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Soil Strategies Soil Strategies Summary of Soil Best Management Practices for Stormwater Management, Erosion Control, New Construction and Landscape Success ¾ Retain and protect native topsoil & vegetation (esp. trees!) • Minimize construction footprint • Store and reuse topsoil from site • Retain “buffer” vegetation along waterways ¾ Restore disturbed soils by tilling 2-4" of compost into upper 8-12" of soil. Rip to loosen compacted subsoil. David McDonald Seattle Public Utilities Existing Landscapes [email protected] and ¾ Retrofit soils with tilled-in compost when re-landscaping Soils for Salmon Project Washington Organic Recycling Council ¾ Mulch beds with organic mulches (leaves, wood chips, www.SoilsforSalmon.org compost), and topdress turf with compost Presentation at “Landscape Stormwater Strategies – A ¾ Avoid overuse of chemicals, which may damage soil life Practical Design Workshop” (advanced) 1/26/06 at UW CUH Why a Soil Strategy is Essential: The Stormwater Problem: The Connection Between Soil and Water Impacts of turning spongy forests into cities 1972-1996: Amount of land with 50% tree cover decreased by 37% in Puget Sound region (from 42% of land down to 27%). 1972 1996 Impervious surface (roads, buildings) increased proportionately. WA population doubled 1962-98. 2.7 million more people by 2020! American Forests What happens to soil functions as we turn forests What happens to streams as we turn forests into cities? into cities? ↑compaction ↑runoff = ↑peak storm flows ↑erosion ↑erosion of stream bank and bed ↑loss of topsoil ↑fine sediment choking spawning gravels ↓soil organisms ↑pollutants (automotive, landscape ↓soil structure fertilizer and pesticides) Forest ↓natural fertility & ↓groundwater recharge disease prevention ↓summer low flows ↑impervious surface ↑summer stream temperature cause: ↓oxygen in spawning gravels ↑winter runoff ↓LWD - logs and rootwads ↑need for irrigation, chemicals that young salmon need ↓biofiltration of pollutants Urban ↓food supply for young salmon King County DNR 1 Chinook Salmon What does current science tell us? What are the impacts? • Biological integrity of streams decreases rapidly when total impervious area in watersheds exceeds 5-10%. • Salmon decline • Traditional stormwater detention structures in developed 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 areas are insufficient to prevent storm damage to streams. • Pollution • Salmon are in trouble unless we change our development practices. •Erosion • We need to: – decrease construction footprint • Flooding – decrease impervious area (roads, houses) & property – maintain natural “buffer zones” along streams damage – preserve native soils and forests – restore ability of disturbed landscapes to detain & • Failing landscapes, infiltrate rainwater resulting in more chemical use • A soil strategy can help. Restoring Soil Functions with Organic Amendments Try to make this….. function like this. Stormwater management Erosion and sediment management • Incorporate 15-30% compost • Compost berms or blankets − (by volume) into soil before slow water, bind surface soil, and planting reduce erosion immediately • Enhance survival/growth of • Compost amendment plantings, helping to stabilize builds soil structure, UW trials, turf on glacial till soil slopes over long term. moisture-holding capacity Berms instead of silt fence • Increases surface Compost- porosity amended till soil – up to 50% reduction in storm water runoff Compost blankets on steep slopes 2 Added benefits of Understanding Soil: soil amendment development from parent “dirt” & rock • Bio-filtration of urban pollutants • Improved fertility & plant vigor: Soil horizons & their evolution – less need for fertilizers and pesticides • Substratum (C) or bedrock (R) – reduced maintenance costs weathers physically & • Reusing “wastes” (yard waste, manure, chemically to subsoil (B) biosolids, construction, landclearing waste) 6 220 • Primarily biological processes Water Use 200 5 Rainfall create topsoil (A) • Reduced summer 4 180 and organic (O) horizons irrigation needs 160 3 140 2 120 1 Rainfall (inches) Water Use (mil gal/day) 100 0 USDA - NRCS Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec http://soils.usda.gov Sub-Soils in the Puget Sound Basin: Understanding soil: Leftovers from glaciers & volcanoes texture, structure, & pore space (thus infiltration) glacial till: unsorted, unstratified mixtures of clay, silt, sand, gravel, and boulders; deposited under ice, or in moraines Soil components: hardpan: till compacted under glacier •“The Dirt” (mineral part) Good soil is about outwash soils: layers sorted by particle - half mineral –sand size by water - sand / gravel / rocks - half space (air & water) – silt lake/marine bed soils: clay or silt that - plus a smaller but –clay essential amount of settled out in lakes & estuaries organic matter & soil life volcanic ash: light, fertile, holds moisture - • Air and Water mostly blown east of Cascades “Loam” is a mix of mudflows: mixed size, compact - like till • Organic Matter sand, silt, clay and organic, and Soil Life formed over time by nature Learn about Puget Sound soils at: www.puyallup.wsu.edu/soilmgmt/Soils.htm (create aggregates & pores) Understanding Soil Biology Common organisms in the soil foodweb Soil life provides essential functions • Nematodes • Bacteria Soil Foodweb Inc. Soil • Fungi Paul R. August, University of Minn. • Arthropods is alive! Inc. Foodweb Soil SSSA • Protozoa USDA-NRCS • Earthworms “Soil Biology Primer” S. Rose & E.T. Elliott Wilhelm Foissner, http://soils.usda.gov/sqi/ University of Salzburg 3 Restoring soil life, to restore soil functions How does soil life create soil structure? Soil organisms create: • Bacteria secretions glue clays, silts and sands together into • soil structure micro-aggregates. • fertility = nutrient cycling • Micro-aggregates are bound together by fungal hyphae, • plant disease protection root hairs and roots. • biofiltration • Spaces are made by moving • erosion control arthropods & earthworms, • stormwater detention and decaying roots. • Only when all organisms are present can roots and water move into the soil with ease. Compost kickstarts the soil ecosystem! (Provides food and home for organisms) S. Rose & E.T. Elliott How does soil life provide fertility (nutrient How does soil life provide plant disease protection? cycling)? Diversity ⇒ predation, parasitization & competition • Soil foodweb stores nutrients in living & dead organic matter with the few disease-causing organisms • Nutrients are released in root zone as organisms eat and • Bacteria cover leaf surfaces, block infection excrete “waste” (nitrogen, etc.) • Mycorrhizal fungi bring nutrients • Ecto- and endo- and water to roots of plants mycorrhizae prevent root Soil Foodweb Inc. infection • Many organisms prey on the few disease-causing organisms Dr. Michael P. Amaranthus, Mycorrhizal Applications Inc. SSSA How does soil life How does soil life filter out urban pollutants? control erosion? • Creates structure • Creates pore spaces, increases infiltration • Breaks down hydrocarbons, pesticides • Sticks soil particles & aggregates together • Converts fertilizers to stable forms, so they are with bacterial slime, fungal hyphae, available to plants but & root hairs (bigger aggregates are won’t wash away harder to move) • Binds heavy metals → “aggregate stability” in soil, so they don’t wash into streams • Promotes rapid plant growth & deep root development 4 How can we enhance & restore soil How does soil life provide stormwater biodiversity, to improve plant growth, water detention / infiltration? quality, and reduce runoff? • Builds soil structure, moisture-holding capacity • Prevent /reduce compaction (keep heavy machinery off) • Increases surface • Reduce intensive use of porosity pesticides & soluble fertilizers UW trials, turf on glacial till soil • Incorporate compost into soil to feed soil life Compost- amended till soil – up to 50% organic matter + soil organisms + time reduction in creates ⇒ storm water soil structure, biofiltration, fertility, & stormwater detention runoff Soil Amendment: A cost-effective solution Improving soil function for new development in existing development • Much better plant survival • Amend soil when re-landscaping = fewer callbacks • Plant native trees & shrubs, especially near waterways • Easier planting • Mulch beds annually with leaves, chips, compost, etc. • Can cut irrigation needs by 50% • Topdress turf areas with compost = 3-7 year payback on (aerate, topdress, rake in) irrigation savings alone Summary of Soil WA State Guidance on soil & LID BMPs: Best Management Practices DOE Stormwater Mgmt. Manual for Western WA New Construction • Equivalency required for Phase 1 NPDES permittees ¾ Retain and protect native topsoil & vegetation (esp. trees!) • Volume V, Chapter 5 - “On-Site Stormwater Mgmt.” • Minimize construction footprint – Downspout, sheet, & concentrated flow dispersion • Store and reuse topsoil from site • Retain “buffer” vegetation along waterways – BMP T5.13 Post-Construction Soil Quality and Depth ¾ Restore disturbed soils by tilling 2-4" of compost – Other Site Design BMP’s including preserving vegetation, into upper 8-12" of soil. Rip to loosen compacted layers. cisterns, roofs, rain gardens, porous paving, soil compaction protection, & T5.35 “Engineered Soil/Landscape Systems” Existing Landscapes • Volume III, Chapter 3 - “Flow Control Design” ¾ Retrofit soils with tilled-in compost when re-landscaping – Downspout
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  • Distinguishing Outewash, Ablation Till and Basal Till
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