a comprehensive guide to lysimetry....
A lysimeter is a device or apparatus that measures water movement in the soil, edaphic or vadose zone.
The definition of lysimeter is muddied and has come to mean many different things. Today, the word lysimeter cannot be used in isolation and is usually a compound noun. As an analogy, there are many types of shoes, so they are often called “tennis shoes” or “dancing shoes”. Similarly, there are many different types of lysimeters including “weighing lysimeter”, “wick lysimeter”, “percolation lysimeter”, and more. It is important to distinguish between different lysimeters because, just like shoes, they are utilized for different types of applications.
As lysimeters measure water movement, or percolation, through the soil they have been used for a variety of applications. Lysimeters are commonly used for research and monitoring including evapotranspiration, nutrient monitoring and leachates, heavy metals and toxicity, pesticides, trace elements, water-use management, and quantifying or modelling the hydrologic, or various chemical, cycles. Lysimeters are used in several industries including mining, landfills, phytocaps, phytoremediation, ecosystem restoration, agriculture, horticulture, forestry, environmental protection, and much more.
what are the different types of lysimeters?
Here is a list of the more common types of lysimeters currently used by scientists, hydrologists and engineers.
– weighing lysimeter
– wick lysimeter
– drainage lysimeter
– percolation lysimeter
– sampling lysimeter
– pore water lysimeter
– rhizon lysimeter
– suction lysimeter
– pan lysimeter
Some of these lysimeters are used interchangeably. For example, a sampling, pore water and suction lysimeter may refer to the same type of device.
A weighing lysimeter is essentially a soil-filled container sitting on a weigh-scale or balance. The weigh-scale measures the total water inputs and outputs simply by the change in weight over time.
In practice, a weighing lysimeter is a highly sophisticated and technologically advanced apparatus. Although a weighing lysimeter can be as simple and has small as a pot on a scale, they can be extremely large and heavy sitting on extremely precise electronic balance to quantify the smallest variations in water content. A weighing lysimeter may also be instrumented with a range of additional sensors including sap flow, soil moisture, temperature, and more.
Weighing lysimeters are ideal for studies on soil evaporation, plant transpiration or evapotranspiration. For example, Freebairn et al (1986) demonstrated the use of small lysimeters for soil evaporation studies. Pearsall et al (2014) assessed the accuracy of sap flow sensors, and measured transpiration, on field weighing lysimeters in California, USA. Akhavan et al (2018) used lysimeters to assess the performance of various evapotranspiration models.
Weighing lysimeters are commercially available from METER Group (formally UMS) who are the world-leading manufacturer of large scale lysimeters. The METER Group Smart Field Lysimeter provides high resolution data on soil water flux, movement and percolation.
wick and drainage lysimeters
Drainage lysimeters are extremely important for many applications especially environmental pollution monitoring, nutrients and leachates. They are widely used in agriculture and horticulture to determine how much salts (salinity), nutrients, pesticides, or other contaminants, are leaving the root zone and potentially entering groundwater or waterways. Similarly, they are widely used in mining, landfill and other heavy industrial applications to monitor heavy metals and toxicity.
The Wick Lysimeter, also known as a Gee Lysimeter or G3 Drain Gauge, is the leading standard drainage lysimeter available for researchers and industry. The G3 manual provides the following explanation on how the wick lysimeter operates:
“Install the Drain Gauge G3 below the root zone. Water infiltrates down through the soil and enters the divergence control tube (DCT). It then flows down through a fiberglass wick into a reservoir. The water is stored in a measurement reservoir until a sample can be removed. The depth of the water in the reservoir or volume of the removed sample can be used to calculate the total drainage since the last date the reservoir was emptied. Chemical analysis can also be performed on the sample. With the drainage rate and chemical concentration in the drainage water, you can calculate the chemical flux through the soil.”
A percolation lysimeter is another type of drainage lysimeter that measures water movement, or percolation, through the soil profile. Whereas the wick or drainage lysimeters have a collection reservoir, the percolation lysimeter consists of a series of soil water sensors (also known as soil moisture or soil humidity sensors) installed down the soil profile. The change in water content, measured by the sensors, can be used to estimate flux, storage and drainage.
A percolation lysimeter can have as many or as few soil moisture sensors as required. The installation and configuration will depend on the application and purpose of the project. A simple design may consist of two sensors: one installed near the soil surface and the other beneath the root zone. Typically, many sensors are installed at multiple depths within the soil profile.
Percolation lysimeters are commonly used in irrigation applications. For example, percolation lysimeters can quantify over-irrigation where water is draining through the soil profile, beneath the crop’s roots, and being wasted. Similarly, percolation lysimeters can determine under-irrigation where water is not reaching roots deep in the soil profile.
Percolation lysimeters are widely used in phytocaps or phytoremediation studies and projects. It is important that the integrity of phytocaps are maintained. Percolation lysimeters can test different phytocap designs and materials. Once installed, percolation lysimeters can determine if there has been a breach or failure in the phytocap by sending alerts and alarms to managers.
The TEROS range of soil water content sensors are ideal for percolation lysimeters. The TEROS sensors can measure soil water content, temperature and electrical conductivity (EC or salinity). The TEROS sensors can be connected to the ZL6 data logger where data can be accessed over the internet. Alternatively, the ES-SYS systems can provide alarms and alerts, as well as data logging and internet access capabilities. It is also possible to connect the TEROS sensors to IoT devices such as LoRaWAN or NB-IoT or Wi-Fi enabled devices.
Alternatively, profile probes are used as a type or percolation lysimeter.
sampling, pore water, rhizon and suction lysimeters
Sampling lysimeters are devices that collect soil solution – that is they collect samples of water. The solution is then analysed in the laboratory, or with gas chromatography or photometers, for parameters such as salts, nutrients, pesticides, heavy metals, toxins, dissolved gases, and more.
Sampling lysimeters are also known as pore water samplers because they can only collect, or sample, unbound, or free moving, water in the pores of soil.
Sampling lysimeters operate on the principle of suction or tension. A porous device, such as a ceramic or a specially designed porous fabric, with pore diameters approximately 0.12 – 0.18 micron diameter, is installed into the soil at the required depth of measurement.
A tube, which is connected to the porous media, then runs to the soil surface. A tension, or suction, is then placed on the tube and this enables solution to move from the soil pores through the porous media and into the lysimeter where it is stored in a syringe or reservoir. The solution sample is then periodically collected for subsequent analysis. Sampling lysimeters are only suitable in saturated, or near saturated, soil conditions.
Pore water samplers are widely used in environmental research and monitoring applications such as quantifying nitrates and leachates in the soil profile, heavy metals at mine sites, or nutrient and salinity dynamics in soil columns and pots in the laboratory or glasshouse. Research by environmental scientists at Macquarie University, Sydney, Australia, used rhizon sampling lysimeters to quantify the effects of earthworms on leachability of lead minerals in soil.
Sampling, pore water, rhizon and suction lysimeters are available from Edaphic Scientific including models for field sampling or others for small pots in a glasshouse. Also, a rhizon box, where the roots of plants can be examined closely, is available.
The pan lysimeter is basically a bucket, or collection reservoir, that is installed in the ground. Water moves through the soil profile and into the reservoir where it is later measured for various parameters such as electrical conductivity (EC), salinity, nutrients, pesticides, or more.
However, pan lysimeters are an inaccurate method and have been superseded by the wick lysimeter (see above). Pan lysimeters are inaccurate because it creates a zero-tension boundary layer within the soil. In unsaturated soils, water is held under tension where water flows from areas of low to high tension. Therefore, water cannot physically flow into the pan lysimeter and it cannot be accurately quantified. The wick lysimeter overcomes this problem and should be used instead of the pan lysimeter.
a video on lysimetry basics