Effects of sediment resuspension on phytoplankton production: teasing apart the influences of light, nutrients and algal entrainment

1. Wind‐induced sediment resuspension can affect planktonic primary productivity by influencing light penetration and nutrient availability, and by contributing meroplankton (algae resuspended from the lake bed) to the water column. We established relationships between sediment resuspension, light and nutrient availability to phytoplankton in a shallow lake on four occasions. 2. The effects of additions of surficial sediments and nutrients on the productivity of phytoplankton communities were measured in 300 mL gas‐tight bottles attached to rotating plankton wheels and exposed to a light gradient, in 24 h incubations at in situ temperatures. 3. While sediment resuspension always increased primary productivity, resuspension released phytoplankton from nutrient limitation in only two of the four experiments because the amount of available nitrogen and phosphorus entrained from the sediments was small compared with typical baseline levels in the water column. In contrast, chlorophyll a entrainment was substantial compared with baseline water column concentrations and the contribution of meroplankton to primary production was important at times, especially when seasonal irradiance in the lake was high. 4. Comparison of the in situ light climate with the threshold of light‐limitation of the phytoplankton indicated that phytoplankton in the lake were only likely to be light‐limited at times of extreme turbidity (e.g. >200 nephelometric turbidity units), particularly when these occur in winter. Therefore, resuspension influenced phytoplankton production mainly via effects on available nutrients and by entraining algae. The importance of each of these varied in time. 5. The partitioning of primary productivity between the water column and sediments in shallow lakes greatly influences the outcome of resuspension events for water column primary productivity.     

Biodegradation of a PAH Mixture by Native Subsurface Microbiota

Laboratory microcosm studies were conducted to estimate biodegradation rates for a mixture of five polycyclic aromatic hydrocarbon compounds (PAHs). Static microcosms were assembled using soil samples from two locations collected at a No. 2 fuel oil-contaminated site in the Atlantic Coastal Plain of Virginia. In microcosms from one location, five PAHs (acenaphthene, fluorene, phenanthrene, pyrene, and benzo(b)fluoranthene) biodegraded at net first-order rates of 1.08, 1.45, 1.13, 1.11, and 1.12 yr^?1, respectively. No observable lag period was noted and degradation in live microcosms ceased with the depletion of oxygen and sulfate after 125 days. In microcosms from a second location, net first-order biodegradation rates after an approximately 2-month lag period were 2.41, 3.28, and 2.98 yr^?1 for fluorene, phenanthrene, and pyrene, respectively. Acenaphthene and benzo(b)fluoranthene mass loss rates in the live microcosms were not statistically different from mass loss rates in control microcosms. Stoichiometric mass balance calculations indicate that the dominant PAH mass loss mechanism was aerobic biodegradation, while abiotic losses (attributed to micropore diffusion and oxidative coupling) ranged from 15 to 33% and biotic losses from sulfate-reduction accounted for 7 to 10% of PAH mass loss. Stoichiometric equations that include biomass yield are presented for PAH oxidation under aerobic and sulfate-reducing conditions.     

The ‘true’ growth efficiency of phytoplankton as influenced by light attenuation and insolation: implications of the photosynthesis-irradiance relationship

The true growth efficiency (c) relates the light energy absorbed by phytoplankton to the production of biomass corrected for constant energy requirement of maintenance. Continuous culture studies have shown that, at constant incident irradiance, the value of c for both prokaryotic and eukaryotic species is constant. Culture data for the relevant conditions of incident light may be used for directly estimating the growth rate from daily insolation of optically deep, fully mixed lakes, when the light absorption by the phytoplankton can be established. In order to examine the influence of vertical light attenuation and daily insolation on c, computations were made on a basis of a photosynthesis-irradiance curve of light-limited Oscillatoria limnetica. For steady state growth, the true growth efficiency is linearly related to the areal quantum efficiency of photosynthesis ( _a ). The computations showed that _a remains constant at fluctuating vertical light attenuation, no matter whether the concentration of tripton or phytoplankton changes. The effect of insolation is great: _a is 0.108 mol O₂/E at very low light, but only 0.014 mol O₂/E at 400 W m^–2 subsurface downward irradiance. The results imply that a c-value obtained from cultures for summer averaged insolation must be corrected: between cloudy and clear days the value may vary by a factor of 2. The true growth efficiency for cultures will decrease by about 10% when the same daily irradiation is dosed sinusoidally instead of constantly.     

Leishmania enriettii: radiation effects and evaluation of radioattenuated organisms for vaccination

The effects of gamma radiation and ultraviolet light on motility, morphology, reproduction, ability to transform from amastigote to promastigote, infectivity, and vaccine potential of Leishmania enriettii were studied. Over 800,000 roentgens (R) was necessary to immobilize immediately the organisms, whereas only 25,000 R rendered them noninfective and 50,000 R made amastigotes unable to transform to promastigotes. Increasing degrees of morphological abnormality were seen with increased radiation doses. Single, double, and triple vaccination with 25,000–100,000 R irradiated organisms had no protective value against L. enriettii.     

Seasonal attenuation of quantum irradiance (400–700 NM) in three Nebraska reserviors

The attenuation of down-welling quantum irradiance (400–700 nm) was monitored seasonally in three eutrophic Nebraska reservoirs from July, 1975, to June, 1976. Measurements were made at four stations in McConaughy, three in Pawnee, and three in Yankee Hill using a commercially available, quantum irradiance sensor. The mean vertical attenuation coefficient () for McConaughy varied within a range of thirty-four-fold (0.16 5.45 m^-1), and this range is apparently the greatest reported and this range is apparently the greatest reported for a freshwater system in which data were collected with a quantum sensor. Annual average values for McConaughy, Yankee Hill, and Pawnee were 0.69 m^–1, 1.08 m^–1, and 1.25 m^–1, respectively. The euphotic zone and the 1% level of subsurface irradiance is discussed with respect to the penetration of photosynthetically active radiation (PAR) into natural waters.This study was supported by a grant from the Office of Water Research and Technology, U.S. Dept. of the Interior, project number A-043-NEB, agreement number 14-34-0001-6028, to James R. Rosowski, School of Life Sciences, University of Nebraska, Lincoln.     

Optimization of quorum quenching mediated bacterial attenuation of Solanum torvum root extract by response surface modelling through Box-Behnken approach

The present study was intended to optimize the quorum sensing inhibitory action of Solanum torvum root extract against Chromobacterium violaceum. Factors such as bacterial density, frequency of administration and concentration of extract were analysed. Plant samples were collected from Thrissur District, Kerala, India. Response surface modelling of factors by Box-Behnken approach was employed for optimizing quorum quenching activity of extract. The adequacy of mathematical model was verified by ANOVA and Cook’s distance table. Results revealed that quorum quenching property of Solanum torvum root extract is highly influenced by variables studied whereas maximum activity was found during administration of 300?µg/ml extract thrice in a day. It was also understood that extract does not possess any bactericidal activity wherein it only silence its quorum sensing mediated functions. This observations can be further used in quorum quenching studies.     

Implementation of natural attenuation at a JP-4 jet fuel release after active remediation

After eighteen months of active remediation at a JP-4 jet-fuel spill, aresidual of unremediated hydrocarbon remained. Further site characterizationwas conducted to evaluate the contribution of natural attenuation to controlexposure to hazards associated with the residual contamination in thesubsurface. Activities included the detailed characterization ofground-water flow through the spill; the distribution of fuel contaminantsin groundwater; and the analysis of soluble electron acceptors moving intothe spill from upgradient. These activities allowed a rigorous evaluation ofthe transport of contaminants from the spill to the receptor of groundwater,the Pasquotank River. The transport of dissolved contaminants of concern,that is benzene, toluene, ethyl benzene, xylene isomers (BTEX) andmethyl-tertiary-butyl ether (MTBE), into the river from the source area wascontrolled by equilibrium dissolution from the fuel spill to the adjacentgroundwater, diffusion in groundwater from the spill to permeable layers inthe aquifer, and advective transport in the permeable layers. The estimatedyearly loading of BTEX compounds and MTBE into the receptor was trivial evenwithout considering biological degradation. The biodegradation ofhydrocarbon dissolved in groundwater through aerobic respiration,denitrification, sulfate reduction, and iron reduction was estimated fromchanges in ground-water chemistry along the flow path. The concentrations oftarget components in permanent monitoring wells continue to decline overtime. Long term monitoring will ensure that the plume is under control, andno further active remediation is required.     

The effect of particle characteristics on the beam attenuation coefficient and output from an optical backscatter sensor

Experiments were conducted to measure optical backscatter and beam transmission of suspensions of 180, 150 and 90 μm sand, and 40 μm clay, in a recirculation tank designed to house an optical backscatterance sensor (O.B.S.) and a beam transmissometer. Particle size was determined using gravimetric techniques and Coulter counter. By contriving known sediment distributions from the fractionated sediment samples, it was found that both the O.B.S. and beam transmissometer responded approximately linearly to narrow band and broad band particle suspensions. The beam transmissometer showed greater sensitivity to the fine-grain fraction of a poly-disperse suspension than the O.B.S.