Environmental Board Background
Lake Austin Hydrilla Management Plan
October 26, 2000
Background
Actions taken to this point
Lake Austin Hydrilla Task Force proposal:
Herbicide Fall Pilot $10,000-$15,000
Lakewide herbicide treatment $100,000 ($500-$1500/acre, varies with depth).
Grass Carp- $12/fish, $10,000 plus $25,000 radio tracking study ($35,000)
Total estimated cost- $150,000
Expected obstacles/challenges
Consequences of inaction
Risks of Implementation of Control Options
Drinking Water Intakes
One drinking water provider (Water District 20, Rob Roy on the Lake) has already reported hydrilla problems at their intakes. They are considering herbicide treatment to control the growth.
Navigation Safety Concerns
As hydrilla density increased over the summer of 2000, serious safety concerns also increased for all recreational users. Austin Parks Police report that they have to assist boaters and jet skiers whose crafts have become trapped in these thick mats at least 3-4 times/day from May to September (peak boating season). They also express concern about the ever-narrowing navigation channel on this lake where boaters are required by law to "stay to the right", as on a highway. In many places, as boaters come around a bend where the hydrilla surfaces well off shore, and they must move towards the center of the lake, often towards oncoming traffic, to avoid the dense growth. This is of particular concern at the Loop 360 Boat Ramp, where the large acreage of dense hydrilla has substantially narrowed ramp access, increasing the chances for a collision.
Swimmer Safety Concerns
Swimmers are also at risk; even in water that is less than 5 feet deep, becoming tangled in hydrilla over 2-3 feet thick often causes panic and puts a swimmer at a potential of drowning. Two drownings on Lake Walter E. Long in September of 1993 were attributed to being tangled in hydrilla after jumping off their boats into mats of the plant. This year at Lake Raven in Huntsville State Park, an adult male drowned over the July 4th weekend while swimming in a designated swimming area that had a dense infestation of hydrilla. Although the death was not directly attributed to hydrilla, observers indicate that the individual was having trouble once he entered water over his head where the hydrilla was topped out. According to the Huntsville Item, it took divers over two hours to find the body because the growth was so dense.
On Lake Austin, property owners report having to keep their family, especially younger children, out of the water (even with lifejackets) due to dense hydrilla growth. One adult male describes jumping off his boat in an attempt to move it through a dense patch of hydrilla to reach his dock. Without his life jacket, he is sure he would not have been able to reach the shore. Other citizens express concern about the possibility of youngsters falling from inner tubes or rafts into the plants and being unable to swim out.
Copper is widely distributed in nature and is an essential element. Nautique contains the active ingredient copper in the formulation of 0.9 lbs copper per gallon of Nautique, or approximately 9.1 % copper. It is an EPA-approved herbicide for use in potable water supplies. It is a Class II Toxicity category because of reversible eye and skin irritation of the concentrated compound. This is a concern primarily to applicators and others who handle it in its concentrated form. Once applied, it is diluted by surrounding water and no longer presents the same concerns to humans or animals.
Nautique is a chelated copper compound with the chelate added to the formula to help the copper stay dissolved in water longer. This chelate helps it be more effective than copper sulfate, which precipitates out of water much faster. The chelate is in the form of ethylenediamine and triethenolamine. The level of application are orders of magnitude below any levels showing toxicity, and toxicity data for each of these (chelates and copper) is discussed in the next section.
The short-term toxicity of Nautique can be compared to other substances by assessing the dose necessary to kill one half of the test animals. This dose is called the lethal dose 50% or the LD 50. This dose is given as the amount in mg per animal body weight in kg needed to produce a lethal effect in 50% of the organisms tested. Thus, the more toxic the substance, the smaller the value for the LD 50. (this information is from NTP Chemical Repository database at www.ntp-db.niehs.nih.gov/NTP_Reports)
Acute oral LD50 (rats) for :
Aspirin 891 mg/kh
Nautique 680 mg/kg
Caffeine 192 mg/kg
Nicotine 50 mg/kg
Another way to look at toxicity of copper is by examining data for aquatic organisms. The following table provides information from the Ecotoxicology database, USEPA and describes the LC 50 (median lethal concentration, or the one at which 50% of organisms are observed to die). These values are for static, not flowing, experimental set ups. It is important to note the exposure period (given in days). For comparison, the copper resulting from an application of Nautique will only be present in the water column at a concentration of 1 mg/L for only 12 hours before precipitating out into the sediment and becoming biologically unavailable in the water column.
|
Species |
Exposure Period, days |
Acute Toxicity LC 50, mg/L |
|
Crayfish |
3 |
8.1 |
|
Fathead Minnows |
4 |
1.6 - 21 |
|
Striped Bass |
4 |
4 |
The following information is also from the Ecotoxicology database, USEPA
Toxicity Ranges for Triethanolamine (chelate used in Nautique)
Goldfish LC50 >5000 mg/L
Daphnia LC 50 1390 mg/L
Fathead minnow 1.06 X 10 4
Ethylene diamine (chelate used in Nautique)
Fathead minnow LC 50 220 mg/L
Guppy LC 50 1544 mg/L
Daphnia EC 50 14 mg/L
LC 50 is median lethal concentration (concentration expected to be lethal to 50 % of organisms tested)
EC 50 is used when an effect other than death is observed)
The City of Austin’s Water and Wastewater Department approved the use of Nautique in Lake Austin for hydrilla control based on the EPA’s labeling of the chemical, which indicates no restrictions for use in a potable water reservoir. The EPA tolerance level for potable water (at the intake) for copper is 1 ppm or mg/L. The higher action level of 1.3 mg/L is acceptable at the tap for in-home samples, and the 1 mg/L intake level allows for 0.3 mg/L of copper that could come from water pipes in houses. The label rate for Nautique application is 1.0 mg/L and actual application will be closer to 0.5 mg/L. It is applied in such a way as to disperse the herbicide, in surrounding untreated water to provide adequate dilution such that drinking water intakes are not impacted by elevated copper levels. Waters treated with Nautique may be used immediately after application for swimming, fishing, drinking, livestock watering or irrigation. Application will be conducted by a licensed applicator.
Background copper levels in the water column for Lake Austin are less than the detection limit of 0.006 mg/L, and the City’s Water and Wastewater Department reports a copper level of the same level, less than 0.006 mg/L, for both raw and treated water at their plants. Copper pipes could provide an additional source of copper, but the treatment process the City uses to treat the water produces thin layer of calcium carbonate scaling along the inside of these pipes. The most recent copper sampling results from homeowners’ taps (done every three years by the Texas Department of Health) indicated that 90% of the homes had less than 0.01 mg/l of copper and none exceeded the action level of 1.3 mg/l.
Another factor in Water and Wastewater’s approval of this herbicide is that the copper does not stay in solution for more than 12-24 hours. City drinking water intakes are at least 3 miles downstream of any possible treatment area, and with the large volume of water that moves through the lake during normal releases, it is anticipated that even after treatment, city raw water intakes will measure no detectable levels of copper. Davenport Ranch water intake is 1500 ft downstream of Loop 360, where a major bed of hydrilla is located. Officials with that water supply corporation have evaluated the low application rate and large dilution expected from surrounding water and concluded that the plan will cause no copper contamination of their raw water. They will be pulling samples during the application to test for copper levels, and are considering not pumping water during the actual application time, since with planning, they can have several hours of storage available to them during the months of October through April. Other drinking water providers that may be in close proximity to a treated area will be notified to allow the opportunity for similar precautions.
Private water users will be notified of any upcoming application to provide them the time to secure alternate source of drinking water for the period of the application. Although detectable levels of copper are not anticipated even in private drinking water intakes, notification will provide an opportunity for homeowners with concerns to use alternate drinking water sources during the short (twelve hour) treatment period.
Nautique is not the only chelated copper product that could be used to control hydrilla, but the high level of public concern for herbicide applications in a potable water supply requires an equally high level of customer service which has been offered by Nautique’s manufacturer. In addition to providing a highly experienced individual for the actual application of the chemical, the manufacturer will provide a technical evaluation of the site before treatment, as well as pre- and post-treatment monitoring of plant growth to determine herbicide effectiveness. Besides the services provided by the manufacturer, the City’s Watershed Protection Department will monitor water column and sediment levels of copper before, during and after the application for a period of months to assess any impacts.
Although herbicide application in Lake Austin was not a preferred solution, it is understood that some control needs to be initiated, and WWW also recommended conducting a pilot study of approximately 10 acres, to determine herbicide effectiveness and cost. This is planned for the fall, after releases have been curtailed, but before water temperatures drop below 60 degrees. WPD will monitor this pilot study for water and sediment copper levels.
Any application of an aquatic herbicide will need to be made at a time when no upstream releases are planned. This is normally between mid-October and March. Because of the multiple factors (water temperature, depth and density of growth) influencing herbicide application and effectiveness, it is difficult to accurately estimate cost of treatment at this time, but an estimate for one contact herbicide is $950.00/acre for hydrilla growing in an average of 10 feet of depth. At this rate, it would cost approximately $200,000 to treat the 200 acres of hydrilla that is currently present.
Within 3-4 days of application, the plants will begin to discolor. The majority of the plant material will sink below the surface, and as it dies, the mass of the plant will disintegrate (it is 90 % water, and once the cell wall breaks down, it loses most of its mass and structure.) Within one week, some pieces of hydrilla may be seen on the surface, but most of the plant material will have disintegrated.
Potential for depression of DO by decaying plant material is minimal due to the size of Lake Austin and the nature of the hydrilla growth on the lake. In small impoundments with 70-80 % cover, treating a large area can result in a drop in DO and impact fish. Lake Austin is a 1600 acre lake with 200 acres of hydrilla growing along a long, linear shoreline. The herbicide application will be focused along either shore, leaving the deeper channel of the lake untreated. There is hydrilla in these areas but it is too deep for effective herbicide treatment. These untreated areas provide two things during application: first, water with normal DO levels that can mix with the areas of decaying vegetation and second, a refugia for fish and other organisms to migrate in the event of a depression of DO along the shore in treated areas. The City plans to coordinate with LCRA during herbicide application to restrict releases during the first twelve hours after treatment (to allow for herbicide action) and then to begin releases to bring in fresh water through the treated areas. This, along with having long stretches of untreated areas adjacent to treated ones, should limit potential for any drop in DO.
It is important to keep in mind healthy hydrilla itself causes huge swings in DO every 24 hours, as the plants continue to respire throughout the night but are not generating oxygen. DO in a dense hydrilla patch has been measured as low as 0.5 mg/L, and this can cause fish kills in areas with no refugia for fish.
Although there is not a large amount of data on this issue, studies in Florida show a large difference between sediment accumulation from copper sulfate (used for algae control) and that from chelated copper. Sediment accumulation of copper in three reservoirs treated for macrophyte control (using chelated copper) range from 34 to 71 mg/kg, while untreated areas ranged from 2 to 10 mg/kg. In examining this data, it is important to remember that treatments were repeated over several years, and that this accumulation is not the result of a single treatment.
However, these data strengthen the concern that Watershed Protection Department staff have about using herbicide as a single control method; without integrating grass carp into the management plan, treatment with herbicides would have to be repeated as often as twice per year for many years to effect any reasonable control. This could result in sediment accumulations of copper similar to those seen in Florida.
Stocking grass carp in Lake Austin presents certain challenges, primarily the issue of the fish impacting game fish habitat and water quality by eating more than the targeted vegetation (hydrilla). To address these, case studies of grass carp stockings were examined.
Lake Conway in Florida is a 1,840 acre lake that was stocked in 1977 with all female grass carp, at a stocking rate of 8 fish/acre of submersed vegetation. No major changes were noted until the second summer after stocking, but two years after stocking, hydrilla was greatly reduced with no noticeable effect on other species. Tapegrass (Vallisneria americana), a non-preferred plant for grass carp, increased dramatically. In 1986 and 1988, in response to increasing hydrilla, additional fish were stocked at 1 and .6 fish per acre, reducing hydrilla by 1989 and keeping it low until the research was published in 1994. In this lake, grass carp have been able to maintain hydrilla at a low level for over 15 years with minimal impact on other aquatic plant species. Although this is a favorable example of what can be obtained with grass carp, Lake Conway has a much more diverse native plant community than Lake Austin, where the presence of the native, less palatable species tapegrass was particularly advantageous, as it expanded to replace hydrilla.
If carp were able to remove most of the hydrilla in Lake Austin, milfoil may expand into areas once dominated by hydrilla. Milfoil is a relatively unpalatable plant, as is tapegrass (milfoil is 14 and tapegrass is 15 on a list of 20, with hydrilla at the top of the list). Although milfoil is not a desirable plant and can be a nuisance, it is at least more easily controlled through lake drawdowns and harvesting than hydrilla has proven to be.
Another lake that has shown success with grass carp is Lake Jacksonville in Texas. This 1,208 acre lake has been the subject of a pilot study by TPWD, involving an integrated approach using minimal herbicide treatment, a low stocking rate of carp and introduction of native plants. In 1997, prior to stocking, there were 80 acres of hydrilla in the lake. 100 grass carp were stocked in conjunction with application of a contact herbicide Aquathol (not appropriate for use in Lake Austin due to drinking water restrictions). This same treatment (100 carp, Aquathol) was repeated in 1998, and following each treatment, native plants were introduced in protective cages. Preliminary results indicated good success, with native plants expanding beyond cages and hydrilla being selectively grazed. However, by Spring 2000, TPWD indicated that additional herbicide treatments were used, and hydrilla acreage has increased to 150 acres.
Lake Cypress Springs (3216 acres) also shows success with grass carp; in 1996 there were 434 acres of hydrilla or 13.5 % cover. 2170 carp (5 fish per acre hydrilla) were stocked in 1997, and in 1998 hydrilla coverage was only 3.6 %.
Pinkston Lake (560 acres) with 322 acres of hydrilla (60% cover). Stocked 2100 grass carp (6.5 fish per acre hydrilla) and coverage steadily declined to 40% in 1999 and 20% in 2000.
Some lakes show inconclusive results, Lake Raven (204 acres) had 100 acres of hydrilla, and one year after stocking 200 fish (.5 per acre of hydrilla), there is no change in coverage.
However, there are documented cases of grass carp removing all the vegetation in a lake: In the early 1980s, Lake Conroe lost all vegetation after the stocking of 20,000 diploid (or breeding) grass carp were stocked. Since that time, TPWD has restricted permitting of carp to only triploid, or sterile fish. Lake McQueeny (364 acres) and Lake Dunlap (335 acres), each with 200 acres of hydrilla, were stocked with 5,000 fish in conjunction with herbicide treatments (both Aquathol and Sonar). One year after stocking, there was no vegetation in either lake. Martin Creek (5434 acres) was stocked with a total of 11,857 fish over a four year period, and now has no hydrilla left.
In many of the cases where fish consumed all vegetation, the stocking rate was many times that proposed for Lake Austin. The impact on the fishery from this total vegetation removal has not been clearly documented, in fact, fishery biologists indicate that McQueeny still has a strong bass fishery in spite of the loss of vegetation. There is reportedly a decline in water quality (increased turbidity and algae blooms) as would be expected with such a severe loss of vegetation.
Although the selection of a stocking rate is not a precise science, the task force has determined that using a low rate is preferable to what happened in lakes such as McQueeny or Dunlap. In those cases, the coverage of hydrilla reached near epidemic proportions while agencies disagreed on control options. With over 50 % cover, there was such a high level of frustration with the infestation that extremely high numbers of fish (25 fish per vegetated acre) were stocked, and vegetative cover was lost.
A Florida study on grass carp in large lakes (1993 Leslie, et.al.) recommends integrating a low stocking rate of carp with other plant control methods, such as reducing the density with herbicides. It also states that it is better to underestimate stocking rates and use supplemental control methods, than to depend solely on carp for control. This, along with control seen in reservoirs such as Lake Cypress Springs and Lake Conway provides support for the task force’s integrated plan.
United States Fish and Wildlife has expressed concerns about carp introduction related to impacts on ecosystems downstream, particularly Barton Springs Pool and the endangered Barton Springs Salamander. Discussions are ongoing with this agency, specifically regarding amending the Barton Springs Salamander Habitat Conservation Plan, which is part of the City’s Section 10a 1b permit, allowing operation of the pool. The minor amendment would address contingency plans for dealing with any carp that might migrate into the pool, to prevent impacts to aquatic plants that provide habitat for the salamander.
During 4 months of 1999, the Lower Colorado River Authority used a harvester for hydrilla control on Lake Bastrop, a power plant lake with approximately 35 % hydrilla cover. 100 acres were targeted for harvesting, but with rapid re-growth and subsequent re-cutting, only 60 acres were actually managed with the harvester. Total cost for this operation was $1,041 per acre, and rates ranged from 2 to 10 acres per week, with an average of seven acres harvested per week. Factors influencing efficiency included density of hydrilla, distance to shore for disposal, weather and maintenance and repairs.
Since June 2000, a privately owned harvester has been operating on Lake Austin through contract with private landowners. Information will be provided by the harvester owner to staff regarding approximately how many acres have been harvested since that time. Their harvesting rate is similar to LCRA’s, at approximately 4-8 hours per acre, depending on density of growth. The cost to private landowners is somewhat higher because they are operating for profit. Rates of re-growth are quite rapid; in many cases, hydrilla has reached the surface and formed dense mats (resulting in requests for re-cutting) within six weeks of initial harvesting. All landowners on Lake Austin are required to provide an area for dewatering of the plant material; most individuals use the dried material as landscape mulch.
An important consideration with harvesting is disposal; there is limited land adjacent to Loop 360 available for dewatering of plant material or landscape disposal. Concern for downstream spread through fragmentation, mortality of juvenile fish and high cost from frequent re-cutting needed during rapid growth periods are also considerations.
One concern with mechanically harvesting aquatic vegetation is the potential to adversely affect fish populations. During normal harvesting operations, small fish are incidentally caught and removed by the harvester. On three occasions during the 1999 summer season at Lake Bastrop, LCRA biologists quantified the size, number and species of fish caught in the harvested hydrilla (see Figure 1). The average collateral catch for the three samples was 189 fish per load of harvested hydrilla.
At an average of 7 loads per acre, these data indicate that harvesting has the potential to kill 1300 fish per harvested acre. The Lake Bastrop fish mortality represents less than 2 percent of the calculated fish population at Lake Bastrop and the numbers generally correspond to those in scientific literature. Mechanical harvesting removed between 2 and 8 percent of the juvenile fish from harvested areas in Saratoga Lake, New York (Mikol 1985) and 32 percent of the fish population in harvested areas in Orange Lake, Florida (Haller et al. 1980). Harvesting removed 21,000 to 31,000 fish per year, representing 25 percent of the fry from Lake Halverson, Wisconsin (Engel 1990). Harvesting removed about 39,000 fish, predominantly bluegill, from Lake Keesus, Wisconsin (Booms 1999). In the Wisconsin study, largemouth bass, unidentified fry and black crappie comprised 24 percent, 16 percent, and 8 percent of the total removed.
In Lake Bastrop, sunfish (47 percent) and juvenile bass (46 percent) represented 93 percent of the fish removed as collateral catch (see Table 1). Of the estimated 130,640 fish removed by the harvester, about 61,640 were bluegill, 60,260 were juvenile bass, 6,440 were Cichlids, and 1,380 were Gambusia. TPWD estimated the replacement value for these fish at $62,700.
Table 1. Estimated Number of Fish
Removed From Lake Bastrop
During Normal Harvesting Operations
|
July |
August |
September |
Subtotal |
Average |
Total* |
Percent |
|
|
Sunfish |
69 |
108 |
91 |
268 |
89 |
61,640 |
47 |
|
Bass |
117 |
52 |
93 |
262 |
87 |
60,260 |
46 |
|
Cichlids |
15 |
11 |
2 |
28 |
9 |
6,440 |
5 |
|
Gambusia |
4 |
2 |
0 |
6 |
2 |
1,380 |
1 |
|
Catfish |
0 |
1 |
2 |
3 |
1 |
690 |
<1 |
|
Minnows |
0 |
1 |
0 |
1 |
0 |
230 |
<1 |
|
205 |
175 |
188 |
568 |
189 |
130,640 |
100 |
*Totals were calculated by multiplying the average number of fish per load times the number of loads cut in 1999 (690).
The implications for Lake Austin are important to consider, especially in comparison with herbicide application. One common argument against herbicide application is that DO levels will drop during plant decay and cause fish kills. Although this is possible (especially in small impoundments), it is not anticipated in lake Austin due to the size of the reservoir and linear nature of the infestation. These data show that harvesting absolutely results in fish mortality, and this does not seem appropriate as a lakewide method.
ADDITIONAL HERBICIDE INFORMATION
The following information was pulled from the Aquatic Plant Control Research Program (U.S. Army Corps of Engineers) website. This, along with the MSDS and label for Nautique are provided as background information on the herbicide.
Complexed Copper - Hydrilla
Complexed (chelated) coppers have been used for many years alone and in mixtures with diquat for control of hydrilla as well as of algae. The copper complexes (ethanolamine, triethanolamine, and ethylenediamine) are the principal formulations used for aquatic macrophytes. There are no restrictions concerning the use of treated water, assuming the copper concentration is less than or equal to 1 mg/L (1 part per million), and the water may be used for domestic purposes, swimming, fishing, and irrigation immediately after treatment. However, these compounds should not be used in soft water where trout are present due to potential for toxicity to fish in low alkalinity waters.
A. Chemical Name and Formulations:
Chemical name:
Copper chelates
NAUTIQUE
® (9.1% Cu from mixed ethanolamine complexes; 110 g Cu/L; 0.91 lb Cu/gal) Soluble concentrateB. Mode of Action:
Copper complexes act as plant cell toxicants and may inhibit photosystem II electron transport. Herbicide activity is greater when plants are photosynthesizing and may be reduced on submersed aquatic plants if there is not adequate penetration of light into the water or if plants are covered with silt or algae. Copper is taken up by aquatic macrophytes and translocated, although the element is not metabolized, and it may be stored or excreted. Copper complexes are not subject to photolysis or volatilization.
C. Application:
Application to slow-moving or quiescent bodies of water, including potable water reservoirs and recreation lakes; golf courses, ornamental, fish, and fire ponds; aquaculture and fish hatchery ponds; irrigation conveyance systems, ditches and canals.
Liquid formulations are applied as the concentrate or diluted with water, or as invert emulsions.
Apply to the surface using a hand or power sprayer; or use a drip system in potable water or conveyance systems (ditches) to overcome effects of dilution. In deeper water (more than 4 ft) liquids are injected below the water surface or through weighted hoses from a boat to provide better mixing in the water column and/or bottom placement.
If weed infestations are heavy, apply in sections or at intervals of 10 to 14 days to avoid excess oxygen consumption by decaying plants and potential fish kill due to low dissolved oxygen.
D. Timing of Application:
To obtain most effective results, apply when growth first begins to appear or create a nuisance. Apply when submersed plants are actively growing but before they reach the water surface. Treat when water temperature is above 15
° C (60° F), preferably early in the day under bright or sunny conditions.E. Application Rates:
Target concentrations of Cu in water should be maintained for 3 hr of contact time for effective treatment. Use higher rates for treating deeper water and heavier infestations. Recommended dose is based on sitespecific water volume, rather than surface area alone.
NAUTIQUE: apply 6.6 - 13.2 L /1,000 m2 (7 - 14 gal/surface acre) for hydrilla.
F. Maximum Water Concentration:
Copper concentration should not exceed 1 mg/L (ppm) by weight copper in potable water.
G. Use Restrictions:
There are no restrictions on the use of treated water immediately following treatment.
Do not use in water containing trout if the carbonate hardness of water does not exceed 50 mg/L (ppm).
Do not discharge into lakes, streams, ponds, estuaries, oceans or public waters unless in accordance with the requirements of an NPDES (National Pollutant Discharge Elimination System) permit and the permitting authority has been notified in writing prior to discharge. Do not discharge effluent containing this product to sewer systems without previously notifying the sewage treatment plant authority. For guidance, contact the State Water Board or Regional Office of the Environmental Protection Agency.
Some states require a permit when copper is used in public water. Consult State Fish and Game or Natural Resource agencies before applying to public waters.
H. Timing of Effects
Effect on hydrilla can be observed as weeds become chlorotic and drop below the surface within 3 to 10 days after treatment; full effects manifested in 3 to 6 weeks.
I. Aquatic Toxicology Data:
Information on the toxicity of a copper herbicide example (CUTRINE-PLUS) to representative aquatic species is shown in the following table. Note that the maximum allowable application rate to water is 1 mg/L (ppm) of copper. NOTE: Nautique is 9.1 % Cu, so is comparable in toxicity to CUTRINE-PLUS.
|
Aquatic Toxicology of CUTRINE-PLUS (9% Cu)1 (Weed Science Society of America (WSSA) 1994) Note: Maximum application rate to water is 1 mg/L (ppm) Cu |
|||
|
Species |
Exposure Period, hr |
Acute Toxicity LC50, mg/L (ppm) |
Water Status |
|
Rainbow trout |
96 |
4 |
Hard water |
|
Bluegill sunfish |
96 |
7.5 |
Hard water |
1
LC50 = lethal concentration which kills 50 percent of individuals. The lower the LC50 number, the greater the toxicity.In soft or acid water, trout and certain other species of fish may be killed at recommended treatment rates. Toxicity generally decreases as water hardness increases.
J. Precautions:
Refer to labels for statement of practical treatment following accidental exposure to or ingestion of the concentrate.
K. Field Instructions:
Water hardness must be considered prior to treatment. Avoid use where pH of water or spray environment is below 6, because of copper ion formation and subsequent toxicity to fish. This toxicity generally decreases as water hardness increases. In soft or acid water, trout and certain other species of fish may be killed at recommended treatment rates.
Avoid contact via drift to desirable plants or crops, as injury may result.
Do not apply through any type of irrigation system, except where conveyance systems are being treated.
Effect of treatment will be observed within 3 to 6 weeks. Retreat areas if regrowth begins to appear and seasonal control is desired, since in heavily infested areas a second application may be necessary. Repeating application too soon after initial application may have no effect.
Apply early in day under calm, bright conditions.
Do not apply when water temperature is below 15o C (60o F).
Since herbicide activity is greater when plants are photosynthesizing, it may be reduced on submersed aquatic plants if light penetration into water is reduced or if plants are covered with algae, silt, or mineral crusts.
To minimize potential hazard of loss of dissolved oxygen in heavily infested and/or smaller water bodies, treat only one-third to one half of the area at a time; wait 1 to 2 weeks to treat remaining areas.
L. Adjuvant Use:
NAUTIQUE may be inverted in an appropriate invert oil and system.
M. Application Techniques:
Apply chemical uniformly over the surface area of infested area.
Treat from shoreline outward toward the center of the water body, preventing entrapment of fish within the treated area.
In heavily infested or smaller water bodies, treat only one third to one half of the area at a time; allow 1 to 2 weeks between successive treatments.
Apply with hand or power sprayer, drip system, or any other method to provide even distribution over the treatment area. (See label recommendations.)
For drip system, base application on accurate measurement of flow rate. Maintain 1 ppm Cu concentration in water for 3 hr.
N. References and Further Reading
Getsinger, Kurt D. (1997). "Appropriate use of aquatic herbicides," Lakeline 17, 20-21, 52-58.
Helsel, Daniel R. (1997). "Important reasons to be cautious about choosing aquatic pesticides," Lakeline 17:16-17, 45-48.
Netherland, M. D. (1991) "Herbicide concentration/exposure time relationships for Eurasian watermilfoil and hydrilla," Proceedings, 25th Annual Meeting, Aquatic Plant Control Research Program, Miscellaneous Paper A-91-3, U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS.
Weed Science Society of America (WSSA). (1994). Herbicide Handbook. 7th edition. WSSA, Champaign, IL.
The following questions (1-12) were asked at the August Environmental Board. #13 and 14 were brought up by staff. Answers were provided in large part by Mike Netherland, PhD. (SePro- Aquatic Research and Development),with some additional comments made by staff.
1. A list of communities/reservoirs in Texas (or elsewhere) that have used the same herbicide (copper complexes) we’re considering, and what sort of results they got.
2. Case studies (or any data) regarding maximum area that can be treated without a significant drop in dissolved oxygen from decaying plant matter.
5. How does this concentration (from #4) affect fish?
6. How does the actual rate/concentration of chemical as it is applied compare to the EPA MCL for copper?
7. If the application concentration (from #6) is higher than the MCL, and the assumption is that the chemical will be diluted to below the MCL by surrounding lake water, what will happen if the application occurs in close proximity to a private drinking water intake?
Water Quality criteria in ug/L:
EPA 9.0-13.0, TNRCC 28-45
Sediment screening levels, in mg/kg
EPA 34-270, TNRCC 33.0
Although the actual application rate is greater than the water quality criteria, it will be applied in less than 10 % of the waterbody (hydrilla covers 200 acres of the 1600 acre lake). A pilot is planned for the fall of only 10 acres and even in the spring during the larger treatment we do not plan to treat the entire 200 acres. This is in part due to cost and also because much of the hydrilla is in water deeper than ten feet, where the pilot may show the herbicide is not effective. Because of this limited size of treatment area in relation to the lake, it is not anticipated that the application will raise the level of copper in the entire waterbody above these values. Monitoring will be done during the pilot study to determine both water column and sediment level impacts.
(conversation with Mary Ambrose, TNRCC Policy and Regulation Division:
If application of herbicide is according to labeled rate and methodology, it is not considered a discharge and requires no permit from TNRCC. The state’s main concerns are regarding notification of public drinking water providers and potential impacts to the waterbody for constituents of concern (i.e., if Lake Austin was listed as an impaired waterbody due to elevated copper levels, which it is not).
1. There are several sites that have used chelated coppers and specifically Nautique to address aquatic plant problems. SePro is working to put a list together for several of the larger systems that have been treated with Nautique. As copper is a required micronutrient, there are no tolerances established Nautique, therefore, there are no drinking, swimming, fishing, or irrigation restrictions on this compound. This information should be available at the time of the public hearing.
To add to Dr. Netherland’s response, the hydrilla is not localized in coves or embayments, but situated linearly along much of the south shore of the lake upstream of Loop 360. Other individuals with experience in applying copper herbicides and more familiar with Lake Austin are quite sure that DO depression is unlikely unless we treat a dense block of 50 acres or more. In this case, the very center of the treated block may experience a low DO, but the untreated waters of the lake alongside the dense treated areas will provide a refugia of normal DO for organisms such as fish to escape to.
In fact, untreated dense mats of hydrilla have been shown to create severe swings in DO, where nighttime levels drop below 1.0 mg/L and go well above 12.0 mg/L during the day. These wide swings occurring throughout much of the hydrilla infestation is more of an impact to water quality than will be seen from any herbicide application.
3. Nautique will impact milfoil, but it is generally much more effective on hydrilla. Due to the fact that a potable water reservoir is being treated, the use of Nautique makes sense due to the fact that there are no drinking water restrictions.
4. Due to the depth of water, Nautique should be used to achieve between 0.5 and 1.0 ppm copper in the water column. The depth of water presents a challenge in getting good distribution of the product from top to bottom. The larger the treatment block, the lower the rate that is likely to provide good control. Moreover, in areas where a longer contact time is likely (protected coves, marinas), you can often get good results at reduced use rates. It is not generally recommended to treating areas less than 1 acre due to rapid dilution.
9. Attempting to harvest the decaying vegetation is unnecessary. Following treatment, the plants will sink to the bottom sediments, thereby making harvesting extremely difficult.
To add to Dr. Netherland’s comments, studies in Florida show a large difference between sediment accumulation from copper sulfate and that from chelated copper. Sediment accumulation of copper in three reservoirs treated for macrophyte control (using chelated copper) range from 34 to 71 mg/kg, while untreated areas ranged from 2 to 10 mg/kg. In examining this data, it is important to remember that treatments were repeated over several years, and that this accumulation is not the result of a single treatment. However, it does strengthen the concern that Watershed Protection Department staff have about using herbicide as a single control method; without integrating grass carp into the management plan, treatment with herbicides would have to be repeated as often as twice per year for many years to effect any reasonable control. This could result in sediment accumulations of copper similar to those seen in Florida.