Relation of soil-, surface-, and ground-water distributions of inorganic nitrogen with topographic position in harvested and unharvested portions of an aspen-dominated catchment in the Boreal Plain

Spatial distributions of soil extractable nitrate (NO3-) and ammonium (NH4+) concentrations were related to surface- and ground-water NO3- and NH4+ concentrations in harvested and forested sections of a catchment dominated by trembling aspen (Populus tremuloides Michx.) in the subhumid boreal forest of Alberta, Canada. NO3- and NH4+ concentrations in soils varied spatially throughout the catchment and were larger in surface soils than in subsurface soils. Spatial distributions of soil inorganic nitrogen (N) concentrations were not explained by the harvested versus the unharvested condition; heterogeneity was instead related to topographic position. NO3- concentrations in both surface and subsurface soils were largest in ephemeral draws and wetlands. NH4+ concentrations in subsurface soils were largest in ephemeral draws and wetlands, but this pattern was not apparent for surface soils. Soil NO3- and NH4+ availability and surface- and ground-water NO3- and NH4+ concentrations reflected soil NO3- and H-4(+) concentrations. N-rich surface soils in both forested and harvested areas have a large potential for releasing N to surface waters. This study indicates that even though topography is subtle in this catchment, topographic position and its soil moisture relations, along with vegetation demand, can influence N transformation and transport in both forested and harvested portions of the Boreal Plain landscape.