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Article Reference Comparison of three SeaWiFS atmospheric correction algorithms for turbid waters using AERONET-OC measurements
The use of satellites to monitor the color of the ocean requires effective removal of the atmospheric signal. This can be performed by extrapolating the aerosol optical properties in the visible from the near-infrared (NIR) spectral region assuming that the seawater is totally absorbant in this latter part of the spectrum. However, the non-negligible water-leaving radiance in the NIR which is characteristic of turbid waters may lead to an overestimate of the atmospheric radiance in the whole visible spectrum with increasing severity at shorter wavelengths. This may result in significant errors, if not complete failure, of various algorithms for the retrieval of chlorophyll-a concentration, inherent optical properties and biogeochemical parameters of surface waters. This paper presents results of an inter-comparison study of three methods that compensate for NIR water-leaving radiances and that are based on very different hypothesis: 1) the standard Sea WiFS algorithm (Stumpfet al., 2003; Bailey et al., 2010) based on a bio-optical model and an iterative process; 2) the algorithm developed by Ruddick et al. (2000) based on the spatial homogeneity of the NIR ratios of the aerosol and water-leaving radiances; and 3) the algorithm of Kuchinke et al. (2009) based on a fully coupled atmosphere-ocean spectral optimization inversion. They are compared using normalized water-leaving radiance nL(w) in the visible. The reference source for comparison is ground-based measurements from three AERONET-Ocean Color sites, one in the Adriatic Sea and two in the East Coast of USA. Based on the matchup exercise, the best overall estimates of the nL(w) are obtained with the latest SeaWiFS standard algorithm version with relative error varying from 14.97\% to 35.27\% for lambda = 490 nm and lambda = 670 nm respectively. The least accurate estimates are given by the algorithm of Ruddick, the relative errors being between 16.36\% and 42.92\% for lambda = 490 nm and lambda = 412 nm, respectively. The algorithm of Kuchinke appears to be the most accurate algorithm at 412 nm (30.02\%), 510 (15.54\%) and 670 nm (32.32\%) using its default optimization and bio-optical model coefficient settings. Similar conclusions are obtained for the aerosol optical properties (aerosol optical thickness tau(865) and the Angstrom exponent, alpha(510, 865)). Those parameters are retrieved more accurately with the SeaWiFS standard algorithm (relative error of 33\% and 54.15\% for tau(865) and alpha(510, 865)). A detailed analysis of the hypotheses of the methods is given for explaining the differences between the algorithms. The determination of the aerosol parameters is critical for the algorithm of Ruddick et al. (2000) while the bio-optical model is critical for the algorithm of Stumpf et al. (2003) utilized in the standard SeaWiFS atmospheric correction and both aerosol and bio-optical model for the coupled atmospheric-ocean algorithm of Kuchinke. The Kuchinke algorithm presents model aerosol-size distributions that differ from real aerosol-size distribution pertaining to the measurements. In conclusion, the results show that for the given atmospheric and oceanic conditions of this study, the SeaWiFS atmospheric correction algorithm is most appropriate for estimating the marine and aerosol parameters in the given turbid waters regions. (C) 2011 Elsevier Inc. All rights reserved.
Located in Library / RBINS Staff Publications
Article Reference Competition between kaolinite flocculation and stabilization in divalent cation solutions dosed with anionic polyacrylamides
Divalent cations have been reported to develop bridges between anionic polyelectrolytes and negatively-charged colloidal particles, thereby enhancing particle flocculation. However, results from this study of kaolinite suspensions dosed with various anionic polyacrylamides (PAMs) reveal that Ca2+ and Mg2+ can lead to colloid stabilization under some conditions. To explain the opposite but coexisting processes of flocculation and stabilization with divalent cations, a conceptual flocculation model with (1) particle-binding divalent cationic bridges between PAM molecules and kaolinite particles and (2) polymer-binding divalent cationic bridges between PAM molecules is proposed. The particle-binding bridges enhanced flocculation and aggregated kaolinite particles in large, easily-settleable flocs whereas the polymer-binding bridges increased steric stabilization by developing polymer layers covering the kaolinite surface. Both the particle-binding and polymer-binding divalent cationic bridges coexist in anionic PAM- and kaolinite-containing suspensions and thus induce the counteracting processes of particle flocculation and stabilization. Therefore, anionic polyelectrolytes in divalent cation-enriched aqueous solutions can sometimes lead to the stabilization of colloidal particles due to the polymer-binding divalent cationic bridges.
Located in Library / RBINS Staff Publications
Article Reference Complementarity effects drive positive diversity effects on biomass production in experimental benthic diatom biofilms
P1. Positive effects of species diversity on ecosystem functioning have often been demonstrated in 'macrobial' communities. This relation and the responsible mechanisms are far less clear for microbial communities. Most experimental studies on microorganisms have used randomly assembled communities that do not resemble natural communities. It is therefore difficult to predict the consequences of realistic, non-random diversity loss. 2. In this study, we used naturally co-occurring diatom species from intertidal mudflats to assemble communities with realistically decreasing diversity and analysed the effect of non-random species loss on biomass production. 3. Our results demonstrate a highly positive biodiversity effect on production, with mixtures outperforming the most productive component species in more than half of the combinations. These strong positive diversity effects could largely be attributed to positive complementarity effects (including both niche complementarity and facilitation), despite the occurrence of negative selection effects which partly counteracted the positive complementarity effects at higher diversities. 4. Facilitative interactions were, at least in part, responsible for the higher biomass production. For one of the species, Cylindrotheca closterium, we show its ability to significantly increase its biomass production in response to substances leaked into the culture medium by other diatom species. In these conditions, the species drastically reduced its pigment concentration, which is typical for mixotrophic growth. 5. Synthesis. We show that both species richness and identity have strong effects on the biomass production of benthic diatom biofilms and that transgressive overyielding is common in these communities. In addition, we show mechanistic evidence for facilitation which is partly responsible for enhanced production. Understanding the mechanisms by which diversity enhances the performance of ecosystems is crucial for predicting the consequences of species loss for ecosystem functioning.
Located in Library / RBINS Staff Publications
Article Reference Complementarity of LA-ICP-MS and petrography in the analysis of Neolithic pottery from the Scheldt River valley, Belgium.
Abstract This paper presents the results of laser ablation – inductively coupled plasma – mass spectrometry (LA-ICP-MS) analysis of the clay fraction in 70 Late Mesolithic and Early/Middle Neolithic pottery sherds from the Scheldt basin and 10 sampled sediments. The elemental concentration results were visualized using multivariate chemometric techniques and compared to the results of petrographic analysis of the same ceramics in order to investigate the complementarity of both approaches. In addition, the results for the pottery and sediments were compared for clay sourcing purposes. Overall, the elemental analysis was able to confirm part of the observations from the petrographic analysis. However, a large part of the ceramics clustering was driven by heterogeneity in the elemental composition that does not stem from differences in the clay source used. Furthermore, no conclusions could be drawn on the use of the sampled sediments for pottery production. Therefore, it is concluded that LA-ICP-MS analysis of the clay fraction in pottery can complement petrography, but petrographic analysis remains indispensable for clay sourcing of pottery from northern Belgium. Keywords: ceramic petrography, LA-ICP-MS, t-SNE, elemental analysis, Neolithic pottery, Belgium
Located in Library / RBINS Staff Publications 2021
Article Reference Complete Characterization of Ocean Color Radiometers
Located in Library / RBINS Staff Publications 2024
Article Reference Complete Coding Sequences of One H9 and Three H7 Low-Pathogenic Influenza Viruses Circulating in Wild Birds in Belgium, 2009 to 2012.
Located in Library / No RBINS Staff publications
Article Reference Complete Mitochondrial Genomes of Ancient Canids Suggest a European Origin of Domestic Dogs
The geographic and temporal origins of the domestic dog remain controversial, as genetic data suggest a domestication process in East Asia beginning 15,000 years ago, whereas the oldest doglike fossils are found in Europe and Siberia and date to >30,000 years ago. We analyzed the mitochondrial genomes of 18 prehistoric canids from Eurasia and the New World, along with a comprehensive panel of modern dogs and wolves. Themitochondrial genomes of all modern dogs are phylogeneticallymost closely related to either ancient or modern canids of Europe. Molecular dating suggests an onset of domestication there 18,800 to 32,100 years ago. These findings imply that domestic dogs are the culmination of a process that initiated with European hunter-gatherers and the canids with whom they interacted.
Located in Library / RBINS Staff Publications
Article Reference chemical/x-molconn-Z Complex effect of projected sea temperature and wind change on flatfish dispersal
Climate change not only alters ocean physics and chemistry but also affects the biota. Larval dispersal patterns from spawning to nursery grounds and larval survival are driven by hydrodynamic processes and shaped by (a)biotic environmental factors. Therefore, it is important to understand the impacts of increased temperature rise and changes in wind speed and direction on larval drift and survival. We apply a particle-tracking model coupled to a 3D-hydrodynamic model of the English Channel and the North Sea to study the dispersal dynamics of the exploited flatfish (common) sole (Solea solea). We first assess model robustness and interannual variability of larval transport over the period 1995-2011. Then, using a subset of representative years (2003-2011), we investigate the impact of climate change on larval dispersal, connectivity patterns and recruitment at the nursery grounds. The impacts of five scenarios inspired by the 2040 projections of the Intergovernmental Panel on Climate Change are discussed and compared with interannual variability. The results suggest that 33% of the year-to-year recruitment variability is explained at a regional scale and that a 9-year period is sufficient to capture interannual variability in dispersal dynamics. In the scenario involving a temperature increase, early spawning and a wind change, the model predicts that (i) dispersal distance (+70%) and pelagic larval duration (+22%) will increase in response to the reduced temperature (–9%) experienced by early hatched larvae, (ii) larval recruitment at the nursery grounds will increase in some areas (36%) and decrease in others (-58%), and (iii) connectivity will show contrasting changes between areas. At the regional scale, our model predicts considerable changes in larval recruitment (+9%) and connectivity (retention -4% and seeding +37%) due to global change. All of these factors affect the distribution and productivity of sole and therefore the functioning of the demersal ecosystem and fisheries management.
Located in Library / RBINS Staff Publications 2018
Article Reference Complex geographical variation patterns in Tropheus duboisi Marlier, 1959 (Perciformes, Cichlidae) from Lake Tanganyika
Intra-specific morphological variation in the cichlid Tropheus duboisi from 10 localities over its entire known distribution area along the central eastern and northern shore of Lake Tanganyika was investigated. This revealed significant differences between various populations that are geographically isolated. These morphological observations only partially correspond to the results of a haplotype network, based on mtDNA. In addition, a difference in the timing of the onset of the adult colour pattern was discovered for one isolated population. The occurrence of morphological intra-specific differentiation is discussed with respect to the basal position of T. duboisi within Tropheus as well as to the presumed morphological stasis of the genus.
Located in Library / No RBINS Staff publications
Article Reference Complex mineralogical-geochemical sequences and weathering events in the supergene ore of the Cu–Co Luiswishi deposit (Katanga, DR Congo).
Located in Library / RBINS Staff Publications 2020