《数学建模》美赛优秀论文：01C Waging War Against the Zebra Mussel.pdf_大学文库

400 The UMAP Journal 22. 4(2001) the calcium concentration in the lake will significantly enhance its suitability as zebra mussel habitat We find that using the goby fish to reduce zebra mussels is not a feasible op tion if the community is concerned with ecological impact, due to the invasive nature of the goby. Environmental Factors in the Spread of Zebra mussels We first discuss the characteristics of a suitable breeding habitat and then address how the population is unintentionally introduced to new areas opulation growth depends on successful reproduction and survival to adulthood. Veligers, zebra mussel larvae, are more sensitive to stress in their surrounding environment and therefore have more stringent survival require ments. Hence, we examine environmental conditions that can cause stress for the zebra mussel, especially in the larval and juvenile stages Ion Concentrations and ph Calcium is required for the viability of zebra mussel populations because it is a major component in their shells. Alkalinity, which is directly linked to calcium concentrations, is an important variable in determining habitat suit- ability for zebra mussels. Calcium concentrations of 12 mg/L and alkalinity corresponding to 50 mg CaCO3/L are required for adult zebra mussel popula tions [Heath 1993]. A calcium concentration of 12 mg/L is also the minimum required for embryo survival, though higher concentrations enhance egg fer tilization and embryo survivorship [ Sprung 1987] Phosphorous and nitrogen are significant factors to zebra mussel population growth because they are critical nutrients for the freshwater phytoplankton that comprise the primary food source of the zebra mussel. Thus, they are an indirect measure of food availability Baker et al. 1993 The pH of the water is another critical factor. Adults require a pH of about 7. 2; in lower pH environments, they experience a net loss of calcium, sodium, and potassium ions, and in very acidic waters adult zebra mussels eventu- ally die because of ion imbalance [Heath, 1993]. Adults can survive in pH 7 environments, but eggs survive only between pH 7.4 to 9.4 [Baker et al. 1993 Temperature Adult mussels can survive temperatures from 0C to 32C, but growth oc curs only above 10C [Morton 1969] and breeding is triggered only in temper atures of at least 12C [Heath 1993]. Higher temperatures increase overall egg

400 The UMAP Journal 22.4 (2001) the calcium concentration in the lake will significantly enhance its suitability as zebra mussel habitat. We find that using the goby fish to reduce zebra mussels is not a feasible option if the community is concerned with ecological impact, due to the invasive nature of the goby. Environmental Factors in the Spread of Zebra Mussels We first discuss the characteristics of a suitable breeding habitat and then address how the population is unintentionally introduced to new areas. Population growth depends on successful reproduction and survival to adulthood. Veligers, zebra mussel larvae, are more sensitive to stress in their surrounding environment and therefore have more stringent survival requirements. Hence, we examine environmental conditions that can cause stress for the zebra mussel, especially in the larval and juvenile stages. Ion Concentrations and pH Calcium is required for the viability of zebra mussel populations because it is a major component in their shells. Alkalinity, which is directly linked to calcium concentrations, is an important variable in determining habitat suitability for zebra mussels. Calcium concentrations of 12 mg/L and alkalinity corresponding to 50 mg CaCO3/L are required for adult zebra mussel populations [Heath 1993]. A calcium concentration of 12 mg/L is also the minimum required for embryo survival, though higher concentrations enhance egg fertilization and embryo survivorship [Sprung 1987]. Phosphorous and nitrogen are significant factors to zebra mussel population growth because they are critical nutrients for the freshwater phytoplankton that comprise the primary food source of the zebra mussel. Thus, they are an indirect measure of food availability [Baker et al. 1993]. The pH of the water is another critical factor. Adults require a pH of about 7.2; in lower pH environments, they experience a net loss of calcium, sodium, and potassium ions, and in very acidic waters adult zebra mussels eventually die because of ion imbalance [Heath, 1993]. Adults can survive in pH 7 environments, but eggs survive only between pH 7.4 to 9.4 [Baker et al. 1993]. Temperature Adult mussels can survive temperatures from 0◦C to 32◦C, but growth occurs only above 10◦C [Morton 1969] and breeding is triggered only in temperatures of at least 12◦C [Heath 1993]. Higher temperatures increase overall egg

Waging War Against the Zebra Mussel 401 production [Borcherding 1995] but also increase metabolism and demand for dissolved oxygen. Zebra mussels require 25%oxygen saturation(2 mg/L)at 25C [Heath 1993]. Based on these values and the data provided for Lake A we find that neither temperature nor dissolved oxygen is a limiting factor of zebra mussel proliferation there. Saltatory Spread Saltatory spread is the movement of a species in large leaps rather than by gradual transitions. It is believed that zebra mussels were introduced to the great Lakes system in 1986 from larvae discharged in ballast water from a commercial ship [Griffiths et al. 1991. As of 1996, zebra mussels had spread to 18 states in the United States(as far south as Louisiana) and two provinces in Canada, almost entirely within commercially navigated waters Johnson and Padilla 1996]-strong evidence that commercial shipping was the primary vector of initial zebra mussel spread in the United States and canada Most of the united states contains environments suitable for zebra mus sel infestation [Strayer 1991], so the identification and elimination of saltatory spread to inland water systems is key to preventing infestation of the western United States. Transient recreational boating seems to be the most likely candi- date for inland spread of the species. Based on this and other studies, it appears that recreational boating represents a substantial threat to the containment of the zebra mussel infestation in america Advective and Diffusive Spread Zebra mussels live the first few weeks of their lives as planktonic larvae that are easily diffused or carried by moving water. This allows for the widespread dissemination of offspring by diffusion, currents, and wind-driven advection within a lake or watershed Johnson and Carlton 1996], which largely explain the species rapid spread [Martel 1993]. However, veligers have been shown to ave high mortality in turbulent waters, and mussel density in streams flowing out ofinfested lakes has been shown to decrease exponentially with the distance downstream [Horvath and Lamberti 1999]. Post-metamorphic zebra mussels have the ability to secrete long monofilament-like mucous threads that increase hydrodynamic drag and allow for faster advective spread [Martel 1993]. These juveniles can survive turbulence much better than veligers, which implies that they are the primary vector of downstream advective spread Zebra Mussel Population Model for lake a Using our model, we attempt to answer two important questions 1. Given chemical information for a given site . is the site suitable for zebra

Waging War Against the Zebra Mussel 401 production [Borcherding 1995] but also increase metabolism and demand for dissolved oxygen. Zebra mussels require 25% oxygen saturation (2 mg/L) at 25◦C [Heath 1993]. Based on these values and the data provided for Lake A, we find that neither temperature nor dissolved oxygen is a limiting factor of zebra mussel proliferation there. Saltatory Spread Saltatory spread is the movement of a species in large leaps rather than by gradual transitions. It is believed that zebra mussels were introduced to the Great Lakes system in 1986 from larvae discharged in ballast water from a commercial ship [Griffiths et al. 1991]. As of 1996, zebra mussels had spread to 18 states in the United States (as far south as Louisiana) and two provinces in Canada, almost entirely within commercially navigated waters [Johnson and Padilla 1996]—strong evidence that commercial shipping was the primary vector of initial zebra mussel spread in the United States and Canada. Most of the United States contains environments suitable for zebra mussel infestation [Strayer 1991], so the identification and elimination of saltatory spread to inland water systems is key to preventing infestation of the western United States. Transient recreational boating seems to be the most likely candidate for inland spread of the species. Based on this and other studies, it appears that recreational boating represents a substantial threat to the containment of the zebra mussel infestation in America. Advective and Diffusive Spread Zebra mussels live the first few weeks of their lives as planktonic larvae that are easily diffused or carried by moving water. This allows for the widespread dissemination of offspring by diffusion, currents, and wind-driven advection within a lake or watershed [Johnson and Carlton 1996], which largely explain the species rapid spread [Martel 1993]. However, veligers have been shown to have high mortality in turbulent waters, and mussel density in streams flowing out of infested lakes has been shown to decrease exponentially with the distance downstream [Horvath and Lamberti 1999]. Post-metamorphic zebra mussels have the ability to secrete long monofilament-like mucous threads that increase hydrodynamic drag and allow for faster advective spread [Martel 1993]. These juveniles can survive turbulence much better than veligers, which implies that they are the primary vector of downstream advective spread. Zebra Mussel Population Model for Lake A Using our model, we attempt to answer two important questions: 1. Given chemical information for a given site, is the site suitable for zebra mussels?

402 The UMAP Journal 22. 4(2001) 2. If a site is determined to be a suitable habitat, will it support a low-or a high-density zebra mussel population? Rather than focusing on developing a complicated model that would predict le exact size of the population, we devised a simple, comprehensive model that answers these questions The inspiration for our model was derived from Ramcharan [1992 Assumptions The density of juveniles collected on the settling plates is proportional to the size of the adult population; this assumption allows us to use the provided data to predict the severity of the zebra mussel infestation. significantly vary with changes in the size of the zebra mussel population The chemical composition and concentrations(such as calcium levels)do no Examining the first data set from Lake A, we find that pH and calcium oncentration are the two most important factors in determining whether zebra mussel population is viable in a given site. This is reasonable, conside that the zebra mussels are very sensitive to ph and they need calcium to br their shells when developing from veligers to juveniles and onto adults We do not include temperature, because although it is important to the ife cycle of the zebra mussel, as long as the temperature is high enough to signal spawning, reproduction will occur. All 10 sites in Lake A had suitable temperatures for spawning We developed a model equation(Model 1)utilizing the values provided for pH and calcium concentration for the 1992 to 1999 period that give a simple measure to predict the viability(v) of a zebra mussel invasion at a particular site. The coefficients of the two variables (ph and [Ca)are used to weight the relative importance of the two factors. The range of values for pH for the ten sites is smaller than the range of values for calcium concentration, thus the coefficients function to equalize the importance of these two factors. The exact values of the coefficients were determined by successively modifying and refining the values until an equation was found that accurately reflected whether the lake site was a suitable habitat or not based on the population data We chose the threshold value of 10. 4 for viability because there appears to be a break there between the sites where zebra mussels survived and the sites where they were absent, and because 10. 4 is close to the value from the equation with 7. 4 for pH and 12 mg/L for calcium concentration. =10pH+0.2la If V >10.4. the site is a suitable habitat for zebra mussel Applying Model 1 to sites 1-10 in Lake A produces Table 1

402 The UMAP Journal 22.4 (2001) 2. If a site is determined to be a suitable habitat, will it support a low- or a high-density zebra mussel population? Rather than focusing on developing a complicated model that would predict the exact size of the population, we devised a simple, comprehensive model that answers these questions. The inspiration for our model was derived from Ramcharan [1992]. Assumptions • The density of juveniles collected on the settling plates is proportional to the size of the adult population; this assumption allows us to use the provided data to predict the severity of the zebra mussel infestation. • The chemical composition and concentrations (such as calcium levels) do not significantly vary with changes in the size of the zebra mussel population. Examining the first data set from Lake A, we find that pH and calcium concentration are the two most important factors in determining whether a zebra mussel population is viable in a given site. This is reasonable, considering that the zebra mussels are very sensitive to pH and they need calcium to build their shells when developing from veligers to juveniles and onto adults. We do not include temperature, because although it is important to the life cycle of the zebra mussel, as long as the temperature is high enough to signal spawning, reproduction will occur. All 10 sites in Lake A had suitable temperatures for spawning. We developed a model equation (Model 1) utilizing the values provided for pH and calcium concentration for the 1992 to 1999 period that give a simple measure to predict the viability (V ) of a zebra mussel invasion at a particular site. The coefficients of the two variables (pH and [Ca]) are used to weight the relative importance of the two factors. The range of values for pH for the ten sites is smaller than the range of values for calcium concentration, thus the coefficients function to equalize the importance of these two factors. The exact values of the coefficients were determined by successively modifying and refining the values until an equation was found that accurately reflected whether the lake site was a suitable habitat or not based on the population data. We chose the threshold value of 10.4 for viability because there appears to be a break there between the sites where zebra mussels survived and the sites where they were absent, and because 10.4 is close to the value from the equation with 7.4 for pH and 12 mg/L for calcium concentration. V = 1.0 pH + 0.2 [Ca] If V > 10.4, the site is a suitable habitat for zebra mussels. Applying Model 1 to sites 1–10 in Lake A produces Table 1

404 The UMAP Journal 22. 4(2001) To improve upon Model l, we account for trends observed in the second data set from Lake A in constructing a more descriptive model to answer question(2) By including parameters for total phosphorus and total nitrogen, we account for the role of food availability on density. Following Ramcharan [1992], we employ the natural logarithms of total phosphorus and total nitrogen. Once again, by successively altering the coefficients, we determine an equation for the density of populations in the lake sites. We define high density as more than 400,000 juveniles/m on the settling plates collected at the peak of the reproductive season D=1.0 pH+0.2 [Ca]+0.1In [TP+0. 4In ITNI D10.5 the site will support a high-density population By averaging the total phosphorus(TP) and total nitrogen(TN) values for each site in the second set of chemical data for Lake A, we calculated tpl and ITN]. USing those values in Model 2, we calculated the density D)for each site, as shown in table 2 Table 2 Density values in sites 1-10 in Lake A site In/TPI In[TN] D low/high mg/L mg/L 2.99-0.59812 hi 2 3.51-0.89211.8 g 079610.5high 4 4.47-0.81410.3 5-4400.87910.6 6|-4560.8529.5 absence 7-412-097110.2 8|-439-0.862103 9|-416-0965103 10-301-040598 absence Model 2 predicts that sites 1, 2, 3, and 5 should be able to support high density populations. The second set of population data used in Figure 2 is consistent with the first set of population data. Figure 2 shows that all four of the high-density sites have an average of more than 400,000 juveniles/m which agrees with the prediction made by our model. In the enlargement of Figure 2, sites 4, 7, 8, and 9 have an average of less than 400,000 juveniles/m2 while sites 6 and 10 have virtually no juvenile zebra mussels The most significant weakness of our model is that it does not predict pop- ulation versus time. Our model simply classifies an area's risk of invasion by examining the levels of critical chemicals to which the zebra mussels are sensitive

404 The UMAP Journal 22.4 (2001) To improve upon Model 1, we account for trends observed in the second data set from Lake A in constructing a more descriptive model to answer question (2). By including parameters for total phosphorus and total nitrogen, we account for the role of food availability on density. Following Ramcharan [1992], we employ the natural logarithms of total phosphorus and total nitrogen. Once again, by successively altering the coefficients, we determine an equation for the density of populations in the lake sites. We define high density as more than 400,000 juveniles/m2 on the settling plates collected at the peak of the reproductive season. D = 1.0 pH + 0.2 [Ca] + 0.1 ln [TP] + 0.4 ln [TN]. If    D 10.5, the site will support a high-density population. By averaging the total phosphorus (TP) and total nitrogen (TN) values for each site in the second set of chemical data for Lake A, we calculated [TP] and [TN]. Using those values in Model 2, we calculated the density (D) for each site, as shown in Table 2. Table 2. Density values in sites 1–10 in Lake A. site ln[TP] ln[TN] D low/high mg/L mg/L 1 −2.99 −0.598 12.5 high 2 −3.51 −0.892 11.8 high 3 −4.30 −0.796 10.5 high 4 −4.47 −0.814 10.3 low 5 −4.40 −0.879 10.6 high 6 −4.56 −0.852 9.5 absence 7 −4.12 −0.971 10.2 low 8 −4.39 −0.862 10.3 low 9 −4.16 −0.965 10.3 low 10 −3.01 −0.405 9.8 absence Model 2 predicts that sites 1, 2, 3, and 5 should be able to support high density populations. The second set of population data used in Figure 2 is consistent with the first set of population data. Figure 2 shows that all four of the high-density sites have an average of more than 400,000 juveniles/m2, which agrees with the prediction made by our model. In the enlargement of Figure 2, sites 4, 7, 8, and 9 have an average of less than 400,000 juveniles/m2, while sites 6 and 10 have virtually no juvenile zebra mussels. The most significant weakness of our model is that it does not predict population versus time. Our model simply classifies an area’s risk of invasion by examining the levels of critical chemicals to which the zebra mussels are sensitive

406 The UMAP Journal 22. 4(2001) Lake b and lake c and determine the level of risk of successful zebra mussel invasion in these two lakes. We averaged the values together for all of the years We also assume that these two lakes are fairly uniform in chemical composition Table 3 Viability and density values for Lake B and Lake C pH [Ca] ITPl ITN Mg/L ng/L Lake b7.6311.56.02×10-30.182993874 Lake C 4.74 1.15 According to our Model 1, Lake B should not be at risk for a zebra mussel invasion because it is not a suitable habitat(V 10.4): this prediction makes sense because the average calcium concentration is 11.5 mg/L, which is below the 12 mg/L threshold. Lake C is in no danger to an invasion, since D=4.97, which corresponds to the fact that both the ph and the calcium concentration are far below the threshold values De-icing Policy for Community of Lake B De-icing compounds increase the solute concentration in the melted ice, lowering its freezing temperature and preventing the ice from reforming. Thus, de-icing compounds are water soluble and can easily enter the water supply The most commonly used de-icers are calcium chloride, calcium magnesium acetate, sodium chloride, and potassium acetate salts. Calcium magnesium ac- etate is popular because it has fewer negative environmental impacts, whereas calcium chloride is widely used because it lowers the freezing point of water more than sodium chloride Ithough these calcium containing compounds may be excellent choices for de-icing agents, our model indicates that using these compounds increases the risk of zebra mussel invasion. According to Model 2, if calcium levels increase in Lake b by 50%(D=9.9), a low density population of zebra mussels can exist Doubling the calcium levels(d= 11.0)will support a high density population De-icing agent can therefore have a significant impact on the zebra mussel population. We recommend that this community use sodium chloride or potassium acetate salts, or decrease the amount of calcium salts used by mixing them with the other noncalcium salts or sand. We also suggest pre-wetting the salts before they are applied to the roads, to reduce the amount entering the water system Lastly, the community should develop a strategy for anti-icing, applying de- icing agents before ice forms, thus decreasing the amount of de-icing ag used in each storm. These efforts should help prevent Lake B from becom habitable by zebra mussels

406 The UMAP Journal 22.4 (2001) Lake B and Lake C and determine the level of risk of successful zebra mussel invasion in these two lakes. We averaged the values together for all of the years. We also assume that these two lakes are fairly uniform in chemical composition. Table 3. Viability and density values for Lake B and Lake C. pH [Ca] [TP] [TN] V D mg/L mg/L mg/L Lake B 7.63 11.5 6.02 × 10−3 0.182 9.93 8.74 Lake C 4.74 1.15 4.97 According to our Model 1, Lake B should not be at risk for a zebra mussel invasion because it is not a suitable habitat (V < 10.4); this prediction makes sense because the average calcium concentration is 11.5 mg/L, which is below the 12 mg/L threshold. Lake C is in no danger to an invasion, since D = 4.97, which corresponds to the fact that both the pH and the calcium concentration are far below the threshold values. De-icing Policy for Community of Lake B De-icing compounds increase the solute concentration in the melted ice, lowering its freezing temperature and preventing the ice from reforming. Thus, de-icing compounds are water soluble and can easily enter the water supply. The most commonly used de-icers are calcium chloride, calcium magnesium acetate, sodium chloride, and potassium acetate salts. Calcium magnesium acetate is popular because it has fewer negative environmental impacts, whereas calcium chloride is widely used because it lowers the freezing point of water more than sodium chloride. Although these calcium containing compounds may be excellent choices for de-icing agents, our model indicates that using these compounds increases the risk of zebra mussel invasion. According to Model 2, if calcium levels increase in Lake B by 50% (D = 9.9), a low density population of zebra mussels can exist. Doubling the calcium levels (D = 11.0) will support a high density population. De-icing agent can therefore have a significant impact on the zebra mussel population. We recommend that this community use sodium chloride or potassium acetate salts, or decrease the amount of calcium salts used by mixing them with the other noncalcium salts or sand. We also suggest pre-wetting the salts before they are applied to the roads, to reduce the amount entering the water system. Lastly, the community should develop a strategy for anti-icing, applying deicing agents before ice forms, thus decreasing the amount of de-icing agent used in each storm. These efforts should help prevent Lake B from becoming habitable by zebra mussels

Waging War Against the Zebra Mussel 407 Methods for Reducing Zebra Mussel Populations It is estimated that $3 billion will be spent in the next decade combating th zebra mussel infestation [Magee et al. 1996]. Besides damaging infrastructure (pipes, tubing, gratings), the zebra mussel is able to out-compete native species for space and food and can destroy commercial and recreational fish stocks Since the zebra mussel body fat stores toxic chemicals, the introduction of these mussels into the food-chain could lead to human consumption of these harmful chemicals. There are three available options for dealing with zebra mussel infestation (1)Introduce a natural predator(the round goby (2& 3)Eradicate and/or control the zebra population by utilizing preventative and reactive control strategies Introducing a natural predator, such as the round goby, may be more prob lematic than the zebra mussel infestation. Although the round goby shows selectivity in consuming zebra mussels over native clams, the goby will non- selectively consume a variety of bait, fishes, and invertebrates IGhedotti et al. 1995]. In addition, the goby is extremely territorial and can aggressively occupy prime breeding areas and successfully compete for food against na tive species. Fortunately, there are more environmentally sound methods of controlling zebra mussel infestations Preventive and reactive Strategies Preventive control methods include implementing restrictive legislation and periodic monitoring of waterways to minimize introduction of zebra mus sels and to improve early detection, thereby facilitating the development of appropriate strategies to eradicate or control the mussel population. Reactive strategies are a more aggressive mode of action in response to a potential or ongoing invasion and should be dependent on the level of infestation Preventive Control Strategies: Legislation and monitoring Legislation is a useful way to coordinate research with monitoring facil ities, commercial industries, and the public. The United States Nonindige nous Aquatic Nuisance Prevention Control Act of 1990(PL 101-646)[ Florida Caribbean Science Center 2001] recommends that recreational vessels exchange ballast water before entering new waters, since this is the primary mode of saltatory non-native species introduction [Boleman et al. 1997]. In addition, the U.S. Code [Legal Information Institute 2001] suggests implementing alter native ballast water management, including modifying the ballast tank and

Waging War Against the Zebra Mussel 407 Methods for Reducing Zebra Mussel Populations It is estimated that $3 billion will be spent in the next decade combating the zebra mussel infestation [Magee et al. 1996]. Besides damaging infrastructure (pipes, tubing, gratings), the zebra mussel is able to out-compete native species for space and food and can destroy commercial and recreational fish stocks. Since the zebra mussel body fat stores toxic chemicals, the introduction of these mussels into the food-chain could lead to human consumption of these harmful chemicals. There are three available options for dealing with zebra mussel infestation: (1) Introduce a natural predator (the round goby). (2 & 3) Eradicate and/or control the zebra population by utilizing preventative and reactive control strategies. Introducing a natural predator, such as the round goby, may be more problematic than the zebra mussel infestation. Although the round goby shows selectivity in consuming zebra mussels over native clams, the goby will nonselectively consume a variety of bait, fishes, and invertebrates [Ghedotti et al. 1995]. In addition, the goby is extremely territorial and can aggressively occupy prime breeding areas and successfully compete for food against native species. Fortunately, there are more environmentally sound methods of controlling zebra mussel infestations. Preventive and Reactive Strategies Preventive control methods include implementing restrictive legislation and periodic monitoring of waterways to minimize introduction of zebra mussels and to improve early detection, thereby facilitating the development of appropriate strategies to eradicate or control the mussel population. Reactive strategies are a more aggressive mode of action in response to a potential or ongoing invasion and should be dependent on the level of infestation. Preventive Control Strategies: Legislation and Monitoring Legislation is a useful way to coordinate research with monitoring facilities, commercial industries, and the public. The United States Nonindigenous Aquatic Nuisance Prevention Control Act of 1990 (P.L. 101–646) [Florida Caribbean Science Center 2001] recommends that recreational vessels exchange ballast water before entering new waters, since this is the primary mode of saltatory non-native species introduction [Boleman et al. 1997]. In addition, the U.S. Code [Legal Information Institute 2001] suggests implementing alternative ballast water management, including modifying the ballast tank and

408 The UMAP Journal 22. 4(2001) intake system to prevent the unintentional introduction of new species. The improved sighting, reporting, and education under this plan will help the pub lic and commercial sectors prevent the spread of zebra mussels Reactive Control Strategies Acute Zebra Mussel Infestation In cases of acute or localized infestations, ap- plying the least expensive method of preventing infrastructure damage is to employ a foul release coating in concert with mechanical cleanings and mechanical filtration. Coating pipes and surfaces in contact with the water with antifouling polymers, such as silicones and fluorochemicals, creates a slippery surface that makes it difficult for zebra mussels to attach [Magee et al. 1996]. These reagents are effective for 2-5 years [Boelman et al. 1997 Analternative and equally successful method of infrastructure protection is the application of zinc thermal spray (zts)on metal surfaces. In addition to preventing corrosion, ZTS is the most durable and long-lasting zebra mussel repellent. The slow dissolution of heavy metal ions from ZTS is toxic to zebra mussels. In addition, the US Army Corps of Engineers Zebra Mussel Control Handbook suggests that low release of heavy metals and a large dilution factor produce minimal secondary effects on nontarget species. However, before implementing this strategy, it is critical that the environmental effects studied and the implementation meet federal standards. Mechanical cleaning is a labor-intensive method of removing zebra mussel from infrastructure. The drawback to simply brushing and scraping zebra mussels off surfaces is that the scrubbings need to be repeated regularly The removed zebra mussels also have to be transported and disposed of in landfills The final strategy for dealing with acute zebra mussel infestation is in- stalling mechanical filtration systems. Water screen filters and strainers can be placed on water intakes. A mesh size of 25-40 mm is able to stop the inflow of veligers and translocation of larger zebra mussels. However, this system requires continuous maintenance Global Zebra Mussel Infestation Severe and large-area infestation and pop- ulation expansion need to be treated with aggressive methods, since it is more beneficial to address the widespread infestation problem rather than fight specific site-related mussel-density problems. Since these methods re- quire widespread application, the expense associated with implementation is higher than the strategies for dealing with acute infestation. There is also a potential for harming native organisms and commercial industries. How ever,after intense scrutiny, the following methods are the most effective ways to control and potentially eradicate severe zebra mussel infestations Thermal treatment. The discharge of heated water is a cost-effective and efficient method for controlling and eradicating the macrofouling ze bra mussel. Since zebra mussels are able to acclimate to temperature

408 The UMAP Journal 22.4 (2001) intake system to prevent the unintentional introduction of new species. The improved sighting, reporting, and education under this plan will help the public and commercial sectors prevent the spread of zebra mussels. Reactive Control Strategies Acute Zebra Mussel Infestation In cases of acute or localized infestations, applying the least expensive method of preventing infrastructure damage is to employ a foul release coating in concert with mechanical cleanings and mechanical filtration. Coating pipes and surfaces in contact with the water with antifouling polymers, such as silicones and fluorochemicals, creates a slippery surface that makes it difficult for zebra mussels to attach [Magee et al. 1996]. These reagents are effective for 2–5 years [Boelman et al. 1997]. An alternative and equally successful method of infrastructure protection is the application of zinc thermal spray (ZTS) on metal surfaces. In addition to preventing corrosion, ZTS is the most durable and long-lasting zebra mussel repellent. The slow dissolution of heavy metal ions from ZTS is toxic to zebra mussels. In addition, the US Army Corps of Engineers Zebra Mussel Control Handbook suggests that low release of heavy metals and a large dilution factor produce minimal secondary effects on nontarget species. However, before implementing this strategy, it is critical that the environmental effects studied and the implementation meet federal standards. Mechanical cleaning is a labor-intensive method of removing zebra mussel from infrastructure. The drawback to simply brushing and scraping zebra mussels off surfaces is that the scrubbings need to be repeated regularly. The removed zebra mussels also have to be transported and disposed of in landfills. The final strategy for dealing with acute zebra mussel infestation is installing mechanical filtration systems. Water screen filters and strainers can be placed on water intakes. A mesh size of 25–40 mm is able to stop the inflow of veligers and translocation of larger zebra mussels. However, this system requires continuous maintenance. Global Zebra Mussel Infestation Severe and large-area infestation and population expansion need to be treated with aggressive methods, since it is more beneficial to address the widespread infestation problem rather than fight specific site-related mussel-density problems. Since these methods require widespread application, the expense associated with implementation is higher than the strategies for dealing with acute infestation. There is also a potential for harming native organisms and commercial industries. However, after intense scrutiny, the following methods are the most effective ways to control and potentially eradicate severe zebra mussel infestations. Thermal treatment. The discharge of heated water is a cost-effective and efficient method for controlling and eradicating the macrofouling zebra mussel. Since zebra mussels are able to acclimate to temperature