Abstract
Changes in land surface albedo can alter ecosystem energy balance and potentially influence climate. We examined the albedo of six bioenergy cropping systems in southwest Michigan USA: ...monocultures of energy sorghum (
Sorghum bicolor
), switchgrass (
Panicum virgatum
L.), and giant miscanthus (
Miscanthus
×
giganteus)
, and polycultures of native grasses, early successional vegetation, and restored prairie. Direct field measurements of surface albedo (
α
s
) from May 2018 through December 2020 at half‐hourly intervals in each system quantified the magnitudes and seasonal differences in albedo (∆
α
) and albedo‐induced radiative forcing (RF
∆
α
). We used a nearby forest as a historical native cover type to estimate reference albedo and RF
∆
α
change upon original land use conversion, and a continuous no‐till maize (
Zea mays L
.) system as a contemporary reference to estimate change upon conversion from annual row crops. Annually,
α
s
differed significantly (
p
< 0.05) among crops in the order: early successional (0.288 ± 0.012SE) >> miscanthus (0.271 ± 0.009) ≈ energy sorghum (0.270 ± 0.010) ≥ switchgrass (0.265 ± 0.009) ≈ restored prairie (0.264 ± 0.012) > native grasses (0.259 ± 0.010) > maize (0.247 ± 0.010). Reference forest had the lowest annual
α
s
(0.134 ± 0.003). Albedo differences among crops during the growing season were also statistically significant, with growing season
α
s
in perennial crops and energy sorghum on average ~20% higher (0.206 ± 0.003) than in no‐till maize (0.184 ± 0.002). Average non‐growing season (NGS)
α
s
(0.370 ± 0.020) was much higher than growing season
α
s
(0.203 ± 0.003) but these NGS differences were not significant. Overall, the original conversion of reference forest and maize landscapes to perennials provided a cooling effect on the local climate (RF
αMAIZE
: −3.83 ± 1.00 W m
−2
; RF
αFOREST
: −16.75 ± 3.01 W m
−2
). Significant differences among cropping systems suggest an additional management intervention for maximizing the positive climate benefit of bioenergy crops, with cellulosic crops on average ~9.1% more reflective than no‐till maize, which itself was about twice as reflective as the reference forest.
To determine the role of grazing on CO2 fluxes in a desert steppe, we used paired eddy-covariance systems to measure the net ecosystem exchange (NEE) and microclimate on adjacent pastures of grazed ...(GS) and ungrazed (FS) steppes on the Mongolian Plateau from 2010 to 2011. The first year was an average precipitation year, while the second year was a dry year. In 2010, there was 91% greater growing seasonal gross ecosystem production (GEP) and 55% greater ecosystem respiration (Re) in the GS than in the FS. As a result, the GS acted as a net carbon uptake of −20 g C m−2 while the FS was a small net carbon release of 10 g C m−2. The greater GEP was mainly caused by the greater photosynthetic capacity due to the suitable environmental conditions and longer growing time in a day and in the growing period accompanied by the enhanced Re that seemed to be responsible for the increased NEE, which compensated for the lower leaf area in the GS. However, an inverse trend was detected in 2011. The seasonal cumulative GEP, Re and NEE were characterized with 92% greater GEP and similar Re in the FS compared with the GS. As a result, the FS acted as a small net carbon uptake of −5 g C m−2, while the GS was a net carbon release of 59 g C m−2. Although the GS had greater carbon uptake in 2010, the variation of daily NEE from both years was lower in the FS, suggesting that the FS has a greater resistance to the changing climate. This also means that future modeling effort should consider year-to-year differences in the carbon balance because relationships between fluxes and climatic regulators change annually in different land use change scenarios.
In a rapidly urbanizing world, heavy air pollution and increasing surface temperature pose significant threats to human health and lives, especially in densely populated cities. In this study, we ...took an information theory perspective to investigate the causal relationship between diel land surface temperature (LST) and transboundary air pollution (TAP) from 2003 to 2020 in the Bangkok Metropolitan Region (BMR), which includes Bangkok Metropolis and its five adjacent provinces. We found an overall increasing trend of LST over the study region, with the mean daytime LST rising faster than nighttime LST. Evident seasonal variations showed high aerosol optical depth (AOD) loadings during the dry period and low loadings at the beginning of the rainy season. Our study revealed that TAP affected diel surface temperature in Bangkok Metropolis significantly. Causality tests show that air pollutants of two adjacent provinces west of Bangkok, i.e., Nakhon Pathom and Samut Sakhon, have a greater influence on the LST of Bangkok than other provinces. Also, the bidirectional relationship indicates that air pollution has a greater impact on daytime LST than nighttime LST. While LST has an insignificant influence on AOD during the daytime, it influences AOD significantly at night. Our study offers a new approach to understanding the causal impact of TAP and can help policymakers to identify the most relevant locations that cause pollution, leading to appropriate planning and management.
The Mongolian Plateau (MP) and Tibetan Plateau (TP) have experienced higher-than-global average warming in recent decades, resulting in many significant changes in ecosystem structure and function. ...Among them are the leaf area index (LAI) and albedo, which play a fundamental role in understanding many causes and consequences of land surface processes and climate. Here, we focused on the spatiotemporal changes of LAI, albedo, and their spatiotemporal relationships on the two roofing landscapes in Eurasia. Based on the MODIS products, we investigated the spatiotemporal changes of albedo(VIS, NIR and SHO) and LAI from 2000 through 2016. We found that there existed a general negative logarithmic relationship between LAI and three measures of albedo on both plateaus. No significant relationship was found for LAI-albedoNIR on the TP, due to more complex land surface canopy characteristics affected by the NIR reflection there. During 2000–2016, overall, annual mean LAI increased significantly by 119.40 × 103 km2 on the MP and by 28.35 × 103 km2 on the TP, while the decreased areas for annual mean albedoVIS were 585.59 × 103 km2 and 235.73 × 103 km2 on the MP and TP, respectively. More importantly, the LAI-albedo relationships varied substantially across the space and over time, with mismatches found in some parts of the landscapes. Substantial additional efforts with observational and/or experimental investigations are needed to explore the underlying mechanisms responsible for these relationships, including the influences of vegetation characteristics and disturbances.
Over 13 million ha of former cropland are enrolled in the US Conservation Reserve Program (CRP), providing well-recognized biodiversity, water quality, and carbon (C) sequestration benefits that ...could be lost on conversion back to agricultural production. Here we provide measurements of the greenhouse gas consequences of converting CRP land to continuous corn, corn–soybean, or perennial grass for biofuel production. No-till soybeans preceded the annual crops and created an initial carbon debt of 10.6 Mg CO2 equivalents (CO2e)·ha–1 that included agronomic inputs, changes in C stocks, altered N2O and CH4 fluxes, and foregone C sequestration less a fossil fuel offset credit. Total debt, which includes future debt created by additional changes in soil C stocks and the loss of substantial future soil C sequestration, can be constrained to 68 Mg CO2e·ha–1 if subsequent crops are under permanent no-till management. If tilled, however, total debt triples to 222 Mg CO2e·ha–1 on account of further soil C loss. Projected C debt repayment periods under no-till management range from 29 to 40 y for corn–soybean and continuous corn, respectively. Under conventional tillage repayment periods are three times longer, from 89 to 123 y, respectively. Alternatively, the direct use of existing CRP grasslands for cellulosic feedstock production would avoid C debt entirely and provide modest climate change mitigation immediately. Incentives for permanent no till and especially permission to harvest CRP biomass for cellulosic biofuel would help to blunt the climate impact of future CRP conversion.
Assessing forest stand conditions in urban and peri-urban areas is essential to support ecosystem service planning and management, as most of the ecosystem services provided are a consequence of ...forest stand characteristics. However, collecting data for assessing forest stand conditions is time consuming and labor intensive. A plausible approach for addressing this issue is to establish a relationship between in situ measurements of stand characteristics and data from airborne laser scanning (LiDAR). In this study we assessed forest stand volume and above-ground biomass (AGB) in a broadleaved urban forest, using a combination of LiDAR-derived metrics, which takes the form of a forest allometric model. We tested various methods for extracting proxies of basal area (BA) and mean stand height (H) from the LiDAR point-cloud distribution and evaluated the performance of different models in estimating forest stand volume and AGB. The best predictors for both models were the scale parameters of the Weibull distribution of all returns (except the first) (proxy of BA) and the 95th percentile of the distribution of all first returns (proxy of H). The R2 were 0.81 (p < 0.01) for the stand volume model and 0.77 (p < 0.01) for the AGB model with a RMSE of 23.66 m3·ha−1 (23.3%) and 19.59 Mg·ha−1 (23.9%), respectively. We found that a combination of two LiDAR-derived variables (i.e., proxy of BA and proxy of H), which take the form of a forest allometric model, can be used to estimate stand volume and above-ground biomass in broadleaved urban forest areas. Our results can be compared to other studies conducted using LiDAR in broadleaved forests with similar methods.
•C/H2O fluxes vary greatly with agro-pastoral land uses in salinized Songnen Plain.•Fenced and clipped meadow have higher transpiration: evapotranspiration ratio.•Grassland C uptake is limited by ...VPD, while paddy is driven by Ta.
Land reclamation and grassland management are important land utilization pattern for effective use and restoration of alkali-saline land in agriculture-pasture transition regions. These large-scale land cover/land use changes (LCLUC) could impose profound and divergent impacts on terrestrial carbon (C) and H2O cycling, hence require precise assessment of ecosystem CO2 uptake and water use differences due to specific land use of the same climate/soil landscape. We initiated clustered eddy covariance flux-tower observations and C/H2O fluxes analysis of 4 adjacent representative land cover and grassland managements types on alkali-saline Songnen Plain, including fenced meadow (as reference land use), clipped meadow, degraded alkali-saline land and paddy field in 2018–2019. Results showed that differences in land use influenced the magnitude and temporal variation of net ecosystem productivity (NEP) and evapotranspiration (ET). Compared to fenced meadow, paddy field increased growing season C uptake by 63.3% and ET by 35.4%, while degraded alkali-saline land and clipped meadow decreased C uptake by 43.0% and 30.6%, and ET by 32.1% and 3.2%. Degraded alkali-saline land barely sequestrate C in dry year, whereas paddy field is least sensitive to inter-annual precipitation variation. Growing season C uptake was advanced in clipped meadow due to increased surface temperature, while monthly ET peaked early at May in paddy field. Agricultural use and specific grassland management also caused large differences in ET partitioning. Fenced meadow had greater ET partitioned into transpiration (69%) than clipped meadow (58%), degraded alkali-saline land and paddy field (41% and 34%, respectively). Water use efficiency appeared greater in clipped meadow and degraded alkali-saline land than in fenced meadow, and responded differently to abiotic factors. Overall, large-scale LCLUC has exerted significant influence on terrestrial C/H2O balances and physical responses in alkali-saline Songnen Plain.
► Ten-year poplar plantation forest in Beijing of China was a strong carbon sink. ► Soil moisture suppressed carbon uptake more than respiration under drought. ► The timing and intensity of drought ...were the main causes of the variation in ecosystem CO2 fluxes.
Poplar plantations are widely used for timber production and ecological restoration in northern China, a region that experiences frequent droughts and water scarcity. An open-path eddy-covariance (EC) system was used to continuously measure the carbon, water, and energy fluxes in a poplar plantation during the growing season (i.e., April–October) over the period 2006–2008 in the Daxing District of Beijing, China. We examined the seasonal and inter-annual variability of gross ecosystem productivity (GEP), net ecosystem exchange (NEE), and ecosystem respiration (ER). Although annual total precipitation was the lowest in 2006, natural rainfall was amended by flood irrigation. In contrast, no supplementary water was provided during a severe drought in spring (i.e., April–June), 2007, resulting in a significant reduction in net ecosystem production (NEP=−NEE). This resulted from the combined effects of larger decrease in GEP than that in ER. Despite the drought – induced reduction in NEP, the plantation forest was a strong carbon sink accumulating 591±62, 641±71, and 929±75gCm−2year−1 for 2006, 2007, and 2008, respectively. The timing of the drought significantly affected the annual GEP. Severe drought during canopy development induced a lasting reduction in carbon exchange throughout the growing season, while the severe drought at the end of growing season did not significantly reduce carbon uptake. Additionally, irrigation reduced negative drought impacts on carbon sequestration. Overall, this fast growing poplar plantation is a strong carbon sink and is sensitive to the changes in environmental conditions.
Urban built-up area, one of the most important measures of an urban landscape, is an essential variable for understanding ecological and socioeconomic processes in urban systems. With an interest in ...urban development in transitional economies in Southeast Asia, we recognized a lack of high-to-medium resolution (<60 m) built-up information for countries in the region, including Vietnam, Laos, Cambodia and Myanmar. In this study, we combined multiple remote sensing data, including Landsat, DMSP/OLS night time light, MODIS NDVI data and other ancillary spatial data, to develop a 30-m resolution urban built-up map of 2010 for the above four countries. Following the trend analysis of the DMSP/OLS time series and the 2010 urban built-up extent, we also quantified the spatiotemporal dynamics of urban built-up areas from 1992 to 2010. Among the four countries, Vietnam had the highest proportion of urban built-up area (0.91%), followed by Myanmar (0.15%), Cambodia (0.12%) and Laos (0.09%). Vietnam was also the fastest in new built-up development (increased ~8.8-times during the 18-year study period), followed by Laos, Cambodia and Myanmar, which increased at 6.0-, 3.6- and 0.24-times, respectively.
Understanding the joint impact of anthropologic and climatic changes on ecosystem function and dynamics is among the frontiers in global environmental change studies. Carbon and water balances are ...especially crucial to the sustainable ecosystem and functional returns in sensitive regions such as the Mongolian Plateau. In this study, the significance of non-climatic component (NCC) on carbon and water use efficiency (CUE and WUE) is quantified among the ecosystem types on the Mongolian Plateau. We mapped the spatial gradients of carbon/water balance and delineated the hotspots of NCC-driven CUE and WUE for 2000-2013 using gross and net primary production (GPP and NPP) and evapotranspiration (ET) products derived from the MODIS databases. Significantly higher CUE and WUE values were found in Mongolia (MG) than in Inner Mongolia (IM) due to both climatic forcing (CF) and NCC. NCC was found to dominate the changes in CUE and WUE in the steppes on the plateau by over 16% and 22%, respectively, but with spatially uneven distributions. NCC-driven WUE values were much higher than those driven by CF. The hotspots for NCC-driven CUE did not overlap with those of WUE, with CUE hotspots concentrated in the east of MG and northeast of IM; WUE hotspots were found in the central and Khangai regions of MG and eastern regions of IM. The NCC-driven CUE area in MG was from population growth and the industrial shares in gross domestic product, while the NCC-driven WUE area was due to livestock growth in MG but driven by the growth of cultivated lands in IM. In sum, we conclude that NCC provoked substantial spatiotemporal changes on carbon and water use. CF and NCC effects on carbon and water balance varied in space, by ecosystem type, and between the two political entities.
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