An assessment of nitrogen saturation in Pinus banksiana plots in the Athabasca Oil Sands Region, Alberta

Abstract

During the past 15 years, there has been a dramatic increase in the amount of reactive nitrogen (N)

Gross N transformations were little affected by 4years of simulated N and S depositions in an aspen-white spruce dominated boreal forest in Alberta, Canada

“…In addition, the fast turnover of the NH 4 + pool in the organic layer may leave little opportunity for nitrifiers to compete for available NH 4 + . Laxton et al (2010) also attributed the below detection net nitrification rates to efficient ecosystem immobilization of current N deposition in the AOSR. Furthermore, net nitrification has long been shown to be absent in soils with pH <5 (Noyes and Conner, 1919;Weber and Gainey, 1962).…”

“…doi:10.1016/j.foreco.2011.04.027 can be expected that several N retention mechanisms may be involved to minimize N losses via gaseous N production and/or leaching to meet microbial and plant N demand (Westbrook and Devito, 2004;Laxton et al, 2010). Possible retentive mechanisms include a tightly coupled microbial N cycle where gross NH 4 + and NO 3 À immobilization rates would be comparable to gross N mineralization and gross nitrification rates, respectively (Corre et al, 2003).…”

“…On the other hand S deposition rates were expected to maintain stable or decrease as new technologies are employed to increase the recovery of S (Golder Associates, 2003). Currently the effects of N and S deposition on the status and dynamics of N in the AOSR are poorly understood, while the biggest concern is eventual N saturation and surface water eutrophication (NSMWG, 2008;Laxton et al, 2010).…”

Nitrogen Cycling in Pinus banksiana and Populus tremuloides Stands in the Athabasca Oil Sands Region, Alberta, Canada

“…Often, throughfall underestimates total N deposition because of foliar uptake (Lindberg et al 1986;Lovett and Lindberg 1993); however, throughfall N can also be enhanced when precipitation washes particles of dry deposition from foliage (Skeffington and Wilson 1988;Houle et al 1999) and, hence, may be an unreliable estimate of N deposition. Based on passive measurements of nitric acid, ammonia, and NO 2 concentrations, dry N deposition at a distance of 30 km is around 1.7 kg Nha −1 , which would increase total deposition to 3 to 4 kg Nha −1 (Laxton et al 2010), which is still low relative to many other parts of the world.…”

“…Concert sites closest (<20 km) to emission sources had increased N concentrations in jack pine (Pinus banksiana Lamb. ) foliage and in epiphytic lichens (Laxton et al 2010) suggesting that forests close to emission sources may be impacted by high N exposure.…”