Heavy Metal Concentration Changes in Sediment Along the Cumberland River as it Flows Through Nashville and Seasons Change
ABSTRACT
Sediment carried in stormwater runoff can be extremely harmful in urban areas due to the numerous pollution-producing activities which happen within those areas, especially since stormwater is not treated before draining into waterways. To see how Nashville managed or contributed to this pollution, we assessed the Cumberland River’s health through pH values of the water, as well as the organic carbon weight and heavy metal concentrations in its sediment. We expected that heavy metal concentrations would increase west of Nashville (after passing through the city) and that pollution would increase in spring due to generally higher rainfall. We found that the concentration of heavy metals was significantly higher (p < 0.05) in the three outflow sample sites when compared to the three inflow sample sites. No significance (p = 0.151) was found in the heavy metal concentration between sample sites in spring vs. winter. The organic carbon content values in each sample showed a significantly larger carbon mass in spring samples when compared to winter samples which was expected due to increased life during spring (p < 0.001). Significance (p = 0.101) wasn’t found in the changes of carbon content as the Cumberland flowed through Nashville. In conclusion, these results support that heavy metal pollution in sediment increases greatly when waterways flow through urban areas such as Nashville. Toxic metals in our waterways affect aquatic life and recreational activities, making it extremely important to continue regulating our growing city with erosion control and soil protection.
INTRODUCTION.
As the Nashville population continues to grow and pollution becomes an increasing concern, our waterways are in peril. Urban areas, hubs of construction, traffic, and people, are the main source of this pollution. Our study will be delving into the Cumberland River’s relationship with the rapidly growing Nashville.
Much of the pollution in waterways comes from sediment, the layer of silt, dirt, and other materials that rest on the bed of waterways [1]. In urban areas, we can trace the root cause of this pollutant to poor erosion control. Typically, vegetative buffers, silt fences, and straw erosion control blankets are used in large construction sites and farming institutions to lessen erosion and prevent sediment from leaving the site, but the management of such practices is not always required or regulated effectively [1]. The danger lies in the fact that eroded soil makes the top layer of sediment become loose and more prone to being washed away by rainwater, and when rainwater travels through populated areas, the sediment it carries absorbs pollutants. In Nashville, stormwater drains directly into the Cumberland without filtration or treatment. The sediment that ends up in the stormwater system is released into the waterway, along with possible toxic waste materials it has picked up.
The Cumberland River is an extremely important waterway as it connects Nashville with the rest of Tennessee along with regions in the Southeast. It is the main water supply for millions of Tennesseans, transportation for steamboats and barges, and is the home to hundreds of native ecosystems and food chains. According to data collected by the Tennessee Department of Environment and Conservation, it is estimated that 36% of streams in the Middle Cumberland Watershed are impaired by sediment pollution [2]. This is considered a public health risk as the sediment pollutants can cause the degradation of waterways over time [2]. Sediment carries with it various heavy metals that can have serious health implications if humans come into contact with them. Keeping in mind the Cumberland is Nashville’s drinking water; Cadmium (Cd) and Chromium (Cr) are known mutagens at some concentrations, and possible carcinogens at other concentrations [3]. Additionally, the bioaccumulation of metals in plants and animals can destroy food chains and eventually hurt the entirety of an ecosystem [4]. pH in the river can significantly impact a freshwater environment as more acidic water makes sediment in the river more prone to release metals, increasing the toxicity of these heavy metals [5]. Heavy metals that are mobilized by acidic water such as aluminum, copper, and zinc can kill fish or make them unable to reproduce.
The goal of our research was to study the relationship between Nashville and the heavy metal concentrations of sediment in the Cumberland River. To do this, we studied three sites to the east of Nashville’s urban center and three sites to the west. By looking at how location along the Cumberland River affects heavy metal concentrations, we determined the impact of urban activities and development on water quality. We hypothesized that heavy metal concentrations in the Cumberland River would increase significantly after passing through Nashville due to the city’s construction, traffic, and other urban activities.
Taking a broader approach, we assumed that seasonal changes to warmer weather may also have a negative effect on water pollution patterns in the Cumberland. As temperatures rise, the increased atmospheric moisture triggers a greater amount of rainfall [6]. Because of this, we hypothesized that water pollution in the spring will be greater because there is a higher chance of various pollutants being transported into the Cumberland by this additional rainfall. These pollutants could be anything from waste from animals to residue metals particulates at a construction site, which would change the levels of carbon content and heavy metals that end up in the river. Therefore, it is predicted that the pH of the river will also decrease because the heavy metals will make the waterway more acidic [6]. We hypothesize that the higher levels of activity during warmer months will lead to increased organic carbon content and heavy metal pollution and decreased water pH of the Cumberland River. Overall, we want to gain an understanding of how seasons contributed to the overall picture of pollution in the Cumberland River.
MATERIALS AND METHODS.
The Cumberland River flows from east to west, joining the Tennessee River and smaller tributaries [7]. To understand how heavy metal concentration patterns change in the Cumberland River after passing through Nashville, we observed three sites to the east, and three sites to the west of the city, a total of six sample sites. The eastern sites are as follows: Lock Two Park (LTP), Peeler Park Ramp (PP), Shelby Park Boat Ramp (SP). The western sites are as follows: Cleece’s Ferry Boat Ramp (CF), Sam’s Creek (SC), Riverview Marina Access (RM). Sample sites were chosen based on their connection to the Cumberland River, accessibility, and being an accurate representation of direction (Fig. 1). Note: some sample sites are boat ramp access points to the Cumberland River.
Sample Collection.
At each sample site (Fig. 1), the sampler dug 5 inches down into the riverbed with a shovel to collect undisturbed sediment to fill a one-gallon size Ziploc bag three quarters full. The area of sediment collection was close to shore, and samples were taken from 0.4-0.5 meters deep in the water. Two 50 ml water samples were taken from the surface of the water. Observations of the water and air temperatures were taken, as well as notices (ex. Invasive species alerts). All the collected samples were then transported back to the lab for analysis the same day. Winter data was collected on March 6th, 2024, and spring data was collected April 17th, 2024.
Water Analysis.
All water samples were tested immediately after returning to the lab using both a pH strip (Whatman) and a probe (Vernier). The Whatman pH strip was held in each test tube for 2 seconds. A 10 second rest time was given to allow the strip to change colors. We determined the pH using the indicator scale on the box provided. The Vernier pH probe was calibrated and submerged into the water sample for 1 minute. Once reading stabilized, the pH level was recorded. Averages of pH probe and strip values were taken for data analysis.
Sediment and Rock Classification.
All of the collected sediment samples were put into an Isotemp drying oven for one week at 70 °C. After samples were completely dried, they were sifted through a 2000-micron (2 mm) metal sifter to separate the fine sediment particles from larger rocks and other foreign objects that were collected in the sample, like fishhooks. Both were separated into two different containers on a site-by-site basis.
X-Ray Fluorescence (XRF) Analysis.
Using a portable Thermo-Scientific Nikon XL3 Analyzer X-Ray fluorescence machine (XRF), we found the elemental composition of each sample site for both seasons. Samples were analyzed with tube voltage, at factory supplied 1¼Cr-½Mo alloy standard calibration, with Mylar Film 2.5 dia., counting time was 120, and results are in ppm.
The full sample preparation was based on the process used by Marguí et. al [8]. Summarizing, we prepared the sediment samples collected and added them to XRF detector cups, simultaneously using a wooden mallet to compress the sample as much as possible, making sure to keep a flat layer for analysis. Then the samples were analyzed using the built-in computer program on the X-Ray fluorescence analysis machine. Using the collected elemental compositions, we isolated a list of specific heavy metals based on other research [1]. We isolated the heavy metals Arsenic (As), Cadmium (Cd), Nickel (Ni), Mercury (Hg), Chromium (Cr), Zinc (Zn), Lead (Pb), and Copper (Cu). Averages of the metal concentrations were used to find a mean heavy metal concentration value for each sample which we then refer to as total heavy metal concentration.
Statistical Analysis.
After collecting values for the heavy metal concentrations and organic carbon content, we ordered the data based on the season each sample was collected and the direction of the river the sample was taken from. We used three two-way ANOVA (analysis of variance) statistical tests to describe the effect of both the direction and seasonal variables. The ANOVA test used in the main study set heavy metal concentration against the independent variables being the directional and seasonal influences. The other ANOVA tests set the water pH and organic carbon against the same variables. The ANOVA tests also showed the interaction between direction and season to observe if these variables have any dependency on one another when it comes to pollution. A q-test was completed in order to exclude any clear outliers to avoid skewing of the data.
RESULTS.
Initially, pH values were collected at each sample site along the Cumberland River in the two different season collections to better understand the fundamental water chemistry at the different sites. We collected these samples at the same access point for each site and plotted them on a map according to the sample site. We observed the water pH of the river decreased by 4% as it flowed to the west of Nashville (p < 0.001; F-value = 218.578; Figure 2, Supplemental Table 1)
Subsequently, we ran analysis testing on the sediment samples collected. We used X-Ray fluorescence (XRF) analysisto analyze the composition of the samples and isolated out our selected heavy metals to conduct further statistical analysis. We observed the heavy metal concentration of the sediment increasing as the Cumberland River flowed through Nashville (p<0.05; F-value=9.526; Figure 3; Supplemental Table 2)To better understand which heavy metals from our selection were contributing the most to this increase, we looked at the individual heavy metals in both the spring and the winter data collection. In comparison, there doesn’t seem to be an outlier in the collection between either season, but we found the drastic decrease of Zinc (Zn) in the CF and RM data sites interesting (Figure 4).
DISCUSSION.
Through our research, we wanted to see how Nashville’s urban activity affects the Cumberland River’s overall health. Typically, when a body of water passes through an urban area, the quality of the water decreases, which is what we anticipated with Nashville. We also wanted to determine how changing seasons affect pollution patterns in the Cumberland River. We measured heavy metal concentration and water pH which are strong indicators of water health and pollution in the river.
We predicted that the Cumberland River’s quality would decrease after flowing through Nashville, which can be quantified through a number of variables. Our results showed that flowing from the east to the west did have a significant impact on the water pH of the river, as the river became more acidic after passing through Nashville. The fluctuations in pH stayed within a certain range. Our data exemplifies that by flowing through Nashville, the Cumberland River increased in heavy metal concentrations. This can likely be attributed to the increase of urban activity in Nashville that creates heavy metal particulates that find their way into the river. The Cumberland River is the main source of drinking water for Nashvillians, so detrimental health concerns for humans must be considered [9]. Metals that accumulate in waterways can be mutagenic or carcinogenic with a probability of 1/1000 [3]. These metals include Ni, Cd, and Cr, which we discovered to be increasing in the Cumberland River after the waterway passes through the city. Metals are dangerous to aquatic organisms and have the potential to bioaccumulate in lower levels of a food chain, eventually affecting higher trophic levels of the ecosystem. This means our first hypothesis, which was to see if flowing through an urban city affects pollution, was supported by our results.
As warmer months approach, increases in plant and animal life are seen throughout nature. This increase shows itself through the generation of additional organic waste, which gets picked up by stormwater and transported into waterways. Because of this, we predicted that the increase of bioactivity during warmer seasons would result in increased water pollution [10]. Our results regarding water pH showed that the spring and winter pH in the Cumberland River were slightly acidic, with winter being below the healthy range of 6.5-9 [10]. Lower/acidic pH is associated with more pollution. This is important because in freshwater environments, the pH can affect how quickly heavy metals dissolve in water and leech onto aquatic organisms. There was also no significance in the changes of heavy metal concentrations between the winter and spring season. Overall, this means that our hypothesis was partly unsupported, because the lower pH in the winter is not supported by changes in heavy metal concentration. We had a lower pH in winter, but the other aspects of pollution had larger values in spring. Because of these two conflicting points our data was inconclusive, leaving our hypothesis unsupported.
It is clear that Nashville plays a harmful role in advancing heavy metal pollution, and action must be taken to minimize it. Some possible preventative measures of controlling sediment pollution can include promoting stronger erosion prevention plans, soil stabilization guidelines, and site inspections on large institutions that contribute the most to loose sediment. Instead of focusing on changing the city’s stormwater system and attempting to control natural circumstances of flooding and drainage, targeting prevention of sediment transport can be more efficient. These tactics have lessened the effect of sediment pollution, particularly in California where they specifically created sediment control programs, which was successful in improving water quality because their focus was on addressing pollution at the source [8].
Some limitations of our study include the small sample size (n=6) and the seasonal dates in early March and April we utilized to categorize “winter” and “spring”. In the future, we would like to look at other ways to measure pollution to add to the results of this study. For example, including summer data as an additional season would give more accurate insight to answering our second hypothesis and taking data with more variable indicators of water quality could be used to further support our first hypothesis. Running a contamination factor or geo-accumulation index assessment could also help quantify the severity of Nashville’s pollution in comparison to the healthy norm. Looking into sources of sediment pollution could help determine which specific industrial activities contribute the most to contaminated sediment which could show Nashville which practices need more management/enforcement of regulations.
ACKNOWLEDGMENTS.
We would like to give a special thanks to the School of Science and Math at Vanderbilt (SSMV) for their continued support of our research. We would also like to thank Dr. Stanton, who was our amazing scientific instructor and mentor throughout this research process. Thank you to Ms. Berbiglia for her presentations about healthy waterways and stormwater management in Nashville and to Dr. Goodbred for allowing us to use his lab and his equipment to run our variable tests.
SUPPORTING INFORMATION.
Supporting Information includes two tables of p-values and f-values for statistical analysis of pH and heavy metal concentration.
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Posted by buchanle on Friday, May 15, 2026 in May 2026.
Tags: Cumberland River, Heavy Metals, Sediment, Waterway Pollution