Justine J. Owen

Greenhouse gas emissions from dairy manure management: a review of field‐based studies

Livestock manure management accounts for almost 10% of greenhouse gas emissions from agriculture globally, and contributes an equal proportion to the US methane emission inventory. Current emissions inventories use emissions factors determined from small-scale laboratory experiments that have not been compared to field-scale measurements. We compiled published data on field-scale measurements of greenhouse gas emissions from working and research dairies and compared these to rates predicted by the IPCC Tier 2 modeling approach. Anaerobic lagoons were the largest source of methane (368 ± 193 kg CH4 hd(-1) yr(-1)), more than three times that from enteric fermentation (~120 kg CH4 hd(-1) yr(-1)). Corrals and solid manure piles were large sources of nitrous oxide (1.5 ± 0.8 and 1.1 ± 0.7 kg N2O hd(-1) yr(-1), respectively). Nitrous oxide emissions from anaerobic lagoons (0.9 ± 0.5 kg N2O hd(-1) yr(-1)) and barns (10 ± 6 kg N2O hd(-1) yr(-1)) were unexpectedly large. Modeled methane emissions underestimated field measurement means for most manure management practices. Modeled nitrous oxide emissions underestimated field measurement means for anaerobic lagoons and manure piles, but overestimated emissions from slurry storage. Revised emissions factors nearly doubled slurry CH4 emissions for Europe and increased N2O emissions from solid piles and lagoons in the United States by an order of magnitude. Our results suggest that current greenhouse gas emission factors generally underestimate emissions from dairy manure and highlight liquid manure systems as promising target areas for greenhouse gas mitigation.

Geomorphologic evidence for the late Pliocene onset of hyperaridity in the Atacama Desert

The Atacama Desert has experienced a long and protracted period of hyperaridity that has resulted in what may be the most unusual biome on Earth, but the duration of this aridity is poorly constrained. We reconstructed aspects of the fluvial and geochemical history of this region using integrated landscape features (alluvial fans, hillslope soils, soil chemistry, river profiles) in the southern portion of the present desert. Topographic reconstructions of a large watershed (11,000 km 2 ) show deep incision and sediment removal between the late Miocene and the end of the Pliocene, and modest to negligible incision in post-Pliocene times. These changes in incision suggest an ∼50–280× reduction in river discharge, which should reflect corresponding changes in precipitation. Changes in the nature of hillslope soils in the Atacama Desert indicate that in the Pliocene or earlier, hillslopes were mantled with silicate-derived soil. This mantle was stripped off and locally deposited as alluvial fans (late Pliocene to early Pleistocene) that now block or otherwise cause a rearrangement of Pliocene and earlier river channels. Finally, the hillslopes have largely accreted a soil mantle of dust and salt since the apparent late Pliocene stripping, suggesting a decline in annual precipitation of at least 125 mm yr -1 or more (mean annual precipitation [MAP] is now -1 ). Embedded in the long post-Pliocene era of salt accumulation, there are a variety of features suggesting overland flow on hillslopes (rills, striped gravel deposits, piping, and water spouts) and large, infrequent storms that infiltrated gentle alluvial fans (due to the depth of salt-rich horizons). Despite evidence for episodes that punctuate the hyperaridity, the magnitude and duration of these pluvial events have been insufficient to remove the regional accumulations of sulfate, chloride, and nitrate. The late Pliocene cessation of many fluvial features is coincident with recent research on the tropical Pacific, which shows that the Pacific was in a permanent El Nino state until ca. 2.2 Ma, at which time sea-surface temperatures offshore of South America declined greatly relative to those of the western Pacific, in turn setting up the present El Nino–Southern Oscillation (ENSO) climate system. These observations indicate that the latest period of aridity has been prolonged and largely continuous, and it appears to have occurred in step with the onset of the ENSO climate system, beginning ∼2 m.y. ago.