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Minnesota National Lakes Assessment Project:

Aquatic Macrophytes in Minnesota Lakes

This report is part of a series based on Minnesota’s

participation in U.S. Environmental Protection Agency’s 2007 National Lake Assessment

Jason Neuman

Minnesota Department of Natural Resources

May 2008

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Minnesota National Lakes Assessment Project:

Aquatic Macrophytes in Minnesota Lakes

ACKNOWLEDGEMENTS

NLAP study coordination: Steve Heiskary, Minnesota Pollution Control Agency (MPCA) & Michael Duval, Minnesota Department of Natural Resources (MDNR) MPCA (Environmental Analysis and Outcomes) sampling team leaders: Jesse Anderson, Steve Heiskary, Matt Lindon, and Kelly O’Hara (emphasis on water quality and sediment sample collection) MPCA student interns – David Tollefson and Monica Brooks MDNR (Section of Fisheries) sampling team: Paul Eiler, Mark Henry, Andy Levar, Dale Lockwood and Jason Neuman (emphasis on near-shore assessment, plant identification and benthic collection) U.S. Forest Service (sampling assistance in Superior National Forest): Jason Butcher, Brent Flatten, and Ken Gebhardt (coordination) Report author: Jason Neuman, MDNR Report Review: Pam Anderson and Steve Heiskary (Environmental Analysis and Outcomes) MPCA and Michael Duval (Fisheries) and David Wright (Ecological Services), MDNR

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Aquatic Macrophytes in Minnesota Lakes

Table of Contents

List of Tables ............................................................................................................................................2

List of Figures...........................................................................................................................................2

Introduction...............................................................................................................................................4

Background...............................................................................................................................................6

Methods ............................................................................................................................................……6

Results and Discussion ............................................................................................................................7

Summary and Conclusions ....................................................................................................................23

References...............................................................................................................................................25

List of Tables Table 1. Summary of plant data for all lakes combined ..................................................................8 Table 2. Summary of plant occurrence by transect from 2007 NLAP lakes .................................11 Table 3. Summary of maximum depth of rooted vegetation for NLAP lakes...............................13 Table 4a&b. Comparison of grid point intercept survey, standard lake survey and NLAP macrophyte surveys for two lakes..................................................................................................21 List of Figures Figure 1. Location of Minnesota’s NLAP lakes as surveyed in 2007 .............................................5 Figure 2. Map of 2007 NLAP lakes plant species richness ...........................................................10 Figure 3. Secchi transparency for NLAP lakes Figure 4. Maximum depth of rooted vegetation ............................................................................15 Figure 5. Floristic Quality Index....................................................................................................16 Figure 6a. Comparison of plant species list between survey techniques sorted by size................17 Figure 6b. Comparison of plant species list between survey techniques sorted by maximum depth ........................................................................................................................................................18 Figure 6c. Comparison of plant species list between survey techniques sorted by secchi disc depth...............................................................................................................................................18 Figure 6d. Comparison of plant species list between survey techniques sorted by latitude..........19 Figure 7. Species richness for MN lakes from standard lake surveys ...........................................20

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Introduction National Lakes Assessment Project (NLAP) Overview The United States Environmental Protection Agency (EPA) has a responsibility to assess the health of the nation’s water resources. One of the methods for assessment is statistically-based surveys. The survey of the nation’s lakes, conducted in 2007, is one of a series of water surveys being conducted by states, tribes, the EPA, and other partners. In addition to lakes, partners will also study coastal waters, wadable streams, rivers, and wetlands in a revolving sequence. The purpose of these surveys is to generate statistically-valid and environmentally relevant reports on the condition of the nation’s water resources of streams, lakes, wetlands and estuaries at nation-wide and regional scales. The goal of the Lakes Survey is to address two key questions about the quality of the nation’s lakes, ponds, and reservoirs: • What percent of the nation’s lakes are in good, fair, and poor condition for key indicators of

trophic state, ecological health, and recreation? • What is the relative importance of key stressors such as nutrients and pathogens? The sampling design for this survey is a probability-based network which provides statistically-valid estimates of the condition of all lakes with known confidence. It is designed using modern survey techniques. Sample sites are selected using a stratified-random design to represent the condition of all lakes across the nation and each region. A total of 909 lakes in the conterminous United States (U.S.) are included in the Lakes Survey. The sample set is comprised of natural and man-made freshwater lakes, ponds, and reservoirs greater than ten acres and at least one meter in depth located in the conterminous U.S. The typical sampling effort at each site includes a variety of samples (measurements) collected at a mid-lake index site (often over the deepest point in the lake) including: a two meter integrated sample for water chemistry, chlorophyll-a, microcystin and algal identification; oxygen and temperature profiles; zooplankton tow; and sediment core sample for diatom reconstruction of total phosphorus (based on top and bottom slices from the core) and surface sediment sample for mercury. In addition, ten random near-shore sites are qualitatively assessed for various littoral and riparian habitat-related measures and a sample for a bacterial indicator was collected. Further details on the survey including methods, parameters measured, and statistical design may be found on the EPA NLAP Web page at: http://www.epa.gov/owow/lakes/lakessurvey/ . Minnesota’s NLAP Overview Minnesota’s 2007 NLAP effort was led by the Minnesota Pollution Control Agency (MPCA) and Minnesota Department of Natural Resources (MDNR). Various other collaborators were engaged in this study as well including the U.S. Forest Service (USFS), Minnesota Department of Agriculture (MDA), and U.S. Geological Survey (USGS). MPCA and MDNR combined on initial planning of the survey and conducted the sampling, which took place in July and August for most lakes. USFS staff were instrumental in sampling of remote lakes in the Boundary Waters Canoe Area Wilderness (BWCAW).

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Minnesota received 41 lakes as a part of the original draw of lakes for the national survey – the most of any of the lower 48 states. Minnesota chose to add nine lakes to the survey to yield the 50 lakes needed for statistically-based statewide estimates of condition (Figure 1). In addition to the 50 lakes, several reference lakes were later selected and sampled by EPA as a part of the overall NLAP effort. Data from the reference lakes provide an additional basis for assessing lake condition as a part of NLAP. Minnesota included several value-added measurements to the survey of lakes. Examples of these add-ons are: pesticide samples (in conjunction with the MDA); water mercury (in conjunction with USGS); sediment samples for analysis of metals, trace organics and other parameters; identification of macrophytes and maximum rooting depth of macrophytes at the random near-shore sites; and samples for microcystin at the index and a random near-shore site. Each of these add-ons and several of the standard assessments will be the subject of a series of reports that draw from the NLAP survey. This report will focus on results from the aquatic macrophyte survey that was conducted at the ten random near-shore sites. The results herein should be viewed as reflective of the macrophyte populations for the 48 lakes sampled based on the sampling approach used in the survey. They are not intended to provide a comprehensive assessment for the individual lakes nor a statistically-valid sample for all Minnesota lakes. Figure 1. Location of Minnesota’s NLAP lakes as surveyed in 2007.

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Report focus: Aquatic Macrophytes in Minnesota lakes Background Changes in aquatic vegetation can be used to monitor environmental changes and water quality in lakes (MDNR 1993). The presence or absence of sensitive plant species in lakes can act as indicators of water quality, while the total number of plant species can help determine the diversity and health of aquatic vegetation. The maximum depth of rooted aquatic vegetation can help to monitor long-term changes in water clarity. Because of these benefits, coupled with the opportunity to sample a randomly selected cross section of Minnesota lakes, information on near-shore aquatic macrophytes was collected to supplement EPA physical habitat assessment protocols as part of the national NLAP study. Methods Vegetation sampling was conducted within each of the ten EPA habitat plots described in section 5.0 of the Field Operations Manual (EPA 2007). These plots measured 15 meters along the shoreline and 10 meters lake-ward. The EPA field manual provides for qualitative assessment of aquatic vegetation (e.g., submerged, emergent, floating) occurring within the littoral zone of sample plots. The supplemental macrophyte sampling provided more detail on species or species groups occurring in the littoral zone of sample plots and further estimated maximum depth of rooted vegetation. Five different surveyors from MDNR Section of Fisheries conducted the plant surveys. Within each of the ten EPA habitat plots surveyors searched for aquatic plant species. Searches were conducted visually and with the aid of a garden rake. Each plant species found was identified and recorded for that plot. Any additional plant species found outside the 15 by 10 meter plots were also recorded separately. Plant species were identified to the lowest taxonomic level possible. For plants that are difficult to identify in the field, down to the species level, i.e. narrowleaf pondweeds, species groups were used. The Wisconsin field guide, “Through the Looking Glass” (Borman et al. 1997), was used as a reference for plant identifications. Scientific names were used to record taxa to avoid confusion associated with common names. The absence of plants were noted on the datasheet to differentiate from a transect that was not sampled for whatever logistical reason (e.g., lightning storm forced crews off the lake). At each of the ten EPA habitat plots an estimate of the maximum depth of rooted vegetation was made by navigating the boat from the near-shore habitat plot towards the center of the lake. At the approximate mid-point of each of the water depth intervals (below) a sample for rooted vegetation was taken with the use of a weighted double-headed garden rake with a length of rope attached to the handle for retrieval.

0.15 meter to 0.75 meter 0.76 meter to 1.5 meter 1.6 meter to 3.0 meter

3.1 meter to 4.6 meter 4.7 meter to 6.1 meter 6.2 meter to 7.6 meter

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A garden rake was used to sample only one time at each of the depth intervals along the transect. To avoid surveyor bias the garden rake was tossed from the same side of the boat each time. If rooted vegetation was found on the garden rake, samples were again taken at the next stratum until no vegetation was recovered on the rake. Water depth was determined either by the use of a graduated sounding rod or sonar depth finder. The depth stratum of maximum rooted vegetation was then recorded for each sampling plot. Additionally at each of the depth intervals, it was recorded whether strongly rooted plants, weakly rooted plants (e.g., Coontail, Bushy pondweed, and macroalgae like Chara and Nitella) or both were present. Results and Discussion Plant sampling was conducted between June 25, and August 22, 2007. A total of 40 aquatic plants species were identified in 48 lakes sampled with the supplemental plant protocols. Of the 40 plant species identified, 22 were submerged species, three were floating leaf, three free-floating, and twelve were emergent. Table 1 contains a list of species and frequency of occurrence as a percentage of the total number of sampling plots for all 48 lakes combined. This provides a reflection of the relative occurrence of these species based on this state-wide sample of 48 lakes and the survey technique employed. The three most commonly observed species were all submerged and included: bushy pondweed (Najas flexilis) 37 percent, coontail (Ceratophyllum demersum) 37 percent, and sago pondweed (Stuckenia pectinata) 35 percent. The most common floating leaf plant was white waterliliy (Nymphaea odorata) 28 percent, while the most frequently observed emergent species was common cattail (Typha Spp.) in 28 percent of all sampling plots. The least frequently sampled species of plant was threesquare bulrush (Scirpus pungens) found in only 0.2 percent of sampling plots. Nearly ninety-seven percent of all sample plots had at least one species of aquatic plant present. Eurasian water milfoil Myriophyllum spicatum and curly-leaf pondweed Potamogeton crispus were only observed in 2.0 and 4.7 percent of all sampling plots respectively. Eurasian water milfoil was observed in only three of the 48 lakes sampled and it was the dominant submerged aquatic macrophyte in only one lake (Nokomis) where it was identified in 100 percent of the sampling plots. In the other two lakes where Eurasian water milfoil was observed (Snail and Norway), the invasive was not a dominant member of the plant community and was not found in any of the ten sampling plots, having only been observed in areas of the lake outside the plots. Curly-leaf pondweed was not observed in Mayo, Pickerel, Nest, Norway, Eagle, Upper Sakatah, or Nokomis during 2007 NLAP macrophyte sampling. However, MDNR staff in previous investigations had identified the exotic invasive in each of these lakes. Additionally, curly-leaf pondweed was discovered in three lakes where it had not been previously documented to occur. These lakes included: August, Pelican, and Woodcock Lakes. It should be noted that the observed distribution and abundance of curly-leaf pondweed was influenced by the fact that sampling was conducted after curly-leaf reaches peak abundance, which in Minnesota is usually by mid-June. For this reason, curly-leaf pondweed was not a dominant part of the plant community in any of the lakes where it was found, and was not observed outside the sampling plots at the time of the NLAP surveys.

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Table 1. Summary of plant taxa occurrence (based on un-weighted summaries of the raw data) as percentage of plots for all lakes combined and coefficient of conservatism value for each taxa. C values range from 1-10. Low values indicate taxa is tolerant to disturbance.

Life Form Scientific name Common name % Frequency of

Occurrence Coefficient of

conservatism “C” Utricularia vulgaris Bladderwort 11.2% 7Najas flexilis Bushy pondweed 37.3% 6Ranunculus sp. Buttercup 0.4% 6Elodea canadensis Canada waterweed 9.8% 3Vallisneria americana Celery 17.8% 6Chara sp. Chara (muskgrass) 19.6% 7Potamogeton richardsonii Clasping leaf pondweed 12.7% 5Ceratophyllum demersum Coontail 36.5% 3Potamogeton crispus Curly-leaf pondweed 4.7% 0Myriophyllum spicatum Eurasian Milfoil 2.0% 0Potamogeton zosteriformis Flat-stem pondweed 26.5% 6Potamogeton natans Floating-leaf pondweed 12.7% 5Potamogeton illinoensis Illinois pondweed 10.8% 6Potamogeton amplifolius Large-leaf pondweed 10.2% 7Megalondonta beckii Marigold 3.1% 8Potamogeton sp. Narrowleaf pondweed 23.5% 7Myriophyllum sibiricum Northern milfoil 27.3% 7Potamogeton robbinsii Robbin's pondweed 4.3% 8Stuckenia pectinata Sago pondweed 35.1% 3Zosterella dubia Star grass 6.7% 6Potamogeton gramineus Variable pondweed 10.2% 7

Submerged

Potamogeton praelongus White-stem pondweed 4.3% 8Brasenia schreberi Watershield 8.8% 7Nymphaea odorata White waterlily 28.2% 6Floating Leaf Nuphar variegata Yellow waterlily 27.3% 6Spirodela polyrhiza Greater Duckweed 2.4% 5Lemna minor Lesser Duckweed 5.3% 5Free Floating Lemna trisulca Star Duckweed 9.8% 6Sagittaria sp. Arrowhead 17.3% 5Scirpus sp. Bulrush 20.2% 5Sparganium spp. Burreed spp. 4.9% 6Phragmites australis Cane 1.8% 1Typha spp. Cattail 28.2% 1Sparganium eurycarpum Giant Burreed 1.2% 5Asclepias incarnata Marsh Milkweed 0.2% 0Carex spp. Sedge spp. 20.6% 0Eleocharis sp. Spikerush 7.8% 5Equisetum fluviatile Swamp Horsetail 5.1% 7Scirpus pungens Threesquare Bulrush 0.2% 5

Emergent

Zizania aquatica Wild rice 8.4% 8

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Species distribution can be measured by how often a particular species is found in random sampling plots located throughout a lake. The frequency of occurrence of a plant species can be used as a quantitative method for documenting changes in vegetation distribution over time (i.e. if a species is present in 75 percent of all plots on a given lake initially, and only five percent of all plots five years later; MDNR 1993). This type of information is important for evaluating and measuring the effects of changes in watershed management or other factors influencing water quality and vegetation. Table 2 summarizes the frequency of occurrence of each of the 40 plant species identified in the selected NLAP lakes. The lakes are listed by columns and sorted from left to right starting with the lakes that have the greatest number of species. The various plant species are listed in rows and are categorized by life forms (i.e. submerged, floating leaf, free-floating, emergent). Pine Mountain Lake in Cass County had the greatest number of plant species identified by the survey (29), followed by Long Lake in Itasca County (28). South Lake in McLeod County had the fewest with only two species observed.

Figure 2 displays spatial trends in the number of plant species identified in each of the NLAP lakes across Minnesota in 2007. General trends in species richness increase from south to north peaking in the north central portion of the State before decreasing in the northeastern arrowhead region. The general trend of increasing species richness from north to south can be explained by water clarity (Figure 3), water chemistry and human disturbance and re-affirms observations made by Moyle (1956). The decrease in species richness in the northeastern portion of the state can be attributed to tannin stained waters and rocky substrate associated with Canadian Shield lakes located throughout the region.

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Figure 2. Map of 2007 NLAP plant species richness and number of species for each lake

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Table 2. Summary of plant occurrence by transect and floristic quality index for 2007 NLAP lakes

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Figure 3. Secchi transparency ranges for NLAP lakes. Based on single measurement from NLAP survey: July-August 2007.

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Because submerged aquatic macrophytes need sunlight for photosynthesis, the maximum depth of water to which rooted aquatic vegetation grows can be used as a way to monitor long term changes in water clarity. The maximum depth stratum of rooted aquatic vegetation on NLAP lakes ranged from 0.15-0.75 meters (m) up to 4.7-6.1 m. Seven lakes (Straight, Pickerel, Pine Mountain, Pelican, Darling, West Leaf, and Pebble) had weakly rooted aquatic vegetation like Chara and Nitella present at the highest depth stratum observed (4.7-6.1 meters). Since Chara and Nitella have the ability to establish themselves at greater depths than other submerged macrophytes, their presence was tracked separately from other more strongly rooted species. Secchi transparency in these lakes ranged from 1.5-2.5 m (Figure 3). South Lake (McLeod County) only had two emergent plant species (cattail and sedges) in the 0.15-0.75 meter depth stratum and had the lowest Secchi transparency in the survey at 0.1 m (Figure 3). Table 3 summarizes the percentage of lakes that contained weakly and strongly rooted aquatic macrophytes at each of the various depth stratums. Only 17 percent of lakes surveyed contained submerged plants that grew to a depth greater than 4.6 meters whereas, 65 percent contained rooted vegetation in depths greater than 1.5 meters of water. The absolute maximum depth of rooted vegetation growth was not verified with alternative sampling methods such as with use of underwater cameras or diving equipment, but the method of sampling used is assumed to be a reliable way to estimate such information. Table 3. Summary of maximum depth of rooted vegetation for NLAP lakes Depth Stratum (meters) 0.15 - 0.75 0.76 –1.5 1.6 – 3.0 3.1 – 4.6 4.7 – 6.1 Percent of lakes with strongly rooted vegetation 90% 75% 52% 2% 0%Percent of lakes with weakly rooted vegetation 10% 19% 13% 25% 17% Figure 4 displays the maximum depth stratum of rooted aquatic vegetation and the geographical distribution of the NLAP lakes. General trends are similar to species richness trends shown in Figure 2 in that maximum depth of rooted aquatic vegetation increases from south to north peaking in the north central portion of the state before decreasing into the northeast. These trends also closely parallel trends in Secchi disk readings taken from the NLAP survey (Figure 3). Floristic quality has been used by Nichols (1999) and Perleberg (2003) to assess the aquatic macrophyte communities of Wisconsin and Minnesota lakes. Floristic quality index (I) was calculated as: NCI = , where N = the number of native macrophyte taxa recorded in a waterbody during a macrophyte survey. C = Average coefficient of conservatism for a lake macrophyte community. Conservatism describes the degree to which a species will tolerate disturbance as well as their substrate preference, turbidity tolerance, rooting strength, primary reproductive means, and tolerance to water draw downs. A coefficient of conservatism, ranging from 1 to 10, was assigned to each macrophyte taxa (Table 1) based on the assignments made by Perleberg for Minnesota macrophyte taxa (Perleberg 2003). Taxa tolerant of disturbance received low values near 1 and intolerant taxa received higher values. The floristic quality index values were calculated for each of the NLAP lakes (Table 2) and ranged from a high value of 30 for Pine Mountain Lake to a low of 1 for South Lake. A map of the floristic quality index for NLAP

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lakes (Figure 5) shows spatial distribution of I values across Minnesota. Some plant taxa have less tolerance to human disturbance and are therefore good indicators of water quality. In most cases trends in floristic quality closely followed those of species richness and maximum depth of rooted vegetation. One exception was Okamanpeedan Lake in Martin County, near the Minnesota/Iowa border that had few numbers of observed plant taxa (4) but a relatively higher I value of 14 based on the presence of more intolerant plant taxa. Metrics like the floristic quality index can be a useful way to systematically evaluate the overall quality of aquatic macrophytes in a lake and make direct comparisons between different lakes across geographical regions. Figure 4. Maximum depth of rooted vegetation

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Figure 5. Floristic Quality Index for NLAP lakes

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To evaluate the effectiveness of the supplemental aquatic macrophyte protocols at characterizing plant communities, a comparison of plant data generated by the NLAP surveys was made between data from previous MDNR plant surveys. These previous surveys included two types of surveys, each with different protocols. The first of these survey types is the standard MDNR lake survey. With this technique surveyors identify aquatic plants along predetermined equidistant transects that extend perpendicularly from shore out to the maximum depth of rooted aquatic vegetation. Plants are sampled from within three meters on either side of the boat along a transect either visually or with the use of a double-headed garden rake. The number of transects sampled varies from 10 to 50 depending on lake size (MDNR 1993). Twenty-one of the 48 NLAP lakes had standard vegetation lake survey data available for comparison. These previous vegetation lake surveys date as far back as June 1993. However, 11 of the surveys were completed after the summer of 2003. A comparison of the number of species (Figure 6a, sorted by surface area) found that on average, the NLAP survey protocols identified only 71 percent of the number of plant species found using the standard vegetation lake survey transects on the same lake. In only one lake (Pine Mountain) did the NLAP survey identify more species than the standard lake survey. No apparent patterns were observed between the two methods relative to surface area, maximum depth, Secchi transparency and latitude (Figures 6a-d). However, increasing species richness with a corresponding increase in latitude was noted (Figure 6d). Figure 7 (Perleberg 2003) shows the statewide distribution of the number of species identified during standard lake surveys conducted by the MDNR from 1993-2000. Trends across Minnesota parallel those identified previously in Figure 2.

Figure 6. Comparison of plant species list between survey techniques. Lakes sorted by: a) surface area, b) maximum depth, c) Secchi depth, and d) latitude.

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The second type of plant survey that has been done in Minnesota to evaluate aquatic macrophytes is the grid point-intercept survey method. The grid point-intercept vegetation survey methodology follows that of Madsen (1999), and the technique has been used in Minnesota by the MDNR. The grid point intercept methodology is described in detail in Chapter 2 of “Minnesota Sensitive Lakeshore Area ID Manual” (MDNR 2008). In the grid point-intercept method, survey points are established throughout the vegetated zone on a grid using the Geographic Information System (GIS). The size of the littoral zone and the shape of the lake determine the number of points and the grid resolution. Within the vegetated zone, 150 to 250 points are sampled to ensure that commonly occurring species are adequately sampled. On most lakes, sample point resolution is 100 square meters. Sampling is conducted primarily from a boat and GPS units are used to navigate to each sample point. Surveyors navigate to within five meters of the survey point coordinates shown on the GPS unit. The boat operator maintains the position of the boat without anchoring and sampling is conducted from a pre-designated side of the boat. All plant species found within an approximate one square meter sample site are identified and recorded. A double headed, weighted garden rake attached to a rope is used to survey vegetation not visible from the surface (MDNR 2008). A relatively limited number of lakes in Minnesota have been sampled using the comprehensive grid point intercept survey. Only two of the 48 NLAP lakes had been sampled using the grid point-intercept sampling protocols and as such we cannot draw definitive conclusions on how the two techniques compare. A comparison of the number and types of species identified in Norway and Pine Mountain Lakes (Table 4a&b) shows that the two techniques produced very similar species lists with regard to submerged macrophyte species. For Norway Lake, curly-leaf

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Figure 7. Species richness for Minnesota lakes from standard lake surveys

pondweed was not identified in late August NLAP sampling. However, it was observed in previous June point intercept surveys in 2004 and 2006. As reported earlier, curly-leaf abundance in Minnesota reaches it peak in the early to mid part June before dieing back for the remainder of the summer.

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Table 4a. Comparison of point intercept and NLAP macrophyte survey results.

Norway Lake 14-Jun-04 6-Jun-06 22-Aug-07 Point Intercept Point Intercept NLAP

Eurasian watermilfoil X X X Muskgrass X X X Sago pondweed X X X Northern watermilfoil X X X Curly-leaf pondweed X X Flatstem pondweed X X X Clasping leaf pondweed X X X Bushy pondweed X X X Narrow-leaf pondweed X X X White-stem pondweed X Wild celery X X X Largeleaf pondweed X Canada waterweed X X Freis Pondweed X X Illinois pondweed X X X Coontail X X X Water Star Grass X X Greater bladderwort X X

SUB

MER

GED

White water buttercup X Yellow waterlily X X X Sedge Sp. X Floating leaf pondweed X X X Bulrush X X X Cattail X X X Spikerush X X X Giant Cane X X Arrowhead X X X EM

ERG

E/FL

OA

T

Wild rice X X TOTAL 24 24 21 Number of submerged 16 16 14

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Table 4b. Comparison of point-intercept, NLAP and standard lake survey results.

Pine Mountain Lake 1-Jul-07 10-Jul-07 Aug-05 Point NLAP Lake Survey

Bushy Pondweed X X X Bladderwort Group X X X Cattail Group X X X Canada Waterweed X X X Chara Muskgrass X X X Coontail X X X Flat-stem Pondweed X X X Floating-leaf Pondweed X X Fries Pondweed X Illinois Pondweed X X X Large-leaf Pondweed X X X Lesser Duckweed X X Narrow-leaf Pondweed Group X X X Northern Water Milfoil X X X Sago Pondweed X X Small Pondweed X Stonewort X Variable-leaf Pondweed X X X Water Moss X Water Stargrass X Water Celery X X X White-stem Pondweed X X X

SUB

MER

GEN

T

Water Buttercup Group X X Arrowhead Group X X X Giant Burreed X X X Grass Group (Gramineae) X Great Water Dock X Greater Duckweed X X Bulrush Group X X X Horsetail Group X X X Needlegrass X Sedge Group X Spikerush X X Star Duckweed X X X Three-square Bulrush X White Waterlily Group X X X Wild Rice X X X

EMER

GEN

T/ F

LOA

TIN

G

Yellow Waterlily Group X X X TOTAL 35 29 26 Number of submerged taxa 22 17 16

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It is important to note that even though the point intercept survey method is designed to be a comprehensive and repeatable plant survey technique, some less common species of plants may only occur in a limited area of a lake. The species list can still vary slightly when repeated later even when sampled using the same method. In Pine Mountain Lake a comparison between all three plant survey techniques is available and shows that the point intercept survey identified the greatest number of species followed by the NLAP survey while the MDNR lake survey identified the fewest number of species. In each case, comparisons between sampling techniques are affected by the level of skill possessed by the surveyor. Additionally, some discrepancies between recording different types of emergent wetland plants species could cause some of the observed disagreement between techniques. In most cases disagreement in the plant species identified in each of the various survey techniques arise from the less commonly observed submerged species and various emergent wetland plant species found. Therefore it seems advisable for the sake of comparison to focus more on the number of submerged aquatic macrophytes found in each of the different surveys. Summary and Conclusions Near-shore and shoreline conditions in Minnesota lakes were evaluated as part of the National Lakes Assessment Program with the EPA physical habitat assessment protocols. Minnesota elected to supplement this assessment with the identification of aquatic macrophytes and maximum rooting depth of macrophytes at the random near-shore sites. Based on our analysis of the 2007 NLAP macrophyte survey and previous aquatic macrophyte surveys on the same lakes in Minnesota the following observations were made:

1. The true abundance and distribution of curly-leaf pondweed, an exotic and invasive plant species, was not well represented by the supplemental macrophyte survey. Because of curly-leaf pondweed’s unique life history, the plant typically dies after June, which is before the NLAP macrophyte sampling occurred. The NLAP survey identified curly-leaf in only 42 percent of the lakes where the plant was previously identified and known to occur. Although curly-leaf pondweed was identified for the first time on three lakes as a result of NLAP macrophyte sampling, previous plant survey data was more than 12 years old on August Lake, 15 years on Pelican and no previous documented plant survey existed for Woodcock Lake. Because of curly-leaf’s potential to become a nuisance and its invasive nature, an early targeted sampling effort for curly-leaf pondweed would be necessary to effectively screen for it presence in a lake and evaluate its true abundance and distribution at time of peak abundance.

2. Ten random near-shore quadrants may not be sufficient to adequately detect the number

of plant taxa present in a lake and to evaluate plant community changes over time. When compared to both the grid point intercept (2 comparisons) and standard lake surveys (21 comparison) used by the MDNR, the NLAP macrophyte add-on sampled consistently fewer species of plants. Although some of the discrepancies may be a result of varying levels in the skill of the surveyor, conventional wisdom suggests that larger lakes would require more sampling effort to detect less abundant taxa, as well as to infer changes in the abundance and distribution of plants over time. Since plant distribution is not equal throughout a lake, sampling over a wide range of substrate types as well as areas with varying levels of human disturbance is desirable. Dependant on sampling goals, a

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potential change to the methodology would be to include the addition of non-random targeted sites that are conducive to aquatic vegetation growth (i.e. undisturbed and protected areas), which may improve the species list for a lake. However, if it is important to estimate the relative abundance of plant species, then the NLAP survey is likely only useful for estimating how often a particular species occurs within the very near shore (15 m) zone.

3. Additional changes in the NLAP macrophyte survey methods could include refinements

in the depth strata used for collecting maximum rooting depth of aquatic vegetation. To detect subtle changes in rooting depth of plants in turbid lakes in the southern portion of the state, depth strata should be no more than one meter wide. The addition of recording the actual maximum depth of rooted vegetation to the nearest 0.3 meter would also enable the direct comparison of such data collected during previous standard lake surveys.

4. Additional analysis of this data should be conducted once the overall NLAP dataset is

more complete. With the addition of water chemistry data spatial patterns in macrophytes could be assessed relative to patterns in lake trophic status and other factors that may influence plant growth and abundance. It may also be desirable to evaluate various patterns in plant abundance for shallow and deep lakes separately to allow for an improved assessment of how nutrients, water chemistry, transparency and other factors may influence plant abundance within these two categories of lakes. From this work it may be possible to develop cumulative distribution functions that might be used to help evaluate macrophyte population in other lakes that are assessed using the NLAP technique.

The desire to collect comprehensive data on macrophyte distribution and abundance to be used to evaluate and detect changes in water quality must be balanced with the effort and time required to collect and analyze such data. If this type of information is determined to be important for future assessments, additional dialog between the MPCA and MDNR will be necessary, to determine how to coordinate sampling efforts to improve efficiency so that sampling resolution is high enough to detect changes in plant composition over time.

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References Borman, S., R. Korth, and J. Temte. 1997. Through the looking glass … A field guide to aquatic plants. Wisconsin Lake Partnership, Stevens Point, WI. 248 pp. Nichols, S. A. 1999. Floristic quality assessment of Wisconsin lake plant communities with example applications. Jour. Lake and Reserv. Mgmt. 15(2): 122-144. 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. www.wes.army.mil/el/aqua Minnesota Department of Natural Resources. 1993. Manual of Instructions for Lake Survey Special Publication Number 147. Division of Division of Fish and Wildlife, Minnesota Department of Natural Resources. Minnesota Department of Natural Resources. 2008. Minnesota’s Sensitive Lakeshore Identification Manual: a conservation strategy for Minnesota lakeshores (version 1). Division of Ecological Resources, Minnesota Department of Natural Resources. Moyle, J.B. 1956. Relationships between the chemistry of Minnesota surface waters and wildlife management. Jour. Wildlife Manage. 30(3):303-320. Perleberg, D.J. 2003. Floristic Quality Assessment of Minnesota Aquatic Macrophyte Communities. Unpublished report. Minnesota Department of Natural Resources, Ecological Services Division, Brainerd. 7 pp. U.S. EPA. 2007. Survey of the Nation’s Lakes: Field Operations Manual. 841-B-07-004. USEPA, Washington DC http://www.epa.gov/owow/lakes/lakessurvey/pdf/lakes_field_op_manual.pdf