Evaluation of aquatic plant control via automated mechanical roller system

Transcription

1 Evaluation of aquatic plant control via automated mechanical roller system T.L. Brandt 1 INTRODUCTION Canadarago Lake (N42 o 48.9, W75 o.4 ), 39 m (128ft) above sea level, is located in the towns of Exeter, Richfield, and Otsego, NY (Harr et al. 198). The Lake is dimictic and of glacial origin, with a maximum depth of 13 m (43 ft), a surface area of 76 ha (1,877 ac), and a watershed of 175 km 2 (43,24 ac). The lake has an extensive littoral zone, the shallow near-shore area, which supports abundant aquatic plant growth (Harr et al. 198). The plant community contains a mixture of native and exotic species, including starry stonewort (Nitellopsis obtusa), a highly invasive species of macroalgae. Starry stonewort was first documented in Canadarago Lake during a survey of the aquatic plant community conducted in 21 (Smith 211); it has come to dominate the plant community in the vicinity of the study site in the northwest end of the lake (Russel and Genco 215) (Figure 1). Invasive aquatic plants are often a nuisance for those residing around a lake. There are various management approaches to minimize the populations of these plants and their impacts on a lake while also attempting to sustain the native aquatic plant populations that help support a healthy lake ecosystem. Some methods that have been and are commonly used are hand and suction harvesting, benthic barriers, hydroraking and rotovating, dredging, introduction of herbivorous insects, mechanical harvesting, drawdown, introducing grass carp, aquatic herbicides, and shading with the use of chemical dyes (NYSFOLA 29). Other means of control include mechanical devices that impede the growth of plants within their reach one such device, The Lake Groomer, was purchased and installed by a property owner The Lake Groomer is advertised as a method to naturally manage the growth and buildup of aquatic weed and muck. The Groomer includes three 7-foot long rollers (covering a diameter of about 42 feet) that are intended to uproot aquatic plants and disturb sediment on the lake floor. A permit from the NYS Department of Environmental Conservation is required to operate the Lake Groomer (NYSDEC 218). The Lake Groomer was used on Canadarago Lake near a property owner s private dock on or near the date of 29 July 217. The NYSDEC permit to install the device specified that operation of the unit take place after 15 July, presumably to reduce impacts to fish spawning (T. Kuettel, permit holder, personal communication). The purpose of this study was to monitor the taxa, density and abundance of aquatic plants in the location of the Lake Groomer and provide insight on its effectiveness in the control of aquatic plant growth. METHODS Sampling locations were chosen using Google s application, My Maps. A 5ft x 5ft grid was laid over the study site, including the location of the Groomer (experimental sites) and the 1 SUNY Oneonta Biological Field Station Intern, summer 217.Current affiliation: SUNY Onoenta.

2 side of the dock that is not exposed to the Groomer (control sites). Sampling locations were created at grid line intersections (Figure 2). Study Site Figure 1. Location of study site at Canadarago Lake. A canoe was used to access sampling locations, which were located using the GPS application. Once the site was reached, the height of the aquatic plants at the intersect were measured using a weight attached to a measuring tape, and a rake toss was performed at each site; rake toss data were recorded using the abundance categories detailed in the Point Intercept Rake Toss Relative Abundance Method, presented in Table 1 (PIRTRAM) (Lord and Johnson 26). A double-headed rake on a rope was thrown from the site and pulled in once the hit the lake s bottom. The plants obtained from each toss were placed in a bag labeled with the site number and taken back to the lab for identification. The aquatic plants were then separated, identified, and assigned an abundance category. The abundance categories are assigned using the criteria listed in Table 1. An aerial photo was taken by a drone of the sampling site on Canadarago Lake at the conclusion of the study.

3 Figure 2. Screenshot of sample sites at Canadarago Lake on Google s application MyMaps.

4 Dry Weight (g/m^2) Table 1. Biomass range estimates of plants by species, utilizing PRTRAM rake toss method. Abundance Field Measure Total Dry Weight (g/m 2 ) mid low high Z = no Categories plants Nothing T = trace plants Fingerful S = sparse plants Handful M = medium plants Rakeful D = dense plants Can t bring in boat RESULTS AND DISCUSSION The height of aquatic vegetation decreased at sites 13, 14, 15, and 16 following installation of the Lake Grooomer. These sites are within the radius of the Lake Groomer s rotating arm. Vegetation growth at Site 5 is low in comparison to the other sites due to traffic associated with a concrete boat launch. On 11 August 217, site 5 had been hand raked by a property user before a sample could be taken (Figure 7). In the sites reached by the Lake Groomer s arm (sites 13, 14, 15, and 16) it can be noted that plant diversity was not greatly affected, as Nitellopsis obtusa was the most prolific species (Figures 3-6) during the first two surveys. By the end of the study, the influence of the Lake Groomer on the plant community was evident (Figure 8). 45 July 13 Plant Community Potamogeton zosteriformis Potamogeton crispus Elodea canadensis Vallisneria americana Ceratophyllum demersum Najas spp. Zosterella dubia Nitellopsis obtusa Myriophyllum spicatum Utricularia sp. Figure 3. Vegetative biodiversity found via rake toss at the sample sites on Canadarago Lake on 13 July based on PIRTRAM categories. The Groomer was NOT active on this date. Site 5 is the location of the concrete boat launch where vegetation cannot easily take root. Sites 13, 14, 15, and 16 are the sites within the reach of the Lake Groomer s rolling arm.

5 Dry Weight (g/m^2) Dry Weight (g/m^2) 45 July 28 Plant Community Potamogeton zosteriformis Potamogeton crispus Elodea canadensis Vallisneria americana Ceratophyllum demersum Najas spp. Zosterella dubia Nitellopsis obtusa Myriophyllum spicatum Utricularia sp. Figure 4. Vegetative biodiversity found via rake toss at the sample sites on Canadarago Lake on 28 July based on PIRTRAM categories. The Groomer was NOT active on this date. Site 5 is the location of the concrete boat launch where vegetation cannot easily take root. Sites 13, 14, 15, and 16 are the sites within the reach of the Lake Groomer s rolling arm August 4 Plant Community Potamogeton zosteriformis Potamogeton crispus Elodea canadensis Vallisneria americana Ceratophyllum demersum Najas spp. Zosterella dubia Nitellopsis obtusa Myriophyllum spicatum Utricularia sp. Figure 5. Vegetative biodiversity found via rake toss at the sample sites on Canadarago Lake on 4 August based on PIRTRAM categories. Site 5 is the location of the concrete boat launch where vegetation cannot easily take root. Sites 13, 14, 15, and 16 are the sites within the reach of the Lake Groomer s rolling arm.

6 Plant Height (ft) Dry Weight (g/m^2) 45 August 11 Plant Community Potamogeton zosteriformis Potamogeton crispus Elodea canadensis Vallisneria americana Ceratophyllum demersum Najas spp. Zosterella dubia Nitellopsis obtusa Myriophyllum spicatum Utricularia sp. Figure 6. Vegetative biodiversity found via rake toss at the sample sites on Canadarago Lake on 11 August based on PIRTRAM categories. Site 5 is the location of the concrete boat launch where vegetation cannot easily take root. Sites 13, 14, 15, and 16 are the sites within the reach of the Lake Groomer s rolling arm /13/17 7/28/17 8/4/17 8/11/17 Pre-Installation Post-Installation Site Zone of lake groomer influence Figure 7. Comparison of plant height with site number at the four different dates sampled. The arm of the Lake Groomer impacted sites 13, 14, 15, and 16. Site 5 is the location of the concrete boat launch where vegetation cannot easily take root.

7 Figure 8. Aerial photo of the study site on Canadarago Lake. The path of the Lake Groomer s arm can be seen to the left of the dock. This path contains sites 13, 14, 15, and 16. The Lake Groomer did succeed in diminishing the presence of aquatic vegetation within its range of operation. Other methods of vegetation control or removal may prove to be more effective in terms of cost and restoration of the functional use of dock-side areas. While a permit from the NYS DEC is required for any plant control technique, hand harvesting requires no additional license and has been shown to be effective. The phone-based GPS application, My Maps, did not meet the mapping needs of this project; an alternative should be used if the project were to be duplicated. In the future, as an alternate means of locating the sample sites, reference points to permanent features could be established (on-shore and on the docks) by recording measured distances and compass headings between them. This would allow one to locate the sites without installing permanent markers in the water or relying on GPS or phone signal. A study of a longer duration may be more useful in determining the season-long effectiveness of the groomer, though placement of the device earlier in the growing season was, in this case, not permitted by NYS DEC. Additionally, an aerial photo of the sampling site should be taken before the Lake Groomer is placed in the water to better illustrate its impact on macrophyte growth.

8 REFERENCES Harr, T.E., G.W. Fuhs, D.M. Green, L.J. Helting, S.B. Smith and S.P. Allen Limnology of Canadarago Lake. In Bloomfield, J.A. (ed.) Lakes of New York State, Vol. III. Ecology of East-Central NY lakes. Academic Press, Inc., New York City, NY. Pp Lord, P.H. and R.L. Johnson, 26. Aquatic plant monitoring guidelines. NYSDEC Freshwater Wetlands Program. NYSFOLA. 29. Diet for a Small Lake: The Expanded Guide to New York State Lake and Watershed Management. 2 nd edition. New York State Federation of Lake Associations, Inc. Russel, R. and M. Genco Distribution of Nitellopsis obtusa (starry stonewort) in Canadarago Lake, NY. In 47 th Ann. Rept. (214). SUNY Oneonta Biol. Fld. Sta., SUNY Oneonta. Smith, T.F Canadarago Lake aquatic macrophyte survey. In 43 rd Ann. Rept. (21). SUNY Oneonta Biol. Fld. Sta., SUNY Oneonta.