This study has been designed to assess the potential to reduce phosphorus
levels in residential runoff by restricting the use of lawn fertilizer
Spring 2001 - Fall 2002
Lawn Fertilizer Experiment
Study Design II.
Real-time Creek Monitoring
Design I. The Lawn Fertilizer Experiment
Six small watersheds have been selected as study sites. Three of these
watersheds are located in Plymouth where the use of fertilizers that
contain phosphorus is restricted, and three are located in Maple Grove,
where there are no such restrictions. These watersheds were carefully
selected to include one newly developed area, one middle-aged, and
one older neighborhood within each of the cities. All of these watersheds
are located within 6 miles of each other to minimize differences in
precipitation patterns, soil types, and aerial loading of phosphorus.
In each of these
watersheds, runoff flows to a single outlet pipe. Automated sampling
equipment was installed at each of these outlet points to collect
detailed flow information and flow-weighted composite water samples.
By determining the mean phosphorus concentration and the total flow
volume for each rain event, we will be able to calculate the total
phosphorus load from each watershed during the monitored period.
If restricting the use of fertilizers containing phosphorus reduces
the amount of phosphorus in residential runoff, we should see significantly
lower phosphorus loading from the Plymouth watersheds when compared
to runoff from the Maple Grove watersheds.
has been collected to assess the potential role of other variables
in leading to differences in phosphorus loading between Maple Grove
and Plymouth. Each city has provided lot size information and percent
impervious area for the watersheds, and surveys will be administered
to all homes within each watershed to determine lawn-care practices
including fertilizer application, watering, mowing, and aeration.
The watersheds in Plymouth were surveyed in the spring of 2001,
but Maple Grove residents will not be surveyed until the fall of
2002 to prevent any changes in lawn-care practices during the planned
monitoring period. To maximize the number of Plymouth residents
using phosphorus-free fertilizer, Hennepin Parks has offered a free
bag of phosphorus-free fertilizer to a select group of homes that
indicated that they had been using fertilizer with phosphorus or
that did not respond to the survey.
Design II. Real-time monitoring of Plymouth and Ridgedale creeks
Two of the major tribuatry streams that flow into Medicine Lake,
Plymouth Creek and Ridgedale Creek, are being monitored. Both monitoring
sites were equipped with ISCO 6712 automated samplers with area-velocity
flow modules and communication modems for remote access. These samplers
were programmed to begin sample collection ata trigger water level
and then collect additional samples based upon the flow in the stream.
Flow data were downloaded weekly and water samples were retrieved
within 24 hours of each flow event. In addition, the Plymouth Creek
site was also equipped with a YSI
sonde to collect DO, temperature, pH and conductivity data. All water
samples were analyzed for total and dissolved phosphorus, total nitrogen,
suspended solids, and in some cases, ammmonia, nitrate, and total
ISCO GLS Automated Water Samplers
ISCO 6712 Automated Water Samplers
ISCO 4120 Submerged Probe Flowloggers
ISCO 4150 Area/Velocity Probe Flowloggers
and Quality Control
Samples analyzed under same QA/QC protocol as Hennepin Parks lake
samples. Blanks, replicates, duplicates, recovery of known additions,
as recommended in Standard Methods 1020 and 1030