Cook, Stefan Hagemann, Sonia I. Seneviratne & Pierre Gentine. Soil moisture–atmosphere feedbacks mitigate declining water availability in drylands. Nature Climate Change, 2021 DOI: 10.1038/s41558-020-00945-z
FOR MORE INFORMATION: Columbia University School of Engineering and Applied Science. “Surprising news: Drylands are not getting drier.” ScienceDaily. ScienceDaily, 4 January 2021. <www.sciencedaily.com/releases/2021/01/210104110418.htm>.
WSU researchers have developed a sustainable wastewater treatment system that relies on electron-producing microbial communities to clean the water.
The work could someday lead to reduced reliance on the energy-intensive processes that are used to move and treat wastewater, which accounts for as much as two percent of the total electrical energy consumption in the United States.
Led by Abdelrhman Mohamed, postdoctoral research associate, and Haluk Beyenal, Paul Hohenschuh Distinguished Professor in the Gene and Linda Voiland School of Chemical Engineering and Bioengineering, the researchers report on their work in the journal, Bioelectrochemistry.
In wastewater treatment, aeration is an energy intensive and necessary procedure to remove contaminants. Pumps work continuously to mix air into water, adding oxygen that bacteria then use to oxidize organic matter and contaminants. In their work, the researchers used a unique microbial fuel cell system they developed as a substitute for external aeration.
“If we cut the energy use even by a small percentage in the U.S., that is billions of dollars in annual costs,” said Mohamed. “Energy costs are one part but that also means reducing environmental emissions, too.”
Microbial fuel cells work by having microbes convert chemical energy to electricity in a manner that is similar to a battery. They don’t generate a lot of electricity, so they have been used in low-power applications especially in remote areas where batteries are not feasible.
In the case of wastewater treatment, the microbial fuel cell can fill the role that aeration and oxygen plays — accepting electrons that bacteria generate as a product of their metabolic work.
In addition to substituting for the oxygen, the system can also generate a small amount of electricity, which can be used to do additional aeration.
“We tried to think about it in two steps,” said Mohamed. “We lower the energy costs because you don’t have to aerate and add oxygen, but the second part is we generate a little power that we can use for some useful applications in the wastewater treatment plant itself.”
“It’s like we’re double dipping,” added Beyenal. “We use the electrodes and then the electron acceptor to promote microbial growth. On the other hand, we gain a little bit of electricity for the pump and to aerate. With this approach it is more powerful and can treat the wastewater faster.”
The fuel cells have been used experimentally in wastewater treatment systems under ideal conditions, but under real-world and varying conditions, they often fail.
“The microbial fuel cells lack internal regulation controlling the potential of anodes and cathodes, and thus cell potential,” said Mohamed. “This can cause system failure.”
In the system the WSU team developed, the researchers added an extra electrode that allows additional control to their fuel cell system. The system is switchable. It can either work by itself as a microbial fuel cell, using no energy as it slowly cleans up waste, or it can be switched to one that uses a smaller amount of energy than aeration and that cleans more intensively. Mohamed invented a cheap portable electronic device that controls the electrodes.
The researchers were able to operate their system for a year in the laboratory without failure as well as at the pilot scale at a test wastewater treatment facility in Moscow, Idaho. The pilot scale treatment facility is owned and operated by University of Idaho Environmental Engineering Professor Erik R. Coats, who was a collaborator on the project. The system removed waste at comparable rates to aeration.
The system could potentially be used entirely independently from the power grid, and the researchers hope it could someday be used for small scale wastewater treatment facilities, such as for clean up around cattle operations or in very rural areas.
“Over time, we have made a lot of progress,” said Mohamed, who first became interested in microbial fuel cells as an undergraduate at WSU. “There are still challenges that we need to overcome to see this as a real application, but it’s exciting to see the field moving significantly over a period of time.”
“These are difficult systems to build,” added Beyenal. “I think everything is so easy when I write the proposal, but this takes a lot of time and a lot of new discovery. There is nothing like this on the market.”
The work was funded by the Office of Naval Research.make a difference: sponsored opportunity
Abdelrhman Mohamed, Hannah M. Zmuda, Phuc T. Ha, Erik R. Coats, Haluk Beyenal. Large-scale switchable potentiostatic/microbial fuel cell bioelectrochemical wastewater treatment system. Bioelectrochemistry, 2020; 107724 DOI: 10.1016/j.bioelechem.2020.107724
FORE MORE INFORMATION: Washington State University. “Electron-producing microbes power sustainable wastewater treatment.” ScienceDaily. ScienceDaily, 17 December 2020. <www.sciencedaily.com/releases/2020/12/201217095511.htm>.
Fertilizer pollution can have significant ripple effects in the food webs of streams and rivers, according to a new analysis of global data. The researchers also found some detection methods could miss pollution in certain types of streams.
The analysis, published in Biological Reviews, combined the results of 184 studies drawn from 885 individual experiments around the globe that investigated the effects of adding nitrogen and phosphorus, the main components of fertilizer, in streams and rivers. While the analysis only included studies where scientists added nitrogen and phosphorus experimentally, nitrogen and phosphorus pollution can run off from farms into streams, lakes, and rivers — as well as from wastewater discharge. At high levels, fertilizer pollution can cause harmful algal blooms and can lead to fish kills.
“Overall, we found that high levels of nutrients affect streams and rivers everywhere,” said the study’s lead author Marcelo Ardón, associate professor of forestry and environmental resources at North Carolina State University. “Wherever we looked, we saw increases in the abundance and biomass of organisms that live in streams, and also the speeding up of processes that happen in streams — how fast algae grow, how fast leaves decompose, and how fast organisms grow that feed on them.”
Across the studies, the researchers saw that nitrogen and phosphorus led to increased growth across the food web, such as in algae, the insects that eat the algae and the fish that eat the insects. In shaded streams where algae doesn’t grow, they reported nitrogen and phosphorus sped decomposition of leaves and boosted growth of organisms that feed on them.
“We saw an average 48 percent increase overall in biomass abundance and activity in all levels of the food web,” Ardón said. “We also found that the food webs responded most strongly when both nitrogen and phosphorus were added together.”
While experts already use the presence of a specific type of chlorophyll — chlorophyll a — in water to detect algae growth, researchers said using that method could miss pollution in waterways where algae do not grow, and where decomposition of leaves or other plant matter is the primary source of food for other organisms.
“The food webs in those streams don’t depend on algae — the trees shade out the algae,” Ardón said. “The streams there depend on leaves that fall in and decompose, which is what the insects, such as caddisflies and stoneflies, are eating. In those detrital-based streams, we found similar responses to increases in nitrogen and phosphorus as has been found in algae.”
Another finding was that factors such as light, temperature, and baseline concentrations of nitrogen and phosphorus impacted the response to increases in the two nutrients.
“All of those things will determine how much of a response you get to increased nitrogen and phosphorus,” said study co-author Ryan Utz of Chatham University.
The findings have implications for environmental policy, Ardón said.
“The EPA has been asking states to come up with ways to reduce runoff of nitrogen and phosphorus into streams, because we know they can cause these really big problems,” said Ardón. “We know that at a big scale, and we don’t really know the details. A lot of states that are coming up with criteria to reduce the amount of nutrients in the water focus only on algal responses. Our study suggests regulators should expand their view.”make a difference: sponsored opportunity
Marcelo Ardón, Lydia H. Zeglin, Ryan M. Utz, Scott D. Cooper, Walter K. Dodds, Rebecca J. Bixby, Ayesha S. Burdett, Jennifer Follstad Shah, Natalie A. Griffiths, Tamara K. Harms, Sherri L. Johnson, Jeremy B. Jones, John S. Kominoski, William H. McDowell, Amy D. Rosemond, Matt T. Trentman, David Van Horn and Amelia Ward. Experimental nitrogen and phosphorus enrichment stimulates multiple trophic levels of algal and detrital-based food webs: a global meta-analysis from streams and rivers. Biological Reviews, 2020 DOI: 10.1111/brv.12673
FOR MORE INFORMATION: North Carolina State University. “Fertilizer runoff in streams and rivers can have cascading effects, analysis shows.” ScienceDaily. ScienceDaily, 17 December 2020. <www.sciencedaily.com/releases/2020/12/201217135317.htm>.
Spend time in any of the world’s great forests and you’ll start seeing the trees as immense pillars holding the heavens aloft while firmly anchored in the earth. It’s as much fact as sentiment. Trees really do link the ground to the sky by exchanging energy and matter between the soil and the atmosphere. Researchers believe that understanding this connection could provide both a wealth of scientific insight into ecosystems and practical applications that address challenges such as water resource conservation and management.
A recent study led by UC Santa Barbara’s Marc Mayes investigates how patterns in tree water loss to the atmosphere, tracked with satellite imagery, relates to groundwater supplies. The results validate at landscape-wide scales ideas that scientists have proposed based on decades of research in labs and greenhouses. What’s more, the techniques lend themselves to an accurate, efficient way of monitoring groundwater resources over large areas. The findings appear in the journal Hydrological Processes.
For all their diversity, most plants have a very simple game plan. Using energy from sunlight, they combine water from the ground with carbon dioxide from the air to produce sugars and oxygen. During photosynthesis, plants open small pores in their leaves to take in CO2, which also allows water to escape. This process of water loss is called evapotranspiration — short for soil evaporation and plant transpiration — and it’s essentially a transaction cost of transporting the ingredients for photosynthesis to the leaves where the process occurs.
Just like evaporating sweat cools down our own bodies, the evapotranspiration from the trees cools down the forest. With the proper understanding and technology, scientists can use thermal image data from satellites as well as manned and unmanned aircraft to understand the relationship between plants and groundwater: cooler temperatures correlate with more evapotranspiration.
“The core hypothesis of this paper is that you can use relationships between plant water use [as] measured by [satellite] image data, and climate data including air temperature and rainfall, to gauge the availability of, and changes in, groundwater resources,” said Mayes, an Earth scientist and remote sensing expert based at the university’s Earth Research Institute (ERI).
Mayes and his colleagues focused on the flora of dryland rivers — those in deserts and Mediterranean climates. Throughout these regions, many plants have evolved adaptations that minimize water loss, like slow growth, water retention or boom-bust lifecycles. However, plants that dominate river channels — species like sycamore, cottonwood and willows — evolved to take advantage of the surplus groundwater the habitat offers relative to the surrounding landscape.
“Rather than slowing down its water use when water becomes scarce, this vegetation will basically drink itself to death,” Mayes said. This makes it a good window into conditions below the surface.
The team used satellite-based thermal imaging to look at temperatures across the San Pedro River corridor in southern Arizona. On cloud-free days the satellites can gather data on surface temperatures at high resolution over large areas of land. By comparing the temperatures along the river to those in nearby, more sparsely vegetated areas, the researchers were able to determine the extent of evapotranspiration along different parts of the river at different times. They found that it correlated with air temperature in water-rich environments and with rainfall in water-scarce environments.
The findings support recent advances in our understanding of plant water use. The hotter and drier the air, the stronger it pulls water from the leaves, and the more water the plant uses. Consequently, Mayes and his colleagues expected to see evapotranspiration vary with air temperature as long as the stream has abundant groundwater for the plants to draw on.
On the other hand, where groundwater is scarce, plants will close the openings on their leaves to avoid water loss; it’s more important to avoid drying out than to take advantage of the extra sunshine on a warm day. As a result, evapotranspiration will correlate much more strongly with rainfall and streamflow, which increases the supply of water to trees through their roots.
Scientists had demonstrated the predictable effect of evapotranspiration in lowering surface temperatures in lab and small field experiments. However, this is the first study to demonstrate its impact over large areas. The technology that made this possible has matured only within the past five years.
“This remote sensing method shows great promise for identifying the relevant climatic versus other controls on tree growth and health, even within narrow bands of vegetation along rivers,” said coauthor Michael Singer, a researcher at ERI and lead investigator on the project that funded Mayes’ work.
In fact, these ecosystems are vitally important to the southwestern U.S. “Despite taking up about 2% of the landscape, over 90% of the biodiversity in the Southwest relies on these ecosystems,” said coauthor Pamela Nagler, a research scientist at the U.S. Geological Survey’s Southwest Biological Science Center.
The same techniques used in the paper could be applied to the perennial challenge of groundwater monitoring. In fact, this idea helped motivate the study in the first place. “It’s very hard to monitor groundwater availability and change[s] in groundwater resources at the really local scales that matter,” Mayes said. “We’re talking about farmers’ fields or river corridors downstream of new housing developments.”
Monitoring wells are effective, but provide information only for one point on the map. What’s more, they are expensive to drill and maintain. Flux towers can measure the exchange of gasses between the surface and the atmosphere, including water vapor. But they have similar drawbacks to wells in terms of cost and scale. Scientists and stakeholders want reliable, cost-effective methods to monitor aquifers that provide wide coverage at the same time as high resolution. It’s a tall order.
While it may not be quite as precise as a well, remote thermal imaging from aircraft and satellites can check off all of these boxes. It offers wide coverage and high resolution using existing infrastructure. And although it works only along stream corridors, “an inordinate amount of agricultural land and human settlements in dry places ends up being where the water is, along stream paths,” Mayes said.
The idea is to look for shifts in the relationships of evapotranspiration to climate variables over time. These changes will signal a switch between water-rich and water-poor conditions. “Detecting that signal over large areas could be a valuable early warning sign of depleting groundwater resources,” Mayes said. The technique could inform monitoring and pragmatic decision-making on groundwater use.
This study is part of a larger Department of Defense (DOD) project aimed at understanding how vulnerable riverine habitats are to droughts on DOD bases in dryland regions of the U.S. “We are using multiple methods to understand when and why these plants become stressed due to lack of water,” said Singer, the project’s lead scientist. “[We hope] this new knowledge can support the management of these sensitive ecological biomes, particularly on military bases in dryland regions, where these pristine habitats support numerous threatened and endangered species.”
Mayes added, “What’s coming down the pipe is a whole ensemble of work looking at ecosystem responses to water scarcity and water stress across space and time that informs ways we both understand ecosystem response and also improve the monitoring.”make a difference: sponsored opportunity
Marc Mayes, Kelly K. Caylor, Michael Bliss Singer, John C. Stella, Dar Roberts, Pamela Nagler. Climate sensitivity of water use by riparian woodlands at landscape scales. Hydrological Processes, 2020; 34 (25): 4884 DOI: 10.1002/hyp.13942
The Clackamas Basin rarely experiences the intense fire activity that burned in the watershed during the Labor Day fires, but new research out of Portland State University shows that wildfires like the Riverside Fire, which grew to 138,000 acres within days, could become more common under a warming climate, even under non-extreme wind conditions.
The study found that wildfire hazard in the Clackamas Basin, which is the second largest source of drinking water for the Portland metro area, will likely increase by mid-century. Projected changes in temperature and relative humidity are expected to lead to longer fire seasons and more severe fire weather in Oregon’s Western Cascade mountains, which in turn will result in larger, more frequent fires.
“Because of shifts in climate, the scenarios that would create extreme fire events all become a little more plausible,” said Andy McEvoy, the study’s lead author and a graduate student in environmental science and management. “There will be that many more days under which those components of a fire — ignition, weather and fuel — can align in a terrible way.”
The group of researchers simulated four climate scenarios from 2040-2069, representing a range of plausible changes in temperature and humidity.
The simulations showed that the fire season increased from as little as eight days to as much as 32 days. The projected annual average area burned increased significantly by 50% under the least impactful scenario (the coolest and wettest of the four) and as much as 540% under the most extreme scenario (the hottest and driest of the four).
“We don’t make the case that one future is more likely than the other, but it helps bracket the plausible outcomes for planning purposes,” said McEvoy, who works as a research fellow in the U.S. Forest Service’s Pacific Northwest Research Station. “The future is very uncertain and if land and resource managers plan just for the average case, their plans are not going to be robust in the face of those worst-case scenarios.”
The researchers, who worked closely with the Clackamas River Water Providers and the Clackamas County Water and Environment Services, said the findings provide regional managers and planners with a tool to develop climate adaptation and risk mitigation strategies. Given the wide range of plausible future wildfire hazards, robust adaptation plans will be ones that maintain essential ecosystem services across the broadest range of scenarios by balancing land use management, fire suppression, and community preparedness strategies.
These efforts could range from designing and testing the effectiveness of fuel breaks — breaks in vegetation that can help firefighters control the spread of fire and protect homes and resources — to identifying susceptible communities and planning evacuations in the event of future extreme wildfires. In those cases, like the Riverside Fire, fuel breaks would not be successful and the only sensible strategy would be timely, safe evacuations.
“They’re planning for an uncertain future,” McEvoy said. “They have to plan using all available tools and adapt to events as they occur.”make a difference: sponsored opportunity
Andy McEvoy, Max Nielsen-Pincus, Andrés Holz, Arielle J. Catalano, Kelly E. Gleason. Projected Impact of Mid-21st Century Climate Change on Wildfire Hazard in a Major Urban Watershed outside Portland, Oregon USA. Fire, 2020; 3 (4): 70 DOI: 10.3390/fire3040070
Although most of the planet is covered by water, only a fraction of it is clean enough for humans to use. Therefore, it is important to recycle this resource whenever possible. Current purification techniques cannot adequately handle the very hot wastewater generated by some industries. But now, researchers reporting in ACS Applied Materials & Interfaces have embedded amine-enhanced nanodiamond particles into membranes to address this challenge.
Some oil recovery methods and other industrial processes result in hot wastewater, which requires energy-intensive cooling before it can be purified through traditional reverse osmosis membranes. After purification, the water then needs to be heated before it can be re-used. At such high temperatures, traditional reverse osmosis membranes filter slowly, allowing more salts, solids and other contaminants to get through. Researchers have embedded extremely tiny nanodiamonds — carbon spheres produced by explosions in small, closed containers without oxygen present — onto these membranes in previous studies. Although the membranes effectively and quickly filtered large volumes of water and can protect against fouling, they were not tested with very hot samples. To optimize the membranes for use with hot wastewater, Khorshidi, Sadrzadeh and colleagues wanted to modify the nanodiamond spheres and embed them in a new way.
The team attached amines to nanodiamonds and bathed them in an ethyl acetate solution to prevent the spheres from clumping. Then, a monomer was added that reacted with the amines to create chemical links to the traditional membrane base. Synergistic effects of the amine links and the ethyl acetate treatment resulted in thicker, more temperature-stable membranes, contributing to improvements in their performance. By increasing the amount of amine-enhanced nanodiamonds in the membrane, the researchers obtained higher filtration rates with a greater proportion of impurities being removed, even after 9 hours at 167 F, when compared to membranes without nanodiamonds. The new method produced membranes that could more effectively treat wastewater at high temperatures, the researchers say.make a difference: sponsored opportunity
Pooria Karami, Behnam Khorshidi, Laleh Shamaei, Eric Beaulieu, João B. P. Soares, Mohtada Sadrzadeh. Nanodiamond-Enabled Thin-Film Nanocomposite Polyamide Membranes for High-Temperature Water Treatment. ACS Applied Materials & Interfaces, 2020; 12 (47): 53274 DOI: 10.1021/acsami.0c15194
FOR MORE INFORMATION: American Chemical Society. “‘Sparkling’ clean water from nanodiamond-embedded membrane filters.” ScienceDaily. ScienceDaily, 9 December 2020. <www.sciencedaily.com/releases/2020/12/201209124933.htm>.
Because of land use and climate change, lakes and reservoirs globally are seeing large decreases in oxygen concentrations in their bottom waters. It is well-documented that low oxygen levels have detrimental effects on fish and water quality, but little is known about how these conditions will affect the concentration of carbon dioxide and methane in freshwaters.
Carbon dioxide and methane are the primary forms of carbon that can be found in the Earth’s atmosphere. Both of these gases are partially responsible for the greenhouse effect, a process that increases global air temperatures. Methane is 34 times more potent of a greenhouse gas than carbon dioxide, so knowing how low oxygen levels within lakes and reservoirs affect both carbon dioxide and methane could have important implications for global warming.
Until now, researchers did not have any empirical data from the whole-ecosystem scale to definitively say how changing oxygen can affect these two greenhouse gases.
“We found that low oxygen levels increased methane concentrations by 15 to 800 times at the whole-ecosystem scale,” said Alexandria Hounshell, a postdoctoral researcher in the Department of Biological Sciences in the College of Science. “Our work shows that low oxygen levels in the bottom waters of lakes and reservoirs will likely increase the global warming potential of these ecosystems by about an order of magnitude.”
Virginia Tech researchers just published these findings in a high-impact paper in Limnology and Oceanography Letters.
To determine a correlation between oxygen and methane concentrations, researchers honed in on two reservoirs outside of Roanoke. In collaboration with the Western Virginia Water Authority, the research team operated an oxygenation system in Falling Creek Reservoir, which pumps oxygen into the bottom waters and allows researchers to study oxygen concentrations on a whole-ecosystem scale. By also monitoring Beaverdam Reservoir, an upstream reservoir without an oxygenation system, they were able to compare greenhouse gas concentrations in the bottom waters of both reservoirs. They ran the experiment over three years to see how consistent their findings were over time.
“Methane levels were much higher when there was no oxygen in the bottom waters of these reservoirs; whereas the carbon dioxide levels were the same, regardless of oxygen levels,” said Cayelan Carey, associate professor of biological sciences and affiliated faculty member of the Global Change Center. “With low oxygen levels, our work shows that you’ll get higher production of methane, which leads to more global warming in the future.”
This study was one of the first to experimentally test at the whole ecosystem-scale how different oxygen levels affect greenhouse gases. Logistically, it is extremely challenging to manipulate entire ecosystems due to their complexity and many moving parts. Even though scientists can use computer modelling and lab experiments, nothing is as definitive as the real thing.
“We were able to do a substitution of space for time because we have these two reservoirs that we can manipulate and contrast with one another to see what the future may look like, as lower bottom water oxygen levels become more common. We can say with high certainty that we are going to see these lakes become bigger methane emitters as oxygen levels decrease,” said Carey.
According to Hounshell, the strength of their results lie in the study’s expanse over multiple years. Despite having a range of meteorological conditions over the three years, the study affirmed that much higher methane concentrations in low oxygen conditions happen consistently every year, no matter the air temperature.
Ultimately, this study is crucial for how researchers, and the general public, think about how freshwater ecosystems produce greenhouse gases in the future. With low oxygen concentrations increasing in lakes and reservoirs across the world, these ecosystems will produce higher concentrations of methane in the future, leading to more global warming.
Of course, these ecological changes are not just happening in the Roanoke region. Around the globe, a number of studies have pointed to changing carbon cycling in terrestrial and marine ecosystems. However, this study is one of the few to address this phenomenon in lakes and reservoirs, which are often neglected in carbon budgets. This study will fill in these knowledge gaps and shine a spotlight on what we can do as citizens to solve this problem.
This study suggests that keeping lakes from experiencing low oxygen concentrations in the first place could further prevent them from hitting the tipping point, when they start to become large methane producers. Small decisions can add up. For example, decreasing runoff into lakes and reservoirs can prevent the depletion of oxygen in their bottom waters. “Don’t put a ton of fertilizer on your lawn, and be really strategic about how much fertilizer you use and how you use it,” said Hounshell.
And greenhouse gases are just a small part of the bigger picture of how reservoirs function in the global carbon cycle. Currently, the research team is conducting follow-up oxygen manipulation studies to elucidate other components that contribute to ecosystem change. They will continue to monitor oxygen manipulations in the two Roanoke reservoirs to see how the reservoir can affect the ecosystem for the long haul.
This project was funded by the Virginia Tech Institute for Critical Technology and Applied Science, the Fralin Life Sciences Institute at Virginia Tech, and by National Science Foundation grant DEB-1753639.make a difference: sponsored opportunity
Alexandria G. Hounshell, Ryan P. McClure, Mary E. Lofton, Cayelan C. Carey. Whole‐ecosystem oxygenation experiments reveal substantially greater hypolimnetic methane concentrations in reservoirs during anoxia. Limnology and Oceanography Letters, 2020; DOI: 10.1002/lol2.10173
A new national study of public water systems found that arsenic levels were not uniform across the U.S., even after implementation of the latest national regulatory standard. In the first study to assess differences in public drinking water arsenic exposures by geographic subgroups, researchers at Columbia University Mailman School of Public Health confirmed there are inequalities in drinking water arsenic exposure across certain sociodemographic subgroups and over time. Community water systems reliant on groundwater, serving smaller populations located in the Southwest, and Hispanic communities were more likely to continue exceeding the national maximum containment level, raising environmental justice concerns. The findings are published online in Environmental Health Perspectives.
“This research has important implications for public health efforts aimed at reducing arsenic exposure levels, and for advancing environmental justice,” said Anne Nigra, PhD, postdoctoral research fellow in environmental health sciences, and first author. “Systematic studies of inequalities in public drinking water exposures have been lacking until now. These findings identify communities in immediate need of additional protective public health measures.”
‘Our objective was to identify subgroups whose public water arsenic concentrations remained above 10 µg/L after the new maximum arsenic contaminant levels were implemented and, therefore, at disproportionate risk of arsenic-related adverse health outcomes such as cardiovascular disease, related cancers, and adverse birth outcomes,” said Ana Navas-Acien, PhD, Professor of Environmental Health Sciences and senior author.
Arsenic is a highly toxic human carcinogen and water contaminant present in many aquifers in the United States. Earlier research by the Columbia research team showed that reducing the MCL from 50 to 10 µg/L prevented an estimated 200-900 cancer cases per year.
The researchers compared community water system arsenic concentrations during (2006-2008) versus after (2009-2011) the initial monitoring period for compliance with EPA’s 10 µg/L arsenic maximum contaminant level (MCL). They estimated three-year average arsenic concentrations for 36,406 local water systems and 2,740 counties and compared differences in means and quantiles of water arsenic between both three-year periods for U.S. regions and sociodemographic subgroups.
Analyses were based on data from two of the largest EPA databases of public water available. Using arsenic monitoring data from the Third Six Year Review period (2006-2011), the researchers studied approximately 13 million analytical records from 139,000 public water systems serving 290 million people annually. Included were data from 46 states, Washington D.C., the Navajo Nation, and American Indian tribes representing 95 percent of all public water systems and 92 percent of the total population served by public water systems nationally.
Regional Differences
For 2006-2008 to 2009-2011, the average community water system arsenic concentrations declined by 10 percent nationwide, by 11.4 percent for the Southwest, and by 37 percent for New England, respectively. Despite the decline in arsenic concentrations, public drinking water arsenic concentrations remained higher for several sociodemographic subgroups — Hispanic communities, the Southwestern U.S, the Pacific Northwest, and the Central Midwest., in particular. Likewise, communities with smaller populations and reliant on groundwater were more likely to have high arsenic levels.
The percent of community water systems with average concentrations arsenic above the 10 µg/L MCL was 2.3% in 2009-2011 vs. 3.2% in 2006-2008. Community water systems that were not compliant with the arsenic MCL were more likely in the Southwest (61 percent), served by groundwater (95 percent), serving smaller populations (an average of 1,102 persons), and serving Hispanic communities (38 percent).
Nigra and Navas-Acien say that estimating public drinking water arsenic exposure for sociodemographic and geographic subgroups is critical for evaluating whether inequalities in arsenic exposure and compliance with the maximum contaminant levels persist across the U.S, to inform future national- and state-level arsenic regulatory efforts, and to investigate whether inequalities in exposure by subgroup contribute to disparities in arsenic-related disease. “Our findings will help address environmental justice concerns and inform public health interventions and regulatory action needed to eliminate exposure inequalities.”
“We urge continued state and federal funding for infrastructure and technical assistance support for small public water systems in order to reduce inequalities and further protect numerous communities in the U.S. affected by elevated drinking water arsenic exposure,” said Nigra.make a difference: sponsored opportunity
Anne E. Nigra, Qixuan Chen, Steven N. Chillrud, Lili Wang, David Harvey, Brian Mailloux, Pam Factor-Litvak, Ana Navas-Acien. Inequalities in Public Water Arsenic Concentrations in Counties and Community Water Systems across the United States, 2006–2011. Environmental Health Perspectives, 2020; 128 (12): 127001 DOI: 10.1289/EHP7313
FOR MORE INFORMATION: Columbia University’s Mailman School of Public Health. “Several U.S. populations and regions exposed to high arsenic concentrations in drinking water.” ScienceDaily. ScienceDaily, 9 December 2020. <www.sciencedaily.com/releases/2020/12/201209094243.htm>.
