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Specific standards do not exist for wood chips, but the Forest Stewardship Council (FSC) certifies wood sources, which guarantees that the wood and bark is responsibly sourced. The FSC Controlled Wood Standard ([https://fsc.org/en/document-centre/documents/resource/373 FSC-STD-040-005 Version 3.0]) requires knowledge of where the wood comes from, an evaluation of the risk that a wood source is in violation with unacceptable categories of wood, and mitigate actions to reduce any risk from the wood source. | Specific standards do not exist for wood chips, but the Forest Stewardship Council (FSC) certifies wood sources, which guarantees that the wood and bark is responsibly sourced. The FSC Controlled Wood Standard ([https://fsc.org/en/document-centre/documents/resource/373 FSC-STD-040-005 Version 3.0]) requires knowledge of where the wood comes from, an evaluation of the risk that a wood source is in violation with unacceptable categories of wood, and mitigate actions to reduce any risk from the wood source. | ||
− | + | Products receiving [https://www.mulchandsoilcouncil.org/certification.php Mulch & Soil Council Certification] must pass rigorous screening and are periodically audited to ensure the products meet Council standards. The certification ensures the product label is accurate and all ingredients are listed, and product claims have been verified. A Mulch & Soil Certification also ensures the mulch contains no chromated copper arsenate. | |
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+ | Some general guidelines for material selection are provided below | ||
+ | *Recycled yard waste from public municipalities or recycled wood scraps such as pallets should be avoided due to inconsistencies in source and potential for unwanted trash or chemical additives in the mulch. If mulch is not available that is certified by the Mulch & Soil Council, it should be free from waste wood material, harmful chemicals, or inorganic dyes. Mulch should not contain any fertilizer, pesticide, or other amendment. If mulch is being used in a nutrient sensitive area, a leachate analysis would ensure the mulch does not contribute to nutrient leachate from the practice.[https://www.conteches.com/stormwater-article/article/180/selecting-the-right-mulch-for-your-biofiltration-practice] | ||
**Organic wood mulch is often a byproduct of the lumber industry (typically shredded bark), wood recycling centers (i.e. pallets) or processed yard waste from public landfills. Other mulches can include grass clippings, pine needles, straw, sawdust, leaf litter, turf, coir and compost, but these should be avoided for biofiltration applications, particularly high flow media, to prevent hydraulic restriction, flotation, maintenance burdens and nutrient leaching among other issues. Composted or aged wood mulch, which is mulch that has had time to decompose, is a better option over fresh wood mulch for use in most landscape practices, including biofiltration. Composted mulch is typically free of disease, insects and weed seeds. Fresh wood mulch can remove nitrogen from the soil, which may be beneficial to nitrogen removal from stormwater, but can strip nitrogen away from landscape plants. Fresh wood mulch is typically available as wood chips and can be more prone to floating, exposing the media surface to erosion and obstructing overflows. Wood chips typically are not as shredded and decomposed as composted mulch which tends to more easily form a mat after a few storm events due to its more fibrous structure. | **Organic wood mulch is often a byproduct of the lumber industry (typically shredded bark), wood recycling centers (i.e. pallets) or processed yard waste from public landfills. Other mulches can include grass clippings, pine needles, straw, sawdust, leaf litter, turf, coir and compost, but these should be avoided for biofiltration applications, particularly high flow media, to prevent hydraulic restriction, flotation, maintenance burdens and nutrient leaching among other issues. Composted or aged wood mulch, which is mulch that has had time to decompose, is a better option over fresh wood mulch for use in most landscape practices, including biofiltration. Composted mulch is typically free of disease, insects and weed seeds. Fresh wood mulch can remove nitrogen from the soil, which may be beneficial to nitrogen removal from stormwater, but can strip nitrogen away from landscape plants. Fresh wood mulch is typically available as wood chips and can be more prone to floating, exposing the media surface to erosion and obstructing overflows. Wood chips typically are not as shredded and decomposed as composted mulch which tends to more easily form a mat after a few storm events due to its more fibrous structure. | ||
**Qualifying mulch feedstock properties for consistency, texture and size helps ensure the mulch will not restrict flow, but also provide necessary pretreatment performance. Mulch with excessive fines or sediment should be avoided as this can reduce infiltration rates, but most mulch sizes should be less than 1 inch. Figure 2 illustrates a shredded hardwood mulch with ideal consistency and texture. Wood mulch can contain additives such as compost, but this should be avoided as a surface layer for biofiltration practices. Mulch particle size and texture not only affects hydraulic function but also floatability. If floating wood mulch is unavoidable, an open mesh netting can be staked over the surface to prevent mulch from escaping the practice. For a quick float qualification test, place mulch in a clear container filled with water. Stir to ensure even wetting and wait approximately 24 hours to observe if most of the mulch has settled. | **Qualifying mulch feedstock properties for consistency, texture and size helps ensure the mulch will not restrict flow, but also provide necessary pretreatment performance. Mulch with excessive fines or sediment should be avoided as this can reduce infiltration rates, but most mulch sizes should be less than 1 inch. Figure 2 illustrates a shredded hardwood mulch with ideal consistency and texture. Wood mulch can contain additives such as compost, but this should be avoided as a surface layer for biofiltration practices. Mulch particle size and texture not only affects hydraulic function but also floatability. If floating wood mulch is unavoidable, an open mesh netting can be staked over the surface to prevent mulch from escaping the practice. For a quick float qualification test, place mulch in a clear container filled with water. Stir to ensure even wetting and wait approximately 24 hours to observe if most of the mulch has settled. |
This page provides information on wood chips. While providing extensive information on wood chips, there is a section focused specifically on stormwater applications for wood chips.
Wood chips are small- to medium-sized pieces of wood formed by cutting or chipping larger pieces of wood such as trees, branches, logging residues, stumps, roots, and wood waste. They include bark, wood, and often leaves. Wood chips are rich in lignin, suberin, tannins. Common mulch sources include cedar, cypress, straw/hay, pine, and spruce.
In stormwater applications, wood chips are used as a mulch to provide one or more beneficial functions. Potential benefits of wood chips include but are not limited to the following. They
Physical and chemical properties of wood chips vary depending on the source, method of production, and age. Because of this variability, this page focuses on generic properties of wood chips used as mulch, except where otherwise stated.
This section includes a discussion of chemical and physical properties of wood chips, and potential contaminants in wood chips,
Chemical and physical properties of wood chips
Leachate from fresh wood chips is acidic, produces chemical oxygen demand, and releases nutrients. Negative aquatic response to leachate has been observed near wood chipping facilities and may be due to COD, phenols, organic compounds, or resin acids such as isopimaric acid (IA) and dehydroabietic acid (DHAA) (Machrafi et al., 2007; Taylor and Carmichael, 2003; Rex et al., 2016). Toxic effects associated with high oxygen demand from wood stockpiles have been observed in nearby receiving waters (Tao et al., 2005; Kannepalli et al., 2016). Studies indicate leaching of nutrients and organic compounds that contribute to oxygen demand decrease with time (Machrafi et al., 2007).
Wood chips from recycled wood may contain creosote and CCA (chromated copper arsenate). Wood chips from recycled wood is often colored with dyes. Dyes are typically organic- or iron-based and have not been found to be toxic. However, if colored wood chips are used, the wood source should be determined University of Massachusetts, Amherst.
Most studies indicate that diseased mulch cannot transmit pathogens to the roots of healthy trees. Mulch should not be incorporated into soil, under which conditions pathogens may be transmitted to trees ([2]; [3]).
In this section we provide information on effects of wood chips on pollutant attenuation and on physical properties of soil and engineered media.
Recommended values for wood chips used in a growth media (Source: see reference list in this section) | |
pH | |
Electrical conductivity (ms/cm) | |
Cation exchange capacity (meq/100g) | |
Nitrogen (%) | |
Phosphorus (%) | |
Potassium (%) | |
Copper (% minimum) | |
C:N ratio (minimum) | |
Lignin (%) | |
Total organic matter (% minimum) | |
Moisture (%) | |
Ash content (%) | |
Impurities | |
Fiber content | |
Expansion | l/kg |
Water holding capacity | l/kg |
Specific standards do not exist for wood chips, but the Forest Stewardship Council (FSC) certifies wood sources, which guarantees that the wood and bark is responsibly sourced. The FSC Controlled Wood Standard (FSC-STD-040-005 Version 3.0) requires knowledge of where the wood comes from, an evaluation of the risk that a wood source is in violation with unacceptable categories of wood, and mitigate actions to reduce any risk from the wood source.
Products receiving Mulch & Soil Council Certification must pass rigorous screening and are periodically audited to ensure the products meet Council standards. The certification ensures the product label is accurate and all ingredients are listed, and product claims have been verified. A Mulch & Soil Certification also ensures the mulch contains no chromated copper arsenate.
Some general guidelines for material selection are provided below
Prabhu and Thomas (2002) provide an extensive discussion of wood chips decomposition.
Keep wood mulch away from the trunks of trees to prevent rot. If you are concerned about termites, use cedar mulch or keep other wood mulches at least 6 inches (15 cm.) from the foundation. Let your mulch age if you aren’t sure of your source. This allows time for any sprays that were used on the tree or diseases it may have had to break down.[7]
Read more at Gardening Know How: Types Of Bark Mulch: Tips For Using Wood Mulch In Gardens https://www.gardeningknowhow.com/garden-how-to/mulch/bark-mulch-in-gardens.htm