Influence of Microplastics on Nitrate Reduction in Floating Wetland Environments
Meredith Sutton
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04/04/2021
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Influence of Microplastics on Nitrate Reduction in Floating Wetland Environments
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- [00:00:04.610]Hello,
- [00:00:05.030]my name is Meredith Sutton and I'm a first year PhD student in the department
- [00:00:09.920]of civil and environmental engineering. Today,
- [00:00:13.040]I'll be talking about a project that I've been working on that is focused on
- [00:00:16.910]looking at the effects of microplastics on nitrogen movement and wetland
- [00:00:20.990]environments.
- [00:00:29.930]So for those of you that don't know what microplastics are,
- [00:00:33.200]they're really just small pieces of plastic.
- [00:00:35.750]A common definition is any plastic particle that is smaller than five
- [00:00:39.740]millimeters.
- [00:00:41.000]They can come from a host of different sources and can quickly become widespread
- [00:00:45.500]and many different environments, including wetland systems,
- [00:00:48.560]which provide a host of different ecosystem surfaces. One, however,
- [00:00:52.880]that is especially important is how they act as a natural filter and treatment
- [00:00:56.780]process for many different contaminants, including nitrates,
- [00:01:00.500]which is my focus for today.
- [00:01:03.500]Wetlands have been constructed artificially to serve as treatment processes for
- [00:01:08.030]water, with high levels of nitrates.
- [00:01:10.550]And one important distinction that I want to point out is the difference between
- [00:01:14.750]constructed treatment wetlands and floating treatment wetlands.
- [00:01:19.070]So constructed wetlands are more of a traditional land-based wetland that are
- [00:01:23.900]built to act like natural wetlands,
- [00:01:26.180]whereas floating treatment wetlands employ wetland plants that are floating on
- [00:01:30.680]mats and a body of water to provide the treatment for this study,
- [00:01:35.270]we'll be focusing on floating treatment wetlands.
- [00:01:38.240]There hasn't been much research on the effects of microplastics on different
- [00:01:42.800]nitrogen cycling processes in the natural environment,
- [00:01:46.730]but there have been studies that have shown that nitrogen cycling,
- [00:01:50.090]both nitrification and denitrification, in wastewater treatment plants were
- [00:01:54.800]impacted by the addition of microplastics.
- [00:01:57.830]So there's a possibility that these processes in the environment are influenced
- [00:02:02.300]as well.
- [00:02:10.580]So this study was conducted using microcosms and in order,
- [00:02:15.500]and you can see the microcosms right here and in order to replicate the
- [00:02:20.180]microbial conditions that would be present in the floating treatment wetlands,
- [00:02:24.440]we took samples from some of the mats and added them to the microcosms.
- [00:02:28.580]So you can see some of the floating treatment wetlands and their mats right
- [00:02:31.880]here. Uh, there were six different trials.
- [00:02:40.040]There are six different trial conditions that were run in triplicate and
- [00:02:43.970]micro-plastics were added to two of the trial conditions.
- [00:02:47.300]The others included looking at the root behavior with no additions and making
- [00:02:52.040]sure that the surfactant Tween 20 that was required for the microplastics
- [00:02:56.990]did not cause any effects on its own.
- [00:03:03.840]This first experiment,
- [00:03:05.490]we use polyethylene microplastics with a circular diameter of one to four
- [00:03:09.870]microns.
- [00:03:11.070]And we started with two different concentration levels at 10 milligrams per
- [00:03:15.000]liter, and a hundred milligrams per liter, which were added to the microcosm.
- [00:03:24.840]After running experiments for a week under anaerobic conditions to look at
- [00:03:28.830]nitrate consumption. These were the results that we were seeing.
- [00:03:32.550]This first graph shows the concentration of nitrate nitrogen over time,
- [00:03:36.900]the lines that are showing a decrease in nitrate, concentration,
- [00:03:42.030]nitrate, concentration, or the microcosms with roots. So these lines right here,
- [00:03:47.460]whereas the ones that show a little change are the samples that do not have
- [00:03:50.610]roots. So these on top,
- [00:03:53.490]this is important as it shows that there are active microbial communities in the
- [00:03:57.780]samples with roots,
- [00:03:59.820]then comparing the two different concentration levels of microplastics in the
- [00:04:03.840]microcosms that have roots. So the ones that are showing a nitrate usage.
- [00:04:08.850]So these right here.
- [00:04:12.870]You can see that they decrease in a fairly similar rate.
- [00:04:16.350]And after a statistical analysis,
- [00:04:18.270]we see that there isn't a significant difference between the two microplastic
- [00:04:22.560]concentrations in regards to the rate of nitrogen consumption,
- [00:04:26.880]nitrate consumption, uh, further,
- [00:04:29.400]we can then look at the comparison in between samples with roots and the samples
- [00:04:33.210]with microplastics and roots.
- [00:04:35.550]So.
- [00:04:37.410]These lines and this line, you can also see their rates here.
- [00:04:41.610]This is the rate with roots only, and these are the two with microplastics.
- [00:04:46.650]while there's a slightly slower rate of nitrate consumption in the samples with
- [00:04:50.430]microplastics and roots, as you can see
- [00:04:54.300]the difference between the two is not statistically significant.
- [00:04:57.480]So we cannot conclude that the addition of microplastics impacts the rate of
- [00:05:01.980]nitrate consumption.
- [00:05:07.440]Moving forward with this research as polyethylene is the plastic type that tends
- [00:05:12.180]to show the most subdued response and other studies,
- [00:05:15.300]I plan to increase the type of plastics tested as well as add an additional
- [00:05:20.190]concentration level at a thousand milligrams per liter. Additionally,
- [00:05:24.270]I plan to add other analysis techniques in order to more accurately study the
- [00:05:28.890]microbial response to the addition of microplastics into the system,
- [00:05:33.780]as well as to better categorize the movement of nitrogen nitrogen within the
- [00:05:37.920]system.
- [00:05:40.020]so thank you for coming to watch my presentation about my research.
- [00:05:43.710]I'd like to thank Dr.
- [00:05:44.760]Miller and his lab group for help with the denitrification methodologies and
- [00:05:48.480]analysis, as well as Dr.
- [00:05:50.430]Tiffany Messer and her lab group for providing the root samples from their
- [00:05:54.540]floating treatment wetland plants.
- [00:05:56.700]Thank you again.
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