Aquatic Plant Point-Intercept Survey for Forest Lake, Washington County, 2013

Transcription

1 Example of Aquatic Plants sampled in July 2013 on Forest Lake Aquatic Plant Point-Intercept Survey for Forest Lake, Washington County, 2013 Point-Intercept Aquatic Plant Survey: July 11 and 12, 2013 Prepared for: Comfort Lake/Forest Lake Watershed District Forest Lake, Minnesota Prepared by: Steve McComas Blue Water Science St. Paul, MN February 2014

2 Aquatic Plant Point-Intercept Survey for Forest Lake, Washington County, 2013 Summary An aquatic plant point-intercept survey (250 meter spacing between points) was conducted on July 11-12, 2013 on Forest Lake (2,271 ac) by Blue Water Science to characterize conditions of native plants. The coverage of native plants is shown in Figure S-1. Native plants grow out to a water depth of about 12 feet and cover approximately 1,173 acres. The dominant plant in the survey was chara followed by coontail. About 60 acres around Forest Lake were treated for curlyleaf pondweed earlier in the summer. In the July survey, the effects of the treatment had occurred. However, curlyleaf pondweed had resprouted and grew out to about 12 feet of water depth and was found at 21 sample sites scattered around the lake. It did not produce heavy growth conditions this late in the year. Figure S-1. Native aquatic plant coverage of Forest Lake on July 11-12, Key: Green shading = light growth, yellow shading = moderate growth, and red shading = heavy growth. -i-

3 Forest Lake has a good diversity of aquatic plants, with 17 submerged species (includes curlyleaf pondweed) and two water lily species. A summary of plant occurrence and relative densities is listed in Table S-1. The most common plant in the lake is chara followed by coontail. Both of these plants are desirable species to have in a lake. Table S-1. Forest Lake aquatic plant occurrences and densities for the July 11-12, 2013 survey. Density ratings are 1-5 with 1 being low and 5 being most dense. Plants grew to a depth of 12 feet. Bulrush (Scirpus sp) Cattails (Typha sp) Spatterdock (Nuphar variegatum) White waterlily (Nymphaea sp) Marsh marigold (Bidens Beckii) Coontail (Ceratophyllum demersum) Chara (Chara sp) Elodea (Elodea canadensis) Star duckweed (Lemna trisulca) Northern watermilfoil (Myriophyllum sibiricum) Naiads (Najas flexilis) Curlyleaf pondweed (Potamogeton crispus) Whitestem pondweed (P. praelongus) Claspingleaf pondweed (P. Richardsonii) Stringy pondweed (P. sp) Flatstem pondweed (P. zosteriformis) Buttercup (Ranunculus sp) Sago pondweed (Stuckenia pectinata) Water celery (Vallisneria americana) Horned pondweed (Zannichellia palustris) Water stargrass (Zosterella dubia) Stations (n=97) % Occur Density Curlyleaf pondweed (top) and native plants (bottom) density and distribution for the July 11, 2013 pointintercept survey. Green shading = light growth and yellow shading = moderate growth. -ii-

4 Aquatic Plant Point-Intercept Survey for Forest Lake, Washington County, 2013 Introduction Forest Lake has an area of 2,271 acres with a littoral area of 1,531 acres (MnDNR). The maximum depth of Forest Lake is 37 feet. An aquatic plant point-intercept survey was conducted on July 11-12, 2013 to characterize the existing plant community and to scout for any occurrence of Eurasian watermilfoil. Results of this survey were also compared to a point-intercept survey conducted by the MnDNR in 2009 (full survey is shown in Appendix A). Figure 1. Contour map of Forest Lake (source: MnDNR). Forest Lake Aquatic Plant Point-Intercept Survey,

5 Methods A point intercept aquatic plant survey of Forest Lake was conducted by Blue Water Science on July 11 and 12, 2013, and 97 points were sampled out to 15 feet of water depth (Figure 2). The deepest depth of plant colonization in Forest Lake was out to 12 feet, although all sites out to 15 feet were sampled. Sample points were placed 250 meters apart on a grid that covered the lake. Each sample point was equal to 9.1 acres. At each sample point, a sampling rake was lowered into the water and a plant sample was taken. The plant species were recorded and the density of each species was assigned. Densities were based on the coverage on the teeth of the rake. Density ratings were from 1 to 5 with 1 being sparse and 5 being a matted nuisance. Based on these sample sites, plant distribution maps were constructed. Figure 2. Sample location map for the aquatic plant surveys conducted on Forest Lake. Green shading represents the littoral zone of Forest Lake. Forest Lake Aquatic Plant Point-Intercept Survey,

6 Curlyleaf pondweed densities are represented on a scale of 1 to 5 with 5 being densest. Light Growth Conditions Plants rarely reach the surface. Navigation and recreational activities are not generally hindered. Stem density: stems/m 2 Biomass: 0-50 g-dry wt/m 2 Estimated TP loading: <1.7 lbs/ac MnDNR rake sample density equivalent for light growth conditions: 1, 2, or 3. Moderate Growth Conditions Broken surface canopy conditions. Navigation and recreational activities may be hindered. Lake users may opt for control. Stem density: stems/m 2 Biomass: g-dry wt/m 2 Estimated TP loading: lbs/ac MnDNR rake sample density equivalent for moderate growth conditions: 2, 3 or sometimes, 4. Heavy Growth Conditions Solid or near solid surface canopy conditions. Navigation and recreational activities are severely limited. Control is necessary for navigation and/or recreation. Stem density: 400+ stems/m 2 Biomass: >300 g-dry wt/m 2 Estimated TP loading: >6.7 lbs/ac MnDNR rake sample density has a scale from 1 to 4. For certain growth conditions where plants top out at the surface, the scale has been extended: 4.5 is equivalent to a near solid surface canopy and a 5 is equivalent to a solid surface canopy. Heavy growth conditions have rake densities of a 4 (early to mid-season with the potential to reach the surface), 4.5, or 5. Forest Lake Aquatic Plant Point-Intercept Survey,

7 Results Forest Lake has a good diversity of aquatic plants, with 17 submerged species (includes curlyleaf pondweed) and two water lily species. A summary of plant occurrence and relative densities is listed in Table 1. The most common plant in the lake is chara followed by coontail. Both of these plants can use nutrients from the water column and help keep lake phosphorus concentrations down. Table 1. Forest Lake aquatic plant occurrences and densities for the July 11-12, 2013 survey. Density ratings are 1-5 with 1 being low and 5 being most dense. Plants grew to a depth of 12 feet. Bulrush (Scirpus sp) Cattails (Typha sp) Spatterdock (Nuphar variegatum) White waterlily (Nymphaea sp) Marsh marigold (Bidens Beckii) Coontail (Ceratophyllum demersum) Chara (Chara sp) Elodea (Elodea canadensis) Star duckweed (Lemna trisulca) Northern watermilfoil (Myriophyllum sibiricum) Naiads (Najas flexilis) Curlyleaf pondweed (Potamogeton crispus) Whitestem pondweed (P. praelongus) Claspingleaf pondweed (P. Richardsonii) Stringy pondweed (P. sp) Flatstem pondweed (P. zosteriformis) Buttercup (Ranunculus sp) Sago pondweed (Stuckenia pectinata) Water celery (Vallisneria americana) Horned pondweed (Zannichellia palustris) Water stargrass (Zosterella dubia) All Stations (n=97) Occur % Occur Density Curlyleaf pondweed (top) and native plants (bottom) density and distribution for the July 11, 2013 pointintercept survey. Green shading = light growth and yellow shading = moderate growth. Forest Lake Aquatic Plant Point-Intercept Survey,

8 Aquatic Plant Maps of Forest Lake from the July 11-12, 2013 Plant Survey Forest Lake Aquatic Plant Point-Intercept Survey,

9 Plant diversity was above average in Forest Lake with a total of 17 submerged aquatic plant species (Table 2). Chara was the most common plant followed by coontail and curlyleaf pondweed. Table 2. Aquatic plant occurrence and density for individual sample points in Forest Lake, July 11 and 12, Site Depth Bulrustails Cat- Spatter White Butter- Chara Clasp- CLP Coon- Elodea Flat- Horn Marsh Naiads NWM Sago Star Stringy Water Water Whitestem No Number (ft) dock Lilies cup ingleaf tail stem mari- gold duckweed celery stargrass plants species TD TD TD TD TD TD TD TD TD TD TD TD TD TD TD TD TD TD TD TD TD TD TD TD TD Forest Lake Aquatic Plant Point-Intercept Survey,

10 Table 2. Aquatic plant occurrence and density for individual sample points in Forest Lake, July 11 and 12, Site Depth Bulrustails Cat- Spatter White Butter- Chara Clasp- CLP Coon- Elodea Flat- Horn Marsh Naiads NWM Sago Star Stringy Water Water Whitestem No Number (ft) dock Lilies cup ingleaf tail stem mari- gold duckweed celery stargrass plants species 58 TD TD TD TD TD TD 79 TD 1 TD D TD D TD TD TD 1 TD TD TD TD TD TD TD Forest Lake Aquatic Plant Point-Intercept Survey,

11 Table 2. Aquatic plant occurrence and density for individual sample points in Forest Lake, July 11 and 12, Site Depth Bulrustails Cat- Spatter White Butter- Chara Clasp- CLP Coon- Elodea Flat- Horn Marsh Naiads NWM Sago Star Stringy Water Water Whitestem No Number (ft) dock Lilies cup ingleaf tail stem mari- gold duckweed celery stargrass plants species TD D Average occurrence (97 sites) (0-15 ft) % occurrence (0-15 ft) Figure 3. Examples of aquatic plants found in Forest Lake in July Forest Lake Aquatic Plant Point-Intercept Survey,

12 Flowering Rush: Flowering rush is a non-native aquatic plant with mostly emergent growth, but has a submerged form as well. It is established in Forest Lake. In the course of the pointintercept survey flowering rush did not show up at any of the sample points but the occurrence of flowering rush was noted. The distribution of flowering rush is shown in Figure 4. Flowering rush appears to be mostly confined in the middle to lower basins, however it was observed at three sites in the upper basin. The heaviest flowering rush growth is found on the western shoreline of the lower basin. It also appears flowering rush may be expanding in distribution compared to a MnDNR survey in 2008 (Appendix B). Figure 4. Locations of flowering rush in Forest Lake in 2013 are shown with blue dots (upper basin), yellow dots (middle basin), and red dots (lower basin). Forest Lake Aquatic Plant Point-Intercept Survey,

13 2009 and 2013 Point-Intercept Surveys: Aquatic plant point-intercept surveys were conducted on June 22, 2009 by the MnDNR (full report in Appendix A) and a recent point-intercept survey was conducted on July 11-12, 2013 by Blue Water Science. Both surveys used 250 meter spacing between points and sampled 97 sites out to 15 feet of water. Table 3. Forest Lake aquatic plant percent occurrences for 2009 (MnDNR) and 2013 (Blue Water Science) surveys June stations (MnDNR) 2013 July 11 and Stations (Blue Water Science) % Occur % Occur Bulrush (Scirpus sp) present 7 Cattails (Typha sp) -- 1 Duckweed (Lemna sp) 1 -- Spatterdock (Nuphar variegatum) 2 2 White waterlily (Nymphaea sp) 3 1 Marsh marigold (Bidens Beckii) 8 2 Coontail (Ceratophyllum demersum) Hornwort (Ceratophyllum sp) 4 -- Chara (Chara sp) Elodea (Elodea canadensis) 2 1 Star duckweed (Lemna trisulca) 3 4 Northern watermilfoil (Myriophyllum sibiricum) Naiads (Najas flexilis) 5 18 Nitella (Nitella sp) 5 -- Cabbage (Potamogeton amplifolius) 4 -- Curlyleaf pondweed (Potamogeton crispus) Variableleaf pondweed (P. diversifolius) 2 -- Illinois pondweed (P. illinoensis) 5 -- Whitestem pondweed (P. praelongus) 4 6 Claspingleaf pondweed (P. Richardsonii) 8 10 Stringy pondweed (P. sp) 2 8 Flatstem pondweed (P. zosteriformis) 20 4 Buttercup (Ranunculus sp) 4 1 Sago pondweed (Stuckenia pectinata) -- 1 Water celery (Vallisneria americana) Horned pondweed (Zannichellia palustris) Water stargrass (Zosterella dubia) 3 4 (Heteranthera dubia) Number of species A few changes may have occurred from 2009 to It appears coontail and naiads increased in distribution from 2009 to On the other hand, it appears flatstem and horned pondweeds may have decreased from 2009 to Chara and northern watermilfoil and several other species appear to have remained about the same. The aquatic plant community appears to be relatively stable with typical variation from year to year. Forest Lake Aquatic Plant Point-Intercept Survey,

14 APPENDIX A MnDNR Point-Intercept Survey

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