Minnesota Dept. of Natural Resources Division of Fish and Wildlife

Section of Fisheries

Aquatic vegetation point intercept survey of Spectacle Lake (30-0135), Isanti County, Minnesota

July 10-11, 2007

Report by: Deb Sewell Fisheries Management Specialist Hinckley Area Fisheries Office

Field crew: Deb Sewell and Dan Wilfond

Summary An aquatic vegetation survey was conducted on Spectacle Lake (30-0135) on July 10-11, 2007. Submerged plants were found growing to a depth of 16 feet, although most species were found in water depths of 10 feet or less. Floating leaved and emergent vegetation were rare. Up to ten species of submerged vegetation were found at each site, with an average species diversity of 4.1. The most common species were muskgrass, northern watermilfoil, and broad leaved Potamogeton species (including variable and Illinois pondweed), which all occurred in over 50% of sample sites. Although non native Eurasian watermilfoil was discovered in Spectacle Lake just prior to this survey, it was not seen at any of the sample sites.

Introduction Spectacle Lake is a 240 acre lake located in western Isanti County in east central Minnesota (Figure 1). The lake is located in the Green Lake Brook drainage of the Rum River watershed (major watershed number 21) of the Mississippi River. Spectacle Lake has 157 acres under 15 feet in depth (65 percent of total lake area), with a maximum depth of 51 feet. Despite having a heavily developed shoreline (148 residences and 2 resorts in 3.7 shoreline miles), Spectacle Lake maintains good water quality, with Secchi disk readings averaging 10+ feet. Spectacle Lake has historically had a diverse aquatic plant community, with 17 emergent species and 26 submerged and floating leaved species documented in surveys (Table 1). Historical information on aquatic vegetation can be found in Fisheries lake surveys dating back to 1949. However, methods were not standardized until the 1996 survey, so quantitative comparisons are not possible with earlier data. Level of identification also varies considerably among the surveys. For example, in the 1976 survey the only submerged vegetation species listed were "Submerged pondweed (Potamogeton sp.)" and "Water milfoil (Myriophyllum exalbescens)". Permits for aquatic plant removal have been granted to lakeshore owners for recreational access. From 1991-2007, 19 permits (individual and multi party) were issued for application of herbicides. Since 2001, 14 permits have been issued for automatic mechanical weed control devices such as Weed Rollers™. In addition, all lakeshore owners are allowed to remove plants from a 2500 square foot area in front of their residence for recreational purposes without a permit. Vegetation survey objectives The purpose of this study was to establish baseline point-intercept data on species composition, abundance, and distribution in Spectacle Lake.

Methods A point intercept vegetation survey was conducted from July 10-11, 2007, according to methodology described by Madsen (1999) and the Minnesota Department of Natural Resources (2007). A Geographic Information System (GIS) was used to generate sample points in a 70 by 70 meter grid. Since previous reports had listed 18 feet as the maximum depth of vegetation growth, the 20 foot contour was used as a mask to eliminate points in deeper areas. 179 points were generated; of these, 29 were excluded during sampling when the extent of plant growth was determined to be no deeper than 17 feet. A Global Position System (GPS) unit (Garmin GPSMap 76) was used to navigate a boat to each sample point. Moderate winds on the survey dates required the 2 person crew to anchor the boat at each point. Once the boat's position was stable, depth was recorded using a depth finder or marked pole. Vegetation was observed on one side of the boat in an area approximately one meter square. A double headed garden rake was used to sample vegetation that could not be visually identified from the boat. The rake was thrown into the water 2-3 times and all plants on the rake were identified. Voucher specimens were collected only for those species the field crew could not positively identify in the field.

Results and discussion The deepest depth of plant growth was determined early in the survey to be 17 feet, and thereafter points with a greater depth were not sampled. Of the 150 points that were in the vegetated zone of the lake, all but two had vegetation present. Two thirds of the sample points occurred in depths of five feet or less; the 4-5 foot depth interval contained the largest number of points (Figure 2). In 2007, the aquatic plant community in Spectacle Lake was diverse, with an average of 4.1 species per sample point (Figure 4). A total of 19 species of plants were sampled; 14 were submersed species, 2 were floating leaf species, and 3 were emergents (Table 2). Some pondweeds (Potamogeton) were difficult to identify to species due to variability in growth and similar characteristics, and thus were lumped into genus-level groups. One of these groups, characterized by broad leaves, included P. gramineus (variable pondweed) and P. illinoensis (Illinois pondweed). The other group was characterized by narrow, threadlike leaves and are referred to as "narrowleaf pondweed". Floating leaf and emergent vegetation were rare, occurring in scattered sites on the east side of the lake. Muskgrass (Chara sp.), a macroalgae species, was the most common submersed species, occurring in 76% of sample points. Northern watermilfoil (Myriophyllum sibiricum or exalbescens) and variable/Illinois pondweed were each seen in over 50 percent of sample points.

Muskgrass and Robbins' pondweed (Potamogeton Robbinsii) were the only species found in 14 feet of water or deeper. Figure 3 shows the depth distribution of the common submersed aquatic plant species. Spectacle Lake has two non-native species, curlyleaf pondweed (Potamogeton crispus), and Eurasian watermilfoil (Myriophyllum spicatum). It is unknown how long curlyleaf pondweed has been in the lake. It was first recorded in the 2007 Fisheries lake survey, but because previous surveys occurred in late summer when curlyleaf pondweed senesces, it may have gone undetected. Curlyleaf pondweed can grow to nuisance levels, particularly in shallow, eutrophic basins with soft substrates, low densities of native plants and low water clarity (Valley et al 2004, Nichols 1999). If water clarity and abundance and diversity of native plants remains high in Spectacle Lake, we don't expect curlyleaf pondweed to become a nuisance. Nevertheless, curlyleaf pondweed, much like other invasive non-native plants, thrives in disturbed environments and will become more abundant if nutrient levels in Spectacle Lake increase. Eurasian watermilfoil was discovered in Spectacle Lake during a fish diversity study being conducted by DNR Fisheries Research three weeks prior to this survey. The non-native plant was documented at three scattered locations on the lake; however, no Eurasian watermilfoil was sampled at any of the 150 sample points, indicating a low abundance in the lake. One sample point was located near one of the sites where Eurasian watermilfoil was found, but that point had no vegetation, possibly from treatment or mechanical removal. Time limitations prevented the survey crew from looking specifically for Eurasian watermilfoil outside of survey points. Madsen (1998) documented a strong relationship between trophic status and dominance of Eurasian watermilfoil. Eurasian watermilfoil thrives in mesotrophic to eutrophic lakes (10-30 ppb total phosphorus). Spectacle Lake had a total phosphorus level of 20 ppb in 2006, so Eurasian watermilfoil has the potential to become abundant in the next few years. Once Eurasian watermilfoil enters a lake, it typically takes 2-3 years to dominate a given area of littoral zone (Madsen et al. 1991). In many lakes, Eurasian watermilfoil hits a period of peak abundance, typically 5-10 years, and then goes into decline (Smith and Barko 1990). In Spectacle Lake, Eurasian watermilfoil has the potential to displace native species, especially northern watermilfoil. However, there is also the potential for Eurasian watermilfoil to utilize areas greater than 16 feet in depth, where few plants now grow, creating additional vegetated habitat for fish and invertebrates.

Recommendations

Conduct annual point intercept surveys for the next four years to document increase of Eurasian watermilfoil.

Increase the number of sample points to at least 200 to provide a larger sample in all

depth zones.

Record depths and sample for vegetation at all points up to 20 feet in depth.

Collect voucher specimens for rare species or those not easily distinguishable from another species.

Map any extensive monospecific vegetation stands that may be encountered in future

surveys.

Develop a vegetation management plan for Spectacle Lake.

References Madsen, J.D. 1998. Predicting the invasion of Eurasian watermilfoil into northern lakes. US

Army Engineer Waterways Experiment Station, Technical Report a-99-2. Vicksburg, Mississippi.

Madsen, J. D. 1999. 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.

Madsen, J.D., J.W. Sutherland, J.A. Bloomfield, L.W. Eichler, and C.W. Boylen. 1991. The decline of native vegetation under dense Eurasian watermilfoil canopies. Journal of Aquatic Plant Management 29: 94-99. Minnesota Department of Natural Resources. 2007. Minnesota’s Sensitive Lakeshore Area

Identification Manual, a comprehensive wildlife conservation strategy for Minnesota lakeshores (version 0.9). Division of Ecological Services, Minnesota Department of Natural Resources.

Nichols, S.A. 1999. Distribution and habitat descriptions of Wisconsin lake plants. Wisconsin Geological and Natural History Survey, Bulletin 96. Madison. Smith, C.S. and J.W. Barko. 1990. Ecology of Eurasian watermilfoil. Journal of Aquatic Plant Management 28: 55-64. Valley, R.D., T.K. Cross, and P. Radomski. 2004. The role of submersed aquatic vegetation as habitat for fish in Minnesota lakes, including the implications of non-native plant invasions and their management. Minnesota Dept. of Natural Resources, Special Publication 160. St. Paul, Minnesota.

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Laurentian Mixed Forest

Prairie ParklandEastern Broadleaf

Forest

TallgrassAspen

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Spectacle Lake

Figure 1. Location of Spectacle Lake (30-0135), Isanti County, Minnesota.

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Figure 2. Depth distribution of vegetation sample points on Spectacle Lake.

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coontailRobbins' pondweedCanada waterweed

largeleaf pondweedIllinois/variable pondweed

characlaspingleaf pondweed

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sago pondweedbushy pondweed

Figure 3. Depth ranges of plant species sampled in Spectacle Lake, 2007.

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Diversity

Figure 4. Number of aquatic plant species present at sample points on Spectacle Lake.

Table 1. List of aquatic plant species that have been recorded in Spectacle Lake Common name Scientific name Survey years Emergent species (17 total) Arrowhead Sagittaria sp. A, C, D, E, F Blue Flag iris Iris versicolor E Cattail Typha latifolia B, C, D, E, F Giant burreed Sparganium eurycarpum D Hardstem bulrush Scirpus acutus A, B, C, D, E, F Jewelweed Impatiens capensis E Needlerush Eleocharis acicularis C Purple loosestrife Lythrum salicaria E Reed canary grass Phalaris arundinacea C, E Reed meadow grass Glyceria grandis E River bulrush Scirpus fluviatilis E Sedge Carex sp. C, D, E Spikerush Eleocharis smallii C, D Stiff wapato Sagittaria rigida C, D Swamp milkweed Asclepias incarnata E Threesquare Scirpus pungens G Water smartweed Polygonum amphibium C, D Submerged and floating leaf species (26 total) Berchtold's pondweed * Potamogeton Berchtoldi D Bushy pondweed Najas flexilis A, D, E, F Canada waterweed Elodea canadensis C, D, E, F Claspingleaf pondweed Potamogeton Richardsonii A, C, D, E, F Coontail Ceratophyllum demersum A, C, D, E, F Curlyleaf pondweed Potamogeton crispus E, G Eurasian watermilfoil Myriophyllum spicatum G Filamentous algae Class Chlorophyceae E Flatstem pondweed Potamogeton zosteriformis A, D, E, F Floatingleaf pondweed Potamogeton natans E Illinois pondweed Potamogeton illinoensis F Largeleaf pondweed Potamogeton amplifolius A, C, D, E, F Largesheath pondweed * Stuckenia vaginata D Muskgrass Chara sp. A, D, E, F Narrowleaf pondweed Potamogeton sp. C, E, F, G Northern watermilfoil Myriophyllum exalbescens A, B, C, D, E, F Nuttall's pondweed * Potamogeton epihydrus D Pondweed (unspecified) Potamogeton sp. B Robbins' pondweed Potamogeton Robbinsii E, F Sago pondweed Stuckenia pectinata A, D, E, F Small pondweed Potamogeton pusillus G Variable pondweed Potamogeton gramineus F, G Water stargrass Zosterella dubia F White waterlily Nymphaea tuberosa A, C, D, E, F Whitestem pondweed Potamogeton praelongius E, F Wild celery Vallisneria americana A, D, E Yellow waterlily Nuphar variegatum A, C, D, E, F * indicates species of questionable identification; no voucher specimens available A) 1949 Fisheries lake survey B) 1976 Fisheries lake survey C) 1986 Fisheries lake survey D) 1996 Fisheries lake survey E) 2006 Fisheries lake survey F) 2007 Fisheries point intercept vegetation survey G) 2007 Fisheries research sampling

Table 2. Aquatic plants present in Spectacle Lake type Common name Scientific name Frequency (%) submerged Muskgrass Chara sp. 76.0 Northern watermilfoil Myriophyllum spicatum 54.7 Illinois pondweed Potamogeton illinoiensis 54.7 Claspingleaf pondweed Potamogeton richardsonii 44.0 Flatstem pondweed Potamogeton zosteriformis 39.3 Robbins' pondweed Potamogeton robbinsii 32.0 Canada waterweed Elodea canadensis 26.7 Narrowleaf pondweed Potamogeton sp. 25.3 Largeleaf pondweed Potamogeton amplifolius 21.3 Whitestem pondweed Potamogeton praelongus 12.7 Coontail Ceratophyllum demersum 8.0 Sago pondweed Stuckenia pectinata 4.7 Bushy pondweed Najas flexilis 2.7 Water stargrass Zosterella dubia 0.7 floatingleaf White waterlily Nymphaea tuberosa 2.0 Yellow waterlily Nuphar variegatum 0.7 emergent Sessile fruited arrowhead,

stiff wapato Sagittaria rigida 2.7

Common cattail Typha latifolia 0.7 Hardstem bulrush Scurpus acutus 0.7

Appendix 1. Attributes of Spectacle Lake compiled from Fisheries Research investigations on Spectacle Lake, 2007. (Source: Ray Valley, MN DNR Fisheries Research Biologist) Lake: Spectacle; Isanti Co. Watershed size (acres) 860 Lake area (acres) 242 Landcover (acres; 2000) Urban 97.9 13.7Ag 263.1 36.9Grassland 42.3 5.9Water 145.4NA Forest 234.8 32.9Wetland 70.9 10.0Shrub 4.2 0.6 Aquatic Plant Diagnostics Max depth of contigous veg growth (m) 4.28 Avg. % biovolume < 5 m deep (+/- SD) 32% (11%) Avg. veg bed size (acres; geostatistics) 4.4 Fish IBI 78Notable intolerants Banded Killifish (Fundulus diaphanus) Blacknose shiner (Notropis heterolepis) Blackchin shiner (Notropis heterodon) Pugnose shiner (Notropis anogenus)

Appendix 2. Percent biovolume (percent of water column occupied by vegetation) of aquatic vegetation on Spectacle Lake, and sites where Eurasian milfoil was sampled in 2007. (Source: Ray Valley, MN DNR Fisheries Research Biologist)

Appendix 3. Spectacle Lake watershed boundary and land use. (Source: Ray Valley, MN DNR Fisheries Research Biologist)