As part of a study, Penn State University evaluated the efficiency of different soil amendments in palustrine wetlands in Tipton, PA. They examined the possibility of using non-toxic organic waste (leaf litter compost) as a soil amendment in wetland projects. Plots of Lurid sedge (Carex lurida) tubers, hand planted in leaf litter, were compared to plots where the Carex was planted in the existing mineral soils.
The survivorship of hand planted Carex was greater in plots treated with leaf litter compost than on plots with the existing mineral soils. Additionally, organic matter, pH, and total nitrogen levels were all significantly greater on leaf litter plots than on the control plots. The results of this study suggest leaf litter compost can help retain soil moisture and provide nutrients that enhance survivorship of vegetation, in this case, hand planted Carex. Leaf litter amendments improved soil aggregation, increased infiltration and aeration, and improved water holding capacity. The cumulative result of this is improved water quality.

This study, which was completed in 1992, has inspired further investigation into the effects of mulching wetlands in order to improve soil function and water quality. Another study, Mulching effects on the seasonally flooded zone of west-central Florida, investigated the use of salvaged marsh surface (SMS). SMS is the transfer of soil from a wetland that will be filled or impacted onto the surface of a wetland creation area in an effort to provide wetland vegetation, organic matter, soil organisms and improved water quality. In this study 17 mulched and 16 non-mulched patches of herbaceous wetlands were studied at the end of the wet season (November) and subsequent dry season (June). Again, the study concluded that mulched wetlands had greater amounts of organic matter than non-mulched wetlands, and therefore a more stable environment for plant communities, which in turn results in better water quality.

Maintaining soil health and water quality by reusing the natural duff layer.
Maple Valley Library (Barbara Swift & Co.)

Prior to constructing this public library in Maple Valley (which was built in a second growth Hemlock-Douglas Fir forest), the duff layer on the forest floor was removed from the construction site and stockpiled for use as mulch upon project completion. The beauty of this technique of reusing the existing duff layer as mulch is multifaceted. One great benefit of this technique is that the existing microbial community alive and well in the duff layer is reintroduced to the site immediately following construction. A healthy microbial community is of critical importance to plant health as it increases the availability of nutrients and water to the rhizosphere. Although through compost tea applications one may attempt to reestablish a site’s microbiology, it is nearly impossible to effectively reintroduce the appropriate diversity of microorganisms to a site by any means other that using portions of the existing soil profile with a healthy native microbial community.

The retentive capacity of the duff layer in Pacific Northwest forests is substantial, so by using existing duff to mulch a site, irrigation requirements are reduced due to the moisture retained in the upper horizons of the soil profile by the duff. Aside from the incredible of benefits of maintaining a health soil food web and increasing water retention on the forest floor, the use of the native duff layer as a mulch on a forested site is also the perfect aesthetic choice. There is nothing that looks better spread across a forest floor than the decomposing organic debris for the plants existing in the forest.

The effects of an organic soil amendment on native plant establishment and physical soil properties on an obliterated forest road.
(Karen D. Bergeron)

This study examined the effects of biosolids compost, the addition of fertilizer, winter wheat seed, and hay mulch on vegetative cover and soil structure.
The intent was to determine the most effective combination of treatments for restoring native vegetation on abandoned logging roads in the Cascade Mountains. Through amending the soil and restoring native vegetation on these logging roads, hill slope hydrology is restored, surface soil erosion is reduced, the re-establishment of native vegetation is encouraged, and ultimately the quality of runoff entering the water body is enhanced.

Through examining the effects of varying combinations amending soils with biosolids, compost, fertilizer, winter wheat seed, and hay mulch on vegetative cover an biomass of native and non-native plants, the results of the study showed that biosolids compost and fertilizer increased native plant biomass and total vegetative cover. Because increased coverage of native plants will ultimately reduce erosion and help enhance water quality, the amendment of these forest roads ultimately enhances the quality of water entering the affected watershed.