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Aquatic Plant Community of

Lakes Ann, Lotus, Lucy, Mitchell, Susan, Riley and Staring within the

Riley Purgatory Bluff Creek Watershed:

Final Report 2009 -‐ 2014

Jonathan D. JaKa and

Raymond M. Newman With input from Joshua M. Knopik

University of Minnesota

31 December 2014

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Table of Contents I. Introduction Page 4

II. Methods Page 4

III. Lake Ann

a. Water Quality Page 9 b. Aquatic Vegetation Community Page 10 c. Milfoil Weevil Population Page 10 d. Aquatic bathymetry and Vegetation Maps Page 14 e. Recommendations Page 15

IV. Lake Lotus

a. Water Quality Page 16 b. Aquatic Vegetation Community Page 17 c. Aquatic bathymetry and Vegetation Maps Page 20 d. Recommendations Page 21

V. Lake Lucy

a. Water Quality Page 22 b. Aquatic Vegetation Community Page 23 c. Milfoil Weevil Population Page 23 d. Recommendations Page 28

VI. Mitchell Lake

a. Water Quality Page 29 b. Aquatic Vegetation Community Page 31 c. Aquatic bathymetry and Vegetation Maps Page 37 d. Recommendations Page 38

VII. Lake Riley

a. Water Quality Page 39 b. Aquatic Vegetation Community Page 41 c. Milfoil Weevil Population Page 41 d. Curlyleaf Pondweed Treatments Page 41 e. Aquatic bathymetry and Vegetation Maps Page 49 f. Recommendations Page 50

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VIII. Lake Staring

a. Water Quality Page 52 b. Aquatic Plant Community Page 53 c. Aquatic Bathymetry and Vegetation Maps Page 58 d. Recommendations Page 59

IX. Lake Susan

a. Water Quality Page 60 b. Aquatic Vegetation Community Page 61 c. Milfoil Weevil Population Page 61 d. Curlyleaf Pondweed Treatments Page 62 e. Aquatic Bathymetry and Vegetation Maps Page 71 f. Aquatic Vegetation Transplants Page 72 g. Recommendations Page 80

Literature Cited Page 81

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I. Introduction

Lakes Ann, Lucy, Riley and Susan are small lakes connected by Riley Creek within the cities of Chanhassen and Eden Prairie, Minnesota in the Riley Creek Subwatershed. Lakes Lotus, Mitchell and Staring, also in Eden Prairie, are within Purgatory Creek Subwatershed. These lakes are part of the Riley-‐Purgatory Bluff Creek Watershed District. Aquatic vegetation surveys were performed on these lakes at various years between May and October 2009, 2010, 2011, 2012, 2013 and 2014. These surveys were conducted to evaluate the response of aquatic plant communities of the lakes to management actions. There are several goals of the project, but the main purpose of our research was to quantify the aquatic plant community response to the removal of common carp (Cyprinus carpio) from the lakes. Carp were removed (by the Sorensen lab) from Lake Susan in winter 2009 and its plant community was surveyed in summer 2009, 2010, 2011, 2012, 2013 and 2014. Carp were also removed from Lucy in January 2010 and plants were surveyed in 2010, 2011 and 2012. Carp were removed from Lake Riley in March 2010 and plant surveys were done in 2011, 2012, 2013 and 2014. Carp removal was still ongoing in Staring Lake during the creation of this report, but the lake was sampled in 2011-‐2014. By repeating these surveys after carp removal, we could assess the change in the aquatic plant community.

A secondary goal of the project was to enhance the recovery of native plants and minimize the dominance of aquatic invasive species. The hypothesis is that removal of carp will lead to a decrease in uprooting of aquatic plants and an increase in water clarity. This will in turn increase the light available to aquatic plants, which will benefit both native and exotic species (Hanson and Butler, 1994). However, invasive species such as Eurasian watermilfoil (Myriophyllum spicatum) and curlyleaf pondweed (Potamogeton crispus) are already established in the lakes, and due to their natural aggressive recruitment, there is concern the invasive species will expand at a faster rate than native species. Techniques to reduce the dominance of the invasive species and enhance native plant communities were evaluated. Transplanting native submersed plants took place in Lake Susan in 2009, 2010 and 2011. Early season endothall herbicide treatments were conducted in the spring of 2013 and 2014 in Lakes Riley and Susan to control curlyleaf pondweed. This final report presents data and results from all years of the study: 2009 (Newman 2009), 2010 (Newman and Knopik 2011), 2011 (Knopik and Newman 2012), 2012 (JaKa et al. 2013), 2013 (JaKa et al. 2014) and 2014. It concludes with recommendations for further management of each of the lakes. II. Methods

Plant communities were surveyed for species occurrence and diversity (point intercept surveys), biomass, curlyleaf pondweed turion densities, and herbivore

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abundance in all the lakes to assess response to carp removal and develop approaches to enhance native plant communities. The success of several approaches to transplanting native submersed plants was also assessed in Lake Susan to determine if transplanting might be used to hasten establishment of diverse native plant communities. Early season, lake-‐wide, endothall herbicide treatments were employed to control curlyleaf pondweed in Lakes Riley and Susan. The goal of the herbicide treatments was not only to control curlyleaf pondweed, but also to determine whether the removal of curlyleaf will enhance the native plant community. Aquatic bathymetry and vegetation sonar data were collected using ciBioBase software (by Contour Innovations) to create bathymetry and lake vegetation maps. Point Intercept Survey:

A point intercept survey approach modeled from the methods described by Madsen (1999) was used to define sampling points to assess the plant community in each lake. Using Arcmap GIS, survey points were generated following a systematic square grid. Grid spacing ranged from 35m to 65m to ensure at least 120 points within the littoral zone (≤4.6m depth) of each lake. The sampling points were loaded into a Garmin GPS 76 and a boat was navigated to each sampling point. A weighted double headed rake (0.3m wide) attached to a rope was then tossed into the lake, allowed to sink and retrieved along the lake bottom for approximately three meters, thus sampling approximately one square meter. The vegetation collected was identified and a semi-‐quantitative density rating (0 to 5) was visually estimated. Frequency of occurrence was determined for each species within the littoral zone and for native and invasive plants. Mean species richness was determined from the total number of taxa present at each site and total number of species found in each lake was also determined. Samples were taken in depths up to 6m to determine the maximum depth of rooted vegetation. Arcmap GIS was used to generate maps to assist in visualizing taxa locations, depth of growth, and richness at sites. Biomass Sampling:

Plant biomass (g dry/m2) was sampled using methods described by Johnson and Newman (2011). A subset of at least forty sampling sites were randomly selected from the point intercept survey points on each lake. At each site, all the plants in a 0.09m2 area were collected with a long handled garden rake that was lowered to the lake bottom, rotated three times to ensure uprooting of all plants, and pulled to the surface (Johnson and Newman 2011). The samples were placed in plastic bags and taken to a lab where the plants were sorted by species and roots removed. The shoots were spun in a salad spinner to remove excess water and the samples were dried at 105˚C for >48 hr

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and weighed. Mean dry biomass was calculated for each species based on all samples taken within the littoral zone. Turions were removed from the dried curlyleaf biomass samples, counted and weighed to get an estimate of turion production. Curlyleaf Pondweed Turion Sampling:

The invasive curlyleaf pondweed is found in many lakes in Minnesota including Lakes Ann, Lotus, Lucy, Mitchell, Riley, Staring and Susan. One of the most common ways curlyleaf pondweed reproduces is by forming over-‐wintering vegetative propagules called turions (Madsen and Crowell 2002). To better understand the curlyleaf pondweed population dynamics in the lakes, we assessed the turion bank in the sediment of Lakes Mitchell, Riley, Staring and Susan. Forty sampling sites in the littoral zone (≤ 4.6m depth) were randomly selected from the littoral zone point intercept sites. The coordinates were entered into a GPS, and a boat was navigated to each point. At each point a petite ponar (225 cm2 area, sample depth ~10 cm) was used to take a sediment sample. Sampling depth and substrate type was noted. The sediment sample was then passed through a 1mm mesh sieve to remove fine sediment. The remaining sample was returned to the lab and turions were enumerated. The turions that had sprouted in the field (plants or sprouts collected with turions attached) were discarded. The remaining turions were stored in transparent freezer bags and placed in a dark refrigerator at 5oC. Every 7 days the samples were examined for sprouting, and sprouted turions were counted and removed. After four weeks, the rate of sprouting of cold turions had declined. At this point the samples were placed at room temperature (21oC) under natural spectrum lighting for 12 hours per day. Samples continued to be examined every 7 days for another 4 weeks and sprouted turions were removed and recorded. Turion viability (proportion) was calculated by taking the ratio of the number of sprouted turions per site (including the turions that were sprouted when collected) to the total number of turions collected per site. The total number of turions collected at each site was expressed as number of turions per square meter. Milfoil Herbivore Abundance:

Surveys were conducted to evaluate the abundance of milfoil herbivores. The milfoil weevil, Euhrychiopsis lecontei, is a native weevil found in many lakes in North America. Much of the weevil’s life cycle is dependent on the milfoil plant. Evidence suggests the milfoil weevil can be effective in controlling Eurasian watermilfoil (Newman 2004). Surveys were conducted on Lakes Ann, Lucy, Riley and Susan in 2011 and 2012, and continued in Lakes Riley and Susan in 2013 and 2014, to determine if milfoil weevils were present or abundant. Weevil surveys were attempted on Lake Staring, but proved futile due to lack of plants. On Lake Susan, repeated surveys were conducted every four

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weeks to quantify and monitor the population throughout the summer in 2010, 2011, 2012, 2013 and 2014. Lake Riley was sampled every four weeks in the summer of 2012, 2013 and 2014. Milfoil herbivore surveys were conducted once in the summer of 2012 on Lakes Ann and Lucy. To sample milfoil herbivores, transects perpendicular to the shoreline were predetermined and geographically spread around the lake. Three sampling points were established on each transect, one at shallow depth (1.5m). At each sampling point the top 0.5m of eight stems of EWM were collected and placed in a sealable bag with water. In a lab, each sample was examined with a 3x magnifying lens, plant stems and meristems were counted, and all herbivores (lepidopterans and weevils) and weevil life stages (eggs, pupae, larvae, and adults) were counted and preserved in 80% ethanol. Water Quality:

Several indicators of water quality were measured periodically on all lakes. Water temperature, dissolved oxygen and photosynthetically active radiation (PAR) readings were recorded in 0.5m depth intervals using a YSI 50B electronic oxygen and temperature meter and a LiCor LI-‐185 quantum sensor. Secchi depths were recorded to the nearest 0.1m. Lake-‐wide Early Season Endothall Herbicide Treatments Early season endothall herbicide treatments were conducted in the spring of 2013 and 2014 in Lakes Riley and Susan. It has been shown that endothall can efficiently control curlyleaf pondweed at temperatures between 10-‐15 ˚C, when native plants shouldn’t be actively growing yet (Skogerboe and Getsinger 2002, Poovey et al. 2012). Using this method of timing, we can effectively target curlyleaf pondweed with little collateral damage to the native plant community (Johnson et al. 2012, Jones et al. 2012). During the early parts of spring when ice came off the study lakes we would begin closely monitoring water temperatures. Once water temperatures approached the treatment temperature threshold we then delineated the densest areas of curlyleaf and provided these areas to the contracted herbicide applicator. We conducted a pretreatment (point intercept and biomass) survey on all treatment lakes, and on an untreated reference Mitchell Lake, just prior to treatments. Post-‐treatment surveys were conducted in all lakes in June to correspond with typical peak curlyleaf abundance and biomass. A third survey was conducted in August in all lakes corresponding with the timing of peak biomass of native plants. Fall turion surveys were completed in October to monitor the turion densities in the sediments, which is essentially the same as monitoring the seed bank for curlyleaf pondweed. Reducing turions in the sediments is

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an important management strategy to the reduction of curlyleaf pondweed (Madsen and Crowell 2002, Johnson et al. 2012). Aquatic Bathymetry and Vegetation Mapping We collected sonar data using a Lowrance HDS 5 Gen 2 Fishfinder during all point intercept surveys in 2013 and 2014. The HDS 5 would record data while we navigated the boat to survey points onto a SD card. From the lab, we would upload the sonar data to the ciBioBase servers. After ciBioBase processed the sonar data we would then have access to bathymetry and vegetation maps as well as a report generated for each lake containing plant and water data such as average biovolume and percent area covered.

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III. Results Lake Ann Lake Ann (DOW ID 10-‐001200) is just south of Lake Lucy and is connected to Lake Lucy by a short channel. Lake Ann has a surface area of 45 hectares (110 acres), with a littoral zone area of about 18 hectares (45 acres), and maximum depth of about 14m (45ft) (MN DNR LakeFinder 2014). Water Quality: Depth profiles for dissolved oxygen (DO) and temperature (Temp) were taken periodically in Lake Ann from 2010 through 2014. Lake Ann has relatively good summer water clarity compared to other lakes in the watershed (Figure 1). Water clarity has not seemed to hinder aquatic plant growth in Lake Ann during years that we surveyed. Dissolved oxygen values did not typically reach hypoxic levels until depths ≥ 4.5m (Figure 1). Figure 1. Secchi depths for Lake Ann 2010 – 2014 (Bajer and Sorensen unpublished data, personal communication) and dissolved oxygen (mg/L) and temperature (°C) profiles taken on 13 July 2010, 21 July 2011, 17 July 2012, 25 July 2013 and 20 August 2014.

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Aquatic Vegetation Survey: Point intercept surveys were conducted in Lake Ann in July and August 2010, July and August 2011, July 2012, July 2013 and August 2014. Lake Ann has the most diverse aquatic plant community of any of the lakes we surveyed for the Riley Purgatory Bluff Creek Watershed District with 27 different species observed in the lake during survey years (Table 1). During all survey years there was good species richness. The highest species richness observed was in 2011 when several sites contained 12 different species per site (Figure 2). Coontail (Ceratophyllum demersum) was always the most frequently occurring plant species in Lake Ann (Figure 3). The second most commonly occurring species observed in Lake was typically the invasive Eurasian watermilfoil. However, in 2014, white water lily was the second most commonly occurring species. Eurasian watermilfoil (Myriophyllum spicatum) has been in steady decline in Lake Ann in both frequency and biomass with the exception of the biomass in 2012 (Figure 3 and 4). We have postulated that the high 2012 biomass may have been the result of an oversampling error in the field, which is supported by an otherwise steady decline of Eurasian watermilfoil frequency and biomass from 2010-‐2014. The invasive curlyleaf pondweed (Potamogeton crispus) was also present in Lake Ann, but at very low frequency and density during all survey years. Both invasive plants species appear to occur below damaging levels at this time. Plants are abundant out to 3m depth (Figure 5) and generally most dense along the north and west shorelines. Overall the native plant community was relatively stable from 2010 to 2014 with small increases and decreases over the five-‐year period (Figures 3 and 4). Total lake-‐wide average native aquatic plant biomass is much greater than total invasive plant biomass, especially in the last two years as invasives have continued to decrease in Lake Ann (Table 2). Milfoil Herbivore Population: Eurasian watermilfoil and the native northern watermilfoil (Myriophyllum sibiricum) were collected in Lake Ann to quantify the milfoil weevil population in the summer of 2010, 2011, and 2012. The highest density of weevils (in all life stages) was observed in 2011, when the average lake-‐wide density was 0.13 weevils per stem (Table 3). The weevil population was relatively low in Lake Ann and may not be sufficient to consistently control Eurasian watermilfoil. However, in conjunction with a healthy and stable native plant community, Eurasian watermilfoil seems to be in decline or maintained at a density below damaging levels.

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Table 1. Aquatic plants found in surveys conducted in Lake Ann 2010 to 2014. Common Name Scientific Name Abbreviation Emergent species Hardstem bulrush Schoenoplectus acutus Sacu Softstem bulrush Schoenoplectus tabernaemontani Sval Cattail Typha spp. Typh Submerged species Coontail Ceratophyllum demersum Cdem Muskgrass Chara spp. Char Canada waterweed Elodea canadensis Ecan Eurasian watermilfoil Myriophyllum spicatum Mspi Northern watermilfoil Myriophyllum sibiricum Msib Bushy pondweed Najas flexilis Nfle Large leaf pondweed Potamogeton amplifolius Pamp Curlyleaf pondweed Potamogeton crispus Pcri Illinois pondweed Potamogeton illinoensis Pill Narrow leaf pondweed Potamogeton pusillus Ppus Flat-stem pondweed Potamogeton zosteriformis Pzos White water buttercup Ranunculus longirostris Rlon Arrowhead, grassy Sagittaria graminea Sgra Sago pondweed Stuckenia pectinata Spec Lesser bladderwort Utricularia minor Umin Greater bladderwort Utricularia vulgaris Uvul Wild celery Vallisneria americana Vame Water stargrass Zosterella dubia Zdub Floating-leaf species Star duckweed Lemna trisulca Ltri White water lily Nymphaea odorata Nodo Yellow water lily Nuphar variegata Nvar Floating-leaf pondweed Potamogeton natans Pnat Long-leaf pondweed Potamogeton nodosus Pnod Variable pondweed Potamogeton gramineus Pgra

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j Figure 2. The number of aquatic plant species present at each site surveyed in Lake Ann, July 2011.

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Figure 3. Frequency of occurrence for some of the most commonly occurring species in Lake Ann found in surveys during the summer of 2010 through 2014. See Table 1 for abbreviations.

Figure 4. Dry aquatic plant biomass (g dry/m2) of the most frequently occurring species in Lake Ann during the summer of 2010 through 2014. See Table 1 for abbreviations.

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Figure 5. Aquatic bathymetry and vegetation map of Lake Ann. Data collected during point intercept aquatic vegetation survey on 25 July 2013. Contour lines are 5ft intervals. Color legend represents percent biovolume (the percentage of the water column taken up by vegetation when vegetation exists) with blue representing no vegetation present and red representing 100% of the water column being taken up by vegetation. Table 2. Mean dry biomass (g dry/m2) of total native species and total exotic species (curlyleaf pondweed and Eurasian watermilfoil) in Lake Ann. Date Native (g dry/m2) Exotic (g dry/m2) July 2010 501.2 255.8 August 2010 635.5 397.5 July 2011 412.4 148.0 August 2011 623.1 165.0 July 2012 887.6 691.8 July 2013 371.2 23.0 August 2014 659.5 26.8

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Table 3. Results of milfoil herbivore population surveys in Lake Ann summer 2010 through 2012. Both Eurasian watermilfoil and northern watermilfoil were collected. Values given are total weevils in all life stages per stem. See Table 1 for abbreviations. Mspi Weevils/Stem Msib Weevils/Stem August 2010 0.12 August 2010 0.09 July 2011 0.13 July 2011 0.07 July 2012 0.08 July 2012 0.03 Recommendations for Lake Ann: Lake Ann’s aquatic plant community is the most healthy and diverse of all lakes that we have surveyed in the watershed. Lake Ann has a high diversity of native aquatic plants with over 25 species regularly present. Eurasian watermilfoil and curlyleaf pondweed do not currently seem to be a nuisance or a threat to the native plant community and the aim should be to maintain the present plant community and distribution. This diverse plant community likely persists due to the very good summer long water clarity and lack of disruptive management. Annual or biennial monitoring would be a good management strategy in Lake Ann. If water clarity were to decrease in the lake for several growing seasons, conditions may then begin to favor the invasive Eurasian watermilfoil and curlyleaf pondweed or both and a strategy to selectively control these plants would be needed. Enhancement of the native milfoil weevil population by restructuring the over abundant sunfish (Lepomis sp.) population would be worth considering if Eurasian watermilfoil begins to increase despite good water clarity.

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IV. Lotus Lake Lotus Lake (DOW ID 10-‐000600) lies within the city limits of Chanhassen, Minnesota in the Purgatory Creek Watershed. It covers about 99 hectares (245 acres), with approximately 74 hectares (182 acres) being littoral zone and a maximum depth of 8.8m (29ft) (MN DNR LakeFinder 2014). Water Quality: Lotus Lake water clarity was typically good from spring to early or mid summer (Figure 6). Clarity dropped to around 1m by the end of most summers. Dissolved oxygen levels were high above 3-‐5m (Figure 6). An equipment failure stopped us from taking dissolved oxygen and temperature readings below 3m in 2014. Figure 6. Secchi depths for Lotus Lake 2011 – 2014 (Bajer and Sorensen unpublished data, personal communication) and dissolved oxygen (mg/L) and temperature (°C) profiles taken on 7 August 2013 and 17 July 2014.

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Aquatic Vegetation Survey: Point intercept surveys were performed on Lotus Lake in the summer of 2013 and 2014. Lotus Lake has a relatively diverse plant community with 18 different aquatic species observed in our two years of surveying (Table 4). Site-‐specific species richness was moderate compared to other lakes in the watershed with as many as 6 species being found at one sampling site during surveys in 2013 and 2014 (Figure 7). Although Lotus Lake has a relatively diverse aquatic plant community, most plants were observed in low frequencies (Figure 8) and low densities (Figure 9) throughout the lake. In both years that we surveyed, coontail was the dominant species in both frequency of occurrence and dry plant biomass. White and yellow water lilies were also among the more common species in Lotus Lake. Eurasian watermilfoil and curlyleaf pondweed were both present in Lotus Lake, but neither was observed in surveys at levels of concern for management. Plants at Lotus Lake are most dense in the northeast bay and along the eastern shoreline in water < 2m deep (Figure 10), covering around 35% of the littoral (Table 5). Both coverage and percent biovolume were low and similar in both 2013 and 2014. Table 4. Aquatic plants found in surveys conducted in Lotus Lake 2013 and 2014. Common Name Scientific Name Abbreviation Emergent species Needle spikerush Eleocharis acicularis Eaci Softstem bulrush Schoenoplectus tabernaemontani Sval Cattail Typha spp. Typh Submerged species Coontail Ceratophyllum demersum Cdem Muskgrass Chara spp. Char Eurasian watermilfoil Myriophyllum spicatum Mspi Bushy pondweed Najas flexilis Nfle Curlyleaf pondweed Potamogeton crispus Pcri Illinois pondweed Potamogeton illinoensis Pill Whitestem pondweed Potamogeton praelongus Ppra Clasping-leaf pondweed Potamogeton richardsonii Pric Narrow leaf pondweed Potamogeton pusillus Ppus Sago pondweed Stuckenia pectinata Spec Water stargrass Zosterella dubia Zdub Floating-leaf species Common duckweed Lemna minor Lmin American lotus Nelumbo lutea Nlut Yellow water lily Nuphar variegata Nvar White water lily Nymphaea odorata Nodo

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Figure 7. The number of aquatic plant species present at each site surveyed in Lotus Lake, July 2014.

Lotus Lake Species Richness 65m spacing July 2014

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Figure 8. Frequency of occurrence for some of the most commonly occurring species in Lotus Lake found in surveys during the summer of 2013 and 2014. See Table 4 for abbreviations. Figure 9. Dry aquatic plant biomass (g dry/m2) for species in Lotus Lake during the summer of 2013 and 2014. See Table 4 for abbreviations.

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Figure 10. Aquatic bathymetry and vegetation maps of Lotus Lake. Data were collected during point intercept aquatic vegetation surveys on 7 August 2013 and 17 July 2014. Contour lines are 5ft intervals. Color legend represents percent biovolume (refers to the percentage of the water column taken up by vegetation when vegetation exists) with blue representing no vegetation present and red representing 100% of the water column being taken up by vegetation. Table 5. Lake-‐wide percent area cover (PAC) and average biovolume (BV) for data collected in August 2013 and July 2014 in Lotus Lake. Values coincide with maps in Figure 10. PAC refers to the overall surface area that vegetation is growing in the surveyed area. Average BV refers to the percentage of the water column taken up by plants when plants exist; areas that have no plants are not factored into this calculation. Date PAC Average BV August 2013 36.0% 40.1% July 2014 34.5% 45.8%

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Recommendations for Lotus Lake: Lotus Lake has a relatively diverse native plant community with a moderate species richness at each site. With the exception of coontail, most plant species exist at low frequency of occurrence and density in Lotus Lake. Invasive Eurasian watermilfoil and curlyleaf pondweed are both present in Lotus Lake but are not currently at levels of concern. Lotus Lake should be monitored occasionally for changes in the native plant community as well as declines in water clarity in the spring and early summer. Persistent declines in water clarity could lead to an increase in more tolerant invasive species and a decline in the already low frequencies of native aquatic plants. Likewise, improved water clarity could result in increased growth of the invasives, which would also affect the native plants. No additional management is recommended at this time however.

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V. Lake Lucy Lake Lucy (DOW ID 10-‐000700) is the headwaters of the Riley Creek Watershed. Lake Lucy has a surface area of about 36 hectares (87 acres), with about 35 hectares (86 acres) of littoral zone, and a maximum depth of 6.8m (22ft) (MN DNR LakeFinder 2014). The outlet of Lake Lucy goes directly into Lake Ann. In an attempt to improve water quality, common carp were removed from Lake Lucy in January 2010 (Bajer and Sorensen, personal communication). Plant assessments began in summer 2010 to quantify the response of the aquatic plant community to the carp removal and ended in 2012.

Water Quality: Water clarity was generally good in the spring and early summer in Lake Lucy (Figure 11). Secchi depths did not typically fall below 1m until August. Dissolved oxygen profiles taken during the summer show an anoxic hypolimnion typically around 2.5 to 3m (Figure 11). Figure 11. Secchi depths for Lake Lucy 2010 – 2012 (Bajer and Sorensen unpublished data, personal communication) and dissolved oxygen (mg/L) and temperature (°C) profiles taken on 9 August 2010, 17 August 2011 and 27 August 2012.

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Aquatic Vegetation Survey: Point intercept surveys were conducted in Lake Lucy in June and August of 2010, 2011, and 2012. Overall there was a moderately diverse plant community in Lake Lucy with 18 different aquatic plant species found during our surveys (Table 6). The maximum species richness per site was 9 species per site during the June 2011 survey (Figure 12). The highest plant coverage was noted in June 2010 when 86% of sites sampled shallower than 4.6m contained plants. Coontail was the most frequently occurring species in all surveys conducted (Figure 13). Star duckweed (Lemna trisulca), white water lily (Nymphaea odorata), greater bladderwort (Utricularia vulgaris) and curlyleaf pondweed were also observed at relatively high frequencies. The plant community appears relatively stable with little to no changes in the frequency of occurrence throughout the years of survey. Coontail, chara (Chara sp.) and white water lily had the highest biomass in Lake Lucy during our surveys (Figure 14). Biomass values appeared to be relatively stable throughout survey years with several species increasing in biomass during the survey years. Chara, Canada waterweed (Elodea canadensis), white water lily and yellow water lily all increased in successive August biomass surveys (Figure 14 bottom). Eurasian watermilfoil was observed during our surveys, but it was observed at less than 1% of sites surveyed and does not seem to be problematic at this time. Curlyleaf pondweed was present in over 40% of sites surveyed at 4.6m or shallower in June 2011 and then declined to less than 20% of sites surveyed in June 2012 (Figure 13 top). However, curlyleaf pondweed had very little biomass present during all survey years (Figure 14). We also conducted fall turion surveys in Lake Lucy in 2010 and 2011. Lake-‐wide average turion density in the sediments in the littoral zone (4.6m and shallower) was 362 turions/m2 in 2010 and 306 turions/m2 in 2011. Milfoil Herbivore Population: Surveys were performed in 2010, 2011 and 2012 to quantify abundance of milfoil weevils in Lake Lucy. We collected Eurasian watermilfoil in 2010 and 2011, but northern watermilfoil was collected in 2012 due to a lack of Eurasian watermilfoil. We only observed milfoil weevils during one survey (2011) and the lake-‐wide weevil population in all life stages was 0.32 weevils per stem (Table 7). No weevils were present during the other two survey years. However, there was an average of 0.14 Paraponyx larvae per stem, another milfoil herbivore, during the 2010 weevils survey (Table 7).

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Table 6. Aquatic plants found in surveys conducted in Lake Lucy 2010 through 2012. Common Name Scientific Name Abbreviation Emergent Cattail Typha spp. Typh Submerged species Coontail Ceratophyllum demersum Cdem Chara Chara spp. Char Canada waterweed Elodea canadensis Ecan Eurasian watermilfoil Myriophyllum spicatum Mspi Northern watermilfoil Myriophyllum sibiricum Msib Curlyleaf pondweed Potamogeton crispus Pcri Narrow leaf pondweed Potamogeton pusillus Ppus Flat-stem pondweed Potamogeton zosteriformis Pzos Sago pondweed Stuckenia pectinata Spec Greater bladderwort Utricularia vulgaris Uvul Water stargrass Zosterella dubia Zdub Floating-leaf Species Star duckweed Lemna trisulca Ltri Lesser duckweed Lemna minor Lmin White water lily Nymphaea odorata Nodo Yellow water ily Nuphar variegata Nvar Greater duckweed Spirodela polyrrhiza Spol Watermeal Wolffia columbiana Wcol

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Figure 12. The number of aquatic plant species present at each site surveyed in Lake Lucy, June 2011.

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Figure 13. Frequency of occurrence for some of the most commonly occurring species in Lake Lucy found in surveys June 2010, 2011 and 2012 and August 2010, 2011 and 2012. See Table 6 for abbreviations.

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Figure 14. Dry aquatic plant biomass (g dry/m2) Lake Lucy from surveys June 2010, 2011 and 2012 and in August 2010, 2011 and 2012. See Table 6 for abbreviations.

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Table 7. Results of milfoil herbivore population surveys in Lake Lucy 2010 through 2012. Surveys in 2010 and 2011 were from Eurasian watermilfoil collections, and collections in 2012 were from northern watermilfoil. Values are lake-‐wide means for weevil and Paraponyx populations expressed as total weevils (in all life stages) or Paraponyx per stem. Mspi Weevils/Stem Paraponynx/Stem August 2010 0.00 0.14 July 2011 0.32 0.00 September 2012 0.00 0.00 Recommendations for Lake Lucy: A relatively healthy and diverse plant community exists in Lake Lucy and any management strategies should be constructed to maintain the native plant community. Eurasian watermilfoil is present in Lake Lucy but at very low levels that are not a problem at this time. Curlyleaf pondweed should be closely monitored in Lake Lucy. Lakeshore homeowners may be controlling curlyleaf with local herbicide applications. However, turion densities in the sediments are high enough to cause concern. If curlyleaf pondweed increases dramatically in the future, Lake Lucy could possibly benefit form a lake-‐wide early season endothall herbicide treatment. Occasional monitoring is recommended to ensure that curlyleaf pondweed is kept in check with current management strategies.

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VI. Mitchell Lake Mitchell Lake (DOW ID 27-‐007000) is within the city limits of Eden Prairie, Minnesota and is classified as a “Natural Environment Lake” by the Minnesota Department of Natural Resources. Mitchell Lake has a surface area of about 46 hectares (114 acres), with a littoral zone area of about 44 hectares (109 acres), and a maximum depth of about 5.8m (19ft) (MN DNR LakeFinder 2014). Surveys conducted on Mitchell Lake were not part of the initial project proposal. The lake is being used as a reference for a Master’s research project conducted by Jonathan JaKa a University of Minnesota graduate student. Surveys on Mitchell Lake are being compared to surveys conducted on Lakes Riley and Susan to ascertain the efficacy of early season curlyleaf control and native pant community response in Lakes Riley and Susan. Both Lakes Riley and Susan had early season endothall herbicide treatments in 2013 and 2014 in an effort to suppress curlyleaf pondweed growth and enhance native plant communities. Mitchell Lake was chosen as a reference lake because there were no curlyleaf pondweed treatments planned for 2013 or 2014 and curlyleaf had been present at high frequencies and densities. Water Quality: Secchi depths declined to about 1m by the end of July in both years we surveyed, 2013 and 2014 (Figure 15). Mid-‐summer dissolved oxygen and temperature profiles showed some dissolved oxygen to the lake bottom in 2013 but an anoxic hypolimnion at depths of 2.5m and below in 2014 (Figure 15).

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Figure 15. Secchi depths for Mitchell Lake and dissolved oxygen (mg/L) and temperature (°C) profiles taken on 22 August 2013 and 8 August 2014.

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Aquatic Vegetation Survey: Aquatic Vegetation surveys were conducted in early and late June and once in August of 2013, and in May, June and August of 2014. Overall there was a fairly diverse aquatic plant community in Mitchell Lake with 20 different species observed in our two survey years (Table 8). Species richness per sampling site was also high in Mitchell Lake, with the highest richness observed in August 2013 when one site contained 10 species per site and several sites contained between 7 and 9 species (Figure 16). Overall the most dominant species in frequency (Figure 17) and biomass (Figure 18) was coontail. However, curlyleaf pondweed occurred quite frequently in the spring and early summer as well and was the most frequently occurring species in early June 2013 (Figure 17). Other commonly occurring species include: star duckweed, white water lily, narrow leaf pondweed (Potamogeton pusillus), flat-‐stem pondweed (Potamogeton zosteriformis) and northern watermilfoil, all of which were typically observed in more than 10% of sites surveyed in the littoral zone. Coontail made up the vast majority of the biomass sampled in Mitchell Lake (Figure 18). Curlyleaf pondweed typically had the second highest biomass in the spring and early summer when it is reaching its peak biomass. Other native plants with higher plant biomass in the summer were northern watermilfoil, star duckweed, narrow leaf pondweed and white water lily. Coontail made up the majority of a significant (p ≤ 0.05) decline in mean total native plant biomass from August 2013 to August 2014 (Figure 19), but many other species declined as well (Figure 18). It is difficult to comment on the stability of the plant community with only two years of survey data. Eurasian watermilfoil and curlyleaf pondweed were both present in Mitchell Lake. Curlyleaf pondweed can reach nuisance levels in the spring and early summer. In late June, after curlyleaf had been controlled in Lakes Riley and Susan, curlyleaf remained at about 50% occurrence in both 2013 and 2014 (Figure 17). Eurasian watermilfoil did not appear to be present at high frequencies. However, the taxon we are calling northern watermilfoil (based on leaflet count) may be a hybrid of Eurasian watermilfoil and northern watermilfoil.

Plants at Mitchell Lake are dense in much of the lake often to depths of 3m and greater (Figure 20). Percent coverage ranged from about 70% to almost 95% of the surveyed area depending on the time year (Table 9). There were some declines in both coverage and average biovolume from 2013 to 2014. Curlyleaf pondweed turion survey: Sediment surveys for curlyleaf pondweed turions were conducted in Mitchell Lake on 17 October 2013 and 14 October 2014. In 2013 Mitchell Lake had a lake-‐wide mean density of 191 turions/m2 with 77% of turions viable. In 2014, the lake-‐wide mean

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density was 173 turions/m2, with about 45% of turions being viable. Although this is a relatively low density of turions in the sediment, it is higher than peak densities at both Lakes Riley and Susan, which had lake-‐wide mean densities of 128 turions/m2 and 87 turions/m2 respectively in fall 2012 before spring herbicide treatments. Mitchell Lake had dense stands of curlyleaf pondweed that will likely continue to add to the turion bank in the sediment. Table 8. Aquatic plants found in surveys conducted in Mitchell Lake 2013 and 2014. Common Name Scientific Name Abbreviation Emergent Species Cattail Typha spp. Typh Submerged Species Coontail Ceratophyllum demersum Cdem Muskgrass Chara spp. Char Canada waterweed Elodea canadensis Ecan Northern watermilfoil Myriophyllum sibiricum Msib Eurasian watermilfoil Myriophyllum spicatum Mspi Bushy pondweed Najas flexillis Nfle Curlyleaf pondweed Potamogeton crispus Pcri Illinois pondweed Potamogeton illinoensis Pill Narrow leaf pondweed Potamogeton pusillus Ppus Flat-stem pondweed Potamogeton zosteriformis Pzos White water buttercup Ranunculus aquatili Rlon Sago pondweed Stuckenia pectinata Spec Greater bladderwort Utricularia vulgaris Uvul Water stargrass Zosterella dubia Zduz Floating-leaf species Lesser duckweed Lemna minor Lmin Star duckweed Lemna trisulca Ltri American lotus Nelumbo lutea Nlut White water lily Nymphaea odorata Nodo Yellow water lily Nuphar variegata Nvar Great duckweed Spriodela polyrrhiza Spol

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Figure 16. The number of aquatic plant species present at each site surveyed in Mitchell Lake, 20 August 2013.

Mitchell Lake Species Richness 50m spacing August 2013

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Figure 17. Frequency of occurrence for some of the most commonly occurring species in Mitchell Lake found in surveys May, June and August 2013 and 2014. See Table 8 for abbreviations.

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Figure 18. Dry plant biomass (g dry/m2) for some of the most commonly occurring species in Mitchell Lake found in surveys May, June and August 2013 and 2014. See Table 8 for abbreviations.

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Mitchell Lake Littoral Zone Mean Total Native Biomass Figure 19. Mean total native aquatic plant biomass ± 1SE (August surveys) in Mitchell Lake 2013 and 2014. The decline from 2013 to 2014 is significant (p ≤ 0.05).

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Figure 20. Aquatic bathymetry and vegetation maps of Mitchell Lake. Data collected during point intercept aquatic vegetation surveys on: 1) 13 June 2013, 2) 20 August 2013, 3) 20 May 2014, 4) 12 June 2014 and 5) 8 August 2014. Contour lines are 5ft intervals. Color legend represents percent biovolume (refers to the percentage of the water column taken up by vegetation when vegetation exists) with blue representing no vegetation present and red representing 100% of the water column being taken up by vegetation.

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Table 9. Lake-‐wide percent area cover (PAC) and average biovolume (BV) for surveys in June and August 2013 and May, July and August 2014 in Mitchell Lake. Values coincide with maps in Figure 20. PAC refers to the overall surface area that vegetation is growing in the surveyed area. Average BV refers to the percentage of the water column taken up by plants when plants exist; areas that have no plants are not factored into this calculation. Date PAC Average BV June 2013 89.4% 66.6% August 2013 75.1% 68.2% May 2014 79.6% 21.3% June 2014 94.4% 60.7% August 2014 70.1% 58.8% Recommendations for Mitchell Lake: Mitchell Lake has a fairly diverse aquatic plant community and efforts should focus on maintaining and enhancing the native plant community. The decline in native aquatic plant biomass from August 2013 to August 2014 is worrisome, but with only two years of data there may not be cause for alarm. The native plant community should be monitored for further declines. Curlyleaf pondweed should also be monitored closely to determine its impact on the native plant community in Mitchell Lake. If curlyleaf pondweed is found to be reducing the native plant community, Mitchell Lake would likely benefit from a lake-‐wide early season endothall herbicide treatment. Although Mitchell Lake is a “Natural Environment Lake”, the Minnesota DNR may grant a variance if treatments were likely to maintain or enhance the native plant community. Because Eurasian watermilfoil is relatively low in abundance, Mitchell may particularly benefit from such a treatment, particularly if Eurasian watermilfoil does not expand. Mitchell should continue to be monitored in May, June and August as a reference lake to compare to Susan and Riley, but much could be learned from an early season curlyleaf treatment and that should be explored for 2016.

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VII. Lake Riley Lake Riley (DOW ID 10-‐000200) is a eutrophic lake located about 2 km downstream of Lake Susan and sits along the Chanhassen and Eden Prairie city boundary. Rice Lake Marsh lies along the Riley Creek between and Lake Susan and Lake Riley. Lake Riley has a surface area of about 120 hectares (300 acres) with a littoral zone of about 45 hectares (110 acres) and a maximum depth of about 15m (49ft). Carp were removed from Lake Riley in March 2010. A Lake Vegetation Management Plan was developed in winter 2013 and approved by the Riley Lake Association and the Minnesota DNR. To control curlyleaf pondweed, Lake Riley was treated with the herbicide endothall on 10 May 2013 and 20 May 2014 after water temperatures rose to between 10-‐15°C. Curlyleaf was delineated prior to treatment and herbicide was applied to approximately 34.5 acres in 2013 and 32 acres in 2014. Water Quality: Lake Riley Secchi depths are typically around 1m by the end of June or beginning of July (Figure 21). Although 2014 had higher water clarity than previous years, water clarity is typically low during summer months. Dissolved oxygen and temperature profiles show an anoxic hypolimnion typically below 4.5 or 5m in August (Figure 21).

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Figure 21. Secchi depths for Lake Riley 2010 through 2014 (Bajer and Sorensen unpublished data, personal communication) and dissolved oxygen (mg/L) and temperature (°C) profiles taken in August 2012 through 2014.

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Aquatic Vegetation Survey: We have conducted point intercept surveys on Lake Riley from 2011 through 2014. Overall there is low plant diversity in Lake Riley with only 11 species being found during four years of surveys (Table 10). The highest species richness per site was observed in a survey completed in August 2014 with 5 species at one site (Figure 22). Most plants are in water < 2m deep. Coontail, curlyleaf pondweed and Eurasian watermilfoil are typically the most frequently occurring species, with the exception of August when curlyleaf is typically not present due to its life cycle (Figure 23). There have been increases in native plant frequency since curlyleaf pondweed treatments began in 2013, but the increases have been slight likely because of poor water clarity. Chara, Canada waterweed, bushy pondweed (Najas flexilis), narrow leaf pondweed and sago pondweed (Stuckenia pectinata) were all observed in August 2014 at their highest frequencies of occurrence since we began surveying (Figure 23 bottom). Coontail, curlyleaf pondweed and Eurasian watermilfoil are also the most dominant species in biomass (Figure 24). Coontail continues to make up the vast majority of the native aquatic plant biomass in Lake Riley, with very little contribution of other native plants to total lake-‐wide native plant biomass. Eurasian watermilfoil and curlyleaf pondweed have both been problematic in Lake Riley. Eurasian watermilfoil continues to be a dominant member of the plant community in the lake with a stable or slightly increasing population (Figure 23 and 24). Curlyleaf pondweed has decreased dramatically in both frequency (Figure 25) and biomass (Figure 26) since treatments began in 2013. Milfoil Herbivore Population: We began monitoring the milfoil herbivore population in 2011 and the maximum density of weevils was observed on 27 August 2014 at 0.68 weevils per stem (Table 11). Although there was a relatively high weevil population in 2012, it declined in 2013 and was low through most of 2014 until the increase in August. Large populations of stunted sunfish may be retarding the weevil population in Lake Riley. The weevil population does not appear to be persistently abundant enough to control Eurasian watermilfoil. Curlyleaf Pondweed Herbicide Treatments: Lake-‐wide early season endothall treatments took place in Lake Riley in the spring of 2013 and 2014. We saw significant declines in curlyleaf frequency (Figure 25), biomass (Figure 26) and turion densities in the sediment (Table 12). Curlyleaf pondweed was observed in over 60% of sites sampled in the littoral zone in 2012 and declined to less than 20% of sties sampled in the littoral zone in 2013 and 2014 post-‐

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treatment (June). The reduction of curlyleaf frequency of occurrence was significant (p ≤ 0.05). At its peak in 2012, we observed a littoral-‐wide average biomass of about 120 g dry/m2. Curlyleaf biomass values declined significantly (p ≤ 0.05) to under 5 g dry/m2 in 2013 and 2014 (Figure 26). Turion densities in the sediments declined significantly (p ≤ 0.05) from a peak of 132 turions/m2 to about 60 turions/m2 in 2013 and 2014 (Table 12). Furthermore, turion viability dropped from over 90% before treatment to 33% in 2014. Although native aquatic plants did not increase significantly in biomass or frequency from 2012 to 2013 or 2012 to 2014, they did not decrease either. In Lake Riley we saw slight increases in some native species in frequency (Figure 23 bottom) and mean total native plant biomass (Figure 27) when comparing August 2013 to August 2014; whereas in Mitchell Lake (untreated reference lake) native aquatic plants significantly decreased (p ≤ 0.05) in mean biomass in the same years (Figure 19). Abundant plant growth is restricted to areas < 2m deep (Figure 28), primarily in the north and the southwest bay. In these areas, biovolume can approach 100%, but drops to near zero in deeper areas. Overall plant cover in the littoral is thus not high (usually ≤ 50%) and mean biovolume is 55% or less (Table 13). Lake Riley Exclosure Study: Exclosure experiments were conducted in Lake Riley in the summer of 2012 and 2013. The intent of the study was to determine if abundant small bluegill sunfish were reducing water clarity. Further description and results from exclosure studies are described in the Annual Report for 2012 and the Summary of Results for 2013 (JaKa et al. 2013 and JaKa et al. 2014) and are not repeated here.

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Table 10. Aquatic plants found in surveys conducted in Lake Riley 2011 through 2014. Common Name Scientific Name Abbreviation

Submerged species Coontail Ceratophyllum demersum Cdem Muskgrass Chara spp. Char Canada waterweed Elodea canadensis Ecan Bushy Pondweed Najas flexilis Nfle Eurasian watermilfoil Myriophyllum spicatum Mspi Curlyleaf pondweed Potamogeton crispus Pcri Narrow leaf pondweed Potamogeton pusillus Ppus Sago pondweed Stuckenia pectinata Spec Horned pondweed Zannichellia palustris Zpal

Floating-leaf Species Common duckweed Lemna minor Lmin White lily Nymphaea odorata Nodo Figure 22. The number of aquatic plant species present at each site surveyed in Lake Riley, August 2014

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Figure 23. Frequency of occurrence for Lake Riley surveys May, June and August 2011, 2012, 2013 and 2014. See Table 10 for abbreviations.

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Figure 24. Dry aquatic plant biomass (g dry/m2) for Lake Riley surveys May, June and August 2011, 2012, 2013 and 2014. See Table 10 for abbreviations.

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Figure 25. Peak frequency of occurrence of curlyleaf pondweed in Lake Riley. The vertical line represents the beginning of herbicide treatment and divides pre-‐ and post-‐ treatment years. Post-‐treatment declines are significant (p ≤ 0.05). Figure 26. Peak biomass (g dry/m2) ± 1SE of curlyleaf pondweed in Lake Riley. The vertical line represents the beginning of herbicide treatments and divides pre-‐ and post-‐ treatment years. Post-‐treatment declines were significant (p ≤ 0.05).

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Table 11. Results of Eurasian watermilfoil herbivore population surveys in Lake Riley 2010 through 2012. Values are lake-‐wide means for weevil populations expressed as total weevils in all life stages per stem. Mspi Weevils/Stem 2011 19 July 0.20 2012 18 June 0.02 9 July 0.38 8 August 0.48 2013 5 June 0.15 27 June 0.08 29 July 0.00 27 August 0.00 2014 5 June 0.06 2 July 0.04 30 July 0.11 27 August 0.68 Table 12. Results from turion surveys conducted October 2011 through 2014. Declines from 2012 to 2014 are significant (p ≤ 0.05). Pcri Turions/m2 Viability Oct-‐2011 45 96% Oct-‐2012 132 99% Oct-‐2013 56 71% Oct-‐2014 61 33%

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Lake Riley Littoral Zone Mean Total Native Biomass Figure 27. Mean total native plant biomass ± 1 SE in the littoral zone (August surveys) in Lake Riley 2011 through 2014. The vertical line represents the beginning of herbicide treatments and divides pre-‐ and post-‐treatment years.

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Figure 28. Aquatic bathymetry and vegetation maps of Lake Riley. Data collected during point intercept aquatic vegetation surveys on: 1) 8 May 2013, 2) 18 June 2013, 3) 14 August 2013, 4) 16 May 2014, 5) 18 June 2014 and 6) 12 August 2014. Contour lines are 5ft intervals. Color legend represents percent biovolume (refers to the percentage of the water column taken up by vegetation when vegetation exists) with blue representing no vegetation present and red representing 100% of the water column being taken up by vegetation.

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Table 13. Lake-‐wide percent area cover (PAC) and average biovolume (BV) for data collected in May, June and August 2013 and May, July and August 2014 in Lake Riley. Values coincide with maps in Figure 28. PAC refers to the overall surface area that vegetation is growing in the surveyed area. Average BV refers to the percentage of the water column taken up by plants when plants exist; areas that have no plants are not factored into this calculation. Date PAC Average BV May 2013 42.9% 36.6% June 2013 60.2% 53.2% August 2013 25.6% 38.5% May 2014 24.6% 15.4% June 2014 50.3% 55.9% August 2014 47.6% 47.7% Recommendations for Lake Riley: Water clarity continues to be an issue in Lake Riley, inhibiting the recovery of the native plant community and expansion of plants into water deeper than 2m. Native plants other than coontail are at low densities and have failed to expand to more than 10% of sites. Approaches to improve water clarity should be addressed in order to enhance the native plant community. There have been slight increases in the native plant community since the early-‐season, lake-‐wide herbicide treatments targeting curlyleaf pondweed control, but water clarity is likely slowing the overall establishment and expansion of the native plant community. Eurasian watermilfoil is also present at nuisance levels and herbicide treatments may be necessary to control it. It is more problematic than the curlyleaf and the high occurrence and persistence of dense milfoil in August is likely further inhibiting establishment of rooted native plants. Selective herbicide treatments to control Eurasian watermilfoil should be considered to help enhance native plants. Herbicide treatments almost certainly will be needed if water clarity is improved by means of alum treatment. The recommended strategy is to implement early season selective control of Eurasian watermilfoil and curlyleaf pond before or concurrent with alum treatments to improve water clarity. These invasives could become even more abundant and aggressive with increased water clarity if they are not managed in anticipation of improved clarity. If the invasives are controlled, the native plants should have more space and light, and less competition from the invasives and be able to establish and expand. If rapid recovery does not occur during the first year of substantially improved

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water clarity, planting or transplanting should be conducted to jump-‐start the native plant recovery, followed by targeted and selective herbicidal control in the next year.

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VIII. Staring Lake Staring Lake is a hypereutrophic lake in the Purgatory Creek Watershed. The lake is about 66 hectares (164 acres), with a maximum depth of 4.9m (16ft) (MN DNR LakeFinder 2014). Staring Lake has a high population of carp (Bajer and Sorensen personal communication) and subsequently is turbid and algae-‐dominated with low water clarity. Efforts have been underway since 2012 to reduce the carp population and a substantial, but still, only partial removal occurred in winter 2014 (Bajer and Sorensen, personal communication). Water quality: The summer Secchi depths have been consistently low, although there was some improvement in the spring during the last two years (Figure 29). Dissolved oxygen profiles show that an anoxic hypolimnion may exist from below 2m to 4m during the summer depending on the year (Figure 29). However, two of the four years show some oxygen throughout the entire water column, likely due to lack of stratification.

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Figure 29. Secchi depths for Staring Lake 2010 through 2014 (Bajer and Sorensen unpublished data, personal communication) and dissolved oxygen (mg/L) and temperature (°C) profiles taken in August 2011 through August 2014. Aquatic Vegetation Survey: Point intercept surveys were conducted in Staring Lake in June and August 2011, 2012, 2013 and 2014. There were slight increases in frequency and new species observed in 2014, but the overall aquatic plant community remains very poor. Species diversity increased to 14 different species observed in the August 2014 (Table 14), however the frequency of occurrence (Figure 30) was very low relative to other lakes described in this report. The maximum species richness per site was observed in the August 2014 survey as well, with one site having 6 species (Figure 31). The species richness per site was typically much lower than 6 in all surveys from 2011 to 2014 on Staring Lake. Curlyleaf pondweed was generally the most frequently occurring species in June and often in August as well (Figure 30). White and yellow water lilies were two

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of the most commonly occurring native species in Staring, likely due to that fact that they are floating leaf species and less impacted by poor water clarity. Their large rhi

aquaticplantcommunityof( lakesann,lotus,lucy,mitchell ......1! !...

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