West Battle Lake. Aquatic Vegetation Survey County Highway 6 Detroit Lakes, MN (218)

Transcription

1 West Battle Lake Aquatic Vegetation Survey County Highway 6 Detroit Lakes, MN (218)

2 Lake: West Battle DOW Number: Date of inspection: June 26-29, 2017 County: Otter Tail Observers: Emelia Hauck, Laura Geyen Author of report: Emelia Hauck Date of report: August 7, 2017 Introduction West Battle (DOW ) is a large 5,565 acre lake located in Otter Tail County near Battle Lake, MN. According to the Department of Natural Resources, West Battle has a maximum depth of 108 feet and contains a littoral area of about 2,496 acres which permits light penetration and allows plant growth. West Battle is classified as a eutrophic lake as measured last in 2016 by mean secchi depth of approximately 12.9 feet throughout the lake. Total phosphorus and chlorophyll-a (values that provide a measure of the amount of algae in the water) are considered low with mean values 11.3 and 3.2 ug/l of West Battle (Table 1). Table 1. Water quality means over the last 10 years for West Battle. Lake Trophic State Mean Secchi depth Phosphorus (ug/l) Chlorophyll a (ug/l) (ft) West Battle Mesotrophic Objectives of Survey This survey describes the aquatic plant community of West Battle including: 1) Vegetation data to include; sample point number, depth, plant taxa observed, and the estimated abundance of each taxon. 2) Identification of taxa to the level of species when possible. 3) Frequency of occurrence of each taxon found, stating the number of points used as the denominator for the calculations. 4) Combined frequency of all aquatic plants found 5) Estimation of maximum depth of submersed vegetation 6) Estimation of abundance of species sampled using MN DNR ranking system 7) Distribution map for common species 8) Determination of any invasive aquatic plants 2

3 Methods The point-intercept survey followed methodology described by Madsen (1999). Geographic Information System (GIS) software was used to generate sample points across the littoral zone in 120 by 120 meter grid resulting in a total of 941 potential survey points on West Battle. In the field, all points were sampled and 10 were added. Vegetation was not found beyond 19 feet in depth. A Global Positioning System (GPS) unit was used to navigate the boat to each sample point. Water depths at each site were recorded in 1-foot increments using an electronic depth finder. A double-headed, weighted garden rake, attached to a rope (Figure 1 and 2) was used to survey vegetation. Vegetation that was found under the surface by use of the double-headed garden rake was assigned a number between 1 and 4; 1 being rare ( 1/3 of the rake head covered), 2 being scattered (>1/3 but 2/3 of the rake head covered), 3 being common (> 2/3 of the rake head covered), and 4 being abundant (plants over top of rake head). Plant identification followed Blickenderfer (2007). Figures 1 and 2. Double-headed, weighted garden rake, attached to a rope used to survey aquatic vegetation. Frequency of occurrence was calculated for each species as the number of sites in which a species occurred divided by the total number of sample sites. Frequency was calculated for all sampled locations as well as locations 15 feet or less. The average number of submersed plants per rake sample was calculated as the total number of plants sampled divided by the number of sample locations. Sampling points were also grouped by water depth and separated into 5 depth zones for analysis. Depth zones included less than 3 feet, 4 to 7 feet, 8 to 11 feet, 12 to 15 feet, and over 15 feet (Figure 8). 3

4 Summary On June 26-29th of 2017, 946 locations were observed and sampled for a point intercept survey of aquatic vegetation (Figure 3). Twenty-one different types of native plants were found across the lake. The weather was decent for the survey with cloudy skies, temperatures reaching 73 degrees and some wind. Figure 3. West Battle Point-Intercept Survey with site description, June 26-29, 2017 Three submerged species made up the majority of plants sampled in West Battle. Chara (Chara sp.) was sampled at 53.9% of all sites and 59.2% of sites less than 24 feet, Nitella (Nitella.) was sampled at 14.6% of all sites and 16% of sites less than 24 feet, and Greater Bladderwart (Utricularia vulgaris) was sampled at 9.5% of all sites and 10.5% of sites less than 24 feet. (Figures 4, 5, 6 and Table 2). 4

5 Figure 4. Locations with Chara present, West Battle, Otter Tail County, MN: June of

6 Figure 5. Locations with Nitella present, West Battle, Otter Tail County, MN: June 26-29,

7 Figure 6. Locations with Greater Bladderwort present, West Battle, Otter Tail County, MN: June 26-29,

8 Figure 7. Locations with Sago Pondweed present, West Battle, Otter Tail County, MN: June 26-29,

9 Figure 8. Locations with Variable Pondweed present, West Battle, Otter Tail County, MN: June 26-29,

10 Table 2. Aquatic plants surveyed from the northeast bay of West Battle, Otter Tail County, MN: June 26-29, West Battle All sampled sites All sites <24 feet Life Form Common Name Scientific Name Count Frequency % Frequency (%) SUMBMERGED - Greater Bladderwort Utricularia vulgaris % 10.5% ANCHORED - These plants grow primarily under the water Bushy Pondweed Najas Flexilis % 2.6% surface. Upper leaves may float Canada Waterweed Elodea canadensis 5 0.5% 0.6% near the surface and flowers Chara Chara sp % 59.2% may extend above the surface. Plants are often rooted or Claspingleaf Pondweed Potamogeton richardsonii 5 0.5% 0.6% anchored to the lake bottom. Coonail Ceratophyllum demersum % 2.0% Flatstem Pondweed Potamogeton zosteriformis % 2.0% Illinois Pondweed Potamogeton illinoensis % 1.9% Marigold Bidens Beckii 1 0.1% 0.1% Minor Bladderwart Utricularia minor 4 0.4% 0.5% Sago Pondweed Potamogeton pectinatus % 6.9% Variable Pondweed Potamogeton gramineus % 4.3% Whitestem Pondweed Potamogeton praelongus 7 0.7% 0.8% Fries Pondweed Potamogeton freisii 6 0.6% 0.7% Nitella Nitella sp % 16.0% FLOATING - LEAF -These plant leaves float on water and are anchored to the bottom of the lake. Floatingleaf Pondweed Potamogeton natans 2 0.2% 0.2% White Waterlily Nymphaea odorata 2 0.1% 0.2% Yellow Waterlily Nuphar variegata 1 0.1% 0.1% Star Duckweed Lemna triscula 2 0.2% 0.2% EMERGENT - These plants Bulrush Scirpus acutus % 2.8% extend well above the water Wild Rice Zizania aquatic surface and are usually found in 1 0.1% 0.1% shallow water, near shore. Total number of plants (species diversity for the lake) 21 Total number of plant occurrences 966 Total number of sites 946 Total number of sites <24 feet

11 Percent of sites with Vegetation Sampling occurred to a maximum depth of 24 feet; however, no plants were found to be growing beyond 20 feet of water. Plant abundance was greatest between nine and sixteen feet of water. As depths increased beyond that range, the presences of vegetation decreased and became less dense (Figure 9). Of the 946 sampled locations in West Battle, 85 sites had no vegetation present. A total of 861 sites were observed at locations with depths of 24 feet or less. 90% Plant Frequency vs. Water Depth 80% 70% 60% 50% 40% 30% West Battle Lake Frequency 20% 10% 0% < >24 Depth (ft) Figure 9. Frequency of vegetation vs. water depth, West Battle, Otter Tail County, MN: June 26-29, The average number of plants per rake sample on West Battle was 1.0 for all sampled depths and 1.1 for depths less than 24 feet. Six was the maximum number of species sampled at one location in West Battle while values of one and two species were sampled regularly (Figure 10). 11

12 Figure 10. Number of species present per site, West Battle, Otter Tail, County, MN: June 26-29,

13 Figure 11. Frequency of occurrence for aquatic plant species in West Battle, Otter Tail County, MN: June Discussion West Battle was found to be a relatively moderately deep lake for northwest Minnesota with a history of excellent water quality. The presence of plants and the depth at which one finds them is related to the water clarity. In areas where the sunlight does not reach the lake s bottom, there won t be plants present. The lake has an average clarity of 12.9 feet, and most plants were found in 8-13 feet of water (Figure 9). The Minnesota DNR lists the littoral area of West Battle to be approximately 45% of the total surface area. In general, the littoral area is approximated as the area of the lake that is 15 feet deep or less, and in this plant survey, no plants were found deeper than 20 feet. In addition, some plants are found more often in lakes with good water clarity, such as Chara and Nitella, which are actually a type of good algae. Chara was found at over half the sample sites on West Battle, and Nitella at 16% (Table 2, Figure 11). Chara has a gritty, bristly feel due to mineral deposits 13

14 on leaf surfaces; emits a strong musky odor when crushed (Figures 12, 18). Nitella is smooth (Figures 13, 17). They have very high ecological value in that they stabilize bottom sediments; provide food for waterfowl and cover for fish. They also support insects and other small aquatic animals, which are important foods for bluegills, small mouth bass, and largemouth bass. Figure 12. Chara. Bulrush is an emergent plant, meaning it sticks up out of the water. It is very important to a lake for many reasons. It provides spawning habitat for crappies, filters the water, and helps to prevent shoreline erosion by acting as a wave break. It is imperative to protect bulrush beds in lakes for these reasons. Larger leave plants, such as the pondweeds, are important spawning and hiding areas for panfish. Figure 13. Nitella No invasive aquatic plants were found in West Battle Lake, which is great news. Vigilance and protection practices by residents can keep invasive plants out in the future. Figure 14. Bulrush. West Battle Lake has relatively low phosphorus levels in the lake and a very sandy bottom, which is likely why there weren t a lot of plants or plant diversity found in the lake. Protecting the lake from extra phosphorus inputs (runoff, septic systems) will keep the plant abundance in the lake low. Aquatic plant communities are important to a body of water because of their ability to maintain water clarity and good fish habitat. Plants in all lakes lock up nutrients in their tissues which limit algae growth keeping lakes clear and healthy. Aquatic plants produce oxygen throughout the water column as a byproduct of photosynthesis, which oxygenates the water column. Plants also help to keep the sediments stable at the bottom of the lake and prevent it from mixing into the water column. Tiny invertebrates called zooplankton eat algae and use plants as a hiding place from predators such as perch, sunfish and crappies. Although there is a good diversity of plants on West Battle, the number of native species per sample point was very low (Figure 9). Unfortunately, if shallow areas of the lake aren t taken care of, the water can become green and murky (switch to the turbid state). If large areas of plants are removed, the sediments can get churned up and nutrients are released. If there are fewer plants to use the nutrients, the algae will use the nutrients and multiply. At the time we surveyed West Battle, dense mats of filamentous algae had formed (figure 10 and figure 13). Once the water is "green" with dense algae, these lakes have mostly muck on the bottom instead of plants because the sunlight can't get through the dense algae to the bottom of the lake. Algaedominated shallow lakes are also not as high of quality habitat for fish and wildlife. If the plants are gone there is no place for aquatic animals to hide. The natural state of shallow lakes is to have abundant aquatic vegetation and clear water. 14

15 What Local Residents Can Do Leave large plant beds alone. Only clear a small area by your dock from swimming. Removal of large areas of plants destabilizes the sediment and causes phosphorus to come up to the surface of the lake and cause algae blooms. It also leaves that area open for invasive species to establish. Protect the lake from additional phosphorus by installing vegetative buffers along the lakeshore to slow and filter runoff. Protect the lake from additional phosphorus and harmful bacteria by properly maintaining your septic system and picking up pet waste. Learn what aquatic invasive plants look like, and check around your dock periodically throughout the summer. Have a couple people designated to check around the public accesses for any new invasive plants periodically throughout the summer. Future Plant Surveys Conducting an aquatic plant survey every 5-10 years is useful in monitoring plant community changes and detecting new aquatic invasive species. Native plant beds are crucial for fish spawning and habitat, so documenting any changes in native plant beds can help explain any change in the fish community. Plant Identification Plants in West Battle Lake that look similar to curly-leaf pondweed: Claspingleaf pondweed Illinois pondweed Variable pondweed The way to tell difference between these look-alikes and curly-leaf pondweed: serrated edges (Figure 15). Curlyleaf pondweed leaves have serrated edges like a butter knife. Also, curly-leaf does not wrap around stem (Claspingleaf does), is not pointed at the end (Illinois is), and branches out of a single central stem (unlike variable) Plants in West Battle Lake that look similar to starry stonewort: Chara Nitella The way to tell the difference between these look-alikes and starry stonewort: star-shaped bulbils (Figure 16). Starry stonewort has star-shaped bulbils and Chara and Nitella do not. Figure 15. Curly-leaf pondweed serrated edges. Figure 16. Starry stonewort with white star-shaped bulbils. 15

16 RMB Survey Photos Figure 17. Native Nitella in West Battle Lake, Otter Tail County, MN: June 26-29,

17 Figure 18. Chara and Bladderwort on West Battle Lake, Otter Tail County, MN: June 26-29,

18 Figure 19. Bladderwort on West Battle Lake, Otter Tail County, MN: June 26-29,

19 Figure 20. Sago Pondweed on West Battle Lake, Otter Tail County, MN: June 26-29,

20 Glossary chlorophyll-a: the pigment in plants that allows them to create energy from light. Measurement of chlorophyll-a is an indirect way of measuring the amount of photosynthesis done by algae. littoral: The zone in a lake where light can reach the bottom (usually 15 feet deep or less). mesotrophic: designation of a lake having a moderate amount of algae. percent frequency of aquatic plants: the percent of the total sites that have the specific aquatic plant. secchi: a measure of the cloudiness/clarity of the water. taxon: a taxonomic category such as genus or species. total phosphorous: an essential nutrient for plants and animals. Too much phosphorous (which can be introduced by fertilized lawns and fields, disturbed land areas, etc.) can have adverse effects, which include algae blooms, accelerated plant growth, and low dissolved oxygen. Literature Cited Blickenderfer, Mary A Field Guide to Identification of Minnesota Aquatic Plants. University of Minnesota Extension. Madsen, J. D Point intercept and line intercept methods for aquatic plant management. APCRP Technical Notes Collection (TN APCRP-M1-02). U.S. Army Engineer Research and Development Center, Vicksburg, MS. 20