Scientists often evaluate Low Impact Development (LID) design by quantifying how much stormwater rain garden systems (cells) can divert from the sewer system. But Dr. Amanda Cording and her research team want to understand what’s happening inside the cell in order to improve the effectiveness of rain garden design (see part 1). Below are the results of their research.
Deep rooted systems were found to have a much better ability to hold the soil in place and remove nutrients.
Key Findings
Cording says that some of her key findings were that the soil media and vegetation selection is absolutely crucial to the performance of these systems. Cording’s team looked at the root layering perspective in three dimensions and found that deep rooted systems were found to have a much better ability to hold the soil in place and remove nutrients throughout the life cycle of the cell. The more surface area the roots covered, the more pollutants the cell would remove. She adds, “Cells with deep-rooted plants were found to be resilient during increased precipitation due to climate change, did well at retaining peak flow rates, and performed well at removing total suspended solids and nutrients predominantly associated with particulates.” Labile nutrients, Cording says, were a completely different story. She says the bioretention systems have to be specifically designed to remove those nutrients through sorption (P) and denitrification (N).
Compost was found to have a negative effect on water quality.
Compost, which is often used as an organic amendment in the soil media to help remove heavy metals and provide nutrients for the plants, was found to have a negative effect on water quality overall, due to the high pre-existing labile N and P content. She says, “It’s intuitive, but at the same time, a lot of these systems are designed based on bloom time and color, and not necessarily on the physical and chemical pollutant removal mechanisms at work.”
Green algal bloom in a small freshwater lake in New Zealand. (Image: Massey University)
What Lies Ahead?
Cording also tested a proprietary bioengineered media in two of her cells which was designed to remove the phosphorous that causes algal blooms in the rivers and streams. She says, “It did a phenomenal job. There was very little phosphorous coming out compared to the traditionally-designed retention cells. Cording, who is now based in Honolulu and works for an ecological engineering company called EcoSolutions, is looking at how to use natural, highly-leached iron rich soils, to get a similar amount of phosphorous removal, and how bioretention can be designed with anoxic storage zones to remove nitrate via denitrification. She says, “These nutrients can be easily removed from stormwater with a little conscious design effort and a splash of chemistry.”
Low Impact Development (LID) is an approach to development (or re-development) that mimics pre-development hydrology and uses ecological engineering to remove pollutants in stormwater and wastewater so it can be reused or replenish groundwater supplies. Examples of LID features include porous pavement, constructed wetlands, green roofs, and rain gardens. LID stormwater bioretention systems such as rain gardens have been proven to work, but are they designed as effectively as they could be? Dr. Amanda Cording (formerly at the University of Vermont) and her team wanted to understand which design factors would make rain gardens more resilient, increase phosphorus adsorption, and reduce nitrates.
Cording and her team wanted to understand what was happening inside bioretention cells.
What’s Happening Inside?
Scientists often evaluate LID design by quantifying how much stormwater the systems (cells) can divert from the sewer system. But Cording and her team wanted to understand what was happening inside the cell. They wondered which types of soil media and infrastructure would optimize a stormwater bioretention system’s ability to improve water quality. She says, “We wanted to gather water quality information coming in and going out of the system. I designed inflow and outflow monitoring infrastructure to measure nutrient and sediment pollution.” The system monitored pollution by sampling stormwater runoff from a paved road surface before and after it went through bioretention cells. Each cell was constructed with different features to test the influence of vegetation and soil media on pollutant removal capabilities.
Bioretention cells at the newly constructed Bioretention Laboratory at the University of Vermont.
Methods Used
To understand what was happening within eight bioretention cells at the newly constructed Bioretention Laboratory at the University of Vermont, Dr. Cording and her team investigated the mechanisms influencing greenhouse gas emissions and nutrient transformations at various depths in engineered soil media. In addition to using her own monitoring infrastructure, Dr. Cording used soil moisture sensors to measure water content within the soil media. She says, “I was comparing different vegetation treatments while simulating increased precipitation due to climate change in the Northeast. I put the soil probes in at 5 cm and 61cm, one on top of the other. Then I looked at the way the EC and the volumetric water content (VWC) changed prior to a storm event, during a storm event, and after a storm event.”
One of the team’s bioretention cells at the University of Vermont.
Cording says the EC and VWC sensors allowed them to get a general sense of what was happening inside the cell over time. She adds, “I used the data when I needed to know more of the story, such as how the conductivity at the surface compared to other depths so we could see if the nutrients in the soil were migrating, and how much was moving down. We were also able to use the sensors to compare the VWC around the roots of different vegetation types. It provided a lot of insight into the dynamic world that exists below the soil surface.”
Next Week: Read about the team’s key findings and what lies ahead for this research.
Limited water availability is a significant issue threatening the agricultural productivity of soybean, reducing yields by as much as 40 percent. Due to climate change, varieties with improved drought tolerance are needed, but phenotyping drought tolerance in the field is challenging, mainly because field drought conditions are unpredictable both spatially and temporally. This has led to the genetic mechanisms governing drought tolerance traits to be poorly understood. Researcher Clinton Steketee at the University of Georgia is trying to improve soybean drought tolerance by using improved screening techniques for drought tolerance traits, identifying new drought tolerant soybean germplasm, and clarifying which genomic regions are responsible for traits that help soybeans cope with water deficit.
Researchers are trying to improve soybean drought tolerance by using better screening techniques for drought tolerance traits.
Which Traits Are Important?
Clinton and his colleagues are evaluating a genetically diverse panel of 211 soybean lines in two different states, Kansas and Georgia, for over two years to help him accomplish his research objectives. These 211 lines come from 30 countries and were selected from geographical areas with low annual precipitation and newly developed soybean lines with enhanced drought-related traits, along with drought susceptible checks. The researchers are looking at traits such as canopy wilting. Some plants will take a few days longer to wilt, allowing these plants to continue their photosynthetic ability to produce biomass for seed production. Other traits that he is interested in evaluating are stomatal conductance, canopy temperature with thermal imaging, relative water content, and carbon isotope discrimination.
The scientists want to monitor traits such as canopy wilting.
Use of Microclimate Stations to Monitor Environmental Conditions
Clinton says to make selection of drought-tolerant lines easier and more predictable, knowledge of field environmental conditions is critical. He says, “You can phenotype all you want, but you need the true phenotype of the plant to be observed under real drought conditions so you can discover the genes for drought tolerance and improve resistance down the line in a breeding program.”
In addition to soil moisture sensors, the team used microclimate weather stations to help monitor water inputs at their two field research sites and determine ideal time periods for phenotyping drought-related traits. Steketee says, “We put microenvironment monitors in the field next to where we were growing our experimental materials. Both locations use those monitors to keep an eye on weather conditions throughout the growing season, measuring temperature, humidity, and precipitation. Since we could access the data remotely, we used that information to help us determine when it was time to go out to the field and look at the plots. We wanted to see big differences between soybean plants if possible, especially in drought conditions. By monitoring the conditions we could just go back to our weather data to show we didn’t get rain for 3 weeks before we took this measurement, proving that we were actually experiencing drought conditions.”
The team identified some lines that performed well.
Results So Far
Though 2015 wasn’t a great year for drought in Georgia, Clinton says there was a period in late July when he was able to measure canopy wilting, and they identified some lines that performed well. He says, “We compared our data to the data collected by our collaborator in Kansas, and there are a few lines that did well in both locations. Hopefully, another year of data will confirm that these plants have advantageous drought tolerance traits, and we’ll be able to probe the advantageous traits out of those lines and integrate them into our breeding program.”
Future Plans
The team will use what’s called a genome-wide association study approach to identify genomic regions responsible for drought tolerance traits of interest. This approach uses phenotypic information collected from the field experiments along with DNA markers throughout the soybean genome to see if that marker is associated with the trait they are interested in. If the scientists find the spot in the genome that is associated with the desired trait, they will then develop genomic tools to be used for selection, integrate that trait into elite germplasm, and ultimately improve the drought tolerance of soybeans.
See weather sensor performance data for the ATMOS 41 weather station.
In Haiti, untreated human waste contaminating urban areas and water sources has led to widespread waterborne illness.
Waterborne disease is the leading cause of death for children under 5. Currently, Haiti is battling the largest cholera outbreak in recent history. Over 1/6 of the population is sickened to date.
Sustainable Organic Integrated Livelihoods (SOIL) has been working to turn human waste into a resource for nutrient management by turning solid waste into compost. (See part 1).
Contaminants making their way into the waterways.
The organization plans on performing experiments with lysimeters, to determine if human waste will contaminate Haitian soil during the composting process.
Even in places where there are toilets, they are often poorly designed or poorly placed. This latrine is located just above a river, where people are getting their bathing and drinking water.
Lysimeters Help Assess Health Hazards
SOIL will use G3 passive capillary lysimeters in an experiment to determine if composting human waste without a barrier between the waste and the soil will result in ecological and/or health hazards. Why? The problem is “jikaka,” or “poo juice.” The compost facility currently redistributes it onto the compost and finishing piles, but they would rather not have to manage it. They believe if they remove the concrete slab and allow composting to occur in contact with soil, the composting process will be easier and faster.
SOIL’s agricultural team conducts studies on the use of compost to improve farming practices and maximize economic benefits of targeted compost application.
The Experiment
The organization will test their idea as they expand their facility. New compost bins and staging areas for finishing have been built absent concrete pads. G3 passive capillary lysimeters have been installed, three beneath the compost bin, and four beneath the first staging area for finishing. They will be used to monitor the amount of moisture (jikaka) that travels through the soil as well as check for anything harmful that travels with it.
SOIL’s human waste compost was found to increase sorghum yields by 400%.
What’s the Futurefor Konpòs Lakay?
SOIL’s agricultural team studies the use of their compost (Konpòs Lakay) in order to optimize farming practices and the economic benefits of targeted compost application. The data they collect will help them expand the market for Konpòs Lakay, which in turn will support the sustainability of SOIL’s sanitation programs.
For more information on SOIL’s waste treatment efforts, visit their website, or watch the video below, a TEDx talk given by SOIL co-founder, Sasha Kramer.
In a continuation of last week’s post, Henry Sintim, PhD student at Washington State University is investigating whether biodegradable mulches are, in fact, what they claim to be (see part I).
Sintim and his team want to understand what’s leaching through the soil as the mulches degrade. He installed passive capillary lysimeters at a 55 cm depth to collect leachate samples for analysis of BDM particulates. He was surprised when the lysimeter readings revealed higher EC measurements.However, the EC in the PE, paper mulch, and no-mulch treatments were also high, hence that could be due to the leaching of accumulated salts in the soil surface. He says, “We have yet to examine the leachate samples for the presence of particulates.”
Installing lysimeters
Composting Alternatives
If the team finds that some of the BDMs do not biodegrade very well in the field, the alternative could be on-farm composting, which would be more viable than having to deal with polyethylene plastic. Sintim and his research team have set up a composting study where they have been digitizing the images of the mulches degrading. He adds, “We buried the mulches in a mesh bag, and periodically we retrieve the bags to study the mulch. There was some black staining on the mesh bag, which we suspect is a nanoparticle called, “carbon black,” used as reinforcing filler in tires and other rubber products.
The team buried the mulches in compost, and periodically they retrieve the mesh bags to study the mulch.
Sintim says the manufacturers do not disclose the actual constituents of their mulches, so he has arranged to examine the mesh bags with WSU’s scanning electron microscope in order to confirm that the stains were due to the presence of particulates. Sintim confirmed that carbon black was used in their experimental BDM, but they don’t know whether the carbon black was made from petroleum products, as there is non-petroleum-based carbon black. He is going to determine whether these particles leach through soil by examining leachate samples from the lysimeter. He will also perform more tests to make sure that these nanoparticles are not going to have any adverse effects on the agro-ecosystem.
What’s in the Future?
While Sintim and his colleagues have made important discoveries, there is still work to be done. He and his team are going to collect three more years’ worth of data to see if there really is a BDM that delivers on its promises and if leaching particles pose a threat to the groundwater.
Henry Sintim, PhD student at Washington State University, is investigating whether biodegradable mulches are, in fact, what they claim to be.
Application of plastic mulches conserves water, and helps in weed, pest, and disease control.
He and his research team want to understand what leaches into the soil as the mulches degrade and which ones perform as well as polyethylene-made plastic mulches (PEs) at weed, pest, and disease control.
Plastic Mulch
Application of plastic mulches in agriculture is a common practice by specialty crop producers worldwide. It conserves water, and helps in weed, pest, and disease control, subsequently improving crop yield and quality. Because PE is durable and does not degrade in the soil, you cannot leave it in the field, which ultimately leads to the question of disposal. When PE is buried in the field, it becomes contaminated with soil and can’t be recycled but instead requires transport to a landfill, increasing production costs. Another problem arises when landfill facilities are not available. When this is the case, growers stockpile PE on their farm, where the rain can wash the mulch down to streams and water bodies. Henry Sintim and his team are investigating whether or not biodegradable plastic mulches (BDMs) could be a viable alternative.
The team installs a lysimeter beneath the mulches.
Biodegradable Alternatives
Substituting PE with BDM could alleviate the need for disposal. However, Sintim says the potential impact on agricultural soil ecosystems needs to be assessed before adopting biodegradable mulch for field use. For instance, do biodegradable mulches really degrade? Sintim explains, “By BDM, we mean it is plastic mulch, but it has been made from pure or partial biobased materials. Though there are plastic mulches advertised as biodegradable, none have actually been proven to biodegrade, so the team is examining degradation of different commercial BDM types over time. They have also included an experimental BDM, in which the constituents were specified by the team.”
Sintim is monitoring the degradation of BDM by assessing the material properties and measuring the particle size and surface area via photography: digitizing and analyzing them using Image J software.
There are indications that some of the BDMs are performing well.
How Well Do the Mulches Compare?
Sintim also wants to find out how well BDMs maintain microclimate in comparison to PE. Since soil temperature and moisture content are important parameters that govern chemical reaction rates and microbial activity, and are likely to vary among the different BDM treatments, he is monitoring soil moisture dynamics using soil moisture and temperature sensors installed at 10 cm and 20 cm depths. In addition, the team has installed sensors directly underneath the mulches to measure surface temperature and light penetration. Reduction of light penetration is the attribute that helps plastic mulches to control weeds. The team is also assessing soil quality using the USDA Soil Quality Test Kit.
Sintim says so far one of the commercial BDMs and the experimental BDM had the same yield performance as PE. He adds, “We don’t have final results yet, and there are a lot of variables that could come into the picture. But I will say there is an indication that some of the BDMs are performing well.”
Next week: Find out how Sintim will determine what’s leaching into the soil and another alternative for polyethylene plastic mulch.
Launched in 2006, the URC has hosted competitions since 2007 and boasts contestants from around the globe, including the United States, Canada, India, Bangladesh, Poland, and Egypt. Each year, contestants are given point scores based on how quickly they complete a series of tasks and how closely each task conforms to parameters outlined by the competition guidelines. This year, teams must complete a terrain traverse, a simulated equipment servicing, an astronaut assist, and the retrieval and measurement of a non-contaminated soil sample.
Collaboration and Challenges
Byron Cragg, Science Team Lead for the Titan Rover Team out of California State University, Fullerton, says it’s been an uphill battle. “We’ve had to design the systems we are using to control our rover, retrieve our data, and keep our data organized from the ground up. We’ve also needed to make our rover robust in case a battery or a motor fails during the competition.”
It is no easy feat to build a rover for the Utah desert, let alone send instrumentation to Mars. This is why it has taken a multi-disciplinary team to build the physical components, robotic arm, telecommunications, and scientific cache on Titan Rover. Cragg says his team consists of scientists, computer engineers, electrical engineers, mechanical engineers, geologists, chemists, and biologists all working together.
A prototype image of the Titan Rover.
Titan Rover Features
The CSU rover is outfitted with sophisticated features like Leap Motion infrared sensors that allow Titan Rover’s robotic arm to be controlled by a human counterpart moving their arm in free space. When the user moves their arm and hand position, the arm on Titan Rover is given a signal from the command center to move accordingly.
Cragg is responsible for the 3D printed science cache that uses a 3” auger and a capacitance sensor to measure a soil sample’s volumetric water content, temperature, and bulk electrical conductivity. During the competition, the team will also be required to construct a stratigraphic column from HD images transmitted by the rover, as well as measure soil temperature at a depth of 10cm.
“It comes down to designing the pieces to communicate and work together to perform the tasks correctly,” Cragg says about the challenges ahead. “It’s one thing to build the rover,” he adds, “but it’s another to complete the requirements.”
While ambitions of a colonized Mars are on the horizon and research pushes on, like the Titan Rover project, progress will require collaboration and teamwork. In the meantime, good luck to all the Earthlings who will be competing in the Utah desert this June.
Many dryland winter canola growers assume that if they plant earlier, they will establish a stronger plant, but Washington State University researcher Megan Reese recently found that this was not the case. She and her team discovered that planting earlier increases risk to the plant, as more water is used, and the reduced amount of water then left after the winter season limits spring regrowth. Megan’s findings could be valuable as water is the most yield-limiting factor in eastern Washington state’s wheat-dominated dryland systems, where winter canola has newly emerged as a rotational crop.
Winter canola is cold hardy, but it’s not as resilient as wheat.
Early Planting:
Winter canola is cold hardy, but it’s not as resilient as wheat. It’s planted in August, much earlier than winter wheat, which is planted in the late fall. In order to survive, winter canola has to establish a hardy taproot system so that plants have reserves to survive the winter. Megan says, “Opinions vary, but anecdotally, a dinner plate sized plant can survive winter fairly well, so that’s why winter canola is planted in August . However, because establishment and germination can be an issue, we decided to try planting in June at Ritzville, Washington, thinking the soil would be more moist and have a cooler seedbed. However, the early planting date had a negative effect on winter survival. Not one of the early plants survived. We found the plants that started earlier used a lot more water, and consequently, the winter rains weren’t enough to refill the soil profile. Excessive growth and bolting also contributed to low survivorship.”
Methods and Moisture Release Curves:
Megan monitored soil water in the profile several different ways. At one location she used a neutron probe and hand-sampled gravimetric soil moisture in the top 30 cm of the profile, and in other locations, she was limited to hand samples. Then she combined those measurements with local weather stations to provide the crop water balance for the canola. Using these data, she was able to determine soil water use as indicated by the water content change through the growing season and calculate the depletion of soil water.
Anecdotally, a dinner plate sized plant can survive winter fairly well.
Megan also took soil samples into the lab from each depth increment at every site and used a chilled mirror hygrometer to construct a moisture release curve. This helped her to define the apparent permanent wilting point at -1.5 MPa. She says, “I was able to then see how efficient canola was at extracting available water, and I could look at available water instead of total water contents, which was more useful in terms of plant accessible moisture in the soil profile. It allowed me a consistentplatform to compare actual water amounts across sites with differing soil types. At one site, 12.5% of the water was unavailable, but in the sandier soils at another site, it was 4%. So there were significant differences in permanent wilting point.”
Water and Physiological Challenges Affect Winter Survival:
Megan found that the June planted canola used every milliliter of available water in the soil profile by late October/early November, but August-planted canola still had some water above wilting left in the profile over the winter, which helped the plants in the spring. She says, “It was a milder winter, so we didn’t get the usual amount of snow and rain, which probably played a role, but we did not see the profile refilled in the June-planted canola. In addition, those June plants were purple and wilted by November, so water stress could have hurt the plants in terms of its defenses. However, I think a larger issue was that they grew so large (the crowns actually elongated and bolted so they weren’t close to the soil) they were more susceptible to the harsh temperatures, whereas the August planted canola were much smaller and their crowns stayed right on the soil surface.” These findings are based on only one year of data, and Megan notes that early plantings have worked well in the milder climate of Pendleton, OR.
What Does it Mean for Farmers?
Megan says, “We were able to surprise a lot of farmers by showing that canola roots access water down to 1.5 to 1.7 m in the fall; it was hard to believe that a winter crop would do that. Also, in my second year’s data, we followed water use all the way through harvest, so we were able to show how much yield we gained for every millimeter of water used, and farmers liked hearing that number as well. I think it’s useful information that incorporates biophysics principles and answers some questions that these new canola producers are interested in. I have three locations this season that we are currently following to give farmers a further idea of what the water use looks like, when canola uses that water, and from where in the soil profile. Hopefully, this research will help them manage their rotations and look at the possibility of adopting canola.”
Climate change scientists face a particular challenge— how to simulate climate change without contributing to it. Paul Heinrich, a Research Informatics Officer associated with the Southwest Experimental Garden Array (SEGA) remembers looking at the numbers for a DOE project that would have used fossil fuel to measure forests’ response to temperature change. “It would have been very, very expensive in fossils fuels to heat a hectare of forest,” he says.
The alternative is, “to use elevation change as a surrogate for climate change so we could do climate change manipulations without the large energy costs.”
An overview of the SEGA sites using elevation change as a surrogate for climate change. For more information on these sites, visit http://www.sega.nau.edu/. Photo credit Paul Heinrich
By monitoring organisms across a temperature gradient it is possible to identify genetic variation and traits within a species that could contribute to a species survival under projected future climates.
Control and Monitoring Infrastructure
SEGA is an infrastructure project started in 2012 after researchers at Northern Arizona University’s Merriam-Powell Center for Environmental Research were awarded a $2.8 million dollar NSF grant with a $1 million match from NAU. Consisting of ten fenced garden sites for genetics-based climate change research, SEGA is set on an elevation gradient from 4000 to 9000 feet in the Southwestern United States. Each SEGA site has an elaborate data collection and control system with meteorological stations and site-specific weather information. Custom-engineered Wireless Sensing Actuating and Relay Nodes (WiSARDs) send data packets to a hub which then send the data back to a centralized server.
Because there is inherent moisture content variability from site to site, volumetric water content and soil water potential sensors have been installed to monitor and maintain moisture levels. If there is a change in soil moisture at one site, soil sensors will detect the difference. Software on the server notes the difference and sends a signal to the other sites, turning on irrigation until the soil moisture matches across sites.
An illustration of SEGA’s cyberinfrastructure and data management system. Photo credit Paul Heinrich.
Having such an elaborate infrastructure creates an opportunity for researchers looking to conduct climate change research. By offering access to the pre-permitted SEGA sites, the hope is that research will generate much-needed data for climate projections and land management decisions.
When asked if the data stream was overwhelming to manage Heinrich said, “Well, not yet. We are just getting started. The system is designed for what SEGA is expected to look like in ten years, where we expect to have 50 billion data points.”
Research Considerations
Climate change projections show temperatures increasing rapidly over the next 50 to 100 years, bringing drought with it. The impact of these changes will be dramatic. Temperature and drought tolerant species will survive, those that are not will die, drastically changing the landscape in areas that are currently water stressed. Pests like the pine beetle and invasive species like cheatgrass will do well in a drier environment where water-stressed natural species will not be able to compete.
Soap Creek, AZ from above. With climate change projections it is likely that more land will become marginal. Photo credit Paul Heinrich.
“Foundational species,” or species that have a disproportionate impact on the ecosystem, are the primary focus of the research efforts at SEGA sites. These are the species that drive productivity, herbivore habitat, and carbon fixation in the ecosystem. Unlike forests in other parts of the United States, forests in the Southwest can be dominated by one or two species, which makes potential research subjects easier to identify.
Genetic Variance
Amy Whipple, an Assistant Professor in Biology and the Director of the Merriam-Powell Research Station who oversees the day-to-day activities at SEGA, has been conducting some of her own research at the garden sites. Whipple has studied Piñon Pine, Southwestern White Pine, and has a proposal to study Cottonwood in process.
Whipple says that models currently suggest that Piñon Pine will be gone from Arizona within the next 50 years, adding that the models do not take into account possibilities for evolution or genetic variance that might help the Piñon survive. Her research is largely asking, will trees from hotter, drier locations have a better chance of surviving climate change? “We’re trying to do that with a number of different species to look for ways to mitigate the effects of climate change in the Southwest.”
Researchers documenting a Piñon Pine. Photo credit Paul Heinrich.
In some of her research on Piñon Pine, it was discovered that four different species were grouped morphologically and geographically from southern Arizona to Central Mexico. While this suggests that the divergence of species has occurred, it also suggests a low migration rate for these tree species. Migration rates of drought and temperature tolerant species is an important consideration when modeling for a future climate. If the migration of genetically adapted species cannot keep up with climate, the land could become marginal as a foundational species dies off.
Climate Change Predictions and Considerations
In the Southwest, there are entire forests that could become grassland in 50 years because the genetic characteristics of the foundational species currently in those regions will not adapt to higher temperatures and drought stress. But what does this mean from a land management perspective?
Ponderosa pine trees, a foundational species in some area of the Southwestern United States.
Environmental conservationists maintain that we should protect the unique species that are in a place and that introducing other organisms or genetic material would be an ethical violation. Environmental interventionists make the argument that climate change has been caused by humans, so we have lost the option of remaining bystanders.
Research, Land Management and Policy
Paul Heinrich says that the route we take to manage the land will depend on our end goals. “Places that have trees now, if you want them to have trees 50 years from now, you are going to have to do something about it. The trees that are on the landscape right now are locally adapted to the past climate. They are not necessarily adapted to the future climate. They are probably maladapted to the future climate.”
To be clear, SEGA’s goal is not to promote or implement assisted migration. Instead, Amy Whipple says, SEGA can test what the effects of assisted migration might be. “In a smaller experimental context, we’re asking: how will these plants do if we move them around? What will happen to them if we don’t move them around?’” The goal is to provide decision makers with the data they need to make informed decisions about how to manage the land.
The Arboretum Meadow in Flagstaff, AZ. Home of one of the SEGA research sites. Photo credit Paul Heinrich.
Whipple’s own view is that we may no longer have the option of doing nothing. “Unless major changes are made for the carbon balance of the planet, keeping things the same is not a viable option. Managing for a static past condition is not viable anymore.”
Remaining Questions
Both Heinrich and Whipple acknowledge that these are inherently difficult questions. Ultimately the public and land managers must make these decisions. In the meantime, data from SEGA research may help ensure better predictions, better decisions, and better outcomes.
Innovative soil scientist, John Buck, and his team have discovered that green roofs have more capacity than people imagined (see part I). Below are some of the challenges he sees for the future, and the type of measurements he suggests researchers take, as they continue to validate the effectiveness of these urban ecosystems.
A green roof is essentially a garden on a roof, but rather than growing plants in soil, installers use a synthetic substrate made of expanded shale, expanded clay, crushed brick, or other highly porous, lightweight material.
New Challenges for Green Roofs
Green roof results are promising, but they present a new challenge: making sure the plants have enough water. The crux of the challenge is that the lightweight, expanded shale/clay substrate material, the standard in green roof design, does a good job of soaking up the water, but has some peculiar properties that are unlike typical soils. Specifically, the expanded shale and expanded clay media tend to be dominated by sand and fine gravel-sized particles that provide a high proportion of macropores, but the interior porosity of the large particles is dominated with micropores. That pore size distribution leads researchers to two important questions— How much water will be readily available for plant growth? And, will the unsaturated hydraulic conductivity be adequate to avoid starving the roots under high-evaporative demand by allowing water to flow to roots from the bulk soil? These are critical questions as green roof technologies continue to evolve.
Researchers wonder, will the unsaturated hydraulic conductivity be adequate to avoid starving the roots under high-evaporative demand.
Measurements Required for Green Roof Validation
Still, Buck has learned a great deal from his work. Considering the wild spatial distribution of summer storms, quantitative green roof performance studies require that rainfall be measured locally. Monitoring of soil volumetric moisture content measurements in concert with rainfall and soil lysimeter measurements of drainage, reveal the degree of total and capillary saturation, drainage rate, and porosity available for storage. Soil water potential sensors, placed within the capillary fringe of water ponded over subsurface drainage layers, can provide useful insights regarding the dryness of the drainage layer and overlying soil, as well as the available storage of stormwater within the drainage layer.
Direct measurement of soil drainage using lysimeters is a key supplemental measurement on green roof performance quantification projects because there is an unmeasured component of water storage where drought-resistant alpine succulents (typically Sedum species) are used on green roofs. The Sedum plants can absorb up to 10 mm of rainfall equivalent in their plant tissues.
Measurement of soil drainage using lysimeters is a key supplemental measurement on green roof performance quantification projects.
Other Projects and Future Plans
At ground level, Buck is quantifying the performance of intensive stormwater infiltration areas known as rain gardens, bioretention areas, or more generically, infiltration-based stormwater best management practices (Infiltration-based BMPs). When monitoring infiltration-based stormwater BMPs, Buck has used similar tools to those used on green roofs, but has added water-level sensors and piezometers. Buck has found that ancillary measurements of electrical conductivity, often available on water content sensors, along with surface and pore water sampling, can be used to document transformations taking place in infiltration systems. These measurements now combine to show that green roofs and infiltration-based BMPs are indeed making a difference to urban environments and contributions to CSOs. The challenge now is how to implement this technology more widely. But, with the validation now in hand, that job should be quite a bit easier.
