Draft Lake Management Plan – November 2016
Truesdale Lake is located in the Town of South Salem, NY. The most common uses of the lake include swimming, canoeing, kayaking and fishing. During the past several years, the use of Truesdale Lake for recreational purposes has been inhibited by issues related to aquatic weeds and harmful algal blooms. These perceived problems result from a host of causes including external and internal loading.
Due to the current status of Truesdale Lake, in combination with the desired uses for this resource, the primary goal for the management of this system is to maximize the number of days that the lake is suitable for recreation, including both contact (swimming) and non-contact (boating) activates. To facilitate the management of this resource for the desired uses, I outline potential management actions and a timeline for restoring ecological balance to this system that should promote sustained use of the lake by the stakeholders.
With maximizing suitable recreation days being the fundamental objective for management, there are underlying ‘means objectives’ that will help to achieve this through the application of specific management strategies to be implemented by stakeholders invested in the long-term, sustainable management of Truesdale Lake. Means objectives include, but are not limited to, reducing the nutrient levels in the lake, reducing the frequency of harmful algal blooms, controlling curly leaf pondweed, controlling the alewife population in the lake, and re-establishing a more natural environmental balance to Truesdale Lake.
Truesdale Lake, located in the Town of South Salem, NY is classified as a eutrophic lake, which means the lake is rich in nutrients and has high levels of primary production. The New York State Department of Environmental Conservation (NYSDEC) classified Truesdale Lake as eutrophic lake due to high levels of total phosphorus, chlorophyll a and low water transparency (Secchi depth; Table 1). Lakes naturally become more eutrophic over long periods of time, but due to human impacts (cultural eutrophication), this process can be significantly accelerated, as has been the case in Truesdale Lake (Table 1).
Table 1. Schema for the classification of lake nutrient status, modified from New York State Department of Environmental Conservation (NYSDEC, 2013). *Data shown for Truesdale Lake represent annual averages from data collected by SUNY Oneonta and by Citizen Science Lake Assessment Program (CSLAP) monitoring 1999–2015.
|Lake status||Phosphorus (µg/l)||Chlorophyll a (µg/l)||Secchi depth (m)|
|Oligotrophic||< 10||< 2||> 5|
|Mesotrophic||10 – 20||2 – 8||2 – 5|
|Eutrophic||> 20||> 8||< 2|
GEOMORPHOLOGY OF TRUESDALE LAKE
Truesdale Lake is an 83-acre, polymictic, class-B lake, created by impoundment in 1925. It is located in Westchester County, New York (NYSDEC, 2008). Truesdale Lake has a 2,000 acre watershed which lies within two states, 51% in the State of New York and 49% in the State of Connecticut (Figure 1). The mean depth in the lake is 2.19 m, and the maximum depth is 4.26 m (Table 2). There is one unnamed perennial inlet (CONN) that is located in the northeast corner of the lake and flows from Pumping Station Swamp in Ridgefield, Connecticut (Ryder, Bartos, & Jantos, 2001). A second, smaller ephemeral inlet (HOYT) is located just north of CONN along Hoyt Street. The outlet is located at the north end of the lake at a concrete dam (Table 2). The dam is an 18-foot spillway with removable boards for winter drawdown (Brancati, 2008). The removable boards allow for a 14-inch water height control and currently are taken out during winter (Brancati, 2008).
Table 2. Truesdale Lake characteristics, modified from SUNY Oneonta calculated from CIBiobase volume divided by area.
|Lake surface area||hectares||33.67|
|Water Quality Classification||B||Contact/non-contact recreation|
|Perenial Tributary (HOYT)||Latitude Longitude||41 17 12.86 N
73 33 10.87 W
|Major Tributary (CONN)||Latitude Longitude||41 16 59.56 N
73 33 3.14 W
|Lake Outlet||Latitude Longitude||41 17 15.28 N
73 33 25.43 W
Figure 1. Truesdale Lake Watershed showing sample locations for tributaries, represented by H (HOYT) and C (CONN), and land-cover classification (CITATION).
Figure 2. Bathymetric map of Truesdale Lake completed by SUNY Oneonta with CIBiobase.
Associations affiliated with Truesdale Lake have been active in the Citizen Statewide Lake Assessment Program (CSLAP) since 1999. Additionally, private lake management companies have collected data about the lake during the past two decades, including a lake evaluation and enhancement plan (Land Tech Consultants, Inc. 2001). In 2005 Allied Biological, Inc. conducted an aquatic macrophyte survey (Allied Biological, Inc, 2005), followed by a lake evaluation by EcoLogic, LLC (2008). Finally, Allied Biological, Inc. (now Solitdue Lake Management) collected data and implemented herbicide and algaecide treatments 2006–2016 (Solitude Lake Management , March 31, 2006). This long history of study and management has resulted in the accumulation of a relatively large amount of information about this system (Appendix A).
Despite intensive study and management, stakeholders are still unable to use Truesdale Lake for recreation during much of the summer season. Current impediments to the desired uses for Truesdale Lake include over-abundance of aquatic plants, harmful algal blooms, and the introduction of invasive alewife (Alosa pseudoharengus). Many of these problems are caused or compounded by external nutrient loading (nitrogen and phosphorus) from the watershed and internal nutrient recycling in the lake itself. As a result, the purpose of this plan was to provide objectives and management strategies for specific ecological parameters to promote and sustain the recreational use of Truesdale Lake in the future, based on information accumulated during the past two decades, and the current management concerns for the use of Truesdale Lake.
Maximize number of days stakeholders can recreate on the lake between May 1st and September 1st such that the lake can be used for a minimum of 100 days during the summer season.
- Reduce frequency and severity of algal blooms
- Reduce chlorophyll-a summer average 20 μg/l in five years
- Reduce nutrient import from watershed
- Reduce internal recycling of nutrients
- Reduce chlorophyll-a summer average 20 μg/l in five years
- Determine the contribution of alewife grazing and reduce abundance if determined problematic (see means objective 5.a. below)
- Revaluate in five years to determine whether further reductions are necessary and/or attainable
- Reduce abundance of curly leaf pond weed (Potomogeton crispus) by 50% in five years
- Reduce nutrient sediment and nutrient import from watershed
- Implement in-lake control methods as needed
- Monitor macrophyte biomass or density to determine success of management actions
- Assess alewife (Alosa pseudoharengus) population status
- Estimate current population abundance and associated risk of impact on desired uses
- Revaluate population estimate after 5 years
- Reduce nutrient levels in order to be removed from New York State Section 303(d) List of Impaired Waters Requiring a TMDL/Other Strategy (NYSDEC, 2014).
- Reduce in-lake nutrient levels by 25% in five years
- Reduce total phosphorus from 56.86 μg/l (1999–2015) to 42.64 μg/l in 5 years
- Reduce total nitrogen from 0.80 mg/l (2002–2015) to 0.60 mg/l in 5 years
- Reduce in-lake nutrient levels by 25% in five years
- Implement annual inspections and enhancements of septic tanks lake-wide where needed
- Continue education and awareness about the effect of septic systems on lake use
- Distribute a follow-up survey about septic system status in five years
- Apply each year for permitting the use of aluminum sulfate as a phosphorus sequestration tool
- Revaluate in five years to determine whether further reductions are necessary and/or attainable
- Attain average Secchi depth of a minimum of 1.5 meters during one summer
- Reduce sediment and nutrient import from watershed
- Implement watershed best management practices
- Reduce internal nutrient recycling in the lake to decrease frequency of algal blooms
- Options include artificial circulation or aluminum sulfate
- Evaluate after summer seasonal use (September 1st)
- Reduce sediment and nutrient import from watershed
- Acquire funding to implement management techniques each year
- Monitor progress to update management objectives and strategies as appropriate
- Limnological monitoring of nutrients and other parameters through CSLAP and/or a lake management company
- Maintain representative records about the amount of time each year that the lake is available for recreational use
1. Algal Blooms
Primary production in lakes is always balanced between plant and algal (phytoplankton) production. This balance can be very sensitive and easy to push toward one end of the spectrum or another (plant or algae dominance) in eutrophic lakes, such as Truesdale Lake, that have high nutrient levels throughout the entire growing season. In Truesdale Lake, the removal of plants early in the year contributes to shifts in primary production that favor phytoplankton blooms throughout the rest of the summer. Phytoplankton play an important part in the food web of a lake as the base of the web. However, not all phytoplankton are beneficial to a lake. For example, blue-green algae (cyanobacteria) can be harmful to humans and pets. Abundant growth of any algae can cause restricted recreational use of a lake because of these concerns, in addition to aesthetic problems (appearance, smell, and taste).
Phosphorus is a limiting nutrient for primary production in many aquatic systems, and as a result its availability in the lake (in addition to other factors) regulates the frequency and duration of algal blooms. Internal loading from lake sediment caused by a reduction of oxygen in the hypolimnion (bottom waters) during stratification events throughout the summer, along with phosphorus from the watershed can result in late summer blue-green algae blooms. These blooms can be potentially harmful to humans and pets due to the production of cyanotoxins by blue-green algae. Not all blue-green algae produce the cyanotoxin and therefore should be tested at the time of an algae bloom to be sure proper warnings can be sent throughout the community. Blue-green and green algae blooms have been common during late summer in Truesdale Lake for some time (NYSDEC, 2013), and they interfere with recreational use of the lake. These blooms have been treated with algaecides (Copper-sulfate and GreenClean Pro) by Allied Biological since 2006 (Appendix A) (Solitude Lake Management , March 31, 2006).
Lake monitoring conducted by SUNY Oneonta from April 2015 through September 2015 documented high levels of chlorophyll-a, which corresponded with high phosphorus concentrations (Figure 3). Algaecides have been used to treat nuisance blooms but these treatments cannot be used late in the growing season due to low Secchi readings and low concentration of dissolved oxygen in the late summer (Schramm, 2015). Stakeholders who have been living around Truesdale Lake for over 40 years have communicated that undocumented copper sulfate treatments date back to the 1950s.
Figure 3. Total phosphorus (µg/l) (dashed line) and chlorophyll-a (solid line) concentrations as determined from samples collected by SUNY Oneonta from April through September 2015.
Management Option 1.1: Algaecides
Algaecides are usually copper-based chemicals used to kill algae cells when growth begins to impact recreational activity in lakes and ponds. Copper sulfate is typically used throughout the state of New York to control algal blooms. Copper inhibits photosynthesis in algal cells, which kills the algae (NYSFOLA, 2009). Copper sulfate can be applied to a lake in either granular or liquid form. Typically there is a 24-hour use restriction in the water body after a treatment has been applied. There are also other forms of algaecides, called chelated copper, that tend to be less toxic in the aquatic environment, but they take longer to work (NYSFOLA, 2009). Chelated copper does stay in the water for a longer time period but is not as effective as copper sulfate. Overall copper sulfate is an effective, fast-acting, short-term control technique for nuisance algae.
Truesdale Lake has been treated with copper sulfate for more than 50 years. In most years prior to 2006 treatments were not documented. Since 2006 Solitude Lake Management has been treating the lake with copper sulfate, and has documented those treatments (Appendix A) (Solitude Lake Management , 2006). The cost for copper sulfate is relatively inexpensive. The cost per acre-foot is typically between $5 and $25. For many lake associations this is a realistic price for temporarily controlling algae. Although copper sulfate is an inexpensive, fast acting treatment option it is only a temporary solution and does not fix the actual cause of the problem. Algae reproduce very rapidly and given the high concentrations of nutrients in Truesdale Lake the algae will return following treatment. Furthermore, due to the number of treatments that have been completed on Truesdale Lake in the past 50 years, the concentration of copper in the sediment of Truesdale Lake are now quite high, 210-240 mg/kg dry weight (Brancati, 2008). As a result, the sediment is considered to be toxic and has the potential to create difficulties related to permitting and application in the future. Long-term, sustainable control of algal blooms in Truesdale Lake will require management of nutrients in the watershed and within the lake.
Management Option 1.2: Nutrient Removal
It is important to recognize that abundant algal growth in a lake is commonly a symptom of high concentrations of nutrients, which is the actual cause of the algal growth. Although effective for temporary remediation, management tools such as copper applications will not solve the underlying problems in Truesdale Lake. As has been observed during the past 50 years, there is the potential for over-reliance on this tool to lead to other problems related to human health that may be of greater concern. Due to these implications, it will be important for the stakeholders of Truesdale Lake to focus long-term, sustained management efforts on the removal of nutrients from this system. These considerations are given a more complete treatment in Management Strategy 4 of this document.
1.3: Artificial circulation
Artificial circulation is a management technique used to prevent stratification and reduce anoxia in lakes and ponds. The process works by adding diffusers to the bottom of the lake. Compressors send air through a pipe, and into diffusers, from which it enters water column. By preventing stratification, the dissolved oxygen concentration at the water sediment interface increases, and internal loading decreases over time, resulting in decreased probability of algae blooms. The circulation of water moves algae throughout the water column, decreasing the amount of time the algae have to photosynthesize in the light. As a result of mixing, chlorophyll-a concentrations generally decrease and water clarity increases.
Truesdale Lake fits all the characteristics for the need of artificial circulation (internal loading, high levels of chlorophyll-a, and little movement of water during summer months). There are, however, additional factors that might influence the utility of this tool for management of algae. The majority of the lake is very shallow and the bottom sediment is primarily soft, decomposed material. This material may be brought into the water column during circulation. A circulation system would also need to be properly designed to fit Truesdale Lake as the lake is nearly a mile long, so a large system would be required. The cost for an artificial circulation system would be around $150 per surface acre (NYSFOLA, 2009). There may also be additional costs if parts of the system fail and maintenance is required.
A lake management company should be contacted for more details if this option is to be considered.
2. Aquatic Plants (Macrophytes)
Truesdale Lake has a large littoral zone relative to the total lake area. Because nearly 90% of Truesdale Lake is less than 18 feet in depth, aquatic plants can grow throughout the lake (Brooking, et al 2014). Macrophytes (aquatic plants and benthic algae) play important roles in lake ecology. Much like algae, these organisms help to form the base of the food web in many systems. Macrophytes also help stabilize sediment, and they provide valuable habitat for young fish and other organisms.
Although macrophytes are important to the ecology of a lake, excessive growth can impair recreational activities such as swimming and boating.
Overabundance of plants was perceived to be one of the primary impediments to in-lake recreation during a recent survey, and during lake association meetings. Specifically, curly leaf pondweed (Potomageton crispus) interferes with recreational activities in the lake until midsummer. Curly leaf pondweed (CLP), is an aquatic invasive species that dominates the macrophyte community in Truesdale Lake from the late spring into the early summer (Shank, 2015; Schramm, 2015). The plant reproduces by seed, fragmentation and turions, which form at the end of its growing season. Turions function as the root structure for the plant and can remain dormant in sediment for several years or until conditions for growth are optimal (Gettys, Haller, & Petty, 2014). CLP reaches peak biomass in the early summer months (June-July) and then dies during early July in New York. Turions remains dormant in the sediment throughout the summer months and begin to germinate as water temperature cools during fall. New growth of CLP begins under the ice, as CLP is a shade tolerant species. This tolerance low light conditions allows CLP to reach peak biomass before other macrophytes begin their growth cycle (Heiskary & Valley, 2012). The growth cycle of CLP reduces competition with other photosynthetic organisms for nutrients and light. Due to this competitive advantage, CLP commonly becomes a dominant plant during the early growing season where it is present.
Management Option 2.1: Herbicides
The Truesdale Lake associations contracted Solitude Lake Management to treat CLP with herbicide applications 2006–2015 (Appendix A) (Solitude Lake Management, 2006). Although herbicide treatments have been successful in immediate control of CLP for maintaining recreational use of the lake, long-term management of CLP does not seem feasible with techniques currently used.
Herbicides have been used in Truesdale Lake for more than 20 years during late spring and early summer to eliminate CLP and allow recreation. Truesdale Lake was treated with either Aquathol K or Sonar AS during May from 2006 to 2015 by Solitude Lake Management Company (Appendix A). The treatment at this time of the year has been effective at controlling curly-leaf pondweed for early season recreation but has not been effective for eradicating CLP because turion formation in this species begins prior to the time of treatment. The herbicides used for treatment are not selective, and therefore all other live plants that are mixed with CLP are also killed. If untreated, the CLP usually senesces by early July; only a few weeks after the herbicide treatment is applied. The rapid control resultant from herbicide treatment may be appealing because of quick results, but there may be more practical long-term management options for CLP. Herbicides are efficient with respect to time and cost invested by a lake association during the short-term, but long-term success in managing CLP will likely need to include targeted reductions in nutrients entering the lake from the surrounding watershed by means of best management practices which can be found in Part 4 of this document. Pairing herbicides with other in-lake management options, along with reducing nutrient levels may be a better option for sustained, long-term control by restoring some natural functions of the lake ecosystem. Some of these alternatives are discussed below.
Using aquatic herbicides as a control method for aquatic vegetation is generally less expensive than other large scale treatment efforts. It is a less time-intensive treatment option than harvesting or benthic barrier set up per acre managed. The cost for an herbicide application may range from $200 to $1500 per acre treated (NYSFOLA, 2009). Because the application process is less time intensive than other management techniques most of the cost is for the chemical, which varies with treatment area, herbicide, and applicator. The NYSDEC allows about half a dozen aquatic herbicides to be used in the state of New York. These herbicides are registered with NYSDEC and an applicator license and permit are needed to apply aquatic herbicides within the state (CITE LAW). Water-use restrictions, with duration dependent on specific chemicals, generally follow the application of aquatic herbicides in New York waters. The timing and intensity of herbicide application depends on seasonal growth of target species and water temperatures. Application timing also varies with physical and chemical characteristics of lakes. For example, shallow lakes warm more quickly than deeper lakes and the growing season begins earlier in shallow lakes as a result. As a result of these requirements, several herbicide can be used as a management technique in the State of New York for CLP control (Table 3) (NYSFOLA, 2009).
Table 3. Aquatic herbicides that can be used in the State of New York that are effective on curly leaf pondweed (NYSFOLA, 2009), showing common name of active ingredient, mode of action, efficacy of killing roots, response time and exposure time in days, and toxicity [high (H), medium (M), low (L)].
|Herbicide||Mode||Kills roots?||Response time (d)||Exposure time (d)||Toxicity|
*Adjustments to current Herbicide Management
Contact Herbicide: Early and Late Season Applications and Spot Treatments
Contact herbicides would be best used on Truesdale Lake for spot treatment of problematic areas that impede recreation for a majority of stakeholders, such as beaches and the south end shallows. A whole-lake treatment with contact herbicide would not be the best option during the spring and early summer for multiple reasons. First, cool water temperatures decrease the efficiency of the treatment (Netherland et al, 2000) so early spring treatment may not be cost-effective. Second, killing all vegetation could result in oxygen depletion in the bottom of the lake, creating an anoxic environment due to decomposition (Gettys et al, 2014). Anoxia at the water-sediment interface can cause internal recycling of nutrients and result in early season algae blooms. Alternatively, refraining from use of contact herbicides in the early season may allow native plants not usually seen in Truesdale Lake to grow. Allowing these late season plants to grow may allow them to sequester abundant nutrients available in the system and reduce the severity of algal blooms.
Systemic Herbicide: Early Spring
Any application of herbicides during early spring would target curly leaf pondweed. If this technique is used, herbicide should be applied as soon as the water body begins to warm. Cooler water temperature decreases the efficiency of herbicides. Given the level of infestation in the lake by CLP (~80% coverage), it will be nearly impossible to eradicate the entire population, and doing so in a single year could have negative consequences for recreation (e.g. increased algal blooms). As a result, it should only be expected that systemic herbicides will be successful for controlling the vegetation in select problem areas to allow for year round recreation.
Similar to the contact herbicide application plan, target areas would be both the TEA beach, the TLPOA beach and the south end shallow areas. Other coves may be areas of concern due to the shallow depths and the number of residents in the bay. Stakeholders should be aware that turions can remain dormant in the sediment of the lake for several years (Sastroutomo, 1981). Therefore, regrowth in treated areas is likely and spot treatment during early spring may not promote long-term, sustainable suppression of CLP in these areas without treating indefinitely.
Management Option 2.2: Mechanical harvesting (hydroraking)
Hydroraking is a non-selective process that uses machines to remove plants from target areas. This management technique is primarily used in shallow areas (e.g., docks and swimming areas) of lakes in the Northeastern United States. The machine used is normally mounted to a barge and has a large rotating rake that removes plants in a fashion that is akin to “mowing the lawn”.
Hydroraking holds promise for use in Truesdale Lake, and may offer an alternative to decades of herbicide applications for achieving localized control in target areas. Typically one to three acres can be harvested per day, and prices range from an estimated $200 to $300 per acre or up to $2,000 per day depending on the company (Holdren et al. 2001; NYSFOLA 2009). One important consideration in the use of this tool is that harvested plants should be removed from the lake area to prevent nutrients from flowing back into the waterbody.
Management Option 2.3: Hand Harvesting
Hand harvesting can be a useful, and potentially free, aquatic plant management technique for small areas along shorelines. The technique is simply the hand-pulling of weeds from a lake, and is very similar to weeding a garden. A rake may be used to assist in weeding areas around docks, beaches and shorelines. By attaching a rope to the handle end of a rake, the rake can be thrown into the lake and pulled back to shore. Aquatic vegetation is then removed from the rake and placed away from the lake to dry out. The drying of the vegetation ensures that the plant is dead and will not reestablish in the lake.
Note: Curly leaf pondweed should not be used as compost material from the lake due to the plants ability to uptake heavy metals that are present in the sediment of the lake (Ali et al. 2000).
Hand harvesting is an easy technique for all stakeholders living directly on the lake to use, and it can help them feel included in the management process. As the stakeholders clear areas near shore, they can see what progress has been made at no cost to them other than time spent pulling plants. This technique has the potential to replace or supplement herbicide spot treatments around stakeholders’ docks, beaches, and shorelines. Hand pulling can be continued as new vegetation grows back around the shoreline. Making sure all or most floating vegetation is removed from the lake is an important aspect to hand pulling as these fragments may recolonize other areas of the lake for some species. For a stakeholder to create a rake system the price may be less than $25. A stakeholder may also go into the water and pull vegetation by hand, which is free but more labor intensive. The Truesdale Lake associations also may hire a company to hand harvest. Prices may vary if a company is hired.
Management Option 2.4: Drawdown
Drawdown can be an inexpensive technique for controlling aquatic vegetation if a lake association has a dam with the ability to lower the water level. This is typically done in the late fall before ice formation. As the water level is dropped (minimum of 3 feet for effective control of most plants), the bottom sediment of the lake is exposed and susceptible to freezing (NYSFOLA, 2009). Vegetation that is present in the frozen sediment may freeze and die. Not all species will be susceptible to freezing as some species of aquatic plants, such as curly leaf pondweed, are resistant to freezing. A drawdown is most successful when the maximum amount of littoral zone being targeted can be exposed to freezing. Drawdown may have the added benefit of preventing ice damage to docks and stone walls. If repairs are needed for docks, detainment walls or spillways the period of the drawdown is an opportune time to do so. The only cost associated with this management option is the time required to remove flashboards from the spillway. A permit is not needed for a drawdown as there are no wetland areas of concern around Truesdale Lake (Figure 1).
The Truesdale Lake associations have the ability to drawdown the lake and have been doing so for many years. This technique can have variable effects on CLP because turions can stay viable in the sediment for several years until conditions are suitable for growth (Sastroutomo, 1981). There also may be concerns about effects of drawdown on non-target, native vegetation. Shallow areas of the lake, less than 3 feet of water, may decrease in vegetation from year to year but recolonization will most likely occur by the following spring. The depth to which the water level can be drawn down is also a factor in the effectiveness of the control method. The maximum potential drawdown in Truesdale Lake is only 14 inches, which is less than the three feet recommended for effective control of shoreline vegetation (NYSFOLA, 2009).
Management Option 2.5: Allow the System to Function Naturally
After years of treatment for aquatic plant control, native plants have been eliminated from the lake on an annual basis and a monoculture of CLP dominates the late spring and early summer growing periods. With no discernable change in CLP abundance since monitoring started, a change in management techniques may allow for more days of recreational activity during the summer. This approach has the potential to increase nutrient sequestration through increased plant growth to reduce severity of algae blooms, and could result in re-establishment of native plants. It should be noted, however, that the overall concentration of nutrients in this system will not decrease through this sequestration, and as such, nutrient reduction will start with best management practices in the watershed and other in-lake techniques. The time and money saved through “doing nothing” during this period could be used to consider other management options in the future or begin nutrient management in the watershed as a long-term solution.
- Aquatic Invasive Species (AIS)
Aquatic invasive species are already present in Truesdale Lake, and their presence can also influence the number of days stakeholder can use the lake for recreation. A great deal of effort is focused on the prevention of invasive species spread between lakes throughout New York State. Stakeholders should be educated about the potential for spread of invasive species into and out of Truesdale Lake as transporting invasive species is illegal in the State of New York, but also can have consequences for lake management. Once an invasive species has been established in a lake ecosystem, it can be difficult or impossible to control, and it may be even more difficult to achieve eradication.
A large number of invasive species exist in New York that potentially could be introduced to Truesdale Lake, with varying effects. These include organisms that range in size and shape from plants and microscopic crustaceans to mussels and fish. One example of an invasive species that is already present and managed in Truesdale Lake is curly leaf pondweed. Species introductions may occur as the result of numerous causes, but very often humans are the primary drivers of biological invasions. The effects of invasives can be highly variable depending upon the biology of the species and the characteristics of the system being invaded.
One recent invasive in Truesdale Lake, alewife (Alosa pseudoharengus), is a member of the herring family that was first documented on 2 June 2016 during a fish kill (only alewife were found dead). The species is native to Atlantic Coast drainages, but within that range it is usually anadromous, meaning the fish spends most of its life at sea then returns to freshwater to migrate upstream and spawn. Alewife have become landlocked in some lakes of the Northeast, both naturally and because of introductions, and they are considered to be invasive in those systems to which they are not native. As a population grows in a lake, the fish can drastically reduce the abundance of large-bodied zooplankton that each algae. This can result in increased frequency and duration of algae blooms. It is unknown how long alewife have been present in Truesdale Lake, although their relatively large body size and the fact that they have fewer gill rakers compared to regional lakes that were invaded in the 1990s (Ducey, in prep) indicates the invasion was relatively recent.
Management Option 3.1: Prevention
One of the primary strategies for the management of invasive species is prevention of spread. Once invasive species become established, it may be very difficult to manage their effects in a way that is not cost-prohibitive. For this reason, pathways into and out of lakes, such as boat launches, have become a focus for AIS spread prevention in NY.
Truesdale Lake has only one boat launch at the TEA beach. Aquatic invasive species signs are posted at the launch as well as several other sites around the lake where boats, kayaks and canoes are stored. A box should be made and put on the ground away from the shoreline of the lake at the launch. Any vegetation on watercraft leaving or entering the lake can be put into the designated area. In addition to these measures, the lake associations have implemented a boat sticker system to ensure the watercraft belongs to lake association members and thus (presumably) pose less risk for the spread any aquatic invasive species. Since gasoline engines are prohibited on Truesdale Lake, watercraft such as small john boats, canoes, kayaks and sailboats are the primary vessels on the water. Residents with lake access should educate guests who bring boats from other lakes about the proper cleaning and maintenance of watercraft to prevent the spread of invasive species (Table 4). More information on disinfecting watercraft can be found at http://www.dec.ny.gov/animals/50267.html.
Table 4. Invasive species in the State of New York that are in the immediate vicinity of Truesdale Lake. Modified from NYSDEC Invasive Species *Present in Truesdale Lake.
|Aquatic invasive species||Distribution||Prevention strategy|
|Brazilian elodea||Long Island and Westchester County||Visual Inspection/Hand Removal|
|Curly-Leaf Pondweed*||Throughout New York State||Visual Inspection/Hand Removal|
|Eurasian Watermilfoil||Throughout New York State||Visual Inspection/Hand Removal|
|Fanwort||Southeastern New York||Visual Inspection/Hand Removal|
|Hydrilla||Widespread on Long Island, Cayuga Lake Inlet and Upper Niagara River||Visual Inspection/Hand Removal|
|Asian Clam||Long Island, Finger Lakes, Chautauqua Lake, Lake Erie and Lake George||Dry or disinfect|
|Zebra Mussel||New York State but not near Westchester County||Dry or disinfect|
|Quagga Mussel||Western and Central New York||Dry or disinfect|
|Alewife*||Throughout New York State||Biological Control, Physical Removal, Education|
Management Options 3.2: established invasive species
There are limited options available for the elimination of the alewife population that is present in Truesdale Lake. Biological controls have been attempted in other NY lakes, with variable success. Commonly used biological controls such as stocking walleye (Sander vitreus) may not be feasible in Truesdale Lake due to its limnology. Walleye are a “cool water” species, and as such they may not survive in the lake given temperature regimes during summer. Truesdale Lake has a year round, total water column average temperature of 18.67˚C. Other options, such as the application of a piscicide like rotenone, would require sacrificing all fish in the lake, and would likely come at a considerable cost.
The best course of action that the Truesdale Lake associations can take to determine an appropriate management strategy is to contact the NYSDEC Region 3 Fisheries office for guidance. Regardless of what action is taken, all options other than “no action” will require NYSDEC involvement in planning, permitting, and implementation. In the future, lake residents should notify the office immediately in the event of fish kills (usually more than 100 fish) in order to facilitate determination of potential causes and impacts on the lake. The Region 3 office of NYSDEC can be contacted at:
NYSDEC Region 3 Office
Main Headquarters: 21 South Putt Corners Road, New Paltz, NY 12561. Telephone: 845-428-3000
Sub-Office: 100 Hillside Ave. Suite 1W, White Plains NY 10603. Telephone: 914-428-2505
The abundance of nutrients such as phosphorus (P) and nitrogen (N) are the underlying cause of many problems (“symptoms”) currently being treated in Truesdale Lake. Phosphorus and nitrogen are important nutrients that promote primary production in aquatic and terrestrial ecosystems. Plants and algae in lakes all use these nutrients to grow when they are available. If surplus in nutrients are present in a lake, primary production can exceed what might be thought of as “natural” levels, and it is at this point that plants and algae begin to interfere with human uses for aquatic resources.
Concentrations of both total phosphorus (TP) and total nitrogen (TN) in Truesdale Lake are high throughout the year (Figures 4 and 5). Internal loading (recycling) of phosphorus occurs within the lake during the summer when bottom waters become anoxic, and TP may reach 300 µg/l. Not only are TP and TN high in the lake, but the two main inlets, HOYT and CONN, have high concentrations throughout the year (Figure 6).
Figure 4. Total phosphorus concentrations (µg/L) in Truesdale Lake from November 2014 through November 2015.
Figure 5. Total nitrogen (mg/L) concentrations in Truesdale Lake from November 2014 – November 2015.
Figure 6. Total phosphorus input of an unnamed perennial inlet (CONN) (Solid Line) and a smaller ephemeral inlet (HOYT) (Dotted Line). CONN sampling dates 4/24/2015 to 9/3/2015. HOYT sampling dates 12/6/2015 to 7/9/2015.
These concentrations are well above the state standard of 20 µg/L set by the NYSDEC (Table 1). Concentrating on watershed management to limit external nutrients going into the lake will allow for in-lake treatment of nutrients, algae, and plants to be more effective. Ultimately, a combination of watershed and in-lake management practices may increase the number of days the lake can be used for recreation.
Management Option 4.1: Nutrient Inactivation with Aluminum Sulfate (alum)
Nutrient inactivation using aluminum sulfate (alum) is predominantly used in lakes that have high levels of internal loading (NYSFOLA, 2009). Alum treatment removes phosphorus from the water column and seals the bottom sediment, which prevent internal loading of phosphorus in the presence of low oxygen concentrations for many years, if external loading is reduced as well (Holdren, Jones, & Taggart, 2001). Many factors affect the longevity of the treatment such as stratification events and external nutrient input (Welch & Cooke, 1999). Like most lake management techniques, there are advantages and disadvantages to alum use.
Currently in New York alum is not registered as a pesticide, which means it cannot be used yet. The NYSDEC also considers the flocculent that forms along the bottom of the lake to be a “fill” that could have negative consequences in water bodies. As such, a State Pollutant Discharge Elimination System (SPDES) permit would likely be needed for alum treatments in the future if this technique is legalized (NYSFOLA, 2009). Currently, there is considerable political pressure to legalize the use of alum for phosphorus inactivation in NY waterbodies. While it is uncertain whether these pressures will result in legislative change, it is a possibility. In that event, Truesdale Lake would be an ideal system for the use of alum based on morphometry and the extent of phosphorus loading, and if stakeholders maintain contact with NYSDEC staff, the lake would likely be an early candidate for treatment. As such, the lake associations on Truesdale Lake should maintain contact with NYSDEC Region 3 office about this possibility.
The initial cost for alum application ranges from $100 per acre to more than $500 per acre depending on dosage and overall goals of the treatment (NYSFOLA, 2009) (Holdren, Jones, & Taggart, 2001). However, this cost is minor compared to other management tools because of the longevity of the treatment (one treatment every five to ten years).
Management Option 4.2: Artificial Circulation
The use of artificial circulation in Truesdale Lake has the potential to reduce the frequency and duration of anoxia in the bottom of the lake by preventing stratification during the growing season. Prevention of anoxia will reduce the likelihood that phosphorus bound in the sediment will be recycled into the lake during summer months, and will likely lead to reductions in algal blooms and macrophyte growth, thus increasing the number of days available for recreation. It should be noted, however, that this management tool will incur a significant startup cost. Circulation also will provide only a short-term solution to problems associated will nutrients already present in the lake, and will not address the source of those nutrients entering the lake from the watershed. Best management practices in combination with a circulation system can potentially lead to more days of recreation on the lake.
Management Option 4.3: Best Management Practices (BMPs)
Readings from the two primary inlets (HOYT and CONN) to Truesdale Lake averaged 40.72 μg/l during December 2014 to November 2015, indicating that the use of best management practices (BMPs) within the watershed has the potential to reduce nutrients entering the lake. BMPs are best known for use in agriculture, but in recent years, a great deal of work has gone into the development of BMPs in urban and suburban watersheds. These include a suite of tools that range from modifications to the management of localized sources of nutrients and storm-water runoff, to more regional and watershed-scale approaches to nutrient and storm-water management. Using these tools, individual stakeholders around Truesdale Lake can make small improvements to help reduce external nutrient loading in the lake.
BMPs are applied within a watershed to reduce the amount of nutrients that may enter a water body. Truesdale Lake is surrounded by an urban environment and has areas that can be impacted by implementing BMPs. BMPs can range from using phosphorus free fertilizers and detergents in homes to allowing buffer zones to grow along the edge of a stakeholder’s lakefront property. Two tools that are readily implemented by property owners, and that have become popular as eco-friendly home improvements are the creation of buffer zones through “lakescaping” and the installation of rain barrels to reduce storm water runoff and provide water for gardening. More information about other tools not covered here can be found in NYSFOLA (2009), which can be accessed at http://www.dec.ny.gov/chemical/82123.html .
Most lake front properties have low cut grass lawns. While this type of landscape may be aesthetically pleasing to a majority of stakeholders, the lawn provides little benefit to limiting nutrient runoff into the lake because of its limited ability to retain water or nutrients in shallow root systems, and because it needs to be frequently maintained by the use of fertilizers, which can add sources of nitrogen and phosphorus to the lake. Furthermore, mowed lawns also promote increased soil erosion and sedimentation in lakes. Increases in sediment and nutrient load across these land-use types can result in increased abundance of algae and aquatic vegetation, thereby reducing the number of days available for recreation in the lake.
A buffer zone of native vegetation between lawns and the lake can improve water, sediment, and nutrient retention that otherwise would run off of residential lawns. Allowing native plants to grow can also provide food and shelter for wildlife such as birds, which may be desirable for homeowners. A buffer zone is an area of un-mowed land that extends from the land and if possible into the water. An ideal buffer zone would be 20 to 25 feet, but a zone 10 to 15 feet would be adequate as well (DNR, 2010). Many people might think of buffer zones as unkempt or overgrown areas of their property that interfere with their aesthetic enjoyment of owning lake-front property. However, a well-manicured buffer zone of native plants that might include shrubs, flowers, or even decorative trees can be as aesthetically pleasing as any other ornamental garden, with the added benefit of promoting recreational use of the lake. The New York State Department of Environmental Conservation maintains a list of native species that can be used for landscaping and storm water retention, available at http://www.dec.ny.gov/docs/water_pdf/swdmappendixh.pdf.
Similar to the creation of buffer zones with lakescaping, the management of storm water can be undertaken by individual property owners as a landscaping project with relatively little cost. To begin, first assess where water flows on your landscape. These areas are most readily identified during or immediately after rainstorms. Areas that pool water may be good areas to build rain gardens to make use of that pooling water, while promoting nutrient sequestration, and reducing storm water runoff and sedimentation in the lake. The addition of rain barrels to down spouts on gutters along the stakeholder’s home will further limit the amount of runoff going into the lake, and the water can be used for watering gardens. Rain barrels are sold in a wide variety of attractive, decorative models, most of which have hose spigots at the bottom to enable connections to water lines. More information about the use of rain barrels in Westchester County can be found at http://planning.westchestergov.com/rain-barrels.
Management Option 4.4: Septic system management
Septic tanks are used by property owners in lieu of sewer systems where municipal sewer systems cannot be built due to logistic or financial restrictions. Typically, wastewater drains from the home into a holding tank. Suspended solids then settle to the bottom and grease floats on top. The water left in the middle of the two layers flows out through a leach field. The purpose of the leach field is to filter out any nutrients remaining in the wastewater before it leaves the system. When designed correctly, septic systems efficiently filter suspended solids and nutrients from sewage, and these systems have relatively little impact on local ecology. In order for septic systems to function properly, they must be designed specifically for a given household based on degree of use, and local geology and hydrology. Furthermore, these systems should be inspected once every five years by law in the Town of Lewisboro to maintain proper function. More information can be found at http://www.lewisborogov.com/cac/page/pump-out-your-septic-system.
All stakeholders around Truesdale Lake use septic systems for wastewater treatment. However, the majority of the watershed is made up of soils that are somewhat limited or very limited in their suitability for septic systems. This is because the depth of the water table tends to be too shallow, slopes tend to be too steep, and the composition of local soils and underlying bedrock tends to promote runoff rather than retention (Jenne, In prep.). Furthermore, he average, most recent year during which home septic systems were inspected or updated in the Truesdale Lake watershed was reported to be 1999 during a 2015 survey (Jenne, In prep.).
Moving forward, regular maintenance of septic systems, and at minimum compliance with local ordinances, should be a goal for all stakeholders in the watershed of Truesdale Lake. The cost to update, replace or inspect a septic system varies on a case to case basis, but the gains in recreational use days for those who use the lake may be well justified.
Management Option 4.5: Stream bank enhancement and storm water management
Runoff from the watershed can be a significant input of nutrients and sediment into a lake. Areas of urbanization with even a moderate percentage of non-permeable surfaces have significant influences on the runoff of these ‘pollutants’ into a lake, especially when compared to forested land covers (NYSFOLA, 2009). Urban best management practices focused on the management of storm water runoff have the potential to drastically reduce the overall nutrient load entering the lake from the watershed. Tools such as stream bank enhancement, sediment traps, and swales may be particularly effective for minimizing runoff, controlling erosion and reducing nutrient loading into Truesdale Lake.
When used in combination with near-lake techniques available to lake-shore property owners (buffer zones, rain barrels, rain gardens), actions taken at the watershed scale have the potential to promote recreational use of Truesdale Lake by reducing nutrient and sediment inputs, and limiting the building blocks needed for excessive plant and algae growth.
With so many different types of projects available for an urban watershed the cost of each individual project will vary. Some options include “smart development” and “green infrastructure” projects that include advanced planning of activities such as pervious pavement that allows rain water to trickle through the pavement rather than flow over top of the surface. Other tools include maintenance activities such as sweeping or cleaning roads at the beginning of spring and end of fall (Holdren, Jones, & Taggart, 2001). Grant opportunities for these projects are available, and are generally supported by a host of state, federal, and private agencies on an annual basis. With a lake and watershed management plan in hand, stakeholders around the lake can work with a lake management company or local/regional planners to secure funding to offset some of the cost of BMPs for the Truesdale Lake watershed. Proposals for this type of work in the Truesdale Lake watershed have been successful in the past (Ryder, Bartos, & Jantos, 2001), and opportunities to continue that work as well as propose new projects become available with some regularity. Grant opportunities for storm water enhancement projects as well as watershed management projects can be found at: http://www.dec.ny.gov/pubs/grants.html and http://www.efc.ny.gov/Default.aspx?tabid=461.
Through a combination of in-lake and watershed management strategies that have established, measureable objectives, there is a strong possibility that Truesdale Lake will be available for more days of recreational use than in years past. Many of the objectives established herein are necessarily long-term in nature, as changes in the ecosystem will not happen quickly. Therefore, it will be necessary to continue monitoring of the lake through the CSLAP program at a minimum in order to assess the success of management strategies as related to fundamental and means objectives defined in this plan. Additional monitoring should be implemented as necessary to collect other relevant data related to strategies undertaken as part of this plan. This monitoring will be important for determining how management actions influence the trophic state of Truesdale Lake, it will allow for adaptive management of this regionally important resource, and it will provide a basis for adjustments to techniques and expectations as work proceeds.
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Appendix A. Treatment schedule for application of herbicides and algaecides by Solitude Lake Management in Truesdale Lake 2006–2015.
|Date||Product Applied||Acres Treated|
|Date||Product Applied||Acres Treated|
|5/14/2015||Aquathol K (UPI)||40|