48 degrees average
No further Limno reports this season
Aquatic Plant Control
The long-term objective of the
District’s aquatic plant control program has been the eradication of noxious
plants (Eurasian water milfoil and coontail) to facilitate public access,
improve water quality and enhance fish habitat. The District understands
that if the abundance of noxious weeds and algae present in the Lake are not
controlled, excessive amounts of nutrients (mainly phosphorous) will continue to
be released into the food chain following plant die-off, providing a food source
for even more abundant vegetation. Extensive growth of aquatic vegetation has
always developed in Big Bear Lake during the
summer months, particularly in the upper fifteen to twenty feet, with the plants
covering approximately 800 acres of the Lake’s
3,000 acre surface. District records indicate that of the weeds harvested, 73%
was milfoil, 20% was coontail and the remaining 7% was a combination of other
types. These statistics confirmed that the two main invasive species, Eurasian
water milfoil and coontail, became so predominant that the native species
were unable to survive. Since 2002, , the
District’s herbicide applications almost completely eliminated these two noxious
plants allowing a variety of native species to
return.
Eurasian water milfoil was described as a “harmful non-indigenous species” in a 1993 report to the U.S. Congress, and the Federal Invasive Species Council has classified this weed as a threat to the water resources of the United States. It is an extremely aggressive plant, and is a threat to most water uses. The excessive growth of this plant in Big Bear Lake was one of the main reasons the Lake was placed on the State of California’s 303d list of impaired water bodies. Along with plant infestation, high nutrient levels were also identified as an impairment. As a result of this listing, the TMDL (Total Maximum Daily Load) process was initiated by the Santa Ana Regional Water Quality Control Board in 2000. It was quickly determined in that process that much of the Lake’s high phosphorous levels are caused by in-lake sources (sediment and aquatic plants). As a result, the TMDL Work Group developed pilot projects and secured grant funding to address various methods of removing the invasive plants and the nutrient-laden sediment.
The District realizes that even though aquatic plant removal is essential to remove nutrients and to provide adequate recreational areas on the Lake, certain types of vascular rooted plants are an important environmental attribute in Big Bear Lake. These plants provide essential habitat for fish life and they produce an abundance of food organisms for all species of fish present. Aquatic plants are also utilized to a significant extent as food by migratory waterfowl and often serve as some control of shoreline erosion. As the invasive species are removed, a return of the native plant species will ensure this essential food source remains in Big Bear Lake.
AQUATIC PLANT OVERVIEW
A wide range of aquatic plants can be found growing in, on, and around a body of water. Based on their various adaptations, some will be found rooted in flowing waters while others can only survive in placid, stagnant areas. Within a natural, well-balanced system, these plants provide food and cover for fish, waterfowl and aquatic vertebrates. They produce oxygen and help stabilize bottom sediments. Like terrestrial plants, aquatic vegetation requires a carbon source, sunlight and nutrients. Dissolved carbon dioxide, bicarbonates and carbonates, typically quite abundant in water, provide a source of carbon for the growth and food production process known as photosynthesis. The energy driving this process is derived from sunlight. Therefore, the depth of the sunlight penetration will limit the depth to which aquatic plants can grow. At the same time, the amount of nutrients available (mainly phosphorous and nitrogen) will limit the quantity of vegetation, which will grow.
Aquatic plants derive their nutrients from the sediments and/or the water column. These nutrients are cycled between the sediments and the water on an annual basis. Adding to this nutrient enrichment of a lake, a process known as eutrophication, are inputs from external sources. Nutrients and sediments are contributed by man's agricultural, domestic and industrial activities through sources such as domestic waste discharges, construction site erosion, lawn and garden fertilizer runoff, and septic tanks. The most noticeable symptom resulting from eutrophication is the development of prolific aquatic plant growth. Eight types of aquatic plants have been identified in Big Bear Lake, of which coontail and milfoil have historically been the most abundant and the most troublesome to navigation, fishing and aesthetics.
PLANT CONTROL METHODS
For
many years, aquatic plant control was achieved by mechanical harvesting.
The harvesting program was implemented every boating
season to provide boating access to private dock systems, commercial marinas and
public launch facilities. It was always considered a short-term solution, much
like mowing the lawn, and actually spread the growth of weeds to other areas of
the Lake. However, beginning in 2004, harvesting was fully replaced with aquatic
herbicide applications. It was determined to be a much more successful means of
control, giving many seasons of relief. Most importantly, herbicides were used
to target the noxious aquatic plants (milfoil and coontail) in an effort to
eliminate them from the Lake. Harvesting and herbicides are discussed more
fully below.
Another very effective means of aquatic plant control is dredging. Removal of the plant roots and creating deeper water where plants are deprived of sunlight and cannot grow is likely the best long-term solution to controlling aquatic weed growth. However, it is not suitable for all areas of the Lake and is generally implemented as part of the need to deepen the Lake for improved navigation, to facilitate ingress and egress to dock systems and for marina harbor improvements
HERBICIDE TREATMENTS
In the summer of 1996, the District completed an experimental application in Grout Bay of a product called Sonar. Sonar is an aquatic herbicide developed specifically for the control of aquatic plants. It has been used for a number of years in other states, but was not approved for use in California until 1996. Sonar has no restrictions on use of the water after application and has been shown to be especially successful in controlling or even eradicating unwanted plants such as coontail and milfoil. These two noxious plants are the targets of the District’s current weed harvesting program and are the most annoying to boaters.
Sonar's active ingredient is Fluridone, which is not a chronic poison or a carcinogen. It works by restricting the plants' ability to make food, causing them to die. This involves inhibiting development of the yellow pigments that protect a plant's chlorophyll from decomposition by sunlight. As the plant’s chlorophyll decreases, so does its capacity to produce food. The visual symptom of Sonar’s action is bleaching on the terminal bud or growing points of the plant. Sonar is selective and controls target weeds slowly. The dilution factor of the product directs which plants will be destroyed.
After many weeks of studying case histories regarding the use of Sonar and actually visiting sites where Sonar had been used, the District determined that a test in Big Bear Lake was the appropriate first step in analyzing Sonar's potential. Grout Bay, on the north shore of the Lake, was selected as the test area as it is very protected from the wind and also from weed harvesting operations. This 35 acre area was initially treated during the first week of August 1996, with additional applications approximately every three weeks throughout the remainder of the summer. District Staff monitored the test area following the applications and concluded that the product results were unsatisfactory. Upon further evaluation, it was determined that the applications occurred too late in the growing season to achieve maximum results. A second series of applications took place in 1998 in the same area of the Lake. The cost for these treatments was approximately $1,000 per acre, and the result was nearly three years of weed-free access in Grout Bay. Based on these results, the District developed a plan to treat specific areas of the Lake again in 2000. However, a federal court of appeals decision on the use of herbicides, chemicals, pesticides and algaecides resulted in new permitting requirements. This made it impossible for the District to proceed as planned.
In January 2001, in order to obtain updated information on weed distribution throughout the Lake, along with an evaluation of current and proposed methods of control, the District retained ReMetrix Inc. to complete a Vegetation Assessment and Management Plan for Big Bear Lake. The report was accompanied by a computer software program designed to help the District coordinate its plant control harvesting program and evaluate the results. This plan will not only be helpful in improving the District’s plant control program, but it will also be an important reference tool when seeking future grant funding for Lake improvement projects.
In December of 2001, the District decided to move forward in the spring of 2002 with an aggressive program for herbicide treatments. Following three dry years with less than normal inflow to the Lake, and a Lake that was 9’6” below full, it was determined that applications in the east end of the Lake, in Boulder Bay and in the Mallard Lagoon/Canvasback Cove areas could achieve many years of relief from the infestation of Eurasian water milfoil. Proposition 13 grant funds were used to initiate a major application of Sonar herbicide in 2003, covering Papoose Bay and along the south shore of the Lake from Big Bear Marina to Eagle Point. Herbicide applications have been used since 2002 to continue the fight against Eurasian water milfoil. Each year, a few acres of milfoil return to the Lake, and they are aggressively treated with the appropriate herbicide. The good news is that some of the native plant species are also returning to the Lake. In 2006, the District established an Aquatic Plant Management Fund, to cover the cost of the annual treatments. The aquatic plant fee collected from dock owners is the source of funds, and it is anticipated there will be sufficient funding for the annual treatment of milfoil and for the annual treatment of nuisance plants around private and marina dock systems.
Weed growth before Sonar
herbicide application
Same area after Sonar
herbicide application
DREDGING
In the Shorezone Alterations/Dredging Section of this management plan, dredging has been identified as one of the controls for aquatic plants. In addition to removing the plant roots, deepening of the Lake deprives the plants of the sunlight they need for growth. Based on an average Lake level of five feet below full, it is recommended that dredging be completed to a depth of eighteen to twenty feet to achieve improved control of of noxious plants. Within a short time, some beneficial native plant species generally return to the dredged area. Dredging is very expensive so improved aquatic plant control is not usually the primary purpose for dredging activity. However, it is one of the benefits achieved when deepening the Lake for improved recreational access.
AQUATIC PLANT MANAGEMENT GOALS
A number of reports have been completed over the years which discuss the problems related to heavy aquatic plant growth in Big Bear Lake. Orville P. Ball and Associates prepared the "Lake Management and Rehabilitative Recommendations of Big Bear Lake", in January 1987. As part of his report, he outlined some recommendations to control rooted vascular plants, mostly milfoil, and indicated that aquatic plant control is one of the most important and expensive elements of the Lake management program. As a result of the report, a map of the Lake was prepared designating prioritized planning criteria for aquatic plant control. At the time this document was being prepared, a new “beneficial use map” was being prepared to ensure the District’s aquatic plant management program meets the requirements of the Total Maximum Daily Load (TMDL) process. It is critical that the appropriate balance of plants, both types and quantity, be achieved to provide sufficient habitat while not adversely affecting other Lake activities.
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