Sandra De Galan

Bio: Sandra De Galan is an academic researcher from Vrije Universiteit Brussel. The author has contributed to research in topics: Corynebacterium glutamicum & Arsenate. The author has an hindex of 8, co-authored 9 publications receiving 373 citations.

The North Sea: source or sink for nitrogen and phosphorus to the Atlantic Ocean?

Abstract: Annual nitrogen and phosphorus budgets for the whole North Sea taking into account the most recent data available were established. The area considered has a total surface of approximately 700,000 km2 and corresponds to the definition by OSPARCOM (Oslo and Paris Commission) with the exclusion of the Skagerrak and Kattegat areas. Input and output fluxes were determined at the marine, atmospheric, sediment and continental boundaries, and riverine inputs based on river flows and nutrient concentrations at the river–estuary interface were corrected for possible estuarine retention. The results showed that the North Sea is an extremely complex system subjected to large inter-annual variability of marine water circulation and freshwater land run-off. Consequently, resulting total N (TN) and P (TP) fluxes are extremely variable from 1 year to another and this has an important influence on the budget of these elements. Total inputs to the North Sea are 8870 ± 4860 kT N year−1 and 494 ± 279 kT P year−1. Denitrification is responsible for the loss of 23 ± 7% of the TN inputs while sediment burial is responsible for the retention of only of 2 ± 2% of the TP input. For TN, due to the large variability on marine and estuarine fluxes, and to the uncertainty related to the denitrification rate, it was concluded that the North Sea could either be a source (1930 kT N year−1) or a sink (1700 kT N year−1) for the waters of the North Atlantic Ocean. For TP it was concluded that the North Sea is mostly a source (−4 to 52 kT P year−1) for the waters of the North Atlantic Ocean.

Dietary exposure to total and toxic arsenic in Belgium: importance of arsenic speciation in North Sea fish.

Abstract: Total and toxic (sum of As(III), As(V), monomethylarsenic (MMA), and dimethylarsenic (DMA)) As concentrations were assessed in 19 respectively 4 different fish and shellfish species from the North Sea. Following results were obtained: (i) for fish an average total As concentration of 12.8 μg/g ww and a P90 value of 30.6 μg/g ww; (ii) for shellfish an average total As concentration of 21.6 μg/g ww and a P90 value of 40.0 μg/g ww; (iii) for fish an average toxic As concentration of 0.132 μg/g ww and a P90 value of 0.232 μg/g ww; (iv) for shellfish an average toxic As concentration of 0.198 μg/g ww and a P90 value of 0.263 μg/g ww. For the Belgian consumer the average daily intake of total arsenic from fish, shellfish, fruit, and soft drinks (the main food carriers of As in Belgium) amounts to 285 μg/day with more than 95% coming from fish and shellfish, while for a high level consumer it amounts to 649 μg/day, more than twice the average value. Using the same daily consumption pattern for the selected food products as for total As, we find that the average daily intake of toxic As amounts to 5.8 μg/day, with a 50% contribution of fish and shellfish and the high level intake to 9.5 μg/day. When considering the FOA/WHO Expert Committee's recommendation for inorganic As intake of 2 μg/kg bw/day or 140 μg/day for a 70 kg person, the toxic dose in Belgium is thus an order of magnitude lower.

Corynebacterium glutamicum survives arsenic stress with arsenate reductases coupled to two distinct redox mechanisms.

Abstract: Arsenate reductases (ArsCs) evolved independently as a defence mechanism against toxic arsenate. In the genome of Corynebacterium glutamicum, there are two arsenic resistance operons (ars1 and ars2) and four potential genes coding for arsenate reductases (Cg_ArsC1, Cg_ArsC2, Cg_ArsC1' and Cg_ArsC4). Using knockout mutants, in vitro reconstitution of redox pathways, arsenic measurements and enzyme kinetics, we show that a single organism has two different classes of arsenate reductases. Cg_ArsC1 and Cg_ArsC2 are single-cysteine monomeric enzymes coupled to the mycothiol/mycoredoxin redox pathway using a mycothiol transferase mechanism. In contrast, Cg_ArsC1' is a three-cysteine containing homodimer that uses a reduction mechanism linked to the thioredoxin pathway with a k(cat)/K(M) value which is 10(3) times higher than the one of Cg_ArsC1 or Cg_ArsC2. Cg_ArsC1' is constitutively expressed at low levels using its own promoter site. It reduces arsenate to arsenite that can then induce the expression of Cg_ArsC1 and Cg_ArsC2. We also solved the X-ray structures of Cg_ArsC1' and Cg_ArsC2. Both enzymes have a typical low-molecular-weight protein tyrosine phosphatases-I fold with a conserved oxyanion binding site. Moreover, Cg_ArsC1' is unique in bearing an N-terminal three-helical bundle that interacts with the active site of the other chain in the dimeric interface.

Stable isotopes as one of nature's ecological recorders

Abstract: Analyses of the natural variation in stable isotopes of components of ecological systems have provided new insights into how these systems function across paleoecological to modern timescales and across a wide range of spatial scales. Isotope abundances of the molecules in biological materials and geochemical profiles are viewed as recorders that can be used to reconstruct ecological processes or to trace ecological activities. Here, we review key short-, medium- and long-term recording capacities of stable isotopes that are currently being applied to ecological questions. The melding of advances in genetics, biochemical profiling and spatial analysis with those in isotope analyses and modeling sophistication opens the door to an exciting future in ecological research.

The radiative forcing potential of different climate geoengineering options

Abstract: . Climate geoengineering proposals seek to rectify the Earth's current and potential future radiative imbalance, either by reducing the absorption of incoming solar (shortwave) radiation, or by removing CO2 from the atmosphere and transferring it to long-lived reservoirs, thus increasing outgoing longwave radiation. A fundamental criterion for evaluating geoengineering options is their climate cooling effectiveness, which we quantify here in terms of radiative forcing potential. We use a simple analytical approach, based on energy balance considerations and pulse response functions for the decay of CO2 perturbations. This aids transparency compared to calculations with complex numerical models, but is not intended to be definitive. It allows us to compare the relative effectiveness of a range of proposals. We consider geoengineering options as additional to large reductions in CO2 emissions. By 2050, some land carbon cycle geoengineering options could be of comparable magnitude to mitigation "wedges", but only stratospheric aerosol injections, albedo enhancement of marine stratocumulus clouds, or sunshades in space have the potential to cool the climate back toward its pre-industrial state. Strong mitigation, combined with global-scale air capture and storage, afforestation, and bio-char production, i.e. enhanced CO2 sinks, might be able to bring CO2 back to its pre-industrial level by 2100, thus removing the need for other geoengineering. Alternatively, strong mitigation stabilising CO2 at 500 ppm, combined with geoengineered increases in the albedo of marine stratiform clouds, grasslands, croplands and human settlements might achieve a patchy cancellation of radiative forcing. Ocean fertilisation options are only worthwhile if sustained on a millennial timescale and phosphorus addition may have greater long-term potential than iron or nitrogen fertilisation. Enhancing ocean upwelling or downwelling have trivial effects on any meaningful timescale. Our approach provides a common framework for the evaluation of climate geoengineering proposals, and our results should help inform the prioritisation of further research into them.