193 research outputs found
Preface: Research and Management for the Conservation of Coastal Lagoon Ecosystems, South–North Comparisons
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Role of macrophytes in the restoration of lagoon environments : ecological succession
No full textLa prise de conscience des risques liés à la dégradation de la qualité des milieux lagunaires vis-à-vis de l’eutrophisation a abouti à la mise en œuvre d’actions de gestion visant à réduire les apports en nutriments. Certaines lagunes sont aujourd’hui en phase de restauration, avec une amélioration notable de la qualité de l’eau liée notamment à la réduction des biomasses phytoplanctoniques. En revanche, la réponse des macrophytes benthiques semble plus complexe et non linéaire. A travers une approche complémentaire basée sur l’analyse statistique des données d’observations acquises de 1998 à 2015 et sur des mesures in situ, cette thèse vise à identifier la dynamique temporelle et spatiale des macrophytes ainsi que leur rôle fonctionnel au cours du processus d'oligotrophisation. Au sein des lagunes méditerranéennes, la salinité et les teneurs en nutriments dans la colonne d'eau sont les principaux paramètres qui structurent la distribution des macrophytes benthiques. L’analyse statistique menée sur 21 lagunes polyhalines et euhalines a permis d'illustrer les premières étapes de restauration. La réduction des apports externes a conduit à un basculement rapide (3-4 ans) d’un système totalement dominé par le phytoplancton vers un système dominé par les macroalgues opportunistes et notamment les ulves. La réduction de la disponibilité en azote dans la colonne d'eau liée au développement des ulves favoriserait le développement des gracilaires (algue rouge) et des chaetomorphes (algue verte filamenteuse). Bien plus que la seule conséquence de la restauration, la présence d'espèces clés jouerait ainsi un rôle central dans la restauration en régulant les flux d'azote et de phosphore au sein du système et en créant les conditions favorables à l'apparition d'autres espèces plus pérennes. Bien que notre théorie décrive une tendance vers le retour des macrophytes pérennes pour les trajectoires de re-oligotrophisation, nous n’avons pas encore pu documenter ce retour dans les lagunes après une longue période d’absence. Ceci, montre l’importance de prendre en compte, entre autres, l’importance des sources internes d’éléments nutritifs et de la connectivité pour la recolonisation des angiospermes dans les lagunes.The growing awareness of the negative impacts of the degradation of the water quality in coastal lagoons because of eutrophication has resulted in public action aiming at the reduction of the nutrient loadings into these lagoons. Hence, some of these coastal lagoons are currently undergoing ecological restoration and have shown a clear improvement of their water quality linked to decreasing phytoplankton biomass in the last 10 years. However, the response of the benthic macrophytes appears more complex, particularly by showing non-linear behaviour. By using complementary approaches including statistical analyses of long-term observations (1998-2015) and in situ measurements, this thesis aims to describe the dynamics of the macrophytes in space and time and to study their functional role during the oligotrophication process. Salinity, depth and nutrient concentrations in the water column represent the main factors that statistically explain the distribution of the benthic macrophyte communities in Mediterranean coastal lagoons. The first steps of the ecological restoration in eutrophied polyhaline and euhaline lagoons has been inferred from the statistical analysis of time series in 21 coastal lagoons. The reduction of the external nutrient loading results in a rapid regime shift (3-4 years) from a phytoplankton-dominated system to a macroalgae-dominated system, with particularly Ulva species. The decreasing inorganic nitrogen concentrations due to uptake by Ulva spp. in the water column appears to facilitate the development of Gracillaria spp. (red algae) and Chaetomorpha spp. (green filamentous algae). While the appearance of these macroalgal species is the result of the ecological restoration, these species also play a central role in this process by regulating the biogeochemical element fluxes. This way these species create more favourable conditions for perennial species. Although for re-oligotrophication trajectories in coastal lagoons our theory describes a tendency towards the return of perennial species, so far, we have not been able to document their return after a long period of absence. This shows, that among other factors, the internal nutrient loading and ecological connectivity are important factors to take into account for the recolonization of angiosperms in coastal lagoons
Response of sedimentary processes to cyanobacteria loading
No full textSedimentation of pelagic cyanobacteria in dystrophic freshwater and oligohaline lagoons results in large inputs of labile organic matter (OM) to the benthos. We used an experimental approach to study the short-term impact of such phenomena on the benthic microbial community metabolism and on the nitrogen (N) fluxes across the sediment-water interface. We hypothesized an increase of respiratory activity, including N loss via denitrification and its recycling to the water column. Our results show that the incorporation within sediments of the settled bloom increases benthic bacterial activities. This is coupled to large DON and NH4+ effluxes, and to a comparatively smaller increase of N2 production, while no significant effects were detected for the benthic fluxes of NOx-. We constructed flow schemes for N compounds, which show that while denitrification was significantly stimulated by amending cyanobacterial biomass to the sediments, it represented less than 1% of total OM mineralization. Interestingly, we observed that total released nitrogen (DIN+DON+N2 efflux) was dominated by DON, which contributed 75–80 % of the net N efflux, suggesting incomplete mineralization of OM. With the measured total N mobilization rate of about 15 mmol N m-2 d-1 it would take more than 4 months to regenerate the total organic N input to sediments (2031 mmol N m-2), which represents the post-bloom deposited particulate organic N. These results suggest limited losses to the atmosphere and slow diffusive recycling of N buried into sediments, mostly as DON. Such regenerated N may eventually be flushed to the open sea or sustain pelagic blooms within the estuarine environment, including cyanobacteria, with a negative feedback for further import of atmospheric nitrogen via N-fixation.</p
Lake La Salada de Chiprana (NE Spain), an example of an Athalassic Salt Lake in a cultural landscape
No full textOn a global scale, athalassic inland salt lakes are abundant, albeit restricted to semiarid and arid climates. La Salada de Chiprana is unique in Western Europe, because it is a permanent and relatively deep (up to 5.6 m) hypersaline lake (40-90 g total dissolved salt L-1) since 1700 AD. It forms part of a cultural landscape, which imposes a challenge for management. The aim of this paper is to describe the specific microbial biota and how they interacted with both animals and plant species during the last 25 years. The deeper parts regularly showed salinity stratification with an anoxic sulfide-rich hypolimnion and a bloom of green sulfur bacteria (Prosthecochloris aestuarii and Chlorobium vibrioforme) at the pycnocline. Despite highly eutrophic conditions, often the top water layer is transparent due to top-down control of phytoplankton populations by the brine shrimp, Artemia parthenogenetica. This allows for the development of submerged aquatic vegetation of the endemic foxtail stonewort Lamprothamnium papulosum var. papulosum f. aragonense, and microbial mat communities build by the cyanobacterium Coleofasciculus (Microcoleus) chthonoplastes coexisting with green filamentous nonsulfur bacteria (Chloroflexaceae). The microbial mats show photosynthetically induced precipitation of high-Mg calcite, which by incorporating viruses represents a mechanism for their fossilization
¿Maximizan todos los ecosistemas su distancia con respecto el equilibrio termodinámico? Un comentario sobre “la ley ecológica de la termodinámica”
No full textSven Erik Jørgensen has boldly proposed a “Fourth Law of Thermodynamics” which he also advocates as the “Ecological Law of Thermodynamics” or ELT (Integration of Ecosystem Theories: A Pattern, Kluwer Academic Publisher). This Law is still a hypothesis and can be tested. I disagree with the generalised way he uses the term “exergy” in his approach. Exergy is commonly defined as a measure of the work capacity of a system. According to the physicists Boltzmann information embodies energy. Jørgensen takes this into account when considering the “exergy” stored in ecosystems; hence, according to his way of calculating the genetic information of the organisms is the mayor contribution to “exergy”. I argue that energy has been embodied in the information during a historical process and that because of fundamental irreversibility this energy cannot be extracted again for work capacity. Moreover, other phenomena mentioned earlier by Ramon Margalef, demonstrate that proliferating information in biota shows uncoupling with respect to its embodied energy content according to the Boltzmann formula. In spite of these objections, some of Sven Erik Jørgensen’s core ideas are exiting and worthwhile testing. I place these within the context of the non-equilibrium thermodynamic theories on “dissipative systems” developed by the physicist Ilya Prigogine.De una forma muy marcada que llama nuestra atención, Sven Erik Jørgensen ha propuesto la “Cuarta Ley de la Termodinámica”, que ha sido también promulgada varias veces como “Ley Ecológica de Termodinámica” (ELT), a ver Integration of Ecosystem Theories: A Pattern, Kluwer Academic Publisher. Hasta hoy, esta Ley es solamente una proposición, pero con la ventaja de representar una verdadera hipótesis con la característica que puede ser falsificada. Yo no estoy acuerdo con la manera generalizada como Jørgensen utiliza el término “exergy” para elaborar su teoría. La “exergy” de un sistema es normalmente definida como una medida de la capacidad de realizar trabajo por un sistema. El físico Boltzmann ha descrito claramente que la información engloba energía. Jørgensen utiliza este principio considerando la cantidad de “exergy” acumulada por el ecosistema. Así pues, Jørgensen considera que la información genética de los organismos que componen el ecosistema representaría la mayor parte de la “exergy” de este ecosistema. Mi opinión es que es absolutamente primordial considerar que esta información ha sido acumulada durante un proceso histórico y a causa de una irreversibilidad fundamental esta información no puede ser extraída otra vez para producir trabajo. Además, otros fenómenos que han sido mencionados en su tiempo por Ramon Margalef nos demuestran que la multiplicación biológica de la información, que prolifera en los ecosistemas, tiene un gasto energético muy inferior de la energía acumulada por la información si es calculada según la formula de Boltzmann. Sin embargo, a pesar de estas objeciones, algunas de las ideas principales de Sven Erik Jørgensen, se colocan en el contexto de la teoría de la termodinámica fuera del equilibrio tal como ha sido elaborado por el físico Ilya Prigogine, las cuales son muy interesantes y merecen ser estudiadas para ser verificadas o falsificadas
Quelle nature demain sur nos littoraux méditerranéens ?
No full textInternational audienceThis article presents the ecological characteristics of the low-lying Languedoc coastline, and its lagoon environment. Coastal rivers play an important role in the dynamics of the coastal strip, and even more so it's increasing urbanization. Concerns about the preservation of "natural" areas are struggling to take precedence over other social usages of the Languedoc coast.Cet article présente les caractéristiques écologiques des côtes basses languedociennes, et de leurs milieux lagunaires. Les fleuves côtiers jouent un rôle important dans la dynamique du cordon littoral, et plus en-core son urbanisation croissante. Les préoccupations de préservation d’espaces « naturels » peinent à prendre le dessus par rapport aux autres usages sociaux du littoral languedocien
Does the Environment “Filter” or “Select” Species? Bridging the Ecologies of Microbes and Macro-Organisms for a Common Niche Assembly Theory
No full textMore than five decades before the introduction of “environmental filtering” in plant and vegetation sciences, Baas Becking proposed that the “environment selects” for studies in microbial ecology. He coupled this with the ubiquity law that he proposed for microbes to obtain the tenet “everything is everywhere, but, the environment selects”. Nowadays, while this tenet is mostly used as a null hypothesis for studies of microbial biogeography, the latter part has large implications for niche assembly theories. In this respect, it is very similar to the idea of “environmental filtering”, although some minor differences exist regarding how both concepts have been applied in macrobial and microbial ecologies. During the second decade of the 21st century, the usefulness of the latter has been questioned due to difficulties in disentangling the roles of environmental (abiotic) filtering and ecological interaction in community assembly. A new vision has emerged in the literature that considers the environmental filter as dynamic and continuously influenced by biotic communities. With a small modification, this scheme provides a solution that can accommodate the ecologies of both microbes and macro-organisms for a common niche assembly theory
Can abandoned Salinas be managed as coastal lagoons?
No full textGECOMARS: International workshop on ecosystem based management, Marseille, France, 4-5 February 2020International audienceTwenty-two of the Mediterranean coastal Salinas in S. France have been abandoned for salt extraction since 1950 and most are now available for nature conservation purposes. Their management is a challenge as the abandoned Salinas are human-modified systems, compartmentalized in salt ponds, with other important modifications in the landscape. These landscape modifications were studied in more detail in two examples by studying historic maps. Thus, for the Salin de Peyriac (Aude), an original endorheic lake (Etang du Doul) was converted into a pre-concentrating pond and nowadays persists as a hypersaline coastal lagoon. Salin des Pesquiers (Var) was created since 1848 within the Etang du Pesquier coastal lagoon. Therefore, the course of the Roubaud River, the tributary to this lagoon, was deviated to flow directly to the sea. Together with the creation of a circumferential canal this resulted in destruction of the original Roubaud delta and its fringing wetlands with ecotones in their freshwater – salt water transition zones. Both abandoned Salinas can in principle be managed as coastal lagoons, because the sediment surfaces of their ponds are located below mean sea level. Nevertheless, the Ecosystem-based management of these systems has to acknowledge a large degree of artificiality. Complete ecological restoration to historic conditions appears unrealistic and is often not desirable. Hence, abandoned Salinas offer many possibilities for creative and experimental management that should be followed by action monitoring and assessed by scientific studies
Ecological trajectories of phytoplankton communities in Mediterranean coastal lagoons during ecosystem restoration
No full textA l’interface entre les milieux marins et continentaux, les lagunes côtières sont des écosystèmes très diversifiés et figurent parmi les milieux les plus productifs. Leur confinement les rend particulièrement vulnérables aux apports nutritifs qu’elles tendent à concentrer. En Languedoc-Roussillon, les lagunes ont été profondément dégradées par les pressions anthropiques, en particulier le complexe des étangs palavasiens qui a souffert d’un enrichissement nutritif intensif provenant des effluents de la station de traitement des eaux de l’agglomération montpelliéraine. Cet enrichissement a engendré un gradient d’eutrophisation dans ces huit lagunes, de la méso- à l’hypertrophie, altérant profondément la structure des producteurs primaires vers une dominance du compartiment phytoplanctonique.Le phytoplancton témoigne d’une réponse rapide à la variabilité environnementale, et son importante diversité spécifique et fonctionnelle reflète une grande diversité de processus écologiques et de fonctionnement écosystémiques. Grâce à ces caractéristiques, ce compartiment a été largement utilisé comme un indicateur du fonctionnement des écosystèmes aquatiques.Depuis décembre 2005, les effluents responsables de l’eutrophisation des lagunes palavasiennes ont été déviés en mer Méditerranée. Cette mesure a réduit de 70 à 83 % les apports en phosphore et azote inorganiques aux lagunes, initiant un processus de restauration écologique. Cette thèse vise à mieux comprendre les processus de restauration des lagunes méditerranéennes au travers de l’étude des trajectoires d’évolution des communautés phytoplanctoniques.L’analyse de 14 ans de données de 2000 à 2013 a permis de montrer que la restauration des lagunes a entrainé une amélioration de la qualité de l’eau principalement liée à la réduction drastique de la biomasse phytoplanctonique. Cette réduction a illustré la chute des abondances de Diatomées (3-5 µm), qui étaient particulièrement favorisées par les apports nutritifs diffus provenant des effluents. L’analyse des trajectoires des communautés phytoplanctoniques depuis la réduction des apports a mis en évidence une modification de leur composition exprimée par une hausse des abondances des Algues vertes et des Dinophytes. Cette modification reflète le changement de l’origine et de la forme des nutriments disponibles induit par la re-oligotrophisation. Elle traduit l’importance des flux d’ammonium et de phosphates sédimentaires dans les lagunes en voie de restauration, pour lesquels les Algues vertes sont très compétitives, et l’importance des stocks de matière organique favorisant les espèces mixotrophes. Le picophytoplancton qui dominait exclusivement les communautés est aujourd’hui transitoirement remplacé par le nano- et le microphytoplancton au cours des efflorescences saisonnières. La variabilité saisonnière de la diversité taxonomique et fonctionnelle (taille cellulaire, régime trophique, croissance) des communautés phytoplanctoniques de deux lagunes du complexe des étangs palavasiens aux niveaux trophiques contrastés a été approfondie, et comparée à celle d’une lagune oligotrophe. Cette analyse a mis en évidence des particularités des communautés, témoignant de fonctionnements écologiques distincts principalement liés à la dégradation des lagunes par l’eutrophisation. Les résultats de cette thèse indiquent que les processus de restauration restent inachevés. La biomasse phytoplanctonique tend à ré-augmenter depuis 2012 en réponse à des conditions climatiques favorables. Le phytoplancton des lagunes palavasiennes réponds toujours fortement à un pulse nutritif, illustrant la vulnérabilité de ces lagunes vis-à-vis de l’enrichissement d’origine anthropique.Located at the interface between marine and continental systems, coastal lagoons are among the most diverse and productive ecosystems. These semi-enclosed ecosystems are very vulnerable to nutrient enrichment. In the Languedoc-Roussillon region, anthropogenic pressures have profoundly damaged the coastal lagoons, especially those belonging to the Palavasian complex close to Montpellier. The latter lagoons have been affected by high nutrient loadings from the sewage treatment plant of the Montpellier agglomeration. This resulted in a trophic gradient among the eight lagoons in the complex, from mesotrophy to hypertrophy, with altered primary producer communities by favoring the predominance of the phytoplankton compartment.The phytoplankton responds very fast to environmental variability. The high specific and functional diversity of the phytoplankton carries information regarding the different ecological processes and ecosystem functioning. Hence, phytoplankton has been widely used as an efficient indicator of aquatic ecosystems functioning.In December 2005, the effluents responsible of the eutrophication of the Palavasian lagoons were diverted into the Mediterranean Sea. This measure resulted in a reduction of the inorganic phosphorous and nitrogen loadings to the lagoons from 70 to 83 %, respectively, and initiated a process of ecological restoration. This thesis aimed to improve the understanding of the restoration process of Mediterranean coastal lagoons by studying phytoplankton communities’ trajectories.The analysis of a database comprising fourteen years of observations from 2000 to 2013 established that the restoration of coastal lagoons gave rise to an improvement of the water quality, linked to a drastic reduction of phytoplankton biomass. The time series showed a sharp drop of the Diatoms (3-5 µm), which before the diversion had been particularly enhanced by the nutrient inputs from the effluents. The analysis of phytoplankton trajectories since the nutrient inputs reduction showed a modification of phytoplankton community composition characterized by an increase of the abundances of Green algae and Dinophytes. This modification reflects the change of the origin and the form of available nutrients caused by the re-oligotrophication. It especially emphasizes the importance of benthic fluxes of phosphate and ammonium, for which Green algae are the most competitive. In addition, the benthic stocks of organic matter may represent a resource for mixotrophic species. Picophytoplankton, which was exclusively dominant in the Palavasian lagoons before the diversion, is now temporarily replaced by nano- and microphytoplankton during seasonal blooms. This is related to their specific strategies to acquire and use nutrients. The seasonal variability of taxonomic and functional phytoplankton diversity (cell size, trophic regime, growth) of two lagoons from the Palavasian complex with contrasted trophic status was studied in more detail, and compared to that of an oligotrophic lagoon. This study showed some particularities of the phytoplankton communities to fit to distinct ecosystem functioning, which can be linked to the degradation caused by eutrophication. The restoration is still unfinished today. The phytoplankton biomass increases since 2012 in response to suitable climatic conditions. The phytoplankton of the Palavasian lagoons still quickly responds to a nutrient pulse, highlighting the lagoon vulnerability to an anthropogenic nutrient input
Quelle nature demain sur nos littoraux méditerranéens ?
No full textInternational audienceThis article presents the ecological characteristics of the low-lying Languedoc coastline, and its lagoon environment. Coastal rivers play an important role in the dynamics of the coastal strip, and even more so it's increasing urbanization. Concerns about the preservation of "natural" areas are struggling to take precedence over other social usages of the Languedoc coast.Cet article présente les caractéristiques écologiques des côtes basses languedociennes, et de leurs milieux lagunaires. Les fleuves côtiers jouent un rôle important dans la dynamique du cordon littoral, et plus en-core son urbanisation croissante. Les préoccupations de préservation d’espaces « naturels » peinent à prendre le dessus par rapport aux autres usages sociaux du littoral languedocien
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