• Skip to main content

California Heartbeat Initiative

UC, Natural Reserve System

  • Home
  • Science
  • Data
  • Research sites
  • About Us
    • Team
    • Partners
    • News
  • Gallery
  • Give Now

News

Arbor Creek Experimental Watershed: watching the flow of water through oak woodlands

August 26, 2020 By Kathleen Wong Leave a Comment

Foothill oak woodlands are among the most familiar ecosystems in California. Supporting deer and squirrels, acorn woodpeckers and oak moths, these habitats occupy tens of thousands of acres across the state. Yet change is coming to these widespread habitats. Like much of the West, California’s foothills are predicted to experience shifts in climate in coming decades. Shifts in the amount and timing of precipitation, together with warming weather, are likely to affect how fast local soils will erode, how much water is stored belowground, and even whether oaks can survive where they are found today.

To understand how these beloved woodlands will fare in a rapidly warming climate, University of California researchers are putting a headwaters stream in the Diablo Range under a hydrological microscope.

Arbor Creek Experimental Watershed
Arbor Creek Experimental Watershed is the site of a new study to examine how vegetation, soils, and climate interact to affect how water flows through California’s oak foothills. Based at the NRS’s Blue Oak Ranch Reserve, the study is a collaboration between researchers at UC Santa Cruz and the NRS’s California Heartbeat Initaitive—Freshwater. Image: Lobsang Wangdu/NRS

“Our globe has a finite amount of water. Once it rains, where does water go? How long does it stay in our hillslopes? And what controls how it leaves in streams and through plants?” asks Margaret Zimmer, a professor of earth and planetary sciences at UC Santa Cruz. 

Zimmer has joined forces on the project with scientists from the California Heartbeat Initiative—Freshwater (CHI-Freshwater). Together they are examining how plants, soils, and climate affect the way water moves through the landscape. What they find will demonstrate whether oaks and the ecosystems they support can survive in the future—or whether the new conditions will leave oak woodlands, and the human communities they funnel water toward—high and dry.

The bucolic laboratory for this study is a catchment dubbed Arbor Creek Experimental Watershed. Located within Blue Oak Ranch Reserve, one of 41 reserves in the UC Natural Reserve System, the site should look familiar to anyone who has traveled through California’s rugged Coast Ranges. High on the western flank of Mount Hamilton, two slopes of ankle-twisting steepness come together in a narrow V. The little valley between them forms the birthplace of an ephemeral creek.

Arbor Creek Experimental Watershed
UC Santa Cruz graduate student Amanda Donaldson installs a lysimeter in Arbor Creek’s soils. The instrument enables scientists to sample the water held between soil particles. The amount of vacuum pressure required to extract a sample indicates how readily plants can access soil moisture. Image: Lobsang Wangdu/NRS

Distinctively different plants

Arbor Creek is a study in contrasts. The sunnier, south-facing slope is furred in bright green annual grasses. The cooler, north-facing slope supports a stand of blue and black oaks, now starting to bud out in leaves.

The compact size of the catchment, together with its dramatic vegetation differences, makes Arbor Creek an ideal study site. “The same amount of precipitation is falling on both slopes, and the subsurface structure is largely the same,” Zimmer says. “This lets us isolate how vegetation may drive differences in the storage and release of water from the landscape,” Zimmer says.

However, tracking the fate of that water isn’t so easy. “We don’t have x-ray vision to see the water underground. It’s hard to visualize where the water’s coming from or going,” she adds.

Arbor Creek Experimental Watershed
The dramatic effect of aspect on vegetation. North-facing slopes (left) are cooler and can support more trees, while hotter, drier south-facing slopes (right) are dominated by grasses. Image: Lobsang WangduNRS

A blanket of sensors

In lieu of Superman powers, Zimmer and her CHI colleagues are deploying a formidable array of instruments. The watershed positively bristles with gauges, meters, wells, and samplers.

The crowns of the hills and both slopes are outfitted with rain gauges. Three Clima-Views, the Swiss army knife of weather stations, are stationed at strategic points. Borehole wells monitor deep groundwater levels, while soil moisture probes track the water content of shallow soils.

Each device is designed to illuminate a portion of Arbor Creek’s water budget. The data they yield will reveal where water is being stored, when the water table fluctuates, and how plants are utilizing this precious seasonal resource.

The ClimaView is the Swiss army knife of weather stations. It collects weather data such as temperature and precipitation, but also leaf condensation, soil moisture, sap flow rates, and wirelessly transmits the information to computers at Blue Oak Ranch Reserve headquarters. Image: courtesy CHI-Freshwater

The benefits of working together

The Arbor Creek research site is relatively new. Zimmer found it after joining the UC Santa Cruz faculty two years ago. At that point, CHI-Freshwater was already planning to conduct intensive landscape studies at Blue Oak Ranch Reserve.

“I toured many different watersheds and experimental forests,” Zimmer says “The big draw to Blue Oak Ranch was the CHI initiative. I saw a lot of opportunities to leverage and bolster CHI’s objectives through my work,” she says.

Becca Fenwick, program manager for CHI-Freshwater, is equally pleased with this chance to do multidisciplinary science. “The breadth of expertise we now have from the people who are taking part in this project is phenomenal. They all bring different pieces of the puzzle,” says the UC Santa Cruz-based researcher.

The fact that Blue Oak Ranch is managed for research sealed the deal. “The staff here do everything in their power to accommodate our requests and make sure we’re supported. Being at a reserve has influenced our productivity and ability to do research,” Zimmer says.

The partnership has made the science more robust as well. By combining their financial resources, Zimmer and CHI were able to deploy more instruments at the research site. “By combining our resources, we’re able to bolster our ability to observe watershed function in these systems,” Zimmer says.

Arbor Creek Experimental Watershed
Chris Causbrook, an undergraduate at UC Santa Cruz, prepares to drill a water sampling well on the north-facing slope of Arbor Creek Experimental Watershed. Image: Lobsang Wangdu/NRS

Calendar of plant thirst

A key part of that budget is consumed by plants, which pull water from the subsurface and release it to the atmosphere. One of Zimmer’s graduate students, Amanda Donaldson, is tracking how plants’ appetite for water varies across the seasons. The out-of-step life cycles of the plants enables her to isolate the appetite of the oaks from that of the grasses.

“Right now, in winter, there are no leaves on the trees. They’re basically sleeping for a couple of months. They’re not taking up water from the subsurface. Versus the grasses, which are green and transpiring. They’re removing water from the first meter or so,” Donaldson says.

As spring wears on, “there will be a time when both the trees and the grasses are transpiring. I want to know how differences in their water use patterns influence subsurface water storage,” she says

By midsummer, the annual grasses have died, and only the trees are transpiring. There’s even a brief point in winter when neither oaks nor grasses are growing.

To quantify the amount of water the trees are transpiring, the team has installed sap flow meters on the trunks of the oaks. On the opposite slope, Donaldson will periodically place a dome over a patch of grass to monitor the rate of photosynthesis.

Peering into the future

How water fluctuates at Arbor Creek offer a glimpse into California’s climate future. “If landscapes become hotter and drier, the south-facing slope may be what the north-facing slope will look like in the relatively near future,” Zimmer says.

Oak savannas that become grasslands will also change the amount of water stored in the ground. That, in turn, affects how much water streams carry to human communities downhill.

The California Heartbeat Initiative aims to correlate water status data from individual plants with image data taken via remote sensing methods such as drones and even satellites. Image: courtesy Maggi Kelly/UC Berkeley

From moisture sensors to pixel data

Donaldson’s information about plants has a ready customer. The CHI-Freshwater team wants to correlate the water status of the plants with images they’re gathering on the site using drones. They want to know whether signals of moisture in the plants and soils are visible on drone and satellite images.

“If we can understand the mechanics of what’s happening in the ground, and detect that change in remote sensing data, we wouldn’t have to dig pits in soils and put sensors across the state,” says Becca Fenwick, coordinator for CHI-Freshwater. “Instead, we could use the remote sensing data to get that same information.”

A mix of waters old and new

The remaining portion of Arbor Creek’s water budget is the moisture absorbed by the hills and trickling down the creek.

Measuring what escapes via the stream is relatively straightforward. To do this, the scientists have installed a white fiberglass chute across the valley’s narrowest point. The water level in the flume indicates the amount of water the creek carries.

But the water that flows down streams isn’t entirely composed of the rain that most recently fell from the sky. In fact, “in any rain event, over 70 percent of the water you see in any stream was already in the soil, and 30 percent or less is actually new water,” says Emilio Grande, another of Zimmer’s graduate students.

Arbor Creek Experimental Watershed
UC Santa Cruz graduate student Emilio Grande sets off to collect samples from the rainwater collector. He will use the samples to estimate how long water resides in the soil before being released to the stream. Image: Lobsang Wangdu/NRS

Dating the water

Grande is puzzling out when the water in the stream arrived at Arbor Creek. Because that information affects water available to plants, it has a direct bearing on Donaldson’s vegetation research.

“If I know the age of the water when it leaves the system, I can say something about how long precipitation is going to reside within the slope, and how long that water potentially will be available for vegetation,” she says.

Estimating the age of water requires examining its various atomic formulations, or isotopes. Warm storms carry water containing heavier isotopes of hydrogen and oxygen than storms that form in the arctic. Grande periodically takes samples from the stream and from the rain gauges to identify the isotopic signatures of individual precipitation events. Once he knows how the isotopes in rain vary with time, he can use numerical models to figure out how much time it takes rainwater to become the water that is seen in the stream.

Modeling water residence

After analyzing water from the catchment across a rainy season, Grande can use established formulas to calculate how much was old water — molecules already stored in the soil— and how much was new—precipitation just delivered from a cloud.

Those equations, however, were developed for places with year round rain.  “I’m trying to come up with something that better describes not only Mediterranean climates but also this kind of ephemeral stream,” Grande says. “Potentially we will come up with a new model that can explain the effect of these starts and stops,” Grande says.

Arbor Creek Experimental Watershed
Emilio Grande labels a sample bag. Image: Lobsang Wangdu/NRS

Isotope analyses

Grande is double checking this technique by analyzing sulfur and hydrogen isotopes in his rain and stream samples. Sulfur provides more accurate dates for “younger” water, while the hydrogen isotope known as tritium can age water that has lingered underground for more than 60 years.

“I am measuring the tritium in the rain when it falls. I am also measuring it in the water from down there at the flume,” Grande says. “Because I know how fast tritium decays, I can figure out how long has passed for that precipitation water to become stream water.”

Grande’s work using radioactive isotopes to study catchment hydrology is on the cutting edge. The technique has only been practiced in a handful of places by very few researchers.

Grande’s findings lend themselves to predicting water storage functions across California, where more than half of rivers run dry for part of the year. Climate models point to less frequent but higher intensity precipitation in coming decades. Grande’s equations will indicate how well hillslopes can absorb those deluges, or how much flooding is in the cards.

Arbor Creek Experimental Watershed
A sediment core extracted from the crown of the north-facing slope. Understanding the size of the sediment particles and uniformity of the geology helps the researchers model how water flows from the hills and into the stream. Image: Lobsang Wangdu/NRS

Preparing for the future

“If we know, we can better prepare ourselves by building bigger reservoirs, preparing for longer droughts, and bracing for higher flow events,” Zimmer says.

The study has already piqued the interest of water resource managers at the Santa Clara Valley Water District. The district, which supplies metropolitan San Jose, is located directly downstream from Blue Oak Ranch. That makes the Arbor Creek findings particularly pertinent for the people of California, Zimmer says. “If you’re trying to develop infrastructure to store or release more water, you need to understand how these systems work, and how watersheds are going to persist in the future.”

Related links

Assessment of water storage in oak woodlands, California Institute for Water Resources

Zimmer Watershed Hydrology at UC Santa Cruz

California Heartbeat Initiative soars ahead, UC Natural Reserve System

Filed Under: Coastal

An island expedition

September 30, 2018 By Kathleen Wong Leave a Comment

two dolphins seen from the deck of the ferry

Santa Cruz Island Reserve, Sept. 25-29, 2018

The CHI team headed to the NRS’s Santa Cruz Island Reserve, located on California’s largest island, for our next site field scouting trip. On the third site visit in our series of 12, we are continuing to try to understand patterns and connections between freshwater availability and the health and distribution of vegetation. Santa Cruz Island is really a special place that we all felt fortunate to explore new research opportunities and collect data.

We spent quite a bit of time with Lynn McLaren-Dewey of the NRS and David Dewey of TNC who shared their years of Island wisdom, stories, insight, and great cooking. One particular observation that we all found interesting was that the Bishop Pine mortality in the last two years on the Island has been absolutely staggering to the point where there is 90% mortality in most areas. At the same time, there seems to have been an observed (by David) increase in the base flow of the creek next to Christy despite the last two years being poor rain years begging the question if large-scale Bishop Pine mortality may have led to more water in downstream channels.

While wind and fog grounded us the first two days, we hiked for several miles to install and survey semi-permanent ground control points (GCPs) to more accurately tie the UAV based imagery to the land and reduce the amount of time spent in the field in the future.

Brief windows of good weather let us capture some data over the following two days. Jim and I used a DJI M100 quadcopter equipped with a Micasense RedEdge multispectral sensor to capture some of the dead standing stands of Bishop Pine to help efforts to map patterns in mortality across the Island. Meanwhile, Kerri and Jacob flew another similarly equipped DJI M100 on a ridgeline in the West End where Kerri has long time series soil moisture data. The hope is to use these field sensors along with our newly captured UAV imagery to understand how patterns in microtopography (derived from the UAV imagery) and fog influence patterns of soil-plant moisture in a generally water-limited environment. Finally, on our way to the boat the last day we flew a 300-acre area near the main ranch that burned in March 2018, since most of the Island has not burned since the 1930s, this became a unique chance to study Island pyrogeography and post-fire vegetation recovery.

All in all we captured about 1,000 acres of data in RGB and multispectral with GCPs and laid out a great permanent plot to revisit seasonally.

I’m really proud that we captured a lot of good data under some tenuous conditions. A huge thank you to Lynn, David, and Lyndall for helping us pull it all off!  Now we have lots of data to process and even more to continue talking about. Attached is a timelapse of one of our drives so those who couldn’t be there can spend ~30 seconds bouncing along the roads with us.

Kelly

Filed Under: Freshwater

Tracking water through California ecosystems

December 12, 2017 By Kathleen Wong Leave a Comment

CHI-Freshwater will employ drones, multispectral cameras, microclimate stations, and other next-generation sensors to reveal how state ecosystems respond to water. The information will help Californians manage landscapes amid a changing climate. Image credit: Greg Crutsinger

OAKLAND, California—The University of California Natural Reserve System has received a $2.179 million grant from the Gordon and Betty Moore Foundation to monitor the pulse of water through state ecosystems. The California Heartbeat Initiative-Freshwater (CHI-Freshwater) will link plant responses to environmental conditions such as heat waves, rainstorms, and drought on a landscape scale. The results will be used to produce forecasts of environmental health that can help Californians weather the vagaries of climate change.

“We live in a state where water is at the core of a lot of things. Given the importance of agriculture and natural habitats to California and its growing population, climate change makes understanding water on the land even more important,” says UC Berkeley biology professor David Ackerly. “California sits at a tipping point, with desert to the south and temperate rainforest to the north. It’s a place where we need to be particularly attentive to the direction of change.”

The initiative will study water in habitats with different hydrologic balances, from northern conifer forests to southern deserts, and from the coasts to the mountains. Most study sites will be part of the more than 756,000 acres of protected lands in the UC Natural Reserve System (NRS). A network of more than 39 wildland sites that includes most major California ecosystems, reserves are managed to support research, teaching, and public service.

CHI-Freshwater
Proposed study sites for CHI-Freshwater include eight NRS reserves and three national parks.

Project scientists will examine how water on the surface and below ground varies, providing information on the types of vegetation different hydrological conditions can support. This will be the first project in the NRS to focus on freshwater and examine a range of habitat types simultaneously with an identical array of climate instruments across the breadth of the state.

“CHI-Freshwater will not only advance our ability to cope with climate change, but establish the reserve system as a resource that directly benefits California,” says Peggy Fiedler, executive director of the UC Natural Reserve System. The project is UC system-wide, involving at least ten NRS reserves plus scientists from all of the UC campuses.

Peggy Fiedler
Peggy Fiedler, Executive Director of the UC Natural Reserve System
David Ackerly
David Ackerly, Professor of Integrative Biology, UC Berkeley
Tod Dowson
Todd Dawson, Professor of Integrative Biology, UC Berkeley
Becca Fenwick
Becca Fenwick, IT Director of the UC Natural Reserve System, UC Santa Cruz

CHI-Freshwater will apply next-generation sensing technology to ecological questions. A standard toolkit consisting of drones, microclimate sensors, multispectral cameras, and other instruments will be deployed at a variety of protected lands across the state. By collecting this suite of information across different geographic locations, habitat types, and seasons, the project will track the hydrological status of wildlands in unprecedented detail.

“We have the drones. We know the cameras and the wireless sensor systems work. We’re just applying it in new ways to help us rethink how we manage land and water together,” says UC Berkeley professor Todd Dawson, a plant physiologist and lead investigator on the project.

CHI-Freshwater
Compared to standard photographs (left), multispectral images (right) can provide a wealth of physiological information about plants. Image credit: Sean Hogan

Drones will enable the researchers to quickly scan vast swaths of land. Once programmed to follow a flight path, drones can follow the same route again and again with a high degree of accuracy. Add to this the ability to cover rugged terrain with ease, and using drones to survey vegetation is far more efficient than collecting the data by hand.

“Using drones to do these surveys has made the whole process so much more doable, and the accuracy of the repeated flight paths gives a glimpse into how the landscape really changes through time,” says Becca Fenwick, NRS Director of IT and CHI-Freshwater coordinator.

Each drone will be outfitted with a pocket-sized multispectral camera. The camera’s sensors detect the red, green, blue, and near-infrared light wavelengths reflected off vegetation. Ratios of these wavelengths can indicate whether it is thirsty, how much water it’s using in photosynthesis, and more.

CHI-Freshwater
Drone camera data can be assembled into three-dimensional orthomosaic images such as this one of a giant sequoia. Such volumetric information can be used to refine models of vegetation water use. Image: courtesy Todd Dawson

Using multispectral cameras to obtain the relative water content of a plant is far easier than the traditional method. The “pressure bomb” technique requires dragging a gas cylinder and cumbersome equipment into the field to examine one plant leaf at a time. CHI-Freshwater will establish reference values for how multispectral image data in different plant species compares with pressure bomb measurements.

Drone camera data can also be stitched together to construct 3D orthomosaic images of trees and other vegetation. These digital models provide volumetric information that can improve the water use estimates for redwood trees and other large, complex plants.

“Because we’re such visual animals, when you see these images, it just clicks. People’s minds race with a million things they want to do with it. That means the tool will be adopted by a lot of people and we can start learning more new things about the environment we haven’t dreamt before,” Dawson says.

Climate information will be gathered by a network of 20 miniaturized sensor nodes laid out across each study site. Each node consists of a thermos-sized, solar-powered weather station that takes continuous measurements of temperature, humidity, barometric pressure, soil moisture, and solar radiation. Nodes provide far greater detail about the environment than the single weather station traditionally used to represent conditions for miles around. Individual nodes communicate wirelessly with one another so data can be automatically transmitted back to a central recording site.

CHI-Freshwater
Each node in CHI-Freshwater wireless sensor networks will consist of an autonomous climate station that can measure factors such as temperature, wind speed, soil moisture, and more. Image credit: Zac Harlow, Blue Oak Ranch Reserve

One such microsensor network has been operating for a decade at the NRS’s Blue Oak Ranch Reserve east of San Jose. Its presence makes the reserve an ideal place to test how to integrate microsensor locations and drone flight paths in CHI-Freshwater protocols. Other planned study sites include Angelo Coast Range Reserve, Boyd Deep Canyon Desert Research Center, Landels-Hill Big Creek Reserve, Point Reyes Field Station, Quail Ridge Reserve, Santa Cruz Island Reserve, Sierra Nevada Aquatic Research Laboratory, Steele/Burnand Anza-Borrego Desert Research Center, and Sequoia and Kings Canyon National Parks.

By taking detailed measurements of how vegetation uses water across the state over a number of years, the researchers plan to link specific ecological effects to climate shifts.

“For example, will south-facing slopes, which already tend to be warmer, heat up as fast or faster? And are plants in some microclimates more sensitive than others? We need information from our sensors to determine this,” Ackerly says.

CHI-Freshwater
Wireless sensor networks, such as this one at Blue Oak Ranch Reserve, can collect detailed information about the microclimates from many different locations within a single study site. CHI-Freshwater will use this data to understand how topography, slope, exposure, and other factors affect water supplies for plants. Image credit: Zac Harlow, Blue Oak Ranch Reserve

CHI-Freshwater will help shrink regional climate models to a scale relevant to individual habitats and neighborhoods. Its data will anchor the myriad possibilities used in the models to real life measurements.

“This is a great opportunity to integrate small, hyper-local scale data and information to regional scale models. We can study what water is doing in one particular site and link it to ground climate data, camera images, drone data, and ultimately to regional satellite data. We’ll be seeing the environment literally from the ground up,” says Fenwick.

The models, in turn, will help generate forecasts useful to land stewards, farmers, policy makers, and the public. For example, biologists conducting habitat restorations might use the information to select plant species able to handle tomorrow’s hotter, drier conditions. Or an almond grower could decide to reduce the number of trees in their orchards to match anticipated water resource reductions.

“CHI-Freshwater builds on a host of technologies we’ve invested in the NRS over the past decade, making the NRS an unparalleled platform for this statewide study,” Fiedler says.

This platform includes instrumentation supporting the Institute for the Study of Ecological and Evolutionary Climate Impacts, funded by a UC President’s Research Catalyst Award; the NRS Climate Station Network, made possible by National Science Foundation and the American Recovery and Reinvestment Act (ARRA) grants; the Hydrowatch program funded by the Keck Foundation; and the Eel River Critical Zone Observatory, part of NSF’s Critical Zone Observatories program.

The Gordon and Betty Moore Foundation fosters path-breaking scientific discovery, environmental conservation, patient care improvements and preservation of the special character of the Bay Area. Visit Moore.org or follow @MooreFound.

Filed Under: Coastal

  • Home
  • Science
  • Data
  • Research sites
  • About Us
  • Partners
  • Gallery
  • Search

© 2023 UCNRS · All Rights Reserved