Developing a Framework to Advance Statewide Phosphorus Reduction Credits for Leaf Collection

Transcription

1 Developing a Framework to Advance Statewide Phosphorus Reduction Credits for Leaf Collection Bill Selbig USGS Wisconsin Water Science Center wrselbig@usgs.gov This information is preliminary and is subject to revision. It is being provided to meet the need for timely best science. The information is provided on the condition that neither the U.S. Geological Survey nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information

2 Leaf Collection to Reduce Phosphorus - Pilot Study Agricultural and urban sources of phosphorus are targeted in the Adaptive Management plan for Rock River TMDL Leaf collection identified as reasonable measure to reduce Total P delivered to lakes What percent reduction in nutrients can municipal separate storm sewer systems (MS4) expect by collecting leaves? Are some leaf collection practices better than others? Source: Rock River Coalition

3 All Leaves Stay All Leaves Gone Study Objectives 1. Collect water-quality samples from a control and test basin to determine if removing leaves will result in detectable changes in phosphorus [ book end approach ] 2. Develop criteria to rapidly assess effectiveness of different leaf collection practices using field survey techniques

4 Control Paired Basin Study Design Test Study Basin Source Area Control Test Area (acres) Streets 17% 19% Driveways 6% 4% Roofs 17% 19% Sidewalks 5% 3% Lawns/Open 55% 54% Other Impervious <1% 0% Tree Cover 45% 68% USGS Monitoring Location

5 Mean Total Phosphorus Concentration, in mg/l April May June-Aug Sept Oct Nov Mean total phosphorus concentration during the calibration period in which there was no leaf collection or street cleaning Control ( ) Test ( ) April May June July August September October November Selbig (2016)

6 Escalated Leaf Management in Test Basin 1. Weekly street cleaning in spring and summer 2. Weekly collection of leaf piles followed by street cleaning in fall

7 Escalated Leaf Management In addition to municipal efforts, USGS field crews would clear all organic debris from street surface prior to rain event

8 Mean Total Phosphorus Concentration, in mg/l Mean total phosphorus concentration during the calibration period compared to the treatment period in which there was weekly leaf collection and/or street cleaning Control ( ) Test ( ) Test (Treatment 2015) April May June July August September October November Selbig (2016)

9 Seasonal Total Phosphorus Yield as a Percent of the 2015 Annual Yield (winter excluded) Control Spring 14% Fall 56% Summer 30% Test Fall 16% Spring 22% Selbig (2016) Summer 62%

10 How Representative Was 2015? 100 acres of medium density residential Standardized rainfall for Madison, WI ( ) Source area concentrations, other than streets, used default values Streets were dominate source of runoff for range of precipitation depths measured Varied concentration of phosphorus by season WinSLAMM v 10.2

11 Year Distribution of Annual Phosphorus Load by Season Season Minimum % Maximum % Mean % 70% 20-Year Seasonal Distribution of Total P Load (winter excluded) (solid horizontal line represents the mean) Spring % Summer % Fall % 30% 20% 10% 0% Spring Fall Summer Preliminary Information Subject to Revision. Not for Citation or Distribution

12 Decimal Perecnt Leaf Collection One of few Options to Reduce Dissolved Phosphorus Leaf collection may be one of only a few options to reduce dissolved Dissolved phosphorus P as a Percentage since of structural Total P controls do not effectively remove the dissolved fraction CONTROL TEST 0 Spring Summer Fall Spring Summer Fall Preliminary Information Subject to Revision. Not for Citation or Distribution

13 Paired Basin Results for Nutrient Load (Log), in grams Selbig (2016)

14 Percent Reduction in Nutrient Load , no statistical change Parameter Spring Summer Fall Total Phosphorus Total Nitrogen Dissolved Phosphorus Dissolved Nitrogen Selbig (2016)

15 All Leaves Stay All Leaves Gone How Does Your City Collect Leaves? Phosphorus Reduction 0% 80%

16 City of Madison Leaf Transfer plus Sweeping 1. Transfer leaf piles from terrace into street then pick up with garbage truck 2. Leaf collection followed by street cleaning 3. Frequency = approximately 4x per season

17 Leaf Transfer and Street Cleaning Every ~20 Days Nutrient Percent Reduction Total Phosphorus 40 Total Nitrogen -- Dissolved Phosphorus 45 Dissolved Nitrogen -- Preliminary Information Subject to Revision. Not for Citation or Distribution Photo Credit: City of Madison

18 All Leaves Stay Transfer and Sweeping ~ 4x All Leaves Gone How Does Your City Collect Leaves? Phosphorus Reduction 40% 0% 80%

19 Next Steps Evaluate other commonly used municipal leaf collection programs - Other municipal practices (vacuum mulching) - Frequency Develop semi-quantitative method to predict phosphorus load in stormwater based on estimate of leaf mass on streets

20 Estimating Phosphorus Load from Leaf Mass on Streets Develop method to rapidly assess the potential benefit of different leaf collection practices without the time and cost of water-quality monitoring

21 Estimating Phosphorus Load from Leaf Mass on Streets Category Average Net Weight, lbs. (80 ft frontage) Lbs. of Leaves Per Foot of curb Preliminary Information Subject to Revision. Not for Citation or Distribution

22 Estimating Phosphorus Load from Leaf Mass on Streets Average = g/lb Category Average Net Weight, lbs. (80 ft frontage) Lbs. of Leaves Per Foot of curb Leachable P per foot of curb (g) Dorney, 1986 Preliminary Information Subject to Revision. Not for Citation or Distribution Dorney (1986)

23 Only the estimated leachable phosphorus prior to rain events were summed Preliminary Information Subject to Revision. Not for Citation or Distribution Survey Dates Rain Date Leachable Phosphorus per foot of curb (mg/ft) Test Area 10/4 10/ /6 Before Swept /6 10/ /11 10/ /15 10/ / /25 10/ / /2 11/ / / /22 11/ /22 11/ /30 0 Leachable P for Rainfalls 15.2 mg

24 Partial Leaf Collection Programs to be Evaluated in Study Base Line: No street cleaning in fall home owners put their leaves on the terrace Madison Program: Leaf collection ~3-4x in fall & street cleaning after collection

25 Average Leachable P Baseline = 7.9 mg/ft Madison = 5.0 mg/ft Percent Difference = 44% Water-Quality Monitoring = 40% Survey Dates Rain Date Leachable P Normalized by Curb Length, mg Baseline Madison Oct 4 10/ Oct 6 10/ Oct 11 10/ Oct 14 10/ Oct 25 10/ Nov 1 11/ Nov Nov 21 11/ Nov 28 11/ Total Leachable P Total Leachable P for Rain Dates Avg. for Rain Dates Preliminary Information Subject to Revision. Not for Citation or Distribution

26 How Could a Leaf Collection Program Relate to Phosphorus Reduction Credits for an Entire City? EXAMPLE CALCULATION: Madison Program (Leaf Collection and Street Cleaning ~4x) = 44% Residential Land Use with High Tree Canopy in Madison = 60% Modeled Annual Phosphorus Contribution in Fall = 43% Annual Phosphorus Reduction Credit = 44% X 60% X 43% = 11 % Photo Credit: Roger Bannerman Preliminary Information Subject to Revision. Not for Citation or Distribution

27 Still Much to Learn Cleaning Frequency Tree Canopy Leaf Accumulation Rate Species of Tree All Photos : USGS Nutrient Reduction in Stormwater Phosphorus in leaves Vacuum Mulching Bagging Transfer Other Street Cleaning Frequency Curbs Land Use Tree Canopy Tree Species Cost Mechanical broom Weekly Yes Residential Low Vacuumassist Monthly No Commercial Medium Other High

28 Example Estimate of Unit Cost of P Removal KNOWN 15,774 tons of leaves collected in 2016 $147 per ton Amount of P in leaves varies ( g/lb) ASSUMED 70% of leaves collected are from MDR 15-25% of MDR leaves are in street Existing Madison collection method gets 40% reduction in P Preliminary Information Subject to Revision. Not for Citation or Distribution

29 Example Estimate of Unit Cost of P Removal 1. 15,774 tons x 70% = 11,042 tons of leaves in MDR 2. 11,042 tons x 25% in street = 2,761 tons of leaves in street 3. 2,761 tons x $147/ton = $405,795 to collect leaves in street 4. 2,761 tons x 0.27 g/lb = 3,286 lbs. of leachable P 5. 3,286 lbs. of P x 40% efficiency = 1,315 lbs. of P removed 6. $405,795 1,315 lbs. = $309/lb. of P Preliminary Information Subject to Revision. Not for Citation or Distribution

30 Measured TDP (g) - Adjusted Amount of Leachable P in Leaves can Vary Increasing Concentration of Dissolved P with Increasing Leaf Mass y = x R² = g/lb ($88/lb) g/lb ($309/lb) 100 y = x R² = , , , , , , ,000 Estimated Leaf Mass (g) Preliminary Information Subject to Revision. Not for Citation or Distribution

31 Questions References Cited: Dorney, J.R., Leachable and total phosphorus in urban street tree leaves. Water Air Soil Poll. 28, Selbig, W.R., 2016, Evaluation of leaf removal as a means to reduce nutrient concentrations and loads in urban stormwater, Science of the Total Environment, 571, pp Funding provided by: