Final Report: CISNet for the Neuse River Estuary, NC: A Program for Evaluating Nitrogen Driven Eutrophication Associated with Changing Land Use in a Coastal Watershed

EPA Grant Number: R826938
Title: CISNet for the Neuse River Estuary, NC: A Program for Evaluating Nitrogen Driven Eutrophication Associated with Changing Land Use in a Coastal Watershed
Investigators: Luettich Jr., Richard A. , Paerl, Hans , Pinckney, Jay
Institution: University of North Carolina at Chapel Hill
EPA Project Officer: Hahn, Intaek
Project Period: October 1, 1998 through September 30, 2001
Project Amount: $555,300
RFA: Ecological Effects of Environmental Stressors Using Coastal Intensive Sites (1998) RFA Text |  Recipients Lists
Research Category: Environmental Statistics , Water Quality , Ecosystems , Ecological Indicators/Assessment/Restoration

Objective:

During the past two decades, the Neuse River Estuary (NRE) has been plagued with nuisance algal blooms, hypoxia, toxicity, and fishkills associated with declining water quality. Increased nitrogen (N) loading associated with human population growth and land use change has been implicated as a principal cause. However, assessment of water quality and its determinants in the NRE is considerably complicated by the need to distinguish long-term trends from the effects of interannual variability and extreme events (e.g., hurricanes). A data archive that spans long time periods (e.g., years to decades) will be required to resolve the many cause and effect relationships determining water quality in a system such as the NRE. The overall objective of the UNC-CH Coastal Intensive Sites Network (CISNet) project was to build on the historical water quality data set in the NRE, and to enhance and expand the ongoing monitoring and process-based research being conducted there. The specific components of this research project were to: (1) monitor water quality; (2) determine atmospheric N loading; (3) identifiy significant N loading from a large coastal farm; (4) monitor circulation and physical properties; and (5) provide data management, archiving, and integration.

Summary/Accomplishments (Outputs/Outcomes):

Monitoring of Water Quality Parameters

CISNet funding allowed us to maintain and expand the water quality monitoring program initiated in 1994 in the NRE. UNC-CH Institute of Marine Sciences (IMS) personnel visited 19 midestuary stations along the NRE at biweekly intervals. Water column profiles of temperature, salinity, irradiance, pH, and dissolved oxygen (DO) were determined at each station. Dissolved nutrients (nitrate, nitrite, ammonium, silicate, ortho-phosphate), particulate carbon and nitrogen, photopigments, and primary productivity were measured in near-surface and near-bottom samples at 11 midchannel stations, a station near the mouth of South River, and two near-shore stations.

Partial results from this monitoring were posted within a day of their collection on our project's Web Site (http://www.marine.unc.edu/neuse/modmon Exit ) as a near-real-time indication of conditions in the system. This information routinely has been accessed by individuals in the North Carolina Department of Environment and Natural Resources (DENR) Division of Water Quality, and used to help assess the short-term potential for fishkills in the NRE (due to the presence of large areas of low-oxygen water), and to help make decisions regarding health advisories for recreational users of the NRE (due to low oxygen or potential contamination from freshwater runoff).

Winter/Spring 1998 and Fall 1999 were periods of high freshwater discharge, and showed up in the estuary as times of anomalously low salinity. Conversely, the low discharge first 8 months of 1999 and all of 2001 were periods of high salinity. DO exhibited a characteristic depletion in the near-bottom waters each year during the warm summer months when stratification was present. This depletion was mildest during the Summer of 1998, which followed the very high discharge winter/spring of that year. Although the high spring discharge supplied additional N to the system, salinity stratification was relatively weak during the summer and therefore vertical mixing may have been more effective at transporting oxygen to the near-bottom waters than in other years. Salinity and DO levels in the Summer of 2000 were reasonably normal, suggesting that the system had physically recovered from the extreme discharge associated with the fall 1999 hurricanes. NOx levels appeared to be directly correlated with discharge, presumably because nutrient loading was higher and flushing time was shorter under high discharge conditions. Low discharge and consequently low flushing rates allowed concentrations to drop substantially (due to extended time for biological uptake), as water traveled down the NRE.

Ammonium and phosphate concentrations were closely related to DO levels, suggesting that these largely reflected internal generation of NH4 and PO4. Algal biomass (Chl-a) sporadically exceeded the impaired use level of 40 µg/L in the NRE. Often, blooms occurred in the winter/spring time period. The wet and high N supply Spring of 1998 did not appear to result in significant algal blooms in the NRE during the summer of that year. Conversely, the largest and most persistent blooms occurred in the winter/spring following the hurricanes of 1999. Thus, it appears that fall/early winter N supply may elicit a more significant gross algal biomass response than winter/spring supply. Diagnostic photopigment analysis used to identify phytoplankton functional groups (i.e., diatoms, dinoflagellates, chlorophytes, cyanobacteria, cryptomonads) indicated that seasonal and/or hurricane-induced variations in river discharge, and the resulting changes in flushing rates, may have differentially affected phytoplankton taxonomic groups as a function of their contrasting growth characteristics. For instance, the relative contribution of chlorophytes, cryptophytes, and diatoms to the total Chl-a pool was enhanced by periods of elevated river flow. We hypothesize that these effects are due to the efficient growth rates and enhanced nutrient uptake rates of these groups. Cyanobacteria, however, demonstrated greater relative biomass when flushing was minimal and residence times were longer. These changes in phytoplankton community structure may have altered trophodynamics and nutrient cycling in the NRE during these years.

Determination of Atmospheric N Loading

Our best estimate is that wet deposition of N, as NH4+, NO3-, and organic N contributes 20 percent (range of 15-51 percent) of the "new" N flux to the NRE. From July 1996 to July 2000, the weekly wet deposition of NH4+, NO3- and dissolved organic N indicate that the annual mean total wet atmospherically deposited (AD)-N flux was 11 kg ha-1 yr-1. Seasonally, the summer (June-August) months contained the highest weekly wet total N deposition; this trend was not driven by precipitation amount. Dry depositional flux (not measured) may double the contribution of AD-N to the system. AD-N is an important source of new N to the NRE as well as other estuarine and coastal ecosystems downwind of major emission sources.

Identification of Significant N Loading From a Large Coastal Farm

A comparison of nutrient concentrations at the mouth of South River and the closest midriver sampling station suggested minimal chronic nutrient loading to the NRE from the large farm that drains into the South River. However, on a few occasions, high nutrient levels were recorded at the mouth of the South River, indicating that episodic events may flush nutrients from the farm into the NRE.

Monitoring of Circulation and Physical Properties

At synoptic timescales (several days and longer), circulation in the NRE is controlled by remote wind forcing over Pamlico Sound. Winds directed toward the northeast drive water from the lower NRE into Pamlico Sound and therefore enhance downstream water flow. Winds directed toward the southwest drive water from Pamlico Sound into the lower NRE. Depending on the strength of this forcing, the flow may completely arrest or reverse freshwater runoff in the estuary. At shorter timescales, the predominant energy in the velocity signal occurs at a roughly semidiurnal frequency. This is due to a wind excited seiche in Pamlico Sound, and not a semidiurnal astronomical tide. Eighty percent of observed hydrographic profiles exhibited bottom hypoxia when the top to bottom salinity difference exceeded 5 psu, and the water temperature exceeded 20°C. A general method was developed to estimate the lateral extent of low-DO bottom water from midchannel hydrographic profiles.

Seasonally averaged salinity values (1997-2000) varied from highest to lowest in the sequence summer, fall, winter, and spring. Seasonally averaged bottom DO values varied from lowest to highest following the sequence summer, fall, spring, and winter. In the summer and winter, salinity stratification increased rapidly from the estuary head to approximately 24 km downstream, where the estuary widens considerably. Beyond this point, salinity stratification decreased slightly but remained near 3 psu. The relationship between stratification and downstream distance was not as clear during the fall and spring. Approximately 35 km downstream summertime, cross-sectional salinity and velocity fields show mean isohaline surfaces that slope downward from the north side of the estuary to the south side of the estuary, and mean along channel flow that is directed upstream near the north shore and downstream near the south shore throughout much of the water column. Near the middle of the cross section, velocity typically is more estuarine with downstream flow at the surface and upstream flow at the bottom. Similar trends in across channel salinity structure and along channel flow exist during all seasons.

A seasonal DO balance was constructed for the bottom waters for the section of the NRE upstream of the bend, where hypoxic conditions and fishkills often are the worst. This effort indicated a primary balance between the rate of local biological consumption/production and the vertical exchange rate. On a seasonal timescale, vertical exchange may be due in part to the two-way turbulence process characteristic of partially mixed estuaries, and due to wind-driven lateral upwelling.

During 1999-2000, autonomous profiling platforms, bottom-mounted Acoustic Doppler current profilers (ADCPs), and bottom-mounted conductivity, temperature, and water depth (CTD) instruments were deployed near the north and south shores of the NRE at station 95. The autonomous profiling platforms were developed as a part of this CISNet project and move a water quality probe vertically through the water column at preprogrammed intervals. Therefore, they are able to collect high resolution information about the hydrographic and water quality structure of the water column over extended periods of time. Data from these instruments clearly identify wind-driven lateral advection of saline, and low DO waters at synoptic and diurnal timescales. Winds blowing southward move fresher, high DO surface water towards the south shore, where it reduces south shore bottom salinity and increases the DO concentration. To compensate for this, saltier, low DO bottom water is moved towards the north, where it upwells near the north shore. The opposite motion occurs for winds blowing northward. We believe that this is a plausible causal mechanism for many of the fishkills that occur in this section of the NRE. The frequent upwelling and downwelling also offer a mechanism for mixing salt, DO, and other dissolved constituents between the upper and lower layers.

Systematic Management, Archival, and Integration of Data From all Ongoing NRE Research

All mid-estuary water quality data are stored in spreadsheets (Microsoft Excel). These data sets also include water quality information gathered by our companion groups at the North Carolina Department of Water Quality (NCDWQ) and Weyerhauser, Inc. The integration of IMS data with NCDWQ and Weyerhauser provides a weekly snapshot of water quality in the NRE. Data from 1994-2001 are available electronically and on compact disc (CD) from IMS, and graphical summaries of the hydrographic data can be found at the Web Site, http://www.marine.unc.edu/neuse/modmon Exit . Included on the CD are specifics on sampling locations, frequencies, and field and laboratory protocols for these three groups monitoring water quality in the NRE.

The integrated water quality data set has become the backbone of water quality modeling efforts in support of the State of North Carolina's effort to set a total maximum daily load (TMDL) on total N for the NRE. Three coordinated but independent modeling studies led by Dr. Jim Bowen at UNC-Charlotte (applying a 2-dimensional laterally averaged mechanistic water quality model), Mr. Tim Wool at the U.S. Environmental Protection Agency (EPA) Region 4 in Athens, GA (applying a 3-dimensional mechanistic water quality model) and Dr. Ken Reckhow at Duke University (applying a Bayesian probabilistic water quality model), were calibrated and verified using this data. These models were used to predict the N loading reduction required for the NRE to meet established Chl-a-based water quality standards. Managers in the NC DENR Division of Water Quality used this information to set a TMDL for total N during 2001.


Journal Articles on this Report : 17 Displayed | Download in RIS Format

Other project views: All 82 publications 21 publications in selected types All 19 journal articles
Type Citation Project Document Sources
Journal Article Borsuk ME, Stow CA, Luettich Jr. RA, Paerl HW, Pinckney JL. Modelling oxygen dynamics in an intermittently stratified estuary: estimation of process rates using field data. Estuarine, Coastal and Shelf Science 2001;52(1):33-49. R826938 (2001)
R826938 (Final)
R825243 (1999)
R825243 (Final)
R827957 (Final)
  • Full-text: ScienceDirect-Full Text HTML
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  • Abstract: ScienceDirect-Abstract
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  • Other: ScienceDirect-Full Text PDF
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  • Journal Article Buzzelli CP, Luettich Jr. RA, Powers SP, Peterson CH, McNinch JE, Pinckney JL, Paerl HW. Estimating the spatial extent of bottom-water hypoxia and habitat degradation in a shallow estuary. Marine Ecology Progress Series 2002;230:103-112. R826938 (2000)
    R826938 (Final)
    R827957 (Final)
    R828677 (2001)
    R828677C001 (Final)
  • Full-text: MEPS-Full Text PDF
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  • Abstract: MEPS-Abstract
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  • Journal Article Hench JL, Bircher JT, Luettich RA. A portable retractable ADCP boom-mount for small boats. Estuaries 2000;23(3):392-399. R826938 (Final)
    not available
    Journal Article Luettich RA, Carr SD, Reynolds-Fleming JV, Fulcher CW, McNinch JE. Semi-diurnal seiching in a shallow, micro-tidal lagoonal estuary. Continental Shelf Research 2002;22(11-13):1669-1681. R826938 (2000)
    R826938 (2001)
    R826938 (Final)
    R828677C001 (2002)
    R828677C001 (2003)
    not available
    Journal Article Paerl HW, Bales JD, Ausley LW, Buzzelli CP, Crowder LB, Eby LA, Go M, Peierls BL, Richardson TL, Ramus JS. Hurricanes' hydrological, ecological effects linger in major U.S. estuary. Eos 2000;81(40):457-462. R826938 (2000)
    R826938 (Final)
    not available
    Journal Article Paerl HW, Bales JD, Ausley LW, Buzzelli CP, Crowder LB, Eby LA, Fear JM, Go M, Peierls BL, Richardson TL and Ramus JS. Ecosystem impacts of three sequential hurricanes (Dennis, Floyd and Irene) on the US's largest lagoonal estuary, Pamlico Sound, NC. Proceedings of the National Academy of Sciences USA 2001;98(10):5655-5660. R826938 (2001)
    R826938 (Final)
  • Full-text from PubMed
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  • Journal Article Paerl HW. Connecting atmospheric nitrogen deposition to coastal eutrophication. Environmental Science & Technology 2002;36(15):323A-326A. R826938 (Final)
    R828677C001 (2002)
    R828677C001 (2003)
    R828677C001 (Final)
    not available
    Journal Article Paerl HW, Dennis RL, Whitall DR. Atmospheric deposition of nitrogen: implications for nutrient over-enrichment of coastal waters. Estuaries and Coasts 2002;25(4):677-693. R826938 (2001)
    R826938 (Final)
    R828677C001 (Final)
  • Abstract: SpringerLink
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  • Other: Prepublication paper
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  • Journal Article Piehler MF, Dyble J, Moisander PH, Pinckney JL, Paerl HW. Effects of modified nutrient concentrations and ratios on the structure and function of the native phytoplankton community in the Neuse River Estuary, North Carolina, USA. Aquatic Ecology 2002;36(3):371-385. R826938 (Final)
    R828677C001 (Final)
  • Abstract: SpringerLink
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  • Journal Article Pinckney JL, Richardson TL, Millie DF, Paerl HW. Application of photopigment biomarkers for quantifying microalgal community composition and in situ growth rates. Organic Geochemistry 2001;32(4):585-595. R826938 (Final)
    R828677 (2001)
    not available
    Journal Article Pinckney JL, Paerl HW, Tester P, Richardson TL. The role of nutrient loading and eutrophication in estuarine ecology. Environmental Health Perspectives 2001;109(Suppl 5):699-706. R826938 (Final)
    not available
    Journal Article Reynolds-Fleming JV, Fleming JG, Luettich RA. Portable autonomous vertical profiler for estuarine applications. Estuaries and Coasts 2002;25(1):142-147. R826938 (Final)
    R828677C001 (Final)
  • Full-text: SpringerLink - Full Text PDF
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  • Abstract: SpringerLink
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  • Journal Article Reynolds-Fleming JV, Luettich Jr. RA. Wind-driven lateral variability in a partially mixed estuary. Estuarine, Coastal and Shelf Science 2004;60(3):395-407. R826938 (Final)
    R827957 (Final)
    R828677C001 (2003)
  • Full-text: ScienceDirect-Full Text HTML
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  • Abstract: ScienceDirect-Abstract
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  • Other: ScienceDirect-Full Text PDF
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  • Journal Article Reynolds-Fleming JV, Luettich Jr RA. Lateral variability of dissolved oxygen and density in a shallow, partially mixed estuary. Estuaries. R826938 (Final)
    not available
    Journal Article Richardson TL, Pinckney JL, Paerl HW. Responses of estuarine phytoplankton communities to nitrogen form and mixing using microcosm bioassays. Estuaries and Coasts 2001;24(6):828-839. R826938 (Final)
    R825243 (1999)
    R825243 (Final)
  • Abstract: Estuaries and Coasts Abstract
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  • Other: Estuaries and Coasts Full-text pdf
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  • Journal Article Whitall DR, Paerl HW. Spatiotemporal variability of wet atmospheric nitrogen deposition to the Neuse River Estuary, North Carolina. Journal of Environmental Quality 2001;30(5):1508-1515. R826938 (2000)
    R826938 (Final)
    R825243 (Final)
  • Abstract from PubMed
  • Full-text: JEQ Full Text
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  • Other: JEQ Full Text pdf
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  • Journal Article Whitall D, Hendrickson B, Paerl H. Importance of atmospherically deposited nitrogen to the annual nitrogen budget of the Neuse River estuary, North Carolina. Environment International 2003;29(2-3):393-399. R826938 (Final)
    not available

    Supplemental Keywords:

    watersheds, estuary, precipitation, nitrogen, ecosystem, circulation, dissolved oxygen, hypoxia, eutrophication, aquatic, ecology, monitoring, Atlantic coast, North Carolina, NC, total maximum daily load, TMDL, stratification, marine science, hydrography, anoxia, phytoplankton., RFA, Scientific Discipline, Geographic Area, Water, Ecosystem Protection/Environmental Exposure & Risk, Nutrients, Ecology, Water & Watershed, Ecosystem/Assessment/Indicators, Ecosystem Protection, Chemistry, State, Monitoring/Modeling, Ecological Effects - Environmental Exposure & Risk, Air Deposition, Southeast, Biology, Watersheds, environmental monitoring, risk assessment, coastal ecosystem, eutrophication, aquatic ecosystem, hydrological stability, ecological exposure, coastal watershed, estuaries, fish kills, meteorology, bioavailability, coastal zone, algal growth, coastal environments, CISNet Program, hypoxia, esturarine eutrophication, estuarine ecosystems, algal blooms, anoxia/hypoxia, aquatic ecosystems, water quality, North Carolina (NC), Neuse River Estuary, stress responses, atmospheric deposition, ecological response, land use, nitrogen

    Relevant Websites:

    http://www.marine.unc.edu/neuse/modmon Exit

    Progress and Final Reports:

    Original Abstract
  • 1999 Progress Report
  • 2000 Progress Report