CWC Technology Brief

COMPOST USE IN WETLAND RESTORATION

Amending wetland soils with compost in wetland restoration projects is potentially a high value-added end-use application for composted organic waste. However, the lack of information on plant growth response and impacts to soil and water is a significant barrier to the increased use of compost products in this end-use application.

In response, the Clean Washington Center (CWC) and the City of Everett, Washington funded a demonstration project to test, monitor, and evaluate the use of compost in a wetland restoration project. Final project results indicate that target species' growth and survival rates increased over unamended control plots, and that no degradation of the surface water or soil occurred. This technology brief describes the methods and findings of the project.

Background

The site used for the demonstration project is located in the Lowell neighborhood of Everett, and was once home to a sawmill. The sawmill has long since been removed, but a filled wetland area has remained on the site for the past fifty years. The fill required the use of a 600-foot culvert to drain water around the two acre area. Beavers living nearby often plugged the culvert, causing an upstream wetland to flood the area and an adjacent railroad right of way.

The City of Everett proposed to expand the upper wetland in order to control flooding and to allow the beavers to remain in the wetland area. As part of the project, the City proposed that all restoration work be accomplished using compost as the wetland substrate, creating an ideal opportunity to test compost's effectiveness for this end-use application.

The Project

The project's goal was to determine if the use of compost in wetlands could decrease the frequency of failure of restoration efforts - thereby enhancing the economic value of compost products. The project used the following criteria to measure success:

· survival of target plant species
· suppression of invasive species
· non-degradation of surface water, and
· diversity of wildlife in the area.

The plan design included fourteen plots (600 ft2 each) using two types of compost, three compost application rates, a control (no compost), and two replicates of each. Soil samples were taken every six months, and included samples of the existing wetland substrate for the purposes of comparison. In addition, the project examined the height of the target species' plants in each plot every six months to compare the growth and survival rate of the plants.

Results

Growth and survival rates (charted on graphs in the full report) indicate that the compost plots were more successful than the control plots. The three compost application rates used were below, at, and above the agronomic rate for nitrogen loading. The growth records indicate no additional value to applying nitrogen above the agronomic rate, which should prevent nitrogen overloading and reduce the risk of surface water contamination.

This demonstration provides evidence that compost can provide strong organic substrate to mimic existing wetland soils; and that compost can safely be used in a wetland setting, if agronomic loading rates are observed.

The full report, Compost Use in Wetland Restoration Projects, is a tool to help properly design wetland restoration projects and promote an understanding of nitrogen dynamics in wetland settings. The information helps designers:

· calculate the nitrogen needs of the wetland plant community,
· determine correct compost application rates for specific plants, and
· prevent overloading of nitrogen and thus, surface water contamination.

Worksheets are included in the full report to enable correct calculation of application/loading rates.

Outreach Efforts

The demonstration project results have been disseminated in several forums. The presentations, commitments, and site tours to date include:

· Washington State Recycling Association annual Conference
· Northwest Biosolids Management Association Conference
· Water Environment Federation Annual Conference
· Biocycle West Coast Conference
· Compost Council Annual Conference
· Site tours for:
- Cowlitz County
- Seattle Metro
- GroCo Compost
- University of Washington

The full report also has been forwarded to the State Department of Ecology (DOE) to support the inclusion of language encouraging the use of compost in wetland restoration in DOE documents. Ultimately, the Clean Washington Center will use the project to help develop guidelines outlining the best procedures for using compost to replicate wetland soils.

This technology brief was prepared by the Clean Washington Center. The Clean Washington Center is the Managing Partner of the Recycling Technology Assistance Partnership (ReTAP). ReTAP's mission is to advance industry's use of recycled materials through technology extension services. ReTAP is an affiliate of the national Manufacturing Extension Partnership (MEP), a program of the U.S. Commerce Department's National Institute of Standards and Technology. ReTAP is also funded by the U.S. Environmental Protection Agency and the American Plastics Council.

Report Dated: June 1996

Fact Sheet Update: October 1996