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Title: 137-CESIUM AND SOIL CARBON IN SMALL AGRICULTURAL WATERSHED

Author
item Ritchie, Jerry
item MCCARTY, GREGORY - ENVIRONMENTAL QUALITY LAB

Submitted to: Soil & Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/22/2002
Publication Date: 3/3/2003
Citation: Ritchie, J.C., McCarty, G.W. 2003. Using 137 cesium to understand soil carbon redistribution on agricultural watershds. Soil and Tillage Research 69(1-2):45-51.

Interpretive Summary: Soil carbon concentrations are significantly correlated with Cs-137 concentrations. Eroding areas in the upland areas as determined using Cs- 137 measurements have significantly less soil carbon that areas of deposition on the upland landscape. These data suggest that Cs-137 may be used to help understand soil carbon dynamics on the landscape. The riparian narea in this study is acting as a filter removing eroded soil materials from the overland flow. Sediment deposition rates measured using Cs-137 for the 1964 to 2000 period averaged 0.3 cm/yr while deposition rates for the period from 1954 to 1964 were significantly greater averaging 1.3 cm/yr. Soil carbon was significantly greater in the riparian soils than the upland soils suggesting both a capture of soil carbon and increased primary productivity probably related to the nitrogen moving into the area by overland and ground water flow. Carbon content of the upland soils and the riparian sediments indicates that riparian buffer systems can be an important component of the carbon budget for the watershed. Our estimate of carbon storage in the riparian wetland is four times that in upland soils in the upper 30 cm of the profile. While carbon in the total profile of the riparian zone (0-200 cm) may be as much as 10-15 times more carbon than in upland soils. In terms of the total amount of organic carbon stored within soil resources of this watershed, this study supports the concept that riparian areas are sinks for carbon and may be significant sites for carbon sequestration.

Technical Abstract: Scientific, political, and social interest have developed recently in the concept of using agricultural soils to sequester carbon. The problem is to determine the patterns of soil erosion and redeposition on the landscape and to relate this to soil carbon patterns. The purpose of this study was to determine the relationship between Cs-137, soil erosion, and soil carbon ndistribution on a small agricultural watershed. Cs-137 was uniformly mixed in the upper 15-20 cm of upland soil profiles. Carbon content of the upland soil profiles ranged from 0.5 to 1.9 % in the 0-20 cm layer while carbon below this tilled layer (20-30 cm) ranged from 0.2 to 1.5 %. Carbon content of the 0-20 cm layer in the riparian area ranged from 0.9 to 33.6 %. Carbon content below 20 cm ranged from 0.6 to 15.4 %. Total carbon in the upper 20 cm of the riparian profile was 10.1 kg/m2 the riparian profiles. This is an increase of total carbon by a factor of 3.8 and 4.7 for the upper 20 cm and upper 30 cm of the riparian profiles, respectively when compared to the upland soil profiles. Carbon and Cs-137 content in the soils were strongly correlated. Carbon content of the 0-20 cm layer was higher (1.4%) in areas of soil deposition than carbon content (1.1%) in areas of soil erosion as determined by the Cs-137 technique. These data suggest that measurements of Cs-137 in the soils can be useful for understanding carbon distribution patterns in surface soil.