Development of key components of a nitrogen budget for a forested watershed on the Canadian Boreal Plain

This investigation, which took place as part of the Forest Watershed and Riparian Disturbance (FORWARD) study in west-central Alberta on the Boreal Plain, measured key components of a nitrogen (N) budget in a relatively undisturbed, forested watershed. The first component examined was N inputs from bulk deposition and the effect of different forest soil/canopy types (upland deciduous, upland conifer and wetland conifer stands) on N flux from the bulk deposition to the forest floor. Annual total dissolved N (TDN) inputs in bulk deposition during the period 1 November 2006 to 31 October 2007 (2007 water year) were 410 mg N m-2. The forest canopy of each soil/canopy types retained N, decreasing annual inorganic N (IN = nitrate [NO3-] + ammonium [NH4+]) flux to the forest floor by approximately 55% and decreasing annual TDN flux to the forest floor by 28 to 41%. There was no detectable difference in N flux of throughfall or stemflow between the different soil/stand types.;Nitrogen export in the surface water was examined for 3 small sub-watersheds within a larger FORWARD study watershed. Each sub-watershed was selected to maximize coverage by one of the main soil/stand types. For the 2007 ice-free period (1 May to 31 October), TDN exports ranged from 25 to 32 mg N m -2. Although TDN exports were similar between the sub-watersheds, there appears to be differences in the forms of N exported from the sub-watersheds. The sub-watershed with high wetland conifer cover exported mainly (over 90%) dissolved organic N (DON), and almost no NO3 -. The two sub-watersheds with no wetlands exported proportionally less DON and much more NO3-. Of the two sub-watersheds with no wetlands, the one comprised of primarily upland conifer stands exported a greater proportion of NH4+ than the sub-watershed with primarily upland deciduous stands. The majority (55 to 79%) of TDN exports were exported from all sub-watersheds during the spring snowmelt. Total N retention within all the sub-watersheds was approximately 93% of bulk deposition inputs.;Key Words: Nitrogen budget, Boreal Plain, bulk deposition, throughfall, mineralization, export;Nitrogen turnover (mineralization) within the forest soils of these soil/canopy types were also examined during a 12-week period from mid-June to mid-September. Net mineralization (ammonification and nitrification) rates in the forest soils (FH and Ae horizons in upland soils and the Of layer in the wetland soils) were highest in the upland deciduous stands (1526 and 82 mg N m -2 for ammonification and nitrification respectively) and lowest in the wetland conifer stands (482 and 33 mg N m-2 for ammonification and nitrification respectively). Seasonally, net mineralization rates were greater during early summer than late summer, possibly because soil and air temperatures were warmer during early summer.