[ Home ] [ AIS ] [ Conservation ] [ Comm-Tech ] [ Env and Ecol ] [ Fisheries ] [ Healthy Lakes ] [ History ] [ Safety ] [ Lake Level ] [ Treasurers ] [ Closed Committees ]
A Summary Of Ten Mile Lake Trends
Based on Volunteer & Consultant 2005 E&E Reports
Prepared by Marty McCleery
General Comment by Del Hogen,
President, Instrumental Research, Inc.
“The water quality of Ten Mile Lake has improved substantially over the
past 20 years and the Main Basin continues to improve from year to year.
Nitrogen concentrations are decreasing steadily in four of the basins;
Main Lake, Long Bay, Kenfield Bay, and Lundstrom Bay. Total nitrogen is
increasing substantially in Flower Pot Bay and Robinson’s bay.
Nutrient phosphorus concentrations in the water column continue to drop,
as does chlorophyll-a. Water clarity
as measured by Secchi disc readings is improving as well.”
The reports are a continuation of the process that began in 1994 which
involves composite surface sampling of Ten Mile Lake, at six sites, three
primary and three secondary. The
primary sites are sampled three times every year, while the secondary sites
rotate so that each is sampled every three years.
Four sites are sampled on the lake and these sites are sampled three
times each summer season. Sampling
dates for the season are as close as possible to May 15, July 15, and September
The Ten Mile Lake Association has gathered 12 years of lake related, water
quality, information. Water clarity
data is in the form of Secchi disc readings.
Chemical macro nutrient concentrations are in the form of total
phosphorus and total nitrogen. Solar energy conversion to carbohydrates is
dependent on Chlorophyll-a.
At this time the collected information can be converted to an easily
understood water quality index, commonly referred to as the Carlson Trophic
State Index (CTSI). The
Carlson Trophic State Index (CTSI) formulas have been selected as the mechanism
for conversion of Ten Mile Lake analytical information to a recognizable scale.
This data conversion allows a direct comparison of the water quality of
Ten Mile Lake to other lakes in the Minnesota Pollution Control Agency (MPCA)
Citizen Lake Monitoring Program (CLMP).
Secchi Disc Readings
Warren Goss started the Ten Mile Lake Secchi disc program and was one of
the first strong advocates for improved lake water quality in Ten Mile Lake.
These efforts continue today through the efforts of Jim Schwartz and Tom
Moore and a host of volunteers on the Environmental and Ecology Committee.
According to the MPCA Secchi disc data, as analyzed by David Wright PhD,
MN Department of Natural Resources, Ten Mile Lake has the second highest
positive change in Secchi disc readings from the two time periods 1988-1991 to
Ten Mile Lake water quality has been managed with an aggressive onsite
septic system upgrade program, and an intensive effort to analyze trends and
changes in water quality and efforts to educate and inform the lakeshore
residence about best management practices.
Carlson Trophic State Index (CTSI)
Robinson’s Bay, and Flower Pot Bay have increasing CTSI units (Carlson
Trophic State Index), meaning poorer water quality.
While Flower Pot Bay only increased two units, Robinson’s Bay increased
a significant eighteen units over the twelve-year sampling period.
The Main Basin and Long Bay are virtually unchanged.
Kenfield Bay and Lundstroms Bay have improved by dropping four and three
The total nitrogen does not fit the CTSI parameters but is important
because it has its own set of environmental consequences.
Total nitrogen levels have been see sawing for many years and will likely
continue. The input levels are
likely to be steady, but the process of denitrification is concentration
dependent. The effluent from onsite
septic systems is a significant source of nitrogen for the bays while airborne
precipitation input affects the lake overall.
The problem caused by nitrogen as nitrate or ammonia is a substantial
lowering of the disease immune response of the trees and shrubs in the flow path
from the septic system. There
is normally a symbiotic relationship between the trees or shrubs and the native
soil fungi. Symbiosis is a working
relationship between partners where each contributes something to the
relationship that the other party needs but cannot produce without the
association. This relationship between the fungi and the tree is lost when
nitrogen soil levels rise.
Estimated Nutrient Budget
With the physical data related to Ten Mile Lake a nutrient budget can be
formulated. The following list of parameters is required to construct such a
- Direct liquid
precipitation to the lake surface.
- Surface water
runoff into the lake.
- Discharge of
nutrients from septic systems into the lake.
discharge from the lake.
- Discharge via
the Boy River.
from the lake water surface.
from the terrestrial vegetation in the watershed.
The chemical components of each item in the above
list are used to build the yearly nutrient budget. As the nutrient content of
each constituent changes, which it will, a response plan can be formulated to
counteract undesirable reactions.
From the sources mentioned, the project was able to
construct a fairly accurate nutrient budget for Ten Mile Lake. The majority of
the chemical nutrients that support the biomass of Ten Mile Lake are internally
recycled nutrients. That is these
nutrients are precipitated to the sediments in the fall and recycled into the
plants, epiphytic algae, and the water column at turnover each year. The
majority of the nutrients accompanying the water effluent from the onsite septic
systems are still being retained in the intervening soils between the septic
system and the lake shoreline. About 15 % of the nutrient budget for Ten Mile
Lake comes from Onsite septic systems.
The nutrient budget load of total phosphorus was 4,505
pounds and total nitrogen was 42,400 pounds for the year.
Outflow of phosphorus via the Boy River is 125 pounds and
nitrogen is 3,750 pounds per year, which is 3 % of the total load for both
phosphorus and nitrogen.
Currently the internal cycling nutrients, the portion of
phosphorus and nitrogen that is redissolved again each year from the lake
sediments, is phosphorus about 6,150 pounds, about 60 % of the total load of
phosphorus, and about 115,600 pounds of nitrogen per year.
Retained phosphorus was 4,380 pounds and retained nitrogen was 38,650
pounds in 2005.
What can we learn from these numbers?
In the not too distant past, about 1970, the phosphorus and nitrogen
internal loading was higher than it is today. The average septic system did not
meet Minnesota standards for onsite wastewater treatment.
This means that almost 50% of the internal cycling nutrients are
currently buried in the bottom sediments. During 2005, about 40 % of both the
phosphorus and nitrogen were precipitated into and added to the bottom
sediments. As long as the sediment
interface remains oxygenated this nutrient load will stay put.
A 200-foot dissolved oxygen (DO) profile was done in
February of 2005 and shows 7.48
milligram per liter of DO at the 200-foot depth (60 meters).
This is an excellent result because even though the bacteria, algae,
invertebrates, and fish have been breathing from the ice covered lake, they have
not been able to deplete the DO more than 5.6 milligrams per liter.
A short period of oxygen removal from any of the deep lake
basins will generate a large influx of internal cycling nutrients from the
bottom sediments. This will in turn
generate higher algae populations. Secchi
disc readings in the main basin of Ten Mile Lake in 1974 were about 12 feet.
Today we get maximum readings of 24 to 26 feet, which means that in 1974
there was twice the mass of nutrients in the water column that there is today.
Boat launch sites are the most likely points for Eurasian
water milfoil to be inoculated into Ten Mile Lake.
For this reason, a fall survey of the aquatic vegetation patches is done
at as many of the boat launch sites on Ten Mile Lake as possible.
There are eight potential launching sites that could become inoculation
areas for Eurasian water milfoil and other exotic species.
No Eurasian Watermilfoil has been found through 2005.
Drinking Water Well Sampling
Sampling your drinking water well water is important for
protection of your health. This is
especially true for seasonal residents that shut off and turn on their water
each year. There is a greater chance
of contamination during shut down and start up.
The nitrogen and bacteriological data collected tells you if you have a
problem with your in home distribution and storage system and can also indicate
a poorly functioning septic system that may be contaminating your well.
Several members took advantage of the TMLA annual well
water testing system. The 2005 well
samples have been about the same number of tests from the North Shore and the
South Shore. The number of positives
is also the same from year to year. The
following data is for the past three years.