Julie Wolf

Downscaling global land cover projections from an integrated assessment model for use in regional analyses: results and evaluation for the US from 2005 to 2095

Projections of land cover change generated from integrated assessment models (IAM) and other economic-based models can be applied for analyses of environmental impacts at sub-regional and landscape scales. For those IAM and economic models that project land cover change at the continental or regional scale, these projections must be downscaled and spatially distributed prior to use in climate or ecosystem models. Downscaling efforts to date have been conducted at the national extent with relatively high spatial resolution (30 m) and at the global extent with relatively coarse spatial resolution (0.5°). We revised existing methods to downscale global land cover change projections for the US to 0.05° resolution using MODIS land cover data as the initial proxy for land class distribution. Land cover change realizations generated here represent a reference scenario and two emissions mitigation pathways (MPs) generated by the global change assessment model (GCAM). Future gridded land cover realizations are constructed for each MODIS plant functional type (PFT) from 2005 to 2095, commensurate with the community land model PFT land classes, and archived for public use. The GCAM land cover realizations provide spatially explicit estimates of potential shifts in croplands, grasslands, shrublands, and forest lands. Downscaling of the MPs indicate a net replacement of grassland by cropland in the western US and by forest in the eastern US. An evaluation of the downscaling method indicates that it is able to reproduce recent changes in cropland and grassland distributions in respective areas in the US, suggesting it could provide relevant insights into the potential impacts of socio-economic and environmental drivers on future changes in land cover.

Spatiotemporal patterns of livestock manure nutrient production in the conterminous United States from 1930 to 2012

Manure nitrogen (N) and phosphorus (P) from livestock husbandry are important components of terrestrial biogeochemical cycling. Assessment of the impacts of livestock manure on terrestrial biogeochemistry requires a compilation and analysis of spatial and temporal patterns of manure nutrients. In this study, we reconstructed county-level manure nutrient data of the conterminous United States (U.S.) in 4- to 5-year increments from 1930 to 2012. Manure N and P were 5.8 9 ± 0.64 Tg N yr.(-1) (Mean ± Standard Deviation) and 1.73 ± 0.29 Tg Pyr.(-1) (1 Tg = 10(12)g), and increased by 46% and 92% from 1930 to 2012, respectively. Prior to 1970, manure provided more N to the U.S. lands than chemical fertilizer use. Since 1970, however, increasing chemical N fertilizer use has exceeded manure N production. Manure was the primary P source in the U.S. during 1930-1969 and 1987-2012, but was lower than P fertilizer use in 1974, 1978, and 1982. High-nutrient-production regions shifted towards eastern and western areas of the U.S. Decreasing small farms and increasing Concentrated Animal Feeding Operations (CAFOs) induced concentrated spatial patterns in manure nutrient loads. Counties with cattle or poultry as the primary manure nutrient contributors expanded significantly from 1930 to 2012, whereas regions with sheep and hog as the primary contributors decreased. We identified regions facing environmental threats associated with livestock farming. Effective management of manure should consider the impacts of CAFOs in manure production, and changes in livestock population structure. The long-term county-level manure nutrient dataset provides improved spatial and temporal information on manure nutrients in the U.S. This dataset is expected to help advance research on nutrient cycling, ammonia volatilization, greenhouse gas (GHG) emissions from livestock husbandry, recovery and reuse of manure nutrients, and impacts of livestock feeding on human health in the context of global change.

Biogenic carbon fluxes from global agricultural production and consumption

Quantification of biogenic carbon fluxes from agricultural lands is needed to generate comprehensive bottom-up estimates of net carbon exchange for global and regional carbon monitoring. We estimated global agricultural carbon fluxes associated with annual crop net primary production (NPP), harvested biomass, and consumption of biomass by humans and livestock. These estimates were combined for a single estimate of net carbon exchange and spatially distributed to 0.05° resolution using Moderate Resolution Imaging Spectroradiometer satellite land cover data. Global crop NPP in 2011 was estimated at 5.25 ± 0.46 Pg C yr−1, of which 2.05 ± 0.05 Pg C yr−1 was harvested and 0.54 Pg C yr−1 was collected from crop residues for livestock fodder. Total livestock feed intake in 2011 was 2.42 ± 0.21 Pg C yr−1, of which 2.31 ± 0.21 Pg C yr−1 was emitted as CO2, 0.07 ± 0.01 Pg C yr−1 was emitted as CH4, and 0.04 Pg C yr−1 was contained within milk and egg production. Livestock grazed an estimated 1.27 Pg C yr−1 in 2011, which constituted 52.4% of total feed intake. Global human food intake was 0.57 ± 0.03 Pg C yr−1 in 2011, the majority of which was respired as CO2. Completed global cropland carbon budgets accounted for the ultimate use of approximately 80% of harvested biomass. The spatial distribution of these fluxes may be used for global carbon monitoring, estimation of regional uncertainty, and for use as input to Earth system models.