Florida Lakes Research Articles

Abrupt Biological Response to Hydrologic and Land-use Changes in Lake Apopka, Florida, USA

Lake Apopka is a shallow, hypereutrophic lake in north-central Florida that experienced an abrupt shift in primary producer community structure (PPCS) in 1947. The PPCS shift was so abrupt anecdotal accounts report that dominant, submersed aquatic vegetation was uprooted by a hurricane in 1947 and replaced by phytoplankton within weeks. Here we propose two hypotheses to explain the sudden shift to phytoplankton. First, hydrologic modification of the drainage basin in the late 1800s lowered the lake level ca. 1.0 m, allowing the ecosystem to accommodate moderate, anthropogenic nutrient enrichment through enhanced production in the macrophyte community. Second, additional hydrologic changes and large-scale agricultural development of floodplain wetlands began in 1942 and altered the pattern and scale of phosphorus loading to the lake that triggered the rapid shift to phytoplankton dominance in 1947. Historic land-use changes and paleolimnological data on biological responses to nutrient loading support these hypotheses.

The use of sedimentary algal pigments to infer historic algal communities in Lake Apopka, Florida

The primary producer community of Lake Apopka, a large (125 km2), shallow (mean depth, 1.7 m), polymictic Florida lake, shifted from macrophyte dominance to phytoplankton dominance in the 1940s. Today, frequent wind resuspension of highly organic, unconsolidated sediments supports a meroplanktonic community that is predominantly diatoms, but during calm periods the algal community is dominated by planktonic cyanobacteria. Sedimentary algal pigments (chlorophyll derivatives and carotenoids) and chemical proxies for nutrient enrichment (polyphosphate, total phosphorus and biogenic silica) in three sediment cores were used to investigate historic changes in primary producers. Sediments were separated into three stratigraphic zones using multivariate statistical techniques. Stratigraphic zonation was established in each core although sediment deposition at one site was insufficient to adequately resolve temporal changes. These results show the importance of selecting suitable sites for paleolimnological studies. The oldest zone represents macrophyte-derived sediments, and the two overlying zones represent phytoplankton-derived sediments deposited since the 1940s. Algal pigments in the most recent sediment zone show little degradation, which might be due to the presence of viable meroplankton in the sediment. After the initial primary producer shift from macrophytes to phytoplankton, the lake experienced a short period of cyanobacterial dominance followed by a period of benthic diatom abundance before being replaced by the present algal community consisting of cyanobacteria and meroplanktonic diatoms. Chlorophyll derivatives and carotenoids were highly correlated with total phosphorus. Historic trends inferred from the data include algal and cyanobacterial productivity that increased with increased phosphorus loading. The study demonstrates that valid paleolimnological proxies for historic eutrophication are available in loosely consolidated sediments of shallow, subtropical lakes.

Accuracy of Angler‐Reported Harvest in Roving Creel Surveys

AbstractHarvest data obtained during roving creel surveys are often based on angler‐reported information without validation. Angler creels were inspected following interviews during roving creel surveys on three Florida lakes. Comparisons between reported and counted harvest revealed significant differences for anglers targeting sunfish Lepomis spp. (22% error) and black crappie Pomoxis nigromaculatus (7% error). Differences were negligible for anglers targeting sunshine bass (female white bass Morone chrysops × male striped bass M. saxatilis), palmetto bass (male white bass × female striped bass), and largemouth bass Micropterus salmoides. Accuracy among species was inversely related to bag limit size; this was attributed to a combination of factors, including species, number and size of fish harvested, limit‐conscious behavior of anglers, and differences among angler groups. Accuracy within species was not significantly influenced by the reported number of fish harvested or trip duration, nor was the interaction of the two significant. Daily total harvest estimates based on reported data were biased for sunfish (19% error) and black crappies (5% error), but correction factors were effective in reducing total errors to 2% for both species. Inspection of creels is recommended for all roving creel survey interviews when accuracy is critical to meeting study objectives. When moderate accuracy is sufficient, angler‐reported harvest may be used if validated or adjusted with a correction factor if found to be inaccurate.

Inputs of dissolved and particulate226Ra to lakes and implications for210Pb dating recent sediments

Gamma spectroscopy was used to measure radioisotope (210Pb, 226Ra, 137Cs) activities in sediment cores from 20 lakes and a wetland in Florida, USA. Nine profiles display relatively low ( 5 dpm g−1) and variable 226Ra activities. In the latter group, most display up-core increases in activity. Upper sediments from two lakes (Round and Rowell) possess very high (>20 dpm g−1) 226Ra activities that exceed total 210Pb activities, clearly illustrating disequlibrium between 226Ra and supported 210Pb. Supported 210Pb activity is generally thought to come from in situ, 226Ra-containing detrital mineral particles, and is typically assumed to be in secular equilibrium with 226Ra activity. Since 1966, Round Lake has been augmented hydrologically with 226Ra-rich (∼6.2 dpm L−1) groundwater pumped from the local deep aquifer. Adsorption of dissolved 226Ra to recent Round Lake sediments probably accounts for the high measured 226Ra activities and the pronounced disequilibrium between 226Ra and supported 210Pb in topmost deposits. We suspect that many Florida waterbodies receive some 226Ra-rich runoff and seepage from groundwater pumped for irrigation, residential use, industrial applications, and mining. This may account for up-core increases in 226Ra activity measured in sediment cores from some Florida lakes. Significant groundwater pumping began within the last century, and there has been insufficient time for supported 210Pb to come into equilibrium with adsorbed 226Ra in uppermost deposits. Input of 226Ra-rich groundwater to lakes may occur in any geographic region where local bedrock contains 238U and its daughters. When dissolved 226Ra adsorbs to recent sediments, it complicates accurate estimation of supported 210Pb activity, and confounds calculation of unsupported 210Pb activity that is used in dating models.

Holocene Gulf Levels: Recognition Issues and an Updated Sea-Level Curve

Abstract Several new concepts have challenged the traditional view of northern Gulf coast sea-level history in recent years. Claims for higher than present mid and late Holocene sea-levels implied substantial sea-level oscillations. Such high-stands, known globally in low latitudes, have never been credibly documented on the Gulf or on unglaciated Atlantic coasts. Lacking direct indications, numerous lines of indirect proof have been suggested. Proxy evidence was based on items as the reinterpreted geological record of NW Florida lakes, estuaries, and depositional conditions of Texas coast landforms. Pleistocene barrier sectors, barrier islands, relict foredune ridges, washover fans/flood-tidal deltas, and other sedimentary units and their morphology were claimed as highstand indicators. Unrealistically old or young radiocarbon and luminescence dates, the result of diagenetic changes and other contamination have resulted in questionable conclusions. A large body of sediment, stratigraphic and geomorphic d...

Valuing environmental benefits of silvopasture practice: a case study of the Lake Okeechobee watershed in Florida

Silvopasture, which combines trees, forages, and shrubs with livestock operations, has potential for limiting phosphorus runoff, sequestering atmospheric carbon dioxide, and improving habitat for wildlife. This study estimates the public demand for these environmental services in south-central Florida's Lake Okeechobee watershed using a stated preference approach. The results from a random parameter logit model reveal that households would pay US$30.24–71.17 per year for 5 years for these environmental benefits. These estimates provide a basis for formulating policies to promote silvopasture practices in the Lake Okeechobee watershed.

Population Characteristics of Siren lacertina and Amphiuma means in North Florida

Abstract I conducted a mark-recapture study of Siren lacertina and Amphiuma means for one year at a lake in north Florida and documented average individual movement, size class distribution, seasonal activity patterns, survival rates, and density estimates. I captured Siren lacertina more frequently in winter and A. means more frequently in spring. Recapture probabilities of both species were low, whereas survival rates and density estimates (1.3 salamanders/m2 for S. lacertina, 0.28 salamanders/m2 for A. means) were high. I recorded no individual movement of over 10 m for either species. Sirens and amphiumas are large, predatory generalists that can have substantial biomass in wetlands (233 g/m2 and 44 g/m2, respectively, at this study site), and therefore can impact many other wetland species. Thus, more attention must be focused on evaluating and monitoring their populations.

Influence of Chironomidae (Diptera) faecal pellet accumulation on lake sediment quality and larval abundance of pestiferous midge Glyptotendipes paripes

Two opposite distribution patterns of larval Glyptotendipes paripes in relation to organic carbon content in sediments of central Florida lakes were discovered. In a majority of examined lakes, G. paripes larvae were most abundant in sand sediment and their density rapidly declined with increased carbon content (type 1 lakes); however, in some cases the opposite was true (type 2 lakes). To elucidate this anomaly, field-collected organic sediments from types 1 and 2 lakes and sand sediment were studied for G. paripes development in the laboratory. Type 1 organic sediment consisted predominantly of fine particles ( 0.25 mm diameter), with significantly higher levels of dissolved oxygen concentrations that were similar to sand sediment. Type 2 organic sediment and sand sediment were conducive to higher survival of G. paripes larvae than fine organic sediment. The larvae in type 2 organic sediment produced longer tubes than in other sediment types. This observation indicates that accumulation of chironomid faecal pellets in lake sediments may change physical properties, such as dissolved oxygen level and consequently alter conditions for survival of chironomid larvae and possibly other benthic fauna.

A spatially explicit computer model for immature distributions of Glyptotendipes paripes (Diptera: Chironomidae) in central Florida lakes

Density and spatial distribution data of immature Glyptotendipes paripes Edwards (Diptera: Chironomidae), in relation to selected water and sediment characteristics prevailing in three central Florida lakes, were used to develop and calibrate a qualitative model of G. paripes distributions with the purpose of developing more efficient sampling plans for research or population management. For the model, each lake habitat was defined by a two-dimensional matrix, while a three-dimensional matrix was used to simulate the life stage-structured population. A Lefkovitch population matrix was used to project survival and development of the population in each spatial unit. The model incorporated lake bathymetry, sediment dry weight, water level, food availability (as a function of Secchi disk transparency) and strength of density dependence as influences on immature survival and adult fecundity. Temperature-dependent development data for G. paripes were incorporated to estimate development time. A simple redistribution function was used to simulate the dispersal of adults over the simulated habitat for oviposition. Immatures and relevant environmental data taken for eight dates, at each of two other central Florida lakes were used to validate the model. The mean correct prediction rate of the model for field density distributions within 0.5 log(n+1) immatures/m2 density in spatial habitat cells was 0.64 and 0.66 for the validation lakes. Presence/absence correct prediction rates were 0.61 and 0.76, while matching to a proposed sampling stratification based on a treatment threshold was 0.85 and 0.88. These values indicate that the model is efficient for preparing stratified immature G. paripes sampling plans for central Florida lakes.

Phosphorus accumulation in the littoral zone of a subtropical lake

In situ mesocosm experiments were performed under summer (1997) and winter (1999) conditions in the littoral zone of a subtropical lake in Florida, USA. The objective was to quantify phosphorus (P) accumulation by various components of the community after adding pulsed doses of dissolved inorganic P. A short-term experiment also was done to quantify the rate of P loss from the water column, with simultaneous use of an inert tracer to confirm that P depletion was not due to leakage of the tanks. In the experiments, added P was rapidly removed from the water; samples collected 3–4 days after adding spikes of near 100 μg l−1 P contained little or no soluble reactive P. In the short-term experiment, we documented that the half-life of added P was approximately 6–8 h in the water column, and that the tanks were not exchanging water with the surrounding lake. Little of the added P ended up in plankton, rooted vascular plants, or sediments. The main sink for P was periphyton, including surface algal mats, benthic algal mats and detritus, and epiphyton. In the summer 1997 experiment, the periphyton was intimately associated with a non-rooted plant (Utricularia), which also may have sequestered P from the water. Structure of the littoral community varied between summer and winter, and this influenced which periphyton component accounted for most of the P removal. In regard to P mass balances, we accounted for 54% of the added P in 1997, when coarse sampling was done. In 1999, when there was more detailed sampling of the community, 92% of the added P was located in various community components. Subtropical littoral periphyton can be a large sink for P, as long as depth and underwater irradiance conditions favor its growth.

CONFLICTING MANAGEMENT GOALS: MANATEES AND INVASIVE COMPETITORS INHIBIT RESTORATION OF A NATIVE MACROPHYTE

Vallisneria americana is a native macrophyte in freshwater and oligohaline ecosystems, often forming meadows that significantly affect ecosystem carbon and nutrient cycling and provide structural habitat. Vallisneria has declined in abundance in several Florida lakes, rivers, and estuaries. We conducted an 11‐month field experiment in Kings Bay, Florida, USA, to determine factors that might affect successful transplantation of Vallisneria and to guide potential future restoration efforts by water resource management agencies. To determine the effects of herbivores and other primary producers on Vallisneria production, we conducted a 2 × 2 factorial experiment at three sites in which we allowed or denied: (1) relatively large herbivores (>3 cm) and (2) other primary producers (e.g., Myriophyllum spicatum, Hydrilla verticillata, Lyngbya sp.) access to 1.5 × 1.5‐m transplanted plots of Vallisneria. Within one month, Vallisneria disappeared from 80% of herbivore‐access plots due primarily to consumption by manatees. Vallisneria density was reduced a variable amount (0–50%) in response to competitors, due to site‐specific variation in natural abundance of other primary producers (at two sites, we observed extensive colonization by other primary producers and a strong treatment effect). Most of this competitive effect was attributable to Eurasian watermilfoil (Myriophyllum spicatum); after pooling Vallisneria density data across sites, we observed a negative exponential relationship between shoot density of Vallisneria and stem density of Myriophyllum for every sampling date. We observed variable recruitment of Vallisneria transplants into larger size classes among sites, but not between treatments, and large, established plants grew at similar rates whether in monospecific or mixed stands, with evidence for reduced mass‐specific growth in dense stands. Hence, a probable mechanism by which Myriophyllum reduces Vallisneria occurs via space limitation, and reduction in Vallisneria densities and/or recruitment and growth of new shoots. We conclude that two different management goals (restoration of Vallisneria and protection of manatees) are in conflict and must be simultaneously considered to devise effective and sustainable ecosystem management scenarios. Due to the highly managed nature of freshwater systems worldwide, the limitations of extrapolating experimental results and the importance of site‐specific pilot experiments should also be recognized.

Metal concentrations in selected organs and tissues of five Red-knobbed Coot (<i>Fulica cristata</i>) populations

The Red-knobbed Coot Fulica cristata is an abundant aquatic bird in South Africa and was anticipated to have indicator abilities for metal pollution. This hypothesis was tested on 83 coot samples collected from five selected aquatic ecosystem areas supporting substantial coot populations, of which various abiotic and biotic components are known to contain varying levels of a number of metals. The aim of this study was achieved by determining the variations in Cd, Cu, Ni and Pb concentrations in liver, kidney, bone and blood samples, with the use of standard flame atomic absorption spectrophotometry techniques. Coots from the Germiston Lake sampling site showed the highest concentrations of cadmium in liver (2.2 µg/g d.w.) and kidney (5.4 µg/g d.w.). The absence of metalprocessing industries in the catchments of the Florida Lake and the Steynsrus farm dams reflects the low liver and kidney concentrations of Cd, Ni and Cu, respectively. The blood of the Natalspruit wetland coots contained the highest dry weight concentrations of Ni (11.4 µg/g), Cd (1.8 µg/g) and Cu (14.4 µg/g). The statistical evaluation points towards small-scale geographical differences, especially in the concentrations of Cu, Ni and Pb and in the liver, kidney and blood. However, in terms of actual metal concentrations recorded, no significant differences existed between coots of the reference site (Steynsrus farm dams) and those from the other four localities. It is concluded that the impact of metal-containing diets on the tissue concentrations of these metals in birds plays a far more significant role compared to the migratory habits or short-range movements of the coots.

Off-Season Spawning of Black Crappie in a North-Central Florida Lake

Black crappies Pomoxis nigromaculatus less than 60 mm total length were observed in December in Orange Lake, Florida, during fishery investigations. Sagittal otoliths were examined for daily growth rings to estimate hatch date. Hatch date ranged from 9 to 29 October 2001; mean hatch date was 20 October, which is the first published occurrence of off-season spawning of black crappies. Fishery managers should be aware of potential seasonal spawning variability when estimating growth.

Lake Apopka Restoration

Lake Apopka RestorationLake Apopka is a 31,000-acre lake located in Central Florida. It is one of the headwater regions of the Ocklawaha Chain of Lakes with the Palatlakaha basin being another contributing headwater region. Through the 1940's, Lake Apopka was the second largest Lake in Florida. It was a premier bass fishing lake and, in the days before major theme parks, was known as one of central Florida's major...Author(s)Joan B. BudzynskiNabil A. MuhaisenSourceProceedings of the Water Environment FederationSubjectSession 71: Watershed Nutrient IssuesDocument typeConference PaperPublisherWater Environment FederationPrint publication date Jan, 2004ISSN1938-6478SICI1938-6478(20040101)2004:9L.1;1-DOI10.2175/193864704784132418Volume / Issue2004 / 9Content sourceWEFTECFirst / last page(s)1 - 9Copyright2004Word count565

Urban lakes and waterbirds: effects of shoreline development on avian distribution

The need to understand how wildlife responds to the broad-ranging impacts of development is becoming increasingly important as human populations around the globe continue to increase and urbanize. We examined waterbird distributional associations with shoreline development, and with littoral and onshore habitat elements on four partially developed urban lakes in central Florida. A total of 34 waterbird species were observed over the summer and winter seasons. Wading bird, marsh bird, and duck abundance was significantly greater than expected along developed shoreline in both seasons on all lakes. Diving bird abundance was significantly greater along developed shoreline in the winter. Species richness was not associated with shoreline development, while species evenness varied by season, being greater along undeveloped shoreline in the summer and along developed shoreline in the winter. Tall-emergent vegetation, open shore, lawn, and canopy appeared to be the primary habitat elements determining waterbird distribution. All guilds were negatively associated with tall-emergent vegetation on two or more lakes over both seasons, whereas wading birds, marsh birds, and ducks were positively associated with open shore in the summer, and wading birds, marsh birds, and diving birds were positively associated with lawn and canopy in the winter. Results showed that a wide range of waterbirds can use urban lakes during the summer and winter seasons, and many individuals can utilize developed shoreline in particular. However, the lack of birds observed along undeveloped shoreline may be explained by the abundance of dense tall-emergent vegetation found along this shoreline. Both littoral and onshore habitat elements should be managed to improve waterbird habitat on urban lakes.

Modeling Phosphorus Dynamics in a Shallow Lake During an Episodic Event

ABSTRACT Wind, current, suspended sediment, dissolved oxygen (DO), pH and phosphorus data were collected in Lake Okeechobee, a shallow lake in south Florida, during a storm event in early 1993. Measured field data indicate that wind and wind-generated waves are major factors responsible for sediment resuspension in the lake. Data also show that soluble reactive phosphorus (SRP) and total dissolved phosphorus (TDP) were inversely-correlated with the DO concentration in the water column. This paper focuses on the use of a vertical one-dimensional model coupling phosphorus dynamics with hydrodynamics and sediment transport processes to simulate the observed episodic event. Model simulations confirmed that resuspension of sediments occurred during the episodic event, with the subsequent increases in phosphorus concentrations. Model results suggest that release of SRP from suspended sediment particles increases as the DO concentration in the water column decreases. By fitting simulated results with field data, an empirical formula describing the effect of the DO concentration on the release of inorganic phosphorus from resuspended sediments has been obtained. Further research to elucidate the detailed mechanism is recommended.

Recovery of submerged plants from high water stress in a large subtropical lake in Florida, USA

The spatial and temporal dynamics of submerged plants were examined in a large subtropical lake in Florida, USA. The objective was to characterize succession of the community following a natural experiment in 2000–2001, when release of water from the lake, followed by a severe drought, reduced water levels by 2 m, alleviating stress of multiple years of high water. A systematic survey of shoreline transects was used to compare attributes of submerged plants under pre-drought versus post-drought conditions. Initially, the plants did not respond to lower water because shoreline areas had high turbidity from resuspended sediments and, later algal blooms. In June 2000, approximately 2 months after the water level was lowered, Chara (a macro-alga) rapidly expanded across the near-shore landscape. For over 1 year, this plant strongly dominated the submerged plant community, with just scattered individuals or isolated beds of vascular plants, including Potamogeton, Vallisneria, and Hydrilla. This included a period when the lake reached a record low elevation, where much of the habitat became dry, and then subsequently re-flooded in late summer 2001. However, in November 2001, Chara rapidly declined and vascular taxa ( Hydrilla and Potamogeton) became dominant. They subsequently increased their biomass and spatial extent, and the previous Chara dominance did not return. Just prior to the loss of Chara, a frontal system passed over the lake, with wind velocities in excess of 30 km h −1 for 3 days. Concentrations of solids in the water more than doubled and uprooted Chara was observed floating in the water. In this large, wind-driven lake, Chara may only be an ephemeral pioneer because, lacking roots, it is probably more sensitive to excessive wind-related stress (e.g. wave energy and scouring) than vascular plants.

Evaluation of Pathogens as Potential Biocontrol Agents of Hydrilla

AbstractDuring a 1‐year survey for micro‐organisms associated with hydrilla, approximately 2200 microbes were recovered from hydrilla, surrounding water and sediment collected from 10 man‐made ponds and three natural lakes in Florida, USA. A representative selection of fungi (651), bacteria (330) and actinomycetes (38) from this collection was screened against hydrilla in bioassays. Severity of damage (DS) was determined on a scale of 0 to 4, where 0 = healthy, 1 = 1–25% damage, 2 = 26–50% damage, 3 = 51–75% damage, and 4 = 76–100% damage (100% = complete kill). Of the 1019 isolates that were examined in this manner, none of the actinomycetes were pathogenic on hydrilla, however two strains of bacteria (0.6% of the bacteria tested), and 42 isolates of fungi (6.5% of the fungi tested) were effective at DS level 4 (DS4) on hydrilla 3 weeks postinoculation. Fungi and bacteria capable of killing hydrilla are considered to have potential as biocontrol agents or as sources of novel herbicidal metabolites. These included Acremonium sp., Botrytis sp., Curvularia sp., Cylindrocarpon sp., Fusarium culmorum and F. moniliforme. The biocontrol potential of F. culmorum has been established in several tests. For maximum bioherbicidal activity of this fungus against hydrilla, its inoculum should be applied at a rate of 5 × 105 conidia/ml at 20–25°C water temperature.

Seasonal variation in plasma sex steroid concentrations in juvenile American alligators

Seasonal variation in plasma sex steroid concentrations is common in mature vertebrates, and is occasionally seen in juvenile animals. In this study, we examine the seasonal pattern of sex hormone concentration in juvenile American alligators ( Alligator mississippiensis) and make a limited comparison of these seasonal patterns on two different lakes in Florida. Male juvenile alligators from a reference lake, Lake Woodruff, displayed temporal patterns in plasma testosterone (T) concentrations that appear to be seasonal. A similar pattern in plasma estradiol-17β (E 2) was observed in juvenile females from Lake Woodruff. Males had significantly elevated T concentrations during the spring and late summer, whereas females had elevated E 2 in the spring and late summer and significantly depressed E 2 concentrations during the winter. A limited 4-month survey of animals from contaminated Lake Apopka found a lack of such seasonality. These results suggest that: (1) healthy wild populations of juvenile alligators have a prolonged peripubescent period that is marked by seasonal hormonal cycles, (2) juvenile alligators exposed to environmental contaminants can lack such seasonal cyclicity, and (3) future studies of juvenile alligators should incorporate such seasonality into the experimental design.

Predicting the Frequencies of High Chlorophyll Levels in Florida Lakes from Average Chlorophyll or Nutrient Data

ABSTRACT An alternative to using average concentrations of phytoplankton chlorophyll in setting lake management goals is to use the frequency that chlorophyll concentrations exceed an established nuisance level. We analyzed 1473 lake-years of data on 438 Florida lakes to develop a series of tables that can be used to predict the frequencies that phytoplankton chlorophylls will exceed concentrations of 10, 20, 30, 40, 50, and 60 mg m−3 in Florida lakes based on the annual average concentrations of chlorophyll, total phosphorus, or total nitrogen. Different tables were created for lakes grouped by TN/TP ratios of >17, <17 but >10, and <10. These tables can be directly applied towards setting lake management goals for those Florida lakes that lack sufficient data to construct their own bloom frequency curves.