bluuebunny/crossref_metadata_2025 huggingface dataset:
Weak coupling of bacterial and algal production in a heterotrophic ecosystem: The Hudson River estuary
Authors: Findlay Stuart , Pace Michael L. , Lints David , Cole Jonathan J. , Caraco Nina F. , Peierls Benjamin
Published: April 2010

Bacterial abundances, biomass, and production were measured over a 3‐yr period at stations along a 158‐km reach of the tidal, freshwater Hudson River. Bacterial abundances ranged from 1 to 10 × 106 cells ml−1 with maximal values in summer. Abundance and production averaged over all stations for the ice‐free season (April through December) were 4.9 and 9.1 × 109 cells liter−1 d−1, respectively, and both were significantly correlated with temperature. Neither bacterial abundance nor production showed significant spatial variability over the study reach. In contrast to the results from many autotrophic ecosystems, annual average bacterial abundances from different stations were not significantly correlated with algal standing stocks, and bacterial production was only weakly related to rates of primary production.

Absolute rates of bacterial C production were greater than phytoplankton primary production, indicating that much of the bacterial secondary production in this portion of the river must be supported by nonphytoplanktonic organic C.
Biological availability of dissolved organic carbon along the Ogeechee River
Authors: Leff Laura G. , Meyer Judy L.
Published: April 2010

Quality of dissolved organic C (DOC) from main‐stem and tributary sites along the Ogeechee River was compared to that of chemically defined organic C substrates in terms of biological availability. Availability was determined by measuring bacterial growth on natural river water (collected at high and low discharges) and defined organic substrates (humic standards and high‐quality sources of C). Availability of DOC to the natural (native) stream bacterial assemblage was compared to that of a defined bacterial inoculum, selected for ability to readily utilize high‐quality substrates. Availability of DOC declined downriver, and DOC in highly colored tributaries was of lower quality than DOC from other sites. In most cases, quality of DOC decreased at high discharge.
Similarity of whole‐sediment molecular diffusion coefficients in freshwater sediments of low and high porosity
Authors: Sweerts Jean‐Pierre R.A. , Kelly Carol A. , Rudd John W. M. , Hesslein Ray , Cappenberg Thomas E.
Published: April 2010

Whole‐sediment molecular difusion coefficients (Ds) for tritiated water in pore waters of various lakes were determined experimentally by adding 3H2O to the overlying water of asphyxiated (without bioirrigation) and unasphyxiated cores and measuring the resulting pore‐water profiles after a period of time. Our objectives were to determine the relationship between Ds and Do (the diffusion coefficient in pure water) in sediments with a wide range of porosities and organic contents and to examine the influence of bioirrigation on solute transport and on the predictability of Ds.

We found that Do/Ds did not change as much as expected with increasing porosity, i.e. in low‐porosity sediments the average Do/Ds was 1.8±0.1 and in high‐porosity sediments it was 1.5±0.2. We also found that the effect of faunal activity on the predictability of Ds was only significant in sediments with high (14,000 ind. m−2) invertebrate populations. This result means that in most freshwater sediments, the sediment diffusion coefficient can be predicted reliably from the molecular diffusion coefficient at in situ temperature.
The major and minor element geochemistry of Lake Baikal
Authors: Falkner Kelly Kenison , Measures Chris I. , Herbelin Sarah E. , Edmond John M. , Weiss Ray F.
Published: April 2010

A comprehensive, joint Soviet‐American study of the chemistry of Lake Baikal, the world’s deepest (1,632 m) lake, was carried out in July 1988. In this paper, we report the major, minor, and preliminary trace element concentrations for three profiles obtained at or near the deepest and central part of the three major basins of the lake. With the exception of Ba, the distributions of major and minor elements were homogeneous, displaying no variations greater than analytical uncertainties. Average concentrations in µmol kg−1 (1 SD) are titration alkalinity = 1,093(6), SO42− = 57.4(1.3), Cl = 12.3(0.7), Ca = 402(7), Mg = 126(1), Na = 155(4), and K = 24.1(1.0); and in nmol kg−1 are Sr = 1,350(30), Li = 296(12), Ba = 74.7(2.6), Rb = 7.10(0.23), and U = 1.77(0.12). Excluding K and CI, these values compare favorably with previously published results. Although some hydrothermal activity is known to occur within the lake, it does not appear to significantly affect major ion cycling. The residence times of the major ions are 330 yr or the same as that of water in the basin and so are controlled predominantly by their riverine fluxes. There is not yet enough information to assess whether hydrothermal processes affect minor element cycles. Ba concentrations decrease with depth, showing abrupt decreases near the bottom at two stations. It appears to undergo some form of uptake at the sediments, but further study is required to discern the processes governing Ba distribution.
Enhanced microbial methane oxidation in water from a deep‐sea hydrothermal vent field at simulated in situ hydrostatic pressures
Authors: de Angelis Marie A. , Baross John A. , Lilley Marvin D.
Published: April 2010

Water from a hydrothermal vent field was incubated in the presence of 14CH4 under conditions of both atmospheric (1 atm) and simulated in situ hydrostatic pressure (∼200 atm). Methane oxidation rates measured in samples incubated at elevated pressures were 21–62% higher than those measured in replicate samples incubated at atmospheric pressure. The magnitude of the observed effect was consistent with that predicted to occur from changes in CH4 activity with depth‐dependent pressure, suggesting that microbial CH4 oxidation is a functionally barophilic process. The data indicate that methane oxidation, as well as other microbial gas consumption processes, is likely to be affected by moderate increases in hydrostatic pressure and that the rates of these processes in the deep sea, based on measurements at atmospheric pressure, may be underestimated.
Estimating estuarine flushing and residence times in Charlotte Harbor, Florida. via salt balance and a box model
Authors: Miller Ronald L. , McPherson Benjamin F.
Published: April 2010

We present a new concept and techniques for processing flow and salinity data and calibrating a box model designed to estimate water residence times in Charlotte Harbor, a large estuary in southwestern Florida. The new concept is that, over many tidal cycles, the tidally averaged “flow” (Qg) of water from the Gulf of Mexico with a salinity of 35‰ can be treated as a constant at any point in the estuary. This flow is used in a simple mixing equation to predict salinity in the estuary at different river inflows, and the predicted salinities are used to compute residence times for water in the estuary. The techniques developed to achieve optimal precision in the relation between river inflow and salinity include a newly derived equation to fit Qg by a least‐squares method and a procedure to determine the optimal averaging period for river inflow. Results from Charlotte Harbor indicate that, under average (70 m3 s−1) river inflow, 95% of the original water present in the harbor flushes into the gulf in 130 d.
Measurement and simulation of prey uptake by marine planktonic ciliates fed plastidic and aplastidic nanoplankton
Authors: Verity Peter G.
Published: April 2010

A laboratory study was conducted to investigate the food preferences of two marine planktonic ciliates, especially the importance of aplastidic nanoplankton in their diets, and the influence of prey quantity and composition on prey uptake. Ingestion, growth, and conversion efficiencies of these ciliates were measured while they fed on single‐ and multiprey assemblages of aplastidic and photosynthetic (plastidic) nanoplankton. Both tintinnid and “naked” oligotrich ciliates ingested and grew on diets of aplastidic nanoplankton. In single‐prey experiments with plastidic and aplastidic nanoplankton of similar size and C : N, ingestion of and growth on aplastidic nanoplankton could exceed those of ciliates fed phytoplankton. The highest growth rates, however, especially in tintinnid ciliates, generally occurred when they were fed nutritious phytoplankton. On multiprey diets, patterns of prey uptake depended on the total spectrum of available food. When ciliates were fed various concentrations of nutritionally acceptable plastidic and aplastidic nanoplankton, each prey was ingested according to relative abundance. However, when offered acceptable prey in combination with apparently nutritionally inadequate or less preferred prey, ciliates showed differential uptake of prey. The experimental data were fit to a feeding model derived from theory describing simple linear competitive inhibition of enzyme‐catalyzed reactions. This was used in conjunction with an encounter model as a diagnostic tool to evaluate the possibility that the measured responses could be due to differences in encounter, capture, handling, and digestion among prey. Results indicated that encounter and capture rates and handling times did not differ sufficiently to account for observed patterns in prey‐uptake. Rather, “poor” prey apparently are ingested at lower rates either because they are actively rejected or digested at lower rates or with reduced efficiency.
Responses to high irradiance contribute to the decline of the spring diatom maximum
Authors: Neale Patrick J. , Heaney S. Ivan , Jaworski George H. M.
Published: April 2010

The effect of high irradiance was studied with cultures and samples from natural populations of the colonial diatom Asterionella formosa Hass. The fluorescence ratio Fv : Fm, where Fv is the difference between DCMU‐enhanced fluorescence (Fm) and normal, dark‐adapted fluorescence (F0), was used as a relative measure of photosynthetic performance. A. formosa grown in batch culture displayed a 70–80% decrease in Fv : Fm during 1 h of exposure to 1,600 µmol quanta m−2 s−1. In addition, sinking rate increased from a mean of 0.23 m d−1 in controls to 0.43 after high irradiance. A. formosa populations were sampled in May, the later stage of the spring abundance maximum in the north basin of Windermere (English Lake District). Diatoms in the upper 1–3 m exhibited low Fv : Fm (0.1–0.2) during near‐surface stratification (four of five dates) but no depression of Fv : Fm on the one occasion of sunny weather and strong surface winds. Near‐surface cell abundances were also significantly lower during high‐irradiance, stratified conditions. The results suggest that high irradiance lowers production rates and increases sedimentation of diatom populations during the later stages of the spring maximum.
On the accuracy of determining light absorption by “yellow substance” through measurements of induced fluorescence
Authors: Ferrari Giovanni M. , Tassan Stelvio
Published: April 2010

Measurements of light absorption [Ay(375)] and induced fluorescence (F) were performed on a set of samples of yellow substance of varying origin, collected in three different coastal areas. The experimental results were characterized by a correlation coefficient r(x, y) = 0.99, significantly higher than previously reported, and yielded the fit (± 1 SD)

urn:x-wiley:00243590:media:lno19913640777:lno19913640777-math-0001

Conversion of measured fluorescence into equivalent absorption by the above expression gave results accurate enough for the remote sensing of water properties.
Deep‐sea benthic sampling with the GOMEX box corer
Authors: Boland Gregory S. , Rowe Gilbert T.
Published: April 2010

The GOMEX box corer has been used extensively for over a decade in the Gulf of Mexico, but the details of its construction and use have heretofore not been published. The advantages of the GOMEX corer accrue from its tripping and closing mechanisms, as well as its modest weight and size. It is comparatively easy to use, safe in rough seas, and modest in cost compared to the cumbersome but widely accepted USNEL spade corer. Comparison of macrofaunal densities in the Norwegian and the Greenland Seas, with data from the same areas with the USNEL corer, suggests that GOMEX sample quality surpasses other quantitative samplers now in use by deep‐sea biologists. Success frequencies appeared to be related to the depth to which the sediment could be penetrated—a function of sediment water content (porosity) and grain size—rather than water depth or sea state.
Core compression and surficial sediment loss of lake sediments of high porosity caused by gravity coring
Authors: Crusius John , Anderson Robert F.
Published: April 2010

We present 210Pb, 137Cs, and 60Co data from three lakes of the Experimental Lakes Area, NW Ontario, with sediments of high porosity and high organic C content which indicate that gravity coring fails to capture the top 5–15 cm of sediment. Compression of gravity cores by a factor of up to 3 is unequivocal throughout at least the top 15 cm of the cores with the highest porosity but is not so significant in cores of lower porosity. Careful freeze coring, by contrast, retrieves an uncompressed core with surficial sediments intact. Porosity data suggest that the compression in the gravity cores does not result from pore‐water loss and therefore must be caused by lateral thinning of the sediments as they enter the corer. Inventories of organisms or pollutants per unit of sediment area estimated from cores suffering from these artifacts would be grossly underestimated.
Effects of toxic cyanobacteria and purified toxins on the survival and feeding of a copepod and three species of Daphnia
Authors: DeMott William R. , Zhang Qing‐Xue , Carmichael Wayne W.
Published: April 2010

Acute toxicity experiments with purified toxins show that four species of zooplankton differ markedly in their physiological sensitivity to cyclic peptide hepatotoxins from Microcystis aeruginosa (microcystin‐LR) and Nodularia spumigena (nodularin). The copepod Diaptomus birgei was most sensitive (48‐h LC50 for microcystin‐LR ranged from 0.45 to 1.00 µg ml‒1), Daphnia pulicaria was least sensitive (48‐h LC50, 21.4 µg ml‒1), and Daphnia hyalina (48‐h LC50, 11.6 µg ml‒1) and Daphnia pulex (48‐h LC50, 9.6 µg ml‒1) were intermediate in sensitivity.

Survivorship in the presence of toxic Microcystis was strongly influenced by both physiological sensitivity and feeding behavior. Relatively good survivorship by D. pulicaria was associated with low sensitivity to purified toxin and rapid feeding inhibition in the presence of toxic cells. In contrast, very poor survivorship by D. pulex was associated with greater physiological sensitivity and nearly uninhibited feeding on toxic Microcystis. Intermediate survivorship by D. birgei was associated with food selection capabilities on the one hand and high physiological sensitivity and uninhibited feeding on the other. Our results suggest that zooplankton have evolved both physiological and behavioral adaptations which enhance their abilities to coexist with toxic cyanobacteria.
Community development alters photosynthesis‐irradiance relations in stream periphyton
Authors: Hill Walter R. , Boston Harry L.
Published: April 2010

The effects of biomass accumulation and community age on the photosynthesis‐irradiance response of periphyton were examined in developmental sequences from three stream locations that differed in canopy cover. (P‐I) curves for four developmental stages from each location were constructed from 14C uptake at six irradiances (22–1,100 µmol quanta m‒2 s‒1) in the laboratory. Photoinhibition in the periphyton from the two shaded sites declined with development, indicating that self‐shading significantly influenced photosynthesis in older communities. Photoinhibition was absent, however, in all of the developmental stages from the high light site. Maximum photosynthesis (Pmax) and slope (α) of the light‐limited portion of the chlorophyll‐specific light response decreased >40% in developing periphyton at all sites. Significant negative correlations between biomass and biomass‐specific Pmax suggested that light or metabolic substrates became progressively more limiting during development. Although there was little community‐level evidence of shade adaptation during development (photosynthesis did not saturate at lower light intensities as development proceeded), periphyton understories appear to retain considerable photosynthetic potential despite significant shading by upper layers.
A mathematical model of the manganese cycle in a seasonally anoxic lake
Authors: Johnson C. A. , Ulrich M. , Sigg L. , Imboden D. M.
Published: April 2010

The processes controlling the Mn cycle in a seasonally anoxic lake (Greifensee, Switzerland) were simulated with a dynamic one‐dimensional vertical lake model (CHEMSEE). The chemical parameters comprised Mn(II), particulate Mn, and oxygen concentrations and the processes included in the calculations were the Mn(II) flux from the sediment, Mn(II) oxidation, and particulate Mn removal from the water column. Field data from Greifensee obtained in 1988 and 1989 were used to determine the validity of the model and to estimate the rate constant values for the processes. Optimal values of the rate constants were determined by comparison of simulated results with field data and were in general agreement with literature values. The Mn(II) flux from the sediment exhibited similar seasonal variations in 1988 and 1989. The results show that it is possible to model the Mn cycle in a dynamic system and highlight the necessity of accurately determining the rate laws of the important processes and their relationships to the oxygen content of the waters.
Speciation and adsorption of arsenic on diagenetic iron oxyhydroxides
Authors: Vitre Richard De , Belzile Nelson , Tessier André
Published: April 2010

Diagenetic Fe and As samples have been obtained from 12 lakes on the Canadian Shield by deposition on Teflon collectors inserted vertically in the surficial sediments. Dissolution of the deposits showed that only arsenate was present, i.e. arsenite concentrations were undetectable. Laboratory batch experiments indicated that As(III) is oxidized rapidly by Fe oxyhydroxides. Apparent equilibrium constants for the absorption of As have been calculated from the Fe and As concentrations dissolved from the deposit of diagenetic material and As concentration in the water overlying the lake sediments. These field‐derived equilibrium constants agree well with laboratory‐derived equilibrium constants for the absorption of arsenate on amorphous Fe oxyhydroxides; the results taken together suggest that the latter laboratory constants can be used for modeling adsorption of inorganic As on Fe oxyhydroxides in natural waters.
Physical properties of Crater Lake, Oregon: A method for the determination of a conductivity‐ and temperature‐dependent expression for salinity
Authors: McManus James , Collier Robert W. , Chen Chen-Tung A. , Dymond J.
Published: April 2010

Active inputs of thermally and chemically enriched fluids at the bottom of Crater Lake create small vertical and horizontal heterogeneities in the deep‐lake temperature and salt distribution. Using an internally recording CTD and a precise definition for salinity as a function of in situ conductivity and temperature, we assess the significant effects of these inputs on the density structure and mixing processes in Crater Lake. To characterize the physical properties of the lake we have developed an experimental approach to derive a specific conductance and temperature‐dependant expression for salinity in freshwater.
Determination of chlorophyll a of inland waters on the basis of spectral reflectance
Authors: Mittenzwey K.‐H. , Ullrich S. , Gitelson A. A. , Kondratiev K. Y.
Published: April 2010

In order to develop algorithms for the remote sensing of Chl a concentrations in mesotrophic and eutrophic waters, we measured the spectral (R) of algal cultures and natural waters. A high squared correlation coefficient (r2 = 0.98; n = 94) was found between Chl a and the reflectance ratio x = R(705 nm)/R(670 nm) of some natural waters for the concentration range between 5 and 350 µg liter‒1, yielding the following regression relationship: Chl a (µg liter‒1) = 89x + 10x2 ‒ 34.
Problems in filtration fractionation of 14C primary productivity samples
Authors: Lignell Risto
Published: April 2010

Sources of error in the fractionation of 14C primary productivity samples were studied in the northern Baltic from 1984 to 1990. Acidification of the whole 14C sample followed by 24 h in open vials to remove 14CO2 (no bubbling) proved to be a simple, accurate, and precise (C.V. 6.9%, n = 128) method for measuring apparent net primary productivity (total organic 14C). In 1985, the total recovery of organic 14C with 0.2‐µm cellulose acetate filters was 81% of the annual apparent net primary production. Different post‐filtration treatments of the cellulose ester filters (rinsing, acidification) all gave significant unaccountable losses of up to 34% of organic 14C. No losses were recorded with glass‐fiber filters. Excess release of dissolved organic 14C due to filtration was generally unimportant, as only minor quantitative or qualitative differences were found between the <0.2‐µm filtrates of the whole and centrifuged samples.
Degradation of gut pigment during feeding by a subantarctic copepod: Importance of feeding history and digestive acclimation
Authors: Mayzaud Patrick , Razouls Suzanne
Published: April 2010

Gut pigment degradation by females of the subantarctic copepod Drepanopus pectinatus was established by measurements of gut fluorescence prior to fecal pellet production. The total amount of pigment lost varied from 0 to 17% while the Chl a unrecovered as pheopigment ranged from 0 to 92%. A linear relationship was observed between food concentration and mean pigment loss per copepod but not with the level of pigment loss as a percentage of total ingestion (pigment destruction efficiency) which varied without clear pattern. A nested ANOVA indicated that pigment destruction efficiency was influenced primarily by the trophic history of the animals (66% of the total variance) and to a minor extent by the experimental food concentrations (12% of the total variance). The hypothesis that gut pigment loss could be related to digestive activity and influenced by digestive acclimation processes (trophic history) was confirmed by the significant exponential relationship between food concentration at the time of copepod capture and the experimentally derived destruction efficiency. Careful consideration should be given to the quantitative or qualitative nature of gut pigment measurements as an in situ index of ingestion.
Squeeze‐water analysis for the determination of microbial metabolites in lake sediments‐Comparison of methods
Authors: Bolliger Reinhard , Brandl Helmut , Höhener Patrick , Hanselmann Kurt W. , Bachofen Reinhard
Published: April 2010

We compared methods for extracting interstitial water from stratified sediments in Lake Geneva and Lake Zurich. Microbial metabolites (NH4+, NO3‒, NO2‒, SO42‒, Mn2+, Fe2+, PO43‒, DOC), pH, conductivity, and VFA (volatile fatty acids such as acetate and propionate) as well as more conservative chemical species (Na+, K+, Ca2+, Mg2+, and H4SiO4) were analyzed in pore‐water samples collected with a high‐pressure squeezing‐filtration method and an in situ equilibrium diffusion technique. Both methods are useful if the limitations of their applicability are appreciated. Among the nonvolatile compounds, squeezing leads to increased concentrations of Na+, K+, HPO42‒, H4SiO4, NO2‒, and DOC. Intracellular metabolites from only partially lysed or still living sediment organisms may be released into the aqueous extract under the influence of very high pressures. The squeezing technique needs to be optimized for pressures that yield pore‐water sample volumes large enough for the required analyses but do not disrupt cells.
Self‐shading of in‐water optical instruments
Authors: Gordon Howard R. , Ding Kuiyuan
Published: April 2010

The self‐shading of in‐water optical radiometers for measuring upwelling (Lu) and irradiance (Eu) is estimated from Monte Carlo simulations of the light field in the presence and absence of the instrument. It is found that the error (ε) induced by the presence of the radiometer is a function of its size and the absorption coefficient (a) of the medium, i.e. when ε 15–20% the error is independent of the scattering coefficient (b). Direct measurement of Lu or Eu with ε ≤ 5% places severe limitations on the instrument size, e.g. in the case of a cylindrical housing and small solar zenith angles (the worst case) the diameter of the instrument must be ≲ 1/30a for Eu and ≲ 1/100a for Lu. A correction method based on a simple model of ε is proposed and it is shown that when used these constraints on the diameter are reduced to 1/6a and 1/30a, respectively, for an after‐correction error of 5%. The self‐shading error is estimated across the spectrum as a function of the pigment concentration of case 1 waters, and it is found that it can be large for typical radiometers, especially at high pigment concentrations or wavelengths >600 nm.
New and recycled primary production in an oligotrophic lake: Insights for summer phosphorus dynamics
Authors: Caraco Nina F. , Cole Jonathan J. , Likens Gene E.
Published: April 2010

Primary production that is supported by new inputs of nutrients from outside the system is distinct from production that is supported by remineralization of nutrients within the system. We applied the concept of new production to Mirror Lake, New Hampshire, and our view of P dynamics in this lake was altered dramatically. New production during midsummer put a large demand on P in surface waters, removing 37 µmol P m−2 d−1. Without new inputs of P, the P content of surface waters would drop to zero in < 1 month. There is, however, a slight increase, not a decrease, in P content of surface waters during summer stratification. Inputs to surface waters during summer months must, therefore, be large. We now believe that higher than average P loading to the lake occurs in summer, despite low runoff inputs.
Wave enhancement of solute exchange within empty burrows
Authors: Webster Ian T.
Published: April 2010

The physical process of supplying solutes such as oxygen to the walls of the burrows of macroinvertebrates within impermeable coastal sediments is examined. When waves are present, the resulting oscillatory water motions through empty burrows are shown to lead to solute dispersion rates many times larger than those that would be due to molecular diffusion acting alone. Consequently, waves can greatly enhance the rate at which solute is supplied to the burrow walls and so increase the overall solute utilization rate by the sediment. Wave enhancement of solute flows into a burrow is shown to depend on several parameters including burrow diameter, burrow length, wave amplitude, wave period, water depth, and the biochemical activity of the burrow walls. Solute flows are predicted to be largest for large wave amplitudes, shallow water depths, large burrow diameters, high solute utilization rates, and wave periods between 10 and 20 s.
Cost of swimming by Daphnia during diel vertical migration
Authors: Dawidowicz Piotr , Loose Carsten J.
Published: April 2010

Daphnia hyalina was grown under simulated conditions of diurnal vertical migration in vertical flow chambers, and its life‐history parameters were evaluated. The amplitudes of the migrations were 3 and 60 m d−1; food conditions were 0.1 and 1.0 mg C liter−1. None of the investigated parameters (fecundity, individual growth rate, age of maturation) was significantly different between long‐ and short‐distance migrating populations at high levels of food, whereas at low levels of food only the individual growth rate was higher in the short‐distance migrating Daphnia. These results suggest that the energy spent to travel the vertical distance does not account for the metabolic costs of diurnal vertical migration.
A simple, inexpensive device for obtaining vertically integrated, quantitative samples of pelagic zooplankton
Authors: Knoechel R. , Campbell C. E.
Published: April 2010

An inexpensive tube sampler con‐structed from readily available parts is described which permits vertically integrated zooplankton samples to be rapidly obtained in lakes. The tube sampler provides population estimates that are quantitatively comparable to those obtained with much greater effort from contiguous Schindler‐Patalas trap samples. Routine use of this tube sampler should facilitate the collection of precise and accurate population data upon which to base our understanding of zooplankton population dynamics and the role of zooplankton in aquatic ecosystems.
Degradation and elemental release rates from phytoplankton debris and their geochemical implications
Authors: Byeong‐Gweon Lee , Fisher Nicholas S.
Published: April 2010

The diatom Thalassiosira pseudonana was held without nutrients in the dark for 22 d; release rates of carbon and seven metals from the cells were determined with radiotracers. Cellular C was lost faster at 18°C (3.6% d−1) than at 4°C (1.0% d−1) due to higher microbial activity at 18°C. C loss rates decreased (from 9.7% d−1 at 18°C and 2.1% d−1 at 4°C) after 7 d. Formalin (24 mM) and HgCl2 (0.9 mM) inhibited microbial activity as indicated by 14CO2 evolution; NaN3 (154 mM) was less effective. Poison‐treated cells leached 33–39% of their C (as DOC) and large quantities of Cd, Se, Zn, and Ag.

Cd, Se, and Zn, primarily in a soluble fraction in the cells, were released at about the same rate as C and were affected by microbial activity and temperature. In contrast, Ag, Am, Ce, and Co were retained to a much greater extent by the decomposing cells, their release was slower than that of C, and temperature and microbial activity had negligible effects on their retention. The results suggest that Cd, Se, and Zn will be rapidly recycled from planktonic debris in surface waters, while Ce, Am, Ag, and Co will be transported by phytoplankton aggregates sinking from surface waters.
Effects of benthic macrofauna and temperature on degradation of macroalgal detritus: The fate of organic carbon
Authors: Kristensen Erik , Andersen Frede Østerguard , Blackburn Thomas Henry
Published: April 2010

The combined effects of bioturbation by the polychaete Nereis diversicolor and temperature (4°, 8°, 16°C) on diagenesis of short‐term (48 h) 14C‐labeled Chondrus crispus (new) detritus added to organic‐poor sandy sediment were examined over 20 d. The overall rate of weight‐specific CO2 production was 5 times higher for C. crispus detritus than for indigenous (old) sediment detritus. N. diversicolor increased sediment O2 uptake and total CO2 production by 30–70%; most of this increase was due to worm respiration. Net release of 14CO2 was not affected by the worms; microbial 14CO2 production was reduced 30%, indicating competitive interaction between worms and bacteria. The activities of N. diversicolor removed 20–50% more of the particulate 14C label in bioturbated sediment than in defaunated. All of this excess loss was recovered in worm tissues. The increase in total CO2 production, but not 14CO2 production, in the presence of N. diversicolor indicated that bioturbation affected the net mineralization of relatively refractory (old) organic matter more than it affected the labile (new) pools. The temperature dependence of carbon diagenesis was not affected significantly by the worms. The microbial component of total benthic metabolism increased more with temperature (activation energy, E = 53–59 kJ mol−1) than worm respiration did (E = 29 kJ mol−1).
Influence of the submersed plant, Potamogeton perfoliatus, on nitrogen cycling in estuarine sediments
Authors: Cufrey Jane M. , Kemp W. Michael
Published: April 2010

Effects of Potamogeton perfoliatus on N transformations in sediments were examined with 15N isotope techniques. Rates of ammonification, nitrification, denitrification, and plant uptake of nitrogen were measured in intact sediments with and without P. perfoliatus twice during the growing season (May and July). Sediments were injected with 15NH4+ and the appearance of 15N over time in overlying water, pore water, and plant tissues was measured. Most of the 15N added was recovered. Rates of bacterial NH4+ utilization (including NH4+ assimilation and nitrification) were similar to gross ammonification rates in vegetated and bare sediments, although rates were highly variable. Root (and rhizome) uptake represented ~90% of total N uptake by the plants in May, but only 20% in July. Tissue‐specific (root or shoot) uptake rates were similar in May and July, although shoot (leaves plus stems) biomass increased faster than root biomass from May to July. Between 70 and 75% of the N taken up by roots was translocated to shoots. Denitrification rates, calculated from the appearance of 15N‐N2 in the overlying and pore water, were significantly greater in vegetated than in bare sediments in July. Nitrification and denitrification were closely coupled, and denitrification in the root zone represented ~16% of total denitrification. In vegetated sediments, ~75% of the 15N lost from sediments was denitrified, and 25% was taken up by the plants. P. perfoliatus had a significant influence on sediment N cycling by direct uptake of NH4+ and NO3− and by indirect mechanisms leading to enhanced nitrification and denitrification.
The role of food patches in maintaining high deep‐sea diversity: Field experiments with hydrodynamically unbiased colonization trays
Authors: Snelgrove P. V. R. , Grassle J. F. , Petrecca R. F.
Published: April 2010

To test whether deep‐sea macrofaunal diversity is enhanced by specialization on small‐scale food patches, we deployed colonization trays by submersible at 900‐m depth for 23 d. Trays were buried flush with the seafloor to minimize potential hydrodynamic bias. Treatments included prefrozen, natural sediment that was unenriched or enriched with either Thalassiosira sp. or Sargassum sp. Density comparisons and rarefaction analysis indicate that Thalassiosira sp. attracted high densities of several taxa of juvenile opportunists, and Sargassum sp. trays were colonized by fewer individuals of a more diverse fauna. Ambient faunal diversity was higher and densities lower than enrichment treatments, although unenriched trays did not attain ambient densities. Results suggest that juveniles, rather than adults, specialize on specific patch types, thus contributing to high deep‐sea diversity; this bottleneck may be fundamentally different from less diverse, shallow‐water macrofaunal assemblages.
Metabolic costs during predator‐induced dielvertical migration of Daphnia
Authors: Dawidowicz Piotr , Loose Carsten J.
Published: April 2010

Life‐history parameters were determined for a cohort of 60 clonal Daphnia magna grown individually in thermally stratified, 1‐m‐long flow‐through tubes under a constant high‐food regime (2.0 mg C liter−1). The individuals could migrate freely in the tubes and their depth was noted at regular intervals. Half of the tubes received water from a reservoir containing a fish. The animals in these tubes stayed deep during the day and higher at night, thus showing a “normal” diel vertical migration behavior. The other half of the tubes was supplied with the same water, but free of fish. The individuals in this set exhibited no diel migration, but stayed in the warm upper strata day and night. The migrating animals in the fish‐treated set grew at rates (0.21 d−1) only a third those of individuals in the no‐fish treatment (0.57 d−1). Most of the difference between the treatments can be attributed to the lower temperatures experienced by the migrating individuals. However, an experiment with no thermal stratification showed that the chemical presence of fish in the water can significantly retard Daphnia growth.
Observations of the second vertical mode of the internal seiche in an alpine lake
Authors: MÜnnich M. , WÜest A. , Imboden D. M.
Published: April 2010

The analysis of wind and temperature data from Alpnacher See (Switzerland) shows the second vertical mode of the internal (baroclinic) seiche to dominate over the first vertical mode. Resonance with diurnal wind is responsible for the high amplitudes of the second mode. Two different models are used to calculate the periods and velocity distribution of the various modes of the internal seiche. First, as a natural extension of Mortimer’s two‐layer model, the eigenvalues of a three‐layer model for a rectangular basin are calculated analytically. The period of the second vertical mode is found to depend strongly on the thickness of the metalimnion. Second, in order to better represent the vertical structure of the water column, a continuous stratification model is adopted and solved analytically for realistic density profiles. The resulting vertical variation of the horizontal velocity is used to calculate local gradient Richardson numbers (Ri) and relate them to the vertical eddy diffusivity estimated with the temperature microstructure method.
The role of planktonic algae in the cycling of Zn and Cu in a productive soft‐water lake
Authors: Reynolds G. L. , Hamilton‐Taylor J.
Published: April 2010

Concentrations of dissolved Zn and Cu were measured alongside biomass (algal numbers, organic C, and Chl a) and dissolved micronutrients (P, Si) over an 8‐week period, covering a pronounced bloom of the diatom, Asterionella. The distribution of dissolved Zn appears to be affected by algal cycling in two ways: in the period up to and including the diatom maximum, dissolved Zn correlates (P < 0.01) positively with phosphate and silicate, indicating atomic C : P : Zn ratios of 106 : 1 : 0.034, and negatively with Chl a; and following stratification, epilimnetic concentrations are significantly (P < 0.01) less than those in the hypolimnion. Dissolved Cu distributions are unaffected by the spring diatom bloom. The Zn and Cu contents of the diatom standing crop were also determined by elemental analysis of suspended particulate material in two consecutive years, providing independent estimates of metal stoichiometry. Mass budgets indicate a substantial removal and transfer to the sediments of Zn via phytoplankton, but a negligible effect on the cycling of Cu.
An explanation of the spectral variation in freshwater CDOM fluorescence
Authors: Vodacek Anthony
Published: April 2010

The variation of freshwater chromophoric (or colored) dissolved organic matter (CDOM) fluorescence with respect to sample pH was examined. Trends from previous studies are supported by results obtained from fluorescence spectra collected during sample titration. The evidence suggests spectral variation of CDOM fluorescence can arise from pH‐dependent photo‐oxidation of a portion of the catechol component of CDOM to coumarin structures. A hypothesis is drawn that the observed shorter wavelength fluorescence exhibited by acid lake samples relative to the spectra of more neutral lake samples is, in part, a result of the inhibition of CDOM photo‐oxidation under the acid conditions. By careful choice of both excitation and emission wavelengths, fluorescence measurements may monitor changes in the composition of CDOM.
DOES A CURRICULUM INTEGRATION INTERVENTION TO IMPROVE THE MATHEMATICS ACHIEVEMENT OF STUDENTS DIMINISH THEIR ACQUISITION OF TECHNICAL COMPETENCE? AN EXPERIMENTAL STUDY IN AGRICULTURAL MECHANICS
Authors: Parr Brian A. , Edwards M. Craig. , Leising James G
Published: April 2010

The purpose of this study was to empirically test the hypothesis that students who participated in a contextualized, mathematics-enhanced high school agricultural power and technology curriculum and aligned instructional approach would not experience significant diminishment in acquisition of technical skills related to agricultural power and technology compared with those students who participated in the traditional curriculum. This study included teachers and students from 38 high schools in the state of Oklahoma (18 experimental classrooms; 20 control classrooms). Students were enrolled in an agricultural power and technology course in the spring semester of 2004. The total number of students who participated was 447 (206 experimental; 241 control). The experimental design employed was a posttest only control group design. One-way analysis of variance (ANOVA) was used to test the study’s null hypothesis. The math-enhanced agricultural power and technology curriculum and aligned instructional approach did not significantly diminish (p > .05) students’ acquisition of technical skills as measured by the National Occupational Competency Testing Institute (NOCTI) Agriculture Mechanics examination. A one-year replication of the study described is recommended.
OVERTLY TEACHING CRITICAL THINKING AND INQUIRY-BASED LEARNING: A COMPARISON OF TWO UNDERGRADUATE BIOTECHNOLOGY CLASSES
Authors: Friedel Curtis , Irani Tracy , Rudd Rick , Gallo Maria , Eckhardt Erin , Ricketts John
Published: April 2010

Some researchers have argued that science classrooms must move away from rote and passive applications of memorized concepts to the use of critical thinking skills as a primary component in facilitating learning. Yet few studies have examined the effect of overtly teaching for critical thinking on subsequent skill development. The purpose of this study was to assess if overtly teaching for critical thinking, as a teaching method, contributed to explaining increases in critical thinking skill scores of undergraduate students enrolled in agricultural biotechnology. One group of students were taught components of critical thinking and then asked to use the newly learned skills in class. A nonequivalent control group was instructed using the inquirybased teaching method. The data exhibited significance between groups giving evidence that overtly teaching for critical thinking improves students’ critical thinking skills as opposed to using the inquiry-based teaching method. Adding gender to the model did not significantly increase the explanation of variance in critical thinking skills. Also, a weak positive correlation was found between the total critical thinking skill score and the total critical thinking disposition score.
THE DEVELOPMENT OF THE INTEGRATED THREE-COMPONENT MODEL OF AGRICULTURAL EDUCATION
Authors: Croom D. Barry
Published: April 2010

This research project sought to determine the origin of the three-component model of agricultural education in the United States and provided a contextual base for future research into the three-component model for agricultural education. The study concluded that each of the three components of the agricultural education model originated at different times in American history but were developed simultaneously. Supervised experience probably originated in colonial America, and formal instruction in agricultural education probably began in 1858. The FFA was officially established in 1928, although similar agricultural youth organizations probably began either at the end of the nineteenth century or the beginning of the twentieth century. This study did not find evidence of an established date or recognized event that created the three-component agricultural education model. The Smith-Hughes Act of 1917 provided a more sophisticated linkage between classroom instruction and supervised experience. This study did not find evidence of a legal basis for the integral nature of the three-component agricultural education model. Instead, the integral nature of the model probably exists out of tradition, or as a result of a philosophical tenet in the agricultural education profession.
FORECASTING DOCTORAL-LEVEL CONTENT IN AGRICULTURAL EDUCATION: VIEWPOINTS OF ENGAGED SCHOLARS IN THE UNITED STATES
Authors: Shinn Glen C. , Briers Gary , Baker Matt
Published: April 2010

In this study, the researchers used a classical Delphi method to re-examine the conceptual framework, definition, and knowledge base of the field. Seventeen engaged scholars, each representing the expert agricultural education community, reached consensus on defining the field of study, 10 knowledge domains, and 67 knowledge objects. The Delphi panel agreed, “Agricultural education–2010, as a field of study, integrates social and behavioral sciences with the natural and applied science of agriculture, renewable natural resources, and environment. The knowledge base for agricultural education–2010 includes planning and needs assessment; curriculum development; learning theory; instructional design; delivery strategies; evaluation; research methods and tools; scholarship and writing; history, philosophy, and ethics; and contextual applications, culture, and diversity—all effecting continual improvement. Agricultural education empowers people to think more critically, to perform more skillfully, to communicate more clearly, to plan and affect change more efficiently, to solve problems more creatively, and to act based on principles—all of which involves vital choices and consequences in a global society.” The Delphi panel concurred on 10 knowledge domains composed of 67 core knowledge objects consisting of fundamental and powerful concepts, knowledge, paradigms, skills, and/or theories that are essential for building professional practice in agricultural education.
FACTORS RELATED TO THE DEVELOPMENTAL EXPERIENCES OF YOUTH SERVING AS 4-H CAMP COUNSELORS
Authors: Carter David N. , Kotrlik Joe W.
Published: April 2010

The purpose of this study was to investigate the developmental experiences of high-school-aged 4-H youth volunteering as counselors at Louisiana 4-H summer camps. A total of 288 counselors from 10 different camping sessions participated in the study. The Youth Experiences Survey 2.0 and the Developmental Experience Survey measured the personal characteristics and developmental experiences of 4-H camp counselors. The results showed that Louisiana 4-H summer camp counselors are active 4-H club participants. Counselors indicated that the highest level of experiences occurred in the areas of Teamwork and Social Skills, Positive Relationships, and Initiative Experiences. Black counselors had higher-level experiences in all aspects of the camping experience. Participation in perceived 4-H leadership and life skill activities had a positive association with Positive Relationships. Multiple regression analyses showed that gender explained a small amount of the variance; females had higher-level experiences in Positive Relationship and Teamwork and Social Skills and males had higher-level experiences in Negative Experiences. The results of this study show that serving as a 4-H camp counselor leads to significant positive experiences. These experiences may enhance counselors’ ability to develop positive leadership and life skills that should be valuable tools in their future.
TEXAS 4-H AGENTS’ PERCEPTIONS OF SELECTED COMPETENCIES IN THE 4-H PROFESSIONAL RESEARCH, KNOWLEDGE, AND COMPETENCIES MODEL
Authors: Harder Amy , Wingenbach Gary J.
Published: April 2010

There are many competencies necessary for success as a 4-H agent. The 4-H Professional Research, Knowledge, and Competencies (PRKC) Model organizes competencies into six domains: (a) Youth Development, (b) Youth Program Development, (c) Volunteerism, (d) Partnerships, (e) Organizational Systems, and (f) Equity, Access and Opportunity (National 4-H Professional Development Task Force, 2004). Previous research (Harder & Dooley, 2007; Seevers, Baca & VanLeeuwen, 2005) identified competencies in the Organizational Systems domain as some of the most important, but most competency research has focused on volunteer management. A modified Borich (1980) model of needs assessment was used to determine the training needs of Texas 4-H agents in the Organizational Systems domain. Agents perceived they were more proficient in the competencies associated with program delivery and less proficient in competencies associated with their own personal wellness. Significant differences existed between perceived proficiency and importance levels for several competencies. Training is most needed in providing the knowledge, skills, and abilities required to overcome the stresses associated with careers as 4-H extension agents.