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Root growth in alternative soil/vegetation covers at Rocky Mountain Arsenal: project report




Brown, Cynthia S., author
Jamiyansharav, Khishigbayar, author

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The three lysimeters of Shell Disposal Trenches (SDT) Resource Conservation and Recovery Act (RCRA)-equivalent cover at Rocky Mountain Arsenal (RMA) exceeded the maximum amount of percolation allowed under the compliance standard in spring 2015 and 2016. The Integrated Cover System RCRA-equivalent (ICS) cover continued to meet the compliance standard. We assessed plant root characteristics in the two cover types and a natural site in an effort to understand the underlying cause of excessive percolation in the SDT cover. Three 4 foot soil cores were collected near each of three lysimeters in each cover type at RMA. Another three soil cores were collected from a native area on the Rocky Mountain Arsenal National Wildlife Refuge. Soil cores were divided into 6 inch samples, soil was washed from the roots in each sample, and roots were analyzed using an optical scanner and image analysis software. Root length density (RLD, length of root per unit volume of soil), mass per volume (MPV, dried root weight per volume of soil), and average diameter (AD) of the roots were measured in each sample. There were two differences in root characteristics between the two cover types. First, RLD in the SDT cover was less than the ICS cover at the deepest depth (43-48 inches). Second, RLD was greater in the SDT cover than ICS cover at the next shallowest depth (37-42 inches). These two differences are likely due to a 6 inch layer of compacted soil in the SDT cover that was created as part of its construction and was not included in the ICS cover design. We did not detect differences between the covers in distribution of MPV or AD with depth. Nor did we detect differences in variation of these root characteristics (coefficient of variation [CV] and deviation from the mean [residual]) that would indicate differences in root heterogeneity between the two cover types. The two cover types were more similar to each other than to the native site. Both cover types had greater RLD at the shallowest depth and greater total RLD than the native site. The SDT cover had greater AD than the natural site; the ICS cover was not different from either. Our results provide little evidence for differences in plant development, in particular root characteristics, causing differences in percolation between SDT and ICS covers. Exploration of differences in the species composition of the plant communities may provide additional insights. However, the physical features that affect movement of water through plants and soil may not be appreciably different among the herbaceous species that occur on the covers of RMA.


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root washing
root scanning
root drying
root weighing
root length density
vegetation cover


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