Cooperator: Wisconsin Department of Natural Resources
Project Chief: Judy A. Horwatich
Location: Dane County
Project Number: BQY15
Period of Project: March 1994–Continuing
updated 2/20/07
Problem
Excessive phosphorus entering lakes is known to promote unsightly weed growth,
decrease recreational uses, and ultimately speed the eutrophication process.
Structural or “end-of-pipe” management practices designed to reduce
phosphorus are generally expensive. Reducing phosphorus at the source may be
a less-expensive alternative. Restricting fertilizer use in the watershed to
phosphorus-free brands would seem to be a potentially inexpensive way to reduce
phosphorus loads to Lake Wingra. However, there is little applicable field evidence
supporting the hypothesis that runoff from fertilized lawns is greater in phosphorus
concentrations than runoff from non-fertilized lawns. A better understanding
of how much water runs off a typical urban lawn and under what conditions will
help watershed investigators to improve their ability to predict the impacts
of management decisions.
 Objective
Objectives are to: (1) determine if the concentrations of total phosphorus, dissolved
phosphorus, suspended solids, and total solids in runoff from fertilized lawns
are different than concentrations from lawns that are not fertilized; (2) use
the concentration data in an existing Source Loading and Management Model (SLAMM)
to estimate phosphorus loads entering Lake Wingra from both fertilized and non-fertilized
lawns; (3) determine the potential reduction in phosphorus loads to Lake Wingra
by restricting fertilizer use in the watershed to phosphorus-free brands; (4)
obtain rainfall and runoff data with site characteristic data for lawns from
different soil types; (5) use the concentration/runoff information to make
improvements to the SLAMM model; and (6) determine the lawn infiltration parameters
from natural and simulated rainfall from roof runoff.
Approach
Lake Wingra Lawn Fertilization Study
(water-quality samplers only)
Lawn-runoff samples were collected from 30 water-quality samplers between May
1999 and September 2001. Fifteen of the samplers were located in lawns that were
fertilized, and the other 15 were in lawns that were not fertilized. Samples
were analyzed for total phosphorus, dissolved phosphorus, total solids, and suspended
solids. Site characteristic data such as soil type and chemical contents, grass
density, lawn slope, soil compaction, and infiltration capacity were measured
for each of the 30 lawns. Several small experiments were conducted in order to
better understand what happens when the bottles overfill and how much phosphorus
is likely to come from grass clippings only.
Lawn Runoff Study (volume/QW samplers)
Runoff volumes are being measured and water-quality samples are being
collected for five specialized samplers in the Lake Wingra watershed. In addition
to the runoff data, several explanatory variables will be measured for each lawn,
including grass density, lawn slope, soil compaction, and infiltration rate.
Using statistical regression techniques, an equation will be developed to help
explain much of the variability in lawn-runoff volumes. Sites were operated
through June 2004.
Progress (January 2006 to June 2006)
Samples have been analyzed for 42 runoff events since May 1999. The five samplers
have recorded runoff data and collected water-quality data for over a dozen snowmelt
and rainfall-runoff events. Data from the runoff and samples has been put in
a spreadsheet format to be analyzed.
Plans (July 2006 to December 2006)
All of the data from the initial lawn-runoff study (water-quality samplers only)
will be analyzed. A U.S. Geological Survey report will be prepared.
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