scholarly journals Soil–atmosphere exchange flux of total gaseous mercury (TGM) at subtropical and temperate forest catchments

2020 ◽  
Vol 20 (24) ◽  
pp. 16117-16133
Author(s):  
Jun Zhou ◽  
Zhangwei Wang ◽  
Xiaoshan Zhang ◽  
Charles T. Driscoll ◽  
Che-Jen Lin
Keyword(s):  
Climate Change ◽  
Land Use ◽  
Solar Radiation ◽  
Open Field ◽  
Temperate Forest ◽  
Subtropical Forest ◽  
Pine Forest ◽  
Broad Leaved Forest ◽  
Leaved Forest ◽  
Soil Hg

Abstract. Evasion from soil is the largest source of mercury (Hg) to the atmosphere from terrestrial ecosystems. To improve our understanding of controls and in estimates of forest soil–atmosphere fluxes of total gaseous Hg (TGM), measurements were made using dynamic flux chambers (DFCs) over 130 and 96 d for each of five plots at a subtropical forest and a temperate forest, respectively. At the subtropical forest, the highest net soil Hg emissions were observed for an open field (24 ± 33 ng m−2 h−1), followed by two coniferous forest plots (2.8 ± 3.9 and 3.5 ±  4.2 ng m−2 h−1), a broad-leaved forest plot (0.18 ±  4.3 ng m−2 h−1) and the remaining wetland site showing net deposition (−0.80 ± 5.1 ng m−2 h−1). At the temperate forest, the highest fluxes and net soil Hg emissions were observed for a wetland (3.81 ± 0.52 ng m−2 h−1) and an open field (1.82 ± 0.79 ng m−2 h−1), with lesser emission rates in the deciduous broad-leaved forest (0.68 ± 1.01 ng m−2 h−1) and deciduous needle-leaved forest (0.32 ± 0.96 ng m−2 h−1) plots, and net deposition at an evergreen pine forest (−0.04 ± 0.81 ng m−2 h−1). High solar radiation and temperature during summer resulted in the high Hg emissions in the subtropical forest and the open field and evergreen pine forest at the temperate forest. At the temperate deciduous plots, the highest Hg emission occurred in spring during the leaf-off period due to direct solar radiation exposure to soils. Fluxes showed strong positive relationships with solar radiation and soil temperature and negative correlations with ambient air TGM concentration in both the subtropical and temperate forests, with area-weighted compensation points of 6.82 and 3.42 ng m−3, respectively. The values of the compensation points suggest that the atmospheric TGM concentration can play a critical role in limiting TGM emissions from the forest floor. Climate change and land use disturbance may increase the compensation points in both temperate and subtropical forests. Future research should focus on the role of legacy soil Hg in reemissions to the atmosphere as decreases in primary emissions drive decreases in TGM concentrations and disturbances of climate change and land use.

scholarly journals Soil-atmosphere exchange flux of total gaseous mercury (TGM) in subtropical and temperate forest catchments

2020 ◽  
Author(s):  
Jun Zhou ◽  
Zhangwei Wang ◽  
Xiaoshan Zhang ◽  
Charles T. Driscoll ◽  
Che-Jen Lin
Keyword(s):  
Solar Radiation ◽  
Open Field ◽  
Temperate Forest ◽  
Temperate Forests ◽  
Subtropical Forest ◽  
Pine Forest ◽  
Emission Rates ◽  
Soil Air ◽  
Soil Atmosphere ◽  
Soil Hg

Abstract. Evasion from soil is the largest source of mercury (Hg) to the atmosphere in terrestrial ecosystems. To improve understanding of controls and reduce uncertainty in estimates of forest soil-atmosphere exchange, soil-air total gaseous Hg (TGM) fluxes were measured for 130 and 96 days for each of four plots at a subtropical forest and a temperate forest, respectively. The soil-air TGM fluxes, measured using dynamic flux chambers (DFC), showed patterns of both emission and deposition at five study plots, with an area-weighted net emission rate of 3.2 and 0.32 ng m−2 hr−1 for the entire subtropical and temperate forests, respectively. At the subtropical forest, the highest fluxes and net soil Hg emission were observed for an open field, with lesser emission rates in coniferous (Masson pine) and broad-leaved (camphor) forests, and net deposition in a wetland. At the temperate forest, the highest fluxes and net soil Hg emission were observed for a wetland and an open field, with lesser emission rates in deciduous broad-leaved and deciduous needle-leaf (larch) forests, and net deposition in an evergreen pine forest (Chinese pine). High solar radiation and temperature in summer resulted in the high Hg emission at the subtropical forest, and open field and evergreen pine forest in the temperate forest. In the temperate deciduous plots, the highest Hg emission was in spring during leaf-off period due to direct solar radiation exposure to soils. Fluxes showed strong positive relationships with solar radiation and soil temperature, and negative correlations with ambient-air TGM concentration in both subtropical and temperate forests, with area-weighted compensation points of 6.82 and 3.42 ng m−3, respectively. The compensation points implicated that the atmospheric TGM concentration plays a critical role in inhibiting the TGM emission from forest floor. More attention should pay to the legacy Hg stored in terrestrial surface as a more important increasing Hg emission source with the decreasing air TGM concentration recently.

scholarly journals Legacies of past land use have a stronger effect on forest carbon exchange than future climate change in a temperate forest landscape

2018 ◽  
Vol 15 (18) ◽  
pp. 5699-5713 ◽  
Author(s):  
Dominik Thom ◽  
Werner Rammer ◽  
Rita Garstenauer ◽  
Rupert Seidl
Keyword(s):  
Climate Change ◽  
Land Use ◽  
Temperate Forest ◽  
Natural Disturbance ◽  
Forest Landscape ◽  
Natural Disturbances ◽  
The Future ◽  
Forest C ◽  
High Uncertainty ◽  
Past Land Use

Abstract. Forest ecosystems play an important role in the global climate system and are thus intensively discussed in the context of climate change mitigation. Over the past decades temperate forests were a carbon (C) sink to the atmosphere. However, it remains unclear to which degree this C uptake is driven by a recovery from past land use and natural disturbances or ongoing climate change, inducing high uncertainty regarding the future temperate forest C sink. Here our objectives were (i) to investigate legacies within the natural disturbance regime by empirically analyzing two disturbance episodes affecting the same landscape 90 years apart, and (ii) to unravel the effects of past land use and natural disturbances as well as the future climate on 21st century forest C uptake by means of simulation modeling. We collected historical data from archives to reconstruct the vegetation and disturbance history of a forest landscape in the Austrian Alps from 1905 to 2013. The effects of legacies and climate were disentangled by individually controlling for past land use, natural disturbances, and future scenarios of climate change in a factorial simulation study. We found only moderate spatial overlap between two episodes of wind and bark beetle disturbance affecting the landscape in the early 20th and 21st century, respectively. Our simulations revealed a high uncertainty about the relationship between the two disturbance episodes, whereas past land use clearly increased the impact of the second disturbance episode on the landscape. The future forest C sink was strongly driven by the cessation of historic land use, while climate change reduced forest C uptake. Compared to land-use change the two past episodes of natural disturbance had only marginal effects on the future carbon cycle. We conclude that neglecting legacies can substantially bias assessments of future forest dynamics.

scholarly journals Monitoring Landscape Changes in Japan Using Classification of Modis Data Combined with a Landscape Transformation Sere (LTS) Model

2015 ◽  
Vol 7 (3) ◽  
pp. 23-38 ◽  
Author(s):  
Ippei Harada ◽  
Keitarou Hara ◽  
Mizuki Tomita ◽  
Kevin Short ◽  
Jonggeol Park
Keyword(s):  
Land Use ◽  
Landscape Change ◽  
Forest Cover ◽  
National Level ◽  
Landscape Changes ◽  
Modis Data ◽  
Landscape Transformation ◽  
Broad Leaved Forest ◽  
Leaved Forest

Abstract Japan, with over 75% forest cover, is one of the most heavily forested countries in the world. Various types of climax forest are distributed according to latitude and altitude. At the same time, human intervention in Japan has historically been intensive, and many forest habitats show the influence of various levels of disturbance. Furthermore, Japanese landscapes are changing rapidly, and a system of efficient monitoring is needed. The aim of this research was to identify major historical trends in Japanese landscape change and to develop a system for identifying and monitoring patterns of landscape change at the national level. To provide a base for comparison, Warmth Index (WI) climatic data was digitalized and utilized to map potential climax vegetation for all of Japan. Extant Land Use Information System (LUIS) data were then modified and digitalized to generate national level Land Use/Land Cover (LU/LC) distribution maps for 1900, 1950 and 1985. In addition, MODIS data for 2001 acquired by the Tokyo University of Information Sciences were utilized for remote LU/LC classification using an unsupervised method on multi-temporal composite data. Eight classification categories were established using the ISODATA (cluster analyses) method; alpine plant communities, evergreen coniferous forest, evergreen broad-leaved forest, deciduous broad-leaved forest, mixed forest, arable land (irrigated rice paddy, non-irrigated, grassland), urban area, river and marsh. The results of the LUIS analyses and MODIS classifications were interpreted in terms of a Landscape Transformation Sere model assuming that under increasing levels of human disturbance the landscape will change through a series of stages. The results showed that overall forest cover in Japan has actually increased over the century covered by the data; from 72.1% in 1900 to 76.9% in 2001. Comparison of the actual vegetation and the potential vegetation as predicted by WI, however, indicated that in many areas the climax vegetation has been replaced by secondary forests such as conifer timber plantations. This trend was especially strong in the warm and mid temperate zones of western Japan. This research also demonstrated that classification of moderate resolution remote sensing data, interpreted within a LTS framework, can be an effective tool for efficient and repeat monitoring of landscape changes at the national level. In the future, the authors plan to continue utilizing this approach to track rapidly occurring changes in Japanese landscapes at the national level.

scholarly journals Succession from pine forest to evergreen broad-leaved forest at Ohki coastal beach in Kochi Prefecture, Shikoku, Japan

2020 ◽  
Vol 25 (1) ◽  
pp. 75-86
Author(s):  
Shin Morisada ◽  
Tatsuya Nozaki ◽  
Midori Ogawa ◽  
Mahito Kamada
Keyword(s):  
Pine Forest ◽  
Broad Leaved Forest ◽  
Coastal Beach ◽  
Kochi Prefecture ◽  
Leaved Forest

scholarly journals Energy and CO2 flux densities above and below a temperate broad-leaved forest and a boreal pine forest

1996 ◽  
Vol 16 (1-2) ◽  
pp. 5-16 ◽  
Author(s):  
D. D. Baldocchi ◽  
C. A. Vogel
Keyword(s):  
Co2 Flux ◽  
Pine Forest ◽  
Broad Leaved Forest ◽  
Leaved Forest

scholarly journals Nitrogen input <sup>15</sup>N signatures are reflected in plant <sup>15</sup>N natural abundances in subtropical forests in China

2017 ◽  
Vol 14 (9) ◽  
pp. 2359-2370 ◽  
Author(s):  
Geshere Abdisa Gurmesa ◽  
Xiankai Lu ◽  
Per Gundersen ◽  
Yunting Fang ◽  
Qinggong Mao ◽  
...  
Keyword(s):  
Southern China ◽  
N Deposition ◽  
Pine Forest ◽  
N Cycling ◽  
N Addition ◽  
Inorganic N ◽  
Subtropical Forests ◽  
Broad Leaved Forest ◽  
Soil Δ15n ◽  
Leaved Forest

Abstract. Natural abundance of 15N (δ15N) in plants and soils can provide time-integrated information related to nitrogen (N) cycling within ecosystems, but it has not been well tested in warm and humid subtropical forests. In this study, we used ecosystem δ15N to assess effects of increased N deposition on N cycling in an old-growth broad-leaved forest and a secondary pine forest in a high-N-deposition area in southern China. We measured δ15N of inorganic N in input and output fluxes under ambient N deposition, and we measured N concentration (%N) and δ15N of major ecosystem compartments under ambient deposition and after decadal N addition at 50 kg N ha−1yr−1, which has a δ15N of −0.7 ‰. Our results showed that the total inorganic N in deposition was 15N-depleted (−10 ‰) mainly due to high input of strongly 15N-depleted NH4+-N. Plant leaves in both forests were also 15N-depleted (−4 to −6 ‰). The broad-leaved forest had higher plant and soil %N and was more 15N-enriched in most ecosystem compartments relative to the pine forest. Nitrogen addition did not significantly affect %N in the broad-leaved forest, indicating that the ecosystem pools are already N-rich. However, %N was marginally increased in pine leaves and significantly increased in understory vegetation in the pine forest. Soil δ15N was not changed significantly by the N addition in either forest. However, the N addition significantly increased the δ15N of plants toward the 15N signature of the added N, indicating incorporation of added N into plants. Thus, plant δ15N was more sensitive to ecosystem N input manipulation than %N in these subtropical forests. We interpret the depleted δ15N of plants as an imprint from the high and 15N-depleted N deposition that may dominate the effects of fractionation that are observed in most warm and humid forests. Fractionation during the steps of N cycling could explain the difference between negative δ15N in plants and positive δ15N in soils, and the increase in soil δ15N with depths. Nevertheless, interpretation of ecosystem δ15N from high-N-deposition regions needs to include data on the deposition 15N signal.

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