Papers by Michael Coveney
Archiv für Hydrobiologie, 2003
A study of in situ primary productivity (light-and dark-bottle oxygen experiments) was conducted ... more A study of in situ primary productivity (light-and dark-bottle oxygen experiments) 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 heterotrophic 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 sedimentation are used as an independent approach to estimate phytoplankton primary production. The magnitude of net primary production ranged from approximately 1 to 2 g C m -2 d -1 for three direct estimates and from to 3 to 5 g C 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 resuspension of meroplankton. Our study shows that obtaining precise and accurate direct estimates of phytoplankton photosynthesis and production are more complex than might be anticipated from the application of standard techniques.
Archiv für Hydrobiologie, 2006
Canadian Journal of Fisheries and Aquatic Sciences, 1993
. Assessment of phytoplankton nutrient limitation in productive waters: application of dilution b... more . Assessment of phytoplankton nutrient limitation in productive waters: application of dilution bioassays. Can. l. Fish. Aquat. Sci. 50: 2208-2221. Excessive nutrient loads to aquatic systems can complicate otherwise predictable relationships between nutrient concentrations and phytoplankton biomass. We conducted six bioassays on surface phytoplankton assemblages collected from productive Lake Apopka, Florida, to measure the effect of nutrient reduction on phytoplankton growth and nutritional state. Lake water was mixed with one of three diluents to create a gradient of ambient nutrient concentrations; nitrogen (N) and phosphorus (P) limitation at each level of dilution was evaluated in a 2 x 2 factorial design. While the addition of N clearly increased the growth of phytoplankton in undiluted Lake Apopka water, the phytoplankton became more P limited with the reduction of particles (30-60% dilution). Regression of algal yields onto total P concentrations from our bottle experiments indicated that an 8 ug-L-1 change in P leads to only a 1 ug-L -1 change in chlorophyll yield, probably due to the high concentration of P in the lake. Because dilution influences factors in addition to ambient nutrient concentrations, results obtained with the technique must be carefully evaluated. Despite this, reduction of particles to improve water quality may, in concept, be a reasonable management scheme in lakes where a large fraction of the nutrients is particulate.
Aquatic Sciences, 2011
The purposes of this study were to assess if Lake Apopka (FL, USA) was autotrophic or heterotroph... more The purposes of this study were to assess if Lake Apopka (FL, USA) was autotrophic or heterotrophic based on the partial pressure of dissolved carbon dioxide (pCO 2 ) in the surface water and to evaluate factors that influence the long-term changes in pCO 2 . Monthly average pH, alkalinity and other limnological variables collected between 1987 and 2006 were used to estimate dissolved inorganic carbon (DIC), pCO 2 and CO 2 flux between surface water and atmosphere. Results indicated that average pCO 2 in the surface water was 196 latm, well below the atmospheric pCO 2 . Direct measurements of DIC concentration on three sampling dates in 2009 also supported pCO 2 undersaturation in Lake Apopka. Supersaturation in CO 2 occurred in this lake in only 13% of the samples from the 20-year record. The surface-water pCO 2 was inversely related to Chl a concentrations. Average annual CO 2 flux was 28.2 g C m -2 year -1 from the atmosphere to the lake water and correlated significantly with Chl a concentration, indicating that biological carbon sequestration led to the low dissolved CO 2 concentration. Low pCO 2 and high invasion rates of atmospheric CO 2 in Lake Apopka indicated persistent autotrophy. High rates of nutrient loading and primary production, a high buffering capacity, a lack of allochthonous loading of organic matter, and the dominance of a planktivorous-benthivorous fish food web have supported long-term net autotrophy in this shallow subtropical eutrophic lake. Our results also showed that lake restoration by the means of nutrient reduction resulted in significantly lower total phosphorus (TP) and Chl a concentrations, and higher pCO 2 .
Limnology and Oceanography, 2010
Controversy exists about the historic shift of primary producer community structure (PPCS) in Lak... more Controversy exists about the historic shift of primary producer community structure (PPCS) in Lake Apopka, a shallow, 125-km 2 lake in central Florida, U.S.A. The controversial questions are: was a lake-wide shift from macrophyte to phytoplankton dominance triggered by a 1947 hurricane or tornadoes spawned by the hurricane within a few weeks or months, or was the shift forced by progressive cultural eutrophication over several years? In 1947, fringing wetlands (35 km 2 ) were being diked and drained for agricultural purposes changing their function from nutrient sinks to nutrient point sources to the lake. We examined whether anthropogenic darkening of the water column induced the PPCS shift during a 0.6-m lake-stage rise. Darkening was defined as lake-bottom photosynthetically available radiation (PAR) # 1.0% of incident PAR. We simulated darkening from changes in the light extinction coefficient (K d ) due to water color, chlorophyll a, and rising lake stage. Simulations predicted that darkening was restricted to 80% of the lake deeper than 2.16 m, a finding consistent with persistence of shallow-water submersed macrophytes after 1947. Anthropogenic wetland draining increased water color, lake stage, and phytoplankton blooms stimulated by phosphorus enrichment, causing a progressive shift to lake-wide phytoplankton dominance over at least several years. The relationship between the 1947 hurricane and the PPCS shift was not causal, but only a temporal coincidence. Our darkening model can be applied to other systems with known bathymetry to predict submersed aquatic vegetation (SAV) coverage from SAV light requirements and water-column light attenuation.
Hydrobiologia, 2001
Bachmann et al.(1999) postulated that wind energy initiated, and has maintained, high turbidity i... more Bachmann et al.(1999) postulated that wind energy initiated, and has maintained, high turbidity in hypertrophic (mean chlorophyll a= 92 µg l-1) Lake Apopka, Florida (mean depth= 1.6 m; area= 12? 500 ha). They asserted that the turbid condition was initiated by a ...
Applied and Environmental Microbiology, 1992
The effects of organic and inorganic nutrient additions on the specific growth rates of bacteriop... more The effects of organic and inorganic nutrient additions on the specific growth rates of bacterioplankton in oligotrophic lake water cultures were investigated. Lake water was first passed through 0.8-μm-pore-size filters (prescreening) to remove bacterivores and to minimize confounding effects of algae. Specific growth rates were calculated from changes in both bacterial cell numbers and biovolumes over 36 h. Gross specific
Environ Manage, 1992
Lake Apopka in Florida, USA, is a large (area=124 km2), hypertrophic (mean total phosphorus=0.220... more Lake Apopka in Florida, USA, is a large (area=124 km2), hypertrophic (mean total phosphorus=0.220 g/m3; mean chlorophyll a=60 mg/m3) lake, with a large sedimentary store of available P (1635 × 106 g P). Phosphorus loading from floodplain farms (132 × 106 g P/yr) has been the primary cause of eutrophication. Assuming elimination of farm P loading, the Vollenweider model predicts a decline in equilibrium P concentration from 0.270 to 0.024 g/m3, if the P sedimentation coefficient (σ) remains constant. It is likely, however, that the value for σ will fall with the elimination of farm loading due to unabated internal P loading from the sediments. Under a worst-case scenario (σ=0), the model predicts that exportation of P from the lake via wetland filtration will greatly accelerate the lake's recovery. Recirculation of lake water through a 21-km2, created wetland and elimination of farm P loading is projected to result in a negative P balance for the lake (-23 × 106 g P/yr) leading to depletion of P stores in the lake in about 60 yr. The estimated cost of the project, 20 million, is less than 3% of the estimated cost of dredging. A 3.65-km2 demonstration project is underway to test and refine the wetland filtration technique. We believe the technique could be cost-effective for other hypertrophic lakes.
Lake and Reservoir Management, Jan 23, 2009
Journal of Lake and Reservoir Management 15(2) :103-120, 1999 © Copyright by the North American L... more Journal of Lake and Reservoir Management 15(2) :103-120, 1999 © Copyright by the North American Lake Management Society 1999 Setting Water Quality Goals for Restoration of Lake Apopka: Inferring Past Conditions Edgar F. Lowe, Lawrence E. Battoe, Michael Coveney ...
![Research paper thumbnail of Experimental evaluation of conversion factors for the [3H]thymidine incorporation assay of bacterial secondary productivity](https://attachments.academia-assets.com/43713689/thumbnails/1.jpg)
Applied and Environmental Microbiology, Aug 1, 1988
The relationship between bacterial growth and incorporation of [methyl-3lHlthymidine in oligotrop... more The relationship between bacterial growth and incorporation of [methyl-3lHlthymidine in oligotrophic lake water cultures was investigated. Prescreening, dilution, and addition of organic and inorganic nutrients were treatments used to prevent bacterivory and stimulate bacterial growth. Growth in unmanipulated samples was estimated through separate measurements of grazing losses. Both bacterial number and biovolume growth responses were measured, and incorporation of [3H]thymidine in both total macromolecules and nucleic acids was assayed. The treatments had significant effects on conversion factors used to relate thymidine incorporation to bacterial growth. Cell number-based factors ranged from 1.1 x 1018 to 38 x 1018 cells mol of total thymidine incorporation-l and varied with treatment up to 10-fold for the same initial bacterial assemblage. In contrast, cell biovolume-based conversion factors were similar for two treatment groups across a 16-fold range of [3H]thymidine incorporation rates: 5.54 x 10'7 ,Im3 mol of total thymidine incorporation-' and 15.2 x 1017 ,um3 mol of nucleic acid incorporation-'. Much of the variation in cell number-based conversion factors was related to changes in apparent mean cell volume of produced bacteria. Phosphorus addition stimulated [3H]thymidine incorporation more than it increased bacterial growth, which resulted in low conversion factors.
Knowledge and Management of Aquatic Ecosystems, 2013
Ecological Engineering, 2015
Applied and environmental microbiology, 1984
New procedures which simplify sample preparation and improve counting efficiency were developed f... more New procedures which simplify sample preparation and improve counting efficiency were developed for double-vial radiorespirometry. Under certain conditions, efficiency of fluor-NaOH-impregnated wicks was not stable, but was adversely affected by water vapor, NaOH concentration, and CO(2) loading. Glass fiber wick material treated with a methanolic fluor-NaOH solution showed improved C counting efficiency (58%) compared with previous methods.
![Research paper thumbnail of Experimental evaluation of conversion factors for the [h]thymidine incorporation assay of bacterial secondary productivity](https://attachments.academia-assets.com/43713681/thumbnails/1.jpg)
Applied and environmental microbiology, 1988
The relationship between bacterial growth and incorporation of [methyl-H]thymidine in oligotrophi... more The relationship between bacterial growth and incorporation of [methyl-H]thymidine in oligotrophic lake water cultures was investigated. Prescreening, dilution, and addition of organic and inorganic nutrients were treatments used to prevent bacterivory and stimulate bacterial growth. Growth in unmanipulated samples was estimated through separate measurements of grazing losses. Both bacterial number and biovolume growth responses were measured, and incorporation of [H]thymidine in both total macromolecules and nucleic acids was assayed. The treatments had significant effects on conversion factors used to relate thymidine incorporation to bacterial growth. Cell number-based factors ranged from 1.1 x 10 to 38 x 10 cells mol of total thymidine incorporation and varied with treatment up to 10-fold for the same initial bacterial assemblage. In contrast, cell biovolume-based conversion factors were similar for two treatment groups across a 16-fold range of [H]thymidine incorporation rates:...
Applied and environmental microbiology, 1992
The effects of organic and inorganic nutrient additions on the specific growth rates of bacteriop... more The effects of organic and inorganic nutrient additions on the specific growth rates of bacterioplankton in oligotrophic lake water cultures were investigated. Lake water was first passed through 0.8-mum-pore-size filters (prescreening) to remove bacterivores and to minimize confounding effects of algae. Specific growth rates were calculated from changes in both bacterial cell numbers and biovolumes over 36 h. Gross specific growth rates in unmanipulated control samples were estimated through separate measurements of grazing losses by use of penicillin. The addition of mixed organic substrates alone to prescreened water did not significantly increase bacterioplankton specific growth rates. The addition of inorganic phosphorus alone significantly increased one or both specific growth rates in three of four experiments, and one experiment showed a secondary stimulation by organic substrates. The stimulatory effects of phosphorus addition were greatest concurrently with the highest alk...
Emerging Topics in Ecotoxicology, 2011
Advances in Experimental Medicine and Biology, 2008
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Papers by Michael Coveney