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*Drake, Kevin, and Michael Hogan. 2015. [https://www.fs.fed.us/psw/partnerships/tahoescience/documents/p067_ForestManagementGuidebook_Final.pdf Forest Management Guidebook An Outcome-Based Approach to Water Quality Protection]. Integrated Environmental Restoration Services, Inc. Publication. 149 p. | *Drake, Kevin, and Michael Hogan. 2015. [https://www.fs.fed.us/psw/partnerships/tahoescience/documents/p067_ForestManagementGuidebook_Final.pdf Forest Management Guidebook An Outcome-Based Approach to Water Quality Protection]. Integrated Environmental Restoration Services, Inc. Publication. 149 p. | ||
*Ergas, Sarina J., Sukalyan Sengupta, Ryan Siegel, Arka Pandit. 2010. [https://ascelibrary.org/doi/pdf/10.1061/%28ASCE%29EE.1943-7870.0000243?casa_token=PEwCrTNhifIAAAAA:7nkDdeGqAFXkG5xvQBSipM6Q1WCrSScbC_lxW4mV71mTx8q3BrdOKgIqUzHmeqTyEqkF4rD6Lnag Performance of Nitrogen Removing Bioretention Systems for Control of Agricultural Runoff]. Journal of Environmental Engineering 136(10). DOI:10.1061/(ASCE)EE.1943-7870.0000243. | *Ergas, Sarina J., Sukalyan Sengupta, Ryan Siegel, Arka Pandit. 2010. [https://ascelibrary.org/doi/pdf/10.1061/%28ASCE%29EE.1943-7870.0000243?casa_token=PEwCrTNhifIAAAAA:7nkDdeGqAFXkG5xvQBSipM6Q1WCrSScbC_lxW4mV71mTx8q3BrdOKgIqUzHmeqTyEqkF4rD6Lnag Performance of Nitrogen Removing Bioretention Systems for Control of Agricultural Runoff]. Journal of Environmental Engineering 136(10). DOI:10.1061/(ASCE)EE.1943-7870.0000243. | ||
− | *Hamid, Rezaei , Lim, C. Jim, Lau, Anthony, Sokhansanj, Shahab. 2016. [https://www.osti.gov/pages/biblio/1328338 Size, shape and flow characterization of ground wood chip and ground wood pellet particles]. Powder Technology. Journal Volume: 301; Journal Issue: C; Journal ID: ISSN 0032-5910. https://doi.org/10.1016/j.powtec.2016.07.016 | + | *Hamid, Rezaei , Lim, C. Jim, Lau, Anthony, Sokhansanj, Shahab. 2016. [https://www.osti.gov/pages/biblio/1328338 Size, shape and flow characterization of ground wood chip and ground wood pellet particles]. Powder Technology. Journal Volume: 301; Journal Issue: C; Journal ID: ISSN 0032-5910. https://doi.org/10.1016/j.powtec.2016.07.016. |
+ | *Healy, M.G., M. Barrett, G. Lanigan, A.J. Serrenho, T. Ibrahim, S. Thornton, S.A. Rolfe, W.E. Huang, and O. Fenton. 2015. ''Optimizing nitrate removal and | ||
+ | evaluating pollution swapping trade-offs from laboratory denitrification bioreactors''. Ecological Engineering 74:290-301. | ||
+ | *Healy, M.G., T.G. Ibrahim, G.J. Lanigan, A.J. Serrenho, and O. Fenton. 2012. ''Nitrate removal rate, efficiency and pollution swapping potential of different organic carbon media in laboratory denitrification bioreactors''. Ecological Engineering 40:198-209. | ||
*Hills, Mindy. 2019. [https://www.conteches.com/stormwater-article/article/180/selecting-the-right-mulch-for-your-biofiltration-practice Selecting the Right Mulch for your Biofiltration Practice]. Contech website accessed May 25, 2021. | *Hills, Mindy. 2019. [https://www.conteches.com/stormwater-article/article/180/selecting-the-right-mulch-for-your-biofiltration-practice Selecting the Right Mulch for your Biofiltration Practice]. Contech website accessed May 25, 2021. | ||
+ | *Husk, B.R., J.S. Sanchez, B.C. Anderson, J.K. Whalen, and B.C. Wootton. 2018. [http://joann-whalen.research.mcgill.ca/publications/Journal%20of%20Soil%20and%20Water%20Conservation%2073--263-273.pdf Removal of phosphorus from agricultural subsurface drainage water with woodchip and mixed-media bioreactors]. Journal of Soil and Water Conservation. May/June: Vol. 73, No. 3. doi:10.2489/jswc.73.3.265. | ||
*Ima, C., and D. Mann. 2007. [https://ecommons.cornell.edu/handle/1813/10618 Physical Properties of Woodchip: Compost Mixtures used as Biofilter Media]. International Commission of Agricultural Engineering. Volume 9. | *Ima, C., and D. Mann. 2007. [https://ecommons.cornell.edu/handle/1813/10618 Physical Properties of Woodchip: Compost Mixtures used as Biofilter Media]. International Commission of Agricultural Engineering. Volume 9. | ||
*Johnson, Will Wheeler, Mara Braddy, and Bruce Bugbee 2017. [https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1800&context=psc_facpub#:~:text=The%20addition%20of%20rice%20hulls,increased%20up%20to%2040%25%20wood.&text=Would%20indicate%20the%20decrease%20in%20water%20holding%20per%20percent%20increase%20in%20wood. Effect of Wood Chips and Rice Hulls on Water Holding Capacity of A Peat--‐based Substrate]. Jakob Crop Physiology Laboratory, Utah State University. April--‐May. | *Johnson, Will Wheeler, Mara Braddy, and Bruce Bugbee 2017. [https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1800&context=psc_facpub#:~:text=The%20addition%20of%20rice%20hulls,increased%20up%20to%2040%25%20wood.&text=Would%20indicate%20the%20decrease%20in%20water%20holding%20per%20percent%20increase%20in%20wood. Effect of Wood Chips and Rice Hulls on Water Holding Capacity of A Peat--‐based Substrate]. Jakob Crop Physiology Laboratory, Utah State University. April--‐May. | ||
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*Mitchell, David K. 2014. [https://vtechworks.lib.vt.edu/handle/10919/64799 Urban Landscape Management Practices as Tools for Stormwater Mitigation by Trees and Soils]. M.S. Thesis. Virginia Polytechnic Institute and State. | *Mitchell, David K. 2014. [https://vtechworks.lib.vt.edu/handle/10919/64799 Urban Landscape Management Practices as Tools for Stormwater Mitigation by Trees and Soils]. M.S. Thesis. Virginia Polytechnic Institute and State. | ||
*New York State Energy Research and Development Authority. 2013. [https://www.nescaum.org/documents/nyserda-rept-13-13_elemental_analysis_of_wood_fuel-201306.pdf/view Elemental Analysis of Wood Fuels – Final Report]. NYSERDA Report 13-13 NYSERDA Contract 11165 June 2013. | *New York State Energy Research and Development Authority. 2013. [https://www.nescaum.org/documents/nyserda-rept-13-13_elemental_analysis_of_wood_fuel-201306.pdf/view Elemental Analysis of Wood Fuels – Final Report]. NYSERDA Report 13-13 NYSERDA Contract 11165 June 2013. | ||
+ | *Parvage, Mohammed Masud, Barbro Ulén, and Holger Kirchmann. 2017. ''Can Organic Materials Reduce Excess Nutrient Leaching from Manure-Rich Paddock Soils?''. J Environ Qual. 46(1):105-112. doi: 10.2134/jeq2016.06.0223. | ||
*Perry, Leonard. [https://pss.uvm.edu/ppp/articles/woodchips.html Wood Chips as Mulch]. University of Vermont Extension. Accessed May 25, 2021. | *Perry, Leonard. [https://pss.uvm.edu/ppp/articles/woodchips.html Wood Chips as Mulch]. University of Vermont Extension. Accessed May 25, 2021. | ||
*Pintor-Ibarra, Luis Fernando, Artemio Carrillo-Parra, Rafael Herrera-Bucio, Pablo López-Albarrán, José G. Rutiaga-Quiñones. 2017. [http://www.woodresearch.sk/wr/201706/03.pdf Physical And Chemical Properties Of Timber By-Products From Pinus Leiophylla, P. Montezumae And P. Pseudostrobus For A Bioenergetics Use]. Wood Research 62 (6):849-862. | *Pintor-Ibarra, Luis Fernando, Artemio Carrillo-Parra, Rafael Herrera-Bucio, Pablo López-Albarrán, José G. Rutiaga-Quiñones. 2017. [http://www.woodresearch.sk/wr/201706/03.pdf Physical And Chemical Properties Of Timber By-Products From Pinus Leiophylla, P. Montezumae And P. Pseudostrobus For A Bioenergetics Use]. Wood Research 62 (6):849-862. | ||
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*Salzman, J.A., E. T. Sullivan, J. R. Neetze1, and C. J. Shiue. 1958. The Water Holding Capacity of wood chips as Compared with Common Livestock Beddings. Minnesots Forestry Notes No. 69. | *Salzman, J.A., E. T. Sullivan, J. R. Neetze1, and C. J. Shiue. 1958. The Water Holding Capacity of wood chips as Compared with Common Livestock Beddings. Minnesots Forestry Notes No. 69. | ||
*Scharenbroch, Bryant C. and Gary W. Watson. 2014. [https://www.treefund.org/wp-content/uploads/2016/12/ScharenbrochWatson_2014_auf.pdf Wood Chips and Compost Improve Soil Quality and Increase Growth of Acer rubrum and Betula nigra in Compacted Urban Soil]. Arboriculture & Urban Forestry. 40(6): 319–331. | *Scharenbroch, Bryant C. and Gary W. Watson. 2014. [https://www.treefund.org/wp-content/uploads/2016/12/ScharenbrochWatson_2014_auf.pdf Wood Chips and Compost Improve Soil Quality and Increase Growth of Acer rubrum and Betula nigra in Compacted Urban Soil]. Arboriculture & Urban Forestry. 40(6): 319–331. | ||
+ | *Sharrer, K.L., L.E. Christianson, C. Lepine, and S.T. Summerfelt. 2016. ''Modeling and mitigation of denitrification ‘woodchip’ bioreactor phosphorus | ||
+ | releases during treatment of aquaculture wastewater''. Ecological Engineering 93:135-143. | ||
*Shaw, David A., Dennis R. Pittenger, Mark McMaster. 2005. [https://ucanr.edu/sites/UrbanHort/files/80238.pdf Water Retention and Evaporative Properties of Landscape Mulches]. 2005. Proc. 26th Annl. Irrigation Show, Phoenix, AZ, Nov. 6-8, 2005. Irrigation Assoc., Falls Church, VA. | *Shaw, David A., Dennis R. Pittenger, Mark McMaster. 2005. [https://ucanr.edu/sites/UrbanHort/files/80238.pdf Water Retention and Evaporative Properties of Landscape Mulches]. 2005. Proc. 26th Annl. Irrigation Show, Phoenix, AZ, Nov. 6-8, 2005. Irrigation Assoc., Falls Church, VA. | ||
*Tahboub, Mohammed B. , William C. Lindemann, Leigh Murray. 2008. [https://journals.ashs.org/hortsci/view/journals/hortsci/43/3/article-p891.xml?ArticleBodyColorStyles=pdf-4377#container-4382-item-4380 Chemical and Physical Properties of Soil Amended with Pecan Wood Chips]. HORT SCIENCE 43(3):891–896. | *Tahboub, Mohammed B. , William C. Lindemann, Leigh Murray. 2008. [https://journals.ashs.org/hortsci/view/journals/hortsci/43/3/article-p891.xml?ArticleBodyColorStyles=pdf-4377#container-4382-item-4380 Chemical and Physical Properties of Soil Amended with Pecan Wood Chips]. HORT SCIENCE 43(3):891–896. |
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. 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.
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.
As discussed below, the properties of mulch vary with several factors, including the tree species, source of chips (e.g. bark, wood), and initial condition of the chips (e.g. age, moisture content, chip size). Aged wood mulch, which is preferred, is commonly available as bark nuggets, and as both shredded softwood (such as cedar or fir) and hardwood. Wood mulch feedstock may be dictated by region as softwoods are more prevalent on the west coast of the U.S. and hardwoods on the east coast. A double shredded bark 3-inch mulch layer is generally used in biofiltration practices. Triple shredded bark mulch may contain too many fines and single shredded may contain larger mulch more prone to floating. Bark nuggets should also be avoided to prevent floating as they are less dense. When softwoods are used, texture should be evaluated as some softwoods can be somewhat “mouse-nest” in appearance and contribute to floating (Hills, 2019).
Fresh wood mulch should be avoided. 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.
Shredded wood should be avoided. Shredded wood mulch tends to clog soil and form a mat which can restrict infiltration.
This section includes a discussion of chemical and physical properties of wood chips, and potential contaminants in wood chips.
Physical and chemical properties of wood chips varies by the source (e.g. species, wood or bark) and the physical dimensions of the wood chips. Chips from wood typically are 70-80 percent cellulose and 20-30 percent lignin, while chips from bark are roughly 50 percent cellulose and 50 percent lignin (Pintor-Ibarra et al., 2017). Other components comprise less than 5 percent of the total dry weight mass of wood chips.
The adjacent table summarizes select physical and chemical properties of wood chips. The table does not differentiate between species or whether the chips are from bark or wood residue. Some general observations regarding these include the following.
Chemical and physical properties of wood chips. For concentrations of metals, link here.
Link to this table
Property | Range found in literature1 | Median value from literature |
---|---|---|
Total phosphorus (mg/kg) | 0.027 - 0.24 | 0.13 |
Total nitrogen (mg/kg) | 0.31 – 1.8 | 0.38 |
Total potassium (mg/kg) | 100-1600 | 709 |
Total carbon (mg/kg) | 434-498 | 47.1 |
pH | 3.34-5.07 | 3.47 |
Cation exchange capacity (cmol/kg)1 |
|
|
Total calcium (mg/kg) | 600-6200 | 1190 |
Total magnesium (%) | 60-6200 | 189 |
Bulk density (g/cm3) | 0.138 - 0.422 | 0.293 |
Water holding capacity (% by wt) | 58.5 | |
Total pore space (%) | 60-63 | 61.5 |
Primary references for this data:
1CEC increased as chip size decreased
The adjacent table summarizes concentrations of heavy metals, selenium, and arsenic in wood chips in comparison with soil reference values (SRVs) and soil leaching values (SLVs). Concentrations in wood chips were typically well below risk criteria, with the only exception being maximum observed arsenic concentration, which exceeded the residential SRV. Additional data was found in the literature but is not included in the table. Other data in the literature show similar results.
Heavy metal concentrations (mg/kg) in wood chips (New York State Energy Research and Development Authority, 2013).
Link to this table
Metal | Mean1 | Median1 | SRV – residential2 | SRV – commercial | SLV3 |
---|---|---|---|---|---|
Vanadium | 0.02 | 0.57 | 1.08 | 16 | 8 |
Chromium (III) | 0.24 | 7.36 | 23160 | 100000 | >100000 |
Manganese | 70.6 | 272 | 2104 | 26000 | 260.4 |
Iron | 18.1 | 345 | 10808 | 100000 | na |
Cobalt | 0.03 | 0.14 | 4.62 | 69 | 54.1 |
Nickel | 0.36 | 1.98 | 170 | 2600 | 352 |
Copper | 1.32 | 3.41 | 2192 | 33000 | 1404 |
Zinc | 5.93 | 17 | 4632 | 70000 | 6008 |
Arsenic | 0.05 | 1.17 | 0.08 | 1.2 | 11.64 |
Cadmium | 0.005 | 0.079 | 1.59 | 23 | 17.62 |
Lead | 0.25 | 1.12 | 300 | 700 | 5401 |
Antimony | 0.005 | 0.397 | 93 | 6.2 | 1.82 |
Barium | 17.4 | 45.9 | 41000 | 3000 | 3368 |
Selenium | 0.04 | 0.09 | 1200 | 77 | 5.28 |
1 13 samples
2SRV=Soil Reference Value (mg/kg)
3SLV=Soil Leaching Value (mg/kg); assumes 3 foot thick media and 3 foot separation from groundwater
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 ([1]; [2]).
In this section we provide information on effects of wood chips on pollutant attenuation and on physical properties of soil and engineered media.
No specific studies of phosphorus retention by wood chips in bioretention systems were found, though there are studies focused on nitrogen removal that also evaluated phosphorus. Christianson et al. (2017) studied a dual system consisting of a wood chip-based denitrification bioreactor coupled with either a steel slag or acid mine treatment residual system to remove phosphorus. The bioreactor did not remove phosphorus. Kuter et al (2017) observed that amending soil receiving biosolids with wood chips resulted in no phosphorus retention. Husk et al. (2018) found wood chip bioreactors vary in their effect on phosphorus leaching, with periods where phosphorus was retained and periods when phosphorus was released. Healy et al. (2012, 2015) and Sharrer et al. (2016) found initial leaching of phosphorus from wood chip bioreactors. Parvage et al. (2017) observed phosphorus retention by wood chips in manure-rich paddock soils. Since studies of nitrogen and phosphorus retention generally utilize dual systems, with one designed for nitrogen removal and the other for phosphorus removal, phosphorus retention by wood chips can be considered to be negligible. Similarly, several studies indicate wood chips are not an important source of phosphorus for vegetation, wood chips would not be expected to leach phosphorus in appreciable amounts.
Wood chips increases the water holding capacity and water retention of soil and bioretention media, though these increases are less than compost and other mulches that have greater surface area (Davis and Whiting, 2013; van Donk et al., 2011; Perry). Shaw et al. (2005) observed an increase in water holding capacity of 0.81 in/ft in a soil in San Diego, California. Salzmon et al. (1958) observed water holding capacities of 99-138 percent of dry weight for wood chips from four species (red and jack pine, aspen, birch), with the lowest adsorption being for birch.
Wood chips reduce soil temperatures by retaining soil water and blocking direct solar radiation, and reduce diurnal temperature fluctuations. Temperature effects are typically limited to the upper 10 cm of the soil or media (Abdul Bari Awan, 1964; Kotze, 2012; van Donk et al., 2011, Perry).
Research shows mixed results for effects of wood chips on soil bulk density. Wood chips appear to have beneficial effects on reducing soil compaction, particularly when incorporated, but minimal impact in uncompacted soils (Choi et al., 2005; Venner et al., 2011; Tahboub et al, 2008; Qu et al., 2019; Scharenbroch and Watson, 2014; Antieau, 2017).
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 |
Specifications exist for wood chips and pellets used for energy. Specific standards do not exist for wood chips used for other practices, 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 Hills, 2019.
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.[5]
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
Using locally produced wood chips is a sustainable activity and keeps a useful product out of landfills.
evaluating pollution swapping trade-offs from laboratory denitrification bioreactors. Ecological Engineering 74:290-301.
releases during treatment of aquaculture wastewater. Ecological Engineering 93:135-143.