Production primaire

Résumé

400px|vignette|Selon les données « couleur de l'océan » recueillies par le capteur SeaWiFS, la production primaire dans l'océan mondial est sensiblement égale à celle sur les terres émergées, bien que la biomasse primaire océanique soit environ 500 fois moins importante que la biomasse terrestre, ce qui traduit la très grande efficacité du phytoplancton océanique (avec notamment les diatomées qui représentent 40 % de la production primaire des écosystèmes marins). Le côté rouge du spectre indique que l'activité chlorophyllienne océanique la plus importante se concentre sur les zones côtières fertilisées par les sels nutritifs liés à l'érosion des sols. La production primaire est la vitesse à laquelle se biosynthétise au niveau de la biomasse une quantité donnée de matière organique à partir de matière minérale et d'un apport d'énergie. C'est un flux exprimé en masse de carbone assimilé par unité de temps. Cette production de matière organique s'effectue principalement grâce à la photo

Source officielle

https://fr.wikipedia.org/wiki/Production_primaire

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Analysis of loads, water quality and certain biological production on the Kis-Balaton Water Protection System

Elise Kaiser

Wetlands are important ecosystems: they are habitats for many key species and act as natural regulators of the environment. They filter water and remove pollutants with the help of plants. Constructed wetlands are artificial wetlands built to treat mainly wastewaters. These artificial ecosystems can also be used for freshwater treatment, such as river water. The Kis-Balaton Water Protection System (KBWPS) is one of them and the main goal of the system is to treat the River Zala water before its entrance in the Lake Balaton. The two mains objectives are to avoid the eutrophication of the Lake Balaton and improve the wetland ecosystems. It is a vast constructed wetland of 71 km2, situated at Southern part of Lake Balaton, in Hungary. The goal of this thesis was to analyze the loads, water quality and biological production of the KBWPS. Interpretation of three different sets of data and field work was carried out. The first set was about inflow and outflow data, from which the removal rates of different nutrients on a long time period were computed. The second data series contained regular water quality monitoring data along the flow path and the goal was to study the inner processes happening in the KBWPS. The last data set was collected on the field and included basic water properties and some biological and physico-chemical measurements, such as primary production or tecton analysis. It allowed to differentiate the water types of the system and their properties and to better understand the inner processes, particularly the biological characteristics of the system. The interpretation of the data series gave background to understand the processes occurring within the system and it helped to characterize the actual different water groups. It drew the main lines for possible more detailed analysis. This work was partly connected to a project aiming at the development of a monitoring system that serves a better management of the KBWPS. Several conclusions can be drawn from the results found in this thesis: • General conclusions on the system, which could apply to other systems of the same type. • Specific conclusions about the operation of the system, which would refer to this system only. • Some management and monitoring suggestions for the future system.

2013

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In this study, a hydrodynamical model is coupled to a biogeochemical model, and then used to simulate the main physical, chemical and biological characteristics of Lake Geneva. The study period, going from 1981 to 2016 was marked by two major changes with concomitant effects: re-oligotrophication by reducing the phosphorus loading and climate change. Thanks to the calibrated model, changes of the ecosystem related to climate change and re-oligotrophication were disentangled. It resulted in a positive effect of the former on phytoplankton biomass and primary production, and a negative effect of the latter. The combined effects of these two majors changes are negative. However, these results have a large uncertainty related to the capacity of the model to reproduce the biological characters of Lake Geneva. The calibration procedure must be improved to ensure a higher relevance of the results.

2020

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Evaluation of photosynthetic competency in time and space is critical for better estimates and models of oceanic primary productivity. This is especially true for areas where the lack of iron (Fe) limits phytoplankton productivity, such as the Southern Ocean. Assessment of photosynthetic competency on large scales remains challenging, but phytoplankton chlorophyll a fluorescence (ChlF) is a signal that holds promise in this respect as it is affected by, and consequently provides information about, the photosynthetic efficiency of the organism. A second process affecting the ChlF signal is heat dissipation of absorbed light energy, referred to as non-photochemical quenching (NPQ). NPQ is triggered when excess energy is absorbed, i.e. when more light is absorbed than can be used directly for photosynthetic carbon fixation. The effect of NPQ on the ChlF signal complicates its interpretation in terms of photosynthetic efficiency, and therefore most approaches relating ChlF parameters to photosynthetic efficiency seek to minimize the influence of NPQ by working under conditions of sub-saturating irradiance. Here, we propose that NPQ itself holds potential as an easily acquired optical signal indicative of phytoplankton physiological state with respect to Fe limitation. We present data from a research voyage to the Subantarctic Zone south of Australia. Incubation experiments confirmed that resident phytoplankton were Fe-limited, as the maximum quantum yield of primary photochemistry, F-v/F-m, measured with a fast repetition rate fluorometer (FRRf), increased significantly with Fe addition. The NPQ "capacity" of the phytoplankton also showed sensitivity to Fe addition, decreasing with increased Fe availability, confirming previous work. The fortuitous presence of a remnant warm-core eddy in the vicinity of the study area allowed comparison of fluorescence behaviour between two distinct water masses, with the colder water showing significantly lower F-v/F-m than the warmer eddy waters, suggesting a difference in Fe limitation status between the two water masses. Again, NPQ capacity measured with the FRRf mirrored the behaviour observed in F-v/F-m, decreasing as F-v/F-m increased in the warmer water mass. We also analysed the diel quenching of underway fluorescence measured with a standard fluorometer, such as is frequently used to monitor ambient chlorophyll a concentrations, and found a significant difference in behaviour between the two water masses. This difference was quantified by defining an NPQ parameter akin to the Stern-Volmer parameterization of NPQ, exploiting the fluorescence quenching induced by diel fluctuations in incident irradiance. We propose that monitoring of this novel NPQ parameter may enable assessment of phytoplankton physiological status (related to Fe availability) based on measurements made with standard fluorometers, as ubiquitously used on moorings, ships, floats and gliders.

2020

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Analysis of loads, water quality and certain biological production on the Kis-Balaton Water Protection System

Elise Kaiser

2013

2020