California Institute for Water Resources
California Institute for Water Resources
California Institute for Water Resources
University of California
California Institute for Water Resources

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The impacts of timber harvest on sediment transport and yield in watersheds

An instrumented forest restoration site in the Middle Fork of the American River Basin. Credit: Safeeq Khan.

After timber harvest or fuel reduction thinning operations, sediment delivery to nearby streams and waterways can increase, potentially affecting water quality, drinking water supplies, habitat, and recreational opportunities.

To effectively reduce these adverse effects of harvest, foresters first need to know the precise causes of sediment increases. Historically, researchers investigating the effects of timber harvest on the land have considered two primary drivers: hydrologic changes following timber harvest or fuel reduction that drive sediment transport, and increased sediment supply from ground disturbances or mass movements that result from those harvest or fuel reduction activities.

While these causes are tightly linked, little is understood about the relative role each plays in transporting sediment from the watersheds. In other words, which is dominant in increasing sediment delivery and transport: increased streamflow due to greater water availability that can sweep up and transport sediment, or a greater supply of sediment entering the waterway in the first place?

A new analytical approach developed by Safeeq Khan, UC Cooperative Extension specialist in water and watershed sciences at UC Merced, and collaborators now provides valuable insights into this issue, and ways to target effective mitigation strategies.

Published in the Journal of Hydrology, the team's study analyzed long-term streamflow and sediment data from two adjacent paired watersheds in the H. J. Andrews Experimental Forest in the western Cascades Range of Oregon. One of the watersheds was harvested and replanted in the 1960s, while the second was not disturbed and used as a control.

“The data is from Oregon, but highly relevant for our work in the Sierra Nevada,” said Khan, lead author of the study. “We have tried to quantify the effect of hydrologic changes and increased sediment supply from logging activities on total sediment yield.”

To isolate the relative contributions of streamflow changes and increased sediment supply on sediment transport, Khan and colleagues developed a statistical reconstruction technique to account for the hydrologic changes following harvest.

“This approach allows us to analyze and estimate background sediment production in the treated watershed during the post-treatment period as if the harvest had not occurred, which is remarkable,” said Khan.

The new approach demonstrated that sharp increases in sediment following harvests can be confidently attributed to ground disturbances associated with timber harvest or thinning operations to reduce fuel. Changes in sediment supply overwhelmingly dominate streamflow in terms of contributions to increased sediment in the watershed.

Streamflow increases alone led to modest increases in sediment, with the watershed transporting about twice as much total sediment as it would have had the area been left unharvested. This effect diminishes more or less exponentially over time, especially with respect to suspended sediment, as bare areas revegetate, which reduces hillslope sediment supply, and as streamflow returns to pre-treatment levels.

Percentage contribution of increased streamflow and sediment supply to suspended and bedload sediment yield

“Once we know the background sediment production, we can easily attribute how much of the increase is due to what mechanisms” said Gordon Grant, a hydrologist with the U.S. Forest Service Pacific Northwest Research Station and co-author on the study.

“Determining that increased sediment in watersheds after harvests is primarily driven by ground disturbance is crucial in targeting mitigation efforts,” explained Khan. “Now, we know that strategies that limit ground disruption – like suspending logs while transporting instead of dragging them, avoiding heavy machinery when and where possible, and mastication and mulching – are likely to be highly effective in reducing sediment yields.”

These changes are most pronounced in the first few years following harvest, but the treated watershed did not return to pre-harvest levels of sediment for two decades, underscoring the long-term effects of harvest on a forest's hydrologic and geomorphic systems.

While clearcutting is no longer practiced on U.S. federal land, it is still the primary timber harvest method used across the globe. Additionally, many other types of forest disturbances such as wildfires, mass tree die-offs, and salvage logging create hydrogeomorphic conditions not too different from clearcutting.

"Our findings provide insights that can help land managers and foresters better target land management and restoration in the future,” said Khan. “We're hopeful that these results will lead to strategies that minimize the long-term impacts and legacies of intense land-use disturbances.”

Posted on Tuesday, August 11, 2020 at 4:48 PM
  • Author: Jaquelyn Lugg, UC Merced

Retaining diverse environment and water scholars through community

Students in the Tripati Lab. Photo courtesy of Center for Diverse Leadership in Science.

By any measure, Aradhna Tripati is a brilliant scientist. She began college full-time at the age of 12, has been on the faculty at UCLA since 2009, and received tenure in 2014. Her lab focuses on the role of the carbon cycle in a changing climate and climate change impacts, and she and the group have published prolifically.

In the last several years, she has turned her attention to creating more opportunities for students like her – those that faced similar barriers. Tripati's upbringing is indeed one unusual for her field. She says, “My parents are from Fiji with Indian ancestry. They immigrated and dealt with racism, incarceration, and homelessness in the US. The scope of these issues for students like me – women and minorities, and including people of various gender identities and sexual orientations – has drawn me toward fostering success for other people from diverse paths that have faced various forms of oppression.”

To ensure that students like her can thrive in science and community engagement, Tripati developed the Center for Diverse Leadership in Science at UCLA. The inclusive program includes not only high school, community college, and undergraduate students, but faculty as well. This intergenerational approach is intentional, aimed at fostering a community that can recruit, retain, and support students at all stages of their education.

“There has been a big focus on recruiting under-represented students into science-related fields. What we've really found over time is that students want to be here, but staying can often be difficult because we don't put as many resources into retention, which just leads to further isolation for those that stay,” says Tripati. “Whether it's more support for college readiness, financial stability, or familial issues, we work to support students to stay in the field. In our program, all students receive some form of financial support, they work on diverse research and outreach or engagement teams, and they have faculty fellows as their advisors. At the same time, those faculty members are being trained to better support students with inclusive mentoring practices. That full spectrum approach is crucial.”

Talking circle for Diversi-Tea. Photo courtesy of Center for Diverse Leadership in Science.

Developing community is also key, notes Tripati. “Science environments can be isolating and competitive for people who may be the first or only person with their identity in a group. We work to create a sense of belonging and build an inclusive community of scholars, researchers, communicators, and professionals who are empowered as leaders,” she says. “My goal is that this will also spread across all of STEM – and across higher education institutions – and far beyond the university and into the organizations our fellows become part of as they go through their careers. Right now, the pipeline is not being developed, and there are high attrition rates for underserved groups at every educational stage, sometimes as high as 50 percent.”

The Center has already trained 118 early career fellows and over 20 faculty fellows. Student fellows propose and then lead community engagement programs that they are personally and professionally invested in. It is clear in hearing from students that it has been the opportunity of a lifetime. They speak to Tripati's warmth and welcoming, to the community that they develop, and to the support that they receive.

For example, Danielle Hoague is a Black doctoral student who grew up in Altadena near an area that was declared a Superfund site due to rocket fuel contaminated groundwater, now they are studying the site and related environmental justice efforts. Naomi Adams is a Black doctoral student in engineering interested in developing technological solutions to public health challenges in vulnerable communities. Venezia Ramirez is a Chicanx student involved in multiple collaborative research projects, including remediation of contaminated soils and waters in East LA, and hopes to go on to work for the government to support communities of color in removing environmental hazards.

“In my mind, science is for everyone. And the issues we face, from climate change to pandemics to inequality, are interrelated and take collaboration to solve. I am motivated by social movements, where many individuals serve as agents of change by listening, learning, amplifying voices, and finding ways to connect with others,” says Tripati. “In the Center, I encourage people to see themselves as both teachers and learners, as community-minded scientists, and to give equal weight to their programs of research and public engagement. Before we started, there was nothing else like this. The demand is unbelievable. And the return on investment is huge. With our model, our fellows practice the skills we need to build and strengthen the fabric of a civil society, where they will be the connective tissue.”

Read more about the Center for Diverse Leadership in Science in their recent Annual Report.

Posted on Monday, June 15, 2020 at 5:29 PM

Golf courses go wild

Maggie Reiter with stakeholders on a naturalized area of a golf course. Photo by James Hempfling.

When we think about golf courses, we tend to picture miles of well-watered, uniformly clipped, and perfectly manicured grass, not drought-tolerant native grass, wildlife habitat, and ecological restoration. However, for Maggie Reiter, a UC Cooperative Extension Turfgrass and Environmental Horticulture Advisor based in Fresno County, this is par for the course.

“I've always worked in the turfgrass and golf course management domain,” says Reiter. “Since I began twelve years ago, the proportion of naturalized areas on golf courses has increased. Now native grass stands and wildlife habitat are projected to make up 26 percent of golf course facilities. From a research and extension perspective, there is little information on management of these natural areas. So, there is a need for expertise on managing golf course naturalized areas for multiple functions, including ecological restoration goals.”

Golf course superintendents and their assistant stand among small research plots on a golf course in Monterey, CA. Photo by Maggie Reiter.

Reiter works with golf course superintendents, who she says are professional stewards of the land. Superintendents seek new methods of maintenance that require less water, fertilizer, and labor and promote landscapes that support biological diversity and conservation in addition to providing a high quality arena for golf. Golf courses have the potential to provide ecosystem services and community-wide ecological benefits, such as capturing stormwater runoff, providing wildlife habitat, sequestering carbon, and relieving urban heat island effects.

One approach Reiter takes to meet these goals is to reduce the amount of maintained turf by converting the less frequently played areas of golf courses to native grasslands. Determining the ideal varieties of grasses to plant can be challenging since there are over 250 grasses native to California. Native grass seeds are more expensive and less readily available than traditional turfgrasses, which limits the options for use in restoring native grasslands in landscapes. Reiter and her team were only able to test 13 native grasses in their field trials. In addition, the establishment period for native perennial grasses can be 2-5 years, in contrast to traditional turf varieties that take a few months.

“That is a surprising challenge I didn't anticipate,” Reiter explains. “Golf course superintendents have expectations for naturalized area establishment that do not align with reality because these California native grasses are so different from conventional turfgrasses. I've spent a tremendous amount of time communicating with golf course superintendents, managers, golfers, and other stakeholders to establish realistic expectations.”

Golf course superintendents discuss demonstrations of naturalized areas on a golf course in Dinuba, CA. Photo by Maggie Reiter.

Once the experimental grasses are established, Reiter, a golfer herself, has to determine the playability of each variety. Playability of a grass has to do with a player's ability to find the golf ball and advance the ball through the grass and is an important factor in designing naturalized areas. Poor playability on a course can slow down the pace of play, which detracts from the golfer's experience. Measuring stand height, plant density, and aboveground biomass indicate visual obstruction, but does this determine playability?

“Measuring playability is an enigma that I think about often, and have no good answer for at this point. There is no consensus in the turfgrass research world on how to measure these complex habitats,” Reiter says. “Engaging in the golf course landscape by playing helps me feel things from the golfer's perspective.”

Native grass research trials in Monterey, CA and Dinuba, CA. Photos by Maggie Reiter.

When Reiter is not on the golf course or working on field trials, she advises schools, parks, and recreational sports fields and provides education on general turfgrass management for her local Master Gardener programs as part of her extension work. It turns out that parks and schools are facing major challenges similar to those on golf courses – the need to conserve water and respond to rising labor costs. Reiter says that golf courses may have more resources to respond to these problems, but the tradeoff is that they have higher expectations for aesthetics and performance from native grasses.

Reiter is relatively early in her career, but no doubt she will continue to work with her partners on golf courses and beyond to solve grand problems and incorporate native grasslands within traditional turf areas.  It is clear that she is passionate about improving land management practices to protect California's natural resources and promote community health and wellness.

“It is important to me to increase the ecological sustainability of golf courses, and more widely, urban landscapes,” she says.

Posted on Wednesday, May 13, 2020 at 1:38 PM

From being an engineer to researching nature’s engineers

Emily Fairfax with a chewed tree, a signature sign of beaver activity.

“When I came face to face with beaver dams for the first time, I had what can only be described as a transformative experience,” says Emily Fairfax, an assistant professor of environmental science and resource management at California State University, Channel Islands. While leading a canoe trip through the Boundary Waters of northern Minnesota, she encountered what she describes as “just these enormous, impressive features” – created by beavers. “You truly realize how sturdy beaver dams are while dragging your canoe over them,” she adds, laughing. “They are incredible from an engineering perspective.”

Despite being taken by the handiwork of beavers in that initial encounter, Fairfax says “I just put that experience in my back pocket for a long time.” After majoring in chemistry and physics in college, she went on to work as an engineer. “But, I kept going fishing, visiting wetlands and creeks, and realized I wanted to be out in these places in my day to day life.”

“Then, I watched the documentary Leave it to Beavers. It was about how beavers fundamentally alter landscapes. I was reminded of the beavers I'd seen in Minnesota and was like, I want to study this. On a bit of a whim, I applied to graduate school, and haven't looked back. Now it's all beavers, all day, and they make me so happy. It turns out rather than being an engineer, I was called to study nature's engineers.”

The documentary also piqued Fairfax's interest in something she hadn't considered: beavers in the desert. “I was struck by these aerial shots of beaver dams in the desert, surrounded by green. At the same time, there were so many news articles about droughts and how everything was drying up. Except the beaver ponds, which were still green and still had water, but I couldn't find any quantitative research behind it.”

Fairfax began to examine satellite imagery of beaver ponds and the large complexes of beaver dams that exist all over the U.S. “The great thing about using remote sensing tools is that I can look back decades and see how the surrounding vegetation responded to beavers during droughts.” Fairfax found that the trees and plants around beaver ponds stayed as green as nearby irrigated agriculture fields. “In essence, beaver ponds made it so surrounding areas didn't experience drought.”

An overview of a large beaver dam complex in the Sequoia National Forest, Domeland Wilderness Area.

Fairfax in the field, visiting the same area in the satellite imagery above: Sequoia National Forest, Domeland Wilderness Area. Photo by Andrew Peterson.

That finding led Fairfax to her current interest in beaver ponds as refuge areas during wildfires. “Again, I would see news stories about dry vegetation as ‘kindling' for wildfires. I started to wonder if beaver dams and ponds might reduce the flammability of the surrounding vegetation. I found that while beavers can't exactly put out fires, they can create what I think of as ‘ribbons of fire resistant landscape.' And that ribbon effect is consistent across different topographies, ecosystems, and climates. Beavers create critically important refuge for many different plants and animals to survive fires,” she says.

Trying to succinctly explain her work led Fairfax to develop what became a viral animation short. “I was job searching and needed an ‘elevator pitch,' but I was struggling with it. I had a mental image that never quite came across in words. I'm not good at sketching, but I had my phone camera and a small beaver toy. It dawned on me that I could make a stop motion animation. I downloaded an app and set up my kitchen table with a cork board I had in the house, leftover fake plants from my wedding, rocks from outside, and felt I had for crafts. Then I just sat there filming while moving the little toy beaver around.”

“All in all, it took four hours to put together this 45 second video. I posted it on Twitter, where I had about 50 followers, but figured at least other beaver people would enjoy it. Then I went on a hike with no phone service. When I got back, a friend had messaged me to say I needed to look at Twitter, and it turned out it had just exploded. There were thousands of views already, which I hadn't expected at all. I think part of what made it engaging was that it was short and all visuals and music with no language, so it was easily shared.”

Fairfax says the best part was not how many people watched it, but that so many people from all over the world wanted to ask her about beavers. “By responding to people's questions, sometimes using Google translate, I got good at being concise because I only had 240 characters. I responded to everyone and wanted people to feel heard. That's ultimately why I do science communication – I want people to be able to ask me science questions, especially about beavers.”

Fairfax holding a beaver skull. Photo by Andrew Peterson.

Fairfax notes that there is still a lot of misinformation about beavers. Because they do chew and knock trees down, and create ponds that can lead to flooding, they can be seen as problematic. “Every state, and sometimes county, handles beavers differently. In the last decade or so, there have been advancements in non-lethal beaver management that are more cost-effective than, for example, removing a beaver dam with dynamite. Plus, if you try to remove a beaver, it's inevitable another one will show up, so it's best to learn how to live with them and understand the good they do. For example, that flooding they can cause is also recharging groundwater.”  

Working in California, Fairfax's biggest task now is locating beavers. She notes that before beaver trapping there were likely upwards of 400 million beavers in North America, meaning they were everywhere. “Trapping took them down to 100,000, and now estimates put them back up to 10 or 20 million. They are prevalent in certain areas like the Colorado Rockies and the Sierra Nevada, but we still don't see them often in many downstream areas that provide great habitat.”

For now, she says, “I've got students hiking streams just looking for signs of them, and when I give public talks, people will sometimes tell me about how they used to see them on a creek in the 70's. That might not seem relevant, but that kind of information is so valuable. So now I'm basically saying to people, if you see a beaver dam anywhere in California, please tell me about it!”

Follow Dr. Fairfax on Twitter @EmilyFairfax.

Posted on Monday, April 27, 2020 at 5:06 PM

Water and COVID-19: An early overview from California

Handwashing is a critical tool in the COVID-19 response. Photo by Kathea Pinto under a Creative Commons ShareAlike license, image was cropped and resized.

The novel coronavirus, COVID-19, is affecting people across the globe, in states and cities, in our backyards, and our own living spaces. Unlike many other kinds of disasters, which are relatively geographically and temporally limited, this one is hitting many millions of people around the world at essentially the same time. However, the experience of COVID-19 is not the same for everyone – it varies by many of the same factors that affect other disaster and public health outcomes including race, income, employment type and status, household responsibilities, and housing status.

Like many people, I spent the early part of 2020 trying to understand what was happening, and settling into a new mode of work in mid-March. It's been a challenge to make sense of how water appears in the COVID-19 response. As I started to compile some initial resources, I wasn't sure what I would find. While related concerns about food safety abound, less has been written about water. However, because hand washing is an essential tool in slowing the spread of COVID-19, the water issues become clear pretty quickly.

First, the novel coronavirus has made it evident once again that access to safe and clean water is, among other things, a critical public health issue. When it comes to water safety, the Centers for Disease Control and the California State Water Boards, among others, have developed clear guidance, with the water boards stating that “state-required treatment process removes viruses, including COVID-19.” Dave Eggerton, executive director of the Association of California Water Agencies, said in an interview with the Public Policy Institute of California: “The virus is not a danger to our public water supplies, and buying bottled water in response to it is unnecessary.”  

However, not everyone has the same access to safe water. Recognizing that, California's Governor Newsom issued an executive order restricting water shut-offs for homes and small businesses and restoring service for some others. CalEPA provided further guidance on the issue. In addition, measures have been taken by some municipalities to provide housing for those without, and to increase the number of hand-washing or other types of hygiene stations that are available for unhoused populations.

While access to safe, clean water is critical, ensuring that waste products are handled correctly is yet another challenge. Many are concerned about things like wipes and paper towels being flushed down toilets due to the very real shortage of toilet paper, which can lead to sewer system problems, including back-ups. As inconvenient as it may be, people are urged to put anything other than toilet paper in the trash – not the toilet – to ensure that sewage overflows do not lead to yet more public health problems.

On the research side, there are some interesting stories emerging. For example, because signs of the novel coronavirus may be detected in sewage, water treatment plants could give some indication of the presence of the virus in the absence of, or in addition to, individual testing. There are also interesting questions related to changes in water use as people's lives have shifted dramatically, and how that will impact utilities.

Because we are still early in the process of dealing with this global pandemic, new information will continue to surface. We have put together a web page that includes links to further resources, including some in multiple languages, and are updating that as more become available.

Please visit our “Water and COVID-19” page for more information, including multi-lingual resources where possible. For information on a broad array of COVID-19 issues, including agriculture, food and nutrition, and gardening, visit the UC Division of Agriculture and Natural Resources information pages.

Posted on Monday, April 13, 2020 at 4:55 PM

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