Measurement of wet deposition of inorganic and organic nitrogen in a forest environment

Abstract

[1] Dissolved inorganic (NO 3 À and NH 4 + ) and organic nitrogen (DON) were measured in precipitation at the University of Michigan Biological Station (UMBS) near Pellston, Michigan, in an open field and under the forest canopy from June to August 2004. Experiments to test the stability of the rain samples were conducted to evaluate different collection methods. Comparison of the two data sets allows the interactions between precipitation and the forest canopy to be examined. In addition, the measurements of wetdeposited total nitrogen were compared to calculated estimates of total dry-deposited nitrogen. Stability tests of the samples indicated that the samples must be frozen during collection. The average distribution of wet-deposited nitrogen for the summer was 32.9 (±0.5)% nitrate, 52.5 (±0.3)% ammonium, and 14.6 (±0.9)% DON in an open field and 42.5 (±0.9)% nitrate, 38.9 (±1.0)% ammonium, and 18.8 (±1.4)% DON under the forest canopy. Canopy-precipitation interactions were observed to cause a 68 (±4)% increase in nitrate, a 4 (±2)% decrease in ammonium, and an 81 (±16)% increase in DON in the collectors under the forest canopy. A comparison of wet and dry nitrogen deposition indicated that dry deposition may contribute more nitrogen than wet deposition to this site. However, our measurements indicate that much of the dry-deposited nitrogen is lost, some of which is likely revolatilized.

Interactions of forests with secondary air pollutants: Some challenges for future research

“…Even in the absence of pathogenic activity, the proliferation of algae on a canopy that is well supplied with nitrogen and water may lead to situations where primary photosynthesis by the leaf is inhibited (Cape et al, 1989). Certainly, the processing of nitrogen within forest canopies is still not well described or understood -transformations from inorganic to organic forms can occur, and organic N can be retained within the canopy, either by epiphytic microbes or by the leaf itself (Hill et al, 2005, Piirainen et al, 1998. In the latter case, the long-term ecological implications of a transfer of the pathway for N uptake from roots to canopies (Rennenberg and Gessler, 1999), although recognised as a problem because of the changes in signalling hormones within the plant, have not been fully explored.…”

Processing of atmospheric nitrogen by clouds above a forest environment

“…Organic as well as inorganic nitrogen may contribute to nitrogen fertilization of forest ecosystems. Measurements of nitrogen concentrations in rain, fog, and cloud water [e.g., Isaac et al , 1990; Zhang and Anastasio , 2001; Keene et al , 2002; Hill et al , 2005] have shown that ammonium and nitrate ions are typically the dominant nitrogen components, but dissolved organic nitrogen (DON) also contributes significantly to the total dissolved nitrogen concentration. Depending on location, organic nitrogen can account for as little as 6% to as much as 80% of the total nitrogen content in rain, fog, and cloud water [ Neff et al , 2002, and references therein].…”

Wet and dry deposition of atmospheric nitrogen at ten sites in Northern China

“…However, the dry deposition of N is often omitted from observation-based flux studies because of the difficulties inherent in directly quantifying the ambient concentrations and deposition velocities of highly reactive N gases and speciated particles (Pryor et al, 1999). Because dry deposition can substantially contribute to total N deposition, neglecting dry deposition will result in an underestimation of the total deposition of N onto surfaces (Hill et al, 2005). Alternatively, inferential modeling has been used extensively as an operational tool to compensate for the absence of measured dry deposition data at regional scales (Flechard et al, 2011).…”