Facility-scale inventory of dairy methane emissions in California: implications for mitigation

Abstract

Abstract. Dairies emit roughly half of total methane (CH4) emissions in California, generating CH4 from both enteric fermentation by ruminant gut microbes and anaerobic decomposition of manure. Representation of these emission processes is essential for management and mitigation of CH4 emissions and is typically done using standardized emission factors applied at large spatial scales (e.g., state level). However, CH4-emitting activities and management decisions vary across facilities, and current inventories do not have sufficiently high spatial resolution to capture changes at this scale. Here, we develop a spatially explicit database of dairies in California, with information from operating permits and California-specific reports detailing herd demographics and manure management at the facility scale. We calculated manure management and enteric fermentation CH4 emissions using two previously published bottom-up approaches and a new farm-specific calculation developed in this work. We also estimate the effect of mitigation strategies – the use of mechanical separators and installation of anaerobic digesters – on CH4 emissions. We predict that implementation of digesters at the 106 dairies that are existing or planned in California will reduce manure CH4 emissions from those facilities by an average of 26 % and total state CH4 emissions by 5 % (or ∼36.5 Gg CH4/yr). In addition to serving as a planning tool for mitigation, this database is useful as a prior for atmospheric observation-based emissions estimates, attribution of emissions to a specific facility, and validation of CH4 emissions reductions from management changes. Raster files of the datasets and associated metadata are available from the Oak Ridge National Laboratory Distributed Active Archive Center for Biogeochemical Dynamics (ORNL DAAC; Marklein and Hopkins, 2020; https://doi.org/10.3334/ORNLDAAC/1814).

Dairy Manure Co-composting with Wood Biochar Plays a Critical Role in Meeting Global Methane Goals

“… 5 We assume a 50% solid separation rate, which is the average efficiency of the four solid–liquid separation technologies reviewed in Hjorth et al 61 We do not consider any manure managed from heifers or calves because manure from immature and nonmilking cows is typically managed through alternative methods such as daily spread or dry lot systems that yield little CH 4 , and according to an analysis by Marklein et al, account for less than 2% of total dairy CH 4 emissions. 9 Current progress on SB 1383, which we use as a baseline in our model, is based on a recent CARB report that estimates that by 2022, the state will have reduced dairy CH 4 emissions by 3.5 MMT and will have 130 anaerobic digestors operating. 8 Our model also accounts for CH 4 reduction contributions from CARB projected reductions in statewide herd population (0.5% in digester + stockpiling and digester + biochar-composting scenarios and 1% in enhanced population reduction scenario), as well as CARB projected increases in the number of other alternative manure management projects (assuming a rate of 1 AAMP project implemented per digester project) likely to be done at smaller farms unable to install anaerobic digesters.…”

“…CH 4 reductions for anaerobic digestion and biochar-composting are relative to a baseline system similar to the model in Owen and Silver in which dairy manure from mature and lactating cows is separated into a solid fraction, which is stockpiled, and a liquid fraction, which is stored in an anaerobic lagoon . We assume a 50% solid separation rate, which is the average efficiency of the four solid–liquid separation technologies reviewed in Hjorth et al We do not consider any manure managed from heifers or calves because manure from immature and nonmilking cows is typically managed through alternative methods such as daily spread or dry lot systems that yield little CH 4 , and according to an analysis by Marklein et al, account for less than 2% of total dairy CH 4 emissions . Current progress on SB 1383, which we use as a baseline in our model, is based on a recent CARB report that estimates that by 2022, the state will have reduced dairy CH 4 emissions by 3.5 MMT and will have 130 anaerobic digestors operating .…”

“…This is especially relevant in dairy-intensive regions such as California, where dairy manure accounts for 25% of total CH 4 emissions. 6 − 9 …”

“…In developed countries, the industrialization of animal agriculture has concentrated emissions, pollution, and manure into feedlots with relatively small physical footprints. − Dairy feedlots in particular present a significant nutrient recycling and GHG mitigation opportunity due to their large stocking densities, high rate of manure production, and spatial decoupling of livestock from feed production. , Optimizing the treatment and reuse of dairy manure could help prevent nutrient loss while substantially reducing CH 4 emissions. This is especially relevant in dairy-intensive regions such as California, where dairy manure accounts for 25% of total CH 4 emissions. − …”

Artificial Intelligence Approach for Estimating Dairy Methane Emissions

“…For example, applying our AI system to the aerial imagery from the National Agriculture Imagery Program (NAIP) used in this study can update dairy CH 4 emissions annually. Because we focus on estimating emissions at the annual scale comparable to existing bottom-up inventories such as California's state inventory and Vista-CA, 11 this work does not attempt to simulate the shortduration dynamic variability of dairy CH 4 emissions. Recently, Marklein et al 11 updated California dairies' spatial information, manually identifying facilities.…”