Benthic Flux Work
 
 
Project Goals

Background

Materials and Methods

Sampling Sites and Field Sampling
Flux Determination
Sediment and Water column Parameters
Results


 
    Project Goals
     
    • Determine the spatial and temporal variability of sediment oxygen demand (SOD), denitrification and nutrient (NH4, NO3, PO4) flux in the upper Neuse River Estuary (NRE)
    • Determine the contribution of internally regenerated nutrients to annual phytoplankton nutrient requirements
    • Correlate benthic fluxes of oxygen, nutrients, and denitrification to sediment and water column properties.

      • Use collected data to develop a model of the system that will help predict estuary response to nutrient reduction plans.
Top

 
Background


Click on image for larger view

 The NRE is a Nitrogen (N) limited drowned river system extending from New Bern, North Carolina to the Pamlico Sound.  It drains a watershed of 16,000km2 and is part of Albermarle Pamlico System, the United States' second largest estuarine complex.  Water quality declines  in the NRE have been widely documented by several researchers (Christian et al. 1986; Pinckney et al. 1997, 1998; Paerl et al. 1998).  The NRE is especially prone to eutrophic problems because the mouth is located behind coastal barrier islands, which limit water exchange.  Density driven stratification is an important and persistent problem in the NRE leading to frequent low oxygen events (Rizzo et al. 1996; Paerl et al. 1998; Luettich et al. 2000).
Top

 


 
 

Materials and Methods

Sampling Sites

Four sampling sites were utilized during the course of this work.  They were situated in the upper NRE between New Bern and the N.C. D.O.T. ferry located at the 90 degree bend in the estuary.  These sites were chosen because they normally enclose the area in the NRE where the interface between fresh Neuse River water and saline Pamlico Sound water occurs.

 
Field Sampling

For the purpose of this study, NRE sediment samples were collected with a hand-operated gravity coring device.  The device allowed cores to be collected directly into incubation chambers, helping to minimize sediment disturbance.  Collected cores were sealed, secured in transportation racks, and returned to the Institute of Marine Sciences (IMS) which is ideally located within 45min of the study site.  Water necessary for the flux incubations was collected at the same time as the cores via a submersible impeller pump.

Top

 
 
Flux Determinations

SOD, denitrification, and nutrient flux rates were determined using laboratory core flux incubation chambers (pictured at left, diagram below).  These chambers consist of 10cm diameter PVC pipe cut into 35 cm lengths.  Collected cores were stored overnight submerged in corresponding site water.  Gentle circulation was maintained to prevent overlying water stratification, and anoxic conditions in the incubators prior to the start of the experiment.  Incubations were started the morning following collection.
The incubation chambers (diagram below) were fitted with a sampling top, which included ports for sample withdrawal and introduction of replacement water.  They also have a magnetic stir bar suspended 10cm below the sampling ports.  Rotating magnets attached to a speed controlled circular platter actuate the stir bars.  This allowed stirring speeds to be carefully adjusted to maintain water column mixing without sediment disturbance.  No attempt was made to adjust stirring speeds to in-situ current velocities.  Samples were collected every 3 hrs. for 12 hours and analyzed immediately on a membrane inlet mass spectrometer (MIMS) for N2 and O2 (Kana et al. 1994, 1998).  Inorganic nutrient samples (NH4+, NO3-, and PO4-3) were collected at the beginning of the incubation and at the final time point.  Nutrient samples were filtered through GF/F filters and stored frozen until analysis with a Lachat QuickChem automated ion analyzer.  At the end of the incubations, water volume and visible benthic macrofauna content were recorded for each core.

Top
 

Sediment and Water column Parameters

During each sampling trip parallel cores were obtained from which samples were taken and analyzed for carbon and nitrogen content, as well as Chlorophyll a concentration.   For each sampling site full water quality data are available from the Paerl Lab supported Neuse River Bloom Project.  Two of the sampling sites M-9, and M-38 also have continuous monitoring stations maintained by the USGS.

Top
 

Results

Data analysis is just now beginning, but conclusions reached thus far include:
 

  • SOD does vary spatially but the differences are probably not biologically significant.  Ave. SOD rates for all study sites could be summarized quite well by using a value of 1.0 mmoles O2/m2*hr.
  • Nutrient release is positively correlated with SOD rates.
  • Both SOD and nutrient release rates are positively correlated with sediment carbon, nitrogen, and Chlorophyll a content.
  • Denitrification rates have been quite variable, ranging from 0 to 7000 mmoles N/m2*day.
Students supported:  John Fear, Josh Loftin

 

Funded by:

Weyerhaeuser Corporation
North Carolina Water Resources Research Institute
Environmental Protection Agency

Top








Send mail to Site Manager with questions or comments about this web site.