2015 Starry Stonewort Inspection and Assessment Report: Lake Koronis, Stearns County MNDNR Division of Ecological and Water Resources

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1 Lake: Koronis (DOW# ) County: Stearns Report type: Starry stonewort Inspection and Assessment MNDNR Field Contributors: Christine Jurek (Invasive Species Specialist), Courtney Millaway (Natural Resource Specialist), Mark Ranweiler (Assistant Invasive Species Specialist), Hora Gezahegn (Hydrologist 2),Mike Bolinski (Watercraft Inspection Supervisor), Keegan Lund (Invasive Species Specialist), Kylie Catoor (Natural Resource Specialist), Allison Gamble (Invasive Species Specialist), Evan Freeman (Watercraft Inspection Supervisor), Brad Carlson (Assistant Area Fisheries Supervisor), Scott Mackenthun (Aquatic Plant Management Specialist- Fisheries), and Gary May (Natural Resource Specialist- Fisheries). Date of report: 24 August 2015 Date of final revision: 30 November 2015 Author[s] of report: Christine Jurek and Courtney Millaway Results: CONFIRMED INFESTED Part 1: Background Lake Koronis is located within the North Fork Crow River Watershed near the city of Paynesville, MN within the counties of Stearns and Meeker. It is a 2,968 acre lake with a littoral area of 1,176 acres. The lake s recorded maximum depth is 132 feet. Common aquatic plants in Lake Koronis include sago pondweed (Stuckenia pectinata), muskgrass (Chara spp.), wild celery (Valisneria americana), white-stem pondweed (Potamogeton praelongus), flat-stem pondweed (Potamogeton zosteriformis), and coontail (Ceratophyllum demersum). Starry stonewort (Nitellopsis obtusa) is a non-native macroalgae in the plant kingdom under the division of Charophyta (freshwater green algae). Starry stonewort is similar to native macroalgae such as muskgrasses and stoneworts that are common in Minnesota. Starry stonewort is a non-vascular plant with smooth green stems, whorled branchlets, and characteristic star-shaped bulbils produced on colorless, clear rhizoids (Figure 1). Starry stonewort can produce dense mats that may displace native aquatic plants and interfere with recreation. These mats may also occupy lake bottoms where fish spawning may occur. 1

2 Figure 1. A starry stonewort specimen that depicts its whorled branchlets in, MN (DOW ). Photo taken on 20 August 2015 by Christine Jurek, MNDNR. Part 2: Confirmation and Area Searches MNDNR Invasive Species Program first became aware of this aquatic invasive species on 18 August 2015 after a MNDNR Fisheries inspection found Starry Stonewort growing in Lake Koronis. This inspection was initiated by reports of homeowners concerned about an abundance of vegetation in Lake Koronis. During the Fisheries inspection, DNR staff pulled up samples of an unknown plant, which they sent to Donna Perleberg, MNDNR Lake Habitat Program, for identification. Donna Perleberg tentatively identified the plant as the invasive starry stonewort and subsequently sent samples to Dr. Kenneth G. Karol, an expert in Molecular Systematics Studies at the New York Botanical Garden, who is familiar with the group of macroalgae to which starry stonewort belong. Dr. Karol confirmed the identification of starry stonewort, Nitellopsis obtusa, on 19 August This was the first confirmation of starry stonewort in Minnesota. 2

3 Since this was the first report of starry stonewort in the state, a rapid response to initially survey the lake was a high priority. An inspection for the presence of starry stonewort on Lake Koronis was conducted by the MNDNR Invasive Species Program on 20 August 2015 and 21 August This initial assessment focused on determining the location of plant within the east bay area, and surveying the shoreline of the lake to determine whether the plant had spread to other locations. More complete, whole lake searches were conducted later in the season. The two-day initial assessment of the littoral area (the portion of the lake that is less than 15 feet in depth) of Lake Koronis identified starry stonewort growing in roughly a 53 acre area, in depths ranging from 2.1 to 5.2 feet (Figure 2). The plant was widely distributed and occurring in high densities in the bay near the public water access off of Highway 55 (Figure 3). The white starshaped bulbils characteristic of starry stonewort were observed (Figure 4). During the inspection, starry stonewort was also observed growing outside of the bay extending into the main basin and one other location on the northeast side of Lake Koronis (Figure 5). MNDNR staff documented the presence of starry stonewort, along with observed native submersed plants, while conducting their inspection. Figure 2. Photo of dense starry stonewort growing throughout the water column in Lake Koronis, Stearns County, MN (DOW ) on 20 August 2015; photo taken by Christine Jurek, MNDNR. 3

4 Figure 3. Starry stonewort plants pulled up by a rake throw at the Highway 55 public water access at Lake Koronis, Stearns County, MN (DOW ) on 20 August Photo taken by Mark Ranweiler, MNDNR. Figure 4. Starry stonewort and its characteristic white star-shaped bulbils in, MN (DOW ). Photo taken on 20 August 2015 by Christine Jurek, MNDNR. 4

5 Figure 5. Observed starry stonewort locations and boat tracks from a two-day initial inspection by MNDNR staff on, MN (DOW ) on 20 and 21 August To assess whether starry stonewort had been spread to surrounding lakes, DNR staff conducted additional searches on area lakes. Searches focused on the area at and around the public water accesses (PWAs). Thus far, starry stonewort has not been observed at the PWAs within a 10 mile radius of Lake Koronis (Appendix A and B). However, starry stonewort was observed growing upstream into Mud Lake, connected to Lake Koronis, up to a distance of 300 feet from the bay, on 25 August Additional searches at area lakes beyond the 10 mile radius are in progress. Part 3: Intensive Field Assessment A more intensive field assessment was then conducted by regional invasive species staff to delineate starry stonewort; this detailed delineation revealed that the starry stonewort was located in the majority of the 250 acres surveyed (Figure 6). Starry stonewort was observed matting to the surface of the water at 7 feet (Figure 7). 5

6 Figure 6. Detailed delineation of starry stonewort in (DOW ) and Mud Lake, Stearns County (DOW ) as of 23 September 2015 (250 acres). Figure 7. An area of starry stonewort that is matting to the surface in (DOW ). Photo taken on 14 September 2015 by Courtney Millaway, MNDNR. 6

7 Part 4: Point-intercept Survey A point-intercept survey was used to assess the distribution of starry stonewort in Lake Koronis. The primary purpose was to document the distribution and abundance of starry stonewort and to collect baseline data so as to be able to compare year to year plant variation (plant presence, spatial location, and abundance). The survey was conducted on several dates between 28 September and 9 October 2015 (see Madsen, 1999 and MN DNR protocols) by Invasive Species Program and Fisheries staff. Sample points were generated using ArcMap GIS software to create a grid of equally spaced points with 130 meter spacing between each point. A Garmin 62stc GPS unit and Lowrance depth finder were used to navigate a boat to each sample point. A double headed rake was tossed once at each point to sample vegetation. Plant samples were assessed on the boat to determine species and abundance (1: rare, 2: scattered, 3: common, 4: abundant). A total of 331 points were sampled up to a depth of 20 feet (Table 1). The aquatic vegetation communities in Lake Koronis were characterized and documented in Tables 1 and 2, including the distribution and abundance of starry stonewort (Figure 8). Frequencies of occurrence percentages (i.e., how often a plant species was found in the lake) were calculated for the littoral zone also (Table 2). Table 1. Summary of point intercepts metrics for (DOW# ). Maximum depth of growth (95%) is the maximum depth of all plants observed in 20 feet of water at the 95% confidence level. Values shaded in grey were calculated within the littoral depth range (0-15 feet). SEP/OCT 2015 Surveyor MN DNR Total # Points Sampled 331 Max Depth of Growth (95%) 10 ft Max Depth of Starry Stonewort 15.1 # Points in Littoral (0-15 feet) 294 % Points w/ Submersed Native Taxa 78% Mean Submersed Native Taxa/ Point 1.4 # Submersed Native Taxa 14 # Submersed Non-Native Taxa 2 7

8 Table 2. Percent frequency of occurrence for submersed and floating vegetation within the littoral zone (0-15 feet) in (DOW# ). Taxonomic Name SUBMERSED NON-NATIVE Common Name SEP/OCT 2015 Nitellopsis obtusa Starry stonewort 17 Potamogeton crispus Curly-leaf pondweed 2 SUBMERSED NATIVE Ceratophyllum demersum Coontail 14 Chara spp./nitella spp. Muskgrass and Stonewort 60 Elodea canadensis Canadian waterweed 1 Heteranthera dubia Water stargrass <1 Myriophyllum sibiricum Northern watermilfoil 14 Najas sp. Naiad 4 Potamogeton illinoensis Illinois pondweed <1 Potamogeton praelongus White-stem pondweed <1 Potamogeton richardsonii Clasping-leaf pondweed 6 Potamogeton robbinsii Fern pondweed 1 Potamogeton zosteriformis Flat-stem pondweed 1 Potamogeton spp. Narrowleaf pondweed 4 Stuckenia pectinata Sago pondweed 16 Vallisneria americana Water celery 21 FLOATING LEAF Nuphar variegata Yellow pond lily <1 Nymphaea odorata White water lily 1 Potamogeton natans Floating-leaf Pondweed <1 8

9 Figure 8: Starry stonewort abundance and distribution in (DOW ) based on a fall point-intercept survey. Submersed aquatic plants were observed at a maximum growth depth of 10 feet (95%). Within the littoral zone, 294 points were sampled and 78 percent of the points had submersed native taxa with an average of 1.4 native submersed species per sample point. Fourteen native submersed plant species were documented during the 2015 survey. Muskgrass and native stoneworts were the most abundant species documented, occurring at 60 percent of the sample points in the littoral zone. Two invasive aquatic species were also recorded (starry stonewort and curly-leaf pondweed). Part 5: Initial Herbicide Treatment and Monitoring To decrease the biomass of starry stonewort near the Highway 55 public water access on Lake Koronis and to minimize spread to other area lakes, a small scale herbicide treatment took place in fall of 2015 (Figure 9). The treatment was conducted by Professional Lake Management on 7 October 2015 using both Cutrine-ultra and Hydrothol 191 (Figure 10). The two herbicides differ in terms of compounds and modes of action. Cutrine-ultra is a copper-based contact pesticide that breaks down the plant s cellular structure and interrupts the ability to photosynthesize. Hydrothol 191 is an endothall-based contact herbicide that inactivates plant protein synthesis. 9

10 Figure 9. Initial Treatment Area (4.0 acres) near the public water access on (DOW ). Figure 10. Commercial herbicide applicators preparing for treatment on (DOW ) on 7 October Photo taken on 7 October 2015 by Courtney Millaway, MNDNR. 10

11 The herbicides were applied to four acres within the bay near the public water access, the channel extending into Mud Lake, and the main basin of Lake Koronis. The starry stonewort growing in the bay reached the water s surface in many areas with matting at average water depths of 4.5 feet. The starry stonewort growing in the channels and up into Mud Lake was observably less dense. In order to maximize the effectiveness of treatment and to monitor the treatment area, the MNDNR temporarily closed the public water access near Highway 55. Recommendations for the initial treatment were based on communication with Dr. John Rogers at Clemson University in South Carolina. The recommendation was 0.5 ppm copper as Cutrine-Ultra in the bottom two feet of the water column in an area of four acres (8 ac-ft. X 1.5 gallons per ac-ft.). Given that the average depth of the treatment area was five feet, the estimated concentration of copper in the whole water column was 0.2 ppm. The rate of Hydrothol 191 at 2.5 gallons in 20 ac-ft. was 0.1 ppm. Herbicides were applied using a rigid hose system that targeted the bottom two feet of the water column. Cutrine- Ultra was applied first, followed by Hydrothol 191. The treatment record is located in Appendix C. Water samples were collected to monitor copper concentrations. Samples were obtained pre-treatment and post-treatment at three locations within the treatment area (Figure 11). Total copper was measured using a photometer (Figure 12) and additional water samples were sent to MN Department of Agriculture labs for verification of the photometer s accuracy. Figure 11. Locations of water samples taken to monitor copper concentrations in Lake Koronis, Stearns County (DOW ) and Mud Lake, Stearns County (DOW ). Waypoints of water samples and Cu concentrations: (001, 002, and 003). 11

12 Figure 12. Keegan Lund, Invasive Species Specialist, using the photometer to measure copper concentrations in the herbicide treatment area on Mud Lake, Stearns County (DOW ). Photo taken on 7 October 2015 by Courtney Millaway, MNDNR. The target copper (Cu) concentration (0.2 ppm) was achieved within 0.5 hours after the herbicide application in two different locations (Table 3). The data indicate that the Cultrine-Ultra (copper product) moved downstream within the first 24 hours and returned to normal Cu levels (<0.04 ppm) after 48 hours. The decline in Cu concentrations may indicate dissipation from the system or microbial and/or algal uptake in the water column. 12

13 Table 3. Pre-treatment and post-treatment copper concentrations (Cutrine-Ultra) collected upstream (Sample Location 001), in the bay (Sample Location 002), and downstream (Sample Location 003) in Lake Koronis, Stearns County (DOW ) and Mud Lake, Stearns County (DOW ). Sample Date Sample Time Notes Sample Location Total Cu ppm (Photometer) 10/7/ :15:00 AM Pre-treatment, samples taken from surface :30:00 PM Post-treatment (0.5hrs), samples taken from surface :30:00 PM Post-treatment (1.5hrs), samples taken at depth :30:00 PM Post-treatment (2.5hrs), samples taken at depth /8/ /9/2015 Post-treatment (23.5hrs), samples taken from surface Post-treatment (48hrs), samples taken from surface Part 6: Post-treatment Survey and Observations A post-treatment survey was conducted on 13 October 2015 (six days after treatment) to monitor the treatment s effectiveness at reducing existing mats of starry stonewort. Nine sampling points were selected within the treatment area and nine sampling points with a similar average depth were selected outside of the treatment area (Figure 13). For the post-treatment survey, we used the same methodology as the point intercept survey described by Madsen (1999) and MN DNR protocols. Relative abundance was also calculated to provide an average of the abundance of a given species (Tables 4-7). 13

14 Figure 13. Post- treatment survey map for (DOW ) and Mud Lake, Stearns County (DOW ). 14

15 Table 4. Starry stonewort abundance: Pre-treatment/ post-treatment results for the treatment area in (DOW ) and Mud Lake, Stearns County (DOW ). TREATMENT AREA Pre-treatment: Sept. 15, 2015 Post-treatment: Oct. 13, 2015 Point ID Depth (ft) SSW Depth (ft) SSW Average Depth (ft) Relative Abundance Plant Code (SSW: Starry Stonewort) Abundance 1-4 Rating (1: Rare; 2: Scattered; 3: Common; 4: Abundant) Table 5. Starry stonewort abundance: Pre-treatment/ post-treatment results for the untreated reference area in (DOW ). REFERENCE AREA Pre-treatment: Sept. 15, 2015 Post-treatment: Oct. 13, 2015 Point ID Depth (ft) SSW Depth (ft) SSW Average Depth (ft) Relative Abundance Plant Code (SSW: Starry Stonewort) Abundance 1-4 Rating (1: Rare; 2: Scattered; 3: Common; 4: Abundant) 15

16 Table 6. Submersed native vegetation abundance: Pre-treatment/ post-treatment results for the treatment area in (DOW ) and Mud Lake, Stearns County (DOW ). TREATMENT AREA Pre-treatment: Sept. 15, 2015 Post-treatment: Oct. 13, 2015 Point ID Depth (ft) CD VA NO PC Depth (ft) CD VA NO PC Average Depth (ft) Relative Abundance Plant Codes (CD: Coontail; VA: Wild Celery; NO: White Waterlily; PC: Curly-leaf Pondweed Abundance 1-4 Rating (1: Rare; 2: Scattered; 3: Common; 4: Abundant) Table 7. Submersed native vegetation abundance: Pre-treatment/post-treatment results for the untreated reference area in (DOW ). REFERENCE AREA Pre-treatment: Sept. 15, 2015 Post-treatment: Oct. 13, 2015 Point ID Depth (ft) CD POR VA HD Depth (ft) CD POR VA HD Average Depth (ft) Relative Abundance Plant Codes (CD: Coontail; POR: Clasping-leaf Pondweed; VA: Wild Celery; HD: Water Stargrass Abundance 1-4 Rating (1: Rare; 2: Scattered; 3: Common; 4: Abundant) 16

17 Post-treatment observations and survey results indicated that the initial herbicide treatment did not reduce the amount of biomass of starry stonewort in the treatment area. Starry stonewort remained green, stiff and had a crunchy feel in both the treatment area (Figures 14 and 15) and untreated reference area (Figure 16). A paired-samples t-test was conducted to compare the abundance of starry stonewort pre-treatment and post-treatment within the treatment area (Table 4). There was not a significant difference in abundance for pre-treatment and post-treatment, p >.05. Our results suggest that the abundance of starry stonewort was not impacted by the herbicides. Table 5 represents the starry stonewort abundance in the untreated reference area. A paired-samples t-test was conducted to compare the abundance of starry stonewort pre-treatment and post-treatment within the untreated reference area. There was a significant difference in abundance for pre-treatment and post-treatment, p <.05. This may be due to the natural senescence of starry stonewort caused by environmental factors in the untreated reference area. Tables 6 and 7 represent the submersed native vegetation abundance in the treatment area and untreated reference area. Overall, the abundance of submerged native vegetation was low in both sites. Statistical tests of significance were not conducted for the native submersed species. Figure 14. Starry stonewort matted to the surface of the water in the treatment area near the Highway 55 public water access after treatment occurred in, MN (DOW ). Photo taken on 13 October by Courtney Millaway, Natural Resource Specialist. 17

18 Figure 15. Starry stonewort pulled up by a rake throw in the treatment area during the post-treatment survey in, MN (DOW ). Photo taken on 13 October by Courtney Millaway, Natural Resource Specialist. Figure 16. Starry stonewort pulled up by a rake throw in the untreated reference area during the posttreatment survey in, MN (DOW ). Photo taken on 13 October by Courtney Millaway, Natural Resource Specialist. 18

19 Part 7: Conclusion The MNDNR has continued to explore other management and prevention options for starry stonewort and will continue to involve stakeholders in discussion of a long-term strategy concerning both prevention and management options on Lake Koronis and Mud Lake. The information described in the various parts of this inspection and assessment report is consistent with steps outlined in the MNDNR s rapid response plan. An outline of the action steps taken in regards to starry stonewort on Lake Koronis has been documented. 19

20 Appendix A. Results from starry stonewort searches at public water accesses within Stearns, Kandiyohi, and Meeker Counties in Minnesota. County Lake DOW Notes: Stonewort at access? (Y/N) Stearns Big mi. radius N Eden mi. radius N Long mi. radius N North Brown's mi. radius N Rice mi. radius N Mud (Vails) mi. radius N Kandiyohi Calhoun mi. radius N Green mi. radius N Long mi. radius N Mud mi. radius N Diamond WIP info N Eagle Bass league N East Solomon Bass league N Florida Bass league N Long Bass league N Nest Bass league N Norway Bass league N Meeker Clear mi. radius N Long mi. radius N Mud mi. radius N Ripley mi. radius N Stella N Washington N 20

21 Appendix B. Map of starry stonewort searches at public water accesses within Stearns, Kandiyohi, and Meeker Counties in Minnesota. 21

22 Appendix C. Professional Lake Management treatment record for (DOW ). 22