Submitted to: Agriculture, Ecosystems and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/21/2011
Publication Date: 3/29/2011
Citation: Owens, L.B., Shipitalo, M.J. 2011. Sediment-bound and dissolved carbon concentration and transport from a small pastured watershed. Agriculture, Ecosystems and Environment. 141(1-2):162-166. Interpretive Summary: One of the environmental issues today is what kind of “carbon footprint” is left by various activities of energy generation and use. How agricultural management practices impact the carbon cycle is an important part of this overall issue. Pasture systems can lose organic carbon dissolved in surface runoff and attached to sediment, and these losses were studied at the North Appalachian Experimental Watershed near Coshocton, Ohio. In a system where a beef cow-calf herd was rotated weekly through 4 pastures during the grazing system, one pasture was used for winter feeding. Surface runoff was measured from each of these pastures throughout the year. Only the pasture used for winter feeding had runoff with measureable amounts of sediment, and those losses occurred during the winter feeding period. Because the cattle were constantly in this pasture during the winter months, the vegetative cover was reduced to less than 50%, which increased the potential for soil loss. Most of the sediment loss and carbon loss occurred with a few large storms. On an individual storm event basis, there was no correlation between the amount of sediment lost and the organic carbon concentration on that sediment. Dissolved organic carbon and sediment attached organic carbon were lost in similar amounts on an event basis and an annual basis. This research indicates that pasture organic carbon losses can be reduced by using management practices that reduce sediment losses. Management simply trying to reduce the carbon concentration on the sediment would not be effective in reducing carbon losses. This work is important to other scientists as well as to land managers and producers.
Technical Abstract: With the current emphasis on the role of carbon in the environment, agricultural systems and their impacts on the carbon cycle are important parts of the overall issue. Pasture systems and organic carbon that is transported attached to sediment has been addressed at the North Appalachian Experimental Watershed near Coshocton, Ohio. In a pasture system where a beef cow-calf herd was rotated weekly among 4 paddocks during the grazing season, one paddock was used for winter feeding. Surface runoff was measured and sampled throughout the year from 4 watersheds, one watershed per paddock. The watershed in the winter paddock was the only watershed to yield measureable levels of sediment loss, and those samples were collected during the dormant season (November – April). With continuous winter occupancy, the percent vegetative cover was often < 50% in the late winter/early spring, which increased the potential for soil loss. During the 10-year period of sample collection, there were 376 runoff events and 115 events with sediment loss >10 kg ha-1 from the watershed in the winter feeding area. The largest 6 events carried nearly 50% of the total sediment and sediment-attached organic C lost during this period. Annual losses of sediment and sediment-OC varied considerably but averaged 2,642 and 140 kg ha-1, respectively. There was no significant correlation between the amount of sediment transported during individual events and the C concentration on the associated sediment. The pasture sediments have a OC enrichment ratio of 1.2-1.5 compared with the 0-2.5 cm soil layer. Pasture sediment-OC concentrations were > 2x the OC concentrations on sediments from nearby row crop watersheds. Pasture sediment OC losses can be reduced by using management practices that reduce sediment losses.