Effects of vegetation and hydrology on Eh in vegetated agricultural drainage ditches with weirs

Author(s): Shoemaker, C.; Kröger, R.; Pierce, S.

Oxidation-reduction potential (Eh) is an important parameter in predicting biogeochemical reactions occurring in waterlogged soils, including nutrient reduction. Specifically, soil Eh can be used to classify the potential of a system for nitrate reduction, providing a convenient and inexpensive tool for assessing the capacity of primary water bodies for denitrification potential. Continuous automated data loggers were developed, tested, and confirmed for accuracy and precision of Eh measurements. These units were then used to test a vegetated agricultural ditch with weirs in order to assess the influence of hydrology and vegetation on Eh. Six two week testing periods were conducted around two weirs from May-September 2012, with plots above each weir undergoing controlled drainage while plots below each weir functioned as controls subjected to conventional drainage. No differences were observed in the median Eh between vegetated and non-vegetated plots or the median Eh of the location of plot about the weir; however hydrologic changes influenced the range of Eh values regardless of vegetation status. The high levels of temporal and spatial Eh variation inherent in soils make it difficult to determine bulk soil Eh shifts over space and time. A one dimensional moving split window analysis was run to elucidate Eh boundaries by reduction potential. Results of this analysis showed marked shifts of Eh on specific probes, but no overall trends. The standard deviation of probes shifted over time, suggesting the use of controlled drainage coupled with vegetation could increase electrochemical heterogeneity in waterlogged soils. This increase in soil electrochemical heterogeneity may indicate increased denitrification potential as a result of controlled drainage in vegetated ditches.

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