Characteristics of CO2, water vapor, and energy exchanges at a headwater wetland ecosystem of the Qinghai Lake

2019 ◽  
Vol 99 (3) ◽  
pp. 227-243
Author(s):  
Shengkui Cao ◽  
Guangchao Cao ◽  
Kelong Chen ◽  
Guangzhao Han ◽  
Ying Liu ◽  
...  
Keyword(s):  
Water Vapor ◽  
Ecosystem Respiration ◽  
Gross Primary Production ◽  
Heat Fluxes ◽  
Qinghai Lake ◽  
Wetland Ecosystem ◽  
Monthly Average ◽  
Headwater Wetland ◽  
Heat Exchanges ◽  
Annual Scale

Ecosystem carbon dioxide (CO2), water vapor, and heat exchanges in alpine wetlands on the Qinghai–Tibetan Plateau are not comprehensively understood. Thus, we studied variability of net ecosystem CO2 exchange (NEE), ecosystem respiration (Re), gross primary production (GPP), evapotranspiration (ET), and heat fluxes over a headwater wetland ecosystem in the Qinghai Lake region. Results showed that the headwater wetland ecosystem was net CO2 absorption on the annual scale, in which monthly NEE, GPP, and Re in two consecutive years varied from −165.16 to 93 g CO2 m−2 mo−1, 6.66 to 384.45 g CO2 m−2 mo−1, and 6.9 to 232.02 g CO2 m−2 mo−1, respectively. The monthly ET from June to September was smaller than precipitation; these results reversed in the remaining months. Annual ET was 362.1 mm in 2015 and 324.96 mm in 2016. The net radiation (Rn), sensible heat (H), latent heat (LE), and ground heat (G) fluxes showed similar monthly patterns. Values of monthly average half-hour Rn, H, LE, and G at the daytime showed Rn > LE > H > G, and the time of the monthly half-hour G peak obviously lagged the Rn, H, and LE. Monthly average Bowen ratios were <1 from May to October, but it reversed in the rest of the months.

Study on Water Vapor Fluxes in Qinghai Lake Alpine Wetland Ecosystem in the Spring

2015 ◽  
Author(s):  
Jing Zhang ◽  
Sheng-Kui Cao ◽  
Guang-Chao Cao ◽  
Ke-Long Chen ◽  
Guang-Zhao Han ◽  
...  
Keyword(s):  
Water Vapor ◽  
Qinghai Lake ◽  
Wetland Ecosystem ◽  
Alpine Wetland

scholarly journals ORCHIDEE-PEAT (revision 4596), a model for northern peatland CO<sub>2</sub>, water, and energy fluxes on daily to annual scales

2018 ◽  
Vol 11 (2) ◽  
pp. 497-519 ◽  
Author(s):  
Chunjing Qiu ◽  
Dan Zhu ◽  
Philippe Ciais ◽  
Bertrand Guenet ◽  
Gerhard Krinner ◽  
...  
Keyword(s):  
Water Table ◽  
Land Surface ◽  
Ecosystem Respiration ◽  
Gross Primary Production ◽  
Peat Soil ◽  
Model Performance ◽  
Grid Cell ◽  
Heat Fluxes ◽  
Surface Model ◽  
Energy Fluxes

Abstract. Peatlands store substantial amounts of carbon and are vulnerable to climate change. We present a modified version of the Organising Carbon and Hydrology In Dynamic Ecosystems (ORCHIDEE) land surface model for simulating the hydrology, surface energy, and CO2 fluxes of peatlands on daily to annual timescales. The model includes a separate soil tile in each 0.5° grid cell, defined from a global peatland map and identified with peat-specific soil hydraulic properties. Runoff from non-peat vegetation within a grid cell containing a fraction of peat is routed to this peat soil tile, which maintains shallow water tables. The water table position separates oxic from anoxic decomposition. The model was evaluated against eddy-covariance (EC) observations from 30 northern peatland sites, with the maximum rate of carboxylation (Vcmax) being optimized at each site. Regarding short-term day-to-day variations, the model performance was good for gross primary production (GPP) (r2 =  0.76; Nash–Sutcliffe modeling efficiency, MEF  =  0.76) and ecosystem respiration (ER, r2 =  0.78, MEF  =  0.75), with lesser accuracy for latent heat fluxes (LE, r2 =  0.42, MEF  =  0.14) and and net ecosystem CO2 exchange (NEE, r2 =  0.38, MEF  =  0.26). Seasonal variations in GPP, ER, NEE, and energy fluxes on monthly scales showed moderate to high r2 values (0.57–0.86). For spatial across-site gradients of annual mean GPP, ER, NEE, and LE, r2 values of 0.93, 0.89, 0.27, and 0.71 were achieved, respectively. Water table (WT) variation was not well predicted (r2 < 0.1), likely due to the uncertain water input to the peat from surrounding areas. However, the poor performance of WT simulation did not greatly affect predictions of ER and NEE. We found a significant relationship between optimized Vcmax and latitude (temperature), which better reflects the spatial gradients of annual NEE than using an average Vcmax value.

Study on the Characteristics of Heat Fluxes in the Qinghai Lake Alpine Wetland Ecosystem over Spring

2015 ◽  
Author(s):  
Yang-Yang Lin ◽  
Sheng-Kui Cao ◽  
Guang-Chao Cao ◽  
Ke-Long Chen ◽  
Jing Zhang ◽  
...  
Keyword(s):  
Heat Fluxes ◽  
Qinghai Lake ◽  
Wetland Ecosystem ◽  
Alpine Wetland

scholarly journals Spatiotemporal Variations in Growing Season Exchanges of CO2, H2O, and Sensible Heat in Agricultural Fields of the Southern Great Plains

2007 ◽  
Vol 11 (17) ◽  
pp. 1-21 ◽  
Author(s):  
Marc L. Fischer ◽  
David P. Billesbach ◽  
Joseph A. Berry ◽  
William J. Riley ◽  
Margaret S. Torn
Keyword(s):  
Regression Model ◽  
Great Plains ◽  
Ecosystem Respiration ◽  
Gross Primary Production ◽  
Growing Season ◽  
Temporal Variations ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Agricultural Fields ◽  
Southern Great Plains

Abstract Climate, vegetation cover, and management create finescale heterogeneity in unirrigated agricultural regions, with important but not well-quantified consequences for spatial and temporal variations in surface CO2, water, and heat fluxes. Eddy covariance fluxes were measured in seven agricultural fields—comprising winter wheat, pasture, and sorghum—in the U.S. Southern Great Plains (SGP) during the 2001–03 growing seasons. Land cover was the dominant source of variation in surface fluxes, with 50%–100% differences between fields planted in winter–spring versus fields planted in summer. Interannual variation was driven mainly by precipitation, which varied more than twofold between years. Peak aboveground biomass and growing season net ecosystem exchange (NEE) of CO2 increased in rough proportion to precipitation. Based on a partitioning of gross fluxes with a regression model, ecosystem respiration increased linearly with gross primary production, but with an offset that increased near the time of seed production. Because the regression model was designed for well-watered periods, it successfully retrieved NEE and ecosystem parameters during the peak growing season and identified periods of moisture limitation during the summer. In summary, the effects of crop type, land management, and water limitation on carbon, water, and energy fluxes were large. Capturing the controlling factors in landscape-scale models will be necessary to estimate the ecological feedbacks to climate and other environmental impacts associated with changing human needs for agricultural production of food, fiber, and energy.

A Positive Feedback Process Related to the Rapid Development of an Extratropical Cyclone over the Kuroshio/Kuroshio Extension

2018 ◽  
Vol 146 (2) ◽  
pp. 417-433 ◽  
Author(s):  
Hidetaka Hirata ◽  
Ryuichi Kawamura ◽  
Masaya Kato ◽  
Taro Shinoda
Keyword(s):  
Water Vapor ◽  
Positive Feedback ◽  
Heat Supply ◽  
Rapid Development ◽  
Kuroshio Extension ◽  
Heat Fluxes ◽  
Latent Heating ◽  
Sensible Heat ◽  
Feedback Process ◽  
The Kuroshio

Abstract The active roles of sensible heat supply from the Kuroshio/Kuroshio Extension in the rapid development of an extratropical cyclone, which occurred in the middle of January 2013, were examined by using a regional cloud-resolving model. In this study, a control experiment and three sensitivity experiments without sensible and latent heat fluxes from the warm currents were conducted. When the cyclone intensified, sensible heat fluxes from these currents become prominent around the cold conveyor belt (CCB) in the control run. Comparisons among the four runs revealed that the sensible heat supply facilitates deepening of the cyclone’s central pressure, CCB development, and enhanced latent heating over the bent-back front. The sensible heat supply enhances convectively unstable conditions within the atmospheric boundary layer along the CCB. The increased convective instability is released by the forced ascent associated with frontogenesis around the bent-back front, eventually promoting updraft and resultant latent heating. Additionally, the sensible heating leads to an increase in the water vapor content of the saturated air related to the CCB through an increase in the saturation mixing ratio. This increased water vapor content reinforces the moisture flux convergence at the bent-back front, contributing to the activation of latent heating. Previous research has proposed a positive feedback process between the CCB and latent heating over the bent-back front in terms of moisture supply from warm currents. Considering the above two effects of the sensible heat supply, this study revises the positive feedback process.

scholarly journals Can land degradation drive differences in the C exchange of two similar semiarid ecosystems?

2018 ◽  
Vol 15 (1) ◽  
pp. 263-278 ◽  
Author(s):  
Ana López-Ballesteros ◽  
Cecilio Oyonarte ◽  
Andrew S. Kowalski ◽  
Penélope Serrano-Ortiz ◽  
Enrique P. Sánchez-Cañete ◽  
...  
Keyword(s):  
Vadose Zone ◽  
Land Degradation ◽  
Ecosystem Respiration ◽  
Gross Primary Production ◽  
Co2 Flux ◽  
C Sequestration ◽  
Co2 Exchange ◽  
Striking Difference ◽  
Soil Variables ◽  
Natural Site

Abstract. Currently, drylands occupy more than one-third of the global terrestrial surface and are recognized as areas vulnerable to land degradation. The concept of land degradation stems from the loss of an ecosystem's biological productivity due to long-term loss of natural vegetation or depletion of soil nutrients. Drylands' key role in the global carbon (C) balance has been recently demonstrated, but the effects of land degradation on C sequestration by these ecosystems still need to be investigated. In the present study, we compared net C and water vapor fluxes, together with satellite, meteorological and vadose zone (CO2, water content and temperature) measurements, between two nearby (∼ 23 km) experimental sites representing “natural” (i.e., site of reference) and “degraded” grazed semiarid grasslands. We utilized data acquired over 6 years from two eddy covariance stations located in southeastern Spain with highly variable precipitation magnitude and distribution. Results show a striking difference in the annual C balances with an average net CO2 exchange of 196 ± 40 (C release) and −23 ± 2 g C m−2 yr−1 (C fixation) for the degraded and natural sites, respectively. At the seasonal scale, differing patterns in net CO2 fluxes were detected over both growing and dry seasons. As expected, during the growing seasons, greater net C uptake over longer periods was observed at the natural site. However, a much greater net C release, probably derived from subterranean ventilation, was measured at the degraded site during drought periods. After subtracting the nonbiological CO2 flux from net CO2 exchange, flux partitioning results point out that, during the 6 years of study, gross primary production, ecosystem respiration and water use efficiency were, on average, 9, 2 and 10 times higher, respectively, at the natural site versus the degraded site. We also tested differences in all monitored meteorological and soil variables and CO2 at 1.50 m belowground was the variable showing the greatest intersite difference, with ∼ 1000 ppm higher at the degraded site. Thus, we believe that subterranean ventilation of this vadose zone CO2, previously observed at both sites, partly drives the differences in C dynamics between them, especially during the dry season. It may be due to enhanced subsoil–atmosphere interconnectivity at the degraded site.

Subcloud and Cloud-Base Latent Heat Fluxes during Shallow Cumulus Convection

2019 ◽  
Vol 77 (3) ◽  
pp. 1081-1100 ◽  
Author(s):  
Neil P. Lareau
Keyword(s):  
Boundary Layer ◽  
Water Vapor ◽  
Latent Heat ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Cloud Base ◽  
Cumulus Convection ◽  
Mixing Ratio ◽  
Convective Boundary ◽  
Water Vapor Mixing Ratio

Abstract Doppler and Raman lidar observations of vertical velocity and water vapor mixing ratio are used to probe the physics and statistics of subcloud and cloud-base latent heat fluxes during cumulus convection at the ARM Southern Great Plains (SGP) site in Oklahoma, United States. The statistical results show that latent heat fluxes increase with height from the surface up to ~0.8Zi (where Zi is the convective boundary layer depth) and then decrease to ~0 at Zi. Peak fluxes aloft exceeding 500 W m−2 are associated with periods of increased cumulus cloud cover and stronger jumps in the mean humidity profile. These entrainment fluxes are much larger than the surface fluxes, indicating substantial drying over the 0–0.8Zi layer accompanied by moistening aloft as the CBL deepens over the diurnal cycle. We also show that the boundary layer humidity budget is approximately closed by computing the flux divergence across the 0–0.8Zi layer. Composite subcloud velocity and water vapor anomalies show that clouds are linked to coherent updraft and moisture plumes. The moisture anomaly is Gaussian, most pronounced above 0.8Zi and systematically wider than the velocity anomaly, which has a narrow central updraft flanked by downdrafts. This size and shape disparity results in downdrafts characterized by a high water vapor mixing ratio and thus a broad joint probability density function (JPDF) of velocity and mixing ratio in the upper CBL. We also show that cloud-base latent heat fluxes can be both positive and negative and that the instantaneous positive fluxes can be very large (~10 000 W m−2). However, since cloud fraction tends to be small, the net impact of these fluxes remains modest.

scholarly journals High Rates of Ecosytem Metabolism in Five Western Rivers

2011 ◽  
Vol 33 ◽  
pp. 115-118
Author(s):  
Robert Hall ◽  
Jennifer Tank ◽  
Michelle Baker ◽  
Emma Rosi-Marshall ◽  
Michael Grace ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Primary Production ◽  
Carbon Cycling ◽  
Carbon Balance ◽  
Carbon Fixation ◽  
Higher Plants ◽  
Ecosystem Respiration ◽  
Gross Primary Production ◽  
Total Rate ◽  
Global Carbon

Primary production and respiration are core functions of river ecosystems that in part determine the carbon balance. Gross primary production (GPP) is the total rate of carbon fixation by autotrophs such as algae and higher plants and is equivalent to photosynthesis. Ecosystem respiration (ER) measures rate at which organic carbon is mineralized to CO2 by all organisms in an ecosystem. Together these fluxes can indicate the base of the food web to support animal production (Marcarelli et al. 2011), can predict the cycling of other elements (Hall and Tank 2003), and can link ecosystems to global carbon cycling (Cole et al. 2007).

scholarly journals Simulating measurable ecosystem carbon and nitrogen dynamics with the mechanistically-defined MEMS 2.0 model

2021 ◽  
Author(s):  
Yao Zhang ◽  
Jocelyn M. Lavallee ◽  
Andy D. Robertson ◽  
Rebecca Even ◽  
Stephen M. Ogle ◽  
...  
Keyword(s):  
Organic Matter ◽  
Soil Water ◽  
Root Zone ◽  
Ecosystem Respiration ◽  
Gross Primary Production ◽  
Total N ◽  
Calibration And Validation ◽  
Biogeochemical Models ◽  
Lower Accuracy ◽  
C Stocks

Abstract. For decades, predominant soil biogeochemical models have used conceptual soil organic matter (SOM) pools and only simulated them to a shallow depth in soil. Efforts to overcome these limitations have prompted the development of new generation SOM models, including MEMS 1.0, which represents measurable biophysical SOM fractions, over the entire root zone, and embodies recent understanding of the processes that govern SOM dynamics. Here we present the result of continued development of the MEMS model, version 2.0. MEMS 2.0 is a full ecosystem model with modules simulating plant growth with above and below-ground inputs, soil water, and temperature by layer, decomposition of plant inputs and SOM, and mineralization and immobilization of nitrogen (N). The model simulates two commonly measured SOM pools – particulate and mineral-associated organic matter (POM and MAOM), respectively. We present results of calibration and validation of the model with several grassland sites in the U.S. MEMS 2.0 generally captured the soil carbon (C) stocks (R2 of 0.89 and 0.6 for calibration and validation, respectively) and their distributions between POM and MAOM throughout the entire soil profile. The simulated soil N matches measurements but with lower accuracy (R2 of 0.73 and 0.31 for calibration and validation of total N in SOM, respectively) than for soil C. Simulated soil water and temperature were compared with measurements and the accuracy is comparable to the other commonly used models. The seasonal variation in gross primary production (GPP; R2 = 0.83), ecosystem respiration (ER; R2 = 0.89), net ecosystem exchange (NEE; R2 = 0.67), and evapotranspiration (ET; R2 = 0.71) were well captured by the model. We will further develop the model to represent forest and agricultural systems and improve it to incorporate new understanding of SOM decomposition.

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