DRAFT DRAFT
Appendix D-1. Control Options[1]
Thermal Shock
Hot water treatment can kill Dreissenid mussels. Long-term exposure to temperatures of 32°C and above are lethal to adult zebra and quagga mussels. Time to death depends upon acclimation temperature of the animal as well as rate of temperature increase. Dreissenid mussels will die in about 1 hour when placed in water of 37°C. At winter acclimation temperatures (5 to 10°C), temperatures of 33°C and above will kill zebra mussels within 13 hours. For further information, see Table 1 below (McMahon et al. 1993). Veligers are more susceptible to high temperatures and will die at temperatures between …….
Freezing
Adult Dreissenid mussels die when aerially exposed to freezing temperatures. In winter, populations can be controlled by dewatering and exposing zebra mussels to freezing air temperatures. Zebra mussels die in 2 days at 0°C and at minus 1.5°C, in 5 to 7 hours at minus 3°C, and in under 2 hours at minus 10°C. Duration to mortality is less for single mussels than for clustered mussels (Payne 1992). Check book for updates.
Oxygen Starvation
Oxygen starvation can be achieved by cycling ambient water through oxygen-starving pumps. The developer of the technology, Wilson J. Browning of Amark Corp, Norfolk County, VA, claims the equipment can cycle 200 million gallons of water. Another method of removing oxygen is to add oxygen scavenging chemicals, such as sodium-meta-bisulfite and hydrogen sulfide gas (USACE-ZMIS at ). Addition of CO2 has also been proposed as a tool to remove oxygen from water in an industrial setting. It should be noted, however, that adult Dreissenid mussels are able to tolerate oxygen deprivation for up to 2 weeks, provided ambient temperatures are low enough (USACE-ZMIS). Impact of low oxygen levels on survival and settlement of veligers ….
Oxygen Starvation - Benthic Mats
Researchers from the Rensselaer Polytechnic Institute in New York are investigating the use of benthic mats that would cover the sediment and adult mussels, thus depriving them of oxygen. Preliminary laboratory bioassays carried out in aquaria demonstrated that benthic mat covering of zebra mussels for 2 weeks resulted in mortality rates of 14.9–100%, while mortality rates were 2.2% or lower for control aquaria without mats. In laboratory studies in which mussels were covered for 4 weeks, mortality rates of 20–100% occurred, and did not vary significantly with duration of covering or size class. Measurements of several water chemistry parameters beneath mats, including dissolved oxygen, ammonia, calcium and magnesium and pH, indicated that dissolved oxygen concentration was the only parameter to exhibit both significant change and a consistent trend over the course of the study, declining from nearly 100% saturation to a mean of 16.5% saturation, and remaining at this level for the duration of the experiment (Sandra Nierzwicki-Bauer, personal communication, 2008).
In field studies carried out in New York’s Saratoga Lake, divers created treatment and control zebra mussel colonies at 2m depths on a rocky substrate by placing rocks with attached mussels on fiberglass screens atop gravel beds. During a field trial where two treatment colonies, composed of about 30,000 mussels each, were covered with 4m2 mats, mortality rates exceeded 99% after nine weeks of covering. As observed in the laboratory tests, dissolved oxygen concentrations declined significantly under the mats, correlating strongly with increased mortality (Sandra Nierzwicki-Bauer, personal communication, 2008).
Desiccation
Desiccation is a viable option for eradicating adult mussels from areas that can be dewatered for several days. Alternatively, desiccation can also act as a population control method in areas that cannot be completely dewatered. For example, reservoir levels can be lowered to expose Dreissenid mussels inhabiting shallow water. Depth of colonization is dependent upon water temperature, oxygen content, and food availability in a particular body of water. Higher population densities tend to be found above the thermocline, but quagga mussels, in particular, have been found exist at depths greater than 100m.
Temperature is positively related, and humidity is negatively related, to adult mussel survival. As humidity increases and temperature decreases, survival increases (Table 1). Aerial exposure of zebra mussels to temperatures exceeding 25°C, will result in 100% mortality in 2.1 days. Temperatures over 32°C are lethal within 5 hours. Instantaneous mortality occurs at 36°C. At temperatures below 30°C, time to mortality is dependent upon relative humidity.
Table 1. Number of days to 100% mortality of adult zebra mussels aerially exposed to different levels of relative humidity and air temperature (McMahon et al. 1993).
Relative Humidity, % / 5 / 15 / 25
95 / 26.6 / 11.7 / 5.2
50 / 16.9 / 7.5 / 3.3
5 / 10.8 / 4.8 / 2.1
Manual Removal
When found in relatively small numbers, manual removal may be an effective way to reduce Dreissenid populations and potentially even eradicate them if reproduction has not yet occurred. Manual removal can take place via hand extraction or via mechanical scraping and suction, typically using divers. In Lake George, New York an effort involving hand harvesting by divers appears to have significantly reduced an introduced population. Divers removed 267 mussels in 1999, followed by a peak of nearly 20,000 in 2000. Since then, ongoing removal efforts have yielded fewer than 2,000 mussels per year (Sandra Nierzwicki-Bauer, personal communication, 2008). The apparent eradication of the nonnative sabellid polychaete worm, Terebrasabella heterouncinata, in California, provides analogous evidence to the role of hand removal as a control technique. After this marine pest was found at an intertidal site outside of an infected abalone culture facility, over 1.6 million native black turban snails (Tegula funebralis)—the preferred native host—were extracted by hand, along with other infested material. This effort reduced the transmission of the pest species to the point that it no longer was detectable in follow-up surveys (Culver and Kuris 2000).
Predation
The relatively soft shells of Dreissenid mussels and their exposure (on substrates as opposed to buried in sediment) make them vulnerable to predation. Possible predators of adult mussels include some species of carp, catfish, bullhead, sucker, sunfish, sturgeon, crayfish, and muskrats. A possible predator of veligers is the American shad. However, there is no evidence of predation control in the Great Lakes, Ohio River, and Poland. There is some evidence of population reduction in the Hudson River. Despite the lack of clear evidence of population control through predation, it is recommended that harvest of predatory species in infested waterbodies be stopped.
Acoustic Deterrents
Several acoustic deterrents have not been proven effective in commercial installations. If developed, acoustic deterrents could be environmentally friendly and have a low likelihood of harming non-targeted organisms. Cavitation is a form of acoustic energy that initiates the formation and collapse of microbubbles. At frequencies between 10 and 380 kHz, this type of energy has demonstrated mortalities of veliger, juvenile, and adult zebra mussels. Exposure times are in the range of seconds for veligers, minutes for juveniles, and hours for adults (Kowalewski, Patrick, and Christie 1993).
Sound treatment using low frequency energy has prevented the settlement of zebra mussels and could be a valid option for reducing the spread of the organisms. Sound waves between 20Hz–20 kHz have caused veligers to detach and sink. Ultrasound waves between 39–41kHz have fragmented veligers in a few seconds and killed adults in 19 to 24 hours (Sonalysts and Aquatic Sciences 1991).
Vibration is the use of solid-borne acoustic energy in mechanical structures. This treatment will only work on structures that can be subjected to vibration and not suffer structural deterioration. Vibrational energy is effective in killing zebra mussel veligers and juveniles at just below 200 Hz and between 10 and 100 kHz (Nalepa and Schloesser 1993).
Plasma pulse technology (Sparktec Environmental, Inc.) has shown some effectiveness in controlling zebra mussels in intake pipes. The system works by releasing stored energy and creating a spark between two electrodes. This causes an intensive shockwave, a steam bubble, and ultraviolet light. (Mackie, Lowery and Cooper 2000). Paper by Shaeffer….. Attempts to re-test this technology by Reclamation have not been successful to-date.
Electrical Deterrents
Small intro required
Continuous low-voltage electrical fields may be able to control adult zebra mussel settlement. However, veligers and juveniles seem to remain relatively unaffected. Adult settlement can be completely prevented with an eight volt A-C current. This technology has recently been successfully applied using electrodes attached to the hull of a vessel to prevent mussel attachment (Smythe and Miller 2003).
Pulse power devices can be utilized to create an electrical field between two electrodes. When the field spans the entire width of the area to be protected, it has been effective in stunning and killing juveniles as they pass through the electrical field. Although not too effective against veligers because of their small body mass, pulse power has also been used successfully to prevent mussel settlement (Smythe and Miller 2003).
Filtration
Media Filters
This technology is capable of removing all stages of all Dreissenid mussels and protecting all downstream systems and components. Sand or media filters are frequently used for protection of individual components in power plants. For protection of moderately sized intakes, infiltration galleries have been constructed in some locations.
Mechanical Self Cleaning Filters
This technology is capable of removing all stages of Dreissenids if an appropriate screen size and configuration is used. Most conventional industrial strainers have strainer screen openings that will prevent some translocating mussel adults and most shell debris from fouling the raw water systems. None, however, will protect against the introduction of larval stage organisms. In most instances, it is not possible to retrofit existing strainers with finer screens and hope for successful mitigation. The performance of such modified strainer or filter tends to deteriorate, excessive clogging of the screen may result in stretching and tearing of the material, the backwash system may prove to be inadequate and the pressure drop caused by the strainer may be unacceptable.
Different types of filters, designed primarily for the removal of small particles, have been tested for Dreissenid veliger control by a number of different organizations. Wedge wire slot filters/strainers have difficulty in excluding veliger stages of Dreissenids. This is likely due to the fact that wedge wire type screen filters are being designed to remove inorganic matter, such as quartz or metal shavings, but they are not designed to stop organic matter from passing through the screen. Organic particles, due to their flexible nature, tend to “sneak through” the wedges of the screen.
Hydrocyclone or centrifugal separators filters were initially thought to be a mitigation option for facilities that already employ this technology for silt removal. A 1992 study (Acres 1992) tested two different centrifugal separators and concluded that the removal rate of larval mussel stages was no greater than 50%. A later study performed by Parsons andHarkins (2002) as part of a ballast water project confirmed demonstrated that a 100µm hydrocyclone filter was 30% less effective in removing both biotic and abiotic materials than either the disc or screen-type automatic backwash filter. The lack of success is probably due to the close to neutral buoyancy of Dreissenid veligers. Recently, hydrocyclone filters have been used successfully for removal of New Zealand mud snails in fish hatchery applications.
Excellent results were obtained by Ontario Power Generation using a continuous backwash, pleated screen filter(Koopmans and Hughes, 1993) and by the New York Power Authority using a modified clean-in-place bag filter (Kahabka and Talgo 1993) in eliminating Dreissenid veligers from incoming water.
Many filters are very good at removing all or most particles from the water stream. but most filtersare not able to process large volumes of water efficiently. Filters that use stainless steel, square weave mesh and automatic backwash seem to have the best balance between particle removal efficiency and volume of water filtered. A number of manufacturers produce such filters, but they must be carefully evaluated to ensure efficacy. A rugged design with a stainless steel mesh no greater than 80 microns in either direction and an efficient self-cleaning system should be capable of preventing the majority of ready-to-settle veligers from entering the downstream system.
Results from filter evaluation tests carried out on the Lower Colorado River
Filtration systems are not appropriate for water streams with continuously high sediment load. Under such conditions, the backwash system may not be able to remove the sediment cake that builds up on the screen. Very efficient backwash systems are capable of coping with higher sediment loads.
UV Radiation
The term ultraviolet is applied to that portion of the electromagnetic spectrum between visible light and x-rays, typically between 190 and 400 nm. This region is commonly subdivided into UVA, UVB and UVC, where UVA corresponds to the longer wavelength (lower energy regime), through to UVC, which corresponds to the shorter wavelength, higher energy end of the UV spectrum.
UV radiation is an effective method for preventing downstream settlement of Dreissenid veligers. Based on work by numerous authors in the early 1990s, the UVB and UVC portions of the spectrum were found to be most effective for Dreissenid veliger control. The basis for the control is thought to be the impact of the UV light on the essential functions of the veliger, thereby inactivating the organism and preventing attachment. The determination of the most effective wavelength and the radiation dose to achieve either immediate or latent mortality of the veligers or juveniles has been the subject of numerous studies.
Medium pressure mercury lamps have been shown as capable of delivering an effective dose to eliminate downstream veliger settlement.
A full-sized pilot UV system was installed at a power plant on Lake Huron in 1999. Twenty medium pressure lamps were arranged in four frames each containing five lamps (Figure 5). The total volume treated was 760 L/s (12,000 USgpm). The system was sized to deliver a radiation dose of 70–100 mWatt-scm2 to all particles passing through. This system was the only means of protection on this cooling system. During the operation of the UV system, lamps had to be serviced, the system experienced numerous upsets and occasionally it was even taken out of service inadvertently. Despite these issues, there was an 85% reduction in settlement in the system, when compared to control (Pickles 2000).
Figure 5. UV lamp rack used in an open channel system for Dreissenid veliger control.
The UV systems currently being tested for control of various species in ballast water are rugged and dependable. They use UV lights installed inside apipe, rather than the open array shown above, and they have been engineered to deliver a maximum dose in the least amount of time.
The effectiveness of a UV system is dependent on the characteristics of the raw water being treated. Factors, such as water transmittance, presence andsize of suspended solids, iron, hardness and temperature all affect the efficacy of the UV system. Treatment systems must be designed for the worst case scenarios. This means designing for peak flows, end of lamp life intensity, minimum transmittance and maximum suspended solids at the installation location. The aim of the system is to achieve 100% immediate or latent mortality in all ready to settle veligers which pass through. If an adequate dose is not delivered at this point, downstream settlement will occur as UV-based systems have no residual toxicity that could impact areas outside the influence of the lamps.
Three separate studies on the Lower Colorado River have shown the extreme effectiveness of medium pressure lamps in preventing quagga mussel settlement downstream.
Chemical Treatment
There are 3 general categories of chemicals used to treat zebra mussel infestations: metallic salts, oxidizing biocides, and non-oxidizing biocides. The most susceptible life stages to chemical treatment are post-spawned mussels that are in a low energy state, and all stages of veligers. Application rates and exposure time required data for these chemicals have been gathered from laboratory studies, power plant, and water treatment plant applications.
Metallic Salts
- Potassium salts—Potassium compounds are toxic to most bivalves, including Dreissenids and corbiculids. Lewis et al. (1996), using flow through experiments in mussel infested waters, concluded that at 20 mg/L caused 100% mortality in adults in 52 days while preventing any new settlement. Total mortality of small zebra mussels (7–11 mm) at a power plant on the Moselle River was achieved in 48 hours using 600 mg/L of KCl (Khalanski 1993). In addition to causing mortality, potassium in various forms has been observed to prevent valve closure in mussels and reduced filtration rates (Wildridge et al. 1996). Potassium chloride is used primarily as an end-of-season treatment for a number of closed loop systems, such as fire protection systems. Potassium chloride seems to be particularly effective in these types of semi-static systems due to mode of action and the fact that it does not possess the inherent demand characteristics typical of oxidants. Concentrations between 88–288 mg/l are necessary to cause swift mortality in adults. Such concentrations will likely kill native mussels as well, but are non-toxic to fish. In 2006, KCl was used to successfully eradicate zebra mussels from a rock quarry pond in Virginia. A 100% kill was attained with minimal environmental impacts to other aquatic species and to the drainage waters downstream. This method seems promising if a lethal concentration of KCl can be maintained for a 2–3 week period. More information about this project can be found at:
Although potassium compounds are non-toxic to higher organisms, such as fish, the toxicity to native bivalves makes the approval for use of potassium salts in once-through systems unlikely.