Restorative Lake Sciences West Spring Lake Road Spring Lake, Michigan Website:

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1 Eagle Lake 2016 Aquatic Vegetation & Water Quality Report & 2017 Management Recommendations October, 2016

2 Eagle Lake 2016 Aquatic Vegetation & Water Quality Report & 2017 Management Recommendations Restorative Lake Sciences West Spring Lake Road Spring Lake, Michigan Website:

3 Table of Contents Section 1: Eagle Lake Summary (2016)... 4 Section 2: Eagle Lake Water Quality Data (2016)... 5 Section 3: Eagle Lake Aquatic Vegetation Data (2016) Section 4: Management Recommendations for

4 Section 1 Eagle Lake 2016 Aquatic Vegetation & Water Quality Report & 2017 Management Recommendations The following Eagle Lake report is a summary of key lake findings collected in T he overall condition of Eagle Lake is ranked in the top 20% of developed lakes of similar size in the state of Michigan. In 2016, the water clarity ranged from feet. Some of this clarity is due to filtration of the water by Zebra Mussels; however, the majority of the clarity is due to coarse bottom sediment that does not create silty, turbid conditions when high wave or boat activity agitates the lake water. Additionally, the lake has enough nutrients (phosphorus and nitrogen) to support some algae and submersed aquatic plant growth, but the nutrient levels are considered moderate. Invasive species such as Eurasian Watermilfoil, Curly-leaf Pondweed, and Starry Stonewort are able to grow in moderate nutrient waters and thus are a challenge to the Eagle Lake ecosystem. However, in 2016, management of these plants was a success. Protection of the 23 native aquatic plant species is paramount for the health of the lake fishery and these plants should not be managed unless they are a nuisance to lakefront property owners and possess navigational and recreational hazards (i.e. canal areas). The lake did experience a high depletion of dissolved oxygen with depth during midlate summer which is common along inland lakes that stratifies. In late September dissolved oxygen ranged from mg/l and the water temperature varied by 3 F. During mid to late summer, the dissolved oxygen was 8.9 mg/l at the surface and 6.0 mg/l at 25 feet. Water temperatures varied by 8 F. Conductivity was moderate. Total phosphorus was moderate and total nitrogen was low. 4

5 Section 2 Eagle Lake Water Quality Data (2016) Did You Know? Eagle Lake has a maximum depth of 32 feet Water Quality Parameters Measured There are hundreds of water quality parameters one can measure on an inland lake but several are the most critical indicators of lake health. These parameters include water temperature (measured in F), dissolved oxygen (measured in mg/l), ph (measured in standard units-su), conductivity (measured in micro-siemens per centimeter-µs/cm), total dissolved solids (mg/l), secchi transparency (feet), total phosphorus, and total nitrogen (both in µg/l), chlorophyll-a (in µg/l), and algal species composition. Water quality was measured in the deep basin of Eagle Lake on September 28, Table 1 below demonstrates how lakes are classified based on key parameters. Eagle Lake would be considered mesotrophic (relatively productive) since it does contain ample phosphorus, nitrogen, and aquatic vegetation growth but has excellent water clarity and moderate algal growth water quality data for Eagle Lake are shown below in Table 2. Table 1. Lake trophic classification (MDNR). Lake Trophic Status Total Phosphorus (µg L -1 ) Chlorophyll-a (µg L -1 ) Secchi Transparency (feet) Oligotrophic < 10.0 < 2.2 > 15.0 Mesotrophic Eutrophic > 20.0 > 6.0 < 7.5 5

6 Table 2. Eagle Lake water quality parameter data collected over the deep basin on September 28, Depth ft. Water Temp ºF DO mg L -1 ph S.U. Cond. µs cm -1 Turb. NTU Total Dissolved Solids mg L -1 Total N mg L -1 Total Phos. mg L < Table 2. Eagle Lake water quality parameter data collected over the deep basin on September 28, Water Clarity (Transparency) Data Secchi transparency is measured with a specialized, weighed Secchi disk. Elevated Secchi transparency readings allow for more aquatic plant and algae growth. The transparency throughout Eagle Lake on September 28, 2016 was adequate (7.5 feet) to allow abundant growth of algae and aquatic plants in the majority of the littoral zone of the lake. Secchi transparency depends on the amount of suspended particles in the water (often due to windy conditions of lake water mixing) and the amount of sunlight present at the time of measurement. Other parameters such as turbidity (measured in NTU s) and Total Dissolved Solids (measured in mg/l) are correlated with water clarity and show an increase as clarity decreases. The Secchi transparency in Eagle Lake averages around 8.5 feet but is often as high as 28.0 feet in early spring (CLMP data). The turbidity and total dissolved solids in Eagle Lake were quite low at 1.0 NTU s and 82 mg/l, respectively during the late September, 2016 sampling event. Total Phosphorus Total phosphorus (TP) is a measure of the amount of phosphorus (P) present in the water column. Phosphorus is the primary nutrient necessary for abundant algae and aquatic plant growth. TP concentrations are usually higher at increased depths due to higher release rates of P from lake sediments under low oxygen (anoxic) conditions. Phosphorus may also be released from sediments as ph increases. Fortunately, even though dissolved oxygen concentrations in Eagle Lake are low during summer stratification, the TP levels are relatively low at the surface and moderate at the bottom and ranged from mg L -1. This would not lead to high nutrient concentrations known as internal loading. 6

7 ph Most Michigan lakes have ph values that range from 6.5 to 9.5. Acidic lakes (ph < 7) are rare in Michigan and are most sensitive to inputs of acidic substances due to a low acid neutralizing capacity (ANC). Eagle Lake is considered slightly basic on the ph scale. The ph of Eagle Lake in late September of 2016 ranged from S.U. which is ideal for an inland lake. Lakes with a mineral (marl) bottom tend to have higher ph values. Conductivity Conductivity is a measure of the amount of mineral ions present in the water, especially those of salts and other dissolved inorganic substances. Conductivity generally increases as the amount of dissolved minerals and salts in a lake increases, and also increases as water temperature increases. The conductivity values for Eagle Lake were moderate and ranged from µs/cm. Severe water quality impairments do not occur until values exceed 800 µs/cm and are toxic to aquatic life around 1,000 µs/cm. Fortunately, the concentrations have declined over the past few years. Chlorophyll-a and Algal Species Composition Chlorophyll-a is a measure of the amount of green plant pigment present in the water, often in the form of planktonic algae. High chlorophyll-a concentrations are indicative of nutrient-enriched lakes. Chlorophyll-a concentrations greater than 6 µg L -1 are found in eutrophic or nutrient-enriched aquatic systems, whereas chlorophyll-a concentrations less than 2.2 µg L-1 are found in nutrient-poor or oligotrophic lakes. The measured chlorophyll-a concentration in Eagle Lake in late September of 2016 was 3.0 µg L -1, which is close to the mean CLMP data values. The algal genera were determined from composite water samples collected over the deep basin of Eagle Lake in 2016 were analyzed with a compound bright field microscope. The genera present included the Chlorophyta (green algae; Figure 1): Scenedesmus sp., Haematococcus sp., Chlorella sp., Euglena sp., Cladophora sp., Pediastrum sp., Radiococcus sp., Gleocystis sp., Pandorina sp., and Chloromonas sp. The Cyanophyta (blue-green algae; Figure 2): Oscillatoria sp., the Bascillariophyta (diatoms; Figure 3): Synedra sp., Navicula sp., Fragilaria sp., Cymbella sp., and Tabellaria sp. The aforementioned species indicate a diverse algal flora and represent a good diversity of alga with an abundance of diatoms that are indicative of great water quality. 7

8 Figure 1. A Green Alga Figure 2. A Blue-Green Alga Figure 3. A Diatom 8

9 Section 3 Aquatic Vegetation Data (2016) Status of Native Aquatic Plant Species in Eagle Lake The native aquatic vegetation present in Eagle Lake is essential for the overall health of the lake and the support of the lake fishery. The May 6, 2016 survey determined that there were a total of 23 native aquatic plant species in Eagle Lake. These include 16 submersed species, 2 floating-leaved species, and 5 emergent species. This indicates a very high biodiversity of aquatic vegetation in Eagle Lake. The overall % cover of the lake by native aquatic plants is low relative to the lake size due to the great mean depth and thus these plants should be protected unless growing near swim areas at nuisance levels. A list of all current native aquatic plant species is shown below in Table 3. The most dominant aquatic plant species included: 1) Thin-leaf Pondweed (Figure 4) which has long, thin, thread-like leaves that attached to a vertical stem both of which are a light beige in color. 2) The macro-alga Chara (Figure 5) which has a skunky odor and lies on the lake bottom, and Wild Celery (Figure 6) which has long, strap-like green leaves that may reach the lake surface. Wild Celery can become a nuisance in shallow areas but the seeds serve as favorable waterfowl food. When the plants fertilize in late summer, a prominent coil is produced on the plant. 9

10 Figure 4. Thin-leaf Pondweed Figure 5. Chara, the macro alga Figure 6. Wild Celery 10

11 Table 3. Native aquatic plant species in Eagle Lake, Cass County, MI (2016). Aquatic Plant Species and Code Aquatic Plant Common Name % Cover in Littoral (Shallow) Zone of Eagle Lake (2016) Chara vulgaris (macroalga) Muskgrass 3.3 Potamogeton pectinatus Thinleaf Pondweed 3.9 Potamogeton gramineus Variable-leaved Pondweed 0.1 Potamogeton zosteriformis Flat-Stem Pondweed 1.4 Potamogeton praelongus White-Stemmed Pondweed 0.1 Potamogeton robbinsii Fern-leaf Pondweed 0.5 Potamogeton illinoensis Illinois Pondweed 1.4 Potamogeton amplifolius Large-leaf Pondweed 0.4 Potamogeton natans Floating-leaf Pondweed 0.4 Vallisneria americana Wild Celery 2.9 Myriophyllum verticillatum Whorled Watermilfoil 0.9 Ceratophyllum demersum Coontail 0.5 Elodea canadensis Common Waterweed 1.4 Utricularia vulgaris Common Bladderwort 0.5 Najas guadalupensis Southern Naiad 0.7 Nymphaea odorata White Waterlily 0.6 Nuphar advena Yellow Waterlily 0.2 Typha latifolia Cattails 0.1 Scirpus acutus Bulrushes 0.3 Arrow arum Arrowhead 0.1 Decodon verticillatus Swamp Loosestrife 0.1 Pontedaria cordata Pickerelweed

12 Status of Invasive (Exotic) Aquatic Plant Species in Eagle Lake The May 6, 2016 whole-lake survey of 173 sampling points demonstrated that approximately 12 acres of invasive Eurasian Watermilfoil (Figure 7) was present in Eagle Lake. A treatment of those areas was conducted on May 18, 2016 by PLM with oversight by RLS. Also treated on May 18, 2016 were approximately 1.8 acres of nuisance invasive Curly-leaf Pondweed (Figure 8) and 10.7 acres of nuisance Starry Stonewort (Figure 9). Milfoil was treated with Renovate OTF, whereas Curly-leaf was treated with Aquathol-K and Starry Stonewort was treated with Komeen crystals. Another lake survey followed on July 14, 2016 which found 1.8 acres of new milfoil growth and 12.7 acres of new Starry Stonewort growth. Both were treated on July 26, 2016 by PLM with RLS oversight. The milfoil was again treated with Renovate OTF and the Starry Stonewort was treated with Komeen crystals. Both species have been tough to reduce given the unprecedented air and water temperatures in 2016 which provided ideal growth conditions. Figures show the treatment areas in 2016 and Figure 13 shows the general aquatic vegetation bio volume. A final aquatic plant inventory in late September determined that the majority of the treated locations were greatly reduced. In some of the shallow canals, the results were questionable due to photo degradation from sunlight. A spring 2017 survey will be needed to see if those areas die back over the winter.. 12

13 Figure 7. Eurasian Watermilfoil Figure 8. Curly-leaf Pondweed Figure 9. Starry Stonewort 13

14 Figure 10. EWM distribution in Eagle Lake, Cass County, MI (May, 2016). Figure 11. Starry Stonewort distribution in Eagle Lake, Cass County, MI (May, 2016). 14

15 Figure 12. Starry Stonewort & EWM distribution in Eagle Lake, Cass County, MI (July, 2016). Note the small areas of EWM in red and blue. Figure 13. Starry Stonewort & EWM distribution in Eagle Lake, Cass County, MI (May, 2016). Note: Blue=no vegetation; Green=low vegetation; Red=High vegetation. 15

16 Section 4 Management Recommendations for 2017 Continuous aquatic vegetation surveys are needed to determine the precise locations of EWM, Starry Stonewort, Curly-leaf Pondweed or other problematic invasives in and around Eagle Lake. These surveys should occur in late-may to early-june and again post-treatment in RLS will be present to oversee the treatments by PLM as in Due to the relative scarcity of native aquatic vegetation in Eagle Lake, the treatment of these species with aquatic herbicides is not recommended (one exception is the overgrowth of nuisance pondweeds and/or algae in the canals). The plan for 2017 includes the use of higher doses of systemic aquatic herbicides (such as triclopyr nearshore and 2,4-D offshore) for the milfoil that may be present and the previously found milfoil from the fall of 2016 (if it survives the winter). Nuisance pondweeds will respond well to Aquathol-K at 2 gallons per acre if present. Water quality parameters in the lake will also be monitored in 2017 by RLS lake scientists. In conclusion, Eagle Lake is a healthy lake with good aquatic plant biodiversity, good water clarity, moderate nutrients, and a healthy lake fishery. Management of the EWM, Starry Stonewort and other invasives as well as protection of the water quality are paramount for the long-term health of the lake. 16

17 Glossary of Scientific Terms used in this Report 1) Biodiversity- The relative abundance or amount of unique and different biological life forms found in a given aquatic ecosystem. A more diverse ecosystem will have many different life forms such as species. 2) Eutrophic- Meaning nutrient-rich refers to a lake condition that consists of high nutrients in the water column, low water clarity, and an over-abundance of algae and aquatic plants. 3) Mesotrophic- Meaning moderate nutrients refers to a lake with a moderate quantity of nutrients that allows the lake to have some eutrophic qualities while still having some nutrient-poor characteristics 4) Oligotrophic- Meaning low in nutrients or nutrient-poor refers to a lake with minimal nutrients to allow for only scarce growth of aquatic plant and algae life. Also associated with very clear waters. 5) Sedimentary Deposits- refers to the type of lake bottom sediments that are present. In some lakes, gravel and sand are prevalent. In others, organic muck, peat, and silt are more common. 17