Long-term flux observation above a subtropical forest canopy
Abstract
The exchange of nitrogen oxides between biosphere and atmosphere plays an important role of global nitrogen cycle, influencing the regional air quality, N deposition, and ecosystem health. The dry deposition of nitrogen is often estimated from inferential method and/or throughfall measurement in forests with certain uncertainty. In this study, a micrometeorological method was applied to directly observe the NOx flux in 2015 and 2016 above the canopy of a Pinus massoniana-dominant subtropical forest in southeastern China, which was thought to be background sites. Both two years deployed a net NOx flux downwards, i.e. N dry deposition of 21.2 kgN ha-1 yr-1 and 7.67 kgN ha-1 yr-1 in 2015 and 2016, respectively. A larger downward flux was found in winter and autumn, with a small emission in the spring, which reflected the possible bi-way exchange balanced by soil-atmosphere exchange and folia-atmosphere exchange. The NOx concentration seemed the most important factor controlling the NOx exchange above canopy, which explained seasonal variation of N deposition and the difference between the two years as the concentration in 2016 was distinctly lower than that in 2015. The dry deposition is underestimated by 73.7% from the throughfall measurement minus the wet-only deposition. The stomatal uptake of NOx is likely to be responsible for the dry deposition underestimation of throughfall measurement. Furthermore, the dry deposition was simultaneously monitored at another subtropical forest, which has already been observed of nitrogen saturation. The dry deposition dynamics would be compared between these two sites.
- Publication:
-
EGU General Assembly Conference Abstracts
- Pub Date:
- April 2019
- Bibcode:
- 2019EGUGA..21..294K