Geographic MAP Modules

Transcription

1 3.0 GEOGRAPHIC MAP MODULES 3.1 LAKE OKEECHOBEE MODULE The Lake Okeechobee Module incorporates the waters and associated ecosystems of the largest lake in the southeastern United States (Figure 3-1). For reasons of simplified contract management and holistic interpretation of related findings, the GE module addresses the bird population utilization of Lake Okeechobee s vegetated areas. Historically, lake stage was much higher (approximately 20 to 22 feet) than as managed today (Aumen 1995) with a target stage of 12.5 to 15.5 feet. Construction of the encircling dike to control flooding and prevent loss of life, lowered lake stage, both coupled with the pre-development morphology of the lake s bottom, have resulted in the current pattern of emergent and SAV. Development in close proximity to Lake Okeechobee and decreased elevation of the land south of the lake preclude dike removal in feasible restoration scenarios. These vegetated areas are comprised of a western and southwestern littoral marsh zone dominated by emergent species, and a shallow nearshore zone periodically dominated by SAV. These areas support significant biotic productivity. Several invasive exotic species (e.g., melaleuca, torpedo grass, hyacinth) have been targeted for management action, and is an ongoing containment effort. Because potential inflow rates far exceed outflow capacity, maintaining the integrity of the dike during high lake stages has, at times, required release of massive quantities of water to the Caloosahatchee and St. Lucie estuaries. Development and channelization of the surrounding basin has resulted in increased runoff of nutrient-rich organic sediments. Additionally, the loss of flushing ability caused by the Herbert Hoover Dike gave rise to increasing loads of nutrients, which deteriorated lake water quality. Since Lake Okeechobee is the principal source of water supply for restoration, continued poor water quality translates into the need for extensive, and expensive, treatment facilities before water can be directed to the southern part of the system. Difficulties associated with maintaining a desirable stage envelope in the face of competing uses for water supply, flood control and natural resource value have adversely affected sustaining the littoral marsh zones of the lake. 3-40

2 FIGURE 3-1: LAKE OKEECHOBEE MODULE BOUNDARY MAP 3-41

3 Monitoring Changes made between 2004 and 2008 Different components (e.g., stage, water quality, plankton) of Lake Okeechobee have been monitored for two to three decades. As a result, the monitoring strategy has matured based on continuing documentation of the effects that external drivers and internal processes impart that define Lake Okeechobee. However, Lake Okeechobee remains a dynamic system. Unusually dry or wet years, and the impact of hurricanes can and have caused rapid and dramatic changes in Lake Okeechobee s condition and character. For the most part, differences in monitoring of Lake Okeechobee as laid out in MAP 2004 versus the current plans of MAP 2009 involve merging previous separate monitoring elements (see Table 3-1). These monitoring elements are primarily conducted by two state agencies (SFWMD and Florida Fish and Wildlife Conservation Commission [FWC]) and the state universities (Florida Atlantic University [FAU], Florida International University [FIU] and University of Florida [UF]). Combining several of the MAP 2004 elements reflect the reality in which these efforts are currently being conducted in the field, i.e., wherever possible sampling has been coordinated to prudently curtail cost and effort. MAP 2009 carries forward the intentions of MAP 2004 to sustain a well-balanced monitoring effort that will generate a holistic sustainable dataset with which to best understand, operate, and utilize Lake Okeechobee s water for environmental gain and benefit Restoration Goals Lake Okeechobee is a key resource not only of importance to agricultural and urban concerns, but important as well in its ecological effect on all South Florida including the Everglades, Florida Bay, estuaries and the other ecosystems downstream of the lake. Efforts to restore Lake Okeechobee focus on (1) maintaining a stage envelope appropriate to the maintenance of a biologically productive littoral and nearshore aquatic vegetative zones and (2) reducing nutrient loads entering the lake to improve water quality and reduce the likelihood of significant algal blooms. Restoration goals for littoral and aquatic vegetation zones include maintaining a more desirable stage envelope, reducing the inflow of nutrients, and reducing eutrophication of Lake Okeechobee in order to allow formation and maintenance of a healthy plant community, maximize areal coverage, and enable biologically-important functions of native vegetation. Specific goals, where available, are available in the RECOVER Lake Okeechobee Performance Measures (evergladesplan.org). In the past, decreases in suitable emergent and SAV habitat have led to reductions in food items (e.g., macroinvertebrates) and disruptions in the food chain, thus decreasing the number and size of fish and causing a shift towards less desirable species. Increased SAV and emergent vegetation coverage should result in improvements in the diversity and richness of the macroinvertebrate community assemblage, which in turn should provide increased food sources to support an increasingly abundant and more diverse fish population. Attaining reduced nutrient levels in Lake Okeechobee is a critical and essential restoration goal. Improved water quality should decrease the degree of treatment necessary before water could be routed south, and as a consequence provide increased quantities of clean water to the Everglades and other associated down-gradient systems. In addition, reducing nutrient 3-42

4 levels should reduce the frequency of excessive algal blooms (greater than 40 parts per billion [ppb] chlorophyll a), which will have positive consequences on macroinvertebrate and fish communities. Improved water quality should reduce the number of pollution-tolerant oligochaetes, thereby resulting in an increased overall quality of the macroinvertebrate assemblage Overview of Lake Okeechobee Hypotheses Clusters As a result of the varied and widely-held concerns, CEMs were developed for Lake Okeechobee to provide a science-based path forward toward restoration (Havens and Gawlik 2005, RECOVER 2007). These models succinctly depict the interrelationships that exist between water level and nutrient condition, and those key flora and faunal communities that respond to or are affected by them. The models consider the three sub-regions within the Lake Okeechobee that are functionally dissimilar, and as a consequence may respond to changes in water level and/or water quality differently. These sub-regions are (1) a littoral marsh dominated by emergent vegetation, (2) a somewhat deeper nearshore region dominated by SAV, and (3) the deeper open water limnetic zone dominated by planktonic producers. The models also reflect Lake Okeechobee s present spatial extent, rather than the larger historical boundaries Emergent-Submerged Vegetation Mosaic Hypothesis Cluster Working Hypotheses The emergent/submerged vegetation mosaic hypothesis cluster (Figure 3-2) is comprised of several sub-hypotheses: Restoration would allow for better control of lake stage, which would allow the nearshore native vegetation mosaic to maximize areal coverage, which in turn would reduce nutrients, stabilize sediments and reduce turbidity providing further positive feedback benefits to the plant community. Restoration would result in improved water quality, and increase the TN to TP ratio, which will result in a shift to phosphorus (P)-limitation and decrease cyanobacterial bloom frequency and severity. Continue ongoing management activities independent of CERP restoration to adequately control exotic vegetation, allowing native emergent and submerged species to more consistently maintain maximal areal coverage. Reestablish the emergent- submerged vegetation mosaic and appropriate water levels will serve to minimize physical damage due to storms. 3-43

5 FIGURE 3-2: LAKE OKEECHOBEE EMERGENT-SUBMERGED VEGETATION MOSAIC HYPOTHESIS CLUSTER DIAGRAM Key: blue squares=drivers, red ovals=stressors, green diamonds=ecological effects, orange hexagons=attributes 3-44

6 Monitoring Components and Sampling Design Monitoring components include transect monitoring, annual vegetation mapping, and exotic plant and emergent plant coverage surveys. These are discussed in detail in the following sections. Transect monitoring. Sampling is conducted monthly at up to 78 sites located along 16 transects in areas of Lake Okeechobee that support submerged plants. The sites represent a subset of sites that were sampled in the Lake Okeechobee ecosystem study in the late 1980s and early 1990s (Zimba et al. 1995), allowing for a comparison of historical data. Sampling has been conducted monthly since fall 2004; however frequency varies from quarterly to monthly depending on how dynamic anticipated changes are expected to be in the plant population (e.g., more frequent sampling is done during periods of recovery from hurricanes. Plant samples are collected at sites along each transect, starting at the shoreline and progressing lakeward until a site is reached that has no plants. Plant sampling is accomplished using a tool constructed of two standard garden rakes bolted together at midpoint to create a tong-like device (Rodusky et al. 2005). The degree of opening is constrained by placing a chain between the two handles so three replicate samplings with the device remove approximately one square meter (m 2 ) of bottom cover. The harvested material is sorted by species, stripped of epiphyton and dried to a constant weight. This sampling effort provides more information on plant responses and relative plant distribution and density to changing water levels on a short time scale than the annual SAV mapping (discussed below), and can be used as input to real-time operations. Annual vegetation mapping. GIS coverage of the nearshore zone is laid onto the map, and common cells are clipped from the final coverage, as is the deeper central limnetic region. This results in a nearshore grid of approximately 750 sampling sites. Coordinates for the grid cell center-points are loaded into Trimble Geo XT global positioning system (GPS) units (differentially corrected) for use in navigating to the sampling sites. A simple program is set up in each data logger so that users can enter information regarding water depth, Secchi depth (a measure of water transparency), sediment type as determined by visual inspection, presence versus absence of vegetation by species and a qualitative estimate of overall plant biomass (sparse, moderate, dense). Ad-hoc interagency exotic plant and emergent plant coverage surveys. Although dependent on species, the general procedure is to qualitatively assess emergent and floating vegetation coverage with interagency representatives by helicopter approximately every two months, and direct control spraying where needed. For trees (i.e., melaleuca, brazilian pepper), crews are deployed roughly once per year to patrol for the plants. A torpedograss and cattail control project manager flies with an aerial contractor prior to treatments to determine areas where chemical control of those species is needed. A new threat that is now being actively controlled is a Central American aquatic grass, Luziola sp., which has begun to colonize areas in Fisheating Bay. The goal is to reduce the amount of area infested by these exotic taxa before they become too large to effectively manage. The melaleuca and torpedo grass control programs are conducted under state mandate; although CERP does include an exotics control project focusing primarily on biocontrol mechanisms. 3-45

7 Predictive and Assessment Tools A model was developed that uses total depth, Secchi disc depth, and sediment type to predict areas in the nearshore region of the lake favorable for SAV growth. A Lake Okeechobee hydrodynamic model currently exists that may jointly be used with the SAV coverage model for predicting the areal extent of SAV growth in the future Key Uncertainties The following key uncertainties prevent development of well-defined restoration goals at this time. Rate at which limnetic zone water quality may improve may require many decades due to internal phosphorus loading and frequent resuspension of bottom sediments. Sufficient additional storage capacity to help maintain a desirable lake stage envelope may not be fiscally feasible. Tropical storms (including hurricanes) may, during the current phase of the Atlantic Multi-Decadal Oscillation, occur with increasing frequency, thereby adversely affecting the SAV community. Decreased rainfall in the Lake Okeechobee watershed due to climate change may cause more frequent droughts and insufficient water storage in the lake for all competing water demands. Rate and extent of continued watershed development are unknown. Increased water supply demands due to development are unknown Macroinvertebrate Community Hypothesis Cluster Working Hypotheses Eutrophication in Lake Okeechobee has resulted in a macroinvertebrate community composition dominated by pollution-tolerant taxa (Warren et al. 1995). Less pollution-tolerant taxa such as mussels (Pelecypoda), mayflies (Ephemeroptera), caddisflies (Trichoptera), dragonflies (Anisoptera), and damselflies (Zygoptera) have been lost as a result. Macroinvertebrate densities and assemblage structure reflect changes in the plant community structure. Adverse changes in macroinvertebrate communities result in negative cascading impacts on fish and other higher-trophic level organisms that utilize them as a food source (Figure 3-3). 3-46

8 FIGURE 3-3: LAKE OKEECHOBEE MACROINVERTEBRATE COMMUNITY HYPOTHESIS CLUSTER DIAGRAM Key: blue squares=drivers, red ovals=stressors, green diamonds=ecological effects, orange hexagons=attributes Monitoring Components and Sampling Design Benthic invertebrate community samples are collected from six sites in each of the three aerially dominant sediment zones (mud, sand, peat) twice annually using a petite ponar dredge (Warren et al. 1995). The macroinvertebrates are identified to the lowest practicable level and community structure metrics such as abundance, species richness, evenness (as per Pielou 1977) and diversity (Shannon s equation, as per Krebs 1999) are reported. Multivariate statistical methods are readily available that provide advanced techniques to investigate complex speciation changes as a function of environmental variables Predictive and Assessment Tools Assessment tools include the above summary statistics. Ordination analysis is conducted to assess spatial and temporal differences in the macroinvertebrate communities. To date, no 3-47

9 predictive tools have been developed to characterize the anticipated post-cerp implementation macroinvertebrate assemblage composition Key Uncertainties The key uncertainties associated with macroinvertebrate community structure in Lake Okeechobee are as follows: The extent to which community structure may be affected by factors other than eutrophication and habitat quality in terms of vegetation coverage is unknown. Grazing by fish and lake stage fluctuations may affect periphyton food quantity and quality. CERP restoration projects may not result in significant reduction in the dominance of pollution-tolerant taxa. Unless some form of direct removal of the resident pool of nutrients in Lake Okeechobee is undertaken, the length of time for tributary nutrient concentration reductions to have a measurable effect on the lake s macroinvertebrate population is unknown, but expected to be very long (e.g. multiple decades) Native Fish Hypothesis Cluster Working Hypotheses Fish integrate the effects of both water management and water quality Fish indirectly reflect the status and health of the invertebrate community Fish require suitable habitat to avoid predation and ensure reproductive success, thus reflecting the status and health of aquatic vegetation (Figure 3-4). 3-48

10 FIGURE 3-4: LAKE OKEECHOBEE NATIVE FISH HYPOTHESIS CLUSTER DIAGRAM Key: blue squares=drivers, red ovals=stressors, green diamonds=ecological effects, orange hexagons=attributes Monitoring Components and Sampling Design Fish populations in limnetic areas were sampled utilizing a trawl methodology at previously established sites and according to procedures from a previous study conducted in Lake Okeechobee from 1987 to 1991 (Bull et al. 1995). Fish populations in the littoral edge and 3-49

11 interior marsh were sampled utilizing electro-fishing techniques at previously established areas and according to procedures developed for an ongoing evaluation of the largemouth bass (Micropterus salmoides) population (Havens et al. 2005). Beginning in Fiscal Year 2009, RECOVER will no longer support this work; however, it is anticipated that the FWC will continue to conduct the monitoring Predictive and Assessment Tools Assessment of fish populations in the nearshore, interior marsh, and open water areas of Lake Okeechobee is accomplished by evaluating metrics such as relative abundance, length, weight and length to weight ratios. No predictive tools have been developed to characterize the post-cerp fish communities Key Uncertainties The key uncertainties associated with fish populations in Lake Okeechobee are as follows: Invasive fish species may be difficult to control and may adversely affect the desired native fish population composition. Uncertainties in the recovery of the macroinvertebrate community are reflected in the fish community, especially as the macroinvertebrate community health may affect juvenile fish foraging Water Quality and Phytoplankton Hypothesis Cluster Working Hypotheses Improvements in Lake Okeechobee water quality are critical to the restoration of the Everglades ecosystem to the south of the lake since it is the primary source of water for restoration in the southern half of the system. Water management and nutrient load management activities, in many cases occurring outside the CERP program, are expected to improve water quality and may result in a reduction in cyanobacterial dominance. As a result of CERP restoration activities, Lake Okeechobee is anticipated to experience reduced cyanobacterial densities and less frequent cyanobacterial blooms (Figure 3-5). It should be noted that the recent paucity of blooms despite lack of reduction in nutrient concentration may indicate that the underlying assumptions regarding the relationship between phytoplankton and nutrient concentration are incorrect. One of the key roles of RECOVER is to continually re-evaluate the CEMS and hypothesis clusters. 3-50

12 FIGURE 3-5: LAKE OKEECHOBEE WATER QUALITY AND PHYTOPLANKTON HYPOTHESIS CLUSTER DIAGRAM Key: blue squares=drivers, red ovals=stressors, green diamonds=ecological effects, orange hexagons=attributes Monitoring Components and Sampling Design For water quality, grab sample data is collected from the eight long-term monitoring (in-lake) stations. For phytoplankton, monthly surface grab data is collected from seven nearshore sites and quarterly integrated water column data is collected from two limnetic and three nearshore sites, respectively Predictive and Assessment Tools Assessment and predictive water quality tools consist of two models: the Lake Okeechobee Water Quality Model (LOWQM), and the Lake Okeechobee Environmental Model (LOEM). 3-51

13 The LOWQM uses long-term water quality data to predict how the limnetic zone of Lake Okeechobee will respond to nutrient management activities such as P-load reduction and sediment management. The LOEM is a more complex model than the LOWQM and is used to assess lake stage and nutrient management scenarios on the nearshore and littoral emergent plant and SAV communities (James and Zhang 2008). Statistical methods used in concert with these models consist of trend analysis, which is conducted with repeated measures analysis of variance (ANOVA) and nonparametric multidimensional ordination analysis Key Uncertainties The key uncertainties associated with water quality and phytoplankton in Lake Okeechobee are as follows: Desired eutrophication reduction and restoration of Lake Okeechobee may be delayed due to the large amount of accumulated phosphorus currently adsorbed in the sediment. The length of time it may take for Lake Okeechobee to evidence significant ecological responses to reductions in influent loading is undefined. The degree that other activities might accelerate this process, as well as the feasibility of their implementation given the necessary large scale and potentially high cost, is uncertain Evolution of the Lake Okeechobee Module between Monitoring and Assessment Plan 2004 and Monitoring and Assessment Plan 2008 TABLE 3-1: MONITORING AND ASSESSMENT PLAN 2004 VERSUS MONITORING AND ASSESSMENT PLAN 2008 LAKE OKEECHOBEE MONITORING COMPONENTS, KEY UNCERTAINTIES, AND SUPPORTING RESEARCH Monitoring Components MAP 2004 Water Quality And Phytoplankton ( ) Submerged Aquatic Vegetation ( ) Monitoring Components MAP 2009 Water Quality And Plankton Emergent/Submerged Vegetation Mosaic Changes Made/Comments The SFWMD DBHYDRO water quality data record begins in Monthly water quality and quarterly plankton (i.e., phytoplankton and zooplankton) monitoring by the SFWMD has been on-going since Monthly SAV transect and annual nearshore SAV coverage monitoring by SFWMD staff is on-going. 3-52

14 Littoral Zone Plant Communities ( ) Monitoring Components MAP 2004 Benthic Macroinvertebrates ( ) Fish Condition And Population Structure ( ) Zooplankton Biomass And Taxonomic Structure ( ) Key Uncertainties and Supporting Research MAP 2004 Aquatic Fauna Relationships to Submerged and Emergent Plant Communities ( ) Fish and Wildlife Relationships to Food Abundance and Composition ( ) Emergent/Submerged Vegetation Mosaic Monitoring Components MAP 2009 Littoral zone plant community monitoring has been combined with the vegetation mosaic monitoring component. Biannual littoral zone emergent vegetation maps, nearshore/littoral bulrush monitoring and exotic vegetation monitoring (bimonthly) are on-going. Changes Made/Comments Benthic Macroinvertebrates Historic data exists for , and Biannual monitoring has been on-going since The FWC has conducted this monitoring since 1987 and is currently supported by RECOVER funding. Native Fish Historic data exists from Annual monitoring has been on-going since 2005 by the FWC. Water Quality And Plankton Key Uncertainties and Supporting Research MAP 2009 Aquatic Fauna Relationships to Submerged and Emergent Plant Communities Fish and Wildlife Relationships to Food Abundance and Composition Monthly water quality and quarterly plankton (i.e., phytoplankton and zooplankton) monitoring by the SFWMD has been on-going. The SFWMD DBHYDRO water quality data record begins in Monthly water quality and quarterly plankton (i.e., phytoplankton and zooplankton) monitoring by the SFWMD has been on-going. The SFWMD DBHYDRO water quality data record begins in Monitoring has been performed by SFWMD since Changes Made/Comments Biannual survey commenced in 2006; suspended in 2007 pending recovery of the SAV and emergent plant communities. Funded by RECOVER. On hold pending recovery of SAV and littoral plant communities as a consequence of the hurricanes and record low lake stages as a result of drought 3-53

15 Fish and Wildlife Relationships to Plant Community Structure and Habitat ( ) Submerged Plant/Periphyton Interrelationships with Light, Nutrients, and Water Depth ( ) Lake Water Phosphorus Relationship to Submerged Plant Biomass and Cover ( ) Fish and Wildlife Relationships to Plant Community Structure and Habitat Submerged Plant/Periphyton Interrelationships with Light, Nutrients, and Water Depth Suspended pending recovery of SAV and littoral plant communities (as above). Quarterly monitoring was suspended in 2006 when the SAV communities disappeared. Biannual monitoring by SFWMD staff commenced in fall Lake Water Phosphorus Relationship to Submerged Plant Suspended pending recovery of the Biomass and Cover SAV communities 3-54