Bioavailability and trophic transfer of humic-bound copper from bacteria to zooplankton

ABSTRACT: The effect of humic acid (HA) on uptake and transfer of Cu by selected marine organisms from the microbial loop was determined. Bacteria grown with and without 15 µg Cu l-1 and with and without 10 mg Suwannee River Humic Acid (SRHA) l-1 were fed to Uronema sp. The Uronema were subsequently fed to Acartia tonsa to determine the effect of humic acid on the uptake and transfer of Cu from bacteria to copepods. The presence of 10 mg SRHA l-1 reduced Cu uptake in A. tonsa by an average of 54% and significantly reduced the negative effects of Cu on reproductive success ofA. tonsa. The percentage of the total Cu residues in A. tonsa resulting from feeding was estimated by exposing A. tonsa to the same conditions with and without pre-exposed Uronema as food. The results indicate that approximately 50% of the Cu residue is due to feeding. Thus, SRHA seems to affect Cu uptake in A. tonsa through binding of free Cu in the water at the same rate as through the food chain. This study demonstrates the importance of complexation of metals by organic matter and trophic transfer processes for organisms critical to estuarine food webs

The prediction of nonlinear longitudinal combustion instability in liquid propellant rockets

An analytical technique was developed to solve nonlinear longitudinal combustion instability problems. The analysis yields the transient and limit cycle behavior of unstable motors and the threshold amplitude required to trigger a linearly stable motor into unstable operation. The limit cycle waveforms were found to exhibit shock wave characteristics for most unstable engine operating conditions. A method of correlating the analytical solutions with experimental data was developed. Calculated results indicate that a second-order solution adequately describes the behavior of combustion instability oscillations over a broad range of engine operating conditions, but that higher order effects must be accounted for in order to investigate engine triggering

Analysis of a theoretically optimized transonic airfoil

Numerical optimization was used in conjunction with an inviscid, full potential equation, transonic flow analysis computer code to design an upper surface contour for a conventional airfoil to improve its supercritical performance. The modified airfoil was tested in a compressible flow wind tunnel. The modified airfoil's performance was evaluated by comparison with test data for the baseline airfoil and for an airfoil developed by optimization of leading edge of the baseline airfoil. While the leading edge modification performed as expected, the upper surface re-design did not produce all of the expected performance improvements. Theoretical solutions computed using a full potential, transonic airfoil code corrected for viscosity were compared to experimental data for the baseline airfoil and the upper surface modification. These correlations showed that the theory predicted the aerodynamics of the baseline airfoil fairly well, but failed to accurately compute drag characteristics for the upper surface modification

Spatial and Temporal Variability in Zooplankton Community Dynamics in Three Urbanized Bayous of the Pensacola Bay System, Florida, USA

Spatial and temporal patterns in zooplankton community composition and abundance in coastal areas of the Gulf of Mexico are not well understood. Spatial and temporal differences in zooplankton community composition and abundance from 10 stations located in four sites are presented (Pensacola Bay and Bayou Texar, Bayou Chico, and Bayou Grande, three adjacent mesohaline-tidal bayous affected by urban and industrial development). Statistically significant differences (P \u3c 0.05) were found in log-biovolume among sites. The mean biovolume of zooplankton was highest in Pensacola Bay (0.38 ml m-3) followed by Bayou Grande (0.21 ml m-3), Bayou Chico (0.14 ml m-3), and Bayou Texar (0.06 ml m-3). Mean zooplankton abundances (organisms m-3) in Pensacola Bay (3,100 m-3) and Bayou Grande (3,000 m-3) were more than double the abundances in Bayou Texar (1,400 m-3) and Bayou Chico (1,100 m-3). The calanoid copepod Acartia tonsa Dana was the dominant species in the study area. The observed differences in the zooplankton community may be attributable to either one or a combination of factors such as water quality (toxicity), predation, and nutrient availability. Zooplankton abundance increased following two hurricanes that impacted the study area

L'Estudi de les funcions utilitzant el full de càlcul com a eina de treball : anàlisi d'un procès constructiu basat en la manipulació i la visualització /

Consultable des del TDXTítol obtingut de la portada digitalitzadaAnalitzem el procés d'aprenentatge de l'alumnat d'ensenyament secundària en relació a l'estudi de funcions amb la utilització del full de càlcul com a eina de treball sota un model metodològic constructiu enfocat en la manipulació la visualització. Com a treball d'innovació pretenem dissenyar i construir una seqüència d'aprenentatge sobre les funcions i implementar la unitat didàctica elaborada. Com a recerca, en primer lloc, analitzar el procés d'aprenentatge dels alumnes en relació als continguts treballats en el tema de funcions, l'eina informàtica (full de càlcul), la metodologia emprada, la unitat didàctica elaborada i l'actitud de l'alumnat. I en segon lloc, millorar la unitat didàctica elaborada i que constitueix part del currículum de l'aprenentatge. Aquests quatre objectius es concreten en: a) Revisar, en procés constructiu, la unitat didàctica dissenyada i elaborar una nova proposta, partint de l'anàlisi i la classificació de les dificultats i/o els errors comesos pels alumnes en relació a l'estudi de les funcions i en l'ús del full de càlcul per estudiar-les i , en concret atenent a les seves característiques, intentant determinar els motius que els provoquen. b) Valorar com influencia, en el procés d'aprenentatge de l'alumnat, el full de càlcul. c) Revisar la metodologia de treball desenvolupada en la innovació didàctica en l'estudi de funcions utilitzant el full de càlcul sota un procés constructiu enfocat en la manipulació i la visualització. d) Concretar les actituds de l'alumnat dintre del seu procés d'aprenentatge.This thesis belongs to the field of Mathematical Didactics (education, learning). We analyse the learning process of the secondary education student in relation to the study of functions with the use of spreadsheets as a work tool with a constructive methodologist model directed to manipulation and visualization. There are two focuses: as an innovation work and as a research work. As an innovation work we design and construct a learning sequence about functions and we create a teaching unit. Therefore, first of all we have prepared a teaching unit thought to study the functions using the spreadsheets at 4th level of obligatory secondary education (ESO in Spanish abbreviation). The students are 15 years old. The study of the functions goes towards the identification of the graphic behaviour of a straight line and a parabola according to the variations of its parameters and to recognize its characteristics across different algebraic situations that have been generated by affine and quadratic function. Secondly, we prepared a new teaching unit thought for Humanities «Bachillerato» (Spanish high school). The students are 16 to 18 years old. The purpose is to find and to recognize the functions, the graphics and the characteristics of the functions from the algebraic expression of the function. The functions studied are exponential, logarithmic, polynomial and rational functions. In the two last functions are applied derivates. As a research, firstly, we have analysed the student learning process in relation to the contents worked on the function subject, computer tool (spreadsheets), methodology used, the teaching unit and the student's attitude. Secondly, we have improved the teaching unit that constitutes a part of the learning curriculum. We have concreted these objectives in: a) to revise, in constructive process, the designed teaching unit and to elaborate a new proposal, b) to value how the spreadsheets affects the student's learning process, c) to revise the work methodology developed in the didactic innovation in the study of the functions using the spreadsheets for manipulation and visualization, d) to concrete the student's attitude within their learning process. Taking into account the objectives above mentioned the stages of our research design are: stage of elaboration, empiric stage and conclusive stage. The first is the stage of elaboration of the teaching unit; the second is the empiric stage, and finally, the conclusive stage where, at the end of every school year at every studied level, we analyse all the information collected during the process development and finally, we draw the conclusions

Benthic Nutrient Flux in a Small Estuary in Northwestern Florida (USA)

Benthic nutrient fluxes of ammonium (NH4+), nitrite/nitrate (NO2- + NO3-), phosphate (PO4-3), and dissolved silica (DSi) were measured in Escambia Bay, an estuary within the larger Pensacola Bay system of northwestern Florida (USA). Our study occurred during a severe drought which reduced riverine inputs to Escambia Bay. Laboratory incubations of field-collected cores were conducted on 8 dates between June and October 2000 to estimate nutrient flux, and cores were collected from locations exhibiting a range of sediment organic matter content. NH4+ flux ranged from – 48.1 to 110.4 μmol m-2 h-1, but the mean flux was 14.6 μmol m-2 h-1. Dissolved silica (DSi) fluxes were also variable (-109. 3 to 145.3 μmol m-2 h-1), but the mean net flux (9.3 μmol m-2 h-1) was from the sediment to the water column. Bay sediment fluxes for NO2-+ NO3- and PO4-3 were less variable during this period (– 7.93 to 28.73 and – 1.74 to 3.29 μmol m-2 h-1 for NO2-+ NO3- and PO4-3, respectively). Low NH4+ fluxes were similar to published estimates from lagoonal Gulf of Mexico (GOM) estuaries, possibly due to the reduced freshwater input. Diminished regeneration of phosphate relative to inorganic nitrogen observed during the study period was consistent with previous research in Pensacola Bay suggesting phytoplankton phosphorus limitation. Finally, the estimated residence time of Escambia Bay and the mean turnover times for NH4+ and NO2-+ NO3- suggested that benthic flux significantly influenced nitrogen concentrations in overlying water

Mapping and Monitoring of Submerged Aquatic Vegetation in Escambia-Pensacola Bay System, Florida

Recently, the distribution and changes in submerged aquatic vegetation (SAY) in the Escambia-Pensacola Bay System in northeastern Florida were monitored by two techniques. One technique used divers to measure changes in the deepwater margin of beds and provided horizontal growth measurements to the nearest centimeter, the other used a differential global positioning system (DGPS) on a small boat to map the perimeter of SAY beds in shallow water. Current distribution of SAY in Escambia Bay shows that most of the SAY losses that occurred during the 1950s to 1970s have been recovered. In Santa Rosa Sound and Pensacola Bay, SAY showed significant increased growth with horizontal growth rates of some beds averaging more than 50 em over the past year. In Big Lagoon, however, SAY has declined an average of 10 em in horizontal coverage along the deepwater edge. Water quality and photosynthetically active radiation light measurements from the Escambia-Pensacola Bay System suggest that increased light availability was associated with the increased seagrass coverage in Santa Rosa Sound and Pensacola Bay, and elevated nutrient concentrations were associated with the seagrass declines in Big Lagoon