Design and Construction of an Experimental Setup to Enhance Mineral Weathering through the Activity of Soil Organisms

Enhanced weathering is a carbon dioxide removal technology that involves the reaction of silicate rock with carbon dioxide and water. Microbes and other soil biota can stimulate this weathering reaction, but the potential impact on enhanced weathering is yet unknown. Here we aim to unravel the impact of various soil biota on enhanced weathering.

One of the soil biota we're interested in is earthworm. Earthworms play a fundamental role in soil. They can increase weathering by respiration, ingestion of soil, production of mucus, or stimulation of microbial activity.

Here we are interested in testing if earthworms can enhance weathering in an artificial system primarily made of minerals. Accurately quantifying weathering rates and associated carbon dioxide capture is the biggest experimental challenge. Different indicators show different weathering rates and do not always scale with carbon dioxide capture.

In this experimental setup, we can measure multiple indicators. Our aim of the protocol is to understand the impacts of earthworms, bacteria, and fungi on weathering rates, while also studying the abiotic factors boosting it. However, the ultimate aim of the protocol is to find the optimal combination of biotic and abiotic factors to maximize carbon dioxide removal.

The main benefits relate to scale and level of control. We are now able to test a much larger number of combinations of soil biota and minerals, all under the same experimental conditions, and that allows us to pick up synergies, interactions that we would never have picked up in more conventional, smaller experimental designs. Our results will showcase the potential of soil biota to draw CO2 from the atmosphere, and if we can prove that, that would be a huge step in finding ways to help mitigate global warming.

To begin, set up the refrigerator and the frame holding the columns in the climate chamber. Lift the lid to open the fridge and move acrylic plate 4 forward. Take pipes of different lengths that have been previously cut to reach the jerrycans and insert them in acrylic plate four, according to their numbers.

Move the acrylic plate four backward. Take the clean funnels, insert them carefully into position in acrylic plate three, and connect them to the corresponding pipes as per their designated numbers. Then take high density polyethylene jerrycans inside the chamber.

Stack these jerrycans in the refrigerator in two layers according to the scheme shown here, and simultaneously connect the tubes to the jerrycans. After completing the refrigeration setup, close the fridge. To begin, construct the refrigerator setup for the leachate collection.

Take the PVC column to incubate rock powder and soil organisms. Also acquire metal rings to hold columns above the funnels. Position the rings a few centimeters from the bottom of the columns.

Acquire material to create a mesh system at the bottom of the columns to filter the leachate. Place the 20 micrometer mesh at the bottom of the column and add a one centimeter layer of plastic beads over this mesh. Next place a 10 micrometer mesh on top of the 20 micrometer mesh.

Secure the meshes in place using two cable ties. Tighten them firmly and remove excess ties by cutting their edges. The setup is now ready to be filled with the organo mineral mixture and inoculated with soil organisms.

To begin, construct the refrigeration for leachate collection and the mesh system at the bottom of the columns. Weigh 400 grams of minerals and 10 grams of organic materials in a bowl according to the desired treatment. Then calculate the water holding capacity using the equation shown here.

Adjust the water holding capacity to 80%based on the mineral type, grain size, and organic source. Mix all the components cautiously using a metal spoon and fill the columns with the thoroughly blended mixture. Position the filled columns in the climate chamber.

Then take the prepared microbial cultures. Using a pipette, inoculate the selected culture on the surface of the columns as per the desired treatment. Acquire earthworms as per the desired density and carefully place them on the surface of the columns as per the desired treatment.

Place the mesh on top of the columns to avoid earthworms escape once they are introduced and to columns without earthworms to maintain the same conditions. Then insert the columns at their respective places in the acrylic sheet two. After setting up the irrigation and control system, click the edit button to edit the settings of each task.

To activate the relay, simply click on the task that requires the relay to be turned on. Then insert the preferred settings in the start date and start time fields. To set the start date and time for the operation, click set repeat and every to set the watering frequency.

To specify the date and time when the relay should stop operating, click on the end repeat date and end repeat time fields. After entering the desired values, click the save changes button. To turn off the relay.

click on the task for which the action is to set the specific relay off. Set the time at which the relay must stop working depending on the water irrigation rate and the watering frequency following the same commands as to set the relay on. Once each relay is set, click on save changes.

The irrigation system will then start watering the columns according to the set flow rates and frequencies. The irrigation system allowed water adjustments in the columns leading to small differences in irrigation rates. The average amount of water was lower for irrigation rates of 50 and 150 milliliters per day, while it was higher for an irrigation rate of 100 milliliters per day.

Values for dissolved inorganic carbon measured at the end of the experiment ranged from 7.352 C to 259.279 milligrams carbon. At the end of the experimental period, earthworms successfully survived in this organo-mineral system, and visual signs of microbial growth could be detected.