Schlanser, Jill (Univ. of California, DavisDept. of Land, Air, and Water Resources, One Shield Ave., Davis, CA, 95616; Phone: 530-754-6536; Email: jcschlanser@ucdavis.edu)

Tracing Dairy-Derived DOC

J.C.S. Schlanser *, P.J.H. Hernes, T.J.H. Harter

DOC transport is a critical component of carbon sequestration models, both as a source term (transport of surface-derived DOC to depth within the soil column) and a loss term (transport via groundwater to rivers where it will eventually be respired). Large dairy operations in California’s central valley generate a great deal of liquid manure which is frequently reapplied to forage crops. Because of enhanced carbon loading at the surface, these systems can be used to study different aspects of DOC transport as it relates to carbon sequestration. This study focuses on the quantity and composition of the dissolved organic matter (DOC) that is transported to groundwater from these operations, and how it is compositionally related to the liquid material applied at the soil surface. The background concentration of DOC in the region of the dairy farm is 4-6ppm, while concentrations in groundwater within the dairy range from just above background levels to as high as 75ppm. Within the wastewater settling ponds, DOC concentrations exceed 400ppm. The transport of organic carbon compounds throughout the phases of a typical dairy operation is examined with a focus on a relatively conservative organic compound, lignin. Lignin is commonly used to determine the origin of organic matter and as a diagenetic indicator. Lignin phenol concentrations in the study site range between nearly 430ppb in settling ponds to just over 10ppb in groundwater-draining canals. These concentrations range above and below the phenolic content of riverine systems, which contain an average of 26ppb lignin-derived phenols. Batch studies are being prepared to gain a better understanding of the potential fractionation of lignin-derived phenolic compounds between the solid and solution phases during transport of DOC through the soil column to groundwater. The results of this study will provide insight to the amount and state of carbon transported as DOC to groundwater from liquid manure fertilization, as well as refining the use of lignin phenols in organic matter characterization by describing any fractionation that may occur through leaching or interactions in the subsurface.