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Posts from the ‘Hydrology’ Category

New Infiltrometer Helps City of Pittsburgh Limit Traditional Stormwater Infrastructure

Though difficult and expensive to repair, the brick-paved streets that still exist in some Pittsburgh, Pennsylvania neighborhoods are worth saving. Dellrose Street, an aging, 900 ft. long, brick road, was in need of repair, but the city of Pittsburgh wanted to limit traditional stormwater infrastructure, such as pipes and catch basins.

Infiltrometer

Dellrose Street permeable paver system

To save the aesthetics of the neighborhood, they hired ms consultants, inc. to design a permeable paver solution for controlling stormwater runoff volumes and peak runoff rates that would traditionally be routed off-site via storm sewers.  Jason Borne, a stormwater engineer for ms consultants who worked on the project says, “What we try to do is understand the in situ infiltration potential of the subsoils to determine the most efficient natural processes for attenuating flows; either through infiltrating excess water volume back into the soil or through slow-release off-site.”  He used the SATURO Infiltrometer to get an idea of how urban fill material would infiltrate water.

Green Infrastructure Aids Natural Infiltration

As Borne and his team investigated what they could do to slow down the runoff, they decided permeable pavers would be a viable solution.  He says, “There’s not much you can do once you put in a hardened surface like a pavement.  Traditional pavement surfaces accelerate the runoff which requires catch basins and large diameter pipes to carry the runoff off-site. We were interested in investigating what some of the urban subsoils, or urban fill would allow us to do from an infiltration perspective.  As we started looking at some of these subsoils, we decided a permeable paver system would be ideal for this particular street.”

Infiltrometer

Subsurface flow barrier installation

Infiltrometers Determine Natural Infiltration Potential

Once the water flowed into the aggregate, the team began to figure out ways to slow it down and promote infiltration.  Borne says, “Basically we came up with a tiered subsurface flow barrier system.  We had about 60 concrete flow barriers across the subgrade within the aggregate base of the road. We needed so many because the longitudinal slope of the road was fairly significant. Behind each of these barriers we stored a portion of the stormwater that would typically run off the site.  The ideal was to remove the stored water through infiltration–to get it down to the subgrade and away, so we used infiltrometers to help us establish where we could maximize infiltration and where we might need to rely on other management methods.”

A Need for Faster Test Times Inspires a Comparison

Borne says that USDA soil surveys are too generalized for green infrastructure applications in urban areas and only give crude approximations of the soil hydraulic conductivity. Understanding the best way to promote natural infiltration requires a very specific infiltration rate or hydraulic conductivity for the location of interest.  He says, “The goal is to excavate down to the desired elevation before construction and find out, through some kind of device what the infiltration potential of the subsoil is.  Typically we use a double ring infiltrometer, but it’s a very manual device. We’re constantly refilling water, and it requires us to be on-site and attentive to what’s happening.  We can’t really multitask, especially in areas of decently infiltrating soils where the device might run out of water in 30 minutes or less. So, in the interest of saving water and time, we used the automated SATURO infiltrometer and the manual double ring infiltrometer concurrently for comparison purposes.”

Next week:  Find out how the two infiltrometers compared.

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German Researchers Directly Measure Climate Change Effects Using Lysimeter Network (part 2)

In Germany, scientists are measuring the effects of tomorrow’s climate change with a vast network of 144 large lysimeters (see part 1).  This week, read about the intense precision required to move the soil-filled lysimeters, how problems are prevented, and how the data is used by scientists worldwide.

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Moving the lysimeters

Moving the Lysimeters is not Easy

As noted previously, one TERENO lysimeter weighs between 2.5 and 3.5 tons depending on the soil and the water saturation, so the problem of  transporting it without compacting the soil or causing cracks in the soil column caused Georg many sleepless nights.   He explains, “We found a truck with an air venting system, which could prevent vibrations in a wide range. We made a wooden support structure, bought 100 car springs, and loaded the lysimeter on this frame.  After some careful preparation and design adjustments, I told the truck driver, ‘take care, I’m recording the entire drive with my acceleration sensor and data logger so I can see if you are driving faster than I allow.”  Each lysimeter soil surface level was marked to check if the lysimeter was rendered useless due to transport, and the truck was not allowed to go over a railway or a bump in the road faster than 2 km per hour to avoid the consequences of compaction and cracking.

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Tensiometers and soil moisture sensors monitor the hydraulic conditions inside the lysimeters.

Preventing Problems

Understanding the water potential inside the intact lysimeter core is not trivial. Georg and his team use maintenance-free tensiometers, which overcome the typical problem of cavitation in dry conditions as they don’t need to be refilled. Still, this parameter is so critical they installed 3 of them and took the median, which can be weighed in case one of the sensors is not working. Georg says, “There is a robust algorithm behind measuring the true field situation with tensiometers.”

What Happens With the Data?

Georg hopes that many researchers will take advantage of the TERENO lysimeter network data (about 4,000 parameters stored near-continuously on a web server). He says, “Researchers have free access to the data and can publish it. It’s wonderful because it’s not only the biggest project of its kind, each site is well-maintained, and all measurements are made with the same equipment, so you can compare all the data.”  (Contact Dr. Thomas Puetz for access). Right now, over 400 researchers are working with those data, which has been used in over 200 papers.

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Lysimeter plant with CO2 fumigation facility in Austria.

What’s the Future?

Georg thinks 40,000 data points arriving every minute will give scientists plenty of information to work on for years to come. Each year, more TERENO standard lysimeters are installed to enlarge the database. The ones in TERENO have a 1 m2 surface area, which is fine for smaller plants like wheat or grass, but is not a good dimension for big plants like trees and shrubs. Georg points out that you have to take into account effort versus good data. Larger lysimeters present exponentially larger challenges. He admits that, “With the TERENO project, they had to make a compromise. All the lysimeters are cut at a depth of 1.5 m. If there is a mistake, it is the same with all the lysimeters, so we can compare on climate change effects.”  He adds, “After six years, we now have a standard TERENO lysimeter design installed over 200 times around the world, where data can be compared through a database, enhancing our understanding of water in an era of climate change.”

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German Researchers Directly Measure Climate Change Effects Using TERENO Lysimeters

In Germany, scientists are measuring the effects of tomorrow’s climate change with a vast network of 144 large lysimeters.

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The goal of these lysimeters is to measure energy balance, water flux and nutrition transport, emission of greenhouse gases, biodiversity, and solute leaching into the groundwater.

In 2008, the Karlsruhe Institute of Technology began to develop a climate feedback monitoring strategy at the Ammer catchment in Southern Bavaria. In 2009, the Research Centre Juelich Institute of Agrosphere, in partnership with the Helmholtz-Network TERENO (Terrestrial Environmental Observatories) began conducting experiments in an expanded approach.  

Throughout Germany, they set up a network of 144 large lysimeters with soil columns from various climatic conditions at sites where climate change may have the largest impact.  In order to directly observe the effects of simulated climate change, soil columns were taken from higher altitudes with lower temperatures to sites at a lower altitude with higher temperatures and vice versa. Extreme events such as heavy rain or intense drought were also experimentally simulated.

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Lysimeter locations in Germany

Georg von Unold, whose company (formerly UMS, now METER) built and installed the lysimeters comments on why the project is so important. “From a scientific perspective, we accept changes for whatever reason they may happen, but it is our responsibility to carefully monitor and predict how these changes cause floods, droughts, and disease. We need to be prepared to react if and before they affect us.”

How Big Are the Lysimeters?

Georg says that each lysimeter holds approximately 3,000 kilograms of soil and has to be moved under compaction control with specialized truck techniques.  He adds,The goal of these lysimeters is to measure energy balance, water flux and nutrition transport, emission of greenhouse gases, biodiversity, and solute leaching into the groundwater. Researchers measure the conditions of water balance in the natural soil surrounding the lysimeters, and then apply those same conditions inside the lysimeters with suction ceramic cups that lay across the bottom of the lysimeter.  These cups both inject and take out water to mimic natural or artificial conditions.”

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Researchers use water content sensors and tensiometers to monitor hydraulic conditions inside the lysimeters.

Researchers monitor the new climate situation with microenvironment monitors and count the various grass species to see which types become dominant and which might disappear. They use water content sensors and tensiometers to monitor hydraulic conditions inside the lysimeters. The systems also use a newly-designed system to inject CO2 into the atmosphere around the plants and soil to study increased carbon effects.  Georg says, “We developed, in cooperation with the HBLFA Raumberg Gumpenstein, a new, fast-responding CO2 enrichment system to study CO2 from plants and soil respiration. We analyze gases like CO2, oxygen, and methane. The chambers are rotated from one lysimeter to another, working 24 hours, 7 days a week.  Each lysimeter is exposed only for a few minutes so as not to change the natural environment.”

Next week:  Read about the intense precision required to move the soil-filled lysimeters, how problems are prevented, and how the data is used by scientists worldwide.

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Top Five Blog Posts in 2016

In case you missed them the first time around, here are the most popular Environmental Biophysics.org blog posts in 2016.

Lysimeters Determine if Human Waste Composting can be More Efficient

Top five blog posts Environmental biophysics

In Haiti, untreated human waste contaminating urban areas and water sources has led to widespread waterborne illness.  Sustainable Organic Integrated Livelihoods (SOIL) has been working to turn human waste into a resource for nutrient management by turning solid waste into compost.  Read more

Estimating Relative Humidity in Soil: How to Stop Doing it Wrong

Top five blog posts Environmental biophysics

Estimating the relative humidity in soil?  Most people do it wrong…every time.  Dr. Gaylon S. Campbell shares a lesson on how to correctly estimate soil relative humidity  from his new book, Soil Physics with Python, which he recently co-authored with Dr. Marco Bittelli.  Read more.

How Many Soil Moisture Sensors Do You Need?

Top five blog posts Environmental biophysics

“How many soil moisture sensors do I need?” is a question that we get from time to time. Fortunately, this is a topic that has received substantial attention by the research community over the past several years. So, we decided to consult the recent literature for insights. Here is what we learned.

Data loggers: To Bury, or Not To Bury

Top five blog posts Environmental biophysics

Globally, the number one reason for data loggers to fail is flooding. Yet, scientists continue to try to find ways to bury their data loggers to avoid constantly removing them for cultivation, spraying, and harvest.  Chris Chambers, head of Sales and Support at Decagon Devices always advises against it. Read more

Founders of Environmental Biophysics:  Champ Tanner

Top five blog posts Environmental biophysics

Image: http://soils.wisc.edu/people/history/champ-tanner/

We interviewed Gaylon Campbell, Ph.D. about his association with one of the founders of environmental biophysics, Champ Tanner.  Read more

And our three most popular blogs of all time:

Do the Standards for Field Capacity and Permanent Wilting Point Need to Be Reexamined?

Top five blog posts Environmental biophysics

We asked scientist, Dr. Gaylon S. Campbell, which scientific idea he thinks impedes progress.  Here’s what he had to say about the standards for field capacity and permanent wilting point.  Read more

Environmental Biophysics Lectures

Top five blog posts Environmental biophysics

During a recent semester at Washington State University a film crew recorded all of the lectures given in the Environmental Biophysics course. The videos from each Environmental Biophysics lecture are posted here for your viewing and educational pleasure.  Read more

Soil Moisture Sensors In a Tree?

Top five blog posts Environmental biophysics

Soil moisture sensors belong in the soil. Unless, of course you are feeling creative, curious, or bored. Then maybe the crazy idea strikes you that if soil moisture sensors measure water content in the soil, why couldn’t they be used to measure water content in a tree?  Read more

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Water Potential: The Science Behind the Measurement (Part 2)

In the second part of this month’s water potential  series (see part 1), we discuss the separate components of a water potential measurementThe total water potential is the sum of four components: matric potential, osmotic potential, gravitational potential, and pressure potential.  Below is a description of each component.

Matric Potential

Matric potential arises because water is attracted to most surfaces through hydrogen bonding and van der Waals forces. This water droplet is pure but no longer free. The matric forces that bind it to the plastic have lowered its potential and you would have to use some energy to remove it from the surface and take it to a pool of pure, free water.

Soil is made up of small particles, providing lots of surfaces that will bind water. This binding is highly dependent on soil type. For example, sandy soil has large particles which provide less surface binding sites, while a silt loam has smaller particles and more surface binding sites.

The following figure showing moisture release curves for three different types of soil demonstrates the effect of surface area. Sand containing 10% water has a high matric potential, and the water is readily available to organisms and plants. Silt loam containing 10% water will have a much lower matric potential, and the water will be significantly less available.

Matric potential is always negative or zero, and is the most significant component of soil water potential in unsaturated conditions.

matric potential

Osmotic Potential

Osmotic potential describes the dilution and binding of water by solutes that are dissolved in the water. This potential is also always negative.

Osmotic potential only affects the system if there is a semi-permeable barrier that blocks the passage of solutes. This is actually quite common in nature. For example, plant roots allow water to pass but block most solutes. Cell membranes also form a semi-permeable barrier. A less-obvious example is the air-water interface, where water can pass into air in the vapor phase, but salts are left behind.

You can calculate osmotic potential from the following equation if you know the concentration of solute in the water.

Ψ_0=CΦVRT    

 

Where C is the concentration of solute (mol/kg), ɸ is the osmotic coefficient (-0.9 to 1 for most solutes), v is the number of ions per mol (NaCl = 2, CaCl2 = 3, sucrose = 1), R is the gas constant, and T is the Kelvin temperature.

Osmotic potential is always negative or zero, and is significant in plants and some salt-affected soils.

Gravitational Potential

Gravitational potential arises because of water’s location in a gravitational field. It can be positive or negative depending on where you are in relation to the specified reference of pure, free water at the soil surface. Gravitational potential is then:

Ψ_G=GH

 

Where G is the gravitational constant (9.8 m s-2) and H is the vertical distance from the reference height to the soil surface (the specified height).

matric potential

You can feel positive pressure as you swim down into a lake or pool.

Pressure Potential

Pressure potential is a hydrostatic or pneumatic pressure being applied to or pulled on the water.  It is a more macroscopic effect acting throughout a larger region of the system.

There are several examples of positive pressure potential in the natural environment.

For example, there is a positive pressure present below the surface of any groundwater. You can feel this pressure yourself as you swim down into a lake or pool. Similarly, a pressure head or positive pressure potential develops as you move below the water table.

Turgor pressure in plants and blood pressure in animals are two more examples of positive pressure potential.

Pressure potential can be calculated from:

Ψ_P=P/Ρ_W

 

Where P is the pressure (Pa) and P_W is the density of water.

Though pressure potential is usually positive, there are important cases where it is not. One is found in plants, where a negative pressure potential in the xylem draws water from the soil up through the roots and into the leaves.

Next Week: Learn the different methods for measuring water potential and their strengths and limitations.

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Secrets of Water Potential: Learn the Science Behind the Measurement

This month in a 3 part series, we will explore water potential –the science behind it and how to measure it effectively.

water potential

To understand water potential, compare the water in a soil sample to water in a drinking glass.

Definition of Water Potential

Water potential is the energy required, per quantity of water, to transport an infinitesimal quantity of water from the sample to a reference pool of pure free water. To understand what that means, compare the water in a soil sample to water in a drinking glass. The water in the glass is relatively free and available; the water in the soil is bound to surfaces, diluted by solutes, and under pressure or tension. In fact, the soil water has a different energy state from “free” water. The free water can be accessed without exerting any energy. The soil water can only be extracted by expending energy. Water potential expresses how much energy you would need to expend to pull that water out of the soil sample.

Water potential is a differential property. For the measurement to have meaning, a reference must be specified. The reference typically specified is pure, free water at the soil surface. The water potential of this reference is zero. Water potential in the environment is almost always less than zero, because you have to add energy to get the water out.

water potential

You can’t tell by measuring heat content whether or not heat will be transferred to another object if the two touch each other.

Extensive vs. Intensive Variables

Water movement in the environment is really a physics problem, and to understand it, we have to distinguish between intensive and extensive variables. The extensive variable describes the extent or amount of matter or energy. The intensive variable describes the intensity or quality of matter or energy. For example, the thermal state of a substance can be described in terms of both heat content and temperature.

The two variables are related, but they are not the same. Heat content depends on mass, specific heat, and temperature. You can’t tell by measuring heat content whether or not heat will be transferred to another object if the two touch each other. So you also don’t know if the object is hot or cold, or whether it will be safe to touch.

These questions are much easier to answer if you know the intensive variable–temperature. In fact, though it can be important to measure both intensive and extensive variables, often the intensive variable gives you more useful information.

In terms of water, the extensive variable is water content, and it tells you the extent, or amount, of water in plant tissue or soil. The intensive variable is water potential, and it describes the intensity or quality of water in plant tissue or soil.  Water content can only tell you how much water you have. If you want to know how fast it can move, you need to measure hydraulic conductivity. If you want to know whether it will move and where it’s going to go, you need water potential.

water potential

If you want to know whether water will move and where it’s going to go, you need water potential.

Two Key Water Potential Questions:

1. Where will water move? Water will always flow from high potential to low potential. This is the second law of thermodynamics—energy flows along the gradient of the intensive variable.

2. What is the availability of water to plants? Liquid water moves from soil to and through roots, through the xylem of plants, to the leaves, and eventually evaporates in the substomatal cavities of the leaf. The driving force for this flow is a water potential gradient. In order for water to flow, therefore, the leaf water potential must be lower than the soil water potential.

Next week learn about the four components of water potential– osmotic potential, gravitational potential, matric potential, and pressure potential.

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Soil Sensors Help Thousand-Year-Old Levees Protect Residents of the Secchia River Valley

In Italy, on January of 2014, one of the Secchia river levees failed, causing millions of dollars in flood damage and two fatalities. Concerned with preventing similar disasters, scientists and geotechnical engineers are using soil sensors to investigate solutions in a project called, INFRASAFE (Intelligent monitoring for safe infrastructures) funded by the Emilia Romagna Region (Italy) on European Funds.  

Secchia river in Italy.

Secchia river in Italy (Image: visitsassuolo.it)

Professor Alberto Lamberti, Professor Guido Gottardi, Department of Civil, Chemical, Environmental, and Materials Engineering, University of Bologna, along with Prof. Marco Bittelli, University of Bologna professor of Soil and Environmental Physics, installed soil sensors along some transects of the Secchia river to monitor water potential and piezometric pressure.  They want to study properties of the compacted levee “soil”, during intense flooding.  Bittelli comments, “Rainfall patterns are changing due to climate change, and we are seeing more intense floods. There is a concern about monitoring levees so that we can, through studying the process, eventually create a warning system.”  

soil sensors

Trench for burying sensor cables.

What Are The Levees Made Of?

Amazingly, some of these levees are very old, built at the beginning of the second millennium to protect the Secchia valley population from floods. “These rudimentary barrages were the starting point of the huge undertakings, aiming at the regulation and stabilization of the river, which were gradually developed and expanded in the following centuries…building up a continuous chain all along the river.” (Marchii et. al., 1995)

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Vegetation in the Secchia River flood plain.

Unlike natural soil with horizons, the soil that makes up the levees is made up of extremely compact clay and other materials, which will pose challenges to the research team in terms of sensor installation.  The team will use soil sensors to determine when the compacted material that makes up the levees gets so saturated it becomes weak.  Bittelli says, “We are looking at the mechanical properties of the levees, but mechanical properties are strongly dependent on hydraulic properties, particularly soil water potential (or soil suction).  A change in water potential changes the mechanical properties and weakens the structure.”  This can happen either when a soil dries below an optimal limit or wets above it; the result is a weakened barrier that can fail under load.

soil sensors

Here the team uses an installation tool to install water content sensors.

Soil Sensors Present Installation Challenges

To solve the installation problems, the team will use a specialized installation tool to insert their water content sensors.  Bittelli says, “Our main challenge is to install sensors deep into the levees without disturbing the soil too much.  It’s very important to have this tool because clearly we cannot dig out a levee; we might be the instigator of a flood. So it was necessary for us to be able to install the sensors in a relatively small borehole.”  The researchers will install the sensors farther down than the current tool allows, so they are modifying it to go down to eight or ten meters.  Bittelli explains, “We used a prototype installation tool which is two meters long. We modified it in the shop and extended it to six meters to be able to install water content sensors at further depths.”

Another challenge facing the research team is how to install water potential sensors without disturbing the levee.  Marco explains, “We placed an MPS-6 into a cylinder of local soil prepared in the lab. A sort of a muffin made of soil with an MPS-6 inside. Then we lowered the cylinder into the borehole, installed the sensor inside, and then slid it down into the hole.  Our goal is to try and keep the structure of the soil intact. Since the cylinder is made of the same local soil, and it is in good contact with the borehole walls, hydraulic continuity will be established.”

soil sensors

Researchers placed a MPS-6 into a cylinder of local soil prepared in the lab.

Unlike installing water content sensors, matric potential sensors don’t need to be installed in undisturbed soil but only require good contact between the sensor and the bulk soil so liquid water can easily equilibrate between the two. The researchers are also contemplating using a small camera with a light so they can see from above if the installation is successful.  

Find Out More

The researchers will collect data at two experimental stations, one on the Po river, and one on the Secchia River. So far, the first installation was successfully performed, and data are collected from the website. Bitteli says the first installation included water content, temperature, and electrical conductivity sensors, water potential sensors, and tensiometers connected to a wireless network that will transmit all the data to a central office for analysis.

You can read more about this project and how it’s progressing here.

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Soil Moisture: An Important Parameter in Weather Monitoring

CoCoRaHS and Weather Monitoring

Each time a rain, hail, or snow storm crosses over your area, volunteers are taking precipitation measurements that are then used to analyze situations ranging from water resource availability to severe storm warnings.  

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CoCoRaHS precipitation data is used by many high profile organizations.

CoCoRaHS (Community Collaborative Rain, Hail and Snow Network) is a non-profit community-based network of volunteers of all ages and backgrounds working together to measure and map precipitation (rain, hail and snow).  Their data is used by the National Weather Service, meteorologists, hydrologists, emergency managers, city utilities, USDA, engineers, farmers, and more.  The organization will soon add another layer to their weather-monitoring efforts:  soil moisture measurement.

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In 1997, a localized flooding event in Fort Collins, Colorado was not well-warned due to lack of high-density precipitation observation.

Why Soil Moisture?

CoCoRaHS originated as the brain child of Nolan Doesken, the state climatologist of Colorado,  in 1997 in response to a localized flooding event in Fort Collins, CO that was not well-warned due to lack of high-density precipitation observations.  Ten years ago the Colorado Climate Center began a partnership with the National Integrated Drought Information System to establish the first regional drought early warning system. This particular system would serve the Upper Colorado River Basin and eastern Colorado.

From the beginning, Nolan was thinking about soil moisture.  He says, “When we first started this project, we identified one weakness of the current climate monitoring systems as the inability to quantitatively assess soil moisture.  Soil moisture is critical as it affects both short term weather forecasts and long-term seasonal forecasts, which are important for drought early warning and avoiding the agricultural consequences of too much or too little soil moisture.”It wasn’t until years later in the drought of 2012, which developed rapidly in the mid and late spring across the intermountain west and central plains that Nolan began planning to use CoCoRaHS as a vehicle for improving the soil moisture aspect of drought early warning.

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The organization intends to measure soil moisture using the gravimetric method.

How Will Volunteers Measure Soil Moisture?

Historically, CoCoRaHS has had success using low-cost measurement tools, stressing training and education, and using an interactive web-site to provide the highest quality data, and soil moisture will be no different.  The organization intends to measure soil moisture using the gravimetric method, where the user will take samples using a soil ring, dry samples in their own oven, and measure sample weight with an electronic scale. Peter Goble, a research assistant at Colorado State, has developed the measurement protocols that volunteers will follow.  He says, “We have installed several different types of soil sensors and tried gravimetric techniques in a field next to the center, and our experience has helped us set up a protocol that gets observers as educated as they can be by the time they take their measurements. The coring device we use is something that came about through trial and error. We were trying to reconcile the fact that we really wanted deeper root zone measurements in order to satisfy drought early-warning-system users, and the need for an inexpensive set of standardized materials that we could send out to observers in a kit.”  Volunteers will take soil samples at each point in a grid pattern, both at the surface and at the 7-9 inch level near the root zone.

What will Happen to the Data?

Initially, while the program is in its test phase, the data will be put in a spreadsheet and shared. However, once CoCoRaHS has finished sending this protocol around the nation to a group of alpha testers, they’ll set up a website infrastructure enabling volunteers to enter their VWC data directly into the CoCoRaHS website.

The need for soil moisture measurement in weather monitoring will outweigh the volunteers’ ability to measure, but there is a solution.

The need for soil moisture measurement in weather monitoring will outweigh the volunteers’ ability to measure, but there is a solution.

Why the Gravimetric Method?

Nolan says the challenge of water content is that soil is highly variable across space.  And if you add issues like sensor performance, improper installation of sensors, problems with soil contact, changes in bulk density, and soil compaction, you end up with inconsistent data.  The gravimetric method will avoid inconsistencies in spatial measurements and ensure higher quality data.

An Overwhelming Task

Nolan says the need for soil moisture measurement in weather monitoring will outweigh the volunteers’ ability to measure, but there is a solution. “People who use soil moisture data in atmospheric applications need high resolution, gridded information in every square kilometer across the country, but it will happen through modeling.  The measurements we take of precipitation and soil moisture will help in the refinement of the weather modules the atmospheric scientists will use as input to their weather prediction models.”

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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.

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.”

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

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.”

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

Example of a typical monitoring station: Surface and sub-surface water elevation and EC monitoring wells, and soil moisture and EC at 30 and 60 cm depths. Sensors connected to 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.

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

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.

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

Some people blame the dams built in the 1970’s 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.”

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“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.

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“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.”

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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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