Chunyi Li

In Beijing, particulate matter (PM) in the atmosphere, especially PM_2.5 and PM₁₀, have attracted public attention because of its adverse effects. A series of studies have investigated the sources and spatial–temporal variation of PM. Wetland has been reported to own the capacity of resolving air problem. To examine the characteristics of the particulate matter in wetlands, the diurnal variation of PM_2.5 and PM₁₀ concentrations with respect to two heights (i.e. 1.5 and 10 m, respectively) and three meteorological factors (i.e. wind speed, temperature, and relative humidity, respectively) was monitored in the Cuihu National Wetland Park in Beijing, and the dry deposition velocity and flux were analysed using the above-mentioned data. Results indicated that (1) As for diurnal variation, the PM concentration constantly decreased at 07:00–16:00 and gradually increased at 16:00–18:00. The maximum instantaneous concentration was observed at 07:00–10:00, while the minimum instantaneous concentration was observed at 13:00–16:00. (2) The annual concentration variation of PM followed the order of dry period > wet period > normal period. (3) The particulate concentrations at 10 m were always greater than those at 1.5 m. (4) The PM concentration was positively correlated to the relative humidity and negatively correlated to the temperature. Wind speed exhibited a complex effect on PM concentration. (5) The regulation of dry deposition efficiency followed the order of spring > winter > summer. (6) Wind speed strongly and positively affected the dry deposition velocity of PM10. The effects of temperature and relative humidity on dry deposition were uncertain. GRAPHICAL ABSTRACT

Atmospheric particulate matter (PM) deposition which involves both dry and wet processes is an important means of controlling air pollution. To investigate the characteristics of dry and wet deposition in wetlands, PM concentrations and meteorological conditions were monitored during summer at heights of 1.5 m, 6 m and 10 m above ground level at Cuihu Wetland (Beijing, China) in order to assess the efficiency of PM2.5 (particles with an aerodynamic size of –2·s^–1) > 1.5 m (0.005 ± 0.002 μg·m^–2·s^–1). And the following deposition fluxes for PM10 were recorded: 10 m (2.163 ± 2.941 μg·m^–2·s^–1) > 1.5 m (1.565 ± 0.872 μg·m^–2·s^–1) > 6 m (0.987 ± 0.595 μg·m^–2·s^–1). In the case of wet deposition, the relative deposition fluxes for PM2.5 and PM10 were 1.5 m > 10 m > 6 m, i.e. there was very little difference between the fluxes for PM2.5 (0.688 ± 0.069 μg·m^–2·s^–1) and for PM10 (0.904 ± 0.103 μg·m^–2·s^–1). It was also noted that rainfall intensity and PM diameter influenced wet deposition efficiency. Dry deposition (63%) was more tilted towards removing PM10 than was the case for wet deposition (37%). In terms of PM2.5 removal, wet deposition (92%) was found to be more efficient.

Peatlands play an essential role in the global carbon (C) and nitrogen (N) cycling. In order to ascertain the draining effects on recent accumulation rates of C (RERCA) and N (RERNA) in the Zoige peatland in the eastern Qinghai-Tibet Plateau, the core samples of peat growth, C and N accumulation for both natural and drained peatlands were measured using ²¹⁰Pb and ¹³⁷Cs dating methods. As a result, RERCA and RERNA showed an increasing trend from the bottom to the surface of the peatland, which was in accordance with the peat accumulation rates. However, the average RERCA in permanently flooded and seasonally flooded peatlands were 1.5–2.5 times that of drainage peatlands, and the average of RERNA were 1.2–1.7 times. Our findings indicate that the Zoige peatland is still in the stage of peat development with a large carbon sequestration capacity, and drainage from human activities leads to the decreasing of RERCA and RERNA, which will contribute to the selection of the effective ways to slow down the anthropogenic effects on the degradation of the Zoige peatland.

By using eddy covariance technique, a year-round (November, 2011-October, 2012) continuous measurement of net ecosystem carbon dioxide exchange (NEE) was conducted in a 4-year old mixed forest plantation in Badaling of Beijing. The forest plantation ecosystem was a net carbon sink in July and August, but a carbon source in the rest months. The monthly net carbon loss and uptake were the largest in April and July, respectively. The annual net ecosystem productivity was (-256 +/- 21) g C x m(-2) x a(-1), in which, the ecosystem respiration was (950 +/- 36) g C x m(-2) x a(-1), and the gross ecosystem productivity was (694 +/- 17) g C x m(-2) x a(-1). The nighttime NEE increased exponentially with the soil temperature at 10 cm depth, with the estimated temperature sensitivity of ecosystem respiration (Q10 ) being 2.2. During the growth season (May-September), the daytime NEE increased with photosynthetically active radiation (PAR) as described by the Michaelis-Menten rectangular hyperbola. The ecosystem quantum yield varied seasonally, ranging from 0.0219 micromol CO2 x micromol(-1) in May to 0.0506 micromol CO2 x micromol(-1) in July. The maximum carbon assimilation rate and the average daytime respiration followed the seasonal trends of PAR and air temperature. In July and August, vapor pressure deficit and soil moisture played a significant role in determining daytime NEE.