Neil W. MacDonald

Landfill Cover Soil, Soil Solution, and Vegetation Responses to Municipal Landfill Leachate Applications

Municipal solid waste landfill leachate must be removed and treated to maintain landfill cover integrity and to prevent contamination of surface and ground waters. From 2003 to 2007, we studied an onsite disposal system in Ottawa County, Michigan, where leachate was spray irrigated on the vegetated landfill cover. We established six 20-m-diameter circular experimental plots on the landfill; three were spray irrigated as part of the operational system, and three remained as untreated control plots. We quantified the effects of leachate application on soil properties, soil solution chemistry, vegetative growth, and estimated solute leaching. The leachate had high mean levels of electrical conductivity (0.6-0.7 S m(-1)), Cl (760-900 mg L(-1)), and NH(4)-N (290-390 mg L(-1)) but was low in metals and volatile organic compounds. High rates of leachate application in 2003 (32 cm) increased soil electrical conductivity and NO(3)-N leaching, so a sequential rotation of spray areas was implemented to limit total leachate application to <9.6 cm yr(-1) per spray area. Concentrations of NO(3)-N and leaching losses remained higher on irrigated plots in subsequent years but were substantially reduced by spray area rotation. Leachate irrigation increased plant biomass but did not significantly affect soil metal concentrations, and plant metal concentrations remained within normal ranges. Rotating spray areas and timing irrigation to conform to seasonal capacities for evapotranspiration reduced the localized impacts of leachate application observed in 2003. Careful monitoring of undiluted leachate applications is required to avoid adverse impacts to vegetation or soils and elevated solute leaching losses.

Hand pulling following mowing and herbicide treatments increases control of spotted knapweed (Centaurea stoebe).

Abstract Extensive areas in the upper Midwest have been invaded by spotted knapweed, and effective management strategies are required to reestablish native plant communities. We examined effects of mowing, mowing plus clopyralid, or mowing plus glyphosate in factorial combination with hand pulling and burning on knapweed abundances on a knapweed-infested site in western Michigan. We applied mowing and herbicide treatments in summer 2008, and seeded all plots with native grasses and forbs in spring 2009. We conducted the knapweed pulling treatment from 2009 to 2012 in July. The prescribed burn was conducted in April 2012. By 2012, hand pulling reduced adult knapweed densities to 0.57 ± 0.12 m−2 (0.053 ± 0.011 ft−2) (mean ± SE), which was 5.8% of nonpulled treatments, juvenile densities to 0.29 ± 0.07 m−2 (2.1% of nonpulled treatments), and seedling densities to 0.07 ± 0.06 m−2 (2.6% of nonpulled treatments). After 3 yr, hand pulling reduced seed bank densities to 68 ± 26 m−2 as compared to 524 ± 254 m−2 in nonpulled treatments and 369 ± 66 m−2 in adjacent untreated areas of the study site. Without hand pulling, effects of mowing or mowing plus glyphosate were short-lived and allowed knapweed to rapidly resurge. In comparison, although a single mowing plus clopyralid treatment maintained significantly reduced densities of knapweed for 4 yr, by 2012 knapweed biomass in the nonpulled clopyralid treatment was approximately 60% of that in the other nonpulled treatments. Burning had minimal impacts on knapweed densities regardless of treatment combination, probably as a result of low fire intensity. Results demonstrated that persistent hand pulling used as a follow-up to single mowing or mowing plus herbicide treatments can be an effective practice for treating isolated spotted knapweed infestations or for removing small numbers of knapweed that survive herbicide applications. Nomenclature: Clopyralid, glyphosate, spotted knapweed, Centaurea stoebe L. Management Implications: We studied the interactive effects of mowing, herbicides, hand pulling, and burning on spotted knapweed control in western Michigan. Effects of a single mowing or mowing plus glyphosate on spotted knapweed were short-lived. In contrast, a single application of mowing plus clopyralid maintained reduced knapweed densities for 4 yr after treatment. In the fourth year, however, knapweed biomass in the nonpulled mowed plus clopyralid treatment was approximately 60% of the other nonpulled treatments, evidence that knapweed was resurging in the clopyralid treatment as well. Contrary to expectations, there were minimal effects of a single spring burn on spotted knapweed densities, probably as a result of suboptimal season of burn and cool burn-day temperatures, which caused low fire intensity. In comparison to other treatments, hand pulling more effectively controlled all knapweed life stages after 3 yr of treatment. Initially, hand-pulling removals were greatest on mowed-only plots (44 ± 7 m−2, mean ± SE), increased in both clopyralid and glyphosate-treated plots in the second year as knapweed populations began to recover from herbicides, and then equalized at greatly reduced levels (0.6 ± 0.1 m−2) across all mowing and herbicide treatments by the fourth year. Removing knapweed by hand requires a large investment of time, however, and this must be taken into account when planning strategies for restoring knapweed-infested sites. To be effective, hand pulling needs to be applied persistently in advance of seed dispersal over several years. Hand pulling can be an effective practice for treating relatively small knapweed infestations in areas being restored to native vegetation, or as a follow-up treatment after herbicides have been used to reduce large infestations. Hand pulling also provides a treatment option in natural areas where herbicides are restricted to prevent damage to native plants.

Native Plant Establishment Success Influenced by Spotted Knapweed (Centaurea stoebe) Control Method

Invasive species frequently need to be controlled as part of efforts to reestablish native species on degraded sites. While the effectiveness of differing control methods are often reported, the impacts these methods have on the establishment of a native plant community are often unknown. To determine methods that effectively reduce spotted knapweed (Centaurea stoebe) while enhancing native species establishment, we tested 12 treatment combinations consisting of an initial site preparation (mowing, mowing + clopyralid, or mowing + glyphosate), in factorial combination with annual adult knapweed hand pulling and/or burning. We established 48 plots and applied site preparation treatments during summer 2008, seeded 23 native forbs and grasses during spring 2009, pulled adult knapweed annually from 2009–2012, and burned in the early spring 2012. During July of 2011 and 2012, percent cover of all species was visually estimated. By 2011, seeded species had established in all treatment plots, including plots that retained greater than 50% knapweed cover, indicating that native species successfully established despite knapweed dominance. Mowing alone had no longterm impacts on community development. Clopyralid favored non-native grass establishment, while glyphosate encouraged non-native forbs. Clopyralid had minimal impacts on native forb establishment, but did effectively control knapweed. Pulling reduced knapweed cover, increased non-native grass cover and enhanced native species establishment. Burning had little impact, possibly due to low intensity and unseasonable weather. On the heavily invaded site we studied, combining the use of clopyralid with hand pulling effectively controlled knapweed and favored the establishment of seeded native grasses and forbs.

Native warm-season grasses resist spotted knapweed resurgence.

rain from established native vegetation to replenish the soil seed bank. Habitat restoration projects can use seed bank information as early warning systems of patterns or degrees of habitat degradation; as changes in above ground vegetation directly impact below ground seed distribution (Looney and Gibson 1995, Cox and Allen 2008). In multiple strategy restoration efforts, seed bank quality can be used as a deciding factor in whether or not to incorporate costly re-vegetation or utilize alternative restoration methods (Abella and Springer 2008). However, we show that even after a heavy infestation of giant reed (Yang et. al 2011), the presence of viable seeds indicate that soil seed banks have the potential to initiate passive restoration.