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We estimated the change in near-surface (0.5 in) lake water and air temperatures in Florida (FL) from 1981 to 2020. We developed a model to predict near-surface temperature using 8000 paired measurements of water and air temperatures taken across the state from 1981 through 2020. The FL water-air temperature model was then used with measured air temperatures to calculate daily near-surface water temperatures at each of 202 points to represent nearby waters that had not been sampled. Average air temperatures in FL have increased by 0.18 °C decade-'and minimum temperatures by 0.30 °C decade-'. Maximum air temperatures demonstrated no change. Average calculated FL annual lake water temperatures increased by 0.14 °C decade-1 with increases in August of 0.14 °C decade-1 and September by 0.18 °C decade- 1. Water temperatures in FL increased at a rate of -74% of the rate of increase of air temperatures. FL increases in air and water temperatures were less than those for the contiguous United States. It is not clear from the literature whether the increases in water temperatures are biologically significant for all of Florida's diverse aquatic biota during the 1 981-2020 period. [ABSTRACT FROM AUTHOR]

Colonial microalgae such as Pediastrum and Scenedesmus of class Chlorophyceae are photosynthetic non-motile freshwater coenobium which have emerged as a promising feedstock for biofuel production and extraction of antioxidative bioactive compounds that could replace the present synthetic antioxidants due to advantages, such as rapid growth rate and high lipid content. A]gal cell growth, lipid accumulation and synthesis of bioactive compounds are susceptible to environmental conditions and this study has inculcated the prevailing ecological condition of high phosphate concentration in Florida lakes given that the state supplies almost 80 percent of the country's phosphate needs. The purpose of the study was to determine the effect of phosphate repletion on lipid production and antioxidant activity by DPPH and hydrogen peroxide radical scavenging biochemical assay on Pediastrum and Scenedesmus cells after 5 weeks of growth. Results indicated that there is a statisti - cally significant 17% increase in lipid content within colonial green algal cells at high phosphate concentration. All solvent fractions in this study efficiently scavenge free radicals, indicating that DPPH and hydrogen peroxide radical scavenging biochemical compounds with both hydrophilic and hydrophobic properties were dispersed in the aqueous residue and organic fractions of control and expel·imental treatments. Higher antioxidative compounds were observed at high phosphate concentrations compared to the control, although statistically not significant. This aligns studies that show how high phosphorus concentrations can induce synthesis of biochemical compounds within microalgal cells. This study postulates that under high phosphate concentration, the mechanism of colonial microalgal production of polar and nonpolar compounds is enhanced as exhibited by the high lipid content and antioxidant production which compels for further investigation. [ABSTRACT FROM AUTHOR]

Short sediment cores (80–100 cm) from three Florida (USA) lakes (Sheelar, Wauberg, and Apopka) that range in trophic status, were analyzed for total organic carbon (TOC), total nitrogen, stable isotopes of organic carbon (δ13CTOC) and biomarkers (n-alkanes and fatty acids), to identify the sources of organic matter in the lake deposits, and to link changes in primary productivity to anthropogenic activities during the last ~ 150 years. Relatively small (0.07 km2), ultra-oligotrophic Lake Sheelar is located in a state park, and sediment analyses indicate stable trophic status in the water body since at least the middle of the nineteenth century. Algal biomarkers are in low abundance throughout the core and terrestrial lipids and δ13CTOC values suggest that vascular plants were the primary source of TOC to the lake sediments during the period of record. In larger, eutrophic Lakes Wauberg (1.5 km2) and Apopka (125 km2), algal-derived biomarkers increase in recent sediments, whereas δ13CTOC values and concentrations of terrestrial biomarkers decrease toward the sediment surface. Increasing dominance through time of autochthonous carbon sources in the Lake Wauberg and Apopka sediment records coincides with specific anthropogenic activities in the respective watersheds. Submersed macrophytes in Lake Wauberg were replaced by algal communities in the mid-1980s, following expansion of residential development in the watershed. Biomarker data from the Lake Apopka core show there was an abrupt transition in the lake in the late 1940s, from domination by vascular plants to domination by algae, which has been documented by other paleolimnological studies that used alternative trophic state indicators. The trophic state shift in Lake Apopka corresponds to a period of increased nutrient input to the lake, associated with extensive farming along the north shore. Florida lakes have experienced different trophic state trajectories over the last ~ 150 years, driven by specific human activities in their respective watersheds. [ABSTRACT FROM AUTHOR]

Crustacean zooplankton data were compiled from long-term observational studies at seven large shallow Florida lakes, to determine whether there are general characteristics in regard to species composition, body size, and biomass. In particular, we examined whether patterns in body size and species richness fit empirical models developed by Stanley Dodson. The lakes included range in size from 125 to 1730 km and encompass mesotrophic to hyper-eutrophic conditions. We found that zooplankton biomass was strongly dominated by one species of calanoid copepod- Arctodiaptomus dorsalis. Large daphnids were absent, and Cladocera assemblages were dominated by small taxa such as Ceriodaphnia, Chydorus, and Eubosmina. The total number of species of pelagic cladocerans (8-12) was consistent with Dodson's predictions based on lake area. The average size of crustacean zooplankton in Florida lakes is small in comparison with temperate communities. A. dorsalis is the smallest calanoid copepod in North America, and the mean length of Cladocera (0.6 mm) is consistent with Dodson's results that size decreases from temperate to tropical zones. Total biomass of crustacean zooplankton was very low, ratios of zooplankton to phytoplankton biomass (0.01-0.1) are among the lowest reported in the literature, and the zooplankton displayed short-lasting early spring peaks in biomass. Cladocera were almost entirely absent in spring and summer. Factors known to occur in Florida lakes, which appear to explain these characteristics of biomass, include intense fish predation and high summer water temperature. [ABSTRACT FROM AUTHOR]

Fifty-seven surface sediment samples from 35 Florida lakes were collected to study testate amoebae. Seven genera, 17 species, and 28 strains were identified in the 46 sediment samples from 31 lakes that contained testate rhizopods. Seven species accounted for ≥90% of the individuals in all samples. Sediment total phosphorus (TPsed), organic matter (OM), and total carbon:total nitrogen ratio (TC:TN) were measured to assess the effect of these variables on thecamoebian assemblages. OM content was the only sediment variable that influenced presence/absence of thecamoebians. Samples with <5% OM contained no thecamoebians. Lakes with multiple surface sediment samples showed high Morisita–Horn similarity values (0.74–0.99), indicating that all sites at which samples were collected in a lake provided representative thecamoebian assemblages. No relationship was observed between thecamoebian diversity indices and sediment variables. Lake trophic state and pH were examined to explore potential water column influences on thecamoebian communities. Highest thecamoebian diversity indices were found in mesotrophic to eutrophic lakes with pH near 8.0. These results suggest that water column conditions have a greater influence on thecamoebian assemblages than do sediment variables. We used multivariate analysis to evaluate the relations between water quality variables and testate rhizopod assemblages. Canonical correspondence analysis (CCA) showed that alkalinity and pH are the water column variables that most influence the relative abundance of species. Thecamoebians thus hold promise as bioindicators of acidification in Florida lakes. Thecamoebian remains in lake sediment cores should be useful to infer past anthropogenic shifts in lake pH. [ABSTRACT FROM AUTHOR]

Surface water structures and associated active stage management and water use have altered many lakes. Assessing the degree of alteration requires an indicator of hydrologic regime as a first step. Water level regime is an organizing principal of soil morphology and the structure and function of wetland vegetative communities in lakes, marshes, ponds, and wet prairies. Although lake classifications have included a wide variety of physical and biological indicators for various purposes, none is based on hydrologic statistics of water level regimes beyond frequency parameters and simple stage range. Statistical measures of exceedance and level change were derived from the gauge record for a sample of 135 lakes. These measures were used in a principal component analysis to derive independent indicators for lake classification. The first two principal components accounted for 88% of the variance of six original variables and identified two indicators of hydrologic regimes: stage range (50%) and stage rise/fall symmetry (38%). These indicators of hydrologic regime classified north Florida lakes into eight groups. The generally close correspondence of lake classes, based on hydrologic statistic indicators, to geomorphic and landscape classifications lends strong support to the general utility of this approach. This method will also be useful because the stage record integrates the inputs and outputs in lake water budgets, thereby providing insight into these components when specific data about their magnitudes are otherwise lacking. [ABSTRACT FROM AUTHOR]

1. The fraction of living and dead phytoplankton cells in seven Florida lakes was assessed by using the cell digestion assay, a non-staining membrane permeability test. The cell digestion assay is an effective method to analyse cell viability in complex natural phytoplankton communities. 2. The lakes examined ranged widely in phytoplankton abundance and community composition. The variability in the percentage of living cells (% LC) was high among the taxonomic groups forming the different phytoplankton communities, ranging from 19.7% to 98% LC. 3. All cells within single cyanobacteria filaments were determined to be either dead or alive, suggesting physiological integration of the cells within colonies. 4. Within each lake, the dominant taxa generally exhibited the highest proportion of living cells. A high proportion of living cells was found to be a characteristic of the different taxa forming the communities of eutrophic lakes. The average value for the % LC for all groups comprising the phytoplankton communities in each of the lakes ranged from 29.9 ± 7.2 to 80.4 ± 4.0 (mean ± SE) and varied strongly and positively with chlorophyll a concentration. 5. These results suggest phytoplankton cell death to be an important process structuring phytoplankton communities in lakes, particularly in oligotrophic ones. [ABSTRACT FROM AUTHOR]

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 constant 226Ra activities, whereas 12 show high (>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. [ABSTRACT FROM AUTHOR]

Anthropogenic phosphorus (P) loads have been implicated in eutrophication of lakes and wetlands throughout Florida. One technology that holds considerable promise for controlling these loads in a cost-effective manner is the use of treatment wetlands. Preliminary research in south Florida on the use of submerged aquatic vegetation (SAV) as the dominant vegetation in these treatment wetlands is reporting higher P removal performance than wetlands dominated by rooted, emergent plants. This research has been based to-date primarily on relatively small-scale mesocosms (5–2000 m2) and on a larger scale treatment wetland (148 ha) that has been operated for about 7 years. Considering the magnitude of engineering decisions and project costs to implement P control in the Everglades Agricultural Area and elsewhere in Florida, it is prudent to look for additional confirmation of P removal performance from other existing SAV-dominated systems in Florida that have a longer operational period. This paper describes an analysis of existing data collected from a number of SAV-dominated, flow-through lakes and rivers in Florida with characteristics similar to the proposed SAV treatment systems. While these existing input–output data were not specifically collected for the purpose of preparing mass balances and P removal rate estimates, they can be judiciously applied to that analysis. The overall conclusion of this analysis is that SAV-dominated lakes and rivers do typically remove P from the water column. The likely long-term sink for this P is the newly accreted sediment. The long-term average P removal rate for 13 SAV-dominated lake and river systems in Florida was 1.2 g/m2 per year. This result compares favorably with an average net sediment P accumulation rate of 1.2 g/m2 per year reported by others for 11 SAV-dominated Florida lakes. These estimated long-term P removal rates are higher than those for full-scale wetlands dominated by emergent vegetation (Treatment Wetlands (1996); Wetlands Ecol. Mgmt. 4 (1997) 159). Average first-order P removal rate constants for SAV-dominated lakes (15 m/year) and rivers (46 m/year) are generally less than those estimated in SAV-dominated mesocosms (60–140 m/year) and similar to a large-scale SAV-dominated stormwater treatment area (STA) (40 m/year). P removals in all of these SAV-dominated systems are influenced by inlet P loading rates, with removal rates positively correlated to both P inlet concentration and hydraulic loading rate (HLR). Based on this analysis, caution is recommended when extrapolating the P removal results from relatively short-term or small-scale mesocosm studies to the design of full-scale, long-term operating SAV-dominated wetlands. [Copyright &y& Elsevier]