Tiffany L. Messer

Groundwater Nitrate Reductions Within Upstream and Downstream Sections of Riparian Buffers

Riparian buffer systems have been found to effectively decrease groundwater nitrate through denitrification. However, the ability to reduce nitrate has been variable and does not always work as effectively as desired. Defining ideal buffer placements that maximize denitrification could protect more stream miles, improving overall water quality.

Tracing the Fate of Nitrate through Restored Wetlands: A Mesocosm 15N Tracer Study

Abstract. Denitrification and plant uptake have been identified as the primary pathways for nitrogen removal within wetlands. However, only denitrification provides complete removal. Understanding the biogeochemical factors that affect nitrogen reduction in these systems could increase the potential for wetlands to be designed for more efficient pollutant removal services. A mesocosm experiment was designed to test wetlands constructed with two soil types from future coastal North Carolina wetland restorations. A 7-day 15 N isotope tracer study was completed in August 2013 to better identify the fate of applied nitrate in these wetland systems. Simulated drainage water was enriched with KNO 3 - 15 N and loaded into the mesocosms. Sediment and biomass samples were taken at the beginning and end of the experiment to assess the biomass and soil 15 N and TN pools. Daily nitrate- 15 N, N 2 - 15 N, nitrate-N, nitrous oxide-N, ammonium-N, and Br - grab samples were taken to determine nitrogen transformation pathways. Dissolved oxygen, pH, water depth, and soil redox were also evaluated. Preliminary results showed significant reductions in nitrate-N (I±=0.05) with 91-92% removal within 7 days. Based on tracer results, estimates of nitrogen removal through plant uptake and denitrification ranged from 25-34% and 35-49% within the wetland mesocosms, respectively. Results quantify plant uptake and denitrification within these wetland systems during the end of the growing season and define the significance of total and temporary nitrogen removal. Findings should provide wetland designers a better understanding of the nitrogen dynamics within these systems, which could improve wetland design methods for increasing nitrogen reduction.

Groundwater nitrate reduction processes in a riparian buffer enrolled in the NC Conservation Reserve Enhancement Program

In an effort to maximize water quality benefits of buffers enrolled in the NC Conservation Reserve Enhancement Program, several buffers were monitored for nitrate in groundwater and in the protected stream. One buffer monitored was located in the upper coastal plain of North Carolina. This buffer averaged 50 meters wide and consisted of 3 zones; a hardwood buffer near the stream, a wide loblolly pine zone, and a grassed zone at the field/buffer interface. Poultry litter was applied by the landowner to a pasture upslope from the grass buffer. Three blocks of groundwater wells, each containing three transects, were installed at shallow depths (1.5-2 m) and deep depths (2.5-3.0 m) and have been monitored for nutrients since 2005. Stream surface water samples were also collected at three points inside the buffer during this time. In June 2008, groundwater wells with depths ranging from 4.2-9.6 m were also installed in the upland and within each block.

Effectiveness of Nitrate Reduction in Riparian Buffers: A Riparian Buffer Hydrologic and Biogeochemical Evaluation

Defining ideal placement of buffers enrolled in NC CREP could maximize stream miles protected, to improve downstream water quality in sensitive streams and estuaries. During the past five years effects on nitrate reduction efficiency of a riparian buffer enrolled in the North Carolina Reserve Enhancement Program (NC CREP) has been evaluated. The buffer width was 40-45 m, and groundwater monitoring well nests were installed in three transects within the buffer. Each well nest contained a shallow (1.5-2.1 m) and deep (2.7-3.4 m) well. Additional wells were installed in the deeper aquifer to measure the quality of that water for comparison to the more shallow wells. Upslope agricultural practices have included soybeans, peanuts, cotton and corn.

Hydrologic Analysis of a Riparian Buffer Enrolled in Conservation Reserve Enhancement Program in North Carolina Using Riparian Ecosystem Management Model (REMM)

Conservation practices such as the installation of riparian buffers along streams are known to reduce the impacts of non-point source pollutants such as nitrogen and phosphorus. A riparian buffer enrolled in the Conservation Reserve Enhancement Program in North Carolina, located in the Tar-Pamlico Watershed, has been monitored for hydrology and water quality since 2005. This buffer site received nitrogen and phosphorus loads from an upland source of inorganic fertilizer for crops like cotton, peanut and soybean. Results from the field studies have shown that the buffers are able to reduce nitrate-nitrogen loads to the streams. The hydrology is a driving factor for biogeochemical reduction of pollutants in the buffers, which often leads to highly variable performance in terms of nitrate-nitrogen reduction. The Riparian Ecosystem Management Model (REMM) was calibrated and will be validated to enhance the understanding of surface and subsurface hydrologic patterns at this buffer. The results showed the simulated water table depths in good agreement with field measured water table depths in block 1 of the research site. The average absolute error (AAE) was 92 mm for the field edge buffer, 120 mm for mid-buffer and 137 mm for the stream buffer zone over a three year period (2005-2007). Characterizing the hydrology at the site was the first step in our attempt to model nitrate losses from the buffer system.