Evaluation of Carbon Fluxes and Trends (2000e2008) in the Greater Platte River Basin: A Sustainability Study for Potential Biofuel Feedstock Development

This study evaluates the carbon fluxes and trends and examines the environmental sustainability (e.g., carbon budget, source or sink) of the potential biofuel feedstock sites identified in the Greater Platte River Basin (GPRB). A 9-year (2000e2008) time series of net ecosystem production (NEP), a measure of net carbon absorption or emission by ecosystems, was used to assess the historical trends and budgets of carbon flux for grasslands in the GPRB. The spatially averaged annual NEP (ANEP) for grassland areas that are possibly suitable for biofuel expansion (productive grasslands) was 71e169 g C m2 year1 during 2000e2008, indicating a carbon sink (more carbon is absorbed than released) in these areas. The spatially averaged ANEP for areas not suitable for biofuel feedstock development (less productive or degraded grasslands) was 47 to 69 g C m2 year1 during 2000e2008, showing a weak carbon source or a weak carbon sink (carbon emitted is nearly equal to carbon absorbed). The 9-year pre-harvest cumulative ANEP was 1166 g C m2 for the suitable areas (a strong carbon sink) and 200 g C m2 for the non-suitable areas (a weak carbon sink). Results demonstrate and confirm that our method of dynamic modeling of ecosystem performance can successfully identify areas desirable and sustainable for future biofuel feedstock development. This study provides useful information for land managers and decision makers to make optimal land use decisions regarding biofuel feedstock development and sustainability

Calibration of remotely sensed, coarse resolution NDVI to CO2 fluxes in a sagebrush–steppe ecosystem

The net ecosystem exchange (NEE) of carbon flux can be partitioned into gross primary productivity (GPP) and respiration (R). The contribution of remote sensing and modeling holds the potential to predict these components and map them spatially and temporally. This has obvious utility to quantify carbon sink and source relationships and to identify improved land management strategies for optimizing carbon sequestration. The objective of our study was to evaluate prediction of 14-day average daytime CO2 fluxes ( Fday) and nighttime CO2 fluxes (Rn) using remote sensing and other data. Fday and Rn were measured with a Bowen ratio–energy balance (BREB) technique in a sagebrush (Artemisia spp.)–steppe ecosystem in northeast Idaho, USA, during 1996–1999. Micrometeorological variables aggregated across 14-day periods and time-integrated Advanced Very High Resolution Radiometer (AVHRR) Normalized Difference Vegetation Index (iNDVI) were determined during four growing seasons (1996–1999) and used to predict Fday and Rn. We found that iNDVI was a strong predictor of Fday (R2= 0.79, n = 66, P \u3c 0.0001). Inclusion of evapotranspiration in the predictive equation led to improved predictions of Fday (R2= 0.82, n = 66, P \u3c 0.0001). Cross-validation indicated that regression tree predictions of Fday were prone to overfitting and that linear regression models were more robust. Multiple regression and regression tree models predicted Rn quite well (R2 = 0.75–0.77, n = 66) with the regression tree model being slightly more robust in cross-validation. Temporal mapping of Fday and Rn is possible with these techniques and would allow the assessment of NEE in sagebrush–steppe ecosystems. Simulations of periodic Fday measurements, as might be provided by a mobile flux tower, indicated that such measurements could be used in combination with iNDVI to accurately predict Fday. These periodic measurements could maximize the utility of expensive flux towers for evaluating various carbon management strategies, carbon certification, and validation and calibration of carbon flux models

Upscaling Carbon Fluxes Over the Great Plains Grasslands: Sinks and Sources

Previous studies suggested that the grasslands may be carbon sinks or near equilibrium, and they often shift between carbon sources in drought years and carbon sinks in other years. It is important to understand the responses of net ecosystem production (NEP) to various climatic conditions across the U.S. Great Plains grasslands. Based on 15 grassland flux towers, we developed a piecewise regression model and mapped the grassland NEP at 250 m spatial resolution over the Great Plains from 2000 to 2008. The results showed that the Great Plains was a net sink with an averaged annual NEP of 24 ± 14 g C m−2 yr−1, ranging from a low value of 0.3 g C m−2 yr−1 in 2002 to a high value of 47.7 g C m−2 yr−1 in 2005. The regional averaged NEP for the entire Great Plains grasslands was estimated to be 336 Tg C yr−1 from 2000 to 2008. In the 9 year period including 4 dry years, the annual NEP was very variable in both space and time. It appeared that the carbon gains for the Great Plains were more sensitive to droughts in the west than the east. The droughts in 2000, 2002, 2006, and 2008 resulted in increased carbon losses over drought‐affected areas, and the Great Plains grasslands turned into a relatively low sink with NEP values of 15.8, 0.3, 20.1, and 10.2 g C m−2 yr−1 for the 4 years, respectively

Evaluation and comparison of gross primary production estimates for the Northern Great Plains grasslands

Two spatially-explicit estimates of gross primary production (GPP) are available for the Northern Great Plains. An empirical piecewise regression (PWR) GPP model was developed from flux tower measurements to map carbon flux across the region. The Moderate Resolution Imaging Spectrometer (MODIS) GPP model is a process-based model that uses flux tower data to calibrate its parameters. Verification and comparison of the regional PWR GPP and the global MODIS GPP are important for the modeling of grassland carbon flux. This study compared GPP estimates from PWR and MODIS models with five towers in the grasslands. Among them, PWR GPP and MODIS GPP showed a good agreement with tower-based GPP at three towers. The global MODIS GPP, however, did not agree well with tower-based GPP at two other towers, probably because of the insensitivity of MODIS model to regional ecosystem and climate change and extreme soil moisture conditions. Cross validation indicated that the PWR model is relatively robust for predicting regional grassland GPP. However, the PWR model should include a wide variety of flux tower data as the training data sets to obtain more accurate results. In addition, GPP maps based on the PWR and MODIS models were compared for the entire region. In the northwest and south, PWR GPP was much higher than MODIS GPP. These areas were characterized by the higher water holding capacity with a lower proportion of C4 grasses in the northwest and a higher proportion of C4 grasses in the south. In the central and southeastern regions, PWR GPP was much lower than MODIS GPP under complicated conditions with generally mixed C3/C4 grasses. The analysis indicated that the global MODIS GPP model has some limitations on detecting moisture stress, which may have been caused by the facts that C3 and C4 grasses are not distinguished, water stress is driven by vapor pressure deficit (VPD) from coarse meteorological data, and MODIS land cover data are unable to differentiate the sub-pixel cropland components

Climate-Driven Interannual Variability in Net Ecosystem Exchange in the Northern Great Plains Grasslands

The Northern Great Plains grasslands respond differently under various climatic conditions; however, there have been no detailed studies investigating the interannual variability in carbon exchange across the entire Northern Great Plains grassland ecosystem. We developed a piecewise regression model to integrate flux tower data with remotely sensed data and mapped the 8-d and 500-m net ecosystem exchange (NEE) for the years from 2000 to 2006. We studied the interannual variability of NEE, characterized the interannual NEE difference in climatically different years, and identified the drought impact on NEE. The results showed that NEE was highly variable in space and time across the 7 yr. Specifically, NEE was consistently low (–35 to 32 g C m-2 yr-1) with an average annual NEE of –2 +/- 24 g C m-2 yr-1 and a cumulative flux of –15 g C m-2. The Northern Great Plains grassland was a weak source for carbon during 2000-2006 because of frequent droughts, which strongly affected the carbon balance, especially in the Western High Plains and Northwestern Great Plains. Comparison of the NEE map with a drought monitor map confirmed a substantial correlation between drought and carbon dynamics. If drought severity or frequency increases in the future, the Northern Great Plains grasslands may become an even greater carbon source. The Rangeland Ecology & Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 202

Adaptive data-driven models for estimating carbon fluxes in the Northern Great Plains

Rangeland carbon fluxes are highly variable in both space and time. Given the expansive areas of rangelands, how rangelands respond to climatic variation, management, and soil potential is important to understanding carbon dynamics. Rangeland carbon fluxes associated with Net Ecosystem Exchange (NEE) were measured from multiple year data sets at five flux tower locations in the Northern Great Plains. These flux tower measurements were combined with 1-km2 spatial data sets of Photosynthetically Active Radiation (PAR), Normalized Difference Vegetation Index (NDVI), temperature, precipitation, seasonal NDVI metrics, and soil characteristics. Flux tower measurements were used to train and select variables for a rule-based piece-wise regression model. The accuracy and stability of the model were assessed through random cross-validation and cross-validation by site and year. Estimates of NEE were produced for each 10-day period during each growing season from 1998 to 2001. Growing season carbon flux estimates were combined with winter flux estimates to derive and map annual estimates of NEE. The rule-based piece-wise regression model is a dynamic, adaptive model that captures the relationships of the spatial data to NEE as conditions evolve throughout the growing season. The carbon dynamics in the Northern Great Plains proved to be in near equilibrium, serving as a small carbon sink in 1999 and as a small carbon source in 1998, 2000, and 2001. Patterns of carbon sinks and sources are very complex, with the carbon dynamics tilting toward sources in the drier west and toward sinks in the east and near the mountains in the extreme west. Significant local variability exists, which initial investigations suggest are likely related to local climate variability, soil properties, and management

Productivity, Respiration, and Light-Response Parameters of World Grassland and Agro-Ecosystems Derived From Flux-Tower Measurements

Grasslands and agroecosystems occupy nearly a third of the land surface area, but their quantitative contribution to the global carbon cycle remains uncertain. We used a set of 316 site-years of year-round net CO2 exchange (Fc) measurements to quantitatively analyze gross primary productivity, ecosystem respiration, and light-response parameters of extensively and intensively managed grasslands, shrublands/savanna, wetlands, and cropland ecosystems worldwide. Analyzed data set included data from 72 flux-tower sites worldwide partitioned into gross photosynthesis (Pg) and ecosystem respiration (Re) components using the light-response functions method (Gilmanov et al. 2003, Bas. Appl. Ecol. 4:167-183) from the RANGEFLUX and WorldGrassAgriflux data sets supplemented by data from 46 sites partitioned using the temperature-response method (Reichstein et al. 2005, Gl. Change. Biol. 11:1424-1439) from the FLUXNET La Thuile data set. Maximum values of the apparent quantum yield (α = 75 mmol mol-1), photosynthetic capacity (Amax = 3.4 mg CO2 m-2 s-1), maximum daily gross photosynthesis (Pg,max = 116 g CO2 m-2 d-1), and gross ecological light-use efficiency (εecol = 59 mmol mol-1) of intensively managed grasslands and high-productive croplands exceed those for forest ecosystems, indicating high potential of non-forest ecosystems for uptake and sequestration of atmospheric CO2. Maximum values of annual gross primary production (8600 g CO2 m-2 yr-1), total ecosystem respiration (7900 g CO2 m-2 yr-1), and net CO2 exchange (2400 g CO2 m-2 yr-1) for non-forest ecosystems are observed in intensively managed grasslands and high-yield crops, and are comparable or higher than in forest ecosystems (excluding tropical forests). On the average, 80% of the non-forest sites were sinks for atmospheric CO2, with mean annual net CO2 uptake 848 g CO2 m-2 yr-1 for intensively managed grasslands and 933 g CO2 m-2 yr-1 for croplands. The new flux-tower data indicate the need to revise substantially previous views of grassland and agricultural ecosystems as being predominantly a source of carbon, or having a neutral role, in the regional and continental carbon budgets

Productivity, Respiration, and Light-Response Parameters of World Grassland and Agro-Ecosystems Derived From Flux-Tower Measurements

Grasslands and agroecosystems occupy nearly a third of the land surface area, but their quantitative contribution to the global carbon cycle remains uncertain. We used a set of 316 site-years of year-round net CO2 exchange (Fc) measurements to quantitatively analyze gross primary productivity, ecosystem respiration, and light-response parameters of extensively and intensively managed grasslands, shrublands/savanna, wetlands, and cropland ecosystems worldwide. Analyzed data set included data from 72 flux-tower sites worldwide partitioned into gross photosynthesis (Pg) and ecosystem respiration (Re) components using the light-response functions method (Gilmanov et al. 2003, Bas. Appl. Ecol. 4:167-183) from the RANGEFLUX and WorldGrassAgriflux data sets supplemented by data from 46 sites partitioned using the temperature-response method (Reichstein et al. 2005, Gl. Change. Biol. 11:1424-1439) from the FLUXNET La Thuile data set. Maximum values of the apparent quantum yield (α = 75 mmol mol-1), photosynthetic capacity (Amax = 3.4 mg CO2 m-2 s-1), maximum daily gross photosynthesis (Pg,max = 116 g CO2 m-2 d-1), and gross ecological light-use efficiency (εecol = 59 mmol mol-1) of intensively managed grasslands and high-productive croplands exceed those for forest ecosystems, indicating high potential of non-forest ecosystems for uptake and sequestration of atmospheric CO2. Maximum values of annual gross primary production (8600 g CO2 m-2 yr-1), total ecosystem respiration (7900 g CO2 m-2 yr-1), and net CO2 exchange (2400 g CO2 m-2 yr-1) for non-forest ecosystems are observed in intensively managed grasslands and high-yield crops, and are comparable or higher than in forest ecosystems (excluding tropical forests). On the average, 80% of the non-forest sites were sinks for atmospheric CO2, with mean annual net CO2 uptake 848 g CO2 m-2 yr-1 for intensively managed grasslands and 933 g CO2 m-2 yr-1 for croplands. The new flux-tower data indicate the need to revise substantially previous views of grassland and agricultural ecosystems as being predominantly a source of carbon, or having a neutral role, in the regional and continental carbon budgets

Integration of CO 2 flux and remotelysensed data for primary production and ecosystem respiration analyses in the Northern Great Plains: potential for quantitative spatial extrapolation

Aim Extrapolation of tower CO2 fluxes will be greatly facilitated if robust relationships between flux components and remotely sensed factors are established. Long-term measurements at five Northern Great Plains locations were used to obtain relationships between CO2 fluxes and photosynthetically active radiation (Q), other on-site factors, and Normalized Difference Vegetation Index (NDVI) from the SPOT VEGETATION data set

Long-Term Dynamics of Production, Respiration, and Net CO2 Exchange in Two Sagebrush-Steppe Ecosystems

We present a synthesis of long-term measurements of CO2 exchange in 2 US Intermountain West sagebrush-steppe ecosystems. The locations near Burns, Oregon (1995-2001), and Dubois, Idaho (1996-2001), are part of the AgriFlux Network of the Agricultural Research Service, United States Department of Agriculture. Measurements of net ecosystem CO2 exchange (Fc) during the growing season were continuously recorded at flux towers using the Bowen ratio-energy balance technique. Data were partitioned into gross primary productivity (Pg) and ecosystem respiration (Re) using the light-response function method. Wintertime fluxes were measured during 1999/2000 and 2000/2001 and used to model fluxes in other winters. Comparison of daytime respiration derived from light-response analysis with nighttime tower measurements showed close correlation, with daytime respiration being on the average higher than nighttime respiration. Maxima of Pg and Re at Burns were both 20 g CO2 m2 d-1 in 1998. Maxima of Pg and Re at Dubois were 37 and 35 g CO2 m-2 d-1, respectively, in 1997. Mean annual gross primary production at Burns was 1 111 (range 475-1 715) g CO2 m-2 y-1 or about 30% lower than that at Dubois (1 602, range 963-2 162 g CO2 m-2 y-1). Across the years, both ecosystems were net sinks for atmospheric CO2 with a mean net ecosystem CO2 exchange of 82 g CO2 m-2 y-1 at Burns and 253 g CO-2 m-2 y-1 at Dubois, but on a yearly basis either site could be a C sink or source, mostly depending on precipitation timing and amount. Total annual precipitation is not a good predictor of carbon sequestration across sites. Our results suggest that Fc should be partitioned into Pg and Re components to allow prediction of seasonal and yearly dynamics of CO2 fluxes. The Rangeland Ecology & Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 2020Legacy DOIs that must be preserved: 10.2458/azu_jrm_v59i6_gilmano