Quantitative aquatic plant surveys were undertaken in 2010 for Saratoga Lake, New York as part of a cooperative effort between Aquatic Control Technologies (ACT) and the Darrin Fresh Water Institute, and supported by the Saratoga Lake Protection and Improvement District (SLPID). The project was designed to obtain data to evaluate aquatic plant management efforts and review potential new strategies. The project included three components: 1) collection of specimens for compilation of a species list, 2) point-intercept frequency and depth data for points distributed in previously treated areas, and 3) point-intercept frequency and depth data for points distributed in herbicide treated areas (southwest end and north of the Kayadeross).
In Saratoga Lake, Eurasian watermilfoil (Myriophyllum spicatum) expanded rapidly after an initial invasion in the 1970’s. Myriophyllum spicatum populations were first confirmed in the mid-1970’s and reported to be the dominant aquatic plant species in the lake by the early-1980’s (Hardt et al. 1983). In 1994, the Saratoga Lake aquatic plant community contained 23 submersed species, 3 native rooted floating-leaf species, 2 native emergent species and 1 free floating species (Eichler and Boylen 1995). Myriophyllum spicatum was the most common plant species, present in 68 percent of survey points. Two other exotic aquatic plant species were reported, Potamogeton crispus and Trapa natans. Potamogeton crispus is seasonally abundant, forming a dense band at the deep margins of Eurasian watermilfoil growth in the spring and early summer. Trapa natans has been reported as scattered individuals on the delta of Kayadeross Creek and in Mannings Cove, however it was absent from the 2008 and 2009 surveys. A number of Trapa natans plants were observed in the area of the Fish Creek boat launch ramp in 2010. Herbicide treatments were incorporated into the aquatic plant management program in 2007 to supplement previously employed lake level drawdown and mechanical harvesting. A three year herbicide treatment effort was initiated with fluridone (Sonar) treatment of the southern margin of the lake in the area of Browns Beach in 2007. Triclopyr (Renovate) herbicide was applied in 2008 and 2009 on the eastern and western margins of the lake, respectively. In August of 2010, the aquatic plant community of Saratoga Lake included 21 submersed species, 3 floating-leaved species, 2 floating species and 2 emergent species for a total of 28 species, 24 of which were collected in the point intercept portion of the survey. These results are comparable to previous surveys in 2009 (26 species, Eichler and Boylen 2009), 2007 and 2008 (25 species, Eichler and Boylen 2007), 2004 (21 species, Eichler and Boylen 2004), 1994 (22 species, Eichler and Boylen 1994), 1982 (21 species, Hardt et al. 1983) and 1969 (20 species, Dean 1969).
Exotic species, dominated by Eurasian watermilfoil, were clearly more abundant lake-wide in 2004, 2007 and 2008 (56%, 53% and 18% of survey points, respectively) than in 2009 (10% of survey points). A slight increase in exotics species abundance (22% of survey points) was observed in 2010. Eurasian watermilfoil remains a common member of the plant community, but at greatly reduced numbers when compared to previous surveys. Eurasian watermilfoil declined from first to tenth most abundant species by frequency of occurrence between 2007 and 2009, however an increase to seventh most abundant species was reported for 2010.
Native species were dominant in 2010. Common native species in the untreated or control areas included Ceratophyllum demersum (61%), Najas guadalupensis (51%), Elodea canadensis (44%), Vallisneria americana (44%), Zosterella dubia (29%), Potamogeton zosteriformes (21%), Potamogeton perfoliatus (16%), Chara/Nitella (13%), Najas flexilis (9%), Potamogeton illinoensis (7%) and Potamogeton pusillus (5%). Eurasian watermilfoil showed signs of regrowth in the previously treated portions of the survey, reported for 21% of survey points an increase of 16% of survey points from 2009.
In the treated areas of Saratoga Lake, Eurasian watermilfoil was present in 29% of survey points in 2010. Common native species in the treated areas included Ceratophyllum demersum (74%), Elodea canadensis (65%), Vallisneria americana (39%), Zosterella dubia (34%), Potamogeton zosteriformes (32%), Najas guadalupensis (26%), Potamogeton praelongus (13%), Potamogeton pusillus (10%) and Chara sp. (7%). With this diversity and distribution of native species, the test for selectivity should be sensitive to a number of species, and native plant restoration in areas formerly inhabited by Eurasian watermilfoil appears to be rapid following management efforts.
In 2004 whole lake species richness was 2.00 ± 0.10 species per survey point. Whole lake species richness has increased steadily since that time to 3.47 ± 0.12 by 2010. The increase in 2010 may have been a sampling artifact since the majority of sampling points outside the littoral zone were eliminated from the 2010 sampling. In the shallow portion of the littoral zone, depths less than 2 meters, species richness was 2.47 ± 0.18 native species per sample in 2004, and rose steadily to peak at 4.22 ± 0.24 native species per sample in 2009. A slight decline to 3.72 ± 0.24 native species per sample was observed in 2010. As expected, species richness in the littoral zone and its shallow fringe was higher than whole lake species richness. Lack of a Eurasian watermilfoil canopy in water depths less than 2 meters may also allow for greater species richness. Native species richness lake-wide and in the treatment zone was higher post-treatment in 2007, 2008 and 2009 than during 2004 (pre-treatment). A slight increase in the lake-wide abundance of exotic species in 2010 occurred in conjunction with a slight decline in total and native species richness.
Principal areas of Eurasian watermilfoil expansion in 2004 were reported in the northeast at Franklins Beach and the southwest in the area of Rileys Cove. Franklins Beach was selected as the control (untreated) area for 2007 while the south end of the lake and Browns Beach area were treated with herbicide (Figure 6). In 2008, the Franklins Beach area was selected for treatment, the west shore including Mannings Cove served as the control, and Browns Beach west across the south end of the lake was assessed 1 year post-treatment. In 2009, the west shore and Mannings Cove areas were treated, the Franklins Beach area was assessed 1 year post-treatment and Browns Beach west across the south end of the lake was assessed 2 years post-treatment. In 2010, spot treatments were conducted at the southern end of the lake and north of the mouth of the Kayadeross Creek. Substantial reduction in Eurasian watermilfoil frequency of occurrence was observed in the treated area between 2008 (pre-treatment) and 2009 (post-treatment) while the previously treated control areas increased from 2% to 5%. Eurasian watermilfoil declined from 26% of littoral zone survey points within the treatment area in 2008 to 9% of comparable survey points post-treatment in 2009. Eurasian watermilfoil increased in frequency of occurrence lakewide in 2010 (22% of survey points), with principal areas of growth in Mannings Cove and the shoal area offshore from Franklins Beach.
Lakewide aquatic plants were found to occur in 90% of survey points in the littoral zone, comparable to prior surveys (range of 88 to 91%), and not indicative of any major change in the aquatic plant population. Eurasian watermilfoil abundance declined from 66% of littoral zone survey points in 2004 to 59% of survey points in 2007, 21% in 2008 and 8% in 2009. In the 2010 survey, Eurasian watermilfoil was present in 22% of whole lake survey points, and 29% of survey points less than 6 m water depth, representing the littoral zone or zone of aquatic plant growth. Exotic species, dominated by Eurasian watermilfoil, were equitably distributed in the previously treated areas (21% of survey points) than the treated area (29%),suggesting durability of treatment regimes from 2007 thru 2009.
Figure 7. A comparison of the distribution of Eurasian watermilfoil (Myriophyllum spicatum) growth in selected areas of Saratoga Lake in 2007 through 2010.
Eurasian watermilfoil abundance declined from 58% of littoral zone survey points within the treatment area in 2004 to 25% of comparable survey points post-treatment in 2007. In 2008, Eurasian watermilfoil abundance continued to decline to 3% of littoral zone survey points within the treatment area. In the control area, Eurasian watermilfoil abundance increased from 74% of survey points in 2004 to 80% of comparable survey points in 2007. In 2008, Eurasian watermilfoil abundance declined to 26% of survey points in untreated areas. In 2009, the decline in Eurasian watermilfoil abundance continued, with lake-wide frequency of occurrence at 7% of survey points. This decline coupled with what appeared to be sub-lethal effects of the herbicide in the untreated areas, suggest efficacy of the herbicide over a much greater area than anticipated. An increase in Eurasian watermilfoil abundance was observed in 2010, primarily in areas not treated for 2 years. Even with the increase, Eurasian watermilfoil abundance remains at less than half of pre-treatment levels.
The littoral zone or maximum depth of colonization (MDOC) by aquatic plants was calculated to extend to a depth of 4.9 meters based on transparency data. Ceratophyllum demersum and Najas guadalupensis, however were commonly found between 5 and 6 meters depth, with occasional Myriophyllum spicatum specimens also encountered, suggesting a littoral zone maximum depth of approximately 6 meters, 1.0 meter greater than reported in 1994. Suppression of canopy formation through mechanical harvesting may allow for light penetration and thus the survival of native plant species in areas of dense Eurasian watermilfoil growth. Changing water clarity may also be a by-product of the invasion of Saratoga Lake by zebra mussels (Dreissena polymorpha) in the mid-1990’s. Improved water clarity is frequently reported following zebra mussel invasions due to their ability to filter large volumes of phytoplankton from the water column. Reduced Eurasian watermilfoil density in shallow waters as a result of winter draw-down and ice scouring has also provided areas for colonization of native species resistant to winter draw-down. Evidence continues to suggest that a native species, Water Stargrass (Zosterella dubia) is replacing Eurasian watermilfoil at the shallow end of its range. The frequency of occurrence of Zosterella dubia has increased substantially, reported in 19% of samples in 1994, 47% of samples in 2004 and 44% of samples in 2007 in the control area. In 2008 through 2010, while still quite abundant, the frequency of occurrence of this species appears to have stabilized at 20% to 30% of survey points lake-wide. The operators of the mechanical harvesters continue to report that Zosterella dubia has become a prevalent species in their harvested materials. Survey results indicate that this species is found growing densely in waters of 1 to 1.5 meters depth at the inner margins of dense Eurasian watermilfoil growth. The growth habit of this species may be a consideration in future management efforts.