Water Resources Research Act Program

Details for Project ID 2013NC181B

A mesocosm study to determine nitrogen assimilation capacity of a restored wetland slated to receive pumped drainage water - a critical component to maximize improvement to the Pamlico Sound

Institute: North Carolina
Year Established: 2013 Start Date: 2013-03-01 End Date: 2014-02-28
Total Federal Funds: $29,914 Total Non-Federal Funds: $15,406

Principal Investigators: Michael Burchell, Stephen W. Broome

Project Summary: A 1,500 ha wetland restoration design is underway in Hyde County, NC, to restore historic hydrology, enhance habitat, and to reduce pollutant loads that discharge to the Pamlico Sound from adjacent agricultural facilities. These goals are all contingent on the development of a water management plan that will divert agricultural drainage water from portions of the 2,910 ha farm, normally pumped into the sound, into the restoration area. Project partners need to know a defensible estimate of the agricultural nutrient loads (particularly nitrogen (N)) that can be assimilated by the restored wetland to confirm that the restoration plan will not impose negative ecological impacts downstream in the Alligator River National Wildlife Refuge. Based on previous field scale studies, conducted after restoration with a “wait and see” approach, we hypothesize the wetland will assimilate N at a high level as diverted drainage water flows through the wetland. This project allows an opportunity to determine N assimilation at the front-end of the project, while simultaneously enhancing the understanding of the mechanisms responsible for the fate of N in wetlands. The proposed project will utilize mesocosm-scale wetlands with restoration site soils to determine the nutrient assimilation potential in the restored wetland, determine maximum hydraulic and nutrient loads that can be diverted away from the Pamlico Sound into the wetland, improve our understanding of the fate of N in these systems with advanced analytical techniques, and increase stakeholder confidence in this and future wetland restoration projects that may lead to measureable improvements in coastal water quality. Six large wetland mesocosms containing wetland soils from the restoration sites were constructed and planted in March 2011 and are ready to begin the study. The wetlands will be loaded with nitrogen (primarily nitrate-nitrogen) at concentrations typical of agricultural drainage water. Nitrate and carbon concentrations in the water will be measured hourly with a state of the art UV spectrophotometer, and will be supplemented with additional laboratory analysis of other nutrient species to calibrate the sensor and gain a clearer picture of the nutrient dynamics in the systems. Additionally, a δ15N isotope tracer study will be completed to examine the contribution of denitrification and plant uptake to the nitrogen balance, and will require analysis of the water, plant biomass, and soil to track changes in the locations and abundance of the tracer throughout the study. Other parameters, such as dissolved oxygen in the water column and soil redox, will be monitored daily to understand biogeochemical changes occurring in the wetlands. Nitrogen removal rates will be determined from this study and coupled with a calibrated hydrologic model (DRAINMOD) of the restoration site to predict with more confidence the volume of drainage water that can be pumped from the agricultural fields into the planned wetland restoration areas. We anticipate the successful completion of this project will solidify partnerships between conservation and agricultural groups, which may lead to larger projects that will have huge impacts on coastal and economic conditions in eastern NC.