Rethinking nutrient management in cities
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Transcript of Rethinking nutrient management in cities
Rethinking Nutrient Management in Ci1es
Lawrence A. Baker University of Minnesota
Low Impact Development Conference August 20, 2013
Why do we need to rethink nutrient management in ci1es?
1. Nutrient-‐impairment has high societal costs: Ø Recrea1on Ø Drinking water Ø Fisheries
2. Current stormwater management does not seem to be effec1ve at reducing nutrient impairment
3. Our non-‐renewable phosphate reserve will become depleted over the coming decades.
Number of nutrient impaired lakes: 150
Number of restored lakes: 1
Satellite-‐inferred lake clarity in the Twin Ci1es region, 1998
hTp://water.umn.edu/lwc/lwc2.html
We are making li,le progress to reduce lake eutrophica5on
Things may get worse: nutrients + heat = blue-‐greens (Michalak et al. 2013)
End-‐of-‐pipe treatment has been expensive and not very effec5ve at reducing nutrients.
3. Tree leaves to street
2. Lawn to street
1. External inputs to watershed
4. P removal by street sweeping
7. Lawn to groundwater
So let’s “think’ upstream.
0.0 1.0 2.0 3.0 4.0
Pre-‐ban fer1lizer
Labrador retriever
Rat terrier
Poly-‐P
Atm. Deposi1on
P input, kg/yr
Flux #1: P inputs to watersheds
Minnesota’s P fer5lizer law reduced P inputs to lawns
0.5 ha lawn 1 dog
Growing turf
Soil inorganic P Soil organic P
Fer1lizer P
Runoff soluble P
Runoff par1culate P
Exported clippings
Mowed grass
Leaching
Conceptual model of P cycling in lawns. Baker, Wilson, Fulton, and Horgan, 2008.
Lawn P cycle
Flux #2: Lawns to streets. An ecological process model for lawns could aid development of targeted, tailored homeowner educa5on
Baker et al., 2008; based on Nowak et al. 2006.
High nutrient export
Lawn-‐to-‐street fluxes are probably dispropor5onate
Source: TCHEP
28.3
15.7 9.6
24.6
11.4 10.4
low maintenance neat and orderly privacy/seclusion beauDful yard supports wildlife naDve plants
Lawn fluxes: Effec5ve homeowner educa5on could be tailored to homeowner’s lawn management preferences.
Data from the Twin Ci1es Household Ecosystem Project (tchep.umn.edu)
Flux #3: Moving upstream (trees to streets): How green are trees?
TP = 2.06x -‐ 0.12 R² = 0.83
COP = 1.40x -‐ 0.13 R² = 0.88
0.0
0.2
0.4
0.6
0.8
0.15 0.20 0.25 0.30 0.35 0.40
P yield, kg/ha
-‐yr
Canopy fracDon
Trees may be an important source of nutrients to streets
0
2
4
6
8
0 20 40 60
Lake clarity, m
Tree canopy cover, %
10:1 20:1
Watershed: Lake ra1o
Do green trees cause green lakes?
Could street sweeping be an efficient way to reduce nutrient inputs to stormwater?
Processing Waste
Food Food Waste
Sewage Biosolids
Treated water
Irriga1on or
biosolids
Agricultural products
Compost or animal animal feed
P fer1lizer
Will we need to create a circular economy for P?
Twin CiDes
1. Most food consumed in the Twin Ci1es is produced in MN, making findings ac5onable
2. Regional analysis of top-‐down & bo,om-‐up conserva5on scenarios
3. Site-‐specific analysis could guide implementa5on of circular P economy Agricultural region
Can we connect the flows of P between farms and ci5es, crea5ng a “circular economy” ?
Human food 1.67
Pet food 0.55
Sewage 2.52
Other P inputs 1.37
Turf fer1lizer 0.12
Biosolids 1.46
Effluent 1.14
Pet waste 0.17
Atmospheric dep. 0.11 Landfills 1.71
Food (0.25) and lawn (0.05) waste
Stream export 0.11
Urban landscapes
Sewage treatment plants
Households & Commercial
Mississippi River
Agricultural system (dairy and hogs)
Ag. fer1lizer 0.22 Animal feed 0.04
Animal products 0.12
Sep1c system 0.23
Soil acc. 0.66
Most P in the TC is buried in landfills. We could move from 4% reuse of P to 2/3 reuse with exis5ng technologies (Baker, 2011)
0% 10% 20% 30%
Milk Meat, poultry, fish
Grains Total vegetables Non-‐fluid dairy
Non-‐caloric sweeteners Fats and oils
Fruits Nuts
Sources of dietary P
Lean flesh; 9%
Bone; 51%
Other; 39%
P content of steer
Losses during processing
Urban food
Con1nuing work: Circular economy for P (Peterson and Baker)
Take home messages:
1. End-‐of-‐pipe stormwater treatment is not very effec1ve and not cost efficient for nutrients
2. Moving “upstream” may work beTer: External nutrients to watersheds Lawns à streets
Trees à streets
3. It may be necessary to create a “circular economy” for P, to prevent a brown devolu1on
4. In Minnesota, closing the P loop may favor peri-‐urban agriculture
Urban flowpath group: Jacques Finlay, Sarah Hobbie, Bob Sterner, Ben Janke, Daniel Nidgorski
Twin Ci1es Household Ecosystem Project
Heidi Peterson
Sponsor acknowledgements: • NSF grants BCS-‐0908998(TCHEP) and DEB9714833 (CAP-‐LTER) • MPCA/EPA 319 program grants: CON000000021155 and CON000000021183 • Ins1tute on the Environment “Discovery” grant
R-‐L: Ross Bintner, Chris Buyarski, Sarah Hobbie, Paula Kalinosky