ALBERT

Description: To understand the responses of the plankton community to the negative large-scale human impacts in a tropical coastal lagoon complex, we carried out a regional survey on primary productivity (PP), community respiration (CR), and contribution of different size fractions of the phytoplankton to overall PP. This comparative study was undertaken in several coastal lagoons within the Outer Delta of the Río Magdalena (Colombia) during the dry season(February/March). PP was measured using the 14C-method with in situ-incubations and CR was determined as oxygen demand, using the Winkler technique. According to their salinities the lagoons were separated into a brackish water group (salinity range 5.9 – 21.8) and a freshwater group, the latter being influenced directly by the Río Magdalena. In all of the lagoons the productive layer did not surpass 1 m in depth due to selfshading by the high density of plankton (brackish lagoons) or due to high amounts of suspended inorganic sediment particles introduced into the freshwater lagoons from the Río Magdalena. The brackish lagoons contained high chl a concentrations (62 – 130 µg/l) and were extremely productive (0.72 – 1.25 mg C/l/h in the most productive depth, usually at 0.1 m). The concentrations of chl a in the freshwater lagoons were much lower (5.5 – 19 µg/l), also the PP (0.073 – 0.32 mg C/l/h). In all of the studied lagoons the photosynthetic active algae were very small, algae 〉20 µm (microalgae) played only a very insignificant role with respect to PP. The assimilation index (AI) was quite high (11.6 – 18.5 mg C/mg chl a /h). Only in two of the lagoons the relatively low AI (6.9 – 7.4 mg C/mg chl a /h) was probably due to senescent phytoplankton algae. The depth-integrated PP rates in the brackish lagoons ranged from 1.40 – 5.76 g C/m2/d. Especially the enormous rate of 5.76 g C/m2/d which was representative for the central part of Ciénaga Grande de Santa Marta demonstrated that this aquatic system belongs to the most productive ones world-wide. In the freshwater lagoons the daily PP measured 0.24 – 0.80 g C/m2. In the brackish lagoons the highly significant correlation between chl a and CR showed that the phytoplankton dark respiration was the dominant component, whereas the absence of a significant correlation in the freshwater lagoons demonstrated that here the heterotrophic microorganisms contributed more to community respiration. Only in three of the seven studied lagoons (among these Ciénaga Grande) planktonic primary production surpassed pelagic respiration, in the remaining four lagoons the deficit of organic material is probably compensated from allochthonous sources such as the mangrove fringes and/or river input.

Description: Para entender las respuestas de los organismos planctónicos a los impactos humanos negativos a gran escala en un complejo costero lagunar tropical, se llevó acabo un estudio regional sobre productividad primaria (PP), respiración de la comunidad planctónica (RC), y contribución de diferentes tamaños de fitoplancton a la productividad total. Este estudio comparativo fue realizado en varias lagunas costeras del Delta Exterior del Río Magdalena durante la estación seca (febrero/marzo). La PP fue medida usando el método 14C con incubaciones in situ y la RC fue determinada por demanda de oxígeno usando la técnica Winkler. De acuerdo con las salinidades, las lagunas fueron separadas en el grupo de agua salobre (rango de salinidad entre 5.9 – 21.8) y en el grupo de agua dulce, este último directamente influenciado por el Río Magdalena. En todas las lagunas la zona productiva no soprepasó 1m de profundidad debido al autosombreo por la alta densidad planctónica (lagunas de agua salobre) o debido a la alta cantidad de sedimentos inorgánicos suspendidos, introducidos por el Río Magdalena a las lagunas de agua dulce. Las lagunas de agua salobre presentaron altas concentraciones de chl a (62 – 130 µg/l) y fueron extremadamente productivas (0.72 – 1.25 mg C/l/h en la profundidad más productiva, generalmente a 0.1 m). Las concentraciones de chl a en las lagunas de agua dulce fueron mucho más bajas (5.5 – 19 µg/l) y también la PP (0.073 – 0.32 mg C/l/h). En todas las lagunas estudiadas las algas fotosinteticamente activas fueron muy pequeñas, las algas 〉20 µm (microalgas) jugaron un papel insignificante con respecto a la PP. El índice de asimilación (IA) fue muy alto (11.6 – 18.5 mg C/mg chl a /h). Solamente en dos de las lagunas el relativamente bajo IA (6.9 – 7.4 mg C/mg chl a /h) fue debido probablemente a fitoplancton senescente. La tasa de PP integrada en las lagunas de agua salobre tuvo un rango de 1.40 – 5.76 g C/m2/d. En especial la enorme tasa de 5.76 g C/m2/d, la cual fue representativa de la parte central de Ciénaga Grande de Santa Marta, demuestra que este sistema acuático pertenece a los más productivos del mundo. En las lagunas de agua dulce la PP diaria estuvo entre 0.24 y 0.80 g C/m2. En las lagunas de agua salobre la correlación altamente significativa entre chl a y RC mostró que la respiración fitoplanctónica fue el componente dominante, mientras que la ausencia de una correlación significativa en las lagunas de agua dulce, demostró que allí los microorganismos heterotróficos contribuyeron más a la respiración de la comunidad. En tres de las siete lagunas (entre estas Ciénaga Grande), la producción primaria planctónica sobrepasó la respiración pelágica. En las otras lagunas la carencia de material orgánico es probablemente compensada por fuentes alóctonas tales como el manglar y/o las descargas riverinas.

Description: Published

Description: Planktonic respiration

Description: The profitability of new investments in fisheries operations is designed to take advantage of unexploited harvest potential of fish stocks in the sea around Cape Verde and off the coast of Senegal and Mauritania. The TAC (Total Allowed Catch) in Cape Verde is estimated between 38000 and 47000 tons and mainly are large pelagic (tuna species) and the mean catch is around 7500 tons per year. The status of fish stocks available to Capeverdian fisheries and the potential to be caught are analysed and available data indicates that there is a substantial scope for expanding fishing for tuna in Cape Verde waters and small pelagic in the waters off Senegal and Mauritania. Two alternative scenarios are discussed. New vessel, which means one of the vessels that are in construction and a used vessel, which means a second hand vessel that was constructed and operated in Norway. The operation plans are elaborated according to the seasons of the species and the availability of the fish stock. The profitability of fishing operations for the two vessels is studied and discussed. In order to see how the profitability of the fishing operations is changing sensitivity analyses is made by changing the days at sea, the price of fish on the market and the value of the crew share. The bank will finance the investment so a loan amortisation schedule is made to show how the loan will be repaid. The results indicate that there are possibilities to expand in a profitable way.

Description: Unpublished

Description: This study addresses the embodied approach of convergence of numerical sequences using the GeoGebra software. We discuss activities that were applied in regular calculus classes, as a part of a research which used a qualitative methodology and aimed to identify contributions of the development of activities based on the embodiment of concepts, with the use of software, to the understanding of the convergence of numerical sequences and to the transition of mathematical thinking from elementary to advanced. Such activities had an exploratory nature and were constructed based on the theoretical frameworks of Advanced Mathematical Thinking and the Three Worlds of Mathematics. For the data collection were used the recordings of the computer screens, audio recordings of the discussion between students, student records in the responses of the activities and field notes of the researchers. The data were analyzed considering relations between the embodiment of the concept of convergence and proceptualization processes and axiomatization and also considering the transition from elementary mathematical thinking to advanced. The results indicate that the activities enabled the formation of the mental image that the convergence of sequences occurs when the sequence terms are approaching a certain value, and thus propitiated the embodiment of the concept of convergence and established cognitive roots for formal definition of convergence by the limit and further theoretical development. They also indicate that relations between different representations were established, which contributed to abstraction of the concept of convergence of sequences and thus for the transition between elementary and advanced mathematical thinking.

Description: Discrete maps have been extensively used to model 2-dimensional chaotic transport in plasmas and fluids. Here we focus on area-preserving maps describing finite Larmor radius (FLR) effects on E  ×  B chaotic transport in magnetized plasmas with zonal flows perturbed by electrostatic drift waves. FLR effects are included by gyro-averaging the Hamiltonians of the maps which, depending on the zonal flow profile, can have monotonic or non-monotonic frequencies. In the limit of zero Larmor radius, the monotonic frequency map reduces to the standard Chirikov-Taylor map, and in the case of non-monotonic frequency, the map reduces to the standard nontwist map. We show that in both cases FLR leads to chaos suppression, changes in the stability of fixed points, and robustness of transport barriers. FLR effects are also responsible for changes in the phase space topology and zonal flow bifurcations. Dynamical systems methods based on the counting of recurrences times are used to quantify the dependence on the Larmor radius of the threshold for the destruction of transport barriers.

Description: A statistical study of finite Larmor radius (FLR) effects on transport driven by electrostatic drift-waves is presented. The study is based on a reduced discrete Hamiltonian dynamical system known as the gyro-averaged standard map (GSM). In this system, FLR effects are incorporated through the gyro-averaging of a simplified weak-turbulence model of electrostatic fluctuations. Formally, the GSM is a modified version of the standard map in which the perturbation amplitude, K 0 , becomes K 0 J 0 ( ρ ̂ ) , where J 0 is the zeroth-order Bessel function and ρ ̂ is the Larmor radius. Assuming a Maxwellian probability density function (pdf) for ρ ̂ , we compute analytically and numerically the pdf and the cumulative distribution function of the effective drift-wave perturbation amplitude K 0 J 0 ( ρ ̂ ) . Using these results, we compute the probability of loss of confinement (i.e., global chaos), P c , and the probability of trapping in the main drift-wave resonance, P t . It is shown that P c provides an upper bound for the escape rate, and that P t provides a good estimate of the particle trapping rate. The analytical results are compared with direct numerical Monte-Carlo simulations of particle transport.