O presente estudo visou reconstruir o histórico de impactos antrópicos na bacia de drenagem do Lago das Garças durante o século XX por meio da deposição de contaminantes no compartimento sedimentar. O Lago das Garças está localizado em uma unidade de conservação, Parque Estadual das Fontes do Ipiranga (PEFI), inserida em área altamente povoada e urbanizada da cidade de São Paulo. Dois testemunhos de sedimento (LG05-03 e LG05-04, com 70 cm e 65 cm, respectivamente) foram amostrados mediante auxílio de mergulhadores no ponto mais profundo do reservatório, sendo, posteriormente, fatiados a cada 1 cm. Em LG05-03 foram quantificadas as distribuições verticais de carbono orgânico total (COT), nutrientes totais (NT e PT), hidrocarbonetos policíclicos aromáticos (HPA), hidrocarbonetos alifáticos (n-alcanos), bem como foi feita a classificação granulométrica. Em LG05-04 foi determinada a deposição de metais pesados (Co, Cr, Cu, Fe, Mn, Ni, Pb e Zn) e a geocronologia através do isótopo radioativo \'ANTPOT. 210 Pb\', usando o modelo CIC (Constant Initial Concentration). Os dados foram analisados por meio de análises estatísticas multivariadas (ACP: Análise de Componentes Principais). Com base nas tendências dos dados e na ACP, foi possível estabelecer três fases principais: Fase I: 64-43 cm (~1894-1975): caracterizada por baixas concentrações de nutrientes e contaminantes, sendo possível recuperar níveis préindustriais destes compostos, propostos como valores de referência regionais. Ainda, com base na razão C/N e em razões entre n-alcanos, notou-se, nesta fase o predomínio de aporte de matéria orgânica de origem alóctone; Fase II: 43-26 cm (~1975-1990): aumento abrupto das concentrações de metais pesados e HPA traçadores de veículos automotores, marcando o aumento da poluição atmosférica devido ao grande crescimento econômico do município e maior circulação de veículos na região. Ainda, foi observado aumento gradual das concentrações de NT e PT, atribuídos aos despejos de esgotos não tratados oriundos da Secretaria de Agricultura e Abastecimento e da Fundação Parque Zoológico; Fase III: 26-0 cm (~1990-2005): aumento mais acentuado das concentrações de nutrientes devido aos despejos de esgotos, acarretando em maior eutrofia do sistema, registrada pelo perfil do n-\'C IND.17\'. Pico das concentrações de HPA traçadores do uso de carvão mineral associado às atividades de uma siderúrgica vizinha (Siderúrgica J.L. Alipeti), bem como queda das concentrações destes traçadores coincidindo com mudanças no processo industrial da empresa. Ainda nesta fase notaram-se aumentos expressivos dos teores e fluxos dos HPA traçadores de veículos automotores, corroborando o cenário de aumento vertiginoso da frota de veículos na última década. Desse modo, este estudo contribuiu com o cenário nacional em termos de manejo de bacias hidrográficas urbanas, incluindo registros desde a época pré-revolução industrial no Brasil (~1894) até os dias atuais, demonstrando o potencial do uso de testemunhos lacustres no resgate de informações relativas à contaminação de ecossistemas aquáticos associadas às atividades antropogênicas. / Present study aimed to reconstruct the human impact history on the Garças Lake Drainage Basin during the 20th Century based on contaminants deposition on the lacustrine sediment. Garças Lake is located in a preservation area, the Parque Estadual das Fontes do Ipiranga (PEFI), located in a highly populated urban area within the city of São Paulo. Two sediment cores (LG05-03 and LG05-04, 70 cm and 65 cm long) were sampled by divers at the deepest site of the lake, which were sliced at 1 cm intervals. Information for LG05-03 included total organic carbon (TOC), total nutrients (TN and TP), polycyclic aromatic hydrocarbons (PAHs), aliphatic hydrocarbons (n-alkanes) and grain size vertical distributions. Deposition of heavy metals (Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn) and the geocronology by \'ANTPOT. 210 Pb\', using CIC model (Constant Initial Concentration), were determined in LG05-04. Data were analyzed by multivariate statistic analysis (PCA, principal components analysis). Based on data trends and PCA, it was possible to recognized three main phases: Phase I: 64-43 cm (~1894-1975) characterized by low nutrients and contaminants concentrations, allowing retrieving preindustrial levels of these compounds, which are proposed as regional reference values. Besides, C/N ratio and n-alkanes ratios demonstrated aloctonous organic matter predominance; Phase II: 43-26 cm (~1975-1990) characterized by the abrupt increase of heavy metals and vehicular PAHs concentration, indicating the atmospheric pollution increase, due to the great economic rise experienced by the city of São Paulo over that time and the higher vehicles circulation in the region. Yet, it was observed a gradual increase in nutrient concentration attributed to the untreated sewage inputs from the São Paulo State Department of Agriculture and Provisioning headquarters and the city Zoo; Phase III: 26-0 cm (~1990-2005) characterized by a marked increase in nutrient concentration related to the untreated sewage inputs, leading to the increase of eutrophication, as registered by the n-\'C IND.17\' distribution. A peak of coal PAHs concentration was also noticed, related to a neighbor steel mill (J.L. Aliperti), followed by a subsequent decrease of these compounds, coincident with industrial procedures changes. Besides, there was an expressive increase in vehicular PAHs concentrations, corroborating the scenery of a drastic raise of vehicles in the last decade. The present study contributed to the national scenario towards urban drainage basin management. It included records since preindustrial time (~1894) up to the present, highlighting the potential use of lacustrine sediment on the retrieval of historical environmental changes of aquatic ecosystems and associated anthropogenic impacts.

Ce travail de thèse a permis de reconstituer la dynamique à long terme de deux écosystèmes lacustres alpins dans les Alpes du sud grâce à l’étude (1) de la variabilité tardi-holocène des paramètres physico-chimiques de l’eau, des niveaux lacustres et des dynamiques de communautés aquatiques, et (2) des types de réponse de ces environnements à des perturbations externes en lien avec les changements du bassin versant et du climat. Les deux séquences sédimentaires prélevées par carottage au lac d’Allos et au lac Petit (Massif du Mercantour, 2200 m) ont permis de reconstituer en détail l’évolution des écosystèmes lacustres depuis les derniers 13,500 cal. BP grâce à trois grands volets : (1) l’étude de fossiles d’espèces aquatiques indicatrices des conditions de vie dans le milieu lacustre (les diatomées et les ostracodes) ; (2) l’analyse des isotopes de l’oxygène contenus dans ces mêmes fossiles afin de reconstituer un signal paléohydrologique ; (3) une comparaison multi-proxy permettant de mettre en lien les changements de l’écosystème lacustre avec les dynamiques du bassin versant. Les résultats obtenus et leur confrontation à un cadre multidisciplinaire très documenté ont permis d’évaluer l’importance première des processus érosifs et des modifications du couvert végétal sur la dynamique lacustre, au travers de changements majeurs dans les communautés aquatiques et les niveaux trophiques. Enfin, les données isotopiques mesurées sur les fossiles de diatomées et d’ostracodes ont mis en évidence des variations paléohydrologiques inédites pour la région : cette approche, novatrice ouvre la perspective d’une reconstitution paléoclimatique de référence pour les Alpes du sud. / The thesis is devoted to the reconstruction of long-term changes in two lacustrine ecosystems in the Southern Alps. This study aims at assessing (1) the lateglacial-holocene variability of water physico-chemistry, lake levels and aquatic species dynamics; and (2) the environmental responses of the lacustrine ecosystem to external forcing (watershed and climate changes), with the study of Lake Allos and the Lake Petit (Mercantour National Park, 2200 m a.s.l). The two sedimentary cored profiles provided a detailed record of the past lacustrine dynamics since 13.500 cal. BP. An integrative approach was carried out including (1) the study of fossils of aquatic bioindicators species (diatoms and ostracods) informing about changes in lacustrine living conditions ; (2) the analysis of oxygen isotopes recorded by these aquatic fossils tracing a palaeohydrological signal ; (3) a multiproxy comparison linking the aquatic environment with changes in watershed dynamics. These results integrated into a rich multidisciplinary framework evidenced the major role of erosion processes and changes in vegetation cover as factors triggering lake responses to disturbance, with concomitant changes in aquatic communities and trophic levels at several timescales. The different geological settings and lake morphologies have also played a significant role, modulating changes in benthic and planktonic aquatic communities over long time periods. Finally, oxygen isotopes records allow to trace for the first time palaeohydrological changes in the region: this innovative approach represents an original outcome for reconstructing a reference past climate for the Southern Alps.

No description available.

Spatial and temporal information on catchment sediment sources and sinks can provide an improved understanding of catchment response to human-induced disturbances. This is essential for the implementation of well-targeted catchment-management decisions. This thesis investigates the nature and timing of catchment response to human activities by examining changes in sediment sources and sinks in a dry-tropical subcatchment of the Great Barrier Reef (GBR) catchment area, in northeastern Australia. Changes in catchment sediment sources, both in terms of spatial provenance and erosion type, are determined using sediment tracing techniques. Results indicate that changes in sediment source contributions over the last 250 years can be linked directly to changes in catchment land use. Sheetwash and rill erosion from cultivated land (40-60%) and channel erosion from grazed areas (30-80%) currently contribute most sediment to the river system. Channel erosion, on a basin-wide scale, appears to be more important than previously considered in this region of Australia. Optically stimulated luminescence and 137Cs dating are used to determine pre-and post- European settlement (ca. 1850) alluvial sedimentation rates. The limitations of using 137Cs as a floodplain sediment dating tool in a low fallout environment, dominated by sediment derived from channel and cultivation sources, are identified. Low magnitude increases in post-disturbance floodplain sedimentation rates (3 to 4 times) are attributed to the naturally high sediment loads in the dry-tropics. These low increases suggest that previous predictions which reflect order of magnitude increases in post-disturbance sediment yields are likely to be overestimates. In-channel bench deposits, formed since European settlement, are common features that appear to be important stores of recently eroded material. The spatially distributed erosion/sediment yield model SedNet is applied, both with generic input parameters and locally-derived data. Outputs are evaluated against available empirically-derived data. The results suggest that previous model estimates using generic input parameters overestimate post-disturbance and underestimate predisturbance sediment yields, exaggerating the impact of European catchment disturbance. This is likely to have important implications for both local-scale and catchment-wide management scenarios in the GBR region. Suggestions for future study and the collection of important empirical data to enable more accurate model performance are made.

Spatial and temporal information on catchment sediment sources and sinks can provide an improved understanding of catchment response to human-induced disturbances. This is essential for the implementation of well-targeted catchment-management decisions. This thesis investigates the nature and timing of catchment response to human activities by examining changes in sediment sources and sinks in a dry-tropical subcatchment of the Great Barrier Reef (GBR) catchment area, in northeastern Australia. Changes in catchment sediment sources, both in terms of spatial provenance and erosion type, are determined using sediment tracing techniques. Results indicate that changes in sediment source contributions over the last 250 years can be linked directly to changes in catchment land use. Sheetwash and rill erosion from cultivated land (40???60%) and channel erosion from grazed areas (30-80%) currently contribute most sediment to the river system. Channel erosion, on a basin-wide scale, appears to be more important than previously considered in this region of Australia. Optically stimulated luminescence and 137Cs dating are used to determine pre-and post- European settlement (ca. 1850) alluvial sedimentation rates. The limitations of using 137Cs as a floodplain sediment dating tool in a low fallout environment, dominated by sediment derived from channel and cultivation sources, are identified. Low magnitude increases in post-disturbance floodplain sedimentation rates (3 to 4 times) are attributed to the naturally high sediment loads in the dry-tropics. These low increases suggest that previous predictions which reflect order of magnitude increases in post-disturbance sediment yields are likely to be overestimates. In-channel bench deposits, formed since European settlement, are common features that appear to be important stores of recently eroded material. The spatially distributed erosion/sediment yield model SedNet is applied, both with generic input parameters and locally-derived data. Outputs are evaluated against available empirically-derived data. The results suggest that previous model estimates using generic input parameters overestimate post-disturbance and underestimate pre-disturbance sediment yields, exaggerating the impact of European catchment disturbance. This is likely to have important implications for both local-scale and catchment-wide management scenarios in the GBR region. Suggestions for future study and the collection of important empirical data to enable more accurate model performance are made.

SUMMARY Communities of epigeic beetles were studied on two water catchments with the different management in the submontaneous area of Bohemian Forest (South Bohemia, Czechia). The Mlýnský stream catchment was characteristic by high representation of unforested habitats (pastures and mowed meadows), Horský stream by higher proportion of forested habitats and non equal management (plots without management, mowed meadows). The microclimatic characteristics (average temperature, average humidity, average wind speed, average radiation) were measured. The method of pitfall trapping was used for beetle sampling. Beetles species were divided into two groups after its preferences to humidity: hygrophilous species and mesophilous species. The degree of human impact was studied by finding of frequency of species of different ecological groups. 57 species was found in the Mlýnský stream and 33 in the Horský stream. The activity of beetles was about five times higher in Mlýnský stream (511 individuals captured) than in the Horský stream (114 indivuduals found). Ubiquitous species prevail in Mlýnský stream and adaptive species in the Horský stream. Stenotopic species were found in the Mlýnský stream only. These results indicate less human impact in Horský stream than in the Mlýnský stream. Frequency of beetle species with the different requirement on the humidity in communites on studied plots indicates the dominance of mesophilous species in Mlýnský stream in comparison with Horský stream. Frequency of hygrophilous species was about three times higher in Horský stream than in Mlýnský stream. The intensity of management affected the beetle structure mainly on the less forested plot of Mlýnský stream. The structure of communites on plots with more intensive management differs from communities on plots with low management. Hygrophilous species prevail on plots with low management of the Mlýnský stream. The effect of management intensity is not documented in Horský stream with the greater proportion of trees.

Communities of epigeic beetles were studied on two water catchments with the different management in the submontaneous area of Bohemian Forest (South Bohemia, Czechia). The Mlýnský stream catchment was characteristic by high representation of unforested habitats (pastures and mowed meadows), Horský stream by higher proportion of forested habitats and non equal management (plots without management). The biomass characteristics (above ground and dry) were measured on studied plots. The method of pitfall trapping was used for beetle sampling. Beetle species were divided into two groups after its preferences to shaded: species occurring in unshaded habitats and species occurring in shaded habitats. The degree of human impact was studied by finding of frequency of species of different ecological groups. The above ground biomass was about 2 time higher in Mlýnský stream than in the Horský stream. The dry biomass was practically the same. 57 species was found in the Mlýnský stream and 33 in the Horský stream. The activity of beetles was about five times higher in Mlýnský stream than in the Horský stream. Ubiquitous species prevail in Mlýnský stream and adaptive species in the Horský stream. Stenotopic species were found in the Mlýnský stream only. These results indicate less human impact in Horský stream than in the Mlýnský stream. Beetles prefering unsheded habitats slightly prevail in Mlýnský stream in comparison with Horský stream. Beetle species characteristical for shaded habitats occur in Horský stream in comparison with Mlýnský stream. The geographical exposition affected the beetle structure mainly in the less forested plot of Mlýnský stream. The structure of communites situated to the south differs from communities situated to the north in Mlýnský stream. The effect of exposition is not documented in Horský stream with the greater proportion of forested size.

O presente estudo visou reconstruir o histórico de impactos antrópicos na bacia de drenagem do Lago das Garças durante o século XX por meio da deposição de contaminantes no compartimento sedimentar. O Lago das Garças está localizado em uma unidade de conservação, Parque Estadual das Fontes do Ipiranga (PEFI), inserida em área altamente povoada e urbanizada da cidade de São Paulo. Dois testemunhos de sedimento (LG05-03 e LG05-04, com 70 cm e 65 cm, respectivamente) foram amostrados mediante auxílio de mergulhadores no ponto mais profundo do reservatório, sendo, posteriormente, fatiados a cada 1 cm. Em LG05-03 foram quantificadas as distribuições verticais de carbono orgânico total (COT), nutrientes totais (NT e PT), hidrocarbonetos policíclicos aromáticos (HPA), hidrocarbonetos alifáticos (n-alcanos), bem como foi feita a classificação granulométrica. Em LG05-04 foi determinada a deposição de metais pesados (Co, Cr, Cu, Fe, Mn, Ni, Pb e Zn) e a geocronologia através do isótopo radioativo \'ANTPOT. 210 Pb\', usando o modelo CIC (Constant Initial Concentration). Os dados foram analisados por meio de análises estatísticas multivariadas (ACP: Análise de Componentes Principais). Com base nas tendências dos dados e na ACP, foi possível estabelecer três fases principais: Fase I: 64-43 cm (~1894-1975): caracterizada por baixas concentrações de nutrientes e contaminantes, sendo possível recuperar níveis préindustriais destes compostos, propostos como valores de referência regionais. Ainda, com base na razão C/N e em razões entre n-alcanos, notou-se, nesta fase o predomínio de aporte de matéria orgânica de origem alóctone; Fase II: 43-26 cm (~1975-1990): aumento abrupto das concentrações de metais pesados e HPA traçadores de veículos automotores, marcando o aumento da poluição atmosférica devido ao grande crescimento econômico do município e maior circulação de veículos na região. Ainda, foi observado aumento gradual das concentrações de NT e PT, atribuídos aos despejos de esgotos não tratados oriundos da Secretaria de Agricultura e Abastecimento e da Fundação Parque Zoológico; Fase III: 26-0 cm (~1990-2005): aumento mais acentuado das concentrações de nutrientes devido aos despejos de esgotos, acarretando em maior eutrofia do sistema, registrada pelo perfil do n-\'C IND.17\'. Pico das concentrações de HPA traçadores do uso de carvão mineral associado às atividades de uma siderúrgica vizinha (Siderúrgica J.L. Alipeti), bem como queda das concentrações destes traçadores coincidindo com mudanças no processo industrial da empresa. Ainda nesta fase notaram-se aumentos expressivos dos teores e fluxos dos HPA traçadores de veículos automotores, corroborando o cenário de aumento vertiginoso da frota de veículos na última década. Desse modo, este estudo contribuiu com o cenário nacional em termos de manejo de bacias hidrográficas urbanas, incluindo registros desde a época pré-revolução industrial no Brasil (~1894) até os dias atuais, demonstrando o potencial do uso de testemunhos lacustres no resgate de informações relativas à contaminação de ecossistemas aquáticos associadas às atividades antropogênicas. / Present study aimed to reconstruct the human impact history on the Garças Lake Drainage Basin during the 20th Century based on contaminants deposition on the lacustrine sediment. Garças Lake is located in a preservation area, the Parque Estadual das Fontes do Ipiranga (PEFI), located in a highly populated urban area within the city of São Paulo. Two sediment cores (LG05-03 and LG05-04, 70 cm and 65 cm long) were sampled by divers at the deepest site of the lake, which were sliced at 1 cm intervals. Information for LG05-03 included total organic carbon (TOC), total nutrients (TN and TP), polycyclic aromatic hydrocarbons (PAHs), aliphatic hydrocarbons (n-alkanes) and grain size vertical distributions. Deposition of heavy metals (Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn) and the geocronology by \'ANTPOT. 210 Pb\', using CIC model (Constant Initial Concentration), were determined in LG05-04. Data were analyzed by multivariate statistic analysis (PCA, principal components analysis). Based on data trends and PCA, it was possible to recognized three main phases: Phase I: 64-43 cm (~1894-1975) characterized by low nutrients and contaminants concentrations, allowing retrieving preindustrial levels of these compounds, which are proposed as regional reference values. Besides, C/N ratio and n-alkanes ratios demonstrated aloctonous organic matter predominance; Phase II: 43-26 cm (~1975-1990) characterized by the abrupt increase of heavy metals and vehicular PAHs concentration, indicating the atmospheric pollution increase, due to the great economic rise experienced by the city of São Paulo over that time and the higher vehicles circulation in the region. Yet, it was observed a gradual increase in nutrient concentration attributed to the untreated sewage inputs from the São Paulo State Department of Agriculture and Provisioning headquarters and the city Zoo; Phase III: 26-0 cm (~1990-2005) characterized by a marked increase in nutrient concentration related to the untreated sewage inputs, leading to the increase of eutrophication, as registered by the n-\'C IND.17\' distribution. A peak of coal PAHs concentration was also noticed, related to a neighbor steel mill (J.L. Aliperti), followed by a subsequent decrease of these compounds, coincident with industrial procedures changes. Besides, there was an expressive increase in vehicular PAHs concentrations, corroborating the scenery of a drastic raise of vehicles in the last decade. The present study contributed to the national scenario towards urban drainage basin management. It included records since preindustrial time (~1894) up to the present, highlighting the potential use of lacustrine sediment on the retrieval of historical environmental changes of aquatic ecosystems and associated anthropogenic impacts.

Different magnitude, intensity and timing of precipitation can impact runoff, hillslope erosion and transport of sediment along river channels.  Human activities, such as dam construction and surface mining can also considerably influence transport of sediment and sediment-bound contaminants. Many river basins of the world are currently subject to changes in climate at the same time as pressures from other human activities increase. However, because there are often complex interactions between such multiple drivers of change, it is challenging to understand and quantify contributions of individual drivers, which is needed in predictive modelling of future sediment and contaminant flows. This thesis considers sediment transport in the Lake Baikal basin, which is hydrologically dominated by the transboundary Selenga River of Russia and Mongolia. The Selenga River basin is, for instance, subject to climate change and increasing pressures from mining, but process complexity is reduced by the fact that the river basin is one of few large basins in the world that still is essentially undammed and unregulated. A combination of field measurement campaigns and modelling methods are used in this thesis, with the aim to: (i) identify historical hydroclimatic trends and their possible causes, (ii) analyse the spatial variability of riverine sediment loading in the mining affected areas, and (iii) investigate sediment transport and storage processes within river channels and in river deltas. Results show that, during the period 1938-2009, the annual maximum daily flow in the Selenga River basin has decreased, as well as the annual number of high flow events, whereas the annual minimum daily flow has increased. These changes in discharge characteristics are consistent with expected impacts of basin-scale permafrost thaw. Both field observations and modelling results show that changes in magnitude and number of high-flow events can considerably influence the transport of bed sediment. In addition, the average discharge has decreased in the past 20 years due to an extended drought. Under conditions of low flow, metal-enriched sediment from mining areas was observed to dominate the river water. If discharge will continue to decrease in the Selenga River (or other mining-impacted rivers of the world), further increases in riverine metal concentrations may hence be one of the consequences. Furthermore, under current conditions of extended drought, less sediment may have been distributed over the floodplain wetlands in the Selenga River delta. Present estimates, however, show that sediment can still be transported to, and deposited within, the banks and water bodies located in the backwater zone of the Selenga River delta. This can aid bank and levee stabilization, support the development of wetlands and foster net sedimentation.​ / Nederbördens olika magnitud, intensitet och tidpunkt kan påverka ytavrinning, vattenerosion och transport av sediment längs flodkanaler. Mänskliga aktiviteter, som dammkonstruktion och gruvdrift i dagbrott kan också påtagligt påverka transport av sediment och sedimentbundna föroreningar. Många avrinningsområden i världen påverkas för närvarande av klimatförändringar samtidigt som trycket från andra mänskliga aktiviteter ökar. Men eftersom det ofta förekommer komplexa interaktioner mellan sådana multipla orsaker till förändring, är det utmanande att förstå och kvantifiera bidrag från enskilda orsaker, vilket behövs vid prediktiv modellering av framtida sediment- och föroreningsflöden. Denna avhandling behandlar sedimenttransport i Bajkalsjöns tillrinningsområde, som hydrologiskt domineras av den internationella Selengafloden i Ryssland och Mongoliet. Selengaflodens tillrinningsområde är exempelvis påverkat av klimatförändringar och ökat tryck från gruvdrift, men processkomplexiteten reduceras av det faktum att tillrinningsområdet är ett av världens få stora som fortfarande väsentligen saknar dammar och flödesreglering. I denna avhandling används en kombination av fältmätningskampanjer och modelleringsmetoder, i syfte att: (i) identifiera historiska hydroklimattrender och deras möjliga orsaker, (ii) analysera den rumsliga variationen i flodens sedimentbelastning inom de gruvpåverkade områdena, och (iii) undersöka sedimenttransport- och retentionsprocesser inom flodkanaler och i floddeltan. Resultaten visar att det årliga maximala dygnsflödet, liksom det årliga antalet högflödeshändelser, har minskat i Selengafloden under perioden 1938-2009, medan det årliga minimala dygnsflödet har ökat. Dessa förändringar i flödeskaraktäristika överensstämmer med förväntade effekter av storskaligt tinande permafrost. Både fältobservationer och modelleringsresultat visar att förändringar i högflödeshändelsers magnitud och årligt antal kan påverka transporten av bottensediment påtagligt. Dessutom har medelflödet minskat under de senaste 20 åren på grund av långvarig torka. Under lågflöden observerades metallberikat sediment från gruvområdena dominera flodvattnet. Om flödena fortsätter att minska i Selengafloden (eller andra gruvdriftspåverkade floder i världen), kan således ytterligare ökningar av flodvattnens metallkoncentrationer vara en av konsekvenserna. Under den långvariga torka som nu råder mängden sediment som fördelats över våtmarkerna i Selengaflodens delta ha minskat. Sediment beräknas dock fortfarande kunna transporteras till och deponeras inom flodbankar och vattenkroppar i Selengadeltats backwaterområden. Detta kan bidra till stabilisering av bankar och skyddsvallar, stödja våtmarkers utveckling och främja nettosedimentering. / Wielkość, czas trwania oraz intensywność opadów atmosferycznych oddziałuje na charakter odpływu, erozję oraz transport osadów rzecznych. Również ingerencja człowieka w środowisko – np. budowa zapór i zbiorników wodnych, czy górnictwo odkrywkowe – w różnym stopniu może wpływać na transport osadów oraz powiązanych z nimi zanieczyszczeń. Wiele dorzeczy na Ziemi, będących pod wpływem obecnych zmian klimatycznych, jest jednocześnie poddawanych narastającej antropopresji. W celu przewidywania przyszłych zmian w transporcie osadów i powiązanych z nimi zanieczyszczeń, potrzeba dogłębnego zrozumienia i oceny wpływu poszczególnych czynników powodujących te zmiany. Taka analiza jest jednak często utrudniona ze względu na złożone interakcje pomiędzy czynnikami powodującymi zmiany. Niniejsza rozprawa doktorska przedstawia wyniki badań związanych z analizą transportu osadów rzecznych w zlewni jeziora Bajkał, zdominowanej hydrologicznie transgraniczną rzeką Selengą, przepływającą przez tereny Rosji i Mongolii. Zlewnia rzeki Selengi podlega współczesnym zmianom klimatycznym oraz wzrastającej presji związanej z górnictwem. Złożoność procesów hydrologicznych jest jednak w tym wypadku ograniczona, ponieważ zlewnia Selengi jest jednym z nielicznych, względnie dużych dorzeczy na świecie, którego przepływy są – jak dotychczas – naturalne, nieuregulowane przez żadne zapory lub zbiorniki wodne. Dla poszczególnych celów: (i) identyfikacji historycznych trendów hydroklimatycznych i ich przyczyn, (ii) analizy przestrzennych zmian w transporcie osadów rzecznych w części zlewni dotkniętej górnictwem odkrywkowym oraz (iii) badania procesów transportu i magazynowania osadów w korycie i delcie rzeki; zostały w pracy zastosowane hydrometryczne dane pomiarowe, dane pochodzące z badań terenowych oraz metody modelowania. Wyniki badań wskazują na to, że w latach 1938-2009 zmalały roczne przepływy maksymalne oraz liczba wezbrań, podczas gdy w tym samym czasie wzrosły roczne przepływy minimalne. Powyższe zmiany są zgodne z oczekiwanym wpływem rozmarzania wiecznej zmarzliny na ustrój przepływów rzecznych. Analiza danych pomiarowych oraz wyników modelowania wskazują na to, że obecne zmiany dotyczące liczby oraz wielkości wezbrań mogą znacznie wpłynąć na transport osadów dennych w korytach rzek. Dodatkowo, w ciągu ostatnich 20 lat (1995-2014), średnie roczne przepływy znacznie spadły ze względu na przedłużający się okres suszy na terenie zlewni. Analiza danych terenowych pochodzących z obszarów górniczych wykazała, że podczas obniżonych przepływów, w zanieczyszczonych znaczną ilością metali osadach rzecznych, dominuje materiał pochodzący z działalności człowieka (około 80\% transportowanych osadów). Należy zatem przewidywać, że jeśli obecne zmiany w ustroju przepływów w dorzeczu Selengi (lub w innych podobnych dorzeczach na świecie) będą postępować, to ich następstwem może być dalszy wzrost koncentracji zanieczyszczeń (metali pochodzących z obszarów górniczych) rzek. Ponadto, w obecnym okresie obniżonych przepływów, na terenach zalewowych i jeziorach delty rzeki Selengi zatrzymuje się prawdopodobnie mniej osadów. Wyniki badań wskazują jednak na to, że osady rzeczne mogą być wciąż transportowane do brzegów i obszarów wodnych znajdujących się w strefie, w której stany wodne cieków delty są pod wpływem stanów wodnych jeziora Bajkału. Akumulacja materiału w tych częściach delty Selengi może pozytywnie wpływać na stabilizację naturalnych wałów oraz mokradeł i zwiększać sedymentację netto. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.</p>

L’altération chimique et l’érosion physique de la croûte continentale mobilisent de grandes quantités de matière sous formes solide et dissoute. Première productrice de sédiments sur le globe, la chaîne Himalayenne délivre ~1 Gt/a de sédiments aux océans. L'importance des différents facteurs qui contrôlent les flux érodés et celle des processus d’érosion (glaciers, glissements de terrain, sols) sont pourtant encore mal définies. Il en va ainsi des facteurs climatiques, en particulier de leur impact au cours des transitions climatiques. Afin de répondre à ces questions, ce travail s’attache à comparer la composition géochimique des produits de l’érosion à celles des sédiments actuels de rivière et des archives sédimentaires de la plaine du Gange. Un premier bilan des processus d’érosion a été établi petite échelle dans le bassin Haut-Himalayan de la Khudi. L’érosion actuelle conséquente de ce bassin de ~3mm/a se produit lors de la mousson, correspond pour l'essentiel à l’érosion des sols et surtout à l'intense activité d'une zone de glissement de terrain. Grâce au développement d'une nouvelle méthode de destruction de la matière organique, la mesure de l’hydratation des silicates a pu être utilisée comme traceur inédit des sols. Sur cette base, l’inversion des compositions des sédiments de la rivière démontre que l’érosion physique est dominée à ~80% par le glissement de terrain, l’érosion de sols étant mineure et comparable aux taux d’érosion des autres bassins alentours. L’érosion chimique qui conduit à un flux d'éléments dissous de 7.9 kt/a (soit une érosion équivalente de 0.02 mm/a) semble dériver de l’altération profonde du substrat rocheux. Néanmoins les flux d'éléments dissous dessinent également une relation marquée avec les flux particulaires durant la mousson, suggérant une altération additionnelle des sédiments au cours du transport fluvial. Une approche similaire a ensuite été menée à l’échelle plus vaste du bassin de la Narayani drainant l’ensemble du Népal central. Grâce à des mesures de courant par ADCP combinées à l’échantillonnage de sédiments en profondeur, un modèle de transport sédimentaire a été utilisé pour intégrer les flux sédimentaires en profondeur et ainsi réviser le taux d’érosion moyen sur le bassin versant à une valeur de ~1.7 mm/a, proche des taux d'érosion long-terme. Un système géochimique associant la mesure du δD des silicates associée aux concentrations en carbonate s’est révélé un traceur diagnostique de l’érosion glaciaire dans le Nord du bassin, tandis que la teneur en matière organique du sédiment a pu être utilisée comme traceur des sols. L’analyse temporelle des flux de sédiments, de leur composition et du signal granulométrique, a ainsi permis d’établir que seule une faible fraction des sédiments (<20%) provenait de l’érosion par les glaciers et les sols. À l'échelle du Népal central, l’érosion physique semble donc également dominée par les glissements déclenchés lors de la période de mousson. Le grand cône alluvial de la Narayani-Gandak, situé au débouché de cette rivière dans la plaine du Ganges, a enregistré l’histoire récente de l’érosion du Népal central. Trois forages réalisés dans ce méga-cône permettent ainsi d'étudier l'évolution de l'altération et de l'érosion en Himalaya au cours du tardi-Pléistocène. Ces dépôts sédimentaires révèlent une étonnante stabilité depuis ~45 ka de la géochimie, des provenances et du degré d’altération des sédiments. Seule l’intensité de l’érosion mesurée par isotopes cosmogéniques semble augmenter au cours de l’Holocène. Par contraste, l’évolution très récente de la distribution de l’érosion dans la chaîne est marquée par un accroissement (x3) de la proportion de matériel des régions basses et plus peuplées de l'Himalaya, montrant que les activités anthropiques, via notamment une forte croissance du réseau routier durant la dernière décennie, [...] / Chemical weathering and physical erosion of the continental crust mobilise huge amounts of both solid and dissolved material. As the first sediment generator on the Earth, the Himalayan range releases around 1 Gt/y of sediment into the ocean. The relative influence of the different factors that control the eroded fluxes and the importance of the erosion processes (such as landslides, glaciers, soils) are as yet poorly understood. The same is true of the climatic factors, especially regarding their impact during climatic transition periods. In order to address those questions, this work focuses on comparing the geochemical composition of erosion products to the composition of present river sediment and of sedimentary records in the Ganga Plain. A first budget of the erosion processes was done on a small scale in the Khudi catchment of Higher Himalaya. The total present-day erosion is considerable, at around 3 mm/y and takes place during the monsoon. It is mainly linked to the soils erosion and more importantly to the intense activity of a landsliding area. The development of a new method for the destruction of organic matter enabled the use of silicates hydration as a tracer for soils. Based on this method, a mathematical inversion of the sediment compositions was performed. It highlights that the landslide is responsible for ~80% of the overall physical erosion. The soil erosion is minor and is comparable to the erosion rates measured in the neighbouring catchments. The chemical erosion leads to a dissolved flux of 7.9 kt/y (corresponding to an erosion rate of 0.02mm/y) and seems to come from the bedrock deep weathering. Nevertheless, the dissolved fluxes also appear to be linked with the particles fluxes during the monsoon. This suggests an additional weathering of the sediment during the fluvial transport. A similar approach was used on a larger scale in the Narayani catchment that drains the whole of Central Nepal. Through ADCP-based current measurements combined with deep sediment sampling, a model for sedimentary transport was used to integrate the deep sediment fluxes. The average catchment-scale erosion rate was then corrected to a value of ~1.7 mm/y, close to the long-term erosion rates. A geochemical system that combines the measurement of the δD of silicates and the concentrations of carbonates was found to be a diagnosis tracer for glacial erosion in the northern part of the catchment. The organic matter ratio was used as a tracer for soils. The temporal analysis of sediment fluxes, as well as the sediment composition and granulometry showed that only a small fraction (< 20%) of the sediment comes from glacial and soils erosion. Over the whole Central Nepal, the physical erosion seems also to be dominated by the landslides that are triggered during the monsoon. The large Narayani-Gandak alluvial fan is located at the river mouth and can be used as a record of the recent history of Central Nepal erosion. Three drillings were done in this fan to enable the study of the evolution of Himalayan weathering and erosion during the Late Pleistocene. The sedimentary deposits display a surprising stability in their geochemistry, their sources and their weathering stage for the last ~45 ky. The erosion intensity derived from cosmogenic nuclides is the only feature that seems to have risen during Holocene. However, the very recent evolution of the erosion distribution in the range is characterised by an increase (x3) of the proportion of products coming from the lower, more densely populated areas. This shows that the anthropogenic activities have had a larger impact on the erosion than the last Pleistocene-Holocene transition, especially through the rapid growth of the road network during the last decade.