About This Project

We know that woodchip barriers can be used to prevent algal blooms, but we don't know if this method is producing toxic methylmercury at a high rate. Funds for my mesocosms will help us understand the risks and benefits of woodchip barriers as a method of stopping algal blooms.

Ask the Scientists

What is the context of this research?

Over the past few decades, eutrophication has become a serious issue around the globe. Eutrophication occurs when excess nutrients (usually nitrogen and/or phosphorus) enter coastal waters and stimulate the growth of algae. This leads to problems such as harmful algal blooms, loss of oxygen, fish kills, and drops in biodiversity. A potential solution to this problem is a permeable reactive barrier, or a PRB. This is a fancy term for a bunch of woodchips that have been buried underground so that groundwater must flow through the chips before it goes into coastal waters. The woodchips are made of carbon and provide an energy source for denitrifying bacteria. These microbes are capable of removing the excess nitrogen from the groundwater that flows through the PRB before it reaches coastal waters, thereby reducing the harmful effects of eutrophication. This carbon source is so plentiful that the barrier is also home to other types of bacteria.

In the past, I have measured large fluxes of hydrogen sulfide coming from the barrier. This indicates the presence of sulfate-reducing bacteria. These bacteria also have the ability to methylate mercury that is in the groundwater. Bascially, mercury in its elemental or ionic form can be quite common in some groundwater systems, especially those near urban or industrialized areas. Sulfate reducing bacteria can take this mercury and alter it through their metabolism to methylmercury, which is the toxic form that is found in fish. If ingested, this can lead to brain damage and other serious health effects.

My goal is therefore to determine whether these barriers are solving one problem (eutrophication) only to create another (toxic methylmercury production). To answer this question, I need to build miniature versions of the barrier (called mesocosms) and add some mercury to see whether methylmercury gets produced as a result. I hypothesize that due to a large presence of sulfate-reducing bacteria, there will be more methylmercury coming out of barrier mesocosms as opposed to control ones (barriers that have no woodchips). We will publish these works in quality, peer reviewed journals and keep our backers fully informed of our progress over the course of the research.

What is the significance of this project?

Most areas that are highly eutrophic are also contaminated with mercury, since both are derived from human sources. Before the barrier can be implemented on a larger scale, I need to determine whether they are safe to use in urban areas with high mercury concentrations. I have measured nutrient concentrations at the barrier in the past, and they are very effective at removing nitrate from groundwater. In fact, if you go in the summer to where the barrier is, you can see that the ground above it is bare of algae, while the rest of the beach is covered! However, if it is producing toxic methylmercury at a high rate, it might not be worth these benefits.

What are the goals of the project?

In order to do my mesocosm experiments, I will need money to build miniature versions of the PRBs and get water flowing through them. The tubing and fittings for each mesocosm would cost $600, and I would need around six replicates. This comes to $3,600. The rest will be spent on a pump, sample containers, and analyses. Right now, there is very little mercury in the groundwater at my study site, which is a good thing, but it means that we still do not know how the PRB will function in water full of mercury. Will it create more toxic methylmercury? The mesocosms will allow me to test this hypothesis by adding groundwater spiked with mercury. These funds would go to answering these questions. If I find that the PRB bacterial community appears to be “healthy” and isn’t producing too much methylmercury, this might be an excellent way to help clean up polluted coastal waters.