Quantifying the water quality benefits of and the nutrient and organic matter dynamics in a restored coastal marsh
Participants: Randall Etheridge, François Birgand, Michael Burchell (Bio&Ag), Molly Mikan, and Chris Osburn (MEAS)
Timeline: April 2010 - December 2012
Funding Agencies: NC Dept. of Environment and Natural Resources
Project Description
Because of their potential to remove nutrients from drainage, salt marsh restorations have been ongoing in North Carolina and other coastal states. How much these restorations improve water quality is still unknown. Assessing the water quality benefits is difficult in salt marshes due to the complicated patterns of flow and incoming nutrient concentrations. Ebb and flow induce wide concentration and flow variations. The classical stage/discharge relationships cannot be used, while nitrogen concentrations within the marsh may also vary greatly due to sources from both upstream agriculture and the downstream estuary.
A salt marsh restoration was strategically implemented between drained row-crop agriculture and a nearby estuary near Beaufort in Eastern North Carolina. Construction of this salt marsh was overseen by members of the Bio&Ag Department and was completed in 2007. This project provides a great opportunity to provide answers to the question of by how much do salt marsh restorations improve water quality.
The goal of this research project is to develop an accurate nitrogen mass balance for the restored salt marsh. An upstream/downstream monitoring design is being used to determine the mass of nitrogen entering and leaving the marsh. The flow and nitrogen concentrations are monitored at both monitoring stations. To accurately monitor the flow, Doppler velocity meters were installed in the tidal creek within trapezoidal flumes. The flumes provide a constant cross section for more accurate bi-directional velocity and water level measurements.
Nitrate, Dissolved Organic Carbon concentrations and turbidity values within the tidal stream are measured at short intervals (10-15 minutes) using recently developed UV-visual spectrophotometers installed near each flow monitoring station. New sensors for measuring Chromophoric Dissolved Organic Matter (CDOM), Dissolved Oxygen (DO), pH, conductivity and temperature will be added in the Spring of 2011.
Fluorescence of CDOM has been shown to give new information on the nature or types of molecules making DOC. Excitation-emission matrices (EEM) can be obtained from a range of fluorescence values in the lab and essentially give a fingerprint of the type of organic matter indicative of its source and origin. The sensor we request will be used to quantify the OM quality in the marsh vastly improving upon largely descriptive studies of DOM conducted to date.
Objectives and deliverables
- Assessment of the performance of the Spectrophotometer instrument to measure local DOC concentrations in situ
- Use the fluorescence data to predict DON concentrations
- Description of the tidal and seasonal dynamics of nutrients and OM in a restored tidal marsh
- Quantification of the fate and sources of OM in a tidal marsh over long periods of time
- Quantification of ability of a restored tidal marsh to retain excess runoff nitrogen and phosphorus
- Provide design guidance for future coastal marsh restoration projects
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This page was last updated on January 12, 2011.
