Qianlai Zhuang - Profile on Academia.edu (original) (raw)

Papers by Qianlai Zhuang

Communications earth & environment, Jul 12, 2022

Atmospheric concentrations of methane, a powerful greenhouse gas, have strongly increased since 2... more Atmospheric concentrations of methane, a powerful greenhouse gas, have strongly increased since 2007. Measurements of stable carbon isotopes of methane can constrain emissions if the isotopic compositions are known; however, isotopic compositions of methane emissions from wetlands are poorly constrained despite their importance. Here, we use a process-based biogeochemistry model to calculate the stable carbon isotopic composition of global wetland methane emissions. We estimate a mean global signature of -61.3 ± 0.7‰ and find that tropical wetland emissions are enriched by ~11‰ relative to boreal wetlands. Our model shows improved resolution of regional, latitudinal and global variations in isotopic composition of wetland emissions. Atmospheric simulation scenarios with the improved wetland isotopic composition suggest that increases in atmospheric methane since 2007 are attributable to rising microbial emissions. Our findings substantially reduce uncertainty in the stable carbon isotopic composition of methane emissions from wetlands and improve understanding of the global methane budget.

Effects of various spatial scales of water table dynamics on the land-atmospheric methane (CH 4) ... more Effects of various spatial scales of water table dynamics on the land-atmospheric methane (CH 4) exchange have not yet been assessed for large regions. Here we used a coupled hydrology-biogeochemistry model to quantify daily CH 4 exchange over the pan-Arctic from 1993 to 2004 at two spatial scales (100 km and 5 km). The effects of sub-grid spatial variability of the water table depth (WTD) on CH 4 emissions were examined with a TOPMODEL-based parameterization scheme for northern high latitudes regions. Our results indicate that 5 km CH 4 emissions (38.1-55.4 Tg CH 4 yr −1 , considering the spatial heterogeneity of WTD) were 42 % larger than 100 km CH 4 emissions (using grid-cell-mean WTD) and the differences in annual CH 4 emissions were due to increased emitting area and enhanced flux density after WTD redistribution. Further, the inclusion of sub-grid WTD spatial heterogeneity also influences the inter-annual variability of CH 4 emissions. Soil temperature plays a more important role in the 100 km estimates, while the 5 km estimates are more influenced by WTD. This study suggests that previous macro-scale biogeochemical models using grid-cell-mean WTD might have underestimated the regional CH 4 budget. The spatial scale-dependent effects of WTD should be considered in future quantifications of regional CH 4 emissions.

Geophysical Research Letters, 2015

The Arctic is rapidly transitioning toward a seasonal sea ice‐free state, perhaps one of the most... more The Arctic is rapidly transitioning toward a seasonal sea ice‐free state, perhaps one of the most apparent examples of climate change in the world. This dramatic change has numerous consequences, including a large increase in air temperatures, which in turn may affect terrestrial methane emissions. Nonetheless, terrestrial and marine environments are seldom jointly analyzed. By comparing satellite observations of Arctic sea ice concentrations to methane emissions simulated by three process‐based biogeochemical models, this study shows that rising wetland methane emissions are associated with sea ice retreat. Our analyses indicate that simulated high‐latitude emissions for 2005–2010 were, on average, 1.7 Tg CH4 yr−1 higher compared to 1981–1990 due to a sea ice‐induced, autumn‐focused, warming. Since these results suggest a continued rise in methane emissions with future sea ice decline, observation programs need to include measurements during the autumn to further investigate the im...

Process-based land surface models are important tools for estimating global wetland methane (CH 4... more Process-based land surface models are important tools for estimating global wetland methane (CH 4) emissions and projecting their behavior across space and time. So far there are no performance assessments of model responses to drivers at multiple time scales. In this study, we apply wavelet analysis to identify the dominant time scales contributing to model uncertainty in the frequency domain. We evaluate seven wetland models at 23 eddy covariance tower sites. Our study first characterizes site-level

Intercomparison of the Wetchimp-Wsl Wetland Methane Models over West Siberia: How Well Can We Simulate High-Latitude Wetland Methane Emissions?

2014 AGU Fall Meeting, Dec 18, 2014

Wetlands and freshwater bodies (mainly lakes) are the largest natural sources of the greenhouse g... more Wetlands and freshwater bodies (mainly lakes) are the largest natural sources of the greenhouse gas CH 4 to the atmosphere. Great efforts have been made to quantify these source emissions and their uncertainties. Previous research suggests that there might be significant uncertainties coming from "double accounting" emissions from freshwater bodies and wetlands. Here we quantify the methane emissions from both land and freshwater bodies in the pan-Arctic with two process-based biogeochemistry models by minimizing the double accounting at the landscape scale. Two non-overlapping dynamic areal change datasets are used to drive the models. We estimate that the total methane emissions from the pan-Arctic are 36.46 ± 1.02 Tg CH 4 yr −1 during 2000-2015, of which wetlands and freshwater bodies are 21.69 ± 0.59 Tg CH 4 yr −1 and 14.76 ± 0.44 Tg CH 4 yr −1 , respectively. Our estimation narrows the difference between previous bottom-up (53.9 Tg CH 4 yr −1) and top-down (29 Tg CH 4 yr −1) estimates. Our correlation analysis shows that air temperature is the most important driver for methane emissions of inland water systems. Wetland emissions are also significantly affected by vapor pressure, while lake emissions are more influenced by precipitation and landscape areal changes. Sensitivity tests indicate that pan-Arctic lake CH 4 emissions were highly influenced by air temperature but less by lake sediment carbon increase.

Northern peatlands have been a large C sink during the Holocene, but whether they will keep being... more Northern peatlands have been a large C sink during the Holocene, but whether they will keep being a C sink under future climate change is uncertain. This study simulates the responses of northern peatlands to future climate until 2300 with a Peatland version Terrestrial Ecosystem Model (PTEM). The simulations are driven with two sets of CMIP5 climate data (IPSL-CM5A-LR and bcc-csm1-1) under three warming scenarios (RCPs 2.6, 4.5 and 8.5). Peatland area expansion, shrinkage, and C accumulation and decomposition are modeled. In the 21st century, northern peatlands are projected to be a C source of 1.2-13.3 Pg C under all climate scenarios except for RCP 2.6 of bcc-csm1-1 (a sink of 0.8 Pg C). During 2100-2300, northern peatlands under all scenarios are a C source under IPSL-CM5A-LR scenarios, being larger sources than bcc-csm1-1 scenarios (5.9-118.3 vs. 0.7-87.6 Pg C). C sources are attributed to (1) the peatland water table depth (WTD) becoming deeper and permafrost thaw increasing decomposition rate; (2) net primary production (NPP) not increasing much as climate warms because peat drying suppresses net N mineralization; and (3) as WTD deepens, peatlands switching from moss-herbaceous dominated to moss-woody dominated, while woody plants require more N for productivity. Under IPSL-CM5A-LR scenarios, northern peatlands remain as a C sink until the pan-Arctic annual temperature reaches −2.6 to −2.89 • C, while this threshold is −2.09 to −2.35 • C under bcc-csm1-1 scenarios. This study predicts a northern peatland sink-to-source shift in around 2050, earlier than previous estimates of after 2100, and emphasizes the vulnerability of northern peatlands to climate change.

Landsat satellite images of the four soil landscapes showing: rocky uplands along Taylor Highway with stable surfaces subject to frequent fires; silty uplands near Hess Creek with mostly stable surfaces with occasional deep thermokarst lakes; gravelly–sandy lowlands on the Yukon Flats with widesp...

Figure 2. Landsat satellite images of the four soil landsca... more Figure 2. Landsat satellite images of the four soil landscapes showing: rocky uplands along Taylor Highway with stable surfaces subject to frequent fires; silty uplands near Hess Creek with mostly stable surfaces with occasional deep thermokarst lakes; gravelly–sandy lowlands on the Yukon Flats with widespread lake drainage associated with thawing permafrost; and peaty–silty lowlands on the Innoko Flats with widespread thermokarst. Sampling locations shown as white dots. Abstract The diversity of ecosystems across boreal landscapes, successional changes after disturbance and complicated permafrost histories, present enormous challenges for assessing how vegetation, water and soil carbon may respond to climate change in boreal regions. To address this complexity, we used a chronosequence approach to assess changes in vegetation composition, water storage and soil organic carbon (SOC) stocks along successional gradients within four landscapes: (1) rocky uplands on ice-poor hillside colluvium, (2) silty uplands on extremely ice-rich loess, (3) gravelly–sandy lowlands on ice-poor eolian sand and (4) peaty–silty lowlands on thick ice-rich peat deposits over reworked lowland loess. In rocky uplands, after fire permafrost thawed rapidly due to low ice contents, soils became well drained and SOC stocks decreased slightly. In silty uplands, after fire permafrost persisted, soils remained saturated and SOC decreased slightly. In gravelly–sandy lowlands where permafrost persisted in drier forest soils, loss of deeper permafrost around lakes has allowed recent widespread drainage of lakes that has exposed limnic material with high SOC to aerobic decomposition. In peaty–silty lowlands, 2–4 m of thaw settlement led to fragmented drainage patterns in isolated thermokarst bogs and flooding of soils, and surface soils accumulated new bog peat. We were not able to detect SOC changes in deeper soils, however, due to high variability. Complicated soil stratigraphy revealed that permafrost has repeatedly aggraded and degraded in all landscapes during the Holocene, although in silty uplands only the upper permafrost was affected. Overall, permafrost thaw has led to the reorganization of vegetation, water storage and flow paths, and patterns of SOC accumulation. However, changes have occurred over different timescales among landscapes: over decades in rocky uplands and gravelly–sandy lowlands in response to fire and lake drainage, over decades to centuries in peaty–silty lowlands with a legacy of complicated Holocene changes, and over centuries in silty uplands where ice-rich soil and ecological recovery protect permafrost.</p

Biogeosciences, 2021

Mosses are ubiquitous in northern terrestrial ecosystems, and play an important role in regional ... more Mosses are ubiquitous in northern terrestrial ecosystems, and play an important role in regional carbon, water and energy cycling. Current global land surface models that do not consider mosses may bias the quantification of regional carbon dynamics. Here we incorporate mosses as a new plant functional type into the process-based Terrestrial Ecosystem Model (TEM 5.0), to develop a new model (TEM_Moss). The new model explicitly quantifies the interactions between vascular plants and mosses and their competition for energy, water, and nutrients. Compared to the estimates using TEM 5.0, the new model estimates that the regional terrestrial soils currently store 132.7 Pg more C and will store 157.5 and 179.1 Pg more C under the RCP8.5 and RCP2.6 scenarios, respectively, by the end of the 21st century. Ensemble regional simulations forced with different parameters for the 21st century with TEM_Moss predict that the region will accumulate 161.1 ± 142.1 Pg C under the RCP2.6 scenario and 186.7 ± 166.1 Pg C under the RCP8.5 scenario over the century. Our study highlights the necessity of coupling moss into Earth system models to adequately quantify terrestrial carbon-climate feedbacks in the Arctic.

Biogeosciences, 2020

A large amount of soil carbon in northern temperate and boreal regions could be emitted as greenh... more A large amount of soil carbon in northern temperate and boreal regions could be emitted as greenhouse gases in a warming future. However, lacking detailed microbial processes such as microbial dormancy in current biogeochemistry models might have biased the quantification of the regional carbon dynamics. Here the effect of microbial dormancy was incorporated into a biogeochemistry model to improve the quantification for the last century and this century. Compared with the previous model without considering the microbial dormancy, the new model estimated the regional soils stored 75.9 Pg more C in the terrestrial ecosystems during the last century and will store 50.4 and 125.2 Pg more C under the RCP8.5 and RCP2.6 scenarios, respectively, in this century. This study highlights the importance of the representation of microbial dormancy in earth system models to adequately quantify the carbon dynamics in the northern temperate and boreal natural terrestrial ecosystems.

Journal of Geophysical Research: Biogeosciences, 2020

Peatlands are a large carbon reservoir. Yet the quantification of their carbon stock still has a ... more Peatlands are a large carbon reservoir. Yet the quantification of their carbon stock still has a large uncertainty due to lacking observational data and well‐tested peatland biogeochemistry models. Here, a process‐based peatland model was calibrated using long‐term peat carbon accumulation data at multiple sites in North America. The model was then applied to quantify the peat carbon accumulation rates and stocks within North America over the last 12,000 years. We estimated that 85–174 Pg carbon was accumulated in North American peatlands over the study period including 0.37–0.76 Pg carbon in subtropical peatlands. During the period from 10,000 to 8,000 years ago, the warmer and wetter conditions might have played an important role in stimulating peat carbon accumulation by enhancing plant photosynthesis. Enhanced peat decomposition due to warming slowed the carbon accumulation through the rest of the Holocene. While recent modeling studies indicate that the northern peatlands will ...

Nature Climate Change, 2020

Journal of Climate, 2019

Carbon balance of terrestrial ecosystems in the northern high latitudes (NHL) is sensitive to cli... more Carbon balance of terrestrial ecosystems in the northern high latitudes (NHL) is sensitive to climate change. It remains uncertain whether current regional carbon uptake capacity can be sustained under future warming. Here the atmospheric CO2 drawdown rate (CDR) between 1974 and 2014, defined as the CO2 decrease in ppm over the number of days in spring or summer, is estimated using atmospheric CO2 observations at Barrow (now known as Utqiaġvik), Alaska. We found that the sensitivity of CDR to interannual seasonal air temperature anomalies has trended toward less carbon uptake for a given amount of warming over this period. Changes in interannual temperature sensitivity of CDR suggest that relatively warm springs now result in less of a carbon uptake enhancement. Similarly, relatively warm summers now result in greater carbon release. These results generally agree with the sensitivity of net carbon exchange (NCE) estimated by atmospheric CO2 inversion. When NCE was aggregated over No...

Biogeosciences Discussions, 2019

A large amount of soil carbon in the Arctic terrestrial ecosystems could be emitted as greenhouse... more A large amount of soil carbon in the Arctic terrestrial ecosystems could be emitted as greenhouse gases in a warming future. However, lacking detailed microbial processes such as microbial dormancy in current biogeochemistry models might have biased the quantification of the regional carbon dynamics. Here the effect of microbial dormancy was incorporated into a biogeochemistry model to improve the quantification for the last and this century. Compared with the previous model without considering the microbial dormancy, the new model estimated the regional soils stored 75.9 Pg more C in the terrestrial ecosystems during the last century, and will store 50.4 Pg and 125.2 Pg more C under the RCP 8.5 and RCP 2.6 scenarios, respectively, in this century. This study highlights the importance of the representation of microbial dormancy in earth system models to adequately quantify the carbon dynamics in the Arctic.

Biogeosciences, 2018

Various levels of representations of biogeochemical processes in current biogeochemistry models c... more Various levels of representations of biogeochemical processes in current biogeochemistry models contribute to a large uncertainty in carbon budget quantification. Here, we present an uncertainty analysis with a process-based biogeochemistry model, the Terrestrial Ecosystem Model (TEM), into which detailed microbial mechanisms were incorporated. Ensemble regional simulations with the new model (MIC-TEM) estimated that the carbon budget of the arctic ecosystems is 76.0 ± 114.8 Pg C during the 20th century, i.e., −3.1 ± 61.7 Pg C under the RCP 2.6 scenario and 94.7 ± 46 Pg C under the RCP 8.5 scenario during the 21st century. Positive values indicate the regional carbon sink while negative values are a source to the atmosphere. Compared to the estimates using a simpler soil decomposition algorithm in TEM, the new model estimated that the arctic terrestrial ecosystems stored 12 Pg less carbon over the 20th century, i.e., 19 and 30 Pg C less under the RCP 8.5 and RCP 2.6 scenarios, respectively, during the 21st century. When soil carbon within depths of 30, 100, and 300 cm was considered as initial carbon in the 21st century simulations, the region was estimated to accumulate 65.4, 88.6, and 109.8 Pg C, respectively, under the RCP 8.5 scenario. In contrast, under the RCP 2.6 scenario, the region lost 0.7, 2.2, and 3 Pg C, respectively, to the atmosphere. We conclude that the future regional carbon budget evaluation largely depends on whether or not adequate microbial activities are represented in earth system models and on the sizes of soil carbon considered in model simulations.

The Cryosphere, 2018

The methane (CH 4) cycle on the Qinghai-Tibet Plateau (QTP), the world's largest high-elevation p... more The methane (CH 4) cycle on the Qinghai-Tibet Plateau (QTP), the world's largest high-elevation permafrost region, is sensitive to climate change and subsequent freezing and thawing dynamics. Yet, its magnitudes, patterns, and environmental controls are still poorly understood. Here, we report results from five continuous year-round CH 4 observations from a typical alpine steppe ecosystem in the QTP permafrost region. Our results suggest that the QTP permafrost region was a CH 4 sink of −0.86 ± 0.23 g CH 4-C m −2 yr −1 over 2012-2016, a rate higher than that of many other permafrost areas, such as the Arctic tundra in northern Greenland, Alaska, and western Siberia. Soil temperature and soil water content were dominant factors controlling CH 4 fluxes; however, their correlations changed with soil depths due to freezing and thawing dynamics. This region was a net CH 4 sink in autumn, but a net source in spring, despite both seasons experiencing similar top soil thawing and freezing dynamics. The opposite CH 4 sourcesink function in spring versus in autumn was likely caused by the respective seasons' specialized freezing and thawing processes, which modified the vertical distribution of soil layers that are highly mixed in autumn, but not in spring. Furthermore, the traditional definition of four seasons failed to capture the pattern of the annual CH 4 cycle. We developed a new seasonal division method based on soil temperature, bacterial activity, and permafrost active layer thickness, which significantly improved the modeling of the annual CH 4 cycle. Collectively, our findings highlight the critical role of fine-scale climate freezing and thawing dynamics in driving permafrost CH 4 dynamics, which needs to be better monitored and modeled in Earth system models.

Biogeosciences Discussions, 2018

A group of soil microbes plays an important role in nitrogen cycling and N2O emissions from natur... more A group of soil microbes plays an important role in nitrogen cycling and N2O emissions from natural ecosystem soils. We developed a trait-based biogeochemical model based on an extant process-based biogeochemistry model, the Terrestrial Ecosystem Model (TEM), by incorporating the detailed microbial 10 physiological processes of nitrification. The effect of ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) was considered in modeling nitrification. The microbial traits including microbial biomass and density were explicitly considered. In addition, nitrogen cycling was coupled with carbon dynamics based on stoichiometry theory between carbon and nitrogen. The model was parameterized using observational data and then applied to quantifying global N2O emissions from global terrestrial ecosystem soils from 15 1990 to 2000. Our estimates of 8.7±1.6 Tg N yr-1 generally agreed with previous estimates during the study period. Tropical forests are a major emitter, accounting for 42% of the global emissions. The model was more sensitive to temperature and precipitation, and less sensitive to soil organic carbon and nitrogen contents. Compared to the model without considering the detailed microbial activities, the new model shows more variations in response to seasonal changes in climate. Our study suggests that further information on microbial diversity and eco-physiology 20 features is needed. The more specific guilds and their traits shall be considered in future soil N2O emission quantifications.

Global change biology, Nov 13, 2018

Across the Arctic, the net ecosystem carbon (C) balance of tundra ecosystems is highly uncertain ... more Across the Arctic, the net ecosystem carbon (C) balance of tundra ecosystems is highly uncertain due to substantial temporal variability of C fluxes and to landscape heterogeneity. We modeled both carbon dioxide (CO ) and methane (CH ) fluxes for the dominant land cover types in a ~100 km sub-Arctic tundra region in northeast European Russia for the period of 2006-2015 using process-based biogeochemical models. Modeled net annual CO fluxes ranged from -300 g C m y [net uptake] in a willow fen to 3 g C m y [net source] in dry lichen tundra. Modeled annual CH emissions ranged from -0.2 to 22.3 g C m y at a peat plateau site and a willow fen site, respectively. Interannual variability over the decade was relatively small (20-25%) in comparison to variability among the land cover types (150%). Using high-resolution land cover classification, the region was a net sink of atmospheric CO across most land cover types but a net source of CH to the atmosphere due to high emissions from permaf...

Ecological applications : a publication of the Ecological Society of America, 2018

Wetlands are critical terrestrial ecosystems in Alaska, covering ~177,000 km , an area greater th... more Wetlands are critical terrestrial ecosystems in Alaska, covering ~177,000 km , an area greater than all the wetlands in the remainder of the United States. To assess the relative influence of changing climate, atmospheric carbon dioxide (CO ) concentration, and fire regime on carbon balance in wetland ecosystems of Alaska, a modeling framework that incorporates a fire disturbance model and two biogeochemical models was used. Spatially explicit simulations were conducted at 1-km resolution for the historical period (1950-2009) and future projection period (2010-2099). Simulations estimated that wetland ecosystems of Alaska lost 175 Tg carbon (C) in the historical period. Ecosystem C storage in 2009 was 5,556 Tg, with 89% of the C stored in soils. The estimated loss of C as CO and biogenic methane (CH ) emissions resulted in wetlands of Alaska increasing the greenhouse gas forcing of climate warming. Simulations for the projection period were conducted for six climate change scenarios...