Last week’s post described what peepers are used for and what this week will involve. After a team meeting Monday, we decided we were ready to start that morning! We decided to finish five peepers that day, which would mean getting pore water samples into about 80 vials for various measurements; each peeper needs about 16 vials: pH, Iron, and sulfide/sulfate vials for each of the four peeper wells, two composite vials, and two for surface water measurements. The pH is measured immediately and the rest are analyzed at the lab.

Before getting a peeper for sample collection, we began by pipetting the appropriate proportions of acids and reagents into the vials so everything would be ready for the pore water samples. It is important to do everything we can in advance, since this is a time-sensitive process and the pore water samples can be contaminated by the higher concentration of oxygen in the air. We weigh the vials before and after adding sample.

The process of getting pore water from a peeper involves multiple moving parts. Samples are drawn into a syringe in a low-oxygen environment created using a vacuum bag (typically used for storing linens in a smaller space) and stream of nitrogen gas. We start with the most reduced well, number four, that was deepest in the water-saturated ground and work up to the first well. This is because the wells will be more exposed to oxygen closer to the surface and we do not want to risk any contamination. We put appropriate measurements of sample into each prepared vial for separate peeper wells, test the pH, gather surface water samples, and make the composite samples. To do this efficiently we had about five people with their own task to speed the process along.

After each day of sample gathering, the completed samples are analyzed at the lab. Michelle and I helped measure the absorbance of sulfide and Iron on the spectrophotometer. This is done using a tall cuvette that we zero with deionized water then fill with sample and quickly get the absorbance back as a decimal.

To the left is a larger version of the peepers placed in many of the wild rice mesocosms at the University of Minnesota Duluth Research and Field Studies Center. The peepers we will be working with have about four wells (the thin rectangles you see) that take in ground water from different depths. This is done by diffusion: distilled water placed in the peepers is replaced by water from the soil. We can then measure for Metals, Iron, Sulfide, Sulfate, and pH at different depths in each tank.

This week, with the team, we are prepping for Peeper week, which involves preparing and labeling about 430 bottles that will hold groundwater samples for analysis. Monday morning, we began helping to write out labels for each individual bottle. Later in the week, we helped to pack all the gear for analyzing groundwater from the peepers, including a pH meter, syringes to draw out the samples, nitrogen bags to keep an low-oxygen environment while drawing samples, and many other supplies. The low-oxygen environment is vital to avoid contaminating the groundwater, since there is a higher concentration of oxygen in the air than in the soil. We will be starting the excitement of peeper week this Tuesday or Wednesday after ensuring everything is ready to go.

Mesocosms at the University of MN Duluth Research & Field Studies Center.

Lab work at Nathan Johnson’s research lab in Voss Kovach Hall at the University of MN Duluth.

This week was focused on gathering water samples from mesocosms containing wild rice and varying levels of sulfur and leaf litter for carbon. The goal is to maintain constant levels of these variables in order to study the affects of mining on wild rice. To keep up the levels of sulfur, water samples from each tank are placed in a spectrophotometer to measure the concentration of sulfur. The measured concentration is subtracted from the goal concentration in order to tell how many grams of sulfur to add to the tanks.

Mesocosms at the University of MN Duluth Research & Field Studies Center.

Lab work at Nathan Johnson’s research lab in Voss Kovach Hall at the University of MN Duluth.