Nitrogen Cycling and Assimilative Capacity of Nitrogen and Phosphorus by Riverine Wetland Forests

摘要

Labeled (15N) nitrate and ammonium were added to swamp surface water and their diffusion to the forest floor was followed. Of the original nitrate added, 46% remained in the surface water of Tar Swamp and 62% in Creeping Swamp after 2 days. Two days after ammonium treatments, corresponding levels were 79% and 81%. As indicated by the absence of recoverable 15N in sediments following nitrate treatments, diffusion of labeled nitrate to the forest floor resulted in its transformation to N2O or N2 by denitrification. Available nitrogen reserves in the sediments were depleted through ammonification and nitrification during annual drydown episodes, and the capacity for additional nitrogen assimilation by the sediments was renewed. An experiment was then conducted to determine the capacity of sediments for sustained nutrient assimilation by adding nitrate, ammonium, phosphate, and secondarily treated sewage effluent to surface water in separate chambers at weekly intervals for 46 weeks.