Estimating Spatial and Temporal Variability of Nitrate Contamination in the United States
Dalton Everhardt
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07/26/2021
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This is a video poster presentation of the work we have been doing over the summer where we have calculated a value called the Net Anthropogenic Nitrogen Input for every county in the continental United States. The resulting data was then visualized and analyzed.
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- [00:00:00.540]Hello! My name is Dalton Everhart
- [00:00:02.910]and this summer I have been working with my graduate advisor, Chuyang Liu,
- [00:00:06.960]and my faculty advisor, Dr.
- [00:00:08.730]Yusong Li on a project titled "Estimating Spatial and Temporal
- [00:00:13.260]Variability of Nitrate Contamination in the United States."
- [00:00:17.040]This short video poster presentation will give an overview of the work that
- [00:00:20.400]we've been doing and the results that we have obtained. But before that,
- [00:00:24.930]I would like to give a little information about the project that I think is
- [00:00:28.200]necessary for you to know. Nitrate is a naturally occurring inorganic
- [00:00:32.910]compound and is often created through a process called nitrification
- [00:00:37.230]where ammonia, which is created by natural sources of nitrogen,
- [00:00:41.370]is oxidized to nitrite and nitrate.
- [00:00:44.730]The United States Environmental Protection Agency has a Maximum Contaminant
- [00:00:48.990]Level or MCL for nitrate in drinking water as 10 milligrams
- [00:00:53.790]per liter as nitrogen. This 10 milligrams per liter
- [00:00:57.690]as nitrogen MCL is put in place to help protect people from the negative impacts
- [00:01:02.370]that exposure to too much nitrate in drinking water can have. Short-term
- [00:01:07.350]exposure can result in methemoglobinemia or blue
- [00:01:12.300]baby syndrome in infants,
- [00:01:13.770]as well as indigestion and anybody above six months or older.
- [00:01:18.360]Long-term exposure to nitrate levels above the MCL have been linked to a
- [00:01:22.920]variety of conditions, including sudden infant death syndrome,
- [00:01:27.030]depression and various cancers. Unfortunately,
- [00:01:30.690]a study conducted by the United States Geological Survey in 2006,
- [00:01:34.950]found that over 1 million private well owners live in areas with the risk of
- [00:01:39.330]exceeding the EPA's MCL for nitrate.
- [00:01:43.570]I also think it's notable to mention that while nitrate is naturally occurring,
- [00:01:47.340]levels above one milligram per liter
- [00:01:49.440]as nitrogen in groundwater is known to suggest human activity in the area
- [00:01:54.630]and that has helped shape our project to only look at sources of nitrogen that
- [00:01:58.260]only exists because of humanity. In this study,
- [00:02:02.130]our aim was to implement the most updated version of a toolbox developed by Hong
- [00:02:06.880]at all.
- [00:02:07.440]In their 2011 paper titled a toolbox for calculating net anthropogenic
- [00:02:12.420]nitrogen inputs, or NANI, to the continental United States at
- [00:02:17.340]the county level, as
- [00:02:19.410]NANI is known to be a predictor of nitrate pollution and, then to visualize and
- [00:02:24.120]analyze the resulting data to find anything of interest or worthy of note.
- [00:02:31.360]Basically, the NANI is a single value reported in kilograms of
- [00:02:35.920]nitrogen per square kilometers per year,
- [00:02:38.500]that takes into account all sources and sinks of anthropogenic nitrogen for a
- [00:02:42.610]particular area, or in our case, a county,
- [00:02:46.240]and is known to be linked with nitrate pollution.
- [00:02:49.060]The NANI is made up of four components:
- [00:02:52.510]Atmospheric Nitrogen Deposition, Fertilizer Nitrogen Application,
- [00:02:56.740]Agricultural Nitrogen Fixation,
- [00:02:58.990]and Net Food and Feed Imports with Net Food and Feed Imports being
- [00:03:03.880]further made up of four more components: Crop Nitrogen Production,
- [00:03:07.900]Animal Nitrogen Production, Animal Nitrogen Consumption,
- [00:03:11.410]and Human Nitrogen Consumption.
- [00:03:13.690]Riverine Nitrogen Export is not used to calculate the NANI,
- [00:03:17.500]but it's included in the diagram because there is a known empirical relationship
- [00:03:21.730]between the two with Riverine Nitrogen Export being equal to
- [00:03:26.110]approximately 30% of the NANI.
- [00:03:29.260]It's also important to note that it's entirely possible for the NANI to
- [00:03:33.190]be negative.
- [00:03:35.520]Moving on to our methodology, since this study is using a standardized toolbox
- [00:03:39.900]developed by another party,
- [00:03:41.520]the calculation of the NANI is a simple process.
- [00:03:45.030]The only input needed from us was an ArcGIS shapefile of the continental
- [00:03:49.140]United States that contains all county boundaries.
- [00:03:52.350]The input is then cross-referenced with the shapefile provided in the toolbox
- [00:03:56.190]so that locations outside of our area of interest or areas not included in the
- [00:04:00.930]toolbox scope were removed.
- [00:04:03.150]The NANI extraction tools are then used to
- [00:04:07.850]attribute publicly available data to each county
- [00:04:11.070]and then the extraction tools process the data.
- [00:04:15.150]After that, the NANI accounting tool is used to calculate the components of
- [00:04:19.810]NANI, and then the NANI itself. In its current iteration,
- [00:04:24.750]the toolbox creates a table of values where a NANI is reported for each
- [00:04:29.490]area. And for the following years:
- [00:04:32.310]1987, 1992, 1997,
- [00:04:36.540]2002,
- [00:04:37.920]2007 and 2012. From there,
- [00:04:41.760]it was up to us to visualize and analyze the data and the best way to
- [00:04:46.710]visualize most spatial data as a map,
- [00:04:49.560]but since our results also have a time component to them,
- [00:04:52.800]we decided that for a virtual poster,
- [00:04:54.780]that a GIF of our maps was an interesting format to visualize our data.
- [00:04:59.580]By watching the GIF as it loops,
- [00:05:01.680]there are a ton of interesting things that can be seen,
- [00:05:04.020]and it's a really useful tool to help see what is going on with the NANI
- [00:05:08.760]over time in particular places.
- [00:05:11.640]Unfortunately due to the large scope of our data and the limited space available
- [00:05:16.470]on our poster, only a few tidbits from our data analysis can be shown.
- [00:05:21.660]The first thing that we thought was interesting to look at was just the national
- [00:05:24.840]average of the NANI over our timeframe.
- [00:05:28.380]As you can see in figure four, from 1987 to 2012
- [00:05:32.190]the national average at the, NANI increased by 25% from
- [00:05:36.870]2849.49 kilograms of nitrogen per square
- [00:05:41.280]kilometers per year to 3569.29 kilograms of
- [00:05:46.110]nitrogen per square kilometers per year,
- [00:05:48.830]which is an extremely concerning statistic
- [00:05:50.850]when you think of the negative health effects of nitrate in our drinking water
- [00:05:54.900]that I listed before. Table one shows the top five
- [00:05:59.780]counties with the highest NANI for 2012
- [00:06:04.210]and an unexpected result from this is that all five of these counties are cities
- [00:06:08.990]two which being a part of New York city and three having quite small areas.
- [00:06:14.150]Further analysis needs to occur.
- [00:06:16.160]But considering that area is a factor of calculating the NANI,
- [00:06:20.540]extremely small areas may artificially increase the NANI.
- [00:06:26.010]The last thing that we wanted to cover in this presentation is to give a few
- [00:06:29.520]specifics about a particular hotspot that can be seen from our GIF of our series
- [00:06:34.320]of maps. Over time we see a general increase of the NANI,
- [00:06:39.120]and a series of seven counties that make up the San Joaquin valley in
- [00:06:43.020]California.
- [00:06:45.600]The San Joaquin Valley is well known for its booming agricultural industry,
- [00:06:49.500]as well as its issues with nitrate and its groundwater. In fact,
- [00:06:54.210]in 2007,
- [00:06:55.230]74% of all California's nitrate violations could be found
- [00:06:59.880]in the San Joaquin Valley. In that same year,
- [00:07:02.670]four of the valley seven counties could be found in a list of the top 100
- [00:07:07.620]counties with the highest NANI
- [00:07:09.750]in the continental United States with Merced county placing the highest from
- [00:07:14.160]the four San Joaquin valley counties at 36th.
- [00:07:20.810]To summarize, the NANI is already known to be a predictor of how much
- [00:07:24.650]nitrate pollution occurs in a particular area and a 25%
- [00:07:29.900]increase in the national average has incurred from 1987 to
- [00:07:34.430]2009 and is a point of concern.
- [00:07:37.700]We have also seen that while cities with small areas or high populations,
- [00:07:42.590]dominate our top five of the NANI
- [00:07:46.010]we have also observed that areas with high amounts of agriculture can also
- [00:07:49.730]place very highly in the NANI scores,
- [00:07:54.260]such as the San Joaquin valley. Unfortunately,
- [00:07:58.010]while I discussed in the introduction
- [00:07:59.810]what happens when nitrate gets into our drinking water and how private well
- [00:08:04.070]owners are at risk,
- [00:08:06.050]a limitation of this study is that the NANI does not give an estimate of how much
- [00:08:10.460]nitrate infiltrates into groundwater.
- [00:08:13.040]It's only known to be an estimation of nitrate in a watershed and have that
- [00:08:17.210]empirical relationship with the Riverine Nitrogen Exports that I mentioned before.
- [00:08:22.940]Going forward future work with this dataset not only includes further analysis
- [00:08:27.590]of all of this vast amount of data,
- [00:08:30.170]but this data is currently planned on being used by my graduate advisor,
- [00:08:33.410]Chuyang Liu,
- [00:08:34.640]as a small part of his work in developing a method to accurately
- [00:08:39.140]predict groundwater nitrate.
- [00:08:41.480]Thank you for listening to our presentation and I hope you enjoy the rest of
- [00:08:44.420]your day.
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