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Posts tagged ‘Water content’

Unraveling the Effects of Dams in Costa Rica (Part 2)

Dr. Rafael Muñoz-Carpena, Professor and University of Florida Water Institute Faculty Fellow and his research team are performing environmental studies on the Palo Verde National Park wetlands, trying to unravel the effects of the dams and how to revert some of the damage (see part one).  This week, find out how the researchers established connectivity in such a remote area,  some of the problems associated with the research, and how the team has addressed some unusual research issues.

ATMOS 41 Weather Station in Palo Verde National Park Wetlands

Surface water elevation gauge station at the Bebedero river. Photo credit: Marco Pazmino Antonio

The Data Challenges of Remote Locations

The team began collecting data, as part of a joint effort with the Organization of Tropical Studies (OTS) research station. However, typical sensors require constant supervision and frequent visits, which imposed a burden on the station staff. There was also the risk of losing data if a sensor malfunction went undetected between monthly visits.  Rafael says, “Sometimes access was not possible due to floods or scheduling issues, so there was a high risk of losing information. To fix the problem (thanks to a National Science Foundation grant awarded to OTS) we integrated the sensors into a system that gives us remote access on a daily basis. This allows us to see the status of the instrumentation in near real-time, and thus coordinate with OTS to replace sensors if needed.”

Fauna in Palo Verde

Glimpse of the fauna in Palo Verde. Photo credit: Alice Alonso

Connectivity Issues

The team had a difficult time finding internet connectivity because the area is so remote. After trying several solutions, they finally built their own cell towers. The stations are now outfitted with cellular-enabled data loggers in conjunction with rain gauges and soil moisture and salinity sensors. The stations also include a standing well to measure surface and river water levels and monitor flooding stages. These are coupled with shallow water table wells, installed below the surface at 3-5 meters.  Rafael says, “These are tidal rivers, so we get a lot of activity up and down. We look at river data in conjunction with inland responses to try and get an idea of the influence of the river on the shallow groundwater nearby. All these data feed into a database that researchers and stakeholders can look at.”

Composite image contrasting the Palo Verde wetland in the 1986 and the wetland in recent days (2012) during the wet seasons. It highlights the encroachment of vegetation and Typha domingensis (cattail), closing the patches of open water and reducing biodiversity and sites for birds feeding and nesting.

Composite image contrasting the Palo Verde wetland in the 1986 and the wetland in recent days (2012) during the wet seasons. It highlights the encroachment of vegetation and Typha domingensis (cattail), closing the patches of open water and reducing biodiversity and sites for birds feeding and nesting.

Internal Drivers

Dr. Muñoz-Carpena says because of the lag in the environmental response, it is not immediately clear to the general public that the wetland behavior is the result of what is happening upstream. People fail to see a connection. Therefore unraveling the data in a way that is clear is the first challenge of the project. He adds, “There are also internal drivers such as park management changes that compound the effects of the dams. Originally park managers tried invasive plant control with fire and cattle. Now they control the invasive with blade-rigged tractors that mow the cattail. But this is a highly expensive and temporary measure with recurrent costs, which provides no definitive solution to the cattail invasion. It’s important to understand the changes are not just the result of what’s happening locally. We need to find permanent solutions by tracking down the root of the problem.”

Endangered Jabiru birds in the trees in Palo Verde National Park

Endangered Jabiru in the Palo Verde National Park. Photo credit: Alice Alonso

Plants are Not the Only Invasives

Cattails are not the only invaders that plague the wetlands. Rafael explains, “The other problem is that there is trafficking going on in the park. The men see these data logger boxes with silver antennas, and they think it’s a camera, so they break off the antennas. We are now putting up signs that say, ‘This is not the government watching you. This is research to protect your environment,’ but we are afraid the next time they will break the boxes and everything that goes with them. We won’t have the manpower or the financial resources to go down there and fix the data loggers for another six months.”

Image of a typical monitoring station set up in a more dry area

Example of a typical monitoring station: Surface and subsurface water elevation and EC monitoring wells, and soil moisture and EC at 30 and 60 cm depths. Sensors connected to a wireless cellular data logger for near-real-time data access. Photo taken during the dry season. Photo credit: Alice Alonso

What’s Next?

Over the last three years the team has collected a high-resolution database of fifteen to thirty minute timed steps, with over 100 sensors deployed in twelve spatially-distributed monitoring stations around the park. With that data, Rafael’s team is conducting exploratory types of analysis to study not only potential drivers of change, but also the cause of the drivers. They want to understand potential initiatives they could introduce to make the system more sustainable. Rafael says, “Once we develop integrated hydrological models and test them for the conditions in Costa Rica, hopefully we can understand the behavior in the past and forecast some different scenarios for the future.” Because many regions in the world suffer the impacts of interbasin water transfer, this research can inform future research policy at a broader scale.

Monkeys hang from a tree branch in Palo Verde National park

Glimpse of the fauna in Palo Verde. Photo credit: Alice Alonso

See a map of the instrumentation network within the Palo Verde National Park.

Conceptual representation of the Palo Verde National Park in the context of the Tempisque watershed system.

Conceptual representation of the Palo Verde National Park in the context of the Tempisque watershed system.

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Unraveling the Effects of Dams in Costa Rica

Thirty years ago, in Costa Rica’s Palo Verde National Park, the wetlands flooded regularly and eco-tourists could view thousands of waterfowl. Today, invasive cattail plants cover portions of the wetland which has subsequently dried up and become colonized by hardwoods. Consequently, the number of birds has fallen dramatically.

Flocks of birds flying against a sunset

The number of birds on Palo Verde National Park has fallen dramatically. (Image: anywherecostarica.com)

Some people blame the dams built in the 1970s which introduced hydrological power and created a large irrigation district in the remote region. Dr. Rafael Muñoz-Carpena, Professor and University of Florida Water Institute Faculty Fellow and his research team are performing environmental studies on the wetlands, trying to unravel the effects of the dams and how to revert some of the damage. Rafael explains, “We have a situation where modern engineering brought about social improvements, helpful renewable resources, and irrigation for abundant food production. But the resulting environmental degradation threatens a natural region in a country that depends on eco-tourism.”

Birds in a river at Palo Verde National Park

“A vast network of mangrove-rich swamp, lagoons, marshes, grassland, limestone outcrops, and forests comprise the 32,266 acre Palo Verde National Park.” (Image and text: anywherecostarica.com)

Are The Dams Responsible?

Dr. Muñoz-Carpena says because of lack of historical data it’s difficult to untangle and separate all the factors that have caused the environmental degradation. He adds, “Thirty years ago Palo Verde National Park was part of a large wetland system which was important to all of Central America because it contained many endangered species and was a wintering ground for migratory birds from North America. The Palo Verde field station on the edge of the wetland, operated by the Organization of Tropical Studies (OTS), attracted birdwatchers and wetland scientists from all over the world.”

In the 1970’s, with international funding, a dam was built in the mountains to collect water from the humid side of Costa Rica in order to generate hydroelectric power. It was clean, abundant, and strategically important.  With the water transferred to the dry side of the country, a large irrigation district was created to not only produce important crops to the region like rice and beans, but to distribute the land among small parcel settlers.

Flock of birds in the grasslands at Palo Verde National Park

“Birding is the principal draw of visitors to the park.” (Image and text: anywherecostarica.com)

Over the years, however, the wetland area slowly degraded to the point where its Ramsar Convention wetland classification is under question. Rafael says that understanding the causes of the degradation, the impacts of the human system, and how the natural and human systems are linked, is the big question of his research, and there are many factors to consider. “The release of the water, ground and surface water (over)use, agriculture, human development, and a larger population are all factors that could contribute to this degradation. Everything compounds in the downstream coastal wetlands. In collaboration with OTS and other partner organizations and universities, we are trying to disentangle these different drivers.”

Grasslands and swamps with mountains in the background

Understanding the causes of the degradation, the impacts of the human system, and how the natural and human systems are linked, is the big question of this research. (Image: anywherecostarica.com)

A Lack of Historical Data

One of the challenges the researchers face is to gather a sufficient amount of temporal and spatial information about what happened in the past forty years.  There are no public repositories of data to tap, and the information is spotty and hard to access. Rafael says, “Thanks to the collaboration of many local partners, we have been able to gather enough information to stitch together a large database out of a collection of non-systematic studies. The biggest challenge is to harmonize data that has been collected by different people in non-consistent ways.” This large database now contains the best long-term record possible for key hydrologic variables: river flow, groundwater stage, precipitation, and evapotranspiration.

The team is also using remote sensing sources to try to obtain time-series data for land-use and vegetation change, and will have those data ground-truthed through instruments that are collecting similar time-series data. Rafael says, “The idea is to build a network that will allow us to overlap some of the previous data sources with our own, validate and upscale the ground data with remote sensing sources, enabling us to put together a detailed picture of what happened.”

Next Week:  Find out how the researchers established connectivity in such a remote area,  some of the problems associated with the research, and how the team has addressed those issues.

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Can Canopy Measurements Determine Soil Moisture? (Part 2)

Dr. Y. Osroosh, now a researcher at Washington State University, believes that plants are the best soil moisture sensors (see part 1).  He and his team have developed a new model for interpreting plant canopy signals to indirectly determine soil moisture in a Fuji apple orchard.  Below are the results of their efforts and what he sees as the future of this research.

Close up of flower blooming

Could plants be the best indicators of soil moisture?

The Results

Osroosh says they expected to see correlations, but such strong relationships were unexpected. The team found that soil water deficit was highly correlated with thermal-based water stress indices in drip-irrigated apple orchard in the mildly-stressed range. The relationships were time-sensitive, meaning that they were valid only at a specific time of day. The measurements taken between 10:00am and 11:00am (late morning, time of maximum transpiration) were highly correlated with soil water deficit, but the “coefficient of determination” decreased quickly and significantly beyond this time window (about half in just one hour, and reached zero in the afternoon hours).  Osroosh says this is a very important finding because researchers still think midday is the best time to measure canopy water stress index (CWSI). He adds, “The apple trees showed an interesting behavior which was nothing like what we are used to seeing in row crops. They regulate their stomata in a way that transpiration rate is intense late in the morning (maximum) and late in the afternoon. During the hot hours of afternoon, they close their stomata to minimize water loss.”

Picture of a corn field

Researchers have found good relationships between CWSI and soil water content in the root zone near the end of the season at high soil water deficits in row crops.

Other Research

Osroosh points to other efforts which have tried to correlate remotely-sensed satellite-based thermal or NIR measurements to soil water content. He says, “The closest studies to ours have been able to find good relationships between CWSI and soil water content in the root zone near the end of the season at high soil water deficits in row crops. Paul Colaizzi, a research agricultural engineer did his PhD research in part on the relationship between canopy temperature, CWSI, and soil water status in Maricopa, Arizona; also motivated by Jackson et al. (1981). Steve Evett and his team at Bushland, Texas are continuing that research as they try to develop a relationship between CWSI and soil water status that will hold up. They are using a CWSI that is integrated over the daylight hours and have found good relationships between CWSI and soil water content in the root zone near the end of the season when plots irrigated at deficits begin to develop big deficits.”

Picture of a green apple on a tree

Osroosh wants to study other apple cultivars, tree species, and perhaps even row crops, under other irrigation systems and climates.

What’s The Future?

In the future, Osroosh hopes to study the limitations of this approach and to find a better way to monitor a large volume of soil in the root zone in real-time (as reference). He says, “We would like to see how universal these equations can be. Right now, I suspect they are crop and soil-specific, but by how much we don’t know. We want to study other apple cultivars, tree species, and perhaps even row crops, under other irrigation systems and climates. We need to monitor crops for health, as well, to make sure what we are measuring is purely a water stress signal. One of our major goals is to develop a sensor-based setup which, after calibration, can be used for “precise non-contact sensing of soil water content” and “stem water potential” in real-time by measuring canopy temperature and micrometeorological parameters.”

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Can Canopy Measurements Determine Soil Moisture?

As a young university student, Dr. Y. Osroosh, now a researcher at Washington State University, wanted to design the most accurate soil moisture sensor.  Over the years, however, he began to realize the complexity and difficulty of the task.  Inspired by the work of Jackson et al. (1981) and researchers in Bushland, TX, he now believes that plants are the best soil moisture sensors.  He and his team developed a new model for interpreting plant canopy signals to indirectly determine soil moisture.

Apples on an open air tree

The team measured microclimatic data in an apple orchard.

How Can Plants Indicate Water in Soil?

Osroosh and his team wanted to use plant stress instead of soil sensors to make irrigation decisions in a drip-irrigated Fuji apple tree orchard. But, the current practice of using the crop water stress index (CWSI) for detecting water stress presented some problems, Osroosh comments, “Currently, scientists use either an empirical CWSI or a theoretical one developed using equations from FAO-56, but the basis for FAO-56 equations is alfalfa or grass, which isn’t similar to apple trees.”  One of the main differences between grass and apple trees is that apple tree leaves are highly linked to atmospheric conditions. They control their stomata to avoid water loss.  

Apple tree canopy in an open air field

There is high degree of coupling between apple leaves and the humidity of the surrounding air.

So Osroosh borrowed a leaf porometer to measure the stomatal conductance of apple trees, and he developed his own crop water stress index, based on what he found.  He explains,We developed a new theoretical crop water stress index specifically for apple trees. It accounts for stomatal regulations in apple trees using a canopy conductance sub-model. It also estimates average actual and potential transpiration rates for the canopy area which is viewed by a thermal infrared sensor (IRT).”

Fuji open air apple orchard (Roza Farm, Prosser, WA).

Fuji apple orchard (Roza Farm, Prosser, WA) where Osroosh performed his research.

What Data Was Used?

Osroosh says they established their new “Apple Tree” CWSI based on the energy budget of a single apple leaf, so “soil heat flux” was not a component in their modeling. He and his team measured soil water deficit using a neutron probe in the top 60 cm of the profile, and they collected canopy surface temperature data using thermal infrared sensors. The team also measured microclimatic data in the orchard.  

Close up of an apple on a tree

Neutron probes were problematic, as they did not allow collection of data in real time.

Osroosh comments, “The accuracy of this approach greatly depends on the accuracy of reference soil moisture measurement methods.  To establish a relationship between CWSI and soil water, we needed to measure soil water content in the root zone precisely. We used a neutron probe, which provides enough precision and volume of influence to meet our requirements.  However, it was a labor and time intensive method which did not allow for real-time measurements, posing a serious limitation.”

Next week: Learn the results of Dr. Osroosh’s experiments, the future of this research, and about other researchers who are trying to achieve similar goals.

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Do Soil Microbes Influence Plant Response to Heat Waves? (Part II)

Rachel Rubin, PhD candidate at Northern Arizona University and her team at Northern Arizona University are investigating the role soil microbes play in plant response to heat waves, including associated impacts to microbial-available and plant-available water (see part 1). Because heat waves threaten plant productivity, they present a growing challenge for agriculture, rangeland management, and restoration. Below are the results of Rachel’s experiments, some of the challenges the team faced, and the future of this research.

A herd of cows grazing in a pasture

Heat waves present a growing challenge for agriculture, rangeland management, and restoration.

Challenges

Rachel says the experiment was not without its difficulties. After devoting weeks towards custom wiring the electrical array, the team had to splice heat-resistant romex wire leading from the lamps to the dimmer switches, because the wires inside the lamp fixtures kept melting. Also, automation was not possible with this system. She explains, “We were out there multiple times a day, checking the treatment, making sure the lamps were still on, and repairing lamps with our multi-tools. We used an infrared camera and an infrared thermometer in the field, so we could constantly see how the heating footprint was being applied to keep it consistent across all the plots.”

Arizona Fescue plant

Arizona Fescue (image: wickipedia.com)

Some Grass was Heat Resistant

Rachel says her biggest finding was that all of the C4 grasses survived the field heat wave, whereas only a third of the Arizona Fescue plants survived. She adds that the initially strong inoculum effects in the greenhouse diminished after outplanting, with no differences between intact, heat-primed inoculum or sterilized inoculum for either plant species in the field. “It may be related to inoculum fatigue,” she explains, “the microbes in the intact treatment may have become exhausted by the time the plants were placed in the field, or maybe they became replaced, consumed, or outcompeted by other microbes within the field site”. Rachel emphasizes that it’s important to conduct more field experiments on plant-microbe interactions. She says, “Field experiments can be more difficult than greenhouse studies, because less is under our control, but we need to embrace this complexity. In practice, inoculants will have to contend with whatever is already present in the field. It’s an exciting time to be in microbial ecology because we are just starting to address how microbes influence each other in real soil communities.”

Grass going to seed in an open-air field

Diminished effects may be related to inoculum fatigue.

What’s In Store?

Now that the team has collected data from the greenhouse and from the heat wave itself, they have started looking at mycorrhizal colonization of plant roots, as well as sequencing of bacterial and archaeal communities from the greenhouse study. Rachel says, “It’s quite an endeavor to link ‘ruler science’ plant restoration to bacterial communities at the cellular level. I’m curious to see if heat waves simply reduce all taxa equally or if there is a re-sorting of the community, favoring genera or species that are really good at handling harsh conditions.”

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Do Soil Microbes Influence Plant Response to Heat Waves?

Rachel Rubin, PhD candidate at Northern Arizona University, is interested in the intersection of extreme climate events and disturbance, which together have a much greater impact on plant communities. She and her team at Northern Arizona University are investigating the role soil microbes play in plant response to heat waves, including associated impacts to microbial-available and plant-available water.

Wheat with sun shining through it

Plants have a tight co-evolutionary history with soil microbes. It has been said that there is no microbe-free plant on earth.

Because heat waves threaten plant productivity, they present a growing challenge for agriculture, rangeland management, and restoration.

Can Soil Microbes Increase Heat Resistance?

Many plants maintain mutualistic associations with a diverse microbiome found within the rhizosphere, the region of soil that directly surrounds plant roots. These “plant growth-promoting rhizobacteria” and arbuscular mycorrhizal fungi provision limiting resources including water, phosphorus and nitrogen in exchange for photosynthetically derived sugars. However, we understand very little about whether extreme events can disrupt these interactions.

Tubes of layered dirt

Fig. 1. Fine roots exploring the inoculum that was added as a band between layers of potting mixture.

Rachel and her team exposed rhizosphere communities to heat stress and evaluated the performance of native grasses both in the greenhouse, and transplanted under an artificial heat wave. They hypothesized that locally-sourced inoculum (a sample of local soil containing the right microbes) or even heat-primed inoculum would help alleviate water stress and improve survival of native grasses.

The Experiments

Rubin started in the greenhouse by planting Blue Grama (Bouteloua gracilis, C4 grass) and Arizona Fescue (Festuca arizonica, C3 grass) and assessed their responsiveness to locally collected soil inoculum that had either been left intact, pre-heated or sterilized (Fig. 1). Rubin says, “We expected that our plants would benefit the most from having intact soil microbe communities. But, we were surprised to find very large differences between plant species. Blue Grama performed the best with intact inoculum, whereas Arizona Fescue performed better with pre-heated or sterilized soil”. This could mean that Blue Grama is more dependent on its microbiome, whereas Arizona Fescue engineers a rhizosphere that contains more parasitic microbes rather than mutualistic microbes. Rachel says that understanding this relationship is important for tailoring plant restoration projects to local conditions. Plants that exhibit high levels of mutualisms with their rhizosphere might require an extra inoculum “boost” in order to successfully establish in highly degraded soil, whereas we should not bother to inoculate plants that tend to harbor parasites within their rhizosphere.

Research plot using infrared sensors and METER soil water content and soil water potential sensors

Fig. 2. A heated plot in the foreground connected to infrared lamps, water content and matric potential sensors, and EM50 data loggers.

After the team studied these responses, they planted the grasses into a degraded section of a grassland and installed an array of 1000-Watt ceramic infrared lamps mounted on steel frames (Fig. 2) to address whether inoculation influenced plant performance and survival. With help from a savvy undergraduate electrical engineering major (Rebecca Valencia), Rubin simulated a two-week heat wave while monitoring soil temperature and moisture using water content and water potential sensors.  She also measured plant performance (height, leaf number and chlorophyll content) before, during, and after the event. Control plots had aluminum “dummy lamps” to account for shading.

An infrared photo of the expirement

An infrared photo, which is how Rachel determined that the heating footprint was evenly distributed on all the plants. The scale bar on the right is in degrees C.

Data obtained from soil sensors helped Rachel to measure heating treatment effects as well as rule out a potential cause for plant mortality: soil moisture. “Soil temperature was on average 10 degrees hotter in heated plots than control plots, but matric potential and soil water content were completely unaffected by heating. This tells us that the grasses died from reasons other than water stress– perhaps a top-kill effect.” Although growing concern over heat waves in agriculture is centered around accompanying droughts, this experiment demonstrates that heating can produce negative effects on some species even when water is in plentiful supply.

Next week:  Learn the results of Rachel’s experiments, some of the challenges the team faced, and the future of this research.

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A New Method for Preventing Snow Mold In Winter Wheat

Each year in early spring, dryland wheat farmers battle for their crop’s survival.  As temperatures climb to 0 degrees C, the dark, wet microclimate underneath the snow begins to propagate snow mold.  

Wheat spikes in a green wheat field

Wheat spikes in a wheat field.

Soil scientist, Dr. Colin Campbell says, “Soil under a blanket of snow can warm as spring temperatures rise, despite their icy covering. Temperatures above freezing and the water from snowmelt are a perfect environment for mold to grow.“

When faced with these weather conditions, wheat growers know they have only a couple of weeks to remove the snow, or large sections of their crop will die off. Melting the snow artificially can be an expensive process, but one southern Idaho wheat grower has found a unique solution that could save both money and the environment.

Fresh fluffy snow

Temperatures above freezing and the water from snowmelt are a perfect environment for mold to grow.

The Old Method  

Traditionally, wheat growers have spread fly ash (ash from coal) on the spring snow to try and speed the melting process.  The black fly ash creates a warmer microclimate by absorbing more solar radiation rather than reflecting it.  To demonstrate its effectiveness, the USDA performed studies using fly ash to speed snow melt, with positive results. However, growers say the challenge is using the method in a way that is economical on dryland wheat where the profit margin is narrow.  Bryce Campbell, a dryland wheat farmer near Burley, ID, says, “Some people use fly ash to get in the field faster or to get the water flowing into the soil, but our primary goal is to prevent snow mold from killing the winter wheat.  If that happens, we have to replant the crop to a spring crop which yields a lot less.  Our goal is to try and keep our crop alive.”  

Field with loose top soil and extensive edging

During heavy rain events, topsoil washed down to the edges of the field, collecting in dikes Campbell constructed.

An Inexpensive New Method

Campbell has used fly ash in the past, but last year, he had a better idea.  He noticed that during heavy rain events, some of his topsoil washed down to the edges of the field, collecting in dikes he constructed and eventually becoming dried and powdery. He wondered if he could use that soil as an economical replacement for fly ash. In the fall, he collected some in a truck and left it to dry completely in the back of his shed; then this season, he spread it over the spring snow. Seeing the results, he decided it was worth the effort, both economically and environmentally.  Campbell estimated the fly ash melt to be approximately 30% faster than the powdered soil because of its darker color, but the soil was free, which made a difference in his bottom line.

wheat crop

If snow mold kills the wheat crop, growers have to replant the crop to a spring crop which yields less.

He adds, “Some of the wheat farmers down the road are using a finely ground coal dust product to melt their snow. It’s a great product, and it works really well for melting snow, but their cost is about $20/acre.  When you spread that on a thousand acres, that’s $20,000.  I can put my soil on a thousand acres, and my only cost is two hours of gathering up the soil plus a day and a half in the tractor for application.”

Next week:  Find out which techniques Campbell uses to save time and money redistributing his displaced soil.

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Which Factors Make Rain Gardens More Effective? (Part 2)

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.

Picture of yellow flowers

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).

Researcher holding dirt in cupped hand

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 freshwater lake

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.”

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Which Factors Make Rain Gardens More Effective?

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.

Rain Garden aerial view

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 diagram

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.”

Garden in bloom in the rain

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.

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Improving Drought Tolerance in Soybean

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.

Seedlings sprouting

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.

Beans growing on a stalk

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.”

Soybeans

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.

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