Our Household Choices in Urban Living:
Understanding Nutrient Cycling in Twin Cities Homes
Thank you for participating in our May 2008 survey entitled “Our Household Choices in Urban Living,” sponsored by the University of Minnesota. Over 3,000 households in Ramsey and Anoka Counties responded to the
survey, answering questions about everyday activities such as transportation, yard management, food consumption,
trash and recycling, and home energy use.
From your responses, we are learning more about how household activities influence the cycles of three main nutrients: carbon, nitrogen and phosphorus. These nutrients are essential for all living organisms, but too much in
one place can also contribute to air and water pollution. A better understanding helps us keep the landscapes we
prefer, reduce air and water pollution, and make plans for healthy and satisfying lives. The choices you make at
home can become part of the solution.
Nutrient Cycling in an Average Twin Cities Household
What activities contribute to a household’s nutrient budget?
Carbon: 8,186 kg per year
Paper Plastic
2%
1%
Landscape
Human
9%
diet
4%
Home
energy
39%
Air travel
8%
Vehicle
travel
37%
Most people think of carbon as carbon dioxide (CO2), the main
contributor to global warming. Eighty-four percent of the carbon used by
our average household comes from fossil fuels (such as oil, coal, or
natural gas) that are burned for home energy, vehicle travel, or air travel.
This carbon immediately enters the atmosphere as carbon dioxide.
But carbon is the backbone of all organic molecules, not just oil. Carbon
is a major component of people, plants, animals – even plastics! The
other sixteen percent of a household’s carbon comes in through food,
paper, plastic, or is used by the growing plants in our landscape.
Nitrogen: 54 kg per year
Water pollution – Three quarters of the nitrogen
that moves through our average household
comes from the food we eat (nitrogen is an
Landscape
important part of protein), or the lawn
26%
fertilizer we use. Some of this nitrogen eventually ends up in our waterways. Excess nitrogen in rivers
Detergents
and lakes can feed algae blooms
3%
that cause lower water clarity and
oxygen levels, bad odor and taste,
and the loss of desirable species.
Pets Home energy
3%
2%
Vehicle travel
21%
Human diet
40%
Air pollution – When fossil fuels
are burned in power plants, home
furnaces, or vehicle and airplane
engines, the high temperatures
convert atmospheric nitrogen
Air travel (N2) into various nitrogen
5%
oxides (NOx) that contribute
to smog, acid rain, and other
problems. One-quarter of our
average household’s nitrogen
comes from these sources.
Phosphorus: 4 kg per year
Sixty percent of a household’s phosphorus comes from human and pet food
(phosphorus is an important part of DNA and other parts of our cells). The
remaining forty percent has not been well studied, but appears to come from
various detergents and other household products that wind up in a household’s
wastewater. Most of the phosphorus that goes into the city sewer eventually goes
from the wastewater treatment plant to the landfill. Septic systems, un-scooped
pet waste, and leaves and grass clippings that wash into the gutter can be sources
of phosphorus (and nitrogen) pollution to our lakes and streams. Phosphorus is
often more important than nitrogen in feeding noxious algae blooms.
Pets
9%
Detergents
etc.
39%
Human diet
52%
We’re All in This Together
More than half of Anoka and Ramsey County respondents were “concerned” or “very concerned”
about negative environmental effects influencing their quality of life.
Fortunately, there are many ways to make improvements.
Carbon: Driving, flying, and home energy create most of a household’s carbon emissions. If you drive to work
every day, you can reduce your commute carbon use by 10% if you carpool, bus, bike, or telecommute just one day
every other week! (see www.metrotransit.org for ideas) The bottom of this page has more ideas and resources for
reducing home energy use.
Nitrogen: If you use more lawn fertilizer than your grass needs, the excess nitrogen becomes water pollution.
Look through the University of Minnesota extension recommendations (snipurl.com/n-fert) to estimate how
much fertilizer your lawn needs. Leaves and grass clippings on driveways, sidewalks, or the street wash into your
local lakes and streams, so mulch them into your lawn or compost them (either on your property or at the
county compost facility). Driving and flying less will help with nitrogen, too, as well as carbon.
Phosphorus: Phosphorus is restricted in lawn fertilizer in Minnesota — make sure you don’t use garden
fertilizer by mistake! Read the label on your bag of fertilizer and look for a set of three numbers like 23-0-6.
The middle number is the percent phosphorus, so this should be a zero. If your pets use the outdoors, scoop
their waste, bag it, and put it in the trash. The landfill can handle the phosphorus better than the waterways can.
Reducing Your Home Energy Use:
Over 50% of Anoka and Ramsey County
respondents have taken actions to reduce
home energy use that will not only reduce
carbon emissions, but also save on energy
costs.
These actions have a real impact on a
household’s carbon budget. While we
can’t predict exactly how much carbon a
particular household will save, our survey
results show that even small actions create
meaningful improvements. For example,
using fluorescent bulbs, installing a
programmable thermostat, or lowering the
heat by two degrees F in winter each result in an average 4% reduction in home-energy carbon emissions.
For more ways to lower your emissions, check out www.energy.gov, www.mnenergychallenge.org, and
sustainablechoices.stanford.edu. There are many things you can do to help create solutions, from simple first
steps to larger commitments. Which ones are right for you?
Tracking Your Own Nutrients
The first step in making any changes is to see where you are. From our survey results, we’ve identified a few
key activities that are major contributors to a household’s carbon and nitrogen emissions. All units are in
kilograms of carbon or nitrogen, per household, per year (one kilogram = 2.2lbs; 1000kg = one metric tonne).
Next, set a goal for reducing your emissions. Ten percent is a big improvement — and it’s easier than you
might think! Take a look at some of the ideas and websites on the previous page to find what works for you.
Finally, track your progress by filling out this calculator again next year. Did you meet your goal?
Survey Average
Your Household’s Nutrient Budget
CARBON:
Electricity:
______________________________
x 0.19 =
_____________________kg C/yr
(your annual electricity use in kwh) ← available by calling your utility
Natural Gas:
______________________________
x 1.49 =
Total home
energy carbon:
3261 kgC/yr
_____________________kg C/yr
(your annual natural gas use in therms) ← available by calling your utility
Vehicle Travel:
(MPG estimates at fueleconomy.gov Add additional vehicles if needed)
Vehicle #1: _________________ ÷ _________________ x 2.24 = ___________________kg C/yr
(miles per year you drive)
(your vehicle’s mpg)
Vehicle #2: _________________ ÷ _________________ x 2.24 = ___________________kg C/yr
(miles per year you drive)
Total vehicle
travel carbon:
3013 kgC/yr
(your vehicle’s mpg)
Air Travel:
(Distance calculator at snipurl.com/airdist Add additional flights if needed)
Flight #1: ___________________ x _____________________ x 0.0067 = ______________kg C/yr
(roundtrip distance, miles)
(# of family members making the trip)
Flight #2: ___________________ x _____________________ x 0.0067 = ______________kg C/yr
(roundtrip distance, miles)
Total air travel
carbon:
624 kgC/yr
(# of family members making the trip)
NITROGEN:
Lawn Fertilizer: Look on the fertilizer bag for how many pounds per bag, and also a set of three
numbers. 23-0-6 is common for lawn fertilizer. These three numbers are the percentages of
nitrogen, phosphorus, and potassium, respectively.
____________________ x _________________x 0.0045 = ________________kg N/yr
(pounds of fertilizer used)
(first number on bag, e.g. 23-0-6 )
— use either of these calculations, but not both —
Alternately, you can estimate your fertilizer use based on the number of times you apply fertilizer
(we assume a standard application rate of 1lb nitrogen per 1,000 square feet). If you hire a lawn
care company, use this equation and enter “3.25” for the number of times you apply fertilizer.
Total lawn
fertilizer
nitrogen:
13 kgN/yr
____________________________ x _________________x 19.8 = ________________kg N/yr
(number of times you apply fertilizer)
(area of your lawn in acres)
What about PHOSPHORUS? Most of our average household’s phosphorus comes from human and pet food. It is
not possible to eat “low-phosphorus” food, since phosphorus is an important part of all the plants and animals
we eat. You need this phosphorus to make DNA, teeth, bones, and many other parts of your cells.
The other forty percent of the phosphorus is very difficult to measure and track directly, but you can look for
phosphorus-free detergents and other household products to help reduce your phosphorus use.
Department of Forest Resources
University of Minnesota
115 Green Hall
1530 Cleveland Ave. N.
St. Paul, MN 55108-6112
How do household activities influence the
cycles of carbon, nitrogen, and phosphorus
in urban and suburban ecosystems?
www.tchep.umn.edu
What’s coming up next?
 An expanded, online version of our Household Flux Calculator
 Science Museum of Minnesota’s “Future Earth” exhibit and
“Science Buzz” online community dialogue
 University of Minnesota Bell Museum’s “Shelter” exhibit
Check back on our website for updates and exhibit dates
Special thanks to the three thousand residents of Ramsey and Anoka Counties who contributed their
time and energy filling out our survey. This would not have been possible without your help.
Additional support from the University of Minnesota-Twin Cities (Ecology, Evolution, and Behavior; Fisheries, Wildlife, and
Conservation Biology; Forest Resources; Soil, Water, and Climate; Water Resources Center), the University of California-Santa Barbara
(Geography), the National Science Foundation, and Cedar Creek Ecosystem Science Reserve.