The Neuse River Estuary receives nutrient inputs from a large watershed that includes urban areas as well as agriculture and hog operations. The Neuse River Estuary is naturally divided into three segments: upper tidal river, middle segment, and lower estuary. The middle segment and the lower estuary are divided by a nearly 90-degree bend. River processes dominate the middle segment, and the Pamlico Sound dominates the lower estuary. A near 90-degree bend in the estuary divides it into a distinct morphometry that interacts with river discharge and wind events to dominate circulation. That configuration creates flushing times ranging from weeks to months. Nutrients are highest in the tidal upper segments and are typically processed in the middle segment.
Vertical stratification occurs in the main channel from spring through fall because of low tidal amplitude, and bottom water hypoxia typically occurs in the middle and lower estuary segments during the summer. Storms can enhance physical mixing in the middle and lower segments and move hypoxic bottom waters from the central channel into shallow areas, affecting fauna in those areas.
Light attenuation is most severe in the upper segment resulting from colored dissolved organic matter (CDOM), suspended sediment, and planktonic algal biomass. Water clarity increases in the lower estuary. Primary production is highest in the upper and middle segments and decreases in the lower estuary. Blooms occur in all segments of the estuary at various times of the year. Diatoms account for about 20 percent of the total phytoplankton community biomass, but do not form extensive blooms. During elevated freshwater discharge, fast-growing chlorophytes form extensive blooms throughout the estuary. Cyanobacteria are most dominant during slow-flow, long resident time summer months. The Neuse River Estuary is historically devoid of submerged aquatic vegetation because of severely restricted light penetration.
Water quality stations established by various research groups are located throughout the Neuse River Estuary and are used to collect nutrient, Secchi disk, temperature, DO, and other data. The data are used to examine spatial and temporal trends and relationships among parameters such as how nitrate and chlorophyll levels change over the salinity gradient.
Because of successful implementation of phosphorus controls in the Neuse River watershed—including limits for municipal and industrial discharges and a phosphate detergent ban—there has been a threefold decrease in phosphorus concentrations in the estuary. The second phase of nutrient control mandates a 30-percent reduction of TN loading from the 1991–1995 average loading to further reduce the frequency and intensity of estuarine algal blooms (National Estuarine Experts Workgroup 2010).
Reference:
National Estuarine Experts Workgroup. 2010. Nutrients in Estuaries: A Summary Report of the National Estuarine Experts Workgroup 2005–2007. U.S. Environmental Protection Agency. Accessed October 2016. https://www.epa.gov/sites/production/files/documents/nutrients-in-estuaries-november-2010.pdf.