Distribution of Articles published per year
(2008 - 2017)
(2008 - 2017)
Total number of journals
Article 0 Reads 1 Citation Grazing effects on surface energy fluxes in a desert steppe on the Mongolian Plateau Published: 17 February 2017
Ecological Applications, doi: 10.1002/eap.1459
Quantifying the surface energy fluxes of grazed and ungrazed steppes is essential to understand the roles of grasslands in local and global climate and in land use change. We used paired eddy-covariance towers to investigate the effects of grazing on energy balance (EB) components: net radiation (Rn), latent heat (LE), sensible heat (H), and soil heat (G) fluxes on adjacent grazed and ungrazed areas in a desert steppe of the Mongolian Plateau for a two-year period (2010–2012). Near 95% of Rn was partitioned as LE and H, whereas the contributions of G and other components of the EB were 5% at an annual scale. H dominated the energy partitioning and shared ~50% of Rn. When comparing the grazed and the ungrazed desert steppe, there was remarkably lower Rn and a lower H, but higher G at the grazed site than at the ungrazed site. Both reduced available energy (Rn − G) and H indicated a “cooling effect” feedback onto the local climate through grazing. Grazing reduced the dry year LE but enhanced the wet year LE. Energy partitioning of LE/Rn was positively correlated with the canopy conductivity, leaf area index, and soil moisture. H/Rn was positively correlated with the vapor pressure deficit but negatively correlated with the soil moisture. Boosted regression tree results showed that LE/Rn was dominated by soil moisture in both years and at both sites, while grazing shifted the H/Rn domination from temperature to soil moisture in the wet year. Grazing not only caused an LE shift between the dry and the wet year, but also triggered a decrease in the H/Rn because of changes in vegetation and soil properties, indicating that the ungrazed area had a greater resistance while the grazed area had a greater sensitivity of EB components to the changing climate.
Article 0 Reads 1 Citation Ecosystem Water-Use Efficiency of Annual Corn and Perennial Grasslands: Contributions from Land-Use History and Species ... Published: 21 April 2016
Ecosystems, doi: 10.1007/s10021-016-9981-2
Carbon and water exchanges between vegetated land surfaces and the atmosphere reveal the ecosystem-scale water-use efficiency (WUE) of primary production. We examined the interacting influence of dominant plant functional groups (C3 and C4) and land-use history on WUEs of annual corn and perennial (restored prairie, switchgrass and smooth brome grass) grasslands in the US Midwest from 2010 through 2013. To this end, we determined ecosystem-level (eWUE) and intrinsic (iWUE) WUEs using eddy covariance and plant carbon isotope ratios, respectively. Corn, switchgrass, and restored prairie were each planted on lands previously managed as grasslands under the USDA Conservation Reserve Program (CRP), or as corn/soybean rotation under conventional agriculture (AGR), while a field of smooth brome grass remained in CRP management. The iWUEs of individual C3 plant species varied little across years. Corn had the highest (4.1) and smooth brome grass the lowest (2.3) overall eWUEs (g C kg−1 H2O) over the 4 years. Corn and switchgrass did not consistently show a significant difference in seasonal eWUE between former CRP and AGR lands, whereas restored prairie had significantly higher seasonal eWUE on former AGR than on former CRP land due to a greater shift from C3 to C4 species on the former AGR land following a drought in 2012. Thus, differences in grassland eWUE were largely determined by the relative dominance of C3 and C4 species within the plant communities. In this humid temperate climate with common short-term and occasional long-term droughts, it is likely that mixed grasslands will become increasingly dominated by C4 grasses over time, with higher yields and eWUE than C3 plants. These results inform models of the interaction between carbon and water cycles in grassland ecosystems under current and future climate and management scenarios.
Article 0 Reads 7 Citations Diurnal to annual changes in latent, sensible heat, and CO2fluxes over a Laurentian Great Lake: A case study in Western ... Published: 01 August 2015
Journal of Geophysical Research: Biogeosciences, doi: 10.1002/2015jg003025
To understand the carbon and energy exchange between the lake surface and the atmosphere, direct measurements of latent, sensible heat, and CO2 fluxes were taken using the eddy covariance (EC) technique in Western Lake Erie during October 2011 to September 2013. We found that the latent heat flux (LE) had a marked one‐peak seasonal change in both years that differed from the diurnal course and lacked a sinusoidal dynamic common in terrestrial ecosystems. Daily mean LE was 4.8 ± 0.1 and 4.3 ± 0.2 MJ m−2 d−1 in Year 1 and Year 2, respectively. The sensible heat flux (H) remained much lower than the LE, with a daily mean of 0.9 ± 0.1 and 1.1 ± 0.1 MJ m−2 d−1 in Year 1 and Year 2, respectively. As a result, the Bowen ratio was <1 during most of the 2 year period, with the lowest summer value at 0.14. The vapor pressure deficit explained 35% of the variation in half hourly LE, while the temperature difference between the water surface and air explained 65% of the variation in half hourly H. Western Lake Erie acted as a small carbon sink holding −19.0 ± 5.4 and −40.2 ± 13.3 g C m−2 in the first and second summers (May–September) but as an annual source of 77.7 ± 18.6 and 49.5 ± 17.9 g C m−2 yr−1 in Year 1 and Year 2, respectively. The CO2 flux ( FCO2) rate varied from −0.45 g C m−2 d−1 to 0.98 g C m−2 d−1. Similar to LE, FCO2 had noticeable diurnal changes during the months that had high chlorophyll a months but not during other months. A significantly negative correlation (P < 0.05) was found between FCO2 and chlorophyll a on monthly fluxes. Three gap‐filling methods, including marginal distribution sampling, mean diurnal variation, and monthly mean, were quantitatively assessed, yielding an uncertainty of 4%, 6%, and 10% in LE, H, and FCO2, respectively.
Article 0 Reads 8 Citations Spatial variability in soil heat flux at three Inner Mongolia steppe ecosystems Published: 01 September 2008
Agricultural and Forest Meteorology, doi: 10.1016/j.agrformet.2008.04.008
Closing the energy budget at flux measurement sites is problematic, even when the fetch extends over flat, homogeneous surfaces with low vegetation cover. We used the residual energy balance and ordinary least square (OLS) linear regression methods to quantify spatial variability in soil heat flux contributing to energy balance closure (EBC), by deploying a mobile energy system within the footprints of three Eddy-covariance towers located in the steppe of Inner Mongolia, China. The EBC at the study sites had a daily average residual of 8–19 W m−2 with OLS slopes of 0.83–0.96. The EBC was better achieved at the wet site than at the dry site. The spatial variability in soil heat flux was 48 W m−2 (13% of Rn) during the day and 15 W m−2 (34%) at night, with an average of 29 W m−2 (24%) across the three sites. A 9% OLS slope difference due to this variability was recorded from our eight plot measurements. A large amount of missing energy (110 W m−2 at peak) could occur with decreasing OLS slope of 23% across the three grassland sites when soil heat flux is not taken into account. In particular, heat storage in the top soil layer not only influenced the magnitude of EBC, but also adjusted soil heat flux to match the ‘truth schedule’. Heat storage in the top soil layer comprised half of the soil heat flux when the heat flux plate was deployed at a depth of 30 mm. If this part of heat storage was neglected, the residual of EBC would increase as large as 60 W m−2 with OLS slope decreasing 9%. Comparing them with the multiple-location soil heat flux measurements, the single-location measurements from near the Eddy-covariance towers obtained a slightly better EBC with the OLS slope increasing by 4%.