Effects of native plant species, mycorrhizal inoculum, and mulch on restoration of reservoir sediment following dam removal, Elwha River, Olympic Peninsula, Washington

摘要

As dams across the country continue to age, successful restoration of dewatered reservoirs remains a critical factor in decisions regarding dam removal. Freshly exposed reservoir sediment may not support rapid reestablishment of native plant species due to poor fertility or absence of arbuscular mycorrhizal fungi propagules. This field study evaluated effects of native revegetation, mycorrhizal inoculation, and mulch on soil characteristics and plant growth of vegetation grown in plots of reservoir sediment over 20 months. All planted plots, even those uninoculated, became mycorrhizal. In all treatments, sediment pH decreased, as did nitrogen and organic matter, compared to original reservoir sediment; aggregate stability increased to twice that oforiginal sediment. Revegetated plots with mulch had significantly greater vegetation cover and more native volunteer species compared to plots without mulch. The mulch also decreased plot runoff tenfold, reducing runoff sediment load to the same degree.Our results suggest that commercial mycorrhizal inoculum is unnecessary since natural inoculum sources sufficiently colonized plants. The most successful treatment for restoration of reservoir sediment was the mulch treatment because native plant growthwas greatest, soil characteristics were improved, and runoff and sediment loads were reduced compared to non-mulched plots.