Papers by Karel Van den Meersche
HAL (Le Centre pour la Communication Scientifique Directe), Oct 13, 2020
Greenhouse gas (CO2, N2O and CH4) exchange measurements between soil and atmosphere are important... more Greenhouse gas (CO2, N2O and CH4) exchange measurements between soil and atmosphere are important data when studying agrosystem functioning. These data can be measured on high temporal resolution with automatic chambers. However, automated chamber systems are expensive which limits the number of measuring points on a same site. Besides, researchers are restrained to integrate and understand the spatial variability of the soil metabolic activity and more generally biogeochemistry cycles that are associated to. For this study, we propose a construction plan for a self-made multiplexed system of automated chambers. We chose a system with an horizontal closure to minimise effects due to overpressure during closing events, and to allow the system to be installed under low branches. Here we present some results of leakage tests and at field functioning during several months. A particular attention has been brought to the material cost, to the electric consumption as well as the implementation simplicity. Technical information about the conception, construction and the use of these chambers and output data analyses are detailed in this paper with the drawings, pilot programming and codes for the data analysis.
VLIZ Special Publication, 2002
Journal of Statistical Software, 2009
An R function is implemented that uses Markov chain Monte Carlo (MCMC) algorithms to uniformly sa... more An R function is implemented that uses Markov chain Monte Carlo (MCMC) algorithms to uniformly sample the feasible region of constrained linear problems. Two existing hit-and-run sampling algorithms are implemented, together with a new algorithm where an MCMC step reflects on the inequality constraints. The new algorithm is more robust compared to the hit-and-run methods, at a small cost of increased calculation time.
Limnology and Oceanography-methods, Apr 4, 2008
Determination of microbial taxonomy based on lipid or pigment spectra requires use of a compositi... more Determination of microbial taxonomy based on lipid or pigment spectra requires use of a compositional estimator. We present a new approach based on Bayesian inference and an implementation in the open software platform R. The Bayesian Compositional Estimator (BCE) aims not only to obtain a maximum likelihood solution, but also to provide a complete estimate of the taxonomic composition, including probability distributions and dependencies between estimated values. BCE results are compared with those obtained with CHEMTAX. The BCE has not only a similar accuracy, but also extracts more information from the data, the most obvious being standard deviation and covariance estimates.
Limnology and Oceanography, 2009
We examined the carbon sources used by bacteria and mesozooplankton in the Scheldt River and estu... more We examined the carbon sources used by bacteria and mesozooplankton in the Scheldt River and estuary (Belgium, The Netherlands) using a combined stable isotope and fatty acid composition approach. Water samples were collected monthly at six stations during 1 yr and analyzed for 13 C of dissolved inorganic carbon, dissolved organic carbon (DOC), and particulate organic carbon (POC). Mesozooplankton was determined up to family, genus, or species level and analyzed for 13 C and fatty acid content. Suspended particles were analyzed for phospholipid fatty acids and their 13 C contents to estimate isotope ratios of phytoplankton groups and heterotrophic bacteria. The carbon isotope signatures of DOC, POC, and bacterial biomass were similar and significantly enriched relative to those of diatoms and green algae, pointing to allochthonous subsidies as an important carbon source for bacteria. The contribution of algae to zooplankton diets as estimated from isotope ratios and fatty acid profiles averaged 41% and 75% respectively, and did not differ significantly among stations, taxa, or age categories. Mesozooplankton relies primarily on grazing on phytoplankton and direct consumption of particulate organic matter. Mesozooplankton appears to receive little of its carbon from DOC via bacteria. tory support, and Tom Maris for providing data on suspended particulate matter and chlorophyll a. Carlo Heip provided guidance and access to research facilities. Jim Cloern and one anonymous reviewer provided constructive feedback. The research was supported by grants from the Flemish Fund for Scientific Research (FWO) and the Netherlands Organisation for Scientific Research (NWO), and by extra funding from the University of Ghent. This is contribution 4397 from the Netherlands Institute of Ecology.
Limnology and Oceanography, May 1, 2004
We tracked flows of carbon and nitrogen during an experimental phytoplankton bloom in a natural e... more We tracked flows of carbon and nitrogen during an experimental phytoplankton bloom in a natural estuarine assemblage in Randers Fjord, Denmark. We used 13 C-labeled dissolved inorganic carbon to trace the transfer of carbon from phytoplankton to bacteria. Ecosystem development was followed over a period of 9 d through changes in the stocks of inorganic nutrients, pigments, particulate organic carbon and nitrogen, dissolved organic carbon (DOC), and algal and bacterial polar-lipid-derived fatty acids (PLFA). We quantified the incorporation of 13 C in phytoplankton and bacterial biomass by carbon isotope analysis of specific PLFA. A dynamic model based on unbalanced algal growth and balanced growth of bacteria and zooplankton adequately reproduced the observations and provided an integral view of carbon and nitrogen dynamics. There were three phases with distinct carbon and nitrogen dynamics. During the first period, nutrients were replete, an algal bloom was observed, and carbon and nitrogen uptake occurred at a constant ratio. Because there was little algal exudation of DOC, transfer of 13 C from phytoplankton to bacteria was delayed by 1 d, compared with the labeling of phytoplankton. In the second phase, the exhaustion of dissolved inorganic nitrogen resulted in decoupling of carbon and nitrogen flows caused by unbalanced algal growth and the exudation of carbon-rich dissolved organic matter by phytoplankton. During the final, nutrient-depleted phase, carbon and nitrogen cycling were dominated by the microbial loop and there was accumulation of DOC. The main source (60%) of DOC was exudation by phytoplankton growing under nitrogen limitation. Heterotrophic processes were the main source of dissolved organic nitrogen (94%). Most of the carbon exudated by algae was respired by the bacteria and did not pass to higher trophic levels. The dynamic model successfully reproduced the evolution of trophic pathways during the transition from nutrient-replete to-depleted conditions, which indicates that simple models provide a powerful tool to study the response of pelagic ecosystems to external forcings.
We estimated annual fluxes of suspended sediments and different carbon species at three sites alo... more We estimated annual fluxes of suspended sediments and different carbon species at three sites along the lower Tana River (Kenya), based on monthly sampling between January 2009 and December 2011. Floodplains are present along large stretches of the lower Tana River. Total suspended matter (TSM), concentrations of particulate and dissolved organic and inorganic carbon (POC, DOC and DIC), as well as their stable isotope composition were determined. Both TSM (24 to 9386 mg L-1) and POC (0.8 to 141.9 mg C L-1) concentrations were highly variable. DOC and DIC concentrations ranged from 0.8 to 5.2 mg C L-1 and 7.1 to 23.5 mg C L-1 , respectively, but their seasonal variations were not systematic. A strong shift in the origin of POC was observed, being dominated by C3-derived carbon (C) during dry conditions (low δ 13 C POC signatures between-28‰ and-25‰), but with significant C4 contributions during higher flow events (δ 13 C POC up to-19.5 ‰). On average, annual suspended sediment fluxes ranged from 3.1 Tg y-1 to 8.7 Tg y-1. Mean annual C fluxes ranged from 36.6 Gg C y-1 to 104.9 Gg C y-1 , 6.0 Gg C y-1 to 13.9 Gg C y-1 and 50.6 Gg C y-1 to 63.6 Gg C y-1 for POC, DOC and DIC, respectively. Tana River floodplains play a critical role in regulating the transport of sediments and organic carbon as reflected by a significant reduction in the sediment, POC and DOC (ranging between 34% and 65% for the 3-year study period).
Plant and Soil
In agroforestry systems, the root distributions and properties of the annual and perennial vegeta... more In agroforestry systems, the root distributions and properties of the annual and perennial vegetation are poorly known, although they are recognized for fostering soil carbon (C) stocks through annual root-derived C inputs and by altering microbial activity. This study aimed to evaluate the potential contribution of roots from the understory vegetation strip (UVS) and the crop to top-and subsoil C stocks (0-100 cm) to a 3-year-old agroforestry system of the alley-cropping type. Methods Root biomass, chemical composition, functional traits and anatomical structure were assessed in parallel to a characterization of soil physicochemical
Agriculture, Ecosystems & Environment
This study investigates spatial-temporal trends in N 2 O emissions from coffee production systems... more This study investigates spatial-temporal trends in N 2 O emissions from coffee production systems in Costa Rica with a focus on the effects of nitrogen fertilisation, topography and soil type. This is done by combining (i) multiyear continuous dynamic chamber measurements from sites with different fertilisation levels, (ii) static chamber measurements taken along a typical sloping coffee field and (iii) measurements from a laboratory incubation experiment with nutrient addition to different soil types. In the field and in the laboratory, additions included standard NPK fertiliser, ammonium nitrate (NH 4 NO 3) as well as potassium nitrate (KNO 3). Soils in a laboratory experiment were incubated under both drained and flooded conditions. Continuous measurements from automatic chambers show that annual N 2 O fluxes were dominated by bursts over few weeks following N-fertilisation with peak emissions up to 60 g N-N 2 O ha − 1 day − 1. A two-month slope experiment with static chambers after KNO 3-fertilisation with 90 kg N ha − 1 showed N 2 O significant differences between the highest daily emission rates from the top and the bottom of the slope (134 ± 20 g N-N 2 O ha − 1 and 336 ± 104 g N-N 2 O ha − 1 , respectively) which can be explained by NO 3 transport downhill and flooded conditions favouring denitrification at the bottom of the slope. Incubation experiments indicate that denitrification is the main process controlling N 2 O emissions but also that nitrification can result in low N 2 O emission rates under drained conditions. It can be concluded that the reported N 2 O emissions from the coffee agroforestry systems are generally low, but may be underestimated, as both poorly drained depressions functioning as N 2 O hotspots as well as temporal N 2 O bursts need to be taken into account.
In alley-cropping systems, the root distributions and traits of the annual and perennial vegetati... more In alley-cropping systems, the root distributions and traits of the annual and perennial vegetation are poorly known, although they are recognized as factors fostering soil carbon (C) stocks through annual root C inputs and by impacts on microbial activity. This study aimed to evaluate the potential contribution of roots from the understory vegetation strip (UVS) and the crop to top-and subsoil C stocks (0-100 cm) in a 3-year-old alley-cropping system. Methods Root biomass, chemical composition, functional traits and anatomical structure were assessed in parallel to a characterization of soil physico-chemical and microbiological properties, including enzymatic activity, at different depths and locations perpendicular to the tree line, re ecting the effect of the distance to the tree. Results The root biomass and traits were heterogeneous in the young alley-cropping system due to the presence of different plant species and the heterogeneity of the soil mineral N content according to the location perpendicular to the tree line. The soil microbiological properties and organic C stocks did not vary horizontally at this stage of agroforestry, but the tight link between root stoichiometry and microbial extracellular enzymatic activities suggested a differentiation of the soil properties in the following years. Conclusion Altogether, our results suggested that increasing the root biomass in topsoil in agroforestry systems can positively contribute to increasing soil organic C stocks, but in deeper soil layers, an increase in litter inputs with high C:N could accentuate microbial N limitations and limit soil C storage.
HAL (Le Centre pour la Communication Scientifique Directe), May 16, 2022
HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific r... more HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. STRADIV System approach for the TRAnsition to bio-DIVersified agroecosystems. Data Management Plan Sandrine Auzoux, Krishna Naudin, Aude Ripoche, Patrice Autfray, Jean-François Bélières, Ollo Sib, Patrice Koffi Kouakou, Der Dabire, Béatrice Rhino, Karel van den Meersche, et al.
Bouillon@ees. kuleuven.be DISTRIBUTION AND COMPOSITION OF ORGANIC CARBON IN THE TANA RIVER BASIN ... more Bouillon@ees. kuleuven.be DISTRIBUTION AND COMPOSITION OF ORGANIC CARBON IN THE TANA RIVER BASIN (KENYA). Few studies have quantified carbon fluxes in African tropical rivers. We report the altitudinal and seasonal patterns in carbon pools and their stable isotope composition from the River Basin (Kenya). Data from February 2008 (end of dry season), September-November 2009 (short rains), and June-July 2010 (end of long rains) are presented. Seasonal data from January 2009-March 2010 are also presented. A consistent downstream increase in TSM was observed during all three sampling campaigns. TSM values were similar for 2008 and 2010 datasets (p>0.05), but significantly higher during the short rains in 2009. δ13C-POC increased downstream (p<0.01), and were predominantly of terrestrial origin as reflected by generally high POC/Chl a ratios. TSM and %POC followed the classical inverse relationship for all years sampled. TSM and POC were highly episodic and highest in periods with high discharge. Seasonal patterns in δ13C-POC signatures coincided closely with δ13C increasing markedly during periods of high discharge and decreasing towards predominantly C3 signatures toward the end of dry periods. This suggests high sediment mobilization during rains occurs mostly in areas with significant grassland cover (C4).
Frankignoulle, M., Borges, A.V., Gazeau, F., Delille, B., Schiettecatte, L.S., Gattuso, J.-P., Ro... more Frankignoulle, M., Borges, A.V., Gazeau, F., Delille, B., Schiettecatte, L.S., Gattuso, J.-P., Rochelle-Newall, E.J., GonzalezBenitez, N., Bonilla-Findji, O., Pizay, M.D., Wollast, R., Vanderborght, J.P., Chou, L., Loijens, M., Folmer, I., Middelburg, J.J., Van-denMeersche K., Boschker, H.T.S., Veuger, B., Duarte, C.M., Barron, C., Navarro, N., Iversen, N., Elliot, M., Hemingway, K.L., Burdon, D., Campuzano-Guillen, F.J., Allen, J.
Éditions Quæ eBooks, 2019
Le Centre pour la Communication Scientifique Directe - HAL - Université de Nantes, Jun 7, 2022
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Papers by Karel Van den Meersche