Southeast Wisconsin s Pewaukee Lake Aquatic Plant Survey 2011

Transcription

1 Southeast Wisconsin s Pewaukee Lake Aquatic Plant Survey 2011 Wisconsin Lutheran College, Biology Dept. Technical Bulletin, 15, December 2011 Prepared by Svetlana Bornschlegl and Robert C. Anderson, PhD Funded by Lake Pewaukee Sanitary District

2 Introduction Aquatic plant populations of Pewaukee Lake, Waukesha County, have been monitored since 1988 in an effort to aid in lake management. Past years results were based on a transect sampling method (Schmoldt & Anderson 2001; Koch & Anderson 2003; SWERPC 2003; Iwen & Anderson 2005; Zappa & Anderson 2007; Zhang & Anderson 2009; Bolda & Anderson 2011). These results indicated a diverse plant community dominated by Eurasian watermilfoil with recent increases in native aquatic plant species such as Elodea, curlyleaf pondweed, flatstem pondweed, coontail and muskgrass. A dramatic increase in the number of native species was noted in 2010 (Bolda & Anderson 2011). This year a grid based point-intercept method was used for assessing the aquatic plant community. Unlike the transect method, this survey allows for a large scale, whole-lake assessment and takes into account the frequency of occurrence, species richness, abundance and maximum depth of plant colonization (Hauxwell 2010). It is important to monitor the plant diversity of a lake as it directly reflects the condition and resiliency of the aquatic community to environmental changes (Dennison et al.1993). As nutrient pollution increases, the state of a lake is altered as well as its ecosystem structure. This process, known as eutrophication, is linked with plant biomass, fish production, and water clarity. By looking at these characteristics of a lake, the state of eutrophication can be determined (Dodds & Whiles 2002). Native and non-native aquatic plants play a large role in this process. One such aquatic plant, Eurasian watermilfoil, an invasive species, has negatively impacted Pewaukee Lake. Its aggressive nature and dominance over native plant species has created a nuisance for lake users and is a detriment to the overall health of the lake. (Buchan & Padilla 2000; SWERPC 2003; Eco-Resource 2007). Other dominant characteristics of Eurasian milfoil include its year-round ability to maintain a large biomass, its early seasonal growth which inhibits other plants access to nutrients and sunlight, and production of phenolic compounds that restrain algal growth and deter herbivores (Madsen et al. 1991; Gross & Sutfeld 1994; Gross et al. 1996). With existing management practices based on plant harvesting Pewaukee Lake sustains a wide variety of native aquatic vegetation, which positively contributes to the natural ecological cycles of the lake by balancing its aquatic food web interactions (Cheruvelil 2001; Madsen et al. 1991). This study reflects the abundance and diversity of native and invasive aquatic plants of Pewaukee Lake and provides information contributing to its effective management.

3 Methods Aquatic plant sampling was conducted on Pewaukee Lake, Waukesha County, June 27-30, and July 1-2, Evenly distributed sampling points were predetermined by the Wisconsin Department of Natural Resources (WDNR) and transferred to a Trimble GeoXM Global Positioning System field unit (Figure 1). Figure 1: Pewaukee Lake, Waukesha County, Wisconsin sampling points established by WDNR in 2011.

4 Figure 2: Example of rope sampler used during survey. Figure 3: Pole sampler used during survey. Each grid point was sampled using the grid based point-intercept monitoring protocol (Hauxwell 2010). A pole sampler was used at depths of 15ft or less (Figure 3). The rake was lowered through the water column and twisted around twice upon reaching the bottom and then pulled up. A rope sampler was used in depths of 15ft or more (Figure 2). The sampler was dropped directly into the water along side of the boat and dragged on the sediment surface for one foot and then brought to surface. Point depth was determined by rake length and a Garmin Fishfinder 240. Depth, site number, dominant sediment type, pole vs. rope, plant species, and rake fullness were recorded at each site. Coverage of rake density was determined by standards set by the protocol (Figure 4). Density of each individual plant species was determined. Plant samples were identified on site and troublesome specimens were taken to Wisconsin Lutheran College s Aquatic Sciences Laboratory for Figure 4: Rake fullness ratings (Hauxwell 2010). further identification using identification keys (Crow and Hellquist 2000 & Boran et al. 1997). A voucher specimen of each species of plant observed was

5 taken to the lab and mounted. These samples of aquatic plants were pressed on herbarium paper and used to aid in identification and kept as a collection record. Results Twenty macrophyte species were identified during the 2011 grid based point-intercept monitoring conducted on Pewaukee Lake, Wisconsin (Table 1). Eurasian watermilfoil, an exotic species, accounted for the highest frequency of occurrence. Curlyleaf pondweed, another exotic species, was also found in the lake. Coontail was the most abundant native species collected. Other predominant native species include muskgrass, northern watermilfoil, slender naiad, elodea, flatstem pondweed, wild celery, and small pondweed. Filamentous algae was also found at a variety of sites (Table 2). Frequency of occurrence of plants differed somewhat between the two major basins of the lake. Seven more species were found in the East Basin than in the West Basin (Figure 5). Seven species including coontail, curly-leaf pondweed, musk grass, Elodea and flat-stem pondweed occurred more frequently in the West Basin of the lake. The majority of plants were found at the five-foot depth in the East Basin and the ten-foot depth in the West Basin. Maximum depth of plant colonization found was 17ft. in the West Basin and 14ft. in the East Basin (Figure 6). Eurasian watermilfoil was much more dense in the East Basin, and especially concentrated in the northwestern part of the basin (Figure 7). Northern watermilfoil, slender naiad, and the density of flat stem was greater in the East Basin than in the West Basin (Figures 8-13). As expected based on the difference in morphology of the basins, plants were distributed much more evenly across the East Basin than the West Basin.

6 Table 1: List of species found in Pewaukee Lake June 27-30, and July 1-2, Aquatic Plant Species Myriophyllum spicatum Potamogeton crispus Ceratophyllum demersum Chara sp. Elodea canadensis Myriophyllum sibiricum Najas flexilis Nuphar advena Nymphaea odorata Potamogeton amplifolius Potamogeton foliosus Potamogeton gramineus Potamogeton natans Potamogeton praelongus Potamogeton pusillus Potamogeton richardsonii Potamogeton robbinsii Potamogeton zosteriformis Stuckenia pectinata Utricularia vulgaris Vallisneria americana Common Name Eurasian watermilfoil Curly- leaf pondweed Coontail Muskgrass Common waterweed Northern watermilfoil Slender naiad Yellow pond lily White water lily Large- leaf pondweed Leafy pondweed Variable pondweed Floating- leaf pondweed White- stem pondweed Small pondweed Clasping- leaf pondweed Fern pondweed Flat- stem pondweed Sago pondweed Common bladderwort Wild celery Filamentous algae

7 Table 2: Frequency of occurrence, relative frequency, and average rake fullness form grid based point intercept sampling (Hauxwell 2010) of Pewaukee Lake,Waukesha County, Wisconsin June 27-30, and July 1-2, Lake: Pewaukee County: Waukesha WBIC: Frequency of occurrence within vegetated areas (%) Frequency of occurrence at sites shallower than maximum depth of plants (%) Relative Frequency (%) Number of sites where species found Average Rake Fullness (1-3 scale) number of visual sightings Total vegetation 1.69 Eurasian watermilfoil x Curly-leaf pondweed x Coontail x Muskgrasses x Common waterweed x Northern watermilfoil x Slender naiad x Yellow pond lily x White water lily x Large-leaf pondweed x Leafy pondweed x Variable pondweed x Floating-leaf pondweed 1 x White-stem pondweed x Small pondweed x Clasping-leaf pondweed x Fern pondweed x Flat-stem pondweed x Sago pondweed x Common bladderwort x Wild celery x Filamentous algae x present (visual or collected)

8 Wild celery Common bladderwort Sago pondweed Flat- stem Fern pondweed Clasping- leaf pondweed Small pondweed White- stem pondweed Variable pondweed Leafy pondweed Large- leaf pondweed White water lily Yellow pond lily Slender naiad Northern water milfoil Elodea Muskgrass Coontail Curly- leaf pondweed Eurasian water milfoil Frequency of occurrence within vegetated areas (%) West Basin East Basin Figure 5: Frequency of occurrence of aquatic plants within vegetated areas June 27-30, and July 1-2, 2011for West and East Basins of Pewaukee Lake. 100 Number of Sites East Basin West Basin Figure 6: Maximum depth of plant colonization June 27-30, and July 1-2, 2011for East and West Basins of Pewaukee Lake.

9 Figure 7: Eurasian watermilfoil density distribution June 27-30, and July 1-2, 2011 for Pewaukee Lake, Waukesha County.

10 Figure 8: Curlyleaf Pondweed density distribution June 27-30, and July 1-2, 2011 for Pewaukee Lake, Waukesha County.

11 Figure 9: Elodea density distribution June 27-30, and July 1-2, 2011 for Pewaukee Lake, Waukesha County.

12 Figure 10: Flat-stem pondweed density distribution June 27-30, and July 1-2, 2011 for Pewaukee Lake, Waukesha County.

13 Figure 11: Northern watermilfoil density distribution June 27-30, and July 1-2, 2011 for Pewaukee Lake, Waukesha County.

14 Figure12: Slender Naiad density distribution June 27-30, and July 1-2, 2011 for Pewaukee Lake, Waukesha County.

15 Figure13: Coontail density distribution June 27-30, and July 1-2, 2011 for Pewaukee Lake, Waukesha County.

16 The Floristic Quality Index (FQI) was determined based on the diversity of plants found during sampling and does not include the invasive species curly-leaf and Eurasian watermilfoil. This measurement shows the tolerance of the lake ecosystem to changes in the environment. Higher FQI indicates a greater tolerance to disturbances in the environment and lower numbers indicate less tolerance. Each macrophyte species has a predetermined c value, or coefficient of conservation which is used to calculate the FQI (Table 2). The calculated FQI for Pewaukee Lake was (Table 3), which is above the average for Wisconsin lakes of 22.2 (Nichols 1999). Table 3: FQI calculations based on species found in Pewaukee Lake June 27-30, and July 1-2, C values determined by the Wisconsin State Herbarium (Nichols 1999). Species Common Name C species present=1 Ceratophyllum demersum Coontail Chara Muskgrasses Elodea canadensis Common waterweed Myriophyllum sibiricum Northern watermilfoil Najas flexilis Slender naiad Nuphar advena Yellow pond lily Nymphaea odorata White water lily Potamogeton amplifolius Large-leaf pondweed Potamogeton foliosus Leafy pondweed Potamogeton gramineus Variable pondweed Potamogeton praelongus White-stem pondweed Potamogeton pusillus Small pondweed Potamogeton richardsonii Clasping-leaf pondweed Potamogeton robbinsii Fern pondweed Potamogeton zosteriformis Flat-stem pondweed Sparganium americanum American bur-reed Stuckenia pectinata Sago pondweed Utricularia vulgaris Common bladderwort Vallisneria americana Wild celery N 18 mean C 6.05 FQI 25.69

17 Table 4: Summary statistics based on grid based point-intercept monitoring (Hauxwell 2010) conducted on Pewaukee Lake, Wisconsin during June 27-30, and July 1-2, Total number of sites visited includes all sites even where no plants were found. Total number of sites with vegetation had at least one plant species per sample. Maximum depth of plants value does not include filamentous algae as it is not used to calculate the FQI. SUMMARY STATS: Total number of sites visited 569 Total number of sites with vegetation 557 Total number of sites shallower than maximum depth of plants 569 Frequency of occurrence at sites shallower than maximum depth of plants Simpson Diversity Index 0.79 Maximum depth of plants (ft) Number of sites sampled using rake on Rope (R) 87 Number of sites sampled using rake on Pole (P) 484 Average number of all species per site (shallower than max depth) 1.88 Average number of all species per site (veg. sites only) 1.93 Average number of native species per site (shallower than max depth) 1.01 Average number of native species per site (veg. sites only) 1.51 Species Richness 20 Species Richness (including visuals) 21 Water clarity based on secchi disk readings increased in both basins between 2008 and 2010 however in 2011 clarity decreased in the East Basin but continued to increase in the West Basin (Figure 14). Based on monthly secchi disk readings it appears that the greatest differences in clarity between basins occurred during early June as well as mid and late July (Figure 15).

18 0-2 Depth in Feet West Basin East Basin Figure 14: Average water clarity levels for East and West Basins of Pewaukee Lake from 1997 to (Lake Pewaukee Sanitary District 2011) West Basin East Basin Figure 15: Water clarity based on secchi disk measurements for Pewaukee Lake from May 31 to September 5, (Lake Pewaukee Sanitary District 2011)

19 Discussion In past years plant surveys on Pewaukee Lake had been based on 14 transects distributed around the lake. This year the grid based point-intercept monitoring approach was used for this comprehensive aquatic plant survey. This method provides a broader perspective of the plant distribution in the lake. Despite this more extensive sampling fewer plant species were observed using this method than the transect method used in 2010 (Bolda & Anderson 2010). This does demonstrate the importance of annual sampling even if the extent of the sampling is not as comprehensive as the whole lake grid based point-intercept survey. The dynamic nature of aquatic plant populations in lakes is clearly seen in the year to year changes in relative frequency of occurrence of the more abundant species found in Pewaukee Lake (Figure 16). This year s survey shows a large increase in Eurasian watermilfoil from 2010 after a two-year decline. Bushy pondweed and coontail increased slightly in 2011from Muskgrass, eel grass, and northern (common) watermilfoil all decreased from 2010 levels. The annual Rela%ve Frequency 60% 50% 40% 30% 20% Coontail Ceratophyllum demersum Muskgrass Chara sp. Common water- milfoil Myriophyllum sibiricum Eurasian water- milfoil Myriophyllum spicatum (2) Bushy pondweed Najas flexilis Eel grass Vallisneria americana 10% 0% Figure 16: Relative frequencies of Eurasian watermilfoil and other aquatic plant species native to Pewaukee Lake. Data based on surveys from 1988 to (Appendix Table 1)

20 variation of Eurasian watermilfoil is typical of this species in North American lakes (Madsen 2009). The fact that native species have maintained a somewhat similar frequency of occurrence through the past 11 years (Figure 16 & Appendix Table 1) is an indication of the effectiveness of the existing aquatic plant management program. Without effective management Eurasian watermilfoil has the ability to cause a dramatic decline and potentially eliminate native species (Madsen 1991). A comparison of this year s Floristic Quality Index to previous years provides further insight into the condition of Pewaukee Lake. The index was calculated to be 17.8 based on aquatic plant sampling in 1967 and has steadily increased through the years (Eco-Resource Consulting 2007). This year s value of puts it well above the state average indicating an above average stress tolerance for the lake. Water clarity levels have continued to increase in the West Basin but this year decreased in the East Basin in comparison to last year. As previously noted this continued increase in water clarity may be due to increases in the zebra mussel population in the lake (Bolda and Anderson 2010). The decline in clarity in the East Basin may simply reflect greater disturbance from natural or human induced causes since this basin is very shallow and the substrate is soft sediment that suspends in the water column quite readily. Results of this survey and annual monitoring in Pewaukee Lake have provided insight into the continued resiliency of this productive lake ecosystem. Continuation of existing management practices as well as local education programs regarding effective riparian management practices in the watershed are highly recommended.

21 Literature Cited Buchan, Lucy A. J., and Dianna K. Padilla Predicting the likelihood of Eurasian Watermilfoil presence in lakes, a macrophyte monitoring tool. Ecological Applications 10: [doi: Bolda, E., and R.C. Anderson Southeast Wisconsin s Pewaukee Lake Aquatic Plant Survey Wisconsin Lutheran College, Biology Dept. Technical Bulletin 013. Boran, S., R. Korth, and J. Temte Through the looking glass: a guide to aquatic plants. DNR Publication FH Reindl Printing, Inc., Merrill, WI. Crow, G.E, and C.Barre Hellquist Aquatic and wetland Plants of Northwestern North America. A revised and enlarged edition of Norman C. Fassett s A Manual of Aquatic Plants. Vol. 1. Pteridophytes, gymnosperns, and angiosperms. University of Wisconsin Press, Madison, WI. Cheruvelil, K, S., P, A. Soranno, and J.D. Madsen, Epiphytic macroinvertabrates along a gradient of Eurasian wtermilfoil cover. Journal of Aquatic management 39: Dennison, W., R. Orth, K. Moore, J. Stevenson, V. Carter, S.Kollar, P. Bergstrom, and R. Batuik Assessing water quality with submersed vegetation. BioScience 43(2): Dodds, W., and M. Whiles Freshwater Ecology, Concepts and Environmental Applications of Limnology. Academic Press. San Diago Eco-Resource Consulting The Aquatic Plants of Pewaukee Lake Tracking the Past, Looking to the Future. Prepared for: Lake Pewaukee Sanitary District. Hauxwell, J., S. Knight, K. Wagner, A. Mikulyuk, M. Nault, M. Porzky and S. Chase Recommended baseline monitoring of aquatic plants in Wisconsin: sampling design, field and laboratory procedures, data entry and analysis, and applications. Wisconsin Department of Natural Resources Bureau of Science Services, PUB-SS Madison, Wisconsin, USA. Koch, P., and R.C. Anderson Southeast Wisconsin s Pewaukee Lake Aquatic Plant Survey Wisconsin Lutheran College, Biology Dept. Technical Bulletin 003. Lake Pewaukee Sanitary District Unpublished records. Madsen, J.D. and R. M. Wersal Aquatic Plant Community and Eurasian watermilfoil (Myriophyllum spicatum L.) Management Assessment in Lake Pend Oreille, Idaho for Geosystems Research Institute Report 5032 Madsen, J.D., J.W. Sutherland, J.A. Bloomfield, L.W. Eichler, and C.W. Boylen The decline of native vegetation under dense Eurasian watermilfoil canopies. Journal of Aquatic Plant Management 29: Nichols, SA Floristic Quality Assessment of Wisconsin Lake Plant Communities with Example Applications. Journal of Lake and Reservoir Management, 15(2):

22 Schmoldt. A.L., and R.C. Anderson Southeast Wisconsin s Pewaukee Lake Aquatic Plant Survey Wisconsin Lutheran College, Biology Dept. Technical Bulletin 002. University of Wisconsin-Madison, Wisconsin Floristic Quality Assessment (WFQA). Retrieved October 27, 2009 from: Zappa, A., and R.C. Anderson Southeast Wisconsin s Pewaukee Lake Aquatic Plant Survey Wisconsin Lutheran College, Biology Dept. Technical Bulletin 011. Zhang, H., and R.C. Anderson Southeast Wisconsin s Pewaukee Lake Aquatic Plant Survey Wisconsin Lutheran College, Biology Dept. Technical Bulletin 012. Acknowledgements: The following students at Wisconsin Lutheran College are thanked for their contribution to plant collection: Emily Bolda and Maria Krause.

23 Appendix Table 1: Frequency of occurrence and relative frequency of occurrence of Pewaukee Lake Plants * data from DNR Long-term trends (SEWRPC 2003) (Zappa, A. and R. C. Anderson. 2006) (Zang & Anderson 2009) 2010 Bolda & Anderson 2010) Species Name Occur. Freq. Freq. Occur. Freq. Freq. Occur. Freq. Freq. Occur. Freq. Freq. Occur. Freq. Coontail Ceratophyllum demersum % 11.1% % 23.8% % 16.7% % 20.1% % 16.7% Muskgrass Chara sp % 8.8% % 3.8% % 9.6% % 6.6% % 7.9% Waterweed Elodea canadensis 6 6.9% 2.0% 6 6.9% 2.5% 7 8.0% 2.6% % 3.3% % 4.5% Lesser duckweed Lemna minor 0.0% 0.0% 0.0% 0.0% 1 1.1% 0.4% 0.0% 0.0% 0.0% 0.0% Common watermilfoil Myriophyllum sibiricum 0.0% 0.0% 0.0% 0.0% 7 8.0% 2.6% % 13.5% 1 0.6% 0.2% Eurasian watermilfoil Myriophyllum spicatum (2) % 29.0% % 27.5% % 21.5% % 15.0% % 27.9% Bushy pondweed Najas flexilis % 13.5% % 11.7% % 15.2% 8 9.3% 2.9% % 14.7% Spiny najas Najas marina (2) 0.0% 0.0% 0.0% 0.0% 1 1.1% 0.4% 0.0% 0.0% 0.0% 0.0% Southern naiad Najas quadalupensis 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% % 14.6% 0.0% 0.0% White water lily Nymphaea odorata 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0 0.0% 0.0% 0.0% 0.0% Large-leaf pondweed Potamogeton amplifolius (3) 3 3.4% 1.0% 2 2.3% 0.8% 5 5.7% 1.9% 6 7.0% 2.2% 8 4.8% 1.6% Curly-leaf pondweed Potamogeton crispus (2) % 7.1% 6 6.9% 2.5% 5 5.7% 1.9% 0.0% 0.0% 4 2.4% 0.8% Thread-leaf pondweed Potamogeton filiformis 0.0% 0.0% 4 4.6% 1.7% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% Leafy pondweed Potamogeton foliosus(3) 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 3 3.5% 1.1% 0.0% 0.0% Variableleaf pondweed Potamogeton gramineus(3) 0 0.0% 0.0% 0 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0 0.0% 0.0% Illinois pondweed Potamogeton illinoensis(3) 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 1 0.6% 0.2% Floating-leaf pondweed Potamogeton natans 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 1 0.6% 0.2% Sago pondweed Potamogeton pectinatus % 3.0% % 9.2% % 8.9% % 7.3% % 6.9% White-stem pondweed Potamogeton praelongus 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 5 3.0% 1.0% Clasping-leaf pondweed Potamogeton richardsonni 0.0% 0.0% 3 3.4% 1.3% 1 1.1% 0.4% 0.0% 0.0% 1 0.6% 0.2% Flat-stemmed pondweed Potamogeton zosteriformis(3) 2 2.3% 0.7% % 4.2% % 3.3% 8 9.3% 2.9% % 3.1% Pondweeds Potamogeton sp % 10.1% 1 1.1% 0.4% 1 1.1% 0.4% 0.0% 0.0% 0.0% 0.0% Bladderwort Utricularia vulgaris or sp.(3) 2 2.3% 0.7% 0.0% 0.0% 3 3.4% 1.1% 1 1.2% 0.4% 2 1.2% 0.4% Eel grass Vallisneria americana % 4.0% 8 9.2% 3.3% % 5.9% % 6.2% % 8.8% Horned pondweed Zannichellia palustris 0.0% 0.0% 2 2.3% 0.8% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% Water strargrass Zosterella dubia 7 8.0% 2.4% 8 9.2% 3.3% 6 6.9% 2.2% % 3.3% % 4.9% Water moss Fontinalis antipyretica Other % 6.4% 1 1.1% 0.4% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% None 1 1.1% 0.3% 7 8.0% 2.9% % 5.2% 2 2.3% 0.7% 0.0% 0.0% Occurrence Total Total quads Total frequency 340.2% 100.0% 267.8% 100.0% 294.3% 100.0% 316.3% 100.0% 295.8% 100.0% Freq.

24 Table 1: Frequency of occurrence and relative frequency of occurrence of Pewaukee Lake Plants (continued) Occur. Freq. Freq. Occur. Freq. Freq. Occur. Freq. Freq. Occur. Freq. Freq. Occur. Freq. Species Name Coontail Ceratophyllum demersum % 15.5% % 14.1% % 6.9% 4 7.8% 4.5% % 7.6% Muskgrass Chara sp % 6.5% 7 4.3% 3.5% % 10.9% 5 9.8% 5.7% % 6.5% Waterweed Elodea canadensis % 5.4% 3 1.9% 1.5% 1 2.0% 1.0% 0 0.0% 0.0% 1 2.0% 1.1% Lesser duckweed Lemna minor 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 1 2.0% 1.1% Common watermilfoil Myriophyllum sibiricum 0.0% 0.0% 0.0% 0.0% % 10.9% % 11.4% 2 3.9% 2.2% Eurasian watermilfoil Myriophyllum spicatum (2) % 26.2% % 43.2% % 40.6% % 48.9% % 43.5% Bushy pondweed Najas flexilis % 14.3% 7 4.3% 3.5% 5 9.8% 5.0% 0.0% 0.0% 2 3.9% 2.2% Spiny najas Najas marina (2) 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% Southern naiad Najas quadalupensis 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% White water lily Nymphaea odorata 0.0% 0.0% 1 0.6% 0.5% 0.0% 0.0% 0.0% 0.0% 1 2.0% 1.1% Large-leaf pondweed Potamogeton amplifolius (3) 4 8.3% 2.4% 3 1.9% 1.5% 4 7.8% 4.0% % 8.0% % 9.8% Curly-leaf pondweed Potamogeton crispus (2) 3 6.3% 1.8% 3 1.9% 1.5% 3 5.9% 3.0% 1 2.0% 1.1% 1 2.0% 1.1% Thread-leaf pondweed Potamogeton filiformis 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% Leafy pondweed Potamogeton foliosus(3) 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% Variableleaf pondweed Potamogeton gramineus(3) % 3.0% % 5.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% Illinois pondweed Potamogeton illinoensis(3) 0.0% 0.0% 0.0% 0.0% 1 2.0% 1.0% 0.0% 0.0% 4 7.8% 4.3% Floating-leaf pondweed Potamogeton natans 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% Sago pondweed Potamogeton pectinatus % 6.5% % 12.6% % 6.9% 3 5.9% 3.4% 4 7.8% 4.3% White-stem pondweed Potamogeton praelongus 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 1 2.0% 1.1% 1 2.0% 1.1% Clasping-leaf pondweed Potamogeton richardsonni 1 2.1% 0.6% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% Flat-stemmed pondweed Potamogeton zosteriformis(3) % 4.8% 4 2.5% 2.0% 2 3.9% 2.0% % 6.8% 5 9.8% 5.4% Pondweeds Potamogeton sp. 0.0% 0.0% 0.0% 0.0% 1 2.0% 1.0% 0.0% 0.0% 0.0% 0.0% Bladderwort Utricularia vulgaris or sp.(3) 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% Eel grass Vallisneria americana % 9.5% % 6.5% % 6.9% % 9.1% % 7.6% Horned pondweed Zannichellia palustris 0.0% 0.0% 8.1% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% Water stargrass Zosterella dubia % 3.6% 9 5.6% 4.5% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% Other 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 1 2.0% 1.1% None 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% Occurrence Total % Total quads Total frequency 350.0% 100.0% 123.6% 100.0% 396.1% 100.0% 172.5% 100.0% 180.4% 100.0% 2. Exotic species 3. Sensitive species Freq.

25 Table 1: Frequency and relative frequency of occurrence of Pewaukee Lake Plants (continued) Species Name Occur. Freq. Occur. Freq. Freq. Freq. Occur. Freq. Coontail Ceratophyllum demersum % 9.90% 29 63% 12% % 15.20% Muskgrass Chara sp % 5.90% 18 39% 7% % 5.20% Waterweed Elodea canadensis % 5.00% 25 54% 10% % 4.40% Lesser duckweed Lemna minor % 0.00% 0 0% 0% % 0.00% Common water-milfoil Myriophyllum sibiricum % 0.00% 34 74% 14% % 7.10% Eurasian water-milfoil Myriophyllum spicatum (2) % 33.70% 39 85% 16% % 40.50% Bushy pondweed Najas flexilis % 10.90% 3 7% 1% % 4.20% White water lily Nymphaea odorata % 0.00% 0 0% 0% % 0.20% Large-leaf pondweed Potamogeton amplifolius (3) % 7.90% 4 9% 2% % 1.40% Curly-leaf pondweed Potamogeton crispus (2) % 3.00% 21 46% 8% % 5.70% Leafy pondweed Potamogeton foliosus(3) 0.00% 0.00% 0% 0% % 0.70% Variableleaf pondweed Potamogeton gramineus(3) 0.00% 0.00% 0% 0% % 0.20% Illinois pondweed Potamogeton illinoensis(3) % 0.00% 4 9% 2% % 0.00% Sago pondweed Potamogeton pectinatus % 8.90% 3 7% 1% % 1.00% White-stem pondweed Potamogeton praelongus % 0.00% 0 0% 0% % 0.90% Clasping-leaf pondweed Potamogeton richardsonni 0.00% 0.00% 0% 0% % 2.10% Flat-stemmed pondweed Potamogeton zosteriformis(3) % 5.90% 14 30% 6% % 4.10% Pondweeds Potamogeton sp % 0.00% 0% 0% % 0.00% Bladderwort Utricularia vulgaris or sp.(3) 0.00% 0.00% 4 9% 2% % 0.30% Eel grass Vallisneria americana % 8.90% 15 33% 6% % 3.50% Water stargrass Zosterella dubia 0.00% 0.00% 22 48% 9% % 0.00% Robbin's pondweed Potamogeton robbinsii 0 0% 0% % 0.10% Long-leaf pondweed Potamogeton nodosus 1 2% 0% % 0.00% Water-thread pondweed Potamogeton diversifolius 3 7% 1% % 0.00% Small pondweed Potamogeton pusillus 1 2% 0% % 3.00% Hill's pondweed Potamogeton hillii 1 2% 0% % 0.00% Floating leaf pondweed Potamogeton natans 1 2% 0% % 0.00% Spiny naiad Najas marina 2 4% 1% % 0.00% Variable pondweed Potgamogeton gramineus 3 7% 1% % 0.20% Fries' pondweed Potamogeton friesii 1 2% 0% % 0.00% Nitella Nitella flexilis 1 2% 0% % 0.00% Occurrence Total Total quads Total frequency % 541% 100% % 100% Freq.