Les activités anthropiques affectent les cycles biogéochimiques globaux, principalement par l'ajout de nutriments dans les écosystèmes. Il est donc crucial de déterminer dans quelle mesure les cycles biogéochimiques globaux peuvent être régulés. Les autotrophes peuvent réguler les réservoirs de nutriments par la consommation des ressources, mais la majorité des ressources leur sont inaccessibles à l'échelle globale. Par des modèles théoriques, nous avons cherché à évaluer la manière dont les autotrophes répondent à la fertilisation à l'échelle globale et leur capacité à réguler les concentrations des nutriments quand leur accessibilité est limitée. Nous avons également étudié les mécanismes qui déterminent la régulation des rapports de Redfield dans l'océan, ainsi que les effets de l'ajout de nutriments sur la production primaire océanique totale. Nous avons montré que les organismes ne régulent pas efficacement les réservoirs de nutriments. Le couplage des cycles biogéochimiques et la compétition entre groupes fonctionnels peuvent altérer, négativement ou positivement, la régulation des cycles biogéochimiques globaux par les organismes. Une régulation inefficace des concentrations de nutriments n'exclut par contre pas une forte régulation des rapports entre ces nutriments, comme dans le cas des rapports de Redfield. La fertilisation des écosystèmes terrestres et océaniques risque donc de fortement impacter la production primaire et les cycles biogéochimiques globaux, à de courtes comme à de grandes échelles de temps. / Anthropogenic activities heavily impact global biogeochemical cycles, mainly through nutrient fertilisation of ecosystems; thus it is crucial to assess the extent to which global biogeochemical cycles are regulated. Autotrophs can regulate nutrient pools locally through resource consumption, but most resources are inaccessible to them at global scales. We used theoretical models to assess how organisms respond nutrient fertilisation at global scales and how they can regulate the concentration of these nutrients when their accessibility of is limited. We further investigated the mechanisms driving the regulation of Redfield ratios in oceans, and the effects of nutrient fertilisation on total oceanic primary production. We showed that organisms cannot efficiently regulate nutrient pools. Mechanisms such as coupling of nutrient cycles and competition between functional groups can alter the strength of biotic regulation of global biogeochemical cycles, either positively or negatively. An inefficient regulation of inaccessible nutrient concentration, however, does not exclude a strong biotic regulation of nutrient ratios, as is the case with Redfield ratios in oceans. Nutrient fertilization of oceanic and terrestrial ecosystems is thus likely to have a strong impact on primary production and global nutrient cycles at both small and long timescales.

Dans cette thèse nous avons simulé la distribution d’éléments traces en Méditerranée, dans le but de mieux contraindre la circulation thermohaline et les cycles biogéochimiques. Pour cela, nous avons utilisé le modèle dynamique à haute résolution NEMO-MED12 couplé avec le modèle de biogéochimie marine PISCES.La Méditerranée offre un cadre particulièrement attrayant pour l’étude des traceurs géochimiques. Il s’agit d’une mer semi-fermée, ce qui permet de mieux contraindre les différentes sources et puits des éléments (poussières atmosphériques, fleuves …). Plus particulièrement, nous avons modélisé le tritium (3H), traceur transitoire couramment utilisé pour l’étude de la variabilité interannuelle de la circulation thermohaline. Nous avons aussi simulé les isotopes de l’hélium (3He, 4He), traceurs conservatifs injectés par l’activité volcanique sous-marine et les sédiments, pour contraindre la circulation profonde. Nous nous sommes intéressés également à la composition isotopique du Néodyme (Nd), traceur permettant d’étudier les échanges de matière avec les marges continentales, ainsi qu’à la modélisation du radiocarbone (14C), qui permet d’avoir des informations uniques sur les variations de la circulation thermohaline et des processus de mélange sur les périodes récentes et passées.Cette ensemble de simulations nouvelles et la confrontation avec des observations récentes d’éléments traces issues de différents programmes d’observation (GEOTRACES, METEOR, PALEOMEX), a apporté une expertise nouvelle et supplémentaire sur la dynamique et les cycles biogéochimique en mer Méditerranée. Ce travail contribue à améliorer le modèle régional NEMO/Med12/PISCES développé pour ce bassin, apporte une expertise essentielle pour développer notre aptitude à prévoir l’évolution future de ce bassin sous la pression du changement anthropique. / Useful diagnostics of the ventilation of the ocean’s interior are derived from geochemical tracers characterized by simple boundary conditions at the ocean’s surface, and a conservative behavior in marine waters. In this thesis, we simulated explicitly some trace elements distribution in the Mediterranean to better constrain the thermohaline circulation and biogeochemical cycles. We used a high resolution physical/biogeochemical model NEMO-MED12-PISCES.The Mediterranean offers a particularly attractive setting for studying geochemical tracers. It’s a semi-enclosed basin, which makes it easier to quantify the various sources and sinks of the elements (atmospheric dust, rivers ...). In particular, we modeled tritium (3H), a transient tracer currently used for the study of the interannual variability of the thermohaline circulation. We also simulated helium isotopes (3He, 4He), useful tracers for investigating the deep ocean circulation.We have simulated the isotopic composition of neodymium (Nd), tracer adapted to investigate the exchanges between dissolved/particulate phases, with the continental margins, and to constrain the modern and paleo thermohaline circulation, as well as radiocarbon (14C), an ideal tracer for studying air-sea gas exchange and for assessing the ventilation rate of the deep water masses over very long timescales.This study is part of the work carried out to assess the robustness of the NEMO-MED12 model, which will be used to study the evolution of the climate and its effect on the biogeochemical cycles in the Mediterranean Sea, and to improve our ability to predict the future evolution of the Mediterranean Sea under the increasing anthropogenic pressure.

Indiana University-Purdue University Indianapolis (IUPUI) / The focus of this study was to document phosphorus (P) and metal cycling in the Eagle Creek Reservoir (ECR), located in Indianapolis, central Indiana. Eagle Creek Reservoir serves the drinking water needs of over 80,000 residents. Within the last several years, algal blooms have created stress to the local treatment facility. The objective of this study was to examine how P cycling from oxygen deprived bottom sediments affects the algal bloom productivity. As such, cores were retrieved from different water depths (7 and 16 m) from portions of the reservoir where high surficial concentrations of organic matter and P were found to occur. The dried samples were analyzed for P, sulfur, iron, barium, cadmium, copper, lead, and zinc, using a strong acid digestion technique. The samples were also analyzed for iron-bound P (Fe-P), authigenic P (A-P), detrital P (D-P), organic P (O-P), reducible iron, and reducible manganese, using a sequential extraction technique. The results from the study showed moisture contents ranged from 16 to 76% and organic matter contents ranged from 2 to 12 wt%. The dry bulk densities were determined to be between 0.27 and 1.68 g cm3. The average percentages of P in ECS-1, as determined by the sequential extraction method, were as follows: Fe-P, 66.2%; A-P, 8.1%; D-P, 4.8%; and O-P, 20.9%. The average percentages of P in ECS-3, as determined by the sequential extraction method, were as follows: Fe-P, 77.0%; A-P, 6.5%; D-P, 2.8%; and O-P, 16.7%. To determine relationships between elements, correlations were calculated. When looking as the relationships between the P fractions and reducible Fe, differences were observed between the different water depths. There was less correlation between reducible Fe and Fe-P, and between O-P and Fe-P, in ECS-3, indicating that Fe-P is more efficiently dissolved and recycled in the deep portion of ECR. The study shows that the Fe-P flux, caused by the iron redox cycle, is persistent and will continue to influence algal bloom productivity in the deeper portions of ECR.

Thesis: Ph. D., Joint Program in Chemical Oceanography (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2014. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references. / The great geologic and climatic diversity of the Fraser River basin in southwestern Canada render it an excellent location for understanding biogeochemical cycling of sediments and terrigenous organic carbon in a relatively pristine, large, temperate watershed. Sediments delivered by all tributaries have the potential to reach the ocean due to a lack of main stem lakes or impoundments, a unique feature for a river of its size. This study documents the concentrations of a suite of dissolved and particulate organic and inorganic constituents, which elucidate spatial and temporal variations in chemical weathering (including carbonate weathering in certain areas) as well as organic carbon mobilization, export, and biogeochemical transformation. Radiogenic strontium isotopes are employed as a tracer of sediment provenance based on the wide variation in bedrock age and lithology in the Fraser basin. The influence of sediments derived from the headwaters is detectable at the river mouth, however more downstream sediment sources predominate, particularly during high discharge conditions. Bulk radiocarbon analyses are used to quantify terrestrial storage timescales of organic carbon and distinguish between petrogenic and biospheric organic carbon, which is critical to assessing the role of rivers in long-term atmospheric CO2 consumption. The estimated terrestrial residence time of biospheric organic carbon in the Fraser basin is 650 years, which is relatively short compared to other larger rivers (Amazon, Ganges-Brahmaputra) in which this assessment has been performed, and is likely related to the limited floodplain storage capacity and non-steady-state post-glacial erosion state of the Fraser River. A large portion of the dissolved inorganic carbon load of the Fraser River (>80%) is estimated to derive from remineralization of dissolved organic carbon, particularly during the annual spring freshet when organic carbon concentrations increase rapidly. This thesis establishes a baseline for carbon cycling in a largely unperturbed modern mid-latitude river system and establishes a framework for future process studies on the mechanisms of organic carbon turnover and organic matter-mineral associations in river systems. / by Britta Marie Voss. / Ph. D.

Tesis por compendio / [ES] El nitrógeno (N) es uno de los elementos más importantes para la vida, pero el desequilibrio provocado sobre el ciclo del N está causando daños importantes a muchos ecosistemas en todo el mundo. En aguas costeras, los procesos del N se ven alterados por fertilizantes, la urbanización o la producción de energía. El objetivo principal de esta tesis es contribuir a la evaluación de cómo la actividad antropogénica y el cambio climático modifican la dinámica del N en aguas costeras. Con este propósito se seleccionaron dos lugares de estudio: la demarcación hidrográfica del Júcar (JRBD) en el Noroeste del Mar Mediterráneo y la Región Hidrológica del Golfo Central (CGHR) al Sur del Golfo de México. La tesis se presenta como una colección de cuatro artículos. El primer artículo evalúa cómo la nitrificación en aguas costeras es alterada por las presiones antropogénicas y en asentamientos urbanos en el JRBD. Mediante la aplicación de un modelo biogeoquímico simple que simula la dinámica del nitrito en nueve áreas costeras, se evaluó el desacoplamiento de los dos pasos de la nitrificación. Las conclusiones indican que las presiones antropogénicas modifican los picos de nitrito en invierno debido a las bajas temperaturas y que el segundo paso de la nitrificación es más sensible a la temperatura, lo que implica que el cambio climático puede contribuir al desacoplamiento. El segundo artículo evalúa las tendencias del nitrógeno inorgánico disuelto (NID) por el cambio climático en el JRBD. El efecto de las variables meteorológicas en las concentraciones de NID se estudió mediante la aplicación de redes neuronales artificiales simples entrenadas con datos de campo. Se observaron tendencias decrecientes de nitrito y nitrato a lo largo del siglo XXI bajo los escenarios climático RCP 4.5 y RCP 8.5, debido al aumento de las temperaturas y a la disminución de las precipitaciones, con cambios más significativos en invierno. El amonio no mostró ninguna tendencia anual significativa, pero se observaron aumentos o disminuciones durante algunos meses. En el tercer artículo se desarrolla un nuevo método basado en teoría de sistemas grises y entropía de Shannon para obtener información útil sobre la contaminación por N en áreas donde los datos disponibles son limitados. El método se aplicó a ocho estuarios del CGHR asociados a manglares. Se desarrollaron dos índices: el índice gris de prioridad de gestión de nitrógeno (GNMP) y el índice gris de presión de uso del suelo (GLUP). Ambos fueron comparados para validar la metodología y los resultados indican que la urbanización sobre playas y manglares es la principal causa de la contaminación de N. El cuarto artículo es un análisis espaciotemporal de la contaminación de N a lo largo de dos ríos que desembocan en una zona turística del CGHR asociada a manglares. Mediante técnicas estadísticas como el análisis de cluster, la prueba de MannKendall y la prueba W de MannWhitney, se realizó una evaluación del origen de la contaminación de N y las variaciones temporales de los compuestos de N. Los resultados concluyen que las concentraciones de N orgánico están aumentando a lo largo de la costa, y la principal fuente identificada fue la descomposición de la especie invasora de jacintos de agua en aguas salinas, que ha cubierto completamente las playas y manglares circundantes potenciado por la contaminación de N. El conjunto de la investigación concluye que tanto la contaminación como el cambio climático alteran el ciclo del N en aguas costeras al modificar elementos importantes del N como la nitrificación, las variaciones interanuales de las concentraciones de N o los ecosistemas costeros. Las diferencias en las características ecológicas y socioeconómicas de las dos zonas de estudio desempeñaron un papel decisivo en las presiones e impactos de las actividades antropogénicas. Además, los métodos desarrollados pueden aplicar / [CAT] El nitrogen (N) és un dels elements més importants per a la vida, però el desequilibri provocat sobre el cicle del N està causant danys importants a molts ecosistemes. En aigües costaneres els processos del N es veuen alterats per fertilitzants, el desenvolupament urbà o la producció d'energia. L'objectiu principal d'aquesta investigació és contribuir a l'avaluació de com l'activitat antropogénica i el canvi climàtic modifiquen la dinàmica del N en aigües costaneres. Amb aquest propòsit es van seleccionar dos llocs d'estudi: la demarcació hidrogràfica del Xúquer (JRBD) al Nord-oest de la Mar Mediterrània i la Regió Hidrològica del Golf Central (CGHR) al Sud del Golf de Mèxic. La tesi es presenta com una col·lecció de quatre articles. El primer article avalua com la nitrificació en aigües costaneres es veu alterada per les pressions antropogèniques i prop dels assentaments urbans en el JRBD. Mitjançant l'aplicació d'un model biogeoquímic que simula la dinàmica del nitrit a nou àrees costaneres, es va avaluar el desacoblament dels dos passos de la nitrificació. Les conclusions indiquen que les pressions antropogèniques modifiquen els pics de nitrit observats a l'hivern a causa de les baixes temperaturas i que el segon pas de la nitrificació és més sensible a la temperatura, la qual cosa implica que el canvi climàtic pot contribuir al desacoblament d'aquests dos passos. El segon article avalua les tendències futures de nitrogen inorgànic dissolt (NID) pel canvi climàtic en el JRBD. L'efecte de les variables meteorològiques en les concentracions de NID es va estudiar mitjançant l'aplicació de xarxes neuronals artificials simples entrenades amb dades de camp. Es van observar tendències decreixents de nitrits i nitrats al llarg del segle XXI sota els escenaris climàtics RCP 4.5 i RCP 8.5, a causa de l'augment de les temperatures i a la disminució de les precipitacions, amb canvis més significatius a l'hivern. L'amoni no va mostrar cap tendència anual significativa, però es van observar augments o disminucions durant alguns mesos. En el tercer article es desenvolupa un nou mètode basat en la teoria dels sistemes grisos i l'entropia de Shannon per a obtindre informació útil sobre la contaminació per N en àrees on les dades disponibles són limitats. El mètode es va aplicar a huit estuaris del CGHR associats a manglars. Es van desenvolupar dos índexs: l'índex gris de prioritat de gestió de nitrogen (GNMP) i l'índex gris de pressió d'ús de la terra (GLUP). Els dos van ser comparats per a validar la metodologia. Els resultats indiquen que el desenvolupament urbà sobre platges i manglars és la principal causa de la contaminació de N en l'àrea d'estudi. El quart article és una anàlisi espacio-temporal de la contaminació de N al llarg de dues rius que desemboquen en una zona turística costanera del CGHR associada a manglars. Mitjançant tècniques estadístiques com l'anàlisi de clúster, les proves MannKendall i W de MannWhitney, es va realitzar una avaluació de l'origen de la contaminació de N i les variacions temporals dels compostos de N. Els resultats conclouen que les concentracions de N orgànic estan augmentant al llarg de la costa, i la principal font identificada va ser la descomposició de l'espècie invasora de jacints d'aigua en aigües salines, que ha cobert completament les platges i manglars circumdants potenciat per la contaminació de N. El conjunt de la investigació conclou que tant la contaminació com el canvi climàtic alteren el cicle del N en aigües costaneres en modificar els processos del N com la nitrificació, les variacions interanuals de les concentracions de N i la destrucció dels ecosistemes costaners. Les diferències en les característiques ecològiques i socioeconòmiques de les dues zones d'estudi van exercir un paper decisiu en les pressions i impactes de les activitats antropogèniques. A més, els mètodes desenvolupats poden / [EN] Nitrogen (N) is one of the most important elements for life on Earth, but the unbalance caused to the N cylce is causing dramatic damage to many ecosystems around the world. In coastal waters, the N processes are altered by anthropogenic activities such as the excessive use of fertilizers, urban development or energy production. The main objective of this research is to contribute to the evaluation of how anthropogenic activities and climate change modify the N dynamics in coastal waters. For this purpose, two study sites were selected: the Jucar River Basin District (JRBD) in the Northwestern Mediterranean Sea (Spain) and the Central Gulf Hydrological Region (CGHR) in the Southern Gulf of Mexico (Mexico). The thesis is presented as a collection of four research articles. The first article evaluates how nitrification in coastal waters is altered by anthropogenic pressures and close to urban settlements in the JRBD. Through the application of a simple biogeochemical model that simulates nitrite dynamics to nine coastal areas, an evaluation of the decoupling of the two steps of nitrification was carried out. The main conclusions indicate that anthropogenic pressures modify the nitrite peaks observed in winter driven by low temperatures. The research also concludes that the second step of nitrification is more sensitive to temperature, which entails that climate change may contribute to the decoupling. The second article evaluates the future trends of dissolved inorganic nitrogen (DIN) concentrations under climate change in the JRBD. The effect of meteorological variables on DIN concentrations was studied through the application of simple artificial neural networks trained with field data. Decreasing trends of nitrite and nitrate concentrations were observed throughout the 21st century under both climatic scenarios RCP 4.5 and RCP 8.5, mainly due to rising temperatures and decreasing rainfall, with major changes expected in winter. On the other hand, ammonium did not show any significant annual trend but it either increased or decreased during some months. The third article develops a new method based on grey systems theory and Shannon entropy to derive useful information regarding N pollution in areas where only limited data is available. The method was applied to eight estuaries of the CGHR associated to mangroves. Two indexes were developed: the Grey Nitrogen Management Priority (GNMP) index and the Grey Land Use Pressure (GLUP) index. The two indexes were then confronted to validate the methodology. The results indicate that the urban development over beaches and mangroves is the leading cause of N pollution in the study area. The fourth article is a spatiotemporal analysis of N pollution along two rivers discharging into a touristic coastal area of the CGHR associated to mangroves. Through statistical techniques such as clustering analysis, the Mann-Kendall test and the Mann-Whitney W-test, an evaluation of the origine of N pollution and the temporal variations of the N compounds was performed. The results conclude than organic N concentrations are increasing along the coast, and the main potential source identified was the decomposition of the invasive species of water hyacinths in saline waters, which has completely covered the surrounding beaches and mangroves, enhanced by N pollution. Overall, the main conclusions are that both pollution and climate change alter the N cycle in coastal waters by modifying N processes such as nitrification, the interannual variations of N concentrations and by destroying the coastal ecosystems. The differences in ecological and socio-economic characteristics of the two study sites played a significant role in the pressures and impacts of anthropogenic activities. Moreover, the methods developed can be applied to other coastal regions to evaluate the anthropogenic alteration of the N cycle worldwide. / This thesis was carried out with an international cotutelle between the Polytechnic University of Valencia in Spain and the Veracruzan University in Mexico. This thesis has been financed by the following scholarships: - Erasmus Mundus - MAYANET Grant Agreement Number 2014-0872/001 - 001, funded with support from the European Commission. - Cotutelle PhD scholarship granted by the Universitat Politècnica de València. - Excellence Scholarship awarded by the Mexican Government through the Mexican Agency for International Development Cooperation (AMEXCID) / Temiño Boes, R. (2020). Anthropogenic alteration of the nitrogen cycle in coastal waters: Case studies from the Mediterranean Sea and the Gulf of Mexico [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/158560 / Compendio

Le but général de ce travail fut de quantifier la silice biogène (BSiO2) dans les sédiments du continuum de l'Escaut (estuaire – zone côtière), ainsi que son taux de recyclage - rétention. Le coefficient de diffusion moléculaire de la DSi a été déterminé pour différentes valeurs de température et deux salinités et une relation empirique reliant le coefficient de diffusion à la température et à la viscosité de la solution a été établie. La distribution longitudinale de la BSiO2 dans les sédiments de surface, ainsi que les profils verticaux de BSiO2 et de silice dissoute ont été déterminés durant différentes saisons en 2004 et 2005. Les flux de DSi ont été également estimés via des expériences d’incubations et par modélisation des profiles verticaux de DSi. Des expériences de dissolution des sédiments ont permis de déterminer (via modélisation) les constantes cinétiques de vitesse de la BSiO2 et une première évaluation du taux de recyclage de la BSiO2 (5 – 70%). Sur base des calculs à partir des profiles de DSi dans l’eau interstitielle, le taux de recyclage de la BSiO2 varie entre 8 et 92% dans l’estuaire, ce qui correspond à une rétention moyenne de la BSiO2 supérieure à 60%, et souligne ainsi l'efficacité du filtre estuarien par rapport à la silice. En revanche, le recyclage de BSiO2 dans la zone côtière apparaît comme très intensif, avec des valeurs souvent supérieures à 40%. Ces résultats montrent l'importance d'inclure les estuaires dans le calcul des budgets globaux de Si. / The general objective of this study was to quantify the BSiO2 in the sediments of the Scheldt continuum, together with its recycling and retention in this area. First an empirical relation linking the diffusion coefficient of DSi to temperature and salinity was determined, via diffusion experiments. The longitudinal BSiO2 distribution in surface sediments and the vertical BSiO2 and DSi profiles in sediment cores where then measured during 2 years and different seasons, together with other parameters characterizing pore waters, such as alkalinity, pH, sulphate… DSi fluxes were also estimated either directly through whole core incubations measurements or via modelling of interstitial water profiles. BSiO2 dissolution experiments allowed the evaluation of the kinetic rate constants also through modelling of the results, and gave preliminary information over the BSiO2 recycling rates (5 – 70%). The recycling rate as obtained from pore water profiles vary between 8 and 92%, with an average value of about 32%, which highlights the importance of the estuarine filter for silica. Recycling is much more intense in the coastal area, with values up to 40%, which we explain by higher salinity and higher sediment permeability. The different experiments and results also indicated that secondary mineral precipitation might be and important process affecting BSiO2 in the Scheldt sediments.<p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Indiana University-Purdue University Indianapolis (IUPUI) / Numerous studies have investigated the fate of pollutants in riparian buffers, but few studies have focused on the control of multiple contaminants simultaneously in riparian zones. To better understand what drives the biogeochemical cycles of multiple contaminants in riparian zones, a 19-month study was conducted in riparian buffers across a range of hydrogeomorphic (HGM) settings in the White River watershed in Indiana. Three research sites [Leary Webber Ditch (LWD), Scott Starling (SS) and White River (WR)] with contrasting hydro-geomorphology were selected. We monitored groundwater table depth, oxidation reduction potential (ORP), dissolved oxygen (DO), dissolved organic carbon (DOC), NO3-, NH4+, soluble reactive phosphorus (SRP), SO42- , total Hg and methylmercury (MeHg). Our results revealed that differences in HGM conditions translated into distinctive site hydrology, but significant differences in site hydrology did not lead to different biogeochemical conditions. Nitrate reduction and sulfate re-oxidation were likely associated with major hydrological events, while sulfate reduction, ammonia and methylmercury production were likely associated with seasonal changes in biogeochemical conditions. Results also suggest that the LWD site was a small sink for nitrate but a source for sulfate and MeHg, the SS site was a small sink for MeHg but had little effect on NO3-, SO42- and SRP, and the WR was an intermediate to a large sink for nitrate, an intermediate sink for SRP, and a small source for MeHg. Land use and point source appears to have played an important role in regulating solute concentrations (NO3-, SRP and THg). Thermodynamic theories probably oversimplify the complex patterns of solute dynamics which, at the sites monitored in the present study, were more strongly impacted by HGM settings, land use, and proximity to a point source.