Black Oak Lake Plant Survey 2011
Susan Knight
May 2012
Summary
Susan Knight, Walt Bates, John Annin, Bob Peirce, and John Clarke performed a point-intercept
aquatic plant survey on Black Oak Lake (WBIC 1630100) on July 11-12, 2011. The sampling
grid included 1036 points of which 344 sites had vegetation. We found 22 plant species
including floating and submersed species growing at a maximum of 22 feet. Floristic Quality
Index was 33.0 and the Aquatic Macrophyte Community Index was 59. There was a diversity of
plant growth types and no invasive species. Together, all of these factors combine to indicate a
good aquatic plant community.
Introduction and Methods
On July 11-12, 2011, Susan Knight Walt Bates, John Annin, Bob Peirce, and John Clarke
conducted a plant survey on Black Oak Lake (WBIC 1630100). Using a point/intercept
sampling technique (Hauxwell et al. 2010), we used a rake on a pole (for depths up to 15’) and a
rake on a rope (used for sites deeper than 15’) to sample 597 points. Some sites were
inaccessible because the lake was too shallow or too deep.
We worked as a team of at least three, with one person driving the boat and navigating to each
point, a second person recording data and a third person (Susan Knight) raking, identifying each
species and determining abundance. At each site we determined depth and bottom substrate (as
muck, sand or rock). We recorded the total rake fullness as 0 (no plants), 1 (a few plants on the
rake), 2 (rake approximately half full) or 3 (rake overflowing with plants). We also rated the
abundance (using a scale of 1 to 3) of each species found at each point. At each site we looked
for species observed within 6 feet of the boat, but not actually collected on the rake (visuals). As
we neared shore, we also conducted a boat survey to collect comments about the shoreline and
shoreline vegetation.
Using data collected in the survey, we calculated Floristic Quality Index (FQI, Nichols 1999) and
Aquatic Macrophyte Community Index (AMCI, Nichols et al. 2000) as tools for assessing the
floristic integrity of Black Oak Lake. FQI is a computation assessing lake quality using two
parameters: the number of species present and the coefficient of conservatism (C) for each
species. C ranges from 1-10 and indicates how pristine an environment a species requires. These
values were assigned by a panel of botanists for each plant species in Wisconsin. FQI is based
on species recognized by Nichols (1999) as native aquatics. Some species collected are not
included in this measure for several reasons: not all aquatic/wetland transition species are
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included (e.g. many sedges), identification is uncertain (e.g. moss or Sparganium sp.), or it may
be an introduced species (none in this study, though European marsh thistle was seen on shore).
Also, visuals are not included in the FQI. Therefore, the total number of plants identified may be
greater than the number of species contributing to the FQI. The C value of each species is
averaged to compute an average C value for the lake and this value is multiplied by the square
root of the number of species seen on the lake. AMCI is a sum of seven parameters, each scaled
1-10 (for a maximum total of 70), and is another assessment of lake quality from plant data.
Results and Discussion
The grid included 1036 sampling points (Table 1), with points 47m apart. In an earlier survey in
2006, the points were 55m apart. By having points closer together, we sampled more sites to
better assess the narrow littoral zone around the deep central basin. We visited 597 points (the
rest were too shallow or too deep to sample) and determined the maximum depth of the plants to
be 22 feet (Figure 1). There was one plant found at 27 feet, but from Figure 1 it appears likely
that this deepest plant was not actually growing at this depth as there are no other plants between
22 and 28 feet. The plants were well distributed from 1 to 22 feet. We determined there were
494 points shallower than 22’ and, of these, 344 sites, or 69.4%, had vegetation (Table 1).
The depth determination indicated broad shallow areas on the west and east basins of the lake,
with the central basin very deep and largely unsampled in this survey (Figure 2). We found a
variety of substrate types, with muck dominating the east and west basins and sand in much of
the central basin and very little rock (Figure 3).
We found the greatest density of plants (greatest rake fullness, Figure 4) just west of the central
deep basin and in the east bay. Plants were found throughout most of the littoral zone, but the
littoral zone is very narrow around the central deep basin. Despite sampling far more sites than
in 2006, the central basin drops off so sharply that we did not have many more sites shallow
enough to have vegetation in this area.
81% of the sites had 1 or 2 species, 17% had 3 or 4 species and 1% had 5 or 6 species (Figure 5).
Clearly, most sites were not diverse, even though there were many species found in the lake. We
found a total of 34 species, including 22 found on the rake, and 12 visuals (seen within 6’ of the
boat, see Tables 2, 3 and 4). Aside from plants found on the rake or within 6’ of the boat, we also
saw many other species further away, captured in our boat survey, but not itemized here.
Fern-leaf pondweed was by far the most common species, occurring at 68% of the vegetated
sites (Figure 6). Fern-leaf pondweed is found through much of WI but especially in the northern
region. It needs a fairly pristine environment as reflected in its coefficient of conservatism of 8.
Other common species include elodea (common water weed) and wild celery (Figure 7), fragrant
or white water lily and dwarf water-milfoil (Figure 8) and large-leaf pondweed and slender naiad
(Figure 9).
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We found no exotic invasive plant species, aside from Eurasian marsh thistle on shore. Together,
the species diversity and the lack of exotics indicate very good water quality and a good aquatic
plant community. We found a variety of plant types, including floating and submersed species.
There was also a variety of plant growth forms, with both short, stiff rosette species, such as
brown-fruited rush and dwarf water-milfoil, typical of sandy, low nutrient and often wave swept
sites and also leafier, taller plants, such as fern-leaf pondweed.
FQI
The Floristic Quality Index (FQI, Nichols 1999,) was 33.1 (Tables 1) and is the higher than
Nichols’ (1999) findings of Lakes in the Northern Lakes and Forests Region of 24.3. FQI can be
high because the average coefficient of conservatism is high and/or the number of species is
high.
Aquatic Macrophyte Community Index (AMCI)
AMCI (Table 5) is a sum of seven parameters, each scaled 1-10 (for a maximum total score of
70), and is another assessment of lake quality from plant data. These seven parameters include
the maximum depth of plant growth, the percent littoral area vegetated, the relative percent
submersed species (as opposed to emergent or floating species), the number of species found, the
relative percent exotic species (0 in this study), Simpson’s Diversity index, and relative percent
sensitive species (defined by Nichols et al. [2000]). The AMCI value for Black Oak Lake is 59,
slightly higher than Nichols et al. (2000) found as an average in northern lakes.
Because AMCI incorporates seven variables, it may characterize the plant community more
broadly and perhaps more adequately than FQI. Each variable is scaled from 1-10 and the closer
to 10, the better the lake condition. Four factors, the maximum depth of plant growth, the
percent littoral area vegetated, the lack of exotic species and the number of sensitive species
rated the maximum score of 10 in Black Oak Lake. The aquatic vegetation grows deeply
enough to earn a10 for this variable, as deeper is considered a “better” plant community factor.
Nichols et al. (2000) argued that too low a percentage of littoral area vegetated indicates
“potentially serious littoral zone habitat limitations”, but that any lake with vegetation in at least
50% of the sites (shallower than maximum plant depth) earns a 10 and, at 69%, Black Oak Lake
is well above this threshold. There were no invasive species in Black Oak Lake and this
garnered 10 points for that variable. The AMCI sensitive species variable (Nichols [2000], Davis
and Brinson [1980]) depends on the number of species found in Black Oak Lake that are listed as
sensitive species and identified as likely to disappear or have decreased biomass by deterioration
of the lake conditions (often turbidity). This value is somewhat analogous to the idea of the
Coefficient of Conservatism (C) used in FQI and the higher the relative frequency of sensitive
species, the better. Black Oak Lake scored a 10 on this variable. Black Oak Lake is also quite
diverse and scored a 9 on number of taxa (different species).
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In Nichol’s scoring scheme, the relative percent submersed species variable does not peak (value
of 10) at 100%, but rather at 75-85%. Nichols et al. (2000) explain that a lake with only
emergent species (few submersed species) usually has poor water clarity while a lake with few
emergents is often devoid of emergent species because the lake is highly developed and
homeowners have removed the emergent species. The healthiest lakes will usually have some
floating or emergent vegetation, leading to a relative percent submersed value of less than 100%.
These authors then give highest points to a lake with a moderate number of submersed species,
but Black Oak Lake was heavily dominated by submersed species, partly because the central
basin littoral zone is steeply banked and is not good habitat for emergent species. Also, the
water level on Black Oak Lake has been low for several years, and possibly this has reduced
emergent vegetation. For these reasons, Black Oak Lake scored 6 on this variable.
The Simpson Diversity Index was calculated as a summary statistic and is used again here as a
component of AMCI. Black Oak Lake’s moderate Simpson diversity index (measuring diversity
and evenness of species distributions) of 0.77 (out of a maximum of 1.0, Table 1) is lower than
Nichols’ (2000) median for Lakes in the Northern Lakes and Forests Region of 0.88 (Table 5).
The Simpson Diversity Index is scaled 1-10 for the AMCI score and Black Oak Lake received a
value of 4 for this variable, contributing to the lower AMCI value. This number is low in Black
Oak Lake primarily because one species, fern-leaf pondweed, is found so frequently and
dominates the flora. Had the same number of species been more evenly distributed, Black Oak
Lake would have had a higher Simpson’s diversity index, and AMCI value. The low score of
the Simpson Diversity Index (4) and the relative frequency of submersed species (6) were largely
responsible for preventing Black Oak Lake from scoring closer to the maximum score of 70.
We found no species of Special Concern, Threatened or Endangered status. However, the
alternate-flowered water-milfoil, the flat-leaf bladderwort and many of the other small rosettetype plants found in Black Oak Lake are especially indicative of high quality aquatic plant
conditions, and is more evidence of the high quality of the Black Oak Lake aquatic plant
community.
Overall, Black Oak Lake has a good aquatic plant community, with good diversity throughout
the lake littoral zone. Several factors, including very good AMCI and FQI scores, the lack of
any invasive species, and the presence of several species found only in pristine conditions
combine to indicate that Black Oak Lake has a very good plant community and water quality.
References
Hauxwell, J., S. Knight, K. Wagner, A. Mikulyuk, M. Nault, M. Porzky and S. Chase. 2010.
Recommended baseline monitoring of aquatic plants in Wisconsin: Sampling design, field and
laboratory procedures, data entry and analysis and applications. Department of Natural
Resources Bureau of Science Services, PUB-SS-1068 2010.
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Nichols, S.A. 1999. Floristic quality assessment of Wisconsin lake plant communities with
example applications. Journal of Lake and Reservoir Management 15(2):133-141.
Nichols, S., S. Weber and B. Shaw. 2000. A proposed aquatic plant community biotic index for
Wisconsin lakes. Environmental Management 26(5): 491-502.
Davis, G. and M. Brinson. 1980. Response of submersed vascular plant communities to
environmental change, US Fish and Wildlife Service Publication, Kearneysville, West Virginia.
FWS/OBS-79/33. 70 p
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Table 1. Black Oak Lake Summary
Acres
584
Number of sampling points
1036
Total number of sites visited
597
Total number of sites with vegetation
344
Total number of sites shallower than
maximum depth of plants
494
Frequency of occurrence at sites
shallower than maximum depth of plants
Simpson Diversity Index
Maximum depth of plants (ft)
Number of sites sampled using rake on
Rope (R)
69.64
0.77
22.0*
120
Number of sites sampled using rake on
Pole (P)
368
Average number of all species per site
(shallower than max depth)
1.08
Average number of all species per site
(veg. sites only)
1.56
Average number of native species per site
(shallower than max depth)
1.08
Average number of native species per site
(veg. sites only)
1.56
Species Richness
22
Species Richness (including visuals)
34
FQI
33.05
AMCI
59
* *One plant found at 27’ but probably not actually growing there. See Figure1.
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Table 2. Species List for Black Oak Lake
Species Name
Water marigold
Waterwort
Needle Spike Rush
Waterweed
Slender waterweed
Pipewort
Brown-fruited rush
Water lobelia
Alternate-flowered water-milfoil
Northern water-milfoil
Dwarf water-milfoil
Naiad
Stonewort
Spatterdock
Fragrant water lily
Large-leaf pondweed
Variable pondweed
Floating-leaf pondweed
Fern-leaf pondweed
Flat-stem pondweed
Flat-leaf bladderwort
Wild celery
Common Name
Bidens beckii
Brasenia schreberi
Chara
Elatine minima
Eleocharis acicularis
Elodea canadensis
Juncus pelocarpus
Lobelia dortmanna
Myriophyllum alterniflorum
Myriophyllum sibiricum
Myriophyllum tenellum
Najas flexilis
Nitella
Nuphar variegata
Nymphaea odorata
Potamogeton amplifolius
Potamogeton gramineus
Potamogeton natans
Potamogeton robbinsii
Potamogeton zosteriformis
Utricularia intermedia
Vallisneria americana
Table 3. Species seen, but not collected on rake (Visuals)
Three-way sedge
Pipewort
Quillwort
Soft rush
Grass-leaved rush
Water smartweed
Pickerelweed
Arrowhead rosette
Soft-stem bulrush
Narrow-leaved bur-reed
Bur-reed
Marsh St. John’s wort
*Identification to be confirmed
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Dulichium arundinaceum
Eriocaulon aquaticum
Isoetes sp.
Juncus effusus
Juncus marginatus*
Polygonum amphibium
Pontederia cordata
Sagittaria sp
Schoenoplectus
tabernaemontani
Sparganium angustifolium
Sparganium sp.
Triadenum fraseri
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Table 4. Most common species in Black Oak Lake
Common Name
Knight 2012
Species Name
Frequency of
Occurrence (%)
Fern-leaf
pondweed
Potamogeton robbinsii
68.02
Dwarf watermilfoil
Myriophyllum tenellum
16.57
Large-leaf
pondweed
Potamogeton amplifolius
15.12
Common
waterweed
Elodea canadensis
11.05
Wild celery
Vallisneria americana
10.47
Slender naiad
Najas flexilis
5.52
Fragrant water lily
Nymphaea odorata
4.65
Northern watermilfoil
Myriophyllum sibiricum
3.78
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Table 5. Aquatic Macrophyte Community Index
Northern Lakes and
Forests Region*
Black Oak Lake
Maximum
Median
AMCI
raw value
AMCI scaled
AMCI Value
value
Max depth of plant
growth (m)
3.5
6.7
10
10
Littoral area
vegetated %
75
69.6
10
10
Submersed Species
Relative %
80
95.1
6
10
Taxa Number
(including visuals)
18
22 (34)
9 (10)
10
Exotic Species
(relative %)
0
0
10
10
Simpson's Diversity
Index
88
77
4
10
Sensitive species
(relative %)
20
65.5
10
10
Total
57
59
70
*Data collected prior
to 2000, Nichols et al.
2000
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Figure 1. Depth distribution of plants
Maximum Depth of Plant Colonization
50
45
40
35
# Sites
30
25
20
15
10
5
0
1
3
5
7
9
11 13 15 17 19 21 23 25 27 29 31 33 35 37 39
Depth Bin (feet)
Figure 2. Depth distribution
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Figure 3. Sediment distribution
Figure 4. Rake Fullness
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Figure 5. Number of Species
Figure 6. Distribution of fern-leaf pondweed and northern water-milfoil
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Figure 7. Distribution of elodea (water weed) and wild celery
Figure 8. Distribution of fragrant water lily and dwarf water-milfoil
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Figure 9. Distribution of large-leaf pondweed and slender naiad
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