Nitrogen Balance of a Drainage Canal in a Managed Forest on the North Carolina Coastal Plain

Altering of the nitrogen cycle, due to human activity, has led to an increase in riverine nitrogen loads, which result in the eutrophication of lakes, streams, estuaries, and near coastal oceans. These riverine nitrogen loads though are usually less than the sum of the nitrogen inputs to the system, indicating that nitrogen is being removed as it is being transported through the flow network. A two-year study was conducted to quantify the different nitrogen species (ammonium, nitrate, and organic-N) inputs, outputs, and the in-stream processes responsible for nitrogen transformations and removal in a 1900 meter section of a drainage canal. The canal section is located in a managed pine plantation on the lower coastal plain of North Carolina. Total nitrogen inputs to the canal section were 562 kg in 2001 and 1394 kg in 2002. Total nitrogen discharge at the outlet was 508 kg in 2001 and 1354 kg in 2002. The mass balance of nitrogen inputs and outflow at the outlet indicate that 54 kg (9%) of total nitrogen was lost to the system in 2001, and 40 kg (3%) of total nitrogen was lost to the system in 2002. This study shows that denitrification in the sediments occurs at a appreciable rate (from 3% to 9% losses in total- N) in the drainage networks of managed tree plantations in the coastal plain of North Carolina.