Among the greatest threats to Florida's water bodies is the uncontrolled growth of exotic aquatic plants. These biological pollutants have caused extensive problems for the economy, water-use, and resource management in Florida. Their introduction and spread have hindered navigation, flood control, recreation such as fishing, and other water sports, and their expansive growths have displaced native wildlife habitat and downgraded water quality (Anonymous 1971). Aquatic plant management is necessary to control many aggressive exotic aquatic and wetland plants in Florida (Joyce 1991). A comparison of the abilities of eight fish species to control nuisance aquatic plants was made by Avault et al. (1968). (Attempted control of aquatic nuisance weeds in the United States with insects is covered in the section on nonindigenous aquatic insects in this report.)
The history of aquatic plant management in Florida parallels the introduction of waterhyacinth (Eichhornia crassipes), alligatorweed (Alternanthera philoxeroides), and hydrilla (Hydrila verticillata) and the development of the state water resources. Before the 1900's, the predominant use of state waters was for commercial navigation. The introduction of waterhyacinth in 1884 quickly and seriously affected the navigability of Florida's rivers (Joyce 1991).
The costs for the control of aquatic plants in Florida are available from several sources, but assessment of their accuracy is difficult because of the possible overlap of reporting periods and funding records. Most management and control of aquatic plants in Florida's public waters are conducted with funding from two public agencies, the Cooperative Aquatic Plant Control Program and the State Funding for Aquatic Plant Control Program. Plant control in navigable waters with public boat ramps is usually conducted under the cooperative program. The role of all state and federal agencies in the control of nuisance plants in Florida is summarized by Nelson and Dupes (1988).
In 1955, the Florida legislature appropriated $226,500 and the Florida Game and Freshwater Fish Commission added $100,000 for a 2-year control of waterhyacinths (Schmitz et al. 1993). During 1984-1987, the cost for the control of nuisance plants under the cooperative program was $5.9 million on 17,501 ha at a cost of $336/ha (Nelson and Dupes 1988).
In 1986, the Water Resources Development Act changed the federal-state cost-sharing ratio from 70:30 to 50:50 and thus decreased the federal share. In 1987, the U.S. Army Corps of Engineers provided 30% of the funds, whereas the state of Florida provided 29%. Local governments, including water management districts, provided 26%. The remaining 15% is estimated expenditure by private individuals based on issued permits for the control of exotic aquatic weeds. Publicly funded weed-control costs in Florida were more than $11.6 million during 1987 (Nelson and Dupes 1988). The average cost per hectare was $462. All control costs included salaries, benefits, equipment rental, herbicides, contractual work, and indirect administrative costs. Almost half of the total control costs were for the control of hydrilla (Buckingham and Habeck 1990). The history and cost of controling hydrilla in Orange and Lochloosa Lakes in Alachua County, Florida was summarized by Hinkle (1995). Weather conditions at the time of application of herbicides, water levels at the time of application and shortly afterwards, water clarity, and hydrilla plants activity growing and not at the surface contributed to the efficacy of the herbicides. Control costs varied from $22 to $2600 per acre depending on the combination of the above conditions with the average cost being $114 per acre.
The identification and appropriate methods for the control of aquatic nuisance plants in aquaculture and in farm ponds is discussed by Thayer et al. (1990). Langeland (1990) discussed the current methods for the control of the four most serious nonindigenous woody pest-plant species in Florida: Australian pine (Casuarina spp.), Brazilian pepper (Schinus terebinthifolius), Asiatic columbine (Aquilegia spp.) and melaleuca (Melaleuca quinquenervia).
Between 1980 and 1989, the approximate cost of aquatic-plant management to public agencies in Florida was at least $104 million (Schmitz 1990). This amount does not include the total cost of aquatic-plant management in areas that are exempt from permit requirements by the Florida Department of Natural Resources. During the same period, more than $43 million were spent on managing the waterhyacinth and the waterlettuce and more than $55 million were spent on managing hydrilla in Florida's public waters. During the fiscal years 1991-1992, $6.2 million of federal, state, and local funds were spent to manage aquatic nuisance plants on 17,223 ha of the state's public lakes and rivers (Schardt 1991). Most of the funds were used to manage hydrilla, waterhyacinth, and waterlettuce. Presently, hydrilla is the most troublesome plant at an annual control expenditure of $7 million (Schmitz et al. 1993). Even with these expenditures, the number of new hydrilla infestations continues to increase. For example, hydrilla started to rapidly spread in Lake Istokpoga in 1987; by 1988 and 1989 more than $1.4 million were spent on fluridone applications to return hydrilla to maintenance control levels (Schmitz et al 1993). Waterhyacinth and waterlettuce are second in control costs of combined annual control expenditures near $2.5 million. The other nonindigenous plant species that were introduced or spread as forage grasses (torpedograss [Panicum repens] and para-grass [Brachiaria mutica]) are third in annual control expenditures. Other exotic plants such as alligatorweed (Alternanthera philoxeroides), salvinia (Salvinia minima), and hygro (Hygrophila polysperma) require approximately $386,000 of the annual $14 million for the control of exotic aquatic plants in Florida's waterways (Schmitz 1990; Schmitz et al. 1991; (Schmitz et al. 1993).
In 1987, the Florida Department of Natural Resources inventoried 481 water bodies and reported water hyacinth in 65% and hydrilla in 45%. Hydrilla covered more than 19,845 ha, a 17% increase since 1983, even though at least 4,860 ha were controlled annually (Buckingham and Habeck 1990).
Most people consider all effects of nonindigenous aquatic plants on the economy as undesirable. However, a full evaluation must weigh the harm against the economic gains by the large aquatic plant industry in Florida (earlier described in more detail). Some consideration also must be given to employment for many families in Florida in the control of nuisance plants. However, only relatively few people profit, but the harm from nuisance plants tends to be permanent and affects all people. A workable system that makes liable individuals or organizations responsible for the cost of correcting problems from introductions of nonindigenous organisms has not been identified. If adequate precautions had been taken before the importation and introduction of the nuisance plants, benefits could possibly have been realized without cost to the taxpayer for control.
Today, the most severe aquatic-plant problems in Florida are caused by water hyacinth and hydrilla. Both species can grow to densities that severely impair or prohibit navigation, restrict the flow of water, and limit or preclude the recreational use of water bodies. To minimize the harm from aquatic weed infestation, millions of dollars are spent each year by federal, state, and local agencies to control aquatic weeds in Florida. Despite the severity of the aquatic- weed problem in Florida, few studies have been conducted of the effects of weed infestations on user groups and the consequences for the economy of Florida (Milon et al. 1986).
Milon et al. (1986) conducted an economic analysis of the benefits of aquatic-weed control in north-central Florida. Their survey was designed to identify sport anglers' preferences and economic values of aquatic-weed control in the vicinity of Orange and Lochloosa lakes in north-central Florida. The responses--although not uniform across the surveyed population--indicated that anglers' decisions to visit fishing sites were influenced by aquatic-weed conditions. Anglers recognized the need for aquatic-weed controls and expressed a significant willingness to pay for different levels of control. The total economic benefits of aquatic-weed control to prevent severe infestation of hyacinth and hydrilla at Orange and Lochloosa lakes was an estimated $386,063 in 1985 (Milon et al. 1986). The incremental benefits of increasing weed control beyond prevention to reduce hyacinth and hydrilla to just small patches around the lakes was $194,433. In addition, aquatic-weed controls sustain a significant contribution for the local economy; total gross expenditures for sport fishing at Orange and Lochloosa lakes were an estimated $5,606,697 (Milon et al. 1986). With the addition of multiplier effects from nonresident expenditures for sport-fishing trips, total regional economic activity of $10,787,289 was attributed to weed control in Orange and Lochloosa lakes (Milon et al. 1986). Later, Milon and Welsh (1989) conducted an economic analysis of sport fishing and the effects of hydrilla management in Lake County, Florida. They reported the results of a telephone and mail survey to identify sport anglers' preferences and economic values for aquatic-plant control in lakes Harris and Griffin in Lake County. The survey was designed to evaluate the effects of different information about the effects of hydrilla management on anglers' preferences and willingness to pay for control. The survey results indicated that anglers prefer to have some hydrilla in lakes, but only few anglers wanted uncontrolled growth. Willingness to pay for hydrilla controls was estimated to range from $50,000 to $176,000/year and depended on the level of control. The largest portion of the benefits from hydrilla controls accrued to anglers from Lake County, however, nonresidents also received significant benefits. In addition, anglers who used the lakes generated total expenditures of more than $1.75 million in Lake County; the largest portion was attributable to resident anglers (Milon and Welsh 1989).
Colle et al. (1987) estimated the total annual expenditures associated with the sport fishing on Orange Lake as approximately $1 million in 1978-79. A decrease of expenditures by 90% in 1977 was due to almost total coverage of the lake by hydrilla
