Frederick J. Aldridge

Can wind-induced resuspension of meroplankton affect phytoplankton dynamics?

Data from Lake Apopka, Florida, are presented to illustrate the importance of wind-induced resuspension of sediments in a shallow, subtropical, hypereutrophic lake. Wind-induced resuspension of meroplankton, primarily planktonic diatoms that settle to the benthic environment, accounts for a large component of the temporal variation in phytoplankton biomass. Chlorophyll concentrations >100 μg/L are highly correlated with wind speed, and the regression of wind speed on chlorophyll accounts for 53% of the temporal variability in chlorophyll. Resting cells of diatoms are also resuspended with the meroplanktonic community. Induction of resting cells that are physiologically dormant occurs in darkness; but within a few hours after exposure to the water-column light and nutrient environment, resting cells become physiologically active. Other types of resting propagules in addition to diatom resting cells also may be resuspended from sediments and affect phytoplankton dynamics. Data from Lake Apopka and other systems are used to develop paradigms about time and depth scales for resuspension of meroplankton and resting propagules in lakes and in the sea.

Phytoplankton community photosynthesis and primary production in a hypereutrophic lake, Lake Apopka, Florida

A study of in situ primary productivity (light- and dark-bottle oxygen exper- iments) was conducted biweekly in 1990 and 1991 to measure volumetric rates of phytoplankton photosynthesis and estimate integral phytoplankton photosynthesis and primary production. Concurrently, ambient conditions including water temperature, photosynthetically active radiation (PAR), Secchi disc transparency, dissolved oxygen and phytoplankton biomass (chlorophyll- a) were measured. Results of both light- and dark-bottle experiments are used to 1) demonstrate that Lake Apopka is not hetero- trophic as reported in the literature, 2) provide preliminary estimates of phytoplankton primary production, 3) discuss shortcomings in experimental methodology and 4) evaluate sources of temporal variability in phytoplankton primary production. No strong seasonal patterns were found in ambient physical and chemical conditions with the exception of water temperature. Whole-basin estimates of net organic carbon sedi- mentation are used as an independent approach to estimate phytoplankton primary pro- duction. The magnitude of net primary production ranged from approximately 1 to 2gCm -2 d -1 for three direct estimates and from to 3 to 5gC m -2 d -1 for the indirect method. We conclude that short-term temporal variability in primary productivity is controlled mainly by meteorological forcing of wind-induced turbulence and resuspen- sion of meroplankton. Our study shows that obtaining precise and accurate direct esti- mates of phytoplankton photosynthesis and production are more complex than might be anticipated from the application of standard techniques.

The Effects of Sediment Resuspension on Phosphorus Available for Algal Growth in a Shallow Subtropical Lake, Lake Okeechobee

ABSTRACT Algal bioassays were conducted to determine whether phosphorus available for algal growth was released during sediment resuspension in Lake Okeechobee. The bioassays included evaluations of resuspension of sediments at different times of the year. Treatments consisted of floc and surface sediment layers mixed with surface lake water, then filtered to remove all but soluble phosphorus. The presence of phosphorus available for algal growth was manifested as the growth responses of unialgal cultures of phosphorus-starved cyanobacteria isolated from Lake Okeechobee. Floc and sediment treatments caused different algal growth responses depending on the sampling dates. In two summer experiments, there was enhanced growth response of the algae in the surface water previously mixed with sediments and floc. This result contrasted with the winter experiments when algal yields were lower in surface water samples mixed with sediment or floc. The results support recent hypotheses that sediment resuspension in ...

Induced triploids and tetraploids in bighead carp, Hypophthalmichthys nobilis, verified by multi-embryo cytofluorometric analysis

Abstract Triploid and tetraploid bighead carp, Hypophthalmichthys nobilis, were produced by applying a hydrostatic pressure shock of 500 atm of 90 s duration. The optimum time of pressure shock after fertilization for triploid and tetraploid production was 4 min and 36 min, respectively. Egg quality as measured by survival in control groups related directly to percent triploids produced. Eighty to 100% triploids were produced when control viability exceeded 59%. No triploids were produced when control viability was less than 40%. Conventional techniques to determine ploidy require labor intensive karyotyping methods or fish large enough to obtain a blood sample for analysis in a particle counter. This paper describes a cytofluorometry technique developed to determine ploidy from fish embryonic tissue. Multiembryo homogenates analyzed 24–28 h after fertilization were used to determine ploidy distribution for each treatment group.

Environmental manipulation to stimulate rotifers in fish rearing ponds

Abstract Four treatments were established in eight small ponds not stocked with fish: a control group (untreated and not fertilized) and three groups treated with organophosphate insecticide (Dylox). One group of Dylox treatment ponds was treated with chemical fertilizer, the second group with chemical and organic fertilizer, and the third group with chemical-organic fertilizer and paddlewheel water agitation. Water analysis and zooplankton samples were collected twice weekly. Rotifers increased in numbers in all treated ponds but no correlations were found between 16 hydrochemical and biological parameters and rotifer numbers. The application of rotifer management techniques for rearing larval fish is discussed.

Net production and net heterotrophy in Lake Apopka : a comment on SCHELSKE et al. (2003). Commentary and Authors' reply

We found the conclusion of SCHELSKE et al. (2003, Arch. Hydrobiol. 157:145-172) that Lake Apopka was not net heterotrophic was incorrect when annual rates of production and respiration for the entire lake ecosystem are taken into consideration. A new carbon budget for the water and sediments showed for the period of study the sum of the annual sources of organic carbon including primary production and inflows (765 g C m -2 yr -1 ) was less than the sum of the annual losses including respiration in the water and sediments and outflows (2497 g C m -2 yr -1 ). Diel oxygen curves demonstrated that it is possible to have oxygen supersaturation at the surface near midday and still have net heterotrophy over 24-h.