|
State of LakesA one-year evaluation was undertaken of the natural resources of the chain-of-lakes system in eastern Palm Beach County, Florida. The waterbodies are natural or once-natural freshwater lakes that lie perched along the western slope of the coastal ridge. Included in the study were Pine Lake, Lake Clarke, Lake Osborne, Lake Ida, Lake Eden, and their connecting waters. Diagnosis of the current status of the lake system was based on analysis of existing databases from local, state, and federal sources, and from a field monitoring program established to fill critical information needs. Information was collected on physical, chemical, and biological parameters of the lakes as well as on land use patterns within the C-51, C-16, and C-15 drainage basins in which the lakes lie. Based on findings of the diagnostic studies, a management plan was developed that is tailored to address specific problems facing the lakes. The goal of the management plan is to provide for the preservation, maintenance, and restoration of aquatic and wetland resources in the chain-of-lakes system, within the constraints imposed by economics and existing development. The management plan addresses restoration of aquatic and wetland communities and their habitats, protection and improvement of water quality, control of nuisance macrophyte biomass, maintenance and enhancement of fisheries resources, and enhancement of environmental awareness and community participation in the lake protection process (Figs. EX-1-6). Projected capital costs for implementing the entire management plan are $5,450,980. An additional $115,230 per year will be required for project maintenance and monitoring. A listing of projects with the highest priority for implementation and projected costs is given in Table EX-1. The lakes have been altered considerably from their original character as a result of: 1) channelization of the flowing waters that fed and drained the lakes and elimination of natural surface water fluctuation regimes; 2) encroachment of urban and residential growth onto associated riparian areas, wetlands, and floodplains; 3) establishment of exotic vegetation, fish, and molluscan species that have disrupted ecosystem function; and 4) degradation of water quality due to nutrient enrichment and bacterial contamination as discharges of domestic and agricultural wastes have increased. The loss of littoral zones and shoreline wetlands in the chain-of-lakes system has been extensive, with well over 50% of the extant wetland area in 1883 missing from the present shoreline. Attendant with the loss of vegetated littoral zones and wetlands is the loss of the functionality they served as biological filters, and the loss of fish and wildlife habitat they provided. Sportfish biomass in littoral habitats of Florida lakes is five times as great as in open waters. Thus, this loss of habitat within the chain-of-lakes is reflected in a fish community that is imbalanced in its overrepresentation of "rough" fishes such as gizzard shad and gar. The key program in the management plan calls for restoration and enhancement of littoral zones and shoreline wetlands to enhance fishery resources, improve and protect water quality, and restore natural plant and animal species diversity. Thirty-two habitat restoration projects are proposed (FW-201-R to FW-232-R), covering over 8.5 miles of shoreline within publicly-owned portions of the lakes and their connecting canals. This area represents 26% of the total lake shoreline. Total costs for implementing the habitat restoration projects of the management plan are estimated at $3,221,180 with an additional $59,650 /yr for maintenance and monitoring. Although historical detail is sparse, the lakes are presumed to have been originally shallow, as are most natural Florida lakes. All of the lakes in the chain have been deepened by dredging. Depth is again being lost through sediment deposition and from the accumulation on the lake floors of excessive aquatic plant growth that has died-off and is decomposing. The sediments likely originate as suspended sediments carried by inflowing waters (canals and outfalls). Comparison of a bathymetric survey conducted as a part of this study with one conducted in 1986 shows a loss of 30-59% of lake volume in Lakes Ida, Eden, and the south lobe of Lake Osborne. Differences in survey methodology may explain some of the loss, but the finding raises cause for concern. The management program includes a survey of sediment composition and distribution in these areas to evaluate dredging feasibility (project FW-302-D). Other strategies of the management plan for reducing particulate loading include the installation of baffle-boxes in storm drains entering the lake system (project FW-403-R), the creation of wetland filtration systems at the mouths of canals (projects FW-210-R and FW-227-R), and the preparation of educational materials to encourage environmentally sensitive landscape design and management by homeowners and industry (FW-603-P). Water quality in the chain-of-lakes system has improved from the 1970's and early 80's as regulatory activities and upgrades in waste treatment facilities have eliminated point-source discharges. Water quality is still impaired, however, as reflected in very high nutrient concentrations, bacterial contamination, reduced dissolved oxygen concentrations, and low water transparency. Mean annual secchi depth of the lakes, which measures the depth of penetration of 10% of visible surface light, is 1.1 m. Values less than 2 m place Florida lakes into a nutrient enriched (eutrophic) category. Concentrations of dissolved oxygen throughout the water column in Pine Lake, Lake Clarke, and Lakes Ida and Eden in August 1995 did not meet State surface water quality standards for Class III freshwaters of 5.0 mg/l. Since 1990, total coliform bacterial counts in Lake Osborne and its inflowing waters have violated state water quality criteria on 20% of all quarterly sampling events. Total nitrogen and total phosphorus concentrations in the lakes greatly exceed the range typically found in unpolluted Florida lakes. Nutrient enrichment has led to occasional algal bloom problems in the lakes, evidenced by chlorophyll a concentrations that reach 40 mg/l or more. Such bloom conditions occurred in Pine Lake in December 1995 and in the south lobe of Lake Osborne and the L13 canal in August 1995. Lack of a correlation between water transparency and chlorophyll a found in this study suggests that light is not limiting to algae and that the water transparency (or lack thereof) of the lakes reflects contributions of both organic and inorganic particles to the suspended load. Preliminary findings are that algal growth in the lakes is limited by nitrogen, as reflected in a ratio of total nitrogen to total phosphorus of less than 10. Further evaluation of nutrient limitation is proposed in the management plan (project FW-301-D), as this information is critical for use in developing sound restoration procedures. If nitrogen is found to be limiting, this suggests that water quality protection will be best achieved by reducing fertilizer inputs to the lakes. Other projects targeting protection and improvement of water quality are proposed as part of the management plan. A coprostanol survey (Project FW-303-D) is in progress to identify whether sewage effluent is entering the lake system in areas adjacent to septic tank usage, as is a survey of the presence of heavy metals in the lakes (FW-304-D). The county surface water quality monitoring program will be expanded to include the establishment of seven permanent lake stations (FW-101-M), which will be monitored twice yearly for biological as well as standard water chemistry parameters. Retrofitting of storm drains with baffle boxes (FW-403-F), and all of the restoration projects involving shoreline wetlands (FW-201 to 232-R) are expected to substantially reduce particulate organic and inorganic inputs and their associated pollutants. Macrophytes play a critical role in the functioning of lake ecosystems, but when overabundant, they can interfere with or eliminate recreation and detract from the aesthetic values of a lake. Excessive growth of macrophytes, particularly of exotic species such as the submersed Hydrilla (Hydrilla verticillata) and the floating water lettuce (Pistia stratiodes), is problematic in the chain-of-lakes. Hydrilla blanketed the surface of Lake Osborne in the 1980's but has been largely brought under control since then through chemical treatment. At present it has escaped control in Lakes Ida and Eden. A new exotic species, the Asian Hygrophila polysperma, has been detected in the chain-of-lake system. This species is of particular concern because no chemical treatment is available for its control. Recognizing that total eradication of macrophytes is neither feasible nor desirable, a goal of the management plan is to develop an integrated aquatic plant management program to achieve maintenance control of nuisance exotic species through improvement and expansion of existing techniques and exploration of alternative technologies. A mechanical harvesting feasibility project (FW-401-F) will evaluate its potential for supplementing macrophyte control by herbicide treatment. The capabilities of a newly-developed system (SAVEWS) for generating instantaneous maps that determine distribution and volumetric coverage of Hydrilla will be evaluated in Project FW-402-F. Such a system has the potential to greatly improve the operational efficiency of the present macrophyte control program (FW-102-M). This program will be expanded by increasing the monitoring frequency of plant distribution and growth in the lakes to allow for earlier detection and problem control. The establishment of an interagency Aquatic Plant Control Task Force (project FW-505-C) is recommended to facilitate information exchange among agencies with jurisdictional authorities for plant control in waterbodies within the chain-of-lakes system. Improved information transfer and coordination among agencies will eliminate redundancy in chemical treatment, minimize environmental risks from overtreatment, and increase program efficiency. Exotic species other than nuisance aquatic plants have also become established in the chain-of-lakes system. Brazilian pepper, melaleuca, earleaf acacia, and Australian pine line much of the undeveloped shorelines of the lakes and connecting canals. The County Parks and Recreation Department is systematically removing these species within park boundaries. This effort will be enhanced in the shoreline habitat restoration projects, along with replanting with native wetland and upland species. Exotic fish and molluscan species are also present in the chain-of-lakes. Twenty-six percent of the 31 fish species present in the system are exotics that have been intentionally or accidentally introduced to the area outside their natural ranges. These species potentially displace native fishes as a result of competition, predation, or disease and once established, are nearly impossible to eradicate. Increasing public awareness of the problems caused by exotics will be addressed through preparation of educational materials (FW-603-P). |
|
 |
 |
 Coastal Resources |
|
Lakes,
Estuaries and Lagoons |
|
Mosquito Control |
|
Natural Areas |
|
Permitting and Regulation |
|
 |