|Chow, Alex - UC DAVIS|
|Tanji, Kenneth - UC DAVIS|
|Dahlgren, Randy - UC DAVIS|
Submitted to: Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 1, 2005
Publication Date: July 11, 2005
Citation: Chow, A.T., Tanji, K.K., Gao, S., Dahlgren, R.A. 2005. Temperature, Water Content and Wet-Dry Cycle Effects on DOC Production and Carbon Mineralization in Agricultural Peat Soils. Soil Biology and Biochemistry, 38, pp 477-488. Interpretive Summary: Agricultural peat soils in the Sacramento-San Joaquin Delta, California have been identified as an important source of dissolved organic carbon (DOC) and trihalomethane precursors in waters exported for drinking. The objectives of thie study were to examine the primary sources of DOC from soil profiles (surface vs. subsurface), factors (temperature, soil water content and wet-dry cycles) controlling DOC production, and the relationship between C mineralization and DOC concentration in cultivated peat soils. Surface and subsurface peat soils were incubated for 60 d under a range of temperature (10, 20, and 30 degree C) and soil water contents (0.3-10.0 g-water g-soil-1). Both CO2-C and DOC were monitored during the incubation period. Significant amount of DOC was produced only in the surface soil under constantly flooded conditions or flooding/non-flooding cycles. The DOC production was independent of temperature and soil water content under non-flooded condition, although CO2 evolution was highly correlated with these parameters. Aromatic carbon and hydrophobic acid contents in surface DOC were increased with wetter incubation treatments. In addition, positive linear correlations (r2=0.87) between CO2-C mineralization rate and DOC concentrations were observed in the surface soil, but negative linear correlations (r2=0.70) were observed in the subsurface soil. Results imply that mineralization of soil organic carbon by microbes prevailed in the subsurface soil. A conceptual model using a kinetic approach is proposed to describe the relationships between CO2-C mineralization rate and DOC concentration in these soils.
Technical Abstract: A series of controlled laboratory experiments were utilized to examine factors affecting dissolved organic carbon (DOC) production and C mineralization rates over a range of conditions experienced resulting from agricultural practices in peat soils from the Sacramento-San Joaquin Delta. We conclude that surface peat soil is a more important source of DOC compared to subsurface peat soils that have experienced long-term anaerobic conditions. DOC is mainly produced in surface peat soils following flooding or wet-dry cycles. DOC concentration was not correlated with incubation temperature or soil water content. However, there were linear correlations between C mineralization rates and DOC concentrations and these correlations were temperature and water content dependent. DOC-CO2 mineralization relationships were best explained by a model consisting of C mineralization from two C substrates (SOC and DOC).