Net ecosystem production and carbon dioxide fluxes in the Scheldt estuarine plume

Background A time series of 4 consecutive years of measurements of the partial pressure of CO2 (pCO2) in the Scheldt estuarine plume is used here to estimate net ecosystem production (NEP). Results NEP in the Scheldt estuarine plume is estimated from the temporal changes of dissolved inorganic carbon (DIC). The strong seasonal variations of NEP are consistent with previous reports on organic carbon dynamics in the area. These variations are related to successive phytoplankton blooms that partly feed seasonally variable heterotrophy the rest of the year. On an annual time scale the Scheldt estuarine plume behaves as a net heterotrophic system sustained with organic carbon input from the Scheldt inner estuary and the Belgian coast. During one of the years of the time-series the estuarine plume behaved annually as a net autotrophic system. This anomalous ecosystem metabolic behaviour seemed to result from a combination of bottom-up factors affecting the spring phytoplankton bloom (increased nutrient delivery and more favourable incoming light conditions). This net autotrophy seemed to lead to a transient aa accumulation of organic carbon, most probably in the sediments, that fed a stronger heterotrophy the following year. Conclusion The present work highlights the potential of using pCO2 data to derive detailed seasonal estimates of NEP in highly dynamic coastal environments. These can be used to determine potential inter-annual variability of NEP due to natural climatic oscillations or due to changes in anthropogenic impacts.EUROTROPH - CARBOOCEAN - CANOPY - SOLAS.BE - COMETS - BELCOLOUR

Assessing the areas under risk of invasion within islands through potential distribution modelling: the case of Pittosporum undulatum in São Miguel, Azores

Copyright © 2009 Elsevier GmbH. All rights reserved.Non-indigenous plant species have been frequently reported as successful invaders in island environments, changing plant community composition and structure. This is the case of the sweet pittosporum (Pittosporum undulatum), native from Australia, which is one of the most successful plant invaders in the Azores archipelago. Data extracted from recent forestry inventories were used to model and map the potential distribution of P. undulatum in São Miguel, the larger island of the Azores. Current distribution of P. undulatum is related to climate, altitude and some human activity effects. Further analysis of the areas under risk of invasion showed that protected areas are under potential threat, although only a few native forest remnants seem to be threatened due to future expansion of P. undulatum, since the current distribution of these native communities has been reduced due to clearing and competition with invasive plants. We discuss the threats that any further expansion of the species will represent for low-altitude native forests, as well as the utility of species distribution models in the assessment of the areas under risk of invasion

Production of dissolved organic matter by phytoplankton and its uptake by heterotrophic prokaryotes in large tropical lakes

In pelagic ecosystems, phytoplankton extracellular release can extensively subsidize the heterotrophic prokaryotic carbon demand. Time-course experiments were carried out to quantify primary production, phytoplankton excretion, and the microbial uptake of freshly released dissolved organic carbon (DOC) derived from phytoplankton extracellular release (DOCp) in four large tropical lakes distributed along a productivity gradient: Kivu, Edward, Albert, and Victoria. The contributions of the major heterotrophic bacterial groups to the uptake of DOCp was also analyzed in Lake Kivu, using microautoradiography coupled to catalyzed reporter deposition fluorescent in situ hybridization. The percentage of extracellular release (PER) varied across the productivity gradient, with higher values at low productivity. Furthermore, PER was significantly related to high light and low phosphate concentrations in the mixed layer and was comparatively higher in oligotrophic tropical lakes than in their temperate counterparts. Both observations suggest that environmental factors play a key role in the control of phytoplankton excretion. Standing stocks of DOCp were small and generally contributed less than 1% to the total DOC because it was rapidly assimilated by prokaryotes. In other words, there was a tight coupling between the production and the heterotrophic consumption of DOCp. None of the major phylogenetic bacterial groups that were investigated differed in their ability to take up DOCp, in contrast with earlier results reported for standard labeled single-molecule substrates (leucine, glucose, adenosine triphosphate). It supports the idea that the metabolic ability to use DOCp is widespread among heterotrophic prokaryotes. Overall, these results highlight the importance of carbon transfer between phytoplankton and bacterioplankton in large African lakes.AFRIVAL - EAGLES East African Great Lake Ecosystem Sensitivity to Changes - CAKI Cycle du Carbone et des Nutriments au Lac Kivu - MICKI Microbial Diversity and Processes in Lake Kiv

A 15-month survey of Dimethylsulfoniopropionate and Dimethylsulfoxide content in Posidonia oceanica

Posidonia oceanica is the only reported seagrass to produce significant amount of dimethylsulfoniopropionate (DMSP). It is also the largest known producer of DMSP among coastal and inter-tidal higher plants. Here, we studied (i) the weekly to seasonal variability and the depth variability of DMSP and its related compound dimethylsulfoxide (DMSO) in P. oceanica leaves of a non-disturbed meadow in Corsica, France, (ii) the weekly to seasonal variability and the depth variability of DMSP to DMSO concentration to assess the potential of the DMSP:DMSO ratio as indicator of stress, and (iii) the relationships between DMSP, DMSO, and the DMSP:DMSO ratio with potential explanatory variables such as light, temperature, photosynthetic activity (effective quantum yield of photosystem II), and leaf size. The overall average concentrations of organosulfured compounds in P. oceanica leaves were 130 ± 39 µmol.g−1 fw for DMSP and 4.9 ± 2.1 µmol.g−1 fw for DMSO. Concentrations of DMSP and DMSO in P. oceanica were overall distinctly higher and exhibited a wider range of variations than other marine primary producers such as Spartina alterniflora, phytoplankton communities, epilithic Cyanobacteria and macroalgae. Concentrations of both DMSP and DMSO in P. oceanica leaves decreased from a maximum in autumn to a minimum in summer; they changed little with depth. Potential explanatory variables except the leaf size, i.e., the leaf age were little or not related to measured concentrations. To explain the seasonal pattern of decreasing concentrations with leaf aging, we hypothesized two putative protection functions of DMSP in young leaves: antioxidant against reactive oxygen species and predator-deterrent. The similar variation of the two molecule concentrations over time and with depth suggested that DMSO content in P. oceanica leaves results from oxidation of DMSP. The DMSP:DMSO ratio remained constant around a mean value of 29.2 ± 9.0 µmol:µmol for the non-disturbed harvested meadow regardless of the time of the year, the depth or the leaf size. As suggested for the salt march plant S. alterniflora, we hypothesized the DMSP:DMSO ratio could be considered as indicator of stress in seagrasses exposed to environmental or anthropogenic stressors. More research would now be needed to confirm the functions of DMSP and DMSO in seagrasses and how the DMSP:DMSO ratio will vary under various disturbances.FCT: 57/2016, UID/Multi/04326/2019.info:eu-repo/semantics/publishedVersio

Mechanisms controlling the air-sea CO2 flux in the North Sea

The mechanisms driving the air–sea exchange of carbon dioxide (CO2CO2) in the North Sea are investigated using the three-dimensional coupled physical–biogeochemical model ECOHAM (ECOlogical-model, HAMburg). We validate our simulations using field data for the years 2001–2002 and identify the controls of the air–sea CO2CO2 flux for two locations representative for the North Sea's biogeochemical provinces. In the seasonally stratified northern region, net CO2CO2 uptake is high (View the MathML source2.06molm-2a-1) due to high net community production (NCP) in the surface water. Overflow production releasing semi-labile dissolved organic carbon needs to be considered for a realistic simulation of the low dissolved inorganic carbon (DIC) concentrations observed during summer. This biologically driven carbon drawdown outcompetes the temperature-driven rise in CO2CO2 partial pressure (pCO2pCO2) during the productive season. In contrast, the permanently mixed southern region is a weak net CO2CO2 source (View the MathML source0.78molm-2a-1). NCP is generally low except for the spring bloom because remineralization parallels primary production. Here, the pCO2pCO2 appears to be controlled by temperature