Eurasian Watermilfoil Management Program and Water Quality Summary for White Bear Lake, Washington County, Minnesota, 2018

Transcription

1 Ramsey County Beach, White Bear Lake, June 4, 2018 Eurasian Watermilfoil Management Program and Water Quality Summary for White Bear Lake, Washington County, Minnesota, 2018 EWM Delineation Conducted on June 4, EWM Treatment: June 20, 2018, 69.9 acres EWM Assessment Conducted on August 23, 2018 Prepared for: White Bear Lake Conservation District November 2018 Prepared by: Steve McComas Blue Water Science St. Paul, MN 55116

2 Eurasian Watermilfoil Management Program and Water Quality Summary for White Bear Lake, Washington County, Minnesota, 2018 Summary White Bear Lake (MnDNR ID: ) is a 2,428 acre lake located in Washington County, Minnesota. An Eurasian watermilfoil delineation was conducted by Blue Water Science on June 4, 2018 (Figure 1). Milfoil was widely distributed in June, ranging from light to moderate growth. Moderate growth had the potential to produce heavy growth and areas with the potential to produce heavy growth were delineated for treatment. An herbicide application treated a total of 69.9 acres. A follow-up Eurasian watermilfoil assessment was conducted on August 23, 2018 to evaluate the status of Eurasian watermilfoil in the treated areas as well as other areas around the lake. The herbicide treatment was generally successful from the perspective that only a few acres of Eurasian watermilfoil had moderate growth based on the assessment survey. No heavy growth or surface matted conditions were observed. Figure 1. [left] EWM delineation map with treatment polygons for June 4, [right] The August 23, 2018 EWM assessment found mostly light to moderate EWM growth (shown with green dots = light growth, yellow dots = moderate growth, red dots = heavy growth, and black dots = no EWM growth) in the 69.9 acres treated in i-

3 EWM Assessment on August 23, 2018 A total of 69.9 acres were treated and 64 acres were evaluated as having fair, good, or excellent control. However, 5.8 acres (Treatment Areas 3 and 4) were considered to exhibit limited control although matted EWM was not observed. Native plant distribution did not appear to be hindered (Table 2). Table 1. Summary of herbicide treatment results for 11 areas totaling 69.9 acres for White Bear Lake in Density ratings are on a scale from 1 to 3 with 3 the heaviest. Herbicide Treatment Areas Acres Delineation (6.4.18) Assessment ( ) EWM Control Results % EWM (occurrence within treatment area) Average EWM Density % EWM (occurrence within treatment area) Average EWM Density Liquid Triclopyr ppm % 7/ % 2/ Fair Liquid Triclopyr ppm % 8/ % 3/8 1.0 Fair Liquid Triclopyr ppm % 8/ % 6/ Limited Liquid Triclopyr ppm % 6/ % 7/ Limited Liquid Triclopyr ppm % 13/ % 1/ Good Liquid Triclopyr ppm % 12/ % 2/ Good Liquid Triclopyr ppm % 6/ % 0/8 0 Excellent Depth Charge* % 4/ % 0/7 0 Excellent Liquid Triclopyr ppm % 2/ % 0/5 0 Excellent 2,4-D, 4 ppm % 3/ % 0/5 0 Excellent Liquid Triclopyr ppm % 4/ % 0/5 0 Excellent TOTAL 69.9 *Depth Charge: 2,4-D and flumioxazin at 2.0 ppm Table 2. Native plant occurrence and densities within treatment area. Density ratings are on a scale from 1 to 3 with 3 the heaviest. Treatment Areas Native Plants % (occurrenc e within treatment area) Native Plant Average Density Native Plants % (occurrenc e within treatment area) Native Plant Average Density 1 100% 12/ % 7/ % 5/ % 7/ % 7/ % 10/ % 6/ % 14/ % 18/ % 13/ % 12/ % 12/ % 5/ % 7/ % 4/ % 6/ % 3/ % 5/ % 4/ % 5/ % 4/ % 5/ ii-

4 Eurasian Watermilfoil Treatments from Eurasian watermilfoil was first observed with a single plant collected near a public dock on the west side of the lake in A history of Eurasian watermilfoil control measures is shown in Table 3. From 1991 through 1995, an aggressive EWM treatment program was implemented to try to stop the spread of EWM within White Bear Lake. The aggressive treatment approaches were discontinued after EWM had basically spread around White Bear Lake at mostly light to moderate growth with some patches of heavier growth. After 1995, there was a period of 13 years ( ) where Eurasian watermilfoil treatments were less than 20 acres (which includes shoreline treatments) per year. Since 2009, Eurasian watermilfoil has been more abundant and is reflected in an increase in treatment acreages. A graph of treatment areas from 1988 through 2018 is shown in Figure 2. Table 3. Eurasian watermilfoil treatment history in White Bear Lake. Year Herbicide (permitted acres) Mechanical (acres) Handpulling (acres) minimal Figure 2. Historical herbicide use in White Bear Lake from 1988 to iii-

5 Overlay of Treatment Areas Showing Persistent EWM Growth from 2010 to 2018 Figure 3. Overlay of treatment maps from iv-

6 White Bear Lake Proposed 2019 EWM Treatment Based on Treatments from Previous Years For EWM control in 2019 it is proposed to treat the persistent heavy growth areas early and then delineate the lake again in June to determine if additional areas of EWM treatment are needed. Areas of persistent growth and potential treatment are shown in Figure 5 and total about 62 acres. These areas have been treated at least 4 out of the last 7 years. A MnDNR permit application for these areas would be submitted in winter. Then EWM would be checked in late May or early June to verify its presence. If it is present in the polygon then that area would be treated. There would be a EWM assessment in August or September to assess EWM control. Figure 4. Proposed 2019 EWM treatment. -v-

7 White Bear Lake Water Quality Summary White Bear Lake Water Clarity and Lake Levels Through 2017: Secchi disc readings for 1969 through 2017 are shown in Figure 5. From 2007 through 2016, water clarity was not as good compared to the period of 2000 through Lake water levels have fluctuated over the years (Figure 6). Secchi Disc (meters) Figure 5. Secchi disc summer averages (from May-September, unless data are lacking) for White Bear Lake. ( data are from Ramsey County). White Bear Lake levels from Ordinary high water level ( feet) Figure 6. Lake levels for White Bear Lake. -vi-

8 Additional Information on the Eurasian Watermilfoil Management Program for White Bear Lake, Washington County, Minnesota, 2018 White Bear Lake, Washington County (ID: ) Lake Area: 2,428 acres (MnDNR) Littoral Area: 1,314 acres (MnDNR) Maximum depth: 83 ft (MnDNR) Project Setting White Bear Lake has a variety of native and non-native aquatic plants. The objectives of the 2018 aquatic plant delineation and assessment were to delineate treatment areas of Eurasian watermilfoil and then assess treatment effectiveness in the 69.9 acres that were treated with herbicides. Figure 7. USGS map of White Bear Lake, Washington County, Minnesota. White Bear Lake Eurasian Watermilfoil Management Program,

9 Methods Eurasian Watermilfoil Delineation and Assessment: Eurasian watermilfoil delineations were conducted by Blue Water Science with the assistance of Mike Parenteau on June 4, The delineations involved cruising around the entire lake and observing milfoil growth and sampling aquatic plants with rakes. A total of 273 sample sites were checked. Areas to be treated were selected based on the growth status of milfoil in late June, the known previous occurrence of milfoil and the importance for navigation and/or recreation in the area. An herbicide application was conducted by Lake Management Inc and a total of 69.9 acres were treated. A follow-up Eurasian watermilfoil assessment was conducted by Steve McComas, Blue Water Science, on August 23, 2018 to evaluate the effectiveness of the herbicide treatment for Eurasian watermilfoil control. A total of 97 sites were checked on the August 23, 2018 assessment. EWM density ratings used in the June delineation and August assessment are shown in the chart below. Chart of EWM Density Ratings for EWM Figure 8. Eurasian watermilfoil rake density ratings from 1 to 3. Native plants used the same rake fullness rating as well. White Bear Lake Eurasian Watermilfoil Management Program,

10 Results - June 4, 2018 EWM Delineation Figure 9. June 4, 2018 delineation map. Eleven areas were delineated for treatment in White Bear Lake Eurasian Watermilfoil Management Program,

11 EWM and Native Plant Results for Individual Sample Sites Table 4. EWM delineation on June 4, Treatment Area Site Depth (ft) Chara EWM CLP Cabbage Coontail Claspingleaf Elodea Fern Native No plants Treatment Area Site Depth (ft) Chara EWM CLP Cabbage Coontail Claspingleaf Elodea Fern Native No plants White Bear Lake Eurasian Watermilfoil Management Program,

12 Treatment Area Site Depth (ft) Chara EWM CLP Cabbage Coontail Claspingleaf Elodea Fern Native No plants Treatment Area Site Depth (ft) Chara EWM CLP Cabbage Coontail Claspingleaf Elodea Fern Native No plants Average Occurrence (273) White Bear Lake Eurasian Watermilfoil Management Program,

13 White Bear Lake Eurasian Watermilfoil Assessment, August 23, 2018 Figure 10. Location of the 16 treatment sites around White Bear Lake on August 23, White Bear Lake Eurasian Watermilfoil Management Program,

14 Table 5. EWM assessment on August 23, Treatment Area Way- Points Depth (ft) EWM EWM from surface Natives No plants Treatment Area Way- Points Depth (ft) EWM EWM from surface Natives No plants Average Occurrence (97) White Bear Lake Eurasian Watermilfoil Management Program,

15 Eurasian Watermilfoil Treatment Maps for (174 ac) 2011 (41.6 ac) 2012 (144 ac) 2013 (100 ac) 2014 (32.8 ac) 2015 (85 ac) 2016 (60.4 ac) 2017 (65.1 ac) 2018 (69.9 ac) Figure 11. Acres of treated EWM for White Bear Lake Eurasian Watermilfoil Management Program,

16 Potential Future Growth of Eurasian Watermilfoil in White Bear Lake Based on Lake Sediment Characteristics Eurasian Watermilfoil Growth Potential in White Bear Lake: Eurasian watermilfoil has been in White Bear Lake since Lake sediment sampling results from 1998, 2009, and 2010 have been used to predict lake bottom areas that have the potential to support light, moderate, or heavy Eurasian watermilfoil growth in the future. Based on the key sediment parameters of NH 4 and organic matter (McComas, unpublished), a table and map were prepared that predict what type of milfoil growth could be expected (Table 6 and Figure 12). The sediment nitrogen conditions in White Bear Lake range from low to moderate concentrations with high nitrogen levels found at 3 sites. Sediments over 10 ppm of nitrogen are candidates for heavy milfoil growth. It has also been found that Eurasian watermilfoil does not grow well in sediments with over 20% organic matter. Site 6, sampled in 2009, and Sites 13 and 14, sampled in 2010 have high organic matter and are not predicted to support heavy milfoil growth even though nitrogen is high. Eurasian watermilfoil may grow widely through the littoral area in White Bear Lake but it is predicted that it will not sustain extensive perennial nuisance matting conditions (which are defined as heavy growth conditions) on a long-term basis. Table 6. White Bear Lake sediment data and ratings for potential heavy EWM growth. Site Depth / 2010 NH 4 Conc (ppm) Organic Matter (%) <10 <0.6 or >20 Potential for Heavy EWM Growth Light (green) to Moderate (yellow) >10 >0.6 or <20 Heavy (red) 1998 Data Light Moderate Light Low Light Moderate Moderate Moderate Low Low Low Moderate Light Moderate Light Light Moderate Moderate Moderate Moderate Low Heavy Moderate Moderate Light Site Depth / 2010 NH 4 Conc (ppm) Organic Matter (%) <10 <0.6 or >20 Potential for Heavy EWM Growth Light (green) to Moderate (yellow) >10 >0.6 or <20 Heavy (red) 2009 Data Moderate Moderate Moderate Moderate Moderate Moderate Moderate 2010 Data Moderate Moderate Moderate Moderate Moderate Light Light White Bear Lake Eurasian Watermilfoil Management Program,

17 White Bear Lake Eurasian Watermilfoil Growth Potential Based on Lake Sediments Figure 12. Sediment sample locations are shown with squares (1998 data) and circles (2009 and 2010 data). The color indicates the potential for heavy Eurasian watermilfoil to occur at that site. Key: green = low; yellow = medium; red = high potential. White Bear Lake Eurasian Watermilfoil Management Program,

18 White Bear Lake Water Quality from : A summary of seasonal water quality averages from 4 sample sites from is shown in Table 7. The location of the sample sites is shown in Figure 13. Transparency has ranged from 3 to 4 meters at most of the sites from Chlorophyll has ranged from 3 to 7 ug/l over the same period. Total phosphorus appears to have increased stating in 2010 but it has not significantly influenced changes in water clarity or in chlorophyll. Table 7. Water quality data for 4 sites around White Bear Lake from 2005 through 2016 (June - September averages). (Source: Ramsey County). Secchi disc (m) Total phosphorus (ug/l) Chlorophyll a (ug/l) AVE AVE AVE Figure 13. Water quality sampling sites. White Bear Lake Eurasian Watermilfoil Management Program,