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Evaluation of Nitrate Concentrations and Potential Sources of Nitrate in Private Water Supply Wells in North Carolina.

Introduction

Nitrogen and Environmental Health

Nitrogen is a crucial element for the development of proteins and other organic substances that directly influence plant and animal life. Insufficient concentrations of plant-available forms of nitrogen, such as nitrate, can limit crop yields and primary production in terrestrial and aquatic environments (Conley et al., 2009; Havlin, Beaton, Tisdale, & Nelson, 1999). Elevated nitrate concentrations in water resources, however, can be detrimental to public and environmental health. For example, research has suggested that prolonged consumption of high concentrations of nitrate in drinking water can increase the risk of cancer, methemoglobinemia (blue baby syndrome), and cumulative dysfunctions in organ systems (Ward et al., 2005).

The maximum contaminant level for nitrate-nitrogen (N[O.sub.3]-N) in drinking water supplies across the U.S. (and North Carolina) is 10,000 [micro]g/L (U.S. Environmental Protection Agency [U.S. EPA], 2009), but concentrations much lower can cause environmental health concerns. For example, concentrations of nitrate-nitrogen that exceed 1,000 [micro]g/L can stimulate hypergrowth of algae in some surface waters, leading to eutrophication (Osmond et al., 2003). Some algae produce toxins such as microcystins that are hazardous to humans and animals, and thus are environmental health threats (North Carolina Department of Environmental Quality, 2015; Smith & Schindler, 2009). Algal blooms can impact drinking water supplies by clogging water filters and imparting undesirable tastes and odors (Dodds et al., 2009). When the algae eventually die and decompose, surface waters can become depleted of dissolved oxygen, leading to fish kills and water use impairment (Conley et al., 2009).

Major water resources in North Carolina including the Neuse River, Tar-Pamlico River, Falls Lake, and Jordan Lake are nutrient sensitive and watershed nutrient management rules have been or are being developed to reduce nitrogen loadings to these waters (North Carolina Department of Environmental Quality, n.d.). Identifying the main contributors of nitrate to water resources is important for policy development that will help protect public and environmental health.

Agricultural Nitrate Sources

There are many different sources of nitrate-nitrogen in the environment including fertilizer, animal waste, human waste, atmospheric deposition, and nitrogen fixation. Nitrogen fertilizer production and application to agriculture fields has increased four-fold since the 1960s (Havlin et al., 1999). The increased nitrogen applications not only led to an increase in crop yields and overall agricultural production but also raised concerns for environmental contamination resulting from nitrate that is not used by the crops (Havlin et al., 1999). Industrial livestock farms, also called confined animal feeding operations (CAFOs), produce animal wastes with elevated concentrations of nitrogen (>400,000 [micro]g/L) that are often spray irrigated, or dried and applied onto crops (Goldberg, 1989; Huang, Yang, & Ling, 2014). Research has shown that nitrate concentrations in groundwater and surface waters near CAFOs and agricultural fields can exceed water-quality standards (Stone, Hunt, Humenik, & Johnson, 1998).

Agriculture is a major industry in North Carolina where farm receipts have totaled over 10 billion/year since 2010 (North Carolina Department of Agriculture and Consumer Services, 2016). There are more than 8 million hogs, 800 million poultry, 800,000 cattle, 1.9 million hectares (ha) of cropland, and 0.46 million ha of pasture in the state (North Carolina Department of Agriculture and Consumer Services, 2016). Commercial fertilizer (such as urea and ammonium nitrate) and manure are applied to approximately 72% and 10% of the cropland, respectively, in North Carolina (North Carolina Department of Agriculture and Consumer Services, 2016; Osmond et al., 2003).

Corn is one of the most commonly grown crops in North Carolina (>325,000 hectares) with nitrogen application rates typically exceeding 136 kg/ha (North Carolina Department of Agriculture and Consumer Services, 2016; North Carolina State Extension, 2017; Osmond et al. 2003). Crop uptake of nitrogen is relatively inefficient (~50%), leading to nitrogen loss via leaching, volatilization, and/ or denitrification (Osmond & Kang, 2008). Therefore, groundwater quality can be influenced by nitrate leaching from agricultural lands receiving fertilizer and manure, especially in well drained, sandy regions of the state (Osmond et al., 2003; Stone et al., 1998).

Septic Systems and Nitrate

Septic systems, or onsite wastewater treatment systems (OWTS), are another potential source of nitrate in groundwater (Del Rosario, Humphrey, Mitra, & O'Driscoll, 2014; Humphrey, O'Driscoll, & Zarate, 2010; Humphrey et al., 2013). OWTS are commonly used for treating wastewater in rural areas of North Carolina and other states (U.S. EPA, 2002). OWTS include a septic tank, conveyance pipes, drainfield trenches, and aerated soil under the drainfield trenches (Humphrey et al., 2013). Septic tank effluent has concentrations of ammonium-nitrogen that often exceed 35,000 [micro]g/L, and the ammonium can be quickly converted to nitrate-nitrogen in aerated soils beneath OWTS drainfield trenches via the nitrification process (Humphrey et al., 2013).

Nitrate concentrations exceeding the maximum contaminant level of 10,000 [micro]g/L have been reported in groundwater near OWTS in numerous studies conducted in North Carolina (Del Rosario et al., 2014; Humphrey et al., 2010; Humphrey et al., 2013; Iverson, O'Driscoll, Humphrey, Manda, & Anderson-Evans, 2015). An estimated 50% of residents in North Carolina use OWTS (Pradhan, Hoover, Austin, & Devine, 2007), and thus OWTS might also be a significant source of nitrate in groundwater.

Atmospheric Deposition

Atmospheric deposition of nitrogen can occur via precipitation (wet deposition) or during movement and settling of aerosol particles by wind (dry deposition) (Gao, Kennish, & McGuirk Flynn, 2007). North Carolina receives on average 100-140 cm of rain in the Piedmont and Coastal Plain regions, and 94-229 cm in the mountains (State Climate Office of North Carolina, 2017). Regions downwind or close to industrialized areas or CAFOs are more likely to show an increased nitrogen load due to atmospheric deposition (Whitall & Paerl, 2001). Nitrogen in the atmosphere as [N.sub.2] gas can be fixed by some terrestrial and aquatic organisms to plant-available forms such as ammonium and converted to organic nitrogen (Havlin et al., 1999). Fixation can also occur via lightning strikes (Meyer, 2014). When the nitrogen-fixing plants and organisms die and decompose, the organic nitrogen in the cells can be mineralized, converted to ammonium and nitrate, and released into the environment (Havlin et al., 1999).

Groundwater Supplies and Nitrate

There are approximately 3 million people (31% of the population) who use groundwater for a water supply in North Carolina (North Carolina Department of Health and Human Services, 2016). The installation of private wells is permitted and regulated at the local level by county health departments. New wells must meet certain criteria for structural standards and setback distances, and are sampled and tested for contamination prior to initial use. The state of North Carolina performs water testing for contaminants such as nitrate for new and existing wells upon request. A database of sample results is kept on file by the state.

Study Goal and Objectives

The goal of this research was to gain a better understanding of potential links between land use and nitrate concentrations in well water across North Carolina. The research objectives included the following: 1) to determine if there are statistically significant correlations between the percentage of land in agriculture, livestock numbers and densities, septic systems, and average groundwater nitrate concentrations in North Carolina counties; 2) to determine the 10 counties in North Carolina with the highest and the 10 counties with the lowest average concentrations of nitrate in groundwater and summarize their associated land-use characteristics; and 3) to determine if there are statistically significant differences in livestock numbers, livestock densities, septic system numbers and densities, and land area in agriculture for the 10 counties with highest average nitrate concentrations in groundwater in comparison with the 10 counties with the lowest average nitrate concentration in groundwater. These analyses were performed to determine which land-use characteristics were strongly associated with relatively high mean concentrations of nitrate in groundwater.

Methods

Groundwater Nitrate Concentrations and Land-Use Characteristics Determination

Groundwater nitrate concentration data (1998-2010) from drinking water wells in North Carolina were obtained from the North Carolina State Laboratory of Public Health. More than 31,000 samples were analyzed during the time frame. The groundwater nitrate data from drinking water wells were organized in spreadsheets and the average nitrate concentration in groundwater samples was calculated for each county (North Carolina Department of Health and Human Services, 2016).

Agricultural land-use characteristics including the number of cattle, poultry, hogs, and cropland acreage were summarized for each county using published data from the North Carolina Department of Agriculture and Consumer Services (2016). The numbers of livestock and acreage in cropland were divided by the total land area for each county to determine the density of livestock and fraction of land in crop production.

The two latest U.S. Census Bureau reports (2000, 2010) did not include information with regards to use of septic systems. Septic system data from the 1990 U.S. Census Bureau and North Carolina Environmental Health Reports were analyzed to obtain a more current number of septic systems used in each county and in the state. The Environmental Health Division of the North Carolina Department of Health and Human Services collects yearly information regarding all onsite wastewater activities including the number of new septic system permits issued (North Carolina Department of Health and Human Services, 2018).

We used the number of operation permits (OPs) issued each year as the unit of measurement for new system installations in each county. The number of OPs issued each year was added to the number of septic systems reported in the 1990 U.S. Census to gain a more current estimate of the number of systems in each county and the state. The average number of people per dwelling as indicated by the 2010 Census was multiplied by the number of systems in each county and divided by the total population to determine the percentage of people using septic systems in each county. The average percentage of population using septic systems was calculated for all 100 North Carolina counties. The number and density of septic systems used in each county were calculated. Septic system density was calculated by dividing the total land area (ha) of a county by the total number of septic systems.

Statistical Analyses

The average concentrations of nitrate in groundwater wells were compared to the numbers and densities of potential nitrate sources to determine if there were statistically significant correlations and to provide insight into the most significant sources of nitrate in groundwater. Nitrate and land-use data were organized by county, and all 100 counties in North Carolina were included in the correlation analyses. More specifically, the number of active septic systems in each county and the density of septic systems; the number and density of hogs, poultry, cattle, and all livestock; and the fraction of total land in agriculture were each compared to the average nitrate concentrations. Spearman correlation analyses were performed with Mini tab 17 statistical software to determine which land-use factors were significantly correlated with nitrate concentrations. Summary tables were developed listing the correlation coefficients and p-values for the comparisons.

There are 100 counties in North Carolina. Characteristics of the 10 counties with the highest average nitrate concentrations (top 10%) were summarized and compared with the 10 counties with the lowest average nitrate concentrations (bottom 10%) to determine if significant differences in numbers and densities of livestock, septic systems, and cropland were observed. It was anticipated that differences in the major land-use characteristics (numbers and densities) that influence groundwater nitrate concentrations would be significant when comparing the counties with the highest and lowest average nitrate concentrations. Comparisons were made using paired t-tests or Mann-Whitney tests (for data that did not follow a normal distribution) to determine if differences in numbers and densities of nitrate sources for the top 10 and bottom 10 counties were statistically significant (p < .05). These analyses were conducted to provide insight into the major factors associated with elevated concentrations of nitrate in groundwater.

Results

Correlations Between Average Nitrate Concentrations and Land-Use Characteristics

There were statistically significant (p < .05) correlations between the average nitrate concentrations in groundwater and various county land-use characteristics including farmland acreage (p < .001), total livestock (p < .001), human population (p = .003), number of poultry (p = .001), number of cattle (p = .007), number of septic systems (p = .038), and number of hogs (p = .049) (Table 1). The correlation coefficients were greatest for farmland acreage (r = .456), total livestock (r = .396), and poultry (r = .331) (Table 1). While there was a statistically significant correlation between the number of septic systems and average nitrate concentrations, the correlation coefficient was the smallest (r = .209) of the potential sources (Table 1).

There were statistically significant correlations between average nitrate concentrations and fraction of land in agriculture (p < .001), and densities of total livestock (p < .001), people (p = .002), poultry (p = .001), hogs (p < .001), cattle (p = .004), and septic systems (p = .047) (Table 2). The correlation coefficients (average nitrate concentration and density of potential sources) were greatest for fraction of land in agriculture (r = .486), hog density (r = .391), total livestock (r = .382), and poultry density (r = .328) (Table 2). Correlation coefficients were smallest for density of septic systems (r = .200) and density of cattle (r = .290) (Table 2).

Counties With Highest and Lowest Average Nitrate Concentrations in Groundwater

The 10 counties with the highest average concentrations of nitrate in groundwater included Cumberland, Edgecombe, Greene, Halifax, Northampton, Richmond, Robeson, Sampson, Wake, and Wayne (Table 3). The overall average groundwater nitrate concentration for these 10 counties was 3,429 [micro]g/L, with a range of 3,003-4,504 [micro]g/L (Table 3). The top 10 counties are clustered in the inner Coastal Plain and Sand Hills region of the state (Figure 1).

The 10 counties with the lowest average nitrate concentrations in groundwater were Beaufort, Camden, Chowan, Clay, Gates, Hyde, Jackson, Macon, Pasquotank, and Perquimans (Table 4). The overall average nitrate concentration for these counties was 510 [micro]g/L, with a range of 500-533 [micro]g/L (Table 4). Seven of these counties are clustered in the Tidewater region of the state, and the other three are clustered in the mountains (Figure 1). The difference in nitrate concentrations between the top 10 and bottom 10 counties was statistically significant (p = .0001).

There were more people (174,199 versus 22,943), septic systems (25,151 versus 9,101), hogs (338,500 versus 8,400), poultry (17,192,710 versus 2,108,540), and cattle (6,430 versus 1,111) in the 10 counties with the highest average nitrate concentrations relative to the 10 counties with the lowest nitrate concentrations (Tables 3 and 4). There was also more land area on average for the top 10 counties (168,551 ha) relative to the bottom 10 counties (130,772 ha), so we also compared densities (numbers/area) of potential sources of nitrate including septic systems, livestock, and fraction of the overall county land that was in agriculture. Similar findings were observed when normalizing the data for land area.

More specifically, there was a higher average fraction of land in agriculture (0.38 versus 0.23) and higher densities of septic systems (0.14/ha versus 0.08/ha), people (0.91/ ha versus 0.22/ha), hogs (1.92/ha versus 0.06/ha), poultry (99.4/ha versus 25.6/ha), and total livestock (101.5/ha versus 25.7/ ha) in the 10 counties with the highest average nitrate concentration (Tables 5 and 6). There were statistically significant differences regarding the fractions of land in agriculture (p = .036), along with density of hogs (p = .0049), poultry (p = .0299), cattle (p = .0257), total livestock (p = .0211), and people (p = .0140) when comparing the top 10 with the bottom 10. While the mean density of septic systems was higher in the top 10 versus bottom 10, the differences were not statistically significant (p = .1041).

Discussion

Agriculture and Groundwater Nitrate Concentrations

There are many potential sources of nitrate in groundwater sampled from water supply wells across North Carolina. Most of the data indicate that agricultural sources such as fertilizers and total livestock (waste) might be the most important contributors of nitrate to groundwater in North Carolina. There was on average 15% more land in agriculture and 75 more livestock/ha in the 10 counties with the highest average nitrate concentrations relative to the 10 counties with the lowest average nitrate concentrations. There were statistically significant (p [less than or equal to] .05) correlations between average nitrate concentrations and fraction of land in agriculture and total livestock densities; and the correlation coefficients were greatest for average nitrate concentration and fraction of land in agriculture, hog density, and total livestock density.

Four of the top 10 counties in North Carolina for hog production were in the top 10 for highest mean nitrate concentrations in groundwater. Those counties included Greene, Robeson, Sampson, and Wayne, which are all located in the Inner Coastal Plain of North Carolina. The total combined number of hogs produced each year by these counties was 2,970,000, which is nearly 40% of all hogs produced in the state (North Carolina Department of Agriculture and Consumer Services, 2016). Prior studies have shown that hog farms can be significant contributors of nitrogen to shallow groundwater (Stone et al., 1998) and surface waters (Mallin, McIver, Robuck, & Dickens, 2015).

The 10 counties with the highest mean concentrations of nitrate were all located in the Inner Coastal Plain or Sand Hills region, where the soils are characterized as permeable, well drained, and prone to nitrate leaching (Gilliam et al., 1996). Row crop and livestock production is extensive in the Inner Coastal Plain. Seven of the 10 counties with the lowest mean nitrate concentrations were in the Tidewater region of the state where row crop and livestock production are not as intensive as the Inner Coastal Plain and the soils have a high organic matter content, are poorly drained, and denitrification potential is high due to these conditions (Havlin et al., 1999).

Septic Systems and Groundwater Nitrate Concentrations

An estimated 4.87 million people in North Carolina were using septic systems in 2010, which was approximately 50% of the total population during that year. The percentage of population using septic systems varied greatly from county to county with a range of 10% to >90%. The last time the U.S. Census Bureau included information on septic system usage, 49% of the population in North Carolina used septic systems, so statewide, the percentage using septic systems has remained steady since 1990. While there were more septic systems and higher densities of septic systems in the 10 counties with the highest average nitrate concentrations, the differences were not statistically significant (p > .05). The correlations between average nitrate concentration and total number of septic systems and density of septic systems in North Carolina counties were significant, but they had the lowest correlation coefficients (r < .021) of the potential sources. Therefore, there was some evidence that septic systems were a contributing source of nitrate to groundwater, but the contributions were not as significant as agriculture.

Conclusions

The goal of this study was to gain a better understanding of how various land uses and nitrate sources might influence groundwater nitrate concentrations in North Carolina. Counties with extensive agricultural production located in geological settings where nitrate leaching potential is great, such as the Inner Coastal Plain, had the highest average concentrations of nitrate in groundwater. Counties with poorly drained, organic soils and less intensive agricultural and livestock production had the lowest average concentrations of nitrate in groundwater. Agriculture is a vital industry in North Carolina for the state's economy and for food production. Continued, substantial funding for the development and implementation of best management practices to reduce nitrogen loss from agricultural fields--especially in the Inner Coastal Plain of North Carolina--is needed to ensure a balance between the environment and economy.

Corresponding Author: Charles Humphrey, Associate Professor, Environmental Health Sciences Program, East Carolina University, 3408 Carol Belk, Greenville, NC 27858. E-mail: humphreyc@ecu.edu.

References

Conley, D.J., Paerl, H.W., Howarth, R.W., Boesch, D.F, Seitzinger, S.P., Havens, K.E., ... Likens, G.E. (2009). Controlling eutrophication: Nitrogen and phosphorus. Science, 323(5917), 1014-1015.

Del Rosario, K.L., Humphrey, C.P., Mitra, S., & O'Driscoll, M.A. (2014). Nitrogen and carbon dynamics beneath on-site wastewater treatment systems in Pitt County, North Carolina. Journal of Water Science and Technology, 69(3), 663-671.

Dodds, W.K., Bouska, W.W., Eitzmann, J.L., Pilger, TJ., Pitts, K.L., Riley, A.J., ... Thornbrugh, D.J. (2009). Eutrophication of U.S. freshwaters: Analysis of potential economic damages. Environmental Science & Technology, 43(1), 12-19.

Gao, Y., Kennish, M.J., & McGuirk Flynn, A. (2007). Atmospheric nitrogen deposition to the New Jersey Coastal Waters and its implications. Ecological Applications, 17(5), S31-S41.

Gilliam, J.W., Huffman, R.L., Daniels, R.B., Buffington, D.E., Morey, A.E., & Leclerc, S.A. (1996). Contamination of surficial aquifers with nitrogen applied to agricultural land (WRRI Project No. 70114). Retrieved from https://repository.lib.ncsu.edu/bitstream/handle/ 1840.4/1868/NC-WRRI-306.pdf?sequence=1&isAllowed=y

Goldberg, VM. (1989). Groundwater pollution by nitrates from livestock wastes. Environmental Health Perspectives, 83, 25-29.

Havlin, J.L., Beaton, J.D., Tisdale, S.L., & Nelson, W.R. (1999). Soil fertility and fertilizers: An introduction to nutrient management (6th ed., pp. 1-7, 86-153). Upper Saddle River, NJ: Prentice Hall.

Huang, H., Yang, J., & Ling, D. (2014). Recovery and removal of ammonia-nitrogen and phosphate from swine wastewater by internal recycling of struvite chlorination product. Bioresource Technology, 172, 253-259.

Humphrey, C.P., Jr., O'Driscoll, M.A., Deal, N.E., Lindbo, D.L., Thieme, S.C., & Zarate-Bermudez, M.A. (2013). Onsite wastewater system nitrogen contributions to groundwater in Coastal North Carolina. Journal of Environmental Health, 76(5), 16-22.

Humphrey, C.P., Jr., O'Driscoll, M.A., & Zarate, M.A. (2010). Controls on groundwater nitrogen contributions from on-site wastewater systems in coastal North Carolina. Water Science and Technology, 62(6), 1448-1455.

Iverson, G., O'Driscoll, M.A., Humphrey, C.P., Jr., Manda, A.K., & Anderson-Evans, E. (2015). Wastewater nitrogen contributions to Coastal Plain watersheds, NC, USA. Water, Air, and Soil Pollution, 226(10), 325.

Mallin, M.A., McIver, M.R., Robuck, A.R., & Dickens, A.K. (2015). Industrial swine and poultry production causes chronic nutrient and fecal microbial stream pollution. Water, Air, and Soil Pollution, 226, 407.

Meyer, R.F (2014, April 17). Understanding nitrates in our water. The Burlington Record. Retrieved from http://www.burlington-record. com/letters/ci_25585509/understanding-nitrates-our-water

North Carolina Department of Agriculture and Consumer Services. (2016). Agricultural statistics. Retrieved from http://www.ncagr. gov/stats/index.htm

North Carolina Department of Environmental Quality, (n.d.). Nutrient sensitive waters and special watersheds. Retrieved from https:// deq.nc.gov/about/divisions/energy-mineral-land-resources/ nsw-special-watersheds

North Carolina Department of Environmental Quality. (2015). Algal blooms, fish kills occurring across portions of the state. Retrieved from https://deq.nc.gov/press-release/algal-blooms-fish-killsoccurring-across-portions-state

North Carolina Department of Health and Human Services. (2016). Well water and health. Retrieved from http://epi.publichealth. nc.gov/oee/wellwater/figures.html

North Carolina Department of Health and Human Services. (2018). On-site water protection branch: On-site wastewater treatment and dispersal systems program resources. Retrieved from http://ehs. ncpublichealth.com/oswp/resources.htm

North Carolina State Extension, College of Agriculture and Life Sciences, North Carolina State University. (2017). 2018 North Carolina agricultural chemicals manual. Retrieved from https://content. ces.ncsu.edu/north-carolina-agricultural-chemicals-manual

Osmond, D.L., Hodges, S.C., Kleiss, H.J., Creamer, N.G., Crozier, C.R., Cubeta, D.H., ... Weisz, R. (2003). Tar-Pamlico River Basin nutrient management education [slide set]. Raleigh, NC: North Carolina Cooperative Extension Service, North Carolina State University.

Osmond, D.L., & Kang, J. (2008). Nutrient removal by crops in North Carolina (AG-439-16W). Soil facts. Retrieved from https://con tent.ces.ncsu.edu/nutrient-removal-by-crops-in-north-carolina

Pradhan, S.S., Hoover, M.T., Austin, R.E., & Devine, H.A. (2007). Potential nitrogen contributions from on-site wastewater treatment systems to North Carolina's river basins and sub-basins. North Carolina Agricultural Research Service Technical Bulletin, 324. Retrieved from www.soil.ncsu.edu/publications/TB324Final may29.pdf

Smith, VH., & Schindler, D.W. (2009). Eutrophication science: Where do we go from here? Trends in Ecology & Evolution, 24(4), 201-207.

State Climate Office of North Carolina. (2017). North Carolina climate office: General synopsis. Retrieved from http://climate.ncsu. edu/climate/synopsis

Stone, K.C., Hunt, P.G., Humenik, FJ., & Johnson, M.H. (1998). Impact of swine waste application on ground and stream water quality in an Eastern Coastal Plain watershed. Transactions of the American Society of Agricultural Engineers (ASAE), 41(6), 1665-1670.

U.S. Census Bureau. (1990). 1990 census data. Retrieved from http:// www.census.gov/main/www/cen1990.html

U.S. Census Bureau. (2010). 2010 census data. Retrieved from http:// www.census.gov/2010census/data

U.S. Environmental Protection Agency. (2002). Onsite wastewater treatment systems manual (EPA/625/R-00/008). Washington, DC: Office of Water, Office of Research and Development. Retrieved from https:// nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=30004GXI.TXT

U.S. Environmental Protection Agency. (2009). National primary drinking water regulations (EPA-816-F-09-004). Washington, DC: Author. Retrieved from http://www.nrc.gov/docs/ML1307/ ML13078A040.pdf

Ward, M.H., deKok, T.M., Levallois, P, Brender, J., Gulis, G., Nolan, B.T., & VanDerslice, J. (2005). Workgroup report: Drinking-water nitrate and health--Recent findings and research needs. Environmental Health Perspectives, 113(11), 1607-1614.

Whitall, D.R., & Paerl, H.W. (2001). Spatiotemporal variability of wet atmospheric nitrogen deposition to the Neuse River Estuary, North Carolina. Journal of Environmental Quality, 30(5), 1508-1515.

Emily Naylor, MSEH, REHS

Stokes County Environmental Health

Charles Humphrey, PhD, REHS

Tim Kelley, PhD

Environmental Health Sciences Program

East Carolina University

Leslie Easter, REHS

Stokes County Environmental Health

Guy Iverson, MS

Coastal Resources

Management Program

East Carolina University

Caption: FIGURE 1 Map of North Carolina Showing Counties With the Highest and Lowest Average Nitrate Concentrations
TABLE 1

Correlations Between Total Number of Potential Sources of Nitrate
and Average Nitrate Concentrations in Groundwater in North
Carolina Counties

Total Number of Sources and           Correlation   p-Value
Average Nitrate Concentrations        Coefficient

Farmland (ha) and average nitrate        .456        <.001
Total livestock and average nitrate      .396        <.001
Poultry and average nitrate              .331        .001
Hogs and average nitrate                 .322        .049
Total people and average nitrate         .300        .003
Cattle and average nitrate               .276        .007
Septic systems and average nitrate       .209        .038

ha = hectares.

TABLE 2

Correlations Between Density of Potential Sources of Nitrate
and Average Nitrate Concentrations in Groundwater in North
Carolina Counties

Density of Source and Average Nitrate      Correlation   p-Value
Concentration                              Coefficient

Fraction agriculture and average nitrate      .486        <.001
Hogs/ha and average nitrate                   .391        <.001
Total livestock/ha and average nitrate        .382        <.001
Poultry/ha and average nitrate                .328        .001
People/ha and average nitrate                 .306        .002
Cattle/ha and average nitrate                 .290        .004
Septic systems/ha and average nitrate         .200        .047

ha = hectares.

TABLE 3

Characteristics of the 10 North Carolina Counties With the Highest
Average Nitrate Concentrations in Groundwater

County        Total County   2010 Census     Average      Septic
               Area (ha)     Population    N[O.sub.3]-N   Systems
                                           ([micro]g/L)

Cumberland      170,494        319,431        3,003       48,233
Edgecombe       131,368        56,552         3,284       10,315
Greene           68,923        21,362         3,196        6,566
Halifax         189,409        54,691         3,214       13,101
Northampton     142,769        22,099         3,520        8,153
Richmond        124,372        46,639         3,397       14,374
Robeson         246,413        134,168        3,909       32,636
Sampson         245,377        63,431         3,134       22,979
Wake            222,057        900,993        4,504       64,106
Wayne           144,324        122,623        3,227       31,052
Average         168,551        174,199        3,439       25,151
SD               60,338        285,873         471        20,071

County         Cattle        Hog       Poultry       Total
              Estimates   Estimates   Estimates    Livestock

Cumberland      2,900      95,000     2,645,000    2,742,900
Edgecombe       2,000      110,000    6,650,000     676,200
Greene          1,400      340,000    4,750,000    5,091,400
Halifax         9,500      45,000         0          54,500
Northampton      900       115,000    9,200,000    9,315,900
Richmond        1,800      50,000     34,910,000   34,961,800
Robeson         8,000      350,000    48,586,900   48,944,900
Sampson        26,000     1,750,000   47,185,000   48,961,000
Wake            3,500         0         9,200        12,700
Wayne           8,300      530,000    17,991,000   18,529,300
Average         6,430      338,500    17,192,710   17,537,640
SD              8,004      551,567    20,406,235   20,759,407

ha = hectares.

TABLE 4

Characteristics of the 10 North Carolina Counties With the Lowest
Average Nitrate Concentrations in Groundwater

County       Total County   2010 Census     Average      Septic
              Area (ha)     Population    N[O.sub.3]-N   Systems
                                          ([micro]g/L)

Beaufort       248,485        47,759          517        19,206
Camden          79,287         9,980          500         3,391
Chowan          60,372        14,793          500         4,504
Clay            57,263        10,587          533         5,510
Gates           89,652        12,197          500         4,416
Hyde           368,972         5,810          500         3,819
Jackson        128,000        40,271          526        17,006
Macon          115,563        33,922          520        20,937
Pasquotank      74,883        40,661          500         7,563
Perquimans      85,247        13,453          500         4,658
Average        130,772        22,943          510         9,101
SD             105,136        16,343           14         7,257

County        Cattle        Hog       Poultry       Total
             Estimates   Estimates   Estimates    Livestock

Beaufort       1,200      50,000         0          51,200
Camden          100          0           0           100
Chowan         1,200       4,000         0          5,200
Clay           1,700         0       2,550,000    2,551,700
Gates           800       30,000     7,850,000    7,880,800
Hyde            ND           0        180,000      180,000
Jackson        1,600         0         4,200        5,800
Macon          2,400         0         1,200        3,600
Pasquotank      300          0           0           300
Perquimans      700          0       10,500,000   10,500,700
Average        1,111       8,400     2,108,540    2,117,940
SD              758       18,138     2,638,829    2,645,344

ha = hectares; ND = no data, if data were not reported for a county.

TABLE 5

Characteristics and Densities of Potential Nitrate Sources for the 10
North Carolina Counties With the Highest Average Nitrate
Concentrations in Groundwater

County         Fraction     Systems/ha   People/ha   Hogs/ha
              Agriculture

Cumberland       0.20          0.28        1.87       0.56
Edgecombe        0.39          0.08        0.43         0
Greene           0.59          0.10        0.31       4.93
Halifax          0.42          0.07        0.29       0.24
Northampton      0.46          0.06        0.15       0.81
Richmond         0.15          0.12        0.37       0.40
Robeson          0.44          0.13        0.54       1.42
Sampson          0.48          0.09        0.26       7.13
Wake             0.15          0.29        4.06         0
Wayne            0.54          0.22        0.85       3.67
Average          0.38          0.14        0.91       1.92
SD               0.16          0.09        1.29       2.54

County        Poultry/ha   Cattle/ha   Livestock/ha

Cumberland      15.50        0.02          16.0
Edgecombe       50.60        0.01          51.5
Greene          68.90        0.02          73.9
Halifax         <0.01        0.05          0.3
Northampton     64.40        0.01          65.3
Richmond        280.70       0.01         281.1
Robeson         197.20       0.03         198.6
Sampson         192.30       0.11         199.5
Wake             0.04        0.02          0.1
Wayne           124.70       0.06         128.4
Average         99.40        0.03         101.5
SD              101.40       0.03         102.2

ha = hectares.

TABLE 6

Characteristics and Densities of Potential Nitrate Sources for
the 10 North Carolina Counties With the Lowest Average Nitrate
Concentrations in Groundwater

County         Fraction     Systems/ha   People/ha   Hogs/ha
              Agriculture

Beaufort         0.24          0.08        0.19       0.20
Camden           0.25          0.04        0.13       <0.01
Chowan           0.39          0.07        0.25       0.07
Clay             0.08          0.10        0.18       <0.01
Gates            0.29          0.05        0.14       0.33
Hyde             0.12          0.01        0.02       <0.01
Jackson          0.05          0.13        0.31       <0.01
Macon            0.08          0.18        0.29       <0.01
Pasquotank       0.39          0.10        0.54       <0.01
Perquimans       0.38          0.05        0.16       <0.01
Average          0.23          0.08        0.22       0.06
SD               0.13          0.05        0.15       0.12

County        Poultry/ha   Cattle/ha   Livestock/ha

Beaufort        <0.01        0.01          0.21
Camden          <0.01        <0.01        <0.01
Chowan          <0.01        0.02          0.09
Clay            44.50        0.03         44.56
Gates           87.60        0.01         87.90
Hyde             0.50        <0.01         0.50
Jackson          0.03        0.01          0.05
Macon            0.01        0.02          0.03
Pasquotank      <0.01        <0.01        <0.01
Perquimans      123.17       0.01         123.18
Average         25.60        0.01         25.70
SD              31.00        0.01         31.10

ha = hectares.
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Title Annotation:ADVANCEMENT OF THE SCIENCE
Author:Naylor, Emily; Humphrey, Charles; Easter, Leslie; Iverson, Guy
Publication:Journal of Environmental Health
Date:May 1, 2018
Words:5450
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