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Title: VARIABLE RAINFALL INTENSITY EFFECTS ON CARBON CHARACTERISTICS OF ERODED SEDIMENTS FROM TWO COASTAL PLAIN ULTISOLS IN GEORGIA

Author
item Strickland, Timothy - Tim
item TRUMAN, CLINTON
item FRAUENFELD, BERNDT - VIENNA AUSTRIA

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/15/2005
Publication Date: 6/1/2005
Citation: Strickland, T.C., Truman, C.C., Frauenfeld, B. 2005. Variable rainfall intensity effects on carbon characteristics of eroded sediments from two coastal plain ultisols in Georgia. Journal of Soil and Water Conservation 60(3):142-148.

Interpretive Summary: Rainfall simulation is a widely accepted method used to evaluate the potential for erosion and associated chemical loss. In the absence of long-term field data, such simulations are commonly used in risk assessments associated with registration decisions for agricultural chemicals. Simulations using a single rainfall rate do not capture regional and/or local variation in soil types or the response of individual soils to natural rainfall pattern. We used rainfall simulation to compare the effects of constant and variable rainfall intensity patterns on sediment carbon loss from a Tifton loamy sand and a Greenville sandy clay loam. We were unable to detect a significant effect of simulation scenario on the total amount of sediment carbon lost from individual soils. However, within-event patterns of sediment enrichment were substantial. We also observed a substantial difference between methodologies when comparing one soil to another. In systems like the southeastern coastal plain, where sandy soils and intense rainfall events are common, substantially more carbon-bound pollutants could be lost than would be predicted from risk modeling scenarios that are based upon data sets developed from constant intensity rainfall scenarios. Our results indicate that further study is warranted that compares the suitability of constant versus variable rate rainfall simulation methodology for use in risk assessment protocols.

Technical Abstract: Watershed carbon loss and the associated potential for facilitated transport of chemicals could be better quantified if the effects of storm intensity variation could be characterized during key phases of the production year. In order to determine the potential for storm-driven variation in organic material transport in coastal plain soils, rainfall simulations were used to evaluate the effects of constant and variable rainfall intensities on sediment carbon loss from a Tifton loamy sand (Plinthic Kandiudult) and a Greenville sandy clay loam (Rhodic Kandiudult). Soils were air dried, sieved (19 mm) and placed in a 1.5 m2 stainless steel erosion pan (Tifton=4% slope; Greenville=7% slope). Simulated rainfall was applied for 70 min as a constant (57 mm h-1) or variable (typical spring storm) event pattern. Runoff, sediment, sediment carbon, sediment nitrogen, and dissolved carbon were measured at 5 min intervals. Only minor differences were observed in the potential for total sediment carbon loss estimated by the two simulation intensities (Tifton, 5.65 ' 6.67 kg ha-1 and Greenville, 13.44 ' 14.40 kg ha-1). Differences were observed in the effect that simulation intensities had on timing and amount of carbon lost via sediment transport and on the carbon enrichment ratio of sediment exported within an individual soil, as well as in the comparison of sediment carbon losses between different soils. Variable rate rainfall simulations appeared to effectively capture the effects of natural rainfall variation, and may result in improved predictions of sediment transported organic contaminants.