Document Type


Publication Date

Spring 2016


Many dams in the U.S. are reaching the ends of their lifespans and dam removal as a form of river ecosystem restoration is becoming more prevalent. Revegetation of newly exposed sediments is an important aspect of ecosystem recovery after dam removal. Understanding the soil environment left behind after dam removal is important for understanding revegetation and ecosystem recovery trends. Physical soil properties and soil biota communities help to determine the success of plants colonizing exposed sediments after reservoirs are drained. I investigated soil properties and biota after dam removal by looking at the Elwha Dam Removal in Olympic National Park, WA. I asked three main questions about how soil conditions and symbiotic arbuscular mycorrhizal fungi (AMF) impact the success of revegetation after dam removal. 1) What is the potential for AMF colonization of plant roots in sediments after dam removal? To investigate this question I conducted an inoculum potential experiment in 2013 using live soil from the Elwha. No significant trends with treatment or sample location were found and there were overall low levels of AMF colonization in plant roots. Appendix I contains a summary of this study. 2) Do soil properties of exposed sediments differ from those of the surrounding environment? I measured soil pH, organic matter, mineral oxides, texture and counted spores in Elwha sediments and compared measurements to those of the mature forest in 2014 and 2015. The sediments had lower levels of organic matter and a finer texture. Appendix II contains a summary of this study. 3) What is the abundance of AMF spores and what is the spatial distribution of spores in exposed sediments? In 2016 I conducted spore counts to see if there was a trend of decreasing spore abundance as the distance from the mature forest increases. Spores were extracted from soil samples collected from the Elwha in 2013 and counted under the microscope. Spore counts indicated a decreasing trend of spore abundance with increased 3 distance from the adjacent forest. In conclusion, reservoir sediments are fine-textured and have a low abundance of AMF spores that decrease in abundance with distance from the forest. Understanding soil conditions and the spatial distribution of AMF spores in soil after dam removal may help to understand the potential for plant success and distribution patterns in the process of ecosystem recovery.


Advisor: Rebecca Bunn, Huxley College of the Environment - Department of Environmental Science