Sensitivity of the global carbonate weathering carbon-sink flux to climate and land-use changes

The response of carbonate weathering carbon-sink flux (CCSF) to its environmental drivers is still not well understood on the global scale. This hinders understanding of the terrestrial carbon cycle. Here, we show that there is likely to be a widespread and consistent increase in the global CCSF (ranging from + 9.8% (RCP4.5) to + 17.1% (RCP8.5)) over the period 1950–2100. In the coming years the increasing temperature might be expected to have a negative impact on carbonate weathering. However, the increasing rainfall and anticipated land-use changes will counteract this, leading to a greater CCSF. This finding has been obtained by using long-term historical (1950–2005) and modeled future (2006–2100) data for two scenarios (RCP4.5 and RCP8.5) for climate and land-use change in our CCSF equilibrium model. This study stresses the potential role that carbonate weathering may play in the evolution of the global carbon cycle over this century

Constrained Path Search with Submodular Function Maximization

In this paper, we study the problem of constrained path search with submodular function maximization (CPS-SM). We aim to find the path with the best submodular function score under a given constraint (e.g., a length limit), where the submodular function score is computed over the set of nodes in this path. This problem can be used in many applications. For example, tourists may want to search the most diversified path (e.g., a path passing by the most diverse facilities such as parks and museums) given that the traveling time is less than 6 hours. We show that the CPS-SM problem is NP-hard. We first propose a concept called “submodular α -dominance” by utilizing the submodular function properties, and we develop an algorithm with a guaranteed error bound based on this concept. By relaxing the submodular α -dominance conditions, we design another more efficient algorithm that has the same error bound. We also utilize the way of bi-directional path search to further improve the efficiency of the algorithms. We finally propose a heuristic algorithm that is efficient yet effective in practice. The experiments conducted on several real datasets show that our proposed algorithms can achieve high accuracy and are faster than one state-of-the-art method by orders of magnitude

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

The evolution of carbonate weathering carbon sinks under climatic and anthropogenic perturbations

The chemical weathering processes of continental rocks are thought to be a major mechanism that control the long-term global climate. Carbonate rock on land surface is the largest carbon reservoir comparing to atmosphere and ocean. The chemical weathering products of carbonates constitutes nearly half of the dissolved loads in terrestrial water systems, although carbonates only covers 15.2% of ice-free continental surface. The aquatic photoautotroph in inland waters can utilize the carbonate weathering product HCO3- to produce organic carbon, thus forming a geological long-term carbon sink. This coupled biological carbon pump effect (BCP) may be responsible to a large proportion of terrestrial missing carbon sink. Due to the rapid dissolution kinetics, carbonate weathering process presents strongly sensitivity to environmental perturbations such as climate change and human land-use conversion. The better understanding of how carbonate weathering related carbon sink evolve under global change is significant to predict the future global carbon cycle and climate dynamics. This cumulative thesis consists of four scientific papers that together characterize the mechanisms and variations of carbonate weathering carbon sink under global change in terms of CO2 capture, inorganic carbon sink transfer, and organic carbon formation. In order to discuss the variation of carbonate weathering carbon sink in a dynamic earth system, a better understanding of the behavior of carbonate weathering process under different natural condition is essential. The first paper of this thesis selects three typical karst catchments with different geo-backgrounds to quantify the impacts of temperature, water flow and vegetation cover on carbonate weathering intensity and related carbon sink flux. Results indicate that the role of climate and vegetation may equally important, which play as a counterbalance effect in controlling the HCO3- concentration and carbon sink flux. Due to the chemo-statistic behavior of solutes flux, the total amount of carbon sink is depending on the water yield rate instead of HCO3- concentration. By comparing the results of three soil pCO2 models with global spring records, the second study find that net primary production (NPP) could be the optimal predictor for evaluating carbonate weathering intensity in most areas. On account of the disproportional influence of HCO3- and water flow on total carbon sink budget, the spatial distribution of carbonate weathering carbon sink flux is mainly dominated by global runoff pattern. By the insight of global spring evidences and the results of global simulations, a new mixed effect model is constructed to predict the historical and future variations of carbonate weathering carbon sink. This model indicates that this carbon sink flux will experience a widespread and consistent increase, ranging from +9.8 % (RCP4.5) to +17.1 % (RCP8.5) during 1950 to 2100. This carbon sink enhancement will mostly occur in low latitudes accompanied by intense human agricultural extension, implying that will have a great potential for human land-use strategies to regulate this carbon sink in the future. Finally, the impacts of different land-use strategies on carbonate weathering coupled biological carbon pump effect (BCP) has been detected in an artificial karst simulation test. Results suggest that DIC fertilization (high HCO3- input) will release the CO2 limitation in high pH aquatic environment, promoting the ecosystem primary production and in-stream organic carbon export. The high HCO3- inputs in grassland and shrubland dominant spring-pond systems lead a higher organic carbon export than that in bare rock land. In summary, the findings in this thesis indicate a considerable feedback that carbonate weathering carbon sink may response to climate and land-use change, which could have a great potential for mitigating the future global warming. Although the increasing global temperature will constrain the carbonate weathering intensity, yet human land-use activities may inversely lead a carbon sink enhancement. The carbonate weathering coupled terrestrial biological carbon pump effect is another key mechanism that can use to increase the atmospheric CO2 remove by human land-use strategies. Results in this thesis stress the significant role of carbonate weathering carbon sink for global carbon cycle and its great potential for mitigating the global warming.Die chemische Verwitterung von Gesteinen ist ein wesentlicher Prozess, der die langfristige Klimaveränderung beeinflusst. Kalk- und Dolomitgesteine stellen hier die größte Quelle an Kohlenstoff dar, verglichen mit Atmosphäre und Ozean. Die chemischen Verwitterungsprodukte der Karbonate tragen fast die Hälfte der Lösungsfracht in terrestrischen Abflußsystemem bei, obwohl Karbonate nur 15.2% der eisfreien Landschaftsoberfläche ausmachen. Photoautotrophe Organismen im Süßwasser können das Verwitterungsprodukt Bikarbonat nutzen, um Kohlenstoff herzustellen, eine weitere Kohlenstoffsenke. Diese gekoppelte biologische Kohlstoffpumpe (BCP) stellt möglicherweise einen Grossteil des fehlenden Anteils an der Kohlenstoffsenke dar.Aufgrund der schnellen Lösungskinetik der Kalklösung reagiert die Karbonatverwitterung schnell auf Umwelteinflüsse wie dem Klimawandel und der Änderung der Landnutzung. Es ist daher essentiell, die Karbonatverwitterung besser zu verstehen, um zukünftige Klimaänderungen besser vorherzusagen. Diese kumulative Doktorarbeit stellt im Zentralteil vier Veröffentlichungen vor, die Mechanismen und Variationen der Karbonatverwitterung beschreiben. Die Karbonatverwitterung als Kohlenstoffsenke braucht ein besseres Verständnis der Reaktion des Verwitterungsprozesses aufgrund von natürlichen Änderungen im Klimasystem. In der ersten Publikation werden deshalb drei verschiedene Einzugsgebiete vorgestellt auf verschiedenen Klimabereichen. Die Ergebnisse zeigen einen Einfluss sowohl von Klima- als auch von Vegetationsänderungen, Die einen gegenteiligen Einfluss auf die Karbonatlösung haben. Vor allem die Abflussmenge kontrolliert den Betrag der Kohlenstoffsenke. In der zweiten Publikation werden drei verschiedene Boden-CO2-Modelle betrachtet und mit dem Chemismus von Quellschüttungen verglichen. Hier stellt sich heraus das die „net primary production“ am besten die Variabilität der Bikarbonat-Variation beschreiben kann. Demnach kontrolliert der Oberflächenabfluss den Betrag der Kohlenstoffsenke am stärksten. In einer dritten Publikation wird mit Hilfe der Quellschüttungsdaten ein neues Modell entwickelt, dass heutige und zukünftige Karbonatverwitterung beschreiben kann. Aus dem Modell lassen sich Anstiege des Kohlenstoffflusses von +9.8% bis +17.1% ableiten für den Zeitraum 1950-2100. Dieser Anstieg findet im Wesentlichen im niedrigen Breiten statt, so dass hier eine Landnutzungsänderung als möglicher Eingriff in die zukünftige Klimaentwicklung in Betracht gezogen werden kann. In einer vierten Publikation werden verschiedene Landnutzungsszenarien in einem Feldlabor nachgestellt. Hier lassen sich Rückschlüsse sowohl auf dem Kohlenstoffkreislauf als auch zum Effekt der biologischen Kohlenstoffpumpe quantifizieren. Die Ergebnisse dieser Doktorarbeit zeigen ein Feedback zwischen natürlichen Klimavariationen und anthropogenen Landnutzungsänderungen einerseits und der Karbonatverwitterung andererseits. Während ein globaler Temperaturanstieg den Betrag der Karbonatverwitterung limitiert, können Landnutzungsänderungen zu einer Erhöhung der Karbonatverwitterung führen. Auch die biologische Kohlenstoffpumpe führt zu einem Anstieg der Karbonatverwitterung