Factors Affecting Nitrogen and Phosphorus Loads in Nutrient-Sensitive Water of Eastern North Carolina

Science Center Objects

Data collected between 1997 and 2008 at 48 stream sites were used to characterize relations between watershed settings and stream nutrient yields throughout central and eastern North Carolina. The focus of the investigation was to identify environmental variables in watersheds that influence nutrient export for supporting the development and prioritization of management strategies for restoring nutrient-impaired streams.

The proposed work will include computation of nutrient (total nitrogen, total nitrate, and total phosphorus) loads in various streams throughout eastern North Carolina. Most stream sites selected for study are located in the Tar-Pamlico River basin, Neuse River Basin, and Cape Fear River basin; a few sites from the Lumber, Chowan, and Roanoke River basins also will be included (map and data table). Statistical analyses will be conducted to examine the influence of particular watershed variables on total nitrogen, total nitrate, and total phosphorus loads at the study locations. The intent of the data analysis is to determine which variables may be a useful indicator for identifying watersheds in NSW with a high potential for exporting nutrients.

The stream sites selected for study, based on existing USGS streamflow gages and available nutrient data, will include locations in both the Piedmont and Coastal Plain Provinces. Available streamflow data from the USGS database and water-quality data from NCDENR and USGS databases will be compiled and processed for use in computing loads at each site. Information on land use cover, density of riparian buffers, streamflow characteristics, groundwater discharge, point sources, and nonpoint sources will be compiled for each watershed. Statistical analyses will be performed to determine which environmental variables may significantly influence total nitrogen, total nitrate, and total phosphorus export in the watersheds selected for study.


The following tasks will be performed to meet the project objectives.

Task 1: Develop list of stream sites for potential evaluation

Potential stream study sites will be based on those that have both a USGS continuous streamflow gage and also are sampled through the NCDENR DWQ ambient water-quality program or USGS project activities. The focus will be on active USGS and NC DWQ stream sites that have sufficient data during the past 5 to 10 years for use in determining streamflow characteristics, percent base flows, and nutrient loadings. A list of potential sites to be included in the study is presented in table 1.

Task 2: Compile and process streamflow data

For each study site selected in Task 1, stream-flow data for the 5-10 year study period will be compiled from the USGS National Water Information System (NWIS) database and processed to determine annual streamflow characteristics for use in statistical correlations with nutrient loadings. Hydrograph separations will be performed on the data to determine the amount of base flow, or percent contribution of the annual stream flow derived from groundwater discharge.

Task 3: Compile and process water-quality data

DWQ will provide nutrient data for each of the ambient monitoring stations paired with a USGS stream-gage site. Monthly water-quality data for the past 5 to 10 years will be combined with the streamflow data (task 2) to compute total nitrogen, total nitrate, and total phosphorus loads at each stream study site. At selected sites, part of the analysis will be to determine if the total in-stream nutrient loads can be separated into that derived from both baseflow (groundwater discharge) and from overland runoff.

Task 4: Compile watershed characteristics

Geographic Information System (GIS) information will be used to determine the types and extent of land use, based on 2001 data, within the drainage area of each stream study site. The density of riparian buffers bounding the streams in each study area also will be determined using GIS methods. The numbers and types of point sources (such as waste-water treatment plant discharges) and nonpoint sources (such as livestock feeding operations) will be compiled for each watershed and incorporated in the GIS datasets. These watershed variables will be used in statistical correlations with the stream nutrient loads to better understand those factors that most significantly influence nutrient export in NSW of eastern North Carolina.

Task 5: Statistical data analysis

All data (tasks 2-4) will be compiled into a database for processing and analysis. The streamflow and watershed data (tasks 2 and 4) will be compared statistically to the nutrient load data (task 3) to determine if there are similarities or differences in loadings based on such things as basin size (drainage area), stream runoff, groundwater discharge, land cover, point sources (such as waste-water treatment plant discharges), and nonpoint sources (such as types and amounts of animal production facilities). Results of the statistical analyses will be used to determine which watershed variables may be useful indicators of watershed potential for exporting or retaining nutrients.

Task 6: Prepare final report describing study results

The USGS will work in collaboration with NCDENR to complete a USGS Scientific Investigations Report that presents and discusses the study results and findings. The focus of the report will be to document the watershed characteristics and nutrient loadings for each streamflow and water-quality monitoring site and to discuss the results of the statistical evaluation of the factors that may influence nutrient loads from the watersheds.


Map of major river basins in North Carolina

Map of major river basins in North Carolina

USGS streamgage sites  DWQ ambient water-quality monitoring sites 
USGS Site #USGS Station nameDrainage area (mi2)DWQ Site #DWQ Station name
Tar Pamlico River Basin    
2081500Tar R nr Tar R, NC167O0100000Tar R at NC96 nr Tar River
2083000Fishing Ck nr Enfield, NC526O4680000Fishing Crk at US301 nr Enfield
2083500Tar R at Tarboro, NC2183O5250000Tar R at NC33 and US64 Bus at Tarboro
2084160Chicod Cr at SR1760 nr Simpson, NC45O6450000Chicod Crk at SR1760 nr Simpson
2084557Van Swamp nr Hoke, NC23O9755000Van Swamp at NC32 nr Hoke
Neuse River Basin    
208521324Little R at SR1461 nr Orange Factory, NC78.2J0820000Little R at SR1461 nr Orange Factory
2085000Eno R at Hillsborough, NC66  
2085070Eno R nr Durham, NC141J0770000Eno R at US501 nr Durham
208524090Mountain Crk at SR1617 nr Bahama, NC8  
208524975Little R below Little R Trib at Fairntosh, NC98.9  
208650112Flat R Trib nr Willardville, NC1.14  
2085500Flat R at Bahama, NC149  
2086500Flat R at dam nr Bahama, NC168J1100000Flat R at SR1004 nr Willardsville
2087580Swift Crk nr Apex, NC21J4414000Swift Crk at SR1152 Holly Springs Rd nr Macedonia
208726005Crabtree Crk at Ebenezer Church Rd nr Raleigh, NC76J3000000Crabtree Crk at SR1649 nr Raleigh
2087183Neuse R nr Falls, NC771J1890000Neuse R at SR2000 nr Falls
2089000Neuse R nr Goldsboro, NC2,399.00J5970000Neuse R at SR1915 nr Goldsboro
208925200Bear Crk at Mays Store Rd, NC57.7J6044500Bear Crk at SR1311 Bear Creek Rd nr Kinston
2089500Neuse R at Kinston, NC2,692.00J6150000Neuse R at NC11 at Kinston
2091814Neuse R nr Fort Barnwell, NC3,900.00J7850000Neuse R at SR1470 nr Fort Barnwell
2090380Contentnea Crk nr Lucama, NC161J6740000Contentnea Crk at NC581 nr Lucama
2091500Contentnea Crk at Hookerton, NC733J7450000Contentnea Crk at NC123 at Hookerton
2092500Trent R nr Trenton, NC168J8690000Trent R at SR1129 nr Trenton
Cape Fear River Basin    
2095000South Buffalo Crk nr Greensboro, NC34B0670000S Buffalo Crk at SR3000 McConnell Rd nr Greensboro
2095500North Buffalo Crk nr Greensboro, NC37.1B0540000N Buffal Crk at SR2832 nr Greensboro
209553650Buffalo Crk at SR2819 nr McLeansville, NC88.5B0540050N Buffalo Crk at SR2770 Hufine Mill Rd nr McLeansville
2094500Reedy Fork nr Gibsonville, NC131B0400000Reedy Fork at SR 2719 High Rock Rd nr Monticello
2096500Haw R at Haw River, NC606B1140000Haw R at NC 49N at Haw River
2096846Cane Crk nr Orange Grove, NC7.54  
2096960Haw R nr Bynum, NC1275B2100000Haw R at SR1713 nr Bynum
2097464Morgan Crk nr White Cross, NC8.35  
2097517Morgan Crk nr Chapel Hill, NC41B3899180Morgan Crk at Mason Farm WWTP entrance at Chapel Hill
2097314New Hope Crk nr Blands, NC75.9B3040000New Hope Crk at SR1107 nr Blands
209741955Northeast Crk at SR1100 nr Genlee, NC21.1B3660000Northeast Crk at SR1100 nr Nelson
209782609White Oak Crk at mouth nr Green Level, NC11.9  
2099000East Fort Deep R nr High Point, NC14.8B4240000E Fork Deep R at SR1541 nr High Point
2104220Rockfish Crk at Raeford, NC93.1B7679300Rockfish Creek at US 401 bypass near Raeford
2102500Cape Fear R at Lillington, NC3464B6370000Cape Fear R at US401 at Lillington
2105769Cape Fear R at lock 1 nr Kelly, NC5255B8350000Cape Fear R at Lock 1 nr Kelly
2106500Black R nr Tomahawk, NC676B8750000Black R at NC411 nr Tomahawk
2093000New R nr Gum Branch, NC94P0600000New R at SR1314 nr Gum Branch
Lumber River Basin    
2133500Drowning Crk nr Hoffman, NC183I2090000Drowning Crk at US1 nr Hoffman
2133624Lumber R nr Maxton, NC365I2750000Lumber R at SR1303 nr Maxton
2134500Lumber R at Boardman, NC1228I5690000Lumber R at US74 at Boardman
2109500Waccamaw R at Freeland, NC680I8970000Waccamaw R at NC130 at Freeland
Chowan River Basin    
2053200Potecasi Crk nr Union, NC225D4150000Potecasi Crk at NC11 nr Union
Roanoke River Basin    
2071000Dan R nr Wentworth, NC1053N2300000Dan R at SR2150 nr Wentworth
2068500Dan R nr Francisco, NC129N0150000Dan R at NC704 nr Francisco