Flowering Rush in Lake Minnetonka in 2016

Transcription

1 A 2016 site with no flowering rush in Browns Bay. This site had over 5,000 square feet of flowering rush in Flowering Rush in Lake Minnetonka in 2016 Prepared for: Minnehaha Creek Watershed District Prepared by: Steve McComas Blue Water Science April 2017

2 Flowering Rush in Lake Minnetonka in 2016 Summary A flowering rush survey was conducted in 2016 on Lake Minnetonka and included all sites that were previously delineated with flowering rush including sites where handpulling and herbicide treatment had occurred in the past. No treatments occurred in A total of 62 flowering rush sites were surveyed. On October 10, 2016, flowering rush was observed at 39 out of 62 sites (Figure S1). Two of the largest areas of colonization were on the north side of Big Island with a coverage of about 1,100 square feet. Other sites were smaller ranging from 10 square feet up to 200 square feet. Flowering rush was found at 7 new sites in 2016 compared to 8 new sites in 2015, based on the benchmark year of However, flowering rush was not observed at 23 sites where it was previously observed. In some years at a site, flowering rush does not sprout and other years it does. It may be that the new sites of flowering rush in 2016 were sites where it was previously established but had not sprouted for a year or two. Flowering rush does not appear to be expanding very quickly in Lake Minnetonka (Figure S2). Handpulling has been effective for flowering rush control in small areas (4,000 square feet or 0.1 acre) or less but still necessary on an annual basis. At 2 sites, handpulling has occurred for 5 years (2011- and 8 sites have had removal for 3 years. Although flowering rush densities have decreased at these sites, it has not been eradicated at those sites. It is uncertain how long removal needs to occur before the root stock and propagules are depleted and will no longer produce new stems. The herbicide diquat was applied in 2014 and The diquat applications in the Maxwell Channel area were successful and no emergent stems were observed after treatments. There was some regrowth in However, treatment using a contact herbicide has only occurred for 2 seasons. It is unclear how many seasons it may take to eradicate flowering rush from a site. Figure S1. Flowering rush survey sites in Summary - i

3 Figure S2. Lake Minnetonka flowering rush locations. Flowering rush is found in the central bays of Lake Minnetonka and has not expanded to the western or eastern regions of the lake. Summary - ii

4 Flowering Rush Sites in Lake Minnetonka in 2015 and 2016: Details of flowering rush areas of growth for specific sites are shown in Figures S3 and S4 and Table S1. All known flowering rush sites were visited in 2016 which included sites first delineated in 2009, 2012, and 2015 (Figure S3). The overall flowering rush community is fairly stable, with minor year to year variation. Flowering rush expansion to new bays was not observed in New sites in 2016 are labeled from The estimated area of flowering rush decreased from 36,335 square feet in 2015 to 4,340 square feet in 2016 (Table S1). A combination of factors likely contributed to the decrease including wave action that knocked over emergent stems and the late survey date may have been a factor. However, flowering rush was still found growing in many areas on the October 10, 2016 survey date. Figure S3. Handpulling sites are shown with squares and labeled 1 through 10. The herbicide diquat w as used in the Maxwell Channel. Summary - iii

5 Table S1. Lake Minnetonka flowering rush delineation conducted in 2015 and 2016 by Blue Water Science. Treatment Area Waypoint (BWS) Total Area (square feet) Total Area (square feet) 1 (new 300 Maxwell 2 1, Channel (new (new (new (new 1, (new (new 4, (new , , , ,000 ( ) 0 ( ) (2,000 on ) 55 6,000 (8.16.1) 0 ( ) (1,000 on ) 56 (new (new (new (new 40 (4 patches) 60 (new (new (new 20 Total Area 36,335 sf 4,340 sf Totals Sites Figure S and 2016 Minnetonka flowering rush sites. Summary - iv

6 Flowering Rush in Lake Minnetonka in 2016 Introduction Flowering rush has been previously surveyed in Lake Minnetonka in 2009 (MnDNR) and 2012 and 2015 (Blue Water Science) and was surveyed again in This project re-surveyed all previous flowering rush sites in Lake Minnetonka. A handpulling program to remove flowering rush was initiated in 2011 at 2 sites in Smith Bay and expanded to 8 more sites in 2013 and continued through In 2015, a total of 10 sites in 5 bays were controlled by handpulling techniques that were conducted by Waterfront Restoration. In addition, a single treatment in the Maxwell Bay Channel was treated with the herbicide diquat. In 2016, no control efforts were conducted and all flowering rush sites were assessed to see where flowering rush was present or absent and to identify new flowering rush sites. Methods Flowering rush was assessed in Lake Minnetonka in For small patches of flowering rush, emergent flowering rush stems were counted and recorded. For larger areas, stems were subsampled using a 0.1 m 2 quadrat (this is equivalent to one square foot). Next, the general area that was colonized was determined either with a measuring tape or it was estimated. Then, the percent of the area actually occupied by flowering rush was estimated and was referred to as the filled area. To calculate the number of stems in a treatment area, the average density per square foot was multiplied by the area (in square feet). Next, the number of stems was multiplied by the percentage of plants in the filled area to determine the total stems in a treatment area. Submerged stem densities were included in beds with emergent stems (Figure 1). Isolated bunches of submerged stems were not counted. Figure 1. Flowering rush beds ranged in size from just a few plants to hundreds of plants. Here is a small flowering rush bed in Lake Minnetonka on July 16, 2015 prior to hand removal. Page 1

7 Results of the 2016 Lake Minnetonka Flowering Rush Survey: Lake Minnetonka flowering rush conditions were assessed on October 10, Previous locations of established flowering rush were inspected and 7 new locations were found in 2016 (Figure 2). New sites did not expand from the previously know areas of colonization, rather new sites were within colonized areas. The 10 handpulling treatment sites and the herbicide treatment area in the Maxwell Channel were visited and delineated for the number of stems. No flowering rush was observed in Maxwell Channel, but light growth was observed at the north end of the channel. No growth was found in the handpulling sites in Smith Bay except for some light growth in the NE end of the bay (Figure 2). The results of the delineation indicate that flowering rush is most common in the north side of Crystal Bay and flowering rush is not expanding rapidly in Lake Minnetonka. However, flowering rush will be a challenge to eradicate, but can be controlled on an annual basis. Figure Minnetonka flowering rush locations and treatment sites. Page 2

8 Flowering Rush Area and Densities in Lake Minnetonka in 2015 and 2016: Details for flowering rush stems and densities for specific sites are shown in Figures 3 and 4 and Table 1. The established flowering rush sites were revisited again in 2016 to add to the data set from 2009, 2012, and 2015 (Figure 3). The overall flowering rush community is fairly stable, with minor year to variation. Although there was 7 new flowering rush sites, there was no expansion in distribution. New sites were found within areas of previous flowering rush growth. Figure 3. Handpulling sites are shown with squares and labeled 1 through 10. The herbicide diquat w as used in the Maxwell Channel. Page 3

9 Table 1. Lake Minnetonka flowering rush delineation conducted in 2015 and 2016 by Blue Water Science. Treatment Area Waypoint (BWS) Total Area (square feet) Total Area (square feet) 1 (new 300 Maxwell 2 1, Channel (new (new (new (new 1, (new (new 4, (new , , , ,000 ( ) 0 ( ) (2,000 on ) 55 6,000 (8.16.1) 0 ( ) (1,000 on ) 56 (new (new (new (new 40 (4 patches) 60 (new (new (new 20 Total Area 36,335 sf 4,340 sf Totals Sites Figure and 2016 Minnetonka flowering rush sites. Page 4

10 Whole Lake Flowering Rush Distribution: Flowering rush has been delineated in 2009, 2012, 2015, and 2016 (Figure 5). The number of flowering rush sites has varied from 42 sites in 2012 to 62 sites in Flowering rush does not sprout at every site on an annual basis. In 2016, flowering rush was found at 39 out of 62 sites. All flowering rush is found in the central bays of Lake Minnetonka. Flowering rush has not been observed in the eastern or western bays of Legend: (61 sites) Red stars: Flowering Rush Lake Minnetonka. Legend: (42 sites) Red stars: Flowering Rush White dots: Sites of flowering rush removal 2011 and 2012 Figure 5. Sites of flowering rush in Lake Minnetonka in 2009, 2012, 2015, and Flowering Rush Sites Page 5

11 Results of Flowering Rush Controls from 2011 through 2015: A summary of hand removal results within flowering rush treatment areas for 2011 through 2015 is shown in Table 3 and locations are shown in Figure 6. Flowering rush has been removed from 3 sites (2, 10, and 11) for 5 years and from 7 sites for 3 years. In general, the mass of flowering rush removed has gone down each year. However the number of stems does not always decrease from year to year. Flowering rush did not reappear at Site 2 after removal in 2011, but did regrow at the other two sites (10 and 11). Hand pulling is effective for controlling flowering rush in small areas, but long term elimination of flowering rush from a site has had mixed results. Table 3. Summary of pre-treatment flowering rush areas and estimated number of stems. In addit ion, the amount of flowering rush removed (pounds of wet weight) for 2011 through 2015 (biomass estimates are from Waterfront Restoration). Green shading indicates untreated reference areas. Post treatment assessments found no flow ering rush in the treatment areas. Site (Blue Water Science) 1 Pre- Treatment square feet (stems) 2,600 (18,368) Biomass removed (lbs-wet wt) 5, , (54) (55) Max Chan 665 (4,658) (pulling) Pre- Treatment square feet (stems) *includes 18,400 stem from the channel entrance (649) 150 (1,050) 800 (5,484) (pulling) Biomass removed (lbs-wet wt) Pre- Treatment square feet (stems) 1,000 (600) 200 (400) 30 (550) 20 (600) 11,000 (59,400) 400 (6,400) 200 (1,000) 300 (1,800) 200 (550) 9 (110) 4,000 (46,000) 4,500 (56,000) 900 (3,800) Biomass removed (lbs-wet wt) Waterfront Restoration Site 309 (1) 268 (2) 38 (3) 5 (4) 954 (5) 1,188 (6) no removal no removal 104 (7) 698 (8) 81 (9) 5 (10) Reference Reference no removal -- Pre- Treatment square feet (stems) 2,780 (2,985) 258 (115) 0 (0) 5 (11) 790 (967) 80 (145) 40 (398) 210 (75) 160 (275) 20 (110) 1,000 (1,350) 3,500 (50,000) 300 (2,140) (herbicide) Biomass removed (lbs-wet wt) no removal no removal 0 Pre- Treatment square feet (stems) 4,000 (13,000) 300 (700) 275 (400) 100 (300) 3,000 (6,600) 300 (2,400) 100 (25) 200 (400) 200 (1,200) 50 (250) 9,000 (72,000) 6,000 (48,000) 1,900 (30,400*) (herbicide) October survey square feet (no treatment) Figure 6. [left] Flowering rush site map for [right] PLM diquat treatment map for the Maxwell Channel. Page 6

12 APPENDIX A: Flowering Rush in 2013, 2014, and 2015 Flowering Rush Control in Lake Minnetonka in 2015: In 2015, treatment of flowering rush employed two different methods, handpulling was conducted at 10 areas and an herbicide application was conducted in the Maxwell Channel. In a qualitative check in October, no emergent flowering rush was observed in the handpulling sites or in the herbicide treated area of Maxwell Channel Minnetonka flowering rush treatment sites for Waterfront Restoration. Key: blue bar = herbicide application and red = handpulling. Flowering rush delineation for 10 treatment areas. Survey conducted on July 16, 2015 by Blue Water Science. Treatment Areas Blue Water Science Waypoints ( Area (sq ft) Waterfront Restoration Emergent Stems Submerged Stems Area (sq ft) Blue Water Science Emergent Stems Submerged Stems ,750 4,100 8,200 4,000 25% coverage: 13, ,500 2,100 2,600 3,000 6, , , ,280 2, , TOTALS 11,940 8,995 15,220 8,325 25,275 Appendix A - i

13 Maxwell Bay Delineation (June 18, for Treatment: Approximately 13 flowering rush sites were delineated for herbicide treatment with diquat on June 18, The total area was estimated at 4,700 square feet or about 0.1 acres. Site ( Size (ft) Square Feet Number of Stems Notes x 10 1,500 12,000 long bed includes open lake area 3 20 x ,400 opposite side of channel 4 10 x ,000 submerged 5 10 x small patch x ,000 patch 8 10 x patch 9 10 x ,000 patch (by bridge, north of bridge) x on land, south of bridge x , patches to end of channel x Crystal Bay: scattered patches 4,700 30,400 TOTAL AREA Maxwell Channel flowering rush on June 18, 2015 with Blue Water Science notes. Appendix A - ii

14 2014 Flowering Rush Densities at Control Sites 2014 Flowering Rush - pre and post extraction survey stem counts. Site # on Map Blue Water Science Sites Waterfront Restoration Sites Estimated Flowering Rush Stems (Emergent) Pre-Treatment Conditions August 18, 2014 Flowering Rush Stems (Submerged) Flowering Rush Stems (Emergent + Submerged) Area (sq ft) Waterfront Restoration Removal (Handpulling Sept 23 - Oct 10, 2014) Submerged Stems Emergent Stems Total Stems lbs Removed Post Treatment Conditions October 14, 2014 Estimated Flowering Rush Stems (Emergent) Flowering Rush Stems (Submerged) Flowering Rush Stems (Emergent + Submerged) ,815 3, ,404 1,554 2,958 2,780 1,211 3,861 5, Totals 2,152 2,902 5,054 4,237 2,041 7,823 9,864 1, PLM Control (Diquat herbicide: 2 applications, Sept 8) Maxwell channel 1, ,140 39,000 1, , Reference Area (No Control) Site 1-R Site 2-R Site 12-R ,350 1, Site 13-R 40,000 10,000 50,000 3, Locations of flowering rush removal sites in 2014, Blue Water Science (left) and Waterfront Restoration (right). Appendix A - iii

15 2013 Flowering Rush Densities at Control Sites Results: Both Blue Water Science and Waterfront Restoration estimated flowering rush areas and the number of stems in areas prior to hand removal. There were some differences in the estimates. Sites 5 and 6 had a large bed and estimating stem densities were complicated due to significant Sagittaria densities. At sites 9 and 11, there may have been significant submerged stems of flowering rush that were not counted by Blue Water Science. Regardless of the exact pre-treatment stem densities, the posttreatment assessment did not find any emergent flowering rush. Sites 5 and 6 were assessed, but flowering rush was difficult to observe within the Sagittaria beds. It is estimated that around 1% of flowering rush stems were likely remaining. It appears hand removal was very effective at all 10 sites. Pre-treatment and post treatment flowering rush stem densities for 2013 sites. Site or Area Treatment Area (sf) Blue Water Science Waterfront Restoration Water Depth (ft) Pre-Treatment Conditions Estimated Estimated Stems Stems (Waterfront (Blue Water Restoration) Science) Aug 14, 2013 Post Treatment Conditions Biomass Estimated Removed Stems (Wet wt-lbs) (Blue Water (Waterfront Science) Restoration) Oct 25, ,000 8, ,800 59, Est. 1% remaining ,000 6,400 1,188 Est. 1% remaining , , , , , * , ,369 10,568 77, ,710 3,650 lbs * included a nearshore area of about 300 feet parallel to shore with occasional bunches of flowering rush Locations of flowering rush removal sites in Appendix A - iv

16 APPENDIX B: Minnehaha Creek Flowering Rush Minnehaha Creek Flowering Rush Survey: The entire length (22 miles) of Minnehaha Creek was surveyed on October 3, 12, and 26, Flowering rush was only found at the eastern end of Minnehaha Creek by the Hiawatha Avenue area. Phragmites was observed in western reaches of Minnehaha Creek but not in the eastern reaches. It appears flowering rush is present only in a relatively short stretch of Minnehaha Creek near the Minnehaha Falls and is not expanding. Minnehaha Creek flowering rush. Key: blue = emergent plants but not flowering rush and red = sample site with flowering rush. Appendix B - i

17 2015 flowering rush sites in the Minnehaha Creek corridor. Minnehaha Creek From Grays Dam to Utley Mill (October 12, Way Point Stems Flowers Notes 7 Phragmites - starts 8 Phragmites - stops 9 Phragmites - starts - left bank 10 Phragmites - stops 11 Phragmites - 50 feet left bank 12 Phragmites - 70 feet left bank 13 Phragmites - 30 feet left bank 14 Cattails stop at 494 bridge, Rice - 10x10 15 Bulrush scattered 16 Cattails feet 17 Cattails feet and phragmites 10x50 18 Cattails 19 Phragmites like plant - yellow 20 Phragmites like plant 21 Cattails, starting after 1st curve after Hopkins Crossroads 22 Phragmites like plant feet 23 Cattails - stop 24 Cattails - start, few emergents in creek, bank drops off Maple Way, there is no flowering rush 25 Phragmites feet left bank 26 In the stream best section 27 Meadow or 1st Lake - possible phragmites Minnehaha Creek Flowering Rush (October 26, Way Point Stems Flowers Notes 28 Utley Park 29 Impressive boulder wall, conditions not conducive to flowering rush growth, no sagittaria, no arrowhead, mostly reed canary grass 30 Xerxes Avenue 31 Reed canary grass 32 Submerged arrowhead 33 Bulrush on a sand bar island 34 WPA wall 35 massive phragmites 36 Cattails at Hiawatha 37 No flowering rush Lower Minnehaha Creek from Hiawatha Avenue to Mississippi River (October 3, Way Point Stems Flowers Notes By culvert Continuous EWM Continuous In park after tunnel 9 0 Before falls 0 No flowering rush observed after falls 0 Below falls to Mississippi River nothing Minnehaha Creek with sample sites for October 12 and 26, 2015 numbered 0-36 (green dots). Sample sites for October 3, 2015 numbered 1-8 (red dots). Appendix B - ii

18 Comparing Flowering Rush in 2009, 2012, and 2015 in Lower Minnehaha Creek: Surveys of flowering rush were conducted in the lower portion of Minnehaha Creek in 2009, 2012, and In 2009, the survey did not go below Minnehaha Falls whereas in 2012 and 2015 it went below the falls to the Mississippi River. Comparing the areas surveyed in 2009, in 2012 and in 2015 indicates flowering rush does not seem to be migrating down the creek. Eight flowering rush sites found below the falls in 2012 but were not observed in survey conducted by the MnDNR and Minneapolis Park and Rec Board 2012 survey conducted by Blue Water Science Legend: (24 sites) Red stars: Flowering Rush 2015 survey conducted by Blue Water Science Legend: (8 sites) Blue dots: no Flowering Rush Red dots: Flowering Rush Sites of flowering rush in the lower portion of Minnehaha Creek in 2009, 2012, and Appendix B - iii

19 Summary of Lower Minnehaha Creek Emergent Plants Four dominant emergent plant species were observed in a 6.1 mile stretch of the lower Minnehaha Creek corridor in the September of 2012 survey. Flowering rush was the most common emergent plant followed by Sagittaria, bulrush, and cattails. Most of the flowering rush sites were clustered in two areas, one was south of Hiawatha Avenue and the other was a stretch of mostly dry stream bed below the Minnehaha Falls. Nearly all the sites where flowering rush was observed were dominated by sand or silty-sand sediments. In 2015, flowering rush was found less frequently. Comparing results from 2009, 2012, and 2015 indicate flowering rush does not seem to have spread to new sites. A majority of the flowering rush in 2009, 2012, and 2015 was found just west of Hiawatha Avenue in the Longfellow Gardens area. Several patches consisting of more than 100 stems were observed. One other site was found with a few individual stems above the Minnehaha Falls. No flowering rush was found below the Minnehaha Falls or above the Lake Nokomis outlet in Summary of emergent plant sites found in Lake Minnetonka and Minnehaha Creek in surveys for 2009, 2012, and (MnDNR) Lake Minnetonka Surveys 2012 (125 mi of shoreline) (MnDNR and MPRB) Minnehaha Creek Surveys (4 miles in 2009) (6.1 miles in 2012) (22 miles in 2012 (BWS) Flowering rush Sagittaria ND ND 17 ND Bulrush ND 31 ND ND 13 ND Cattails ND 166 ND ND 10 ND All Sites (BWS) A pictorial of Minnehaha Creek corridor conditions from Grays Bay (the source) to the end where it discharges to the Mississippi River is shown in Appendix A. References McComas, S. and J. Stuckert Flowering rush survey of Lake Minnetonka and lower portion of Minnehaha Creek. Hennepin County, Minnesota in Prepared for MCWD, Minnetonka, MN. Appendix B - iv