Blue Water Science
550 South Snelling Avenue
St. Paul, MN 55116
Original Message —–
Sent: Sunday, May 17, 2009 8:35 AMSubject: weed removalHi Steve McComas,The Lake Volney Association would like to investigate curly leaf pond weed removal by harvesting machine / contractor. Could you recommend a contractor to do this and any guess as to the cost.Thank you.
Lake Soil Fertility of Littoral Zone Sediments
in Lake Volney, Le Sueur County, MN
[Survey Conducted November 9, 2002]
Updated October 2004
Prepared by: Steve McComas (Blue Water Science)
Submitted to: Le Sueur County, Le Center, Minnesota
Lake sediments were collected in 4 to 7 feet of water depth from Lake Volney November 9,
2002. The lake “soils” were analyzed for 16 parameters including nitrogen, phosphorus, and
potassium. Other studies have found a correlation of elevated exchangeable ammonium-nitrogen
sediment concentrations with nuisance growth of Eurasian watermilfoil (EWM). A nuisance is
defined as milfoil matting at the water surface in a continuous canopy covering an area greater
than 2,500 square feet. At lower nitrogen values, we have found that EWM can still grow, but
not necessary to nuisance conditions. In these cases, removal is often unnecessary.
For curlyleaf pondweed, high sediment nitrogen does not appear to produce heavy curlyleaf
growth. However, four other sediment parameters are correlated with curlyleaf pondweed
growth characteristics. For heavy nuisance curlyleaf growth to occur in a lake being tested, like
Volney, all four parameters from a sediment site need to be within range of the reference
nuisance category. For Lake Volney, most of the sediments tested had a low pH and low organic
matter content. These conditions have not been found to produce heavy nuisance growth in other
lakes (McComas, unpublished). Therefore, no areas in Lake Volney are predicted to support
heavy curlyleaf growth. However, a number of areas could support a light nuisance growth.
Based on lake sediment analyses of Lake Volney sediments, a number of areas have the potential
to support nuisance EWM. Nitrogen levels were found to range from low to high with the
highest readings in the west and of Lake Volney. The high readings correlated with sediments
high in organic matter. Based on lake sediment results, if Eurasian watermilfoil was to invade
Lake Volney we would predict potential nuisance acreages to be less than 42 acres.
Often factors could limit nuisance growth including reduced light penetration due to algae
Soil Fertility Evaluation, 2004 1
The use of lake soil fertility sampling to predict curlyleaf pondweed and
Eurasian watermilfoil growth or aquatic plant growth in general is an
evolving area. Based on results from other lakes, it appears nitrogen (as
exchangeable ammonium) is important for producing nuisance matting of
Eurasian watermilfoil. There appears to be a nitrogen threshold for
nuisance milfoil growth. When nitrogen concentrations (as exchangeable
ammonia) are greater than about 10 ppm, nuisance milfoil conditions are
found in many lakes. Organic matter is also another leading indicator for
potential nuisance milfoil growth and this is probably because organic
matter and nitrogen are related so when there is also high organic matter
there is high nitrogen. Based on results from other lakes we predict that
the combination of high organic matter and high nitrogen values (as
exchangeable ammonium) will sustain nuisance milfoil growth in shallow
water (less than 12 feet) on an annual basis unless some other factor limits
growth. Limiting factors include things such as milfoil weevils, light
penetration, and other unknown variables. When lake bottom areas have
moderate fertility, we predict there is the potential to support nuisance
growth in some years, but not on a continuous basis.
The objective of this lake soil fertility survey was to characterize Lake
Volney soils in the littoral zone in order to better predict where nuisance
areas of milfoil growth could occur in the future.
Lake Soil Collection. Sediment samples were collected from depthsranging from 4 to 7 feet using a modified soil auger, 5.2 inches in diameter
(Figure 1). Soils were sampled to a depth of 6 inches. The lake soil from
the sampler was transferred to 1-gallon zip-lock bags and delivered to a
soil testing laboratory.
Lake sediment samples were collected from sites where plants were
present or from open areas were plants were absent. At each sample
location, within about a 10-foot radius we noted all aquatic plant species
and rated their density on a scale from 1 to 5 with one representing a low
Soil sample locations are shown in Figure 2.
Soil Fertility Evaluation, 2004 2
Figure 1. Soil auger used to collect lake sediments.
Figure 2. Lake soil sample locations.
Soil Fertility Evaluation, 2004 3
Lake Soil Analysis: At the lab, sediment samples were air dried at roomtemperature, crushed and sieved through a 2 mm mesh sieve. Sediment
samples were analyzed using standard agricultural soil testing methods.
Sixteen parameters were tested for each soil sample. A summary of
extractants and procedures is shown in Table 1. Routine soil test results
are given on a weight per volume basis.
Table 1. Soil testing extractants used by Eco-Agri Laboratories, Willmar. These are
standard extractants used for routine soil tests by most Midwestern soil testing
laboratories (reference: Western States Laboratory Proficiency Testing Program: Soil
and Plant Analytical Methods, 1996-Version 3).
P-Bray 0.025M HCL in 0.03M NH4FP-Olsen 0.5M NaHCO3
NH4-N 2N KCLK, Ca, Mg, Na 1N NH4OAc (ammonium acetate)Fe, Mn, Zn, Cu DTPA (diethylenetriamine pentaacetic acid)
B Hot water
Organic matter K
2Cr2O7 (Walkey-Black Method)CEC Sum of exchangeable bases (K, Ca, Mg, Na)
Reporting Lake Soil Analysis Results: Lake soils and terrestrial soils aresimilar from the standpoint that both provide a medium for rooting and
supply nutrients to the plant.
However, lake soils are also different from terrestrial soils. Lake soils (or
sediments) are water logged, generally anaerobic and their bulk density
ranges from being very light to very dense compared to terrestrial soils.
There has been discussion for a long time on how to express analytical
results from soil sampling. Lake sediment research results are often
expressed as grams of a substance per kilogram of lake sediment,
commonly referred to as a weight basis (mg/kg). However, in the
terrestrial sector, better relate to plant production and potential fertilizer
applications to better crop yields, soil results typically are expressed as
grams of a substance per cubic foot of soil, commonly referred to as a
weight per volume basis. Because plants grow in a volume of soil and not
a weight of soil, farmers and producers typically work with results on a
weight per volume basis.
That is the approach used here for lake sediment results: they are reported
on a weight per volume basis or μg/cm3.
Soil Fertility Evaluation, 2004 4
A bulk density adjustment was applied to lake sediment results as well.
For agricultural purposes, in order to standardize soil test results
throughout the Midwest, a standard scoop volume of soil has been used.
The standard scoop is approximately a 5-gram soil sample. Assuming an
average bulk density for an agricultural soil, a standard volume of a scoop
has been a quick way to prepare soils for analysis, which is convenient
when a farmer is waiting for results to prepare for a fertilizer program. It
is assumed a typical silt loam and clay texture soil has a bulk density of
1.18 grams per cm . Therefore
3 a scoop size of 4.25 cm3 has been used togenerate a 5-gram sample. It is assumed a sandy soil has a bulk density of
1.25 grams per cm
3 and therefore a 4.00 cm3 scoop has been used togenerate a 5-gram sample. Using this type of standard weight-volume
measurement, the lab can use standard volumes of extractants and results
are reported in ppm which is close to μg/cm
3. For all sediment resultsreported here, a scoop volume of 4.25 cm3 was used.However lake sediment bulk density has wide variations and only a single
scoop volume of 4.25 cm
3 was used for all samples. This would notnecessarily produce a 5-gram sample. Therefore, for our reporting, we
have used corrected weight volume measurements and results have been
adjusted based on the actual lake sediment bulk density. We used a
standard scoop volume of 4.25 cm
3, but sediment samples were weighed.Because test results are based on the premise of a 5 gram sample, if our
sediment sample was less than 5 grams, then the reported concentrations
were adjusted down to account for the less dense bulk density. If a scoop
volume weighed greater than 5.0 grams than the reported concentrations
were adjusted up. For example, if a 5-gram scoop of lake sediment
weighed 2.0 grams, then the correction factor is 2.00 g/ 5.00 g = 0.40. If
the concentration was 10 ppm based on 5 gram, then it should be 0.40 x 10
ppm = 4 ppm based on 2 grams. The results could be written as 4 ppm or
3. Likewise, if a 5-gram scoop of lake sediment weighed 6 grams,then the correction factor is 6.00 g / 5.00 g = 1.20. If the concentration
was 10 ppm based on a 5 gram scoop, then it should be 1.20 x 10 ppm =
12 ppm based on 6 grams. The result could be written as 12 ppm or 12
Soil Fertility Evaluation, 2004 5
Lake Volney Sediment Results
Lake sediments were sampled on 12 transects around Lake Volney in
water depths from 4 to 8 feet. On several transects sediments were
collected at 2 water depths. A total of 21 samples were collected. At each
location the types of plants were identified as well.
Curlyleaf pondweed, an exotic plant was found on most transects, but
Eurasian watermilfoil was not found in Lake Volney. Native plants were
absent at most sample locations as well.
Results of the lake sediment analysis are listed in Table 2.
Lake sediment data were used to gage the potential of nuisance growth of
curlyleaf pondweed and Eurasian watermilfoil and maps were prepared to
delineate potential nuisance growth areas. Maps are shown in Figures 3
Table 2. Lake sediment data from Lake Volney. Sediments were collected on November
Potential for Curlyleaf Pondweed Nuisance Growth in Lake VolneyFor curlyleaf pondweed, high sediment nitrogen does not appear to produce heavy curlyleaf
growth. However, four other sediment parameters are correlated with curlyleaf pondweed
growth characteristics. The means of the sediment determinations as they correlated to three
curlyleaf growth categories are shown in Table 3. For heavy nuisance curlyleaf growth to occur
in a lake being tested, like Volney, all four parameters from a sediment site need to be within
range of the reference nuisance category. For Lake Volney, most of the sediments tested had a
low pH and low organic matter content. These conditions have not been found to produce heavy
nuisance growth in other lakes (McComas, unpublished). Therefore, no areas in Lake Volney are
predicted to support heavy curlyleaf growth. However, a number of areas could support a light
nuisance growth (Figure 3).
Table 3. Lake Volney sediment data and ratings for potential nuisance curlyleaf pondweed growth.
nuisance growth of curlyleaf pondweed.
Figure 3. Sediment sample locations are on the map. The light green shading indicates the potential for lightSoil Fertility Evaluation, 2004 9
Potential for Eurasian Watermilfoil Nuisance Growth in Lake Volney
The potential for nuisance EWM growth has been correlated to high sediment nitrogen and
organic matter less than 20%, For a high potential rating both nitrogen and organic matter had to
have a high potential rating. For a medium potential rating only organic matter had to meet the
criteria. When organic matter is greater than 20% and sediment nitrogen (as NH
4) is less than 10ppm, nuisance EWM growth is not expected.
Table 4. Lake Volney sediment data and ratings for potential nuisance EWM growth.