Effects of In-Stream Processes on the Fate of Nitrogen and Phosphorous in Drainage Canals of Forested Watersheds

Abstract

As time progressed and populations increased, human activities related to the production of resources such as food, timber, clothing, and energy have focused on enhancing biological systems to increase yields. This has resulted in the altering of the natural cycles of nitrogen and phosphorous throughout the world. The objectives of this study were to; 1. conduct a literature review of forest stream hydrologic and nutrient inputs, outputs, and transformations and their associated contributions to the overall budgets, 2. quantify these inputs, outputs, and transformations for a drainage network section in the lower coastal plain of North Carolina, and 3. develop a mathematical relationship to describe nitrate removal from forest drainage systems that can be used in modeling.

Upstream inflow, rainfall/throughfall, and subsurface flow along with litterfall and lateral movement were measured as inputs, outflow at the outlet and denitrification were measures as outputs to the drainage section. Denitrification was estimated using seven methods; in stream tanks, undisturbed cores, background N15 and O18 concentrations, N15 enrichment, diffusion calculations, mass balance, and modeling.

During this study, 6.7 kg of nitrate was removed through demitrification during the first years flow period (85 days) and 19.8 kg dur4ing the second years flow period (82 days) from the 1900 meter log and 3 meter wide drainage canal section studied.

The mathematical relationship to describe the nitrate removal rate is based on a depth and concentration independent term which takes temperature into account. This relationship is based on a term called a mass transfer coefficient (r). This relationship resulted in a mass transfer coefficient (r) of 0.064 m/day at 25oC.