Edward Laws - Academia.edu (original) (raw)

Papers by Edward Laws

Pacific Science, 2001

Dark 14 CO 2 incorporation into protein was determined from 24-hr incubations using size-fraction... more Dark 14 CO 2 incorporation into protein was determined from 24-hr incubations using size-fractionated natural phytoplankton populations from Ka Åne`ohe Bay, Hawai`i, enriched with either ammonium or ammonium plus phosphorus. Response to ammonium addition was maximum at an ammonium concentration of 3±4 mM. Dark 14 CO 2 assimilation was suppressed by addition of both ammonium and phosphorus, but percentage incorporation into protein was not signi®cantly different from addition of ammonium alone. About 75 q 1% of the 14 C taken up by the cells was incorporated into either protein or low-molecular-weight intermediate compounds. Cells smaller than 10 mm showed little response to nutrient additions. However, cells in the 10-to 35-mm size fraction incorporated signi®cantly more 14 C into protein when nutrients were added. C : N ratios calculated from the percentage of 14 C incorporated into protein were most variable temporally in the 10-to 35-mm size group and least variable in the picoplankton (0.2±2.0 mm). Nutrient limitation indices (NLIs) calculated from the quotient of C : N ratios in control and nutrient-enriched cultures were not signi®cantly different for the picoplankton and 2-to 10-mm size fraction. The NLI for the 10-to 35-mm size fraction was signi®cantly lower and implied a modest degree of nutrient limitation. The results suggest that cells smaller than 10 mm are growing at close to nutrient-saturated rates much of the time in Ka Åne`ohe Bay. However, larger cells appear to experience a signi®cant degree of nutrient limitation at some times, particularly when chlorophyll a concentrations are less than about 1 mg m À3. Dark protein synthesis appears to be a useful modi®cation of previous methods based on the dark uptake of 14 CO 2 for studying nutrient limitation.

Proceedings of the National Academy of Sciences of the United States of America, May 22, 2007

Estuaries and Coasts, Jan 7, 2015

Rates of accumulation of particulate organic carbon (POC) and particulate inorganic carbon (PIC) ... more Rates of accumulation of particulate organic carbon (POC) and particulate inorganic carbon (PIC) as well as soil accretion rates were determined in the Yellow River Delta (YRD) and Liaohe Delta (LHD) in northeastern China. Rates of carbon accumulation were dominated by PIC accumulation in the YRD and by POC accumulation in the LHD. Rates of POC accumulation at sites above mean sea level were similar in the two deltas, 141±17 g C m −2 y −1 , but were much higher, 381± 10 g C m −2 y −1 , at sites in the LHD below mean sea level. High rates of PIC accumulation in the YRD, 916±133 g C m −2 y −1 , reflect the very high concentration of dissolved inorganic carbon in the Yellow River, which in turn reflects the erosion of carbonate-rich glacial dust and evaporates minerals in the Loess Plateau, the excess of evaporation over precipitation in the watershed, and the fact that much of the flow in the river is diverted to irrigate crops. In both river deltas, accumulation of PIC was positively correlated with accumulation of POC, although the sources of the PIC are allochthonous and the sources of the POC are primarily autochthonous. Rates of POC accumulation were closely correlated with the species of wetland plants in the deltas. Although the rates of PIC accumulation in the YRD are exceptional, anthropogenic effects, including climate change, are creating conditions that will likely enhance PIC accumulation in many other river deltas.

Deep-sea research, 1989

Autotrophic carbon and nitrogen assimilation rates and the fluxes of particulate carbon (PC) and ... more Autotrophic carbon and nitrogen assimilation rates and the fluxes of particulate carbon (PC) and particulate nitrogen (PN) into sediment traps positioned near the base of the euphotic zone were measured at 260N, 155°W in the North Pacific subtropical gyre. Carbon assimilation uncorrected and corrected for grazing and algal respiration losses averaged 484 _+ 81 and 692 _+ 115 mg C m-Zd-1, respectively. Carbon:nitr0gen assimilation ratios were always higher than the Redfield ratio and averaged 7.1 + 0.6 g C giN. Absolute growth rates were estimated to be 69 +_ 10% of nutrient-saturated values. A comparison of conical and cylindrical sediment traps indicated that the conical traps underestimated PN and PC fluxes by factors of 30 and 40, respectively. This undertrapping probably occurred in part because the effective trapping area of the conical traps is significantly less than the mouth area of the trap for slowly sinking particles. However, several lines of evidence suggest that the major cause of the discrepancy was the breakup of marine snow aggregates that encountered the sloping sides of the conical traps. The fratios calculated from PN fluxes into the cylindrical traps varied by about a factor of three and averaged 19 _+ 10%. Part of the temporal variability in the f ratio appeared to be due to the fact that particulate material accumulated in the euphotic zone during storm events and subsequently appeared as a large flux of PN as the storm dissipated. The PC:PN ratio of the material that sedimented at the base of the euphoric zone (9.2 + 1.1 g C g-~N) was consistently higher than the corresponding autotrophic assimilation rate ratio. Because of this fact net community production exceeded new production in terms of carbon by about 30%. The latter was calculated by multiplying the downward flux of PN by the antotrophic carbon:nitrogen assimilation rate ratio.

Water, 2021

Phytoplankton growth rates and zooplankton grazing rates were estimated on 16 occasions over a pe... more Phytoplankton growth rates and zooplankton grazing rates were estimated on 16 occasions over a period of 17 months in University Lake, a highly eutrophic lake on the campus of Louisiana State University. Phytoplankton growth rates and chlorophyll a concentrations averaged 1.0 ± 0.2 d−1 and 240 ± 120 mg m−3, respectively. Chlorophyll a concentrations were at or above the inflection point of the Holling type I curve that described the relationship between zooplankton grazing rates and chlorophyll a concentrations. In most cases, it was necessary to dilute lake water by more than a factor of 4 before zooplankton grazing rates became sensitive to chlorophyll a concentrations. Chlorophyll a concentrations were positively correlated with temperature and were roughly fourfold higher at 30 °C than at 15 °C. An analysis of the temperature dependence of the growth rates and grazing rates in this study and 87 other paired estimates of limnetic phytoplankton growth rates and zooplankton grazing...

Frontiers in Microbiology, 2021

Bacteria play a pivotal role in shaping ecosystems and contributing to elemental cycling and ener... more Bacteria play a pivotal role in shaping ecosystems and contributing to elemental cycling and energy flow in the oceans. However, few studies have focused on bacteria at a trans-basin scale, and studies across the subtropical Northwest Pacific Ocean (NWPO), one of the largest biomes on Earth, have been especially lacking. Although the recently developed high-throughput quantitative sequencing methodology can simultaneously provide information on relative abundance, quantitative abundance, and taxonomic affiliations, it has not been thoroughly evaluated. We collected surface seawater samples for high-throughput, quantitative sequencing of 16S rRNA genes on a transect across the subtropical NWPO to elucidate the distribution of bacterial taxa, patterns of their community structure, and the factors that are potentially important regulators of that structure. We used the quantitative and relative abundances of bacterial taxa to test hypotheses related to their ecology. Total 16S rRNA gen...

Foxes are timid yet resourceful animals that are integrated into many urban environments. Because... more Foxes are timid yet resourceful animals that are integrated into many urban environments. Because they are elusive, collecting information about the number of urban foxes, their diet and spatial distribution, their interactions with the ecological community in their urban habitat, as well as residents’ response to them, is difficult. Involving stakeholders to participate in the data collection on wildlife via citizen science on social media is one way to overcome this complication, while simultaneously engaging residents in the ecology happening around them. Therefore, we used social media as the platform to engage the public to document and map the foxes in Baton Rouge, LA. Local residents were asked to post sightings and/or photographs of foxes they observed, with the location, onto our Facebook Page at Fox Finders of Baton Rouge, on Twitter at @FoxFindersBR, or on Twitter and Instagram with the hashtag #findfoxlsu. This information was added onto an ArcGIS story map. Types of pub...

Science of The Total Environment, 2019

• Determination of water masses occurring in Taiwan Strait • The ciliates were dominantly compris... more • Determination of water masses occurring in Taiwan Strait • The ciliates were dominantly comprised of Spirotrichea and Phyllopharyngea. • Ciliate alpha diversity was associated with water chemistry and food abundance. • Three biogeographic provinces of ciliates were found on a regional scale. • Water mass-driven spatial effects and environmental heterogeneity largely shape ciliate biogeography.

Nature Communications, 2019

The major biogeochemical cycles of marine ecosystems are driven by solar energy. Energy that is i... more The major biogeochemical cycles of marine ecosystems are driven by solar energy. Energy that is initially captured through photosynthesis is transformed and transported to great ocean depths via complex, yet poorly understood, energy flow networks. Herein we show that the chemical composition and specific energy (Joules per unit mass or organic carbon) of sinking particulate matter collected in the North Pacific Subtropical Gyre reveal dramatic changes in the upper 500 m of the water column as particles sink and age. In contrast to these upper water column processes, particles reaching the deep sea (4000 m) are energy-replete with organic carbon-specific energy values similar to surface phytoplankton. These enigmatic results suggest that the particles collected in the abyssal zone must be transported by rapid sinking processes. These fast-sinking particles control the pace of deep-sea benthic communities that live a feast-or-famine existence in an otherwise energy-depleted habitat.

Marine and Freshwater Research, 2018

The carbon sequestration rate (CSR) in deltaic wetlands is associated with the nutrient balance, ... more The carbon sequestration rate (CSR) in deltaic wetlands is associated with the nutrient balance, sediment (soil) accretion rate (SAR) and geological and climatic conditions. To explore the relationships between these factors, micronutrients; C, N, and P concentrations; and ages determined using either paleosols or radiometric dating with 210Pb were analysed from a total of 14 cores from the Yellow River delta (YRD) and Liaohe delta (LHD) wetlands, collected in 2007 and 2012 respectively. With the exception of Ca, concentrations of N, organic C, Cu, Zn, Fe, Mn, Mg, K, Al and H+ were significantly higher in the wetland soils of the LHD, but organic CSR was virtually identical at the two sites, ~140gCm–2year–1 at sites above mean sea level (MSL). SAR and organic CSR at LHD sites below MSL were ~2.8 times the corresponding rates at sites above MSL. SAR and total CSR were much higher in the YRD than LHD because of the much greater accumulation rate of CaCO3 in the YRD. Organic CSRs were ...

Water, 2017

University Lake, a shallow, artificial, urban lake adjacent to the campus of Louisiana State Univ... more University Lake, a shallow, artificial, urban lake adjacent to the campus of Louisiana State University, has a long history of water quality problems, including algal blooms, fish kills, and high concentrations of fecal indicator bacteria. Periodic dredging of the lake is necessary to prevent its return to swampland. This study was undertaken to elucidate the roles of allochthonous versus autochthonous nutrients as causes of water quality problems in the lake, with the expectation that this information would help identify strategies for lake restoration. Photosynthetic rates and concentrations of inorganic nutrients and phytoplankton pigments were measured over a period of one year. More than 90% of the chlorophyll a (chl a) in the lake was accounted for by Chlorophyceae, Cyanophyceae, and Bacillariophyceae. Concentrations of chl a, which averaged 75 μg L−1, fluctuated weekly during dry weather by as much as a factor of four. Phytoplankton growth rates were about 30% higher 1–2 days...

The objective of this project was to improve the technology of outdoor mass culture of microa1gae... more The objective of this project was to improve the technology of outdoor mass culture of microa1gae for oil production by investigation of species/strains, optimization of culture conditions t and development of strategies that increase efficiency and improve yield. Specific objectives of the subcontract were to determine if selected marine strains of microalgae could grow in water types found in the southwestern U.S., to evaluate and optimize yields of desert oil producing strains in outdoor culture, and to evaluate management strategies that will improve the efficiency or increase yields in outdoor flume culture systems. Discussion A shallow flume system for the mass culture of microalgae has been developed and constructed by the University of Hawaii. Briefly, the system concept includes shallow channels circulated at a high flow rate containing very dense algal cultures. Airlift pumps, restricted within 15 cm PVC pipes, are used for recirculation and gas exchange. A major contribution of the Hawaii project has been the development of a system that introduces ordered vertical mixing into the culture as a byproduct of stream flow. Small foils, similar in design to .airplane wings, are suspended in the flowstream at a relatively high angle of attack. Vortices are generated at the tips of each of these foils and are propagated downstream. Arrays of foils are positioned every 1.2m along the culture flume. Observations of the vortex rotation rates have indicated that cells are exposed to a light-dark cycle time of 1 to 2 seconds in this mixing regime. This light-dark cycle avoids prolonged exposure of the cells to bright light and associated low photosynthetic efficiencies. Amajor accompl ishment of the past ten months I work was the identification of a microa1gal species which can be grown successfully in the system on a 12-month basis without temperature control t and which produces large quantities of lipids when silicate stressed. This species ;s a diatom of the genus Cyclotella which was isolated from an estuary in the southeastern U.S. The species grows well in both seawater and water types characteristic of saline groHnd-waters found in the southwestern U.S. at salinities from 7 0/ 0 0 to 50 /00, and is not adversely affected by the warm temperatures (30-34°C) encountered in a shallow culture system during the summer months. Yields of about 34 9 AFDW/m 2/d were obtained with this organism during ten-day factorial growth experiments. The composition of Cyclotel1a was found to change from about 25% lipid carbon to over 50% lipid carbon over a time period of one day when the silicate concentration of the growth medium dropped to 0.5-1.0 uM. This increase in cellular lipid content occurred at cell densities typical of operating conditions in the outdoor flumes, and is associated with a large increase in the rate of lipid synthesis rather than merely a conversion of other cellular constituents to lipids. The mechanism responsible for this rapid increase in lipid synthesis is apparently the blockage of cell division 1 due to the lack of sil icate required for frustule formation. During the period of silicate stress the (liatom frustules 'appear, to become fragile and subject to significant damage caused by the buffeting in the airlift..driven flume system. As a result it appears that the "f'[at tentnq up" process will have to be performed in a less turbulent system. An analysis of the efficiency of the mass culture system revealed that operation of the airlift at full power during the evening hours was almost certainly unnecessary, and that a reduction in the supply of air to the airlifts by as much as. 90% at night had no significant effect on production. Reducing the input of CO.? to the system by allowing the pH to rise to 8.5 rather than 7.5 resu1~d in no significant change in photosynthetic efficiency, but eliminating CO, additions altogether reduced photosynthetic efficiency by more than a facto~ of two in a culture of ~ suecica. The cost •effectiveness of CO? input reduction will depend on the cost of CO 2 versus the value of the product algae. Conclusions The project is making good progress toward identifying a suitable microalgal species and associated culture system which can be used for the mass culture of oil-producing microa1gae. Silicate starvation appears to be an effective way to trigger lipid synthesis in diatoms, as evidenced by the need to add CO? to a dense cul ture ; n order to bri ng about 1; pid synthes i s duri ng si 1i cate starvation. This approach appears to have the potential for nearly doubling the rate of lipid synthesis over that attainable in-a silicate-replete medium. A strain of ~clote1la isolated from an estuary in the southeastern U.S. increases its~ipid content to over 50% on a carbon basis during only one day of silicate starvation, produces biomass yields (34 9 AFDW/m 2/d) comparable to the high yields previously achieved with Tetraselmis suecica, and is virtually unaffected by predator or competitor problems in outdoor mass culture. This species appears to be a very strong candidate for use as an oil-producing microalgal strain.

Environmental Science & Technology, 2006

Estuaries and Coasts, 2015

Applied and Environmental Microbiology, 1986

A method is presented for determining both the average turnover rate and the standard deviation o... more A method is presented for determining both the average turnover rate and the standard deviation of the average turnover rate of the adenine nucleotide (AN) pool within a population of microorganisms. The method requires the calculation of the initial slope and curvature of a plot of AN specific activity versus time following the introduction of [ 3 H]adenine. An analysis of noise-corrupted data indicated that the method is capable of detecting a lack of uniformity in the turnover rate when the coefficient of variation of the turnover rate exceeds 39%. An analysis of field data revealed a significant lack of uniformity in the turnover rates of microbial communities in a marine sediment sample and freshwater pond but no significant nonuniformity in the turnover rates of microbial communities in a seawater sample and in a second freshwater pond. Although the method has been applied only to the analysis of AN turnover rates, it is applicable to any intracellular pool for which a suitabl...

$Research paper thumbnail of {"__content__"=>"Using a trait-based approach to optimize mixotrophic growth of the red microalga towards fatty acid production.", "i"=>{"__content__"=>"Porphyridium purpureum"}}$

Biotechnology for biofuels, 2018

Organic carbon sources have been reported to simultaneously increase the growth and lipid accumul... more Organic carbon sources have been reported to simultaneously increase the growth and lipid accumulation in microalgae. However, there have been no studies of the mixotrophic growth of in organic carbon media. In this study, three organic carbon sources, glucose, sodium acetate, and glycerol were used as substrates for the mixotrophic growth of . Moreover, a novel trait-based approach combined with Generalized Additive Modeling was conducted to determine the dosage of each organic carbon source that optimized the concentration of cell biomass or fatty acid. A 0.50% (/) dosage of glucose was optimum for the enhancement of the cell growth of , whereas sodium acetate performed well in enhancing cell growth, arachidonic acid (ARA) and eicosapentaenoic acid (EPA) content, and glycerol was characterized by its best performance in promoting both cell growth and ARA/EPA ratio. The optimum dosages of sodium acetate and glycerol for the ARA concentration were 0.25% (/) and 0.38% (/), respective...

$Research paper thumbnail of {"__content__"=>"Relative Contributions of and Bacteriophage to Bacterial Cell Death under Various Environmental Conditions.", "i"=>{"__content__"=>"Halobacteriovorax"}}$

mBio, Jan 7, 2018

The role of protists and bacteriophages in bacterial predation in the microbial food web has been... more The role of protists and bacteriophages in bacterial predation in the microbial food web has been well studied. There is mounting evidence that and like organisms (BALOs) also contribute to bacterial mortality and, in some cases, more so than bacteriophages. A full understanding of the ecologic function of the microbial food web requires recognition of all major predators and the magnitude of each predator's contribution. Here we investigated the contribution of , one of the BALOs, and bacteriophages when incubated with their common prey, , in a seawater microcosm. We observed that was the greatest responder to the prey, increasing 18-fold with a simultaneous 4.4-log-unit reduction of at 40 h, whereas the bacteriophage population showed no significant increase. In subsequent experiments to formulate a medium that would support the predatory activities and replication of both predators, low-nutrient media favored the predation and replication of the , whereas higher-nutrient medi...

The ISME journal, Jan 7, 2015

Predation on bacteria and accompanying mortality are important mechanisms in controlling bacteria... more Predation on bacteria and accompanying mortality are important mechanisms in controlling bacterial populations and recycling of nutrients through the microbial loop. The agents most investigated and seen as responsible for bacterial mortality are viruses and protists. However, a body of evidence suggests that predatory bacteria such as the Halobacteriovorax (formerly Bacteriovorax), a Bdellovibrio-like organism, contribute substantially to bacterial death. Until now, conclusive evidence has been lacking. The goal of this study was to better understand the contributors to bacterial mortality by addressing the poorly understood role of Halobacteriovorax and how their role compares with that of viruses. The results revealed that when a concentrated suspension of Vibrio parahaemolyticus was added into microcosms of estuarine waters, the native Halobacteriovorax were the predators that responded first and most rapidly. Their numbers increased by four orders of magnitude, whereas V. parah...