Les mollusques continentaux sont des enregistreurs très sensibles des conditions environnementales locales et de leurs moindres variations. Malgré le caractère très local des malacofaunes, les référentiels malacologiques constitués dans le nord-ouest de l'Europe pour le Tardiglaciaire et le début de l'Holocène ont démontré la valeur régionale de cet indicateur. Cette dimension a pu être abordée par la multiplication des observations qui a permis de différencier des caractères généraux par rapport à des variations ponctuelles. C'est dans cette optique que sont ici étudiées les données malacologiques de la seconde moitié de l'Holocène dans les plaines alluviales du bassin de la Seine. En présentant une synthèse des données collectées sur une quinzaine de sites, ce travail a pour objectif de fournir un référentiel malacologique des grandes étapes environnementales s’étant succédé dans ces espaces et d’évaluer le rôle des sociétés humaines dans ces transformations. Il est montré qu’une trajectoire environnementale commune est partagée sur l’ensemble des sites étudiés. Durant la première moitié de l’Holocène, les plaines sont occupées par des boisements et l’impact anthropique paraît limité aux abords immédiats des sites archéologiques. Le paysage s’ouvre et s’humidifie durant le Subboréal, en particulier durant l’âge du Bronze. Au moment du passage à l’âge du Fer, à la transition Subboréal/Subatlantique, les plaines alluviales sont déjà largement défrichées et leur paysage est même largement homogénéisé. Ces résultats malacologiques sont ensuite discutés au regard des phases d'occupations humaines et confrontés aux résultats obtenus sur d'autres indicateurs à l’échelle régionale (palynologie, géomorphologie) mais également comparés aux autres référentiels malacologiques construits aux échelles nord-ouest et centre européennes, afin d’évaluer si les changements enregistrés sont perçus à large échelle et dans le but de comprendre leurs causalités. / Continental molluscs are very sensitive indicators of local environmental conditions. Molluscs are representative of local environments, but previous studies have demonstrated the consistency of the Lateglacial and Early Holocene malacological successions throughout North-Western Europe. This result has been obtained thanks to a high number of analyses that enabled to distinguish general characteristics from local variations. The present study focuses on the malacological data from the second half of the Holocene in the floodplains of the Seine basin. By presenting a synthesis of the data collected over fifteen sites, this work aims to provide a malacological framework of the major environmental steps recorded in the floodplains of the Seine basin and to assess the role of human societies in some of the observed transformations. It is demonstrated that a common environmental trajectory is shared on all the studied sites. During the first half of the Holocene, floodplains are dominated by woodlands and the anthropogenic impact seems limited to the immediate vicinity of archaeological sites. The landscape becomes more open and moister during the Subboreal, in particular during the Bronze Age. At the transition between the Subboreal and the Subatlantic, at the beginning of the Iron Age, alluvial plains are already widely cleared of trees and their landscape appears to be largely homogenised. These malacological results are then discussed in relation to human settlements and compared with other indicators at the regional level (palynology, geomorphology). They are also compared with other malacological framework, built in north-western and central Europe, in order to assess whether the changes recorded are observed on a large scale and to understand their causalities.

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This thesis examines geomorphic processes that impact thermal stratification within floodplain lakes. Previously, thermal stratification was not thought prevalent in these numerous small water bodies, despite being found in small reservoirs. Thermal stratification leads to long term anoxia in the bottom waters and the release of metals and nutrients from the sediments. This can result in water quality problems such as algal blooms (including potentially toxic cyanobacteria), loss of fish habitat and deterioration of wetland habitat. Four floodplain lakes of the Macdonald River Valley NSW were profiled and tested over 3?? years to assess to what extent, under what conditions, and with what chemical and physical effects, they thermally stratified and destratified. The morphometry, bed facies, vegetation, hydrology and local weather patterns for each lake were also investigated. Physical and chemical analyses found elevated nutrients in all four lakes and higher concentrations of total phosphorous and total nitrogen in the bottom waters. These results were not dependant on stable thermal stratification and long-term anoxia in the bottom waters. Inflow samples had much higher concentrations of nutrients than the lake samples, so the catchment is the likely source. Samples were analysed for phytoplankton and significant populations of potentially toxic cyanobacteria were present. Stratification depended upon whether the lake was "sheltered" from wind stirring or from incident radiation, either topographically by steep slopes surrounding the lakes, or by submerged and emergent vegetation. Aquatic vegetation limits the amount of transfer of turbulent kinetic energy from wind shear and the amount of incident radiation received. At one lake, sheltered areas reached temperatures much higher than less sheltered areas. Topographic sheltering can make a difference of up to three degrees Celsius across the lake surface. Destratification depended on wind speed, wind direction and orientation of the lake to the dominant wind direction. An extension to the classification of fluvial lakes (from Timms 1992) is presented, with further subdivisions to describe the lakes as "sheltered" or "open" and the type of sheltering (vegetation or topography) present.

<p>The general perception today is that the Shashi-Limpopo Basin in southern Africa is hot and dry and not conducive to human habitation. Today there is no doubt that the Shashi-Limpopo Basin has been home to many communities throughout the pre-historical period. A study of the changing ecological conditions in the Mateke Hills and the Shashi-Limpopo Valley as well as historical and present day land-usage offers an alternative explanation of how prehistoric communities could have interacted with this changing landscape. The archaeological record, historical sources and recent land-use patterns show that settlement location has always been orientated towards the rivers and circumscribed environments. The mosaic of floodplains, wetlands, drylands and circumscribed zones provided the ideal ecological setting for the development of socio-political complexity in southern Africa. The resilience of these semi arid savanna regions together with human innovation and local knowledge ensured that societies continued to derive subsistence even in the face of seasonal variability in rainfall and even climate change.</p>

The general perception today is that the Shashi-Limpopo Basin in southern Africa is hot and dry and not conducive to human habitation. Today there is no doubt that the Shashi-Limpopo Basin has been home to many communities throughout the pre-historical period. A study of the changing ecological conditions in the Mateke Hills and the Shashi-Limpopo Valley as well as historical and present day land-usage offers an alternative explanation of how prehistoric communities could have interacted with this changing landscape. The archaeological record, historical sources and recent land-use patterns show that settlement location has always been orientated towards the rivers and circumscribed environments. The mosaic of floodplains, wetlands, drylands and circumscribed zones provided the ideal ecological setting for the development of socio-political complexity in southern Africa. The resilience of these semi arid savanna regions together with human innovation and local knowledge ensured that societies continued to derive subsistence even in the face of seasonal variability in rainfall and even climate change.

A social survey of the communities living adjacent to the Pongolo river floodplain was carried out, in order to understand the perceptions of the impact of artificial flood releases on the general use of natural resources of Pongolo floodplain in terms of: general resource use, stream flow, water quality and subsistence agriculture. The results show that floodplain communities perceive that the present artificial flood releases which are intended to maintain the environmental requirements of the floodplain are not meeting their needs nor the needs of the environment. Key perceptions on environmental impacts identified are: (i) reduction in water required to maintain floodplain resources, (ii) deterioration in water quality and (iii) decrease in available floodplain land and natural resources. / Thesis (M.Env.Dev.) - University of KwaZulu-Natal, Pietermaritzburg, 2007.

The impounding of the waters of the Pongolo river, upstream of its floodplain on the Mocambique coastal plain, may adversely affect the functioning of the floodplain system. A multidisciplinary study of the functioning of the floodplain was initiated to provide a basis for the development of a management strategy for the floodplain. The study reported in this dissertation considered the flood dependence and functioning of the vegetation of the seasonally inundated area. The vegetation was mapped and the communities ordinated, according to the Braun-Blanquet technique, in relation to their positions relative to high flood level (HFL) and the level of the water after flood subsidence (i.e. maximum retention level, MRL). Community distribution was shown to be strictly determined by both the height of the floods and by the MRL. It was concluded that periodic floods are essential for the maintenance of the communities. The Cynodon dactylon (L.) Pers. Community, which forms extensive meadows in the zone of periodic inundation, was studied in detail. As the water level receded during winter, productivity was high (up to 23 kg ha¯¹ d¯¹1 dry mass) and a palatable sward was produced. This is heavily grazed by domestic stock, but as the soil dries out and water stress becomes significant, production decreases, C. dactylon becomes less palatable, and grazing shifts to newly exposed areas. The shift in grazing allows the build up of a large standing crop of both grazeable and ungrazeable (below ground and stolons) material. At the time of inundation by the next floods c. 910 kg ha¯¹ of dry mass, c. 17 kg ha¯¹ nitrogen and c. 2 kg ha¯¹ phosphorus have been removed by grazers. It is concluded that this production, which is flood dependent, forms an important supplement to stock grazing during winter. It is suggested that this source of grazing could be stimulated by irrigation during winter. Cynodon dactylon is shown to decompose rapidly during inundation, losing half of its mass and nutrients in c . 28 days. It therefore represents a major energy and nutrient input during the aquatic phase. The extent to which it is grazed during submergence is unknown. The nutrient input is derived ultimately from the soils of the inundated areas and, since nutrients are being removed by both terrestrial grazers and flushing, continued production is reliant upon the annual sediment load reaching the floodplain. Most of the sediment load will now be deposited in the impoundment, and fertilization may be necessary to maintain productivity. The response of C. dactylon to the seasonal fluctuations in water level are used to formulate proposals for water release from the dam. These include proposals for the short-term, i.e. until the demand for irrigation water conflicts with the requirements of the floodplain, and for the long-term, when less water will be available for the floodplain / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1981.

Poor people in rural areas of developing countries are considered to be particularly vulnerable. Research shows that the rural poor tend to live in risky environments and face greater difficulties coping because they are excluded from formal safety nets and have few assets. Today, there is much concern that risk, especially environmental risk, contributes to perpetuate poverty and threatens livelihood security, yet our understanding of the implications of environmental risk for rural livelihood remains incipient. This dissertation explores peasant livelihood within the context of environmental change through a study of peasant responses to rapid river changes along the Central Ucayali River, a highly active meandering river and a major Amazon tributary in Peru. / Livelihood responses to floodplain dynamics were examined using the case of a recent meander cut-off near the city of Pucallpa as a "natural experiment." Participant observation and a household survey with 68 ribereno households, in three different villages upstream and downstream from the cut-off, served to investigate: (1) livelihood before and after the cut-off; (2) the role of humans in facilitating the cut-off, (3) land tenure; and (4) the links between shocks and asset evolution. / Descriptive analysis indicates that riberenos modified their livelihoods in response to the biophysical changes attributed to the cut-off and derived important economic opportunities. Results suggest that riberenos actually intervened to facilitate the cut-off to reduce travel time and make boat travel safer. Despite the potential for unclear rights and overlapping claims, due to land instability and the coexistence of formal and customary tenure rules, land disputes did not result in physical violence. Examples from two villages were used to illustrate how tenure rules are renegotiated as the resource base expands or contracts. Descriptive and statistical analyses show that riverbank slumps were the main form of risk along the Ucayali and, despite their direct effect on land holdings, environmental shocks did not necessarily constrain land accumulation or increase inequality. This study argues that environmental risk can increase vulnerability and reduce welfare but, under certain circumstances it creates new opportunities for rural people in developing countries. The implications of these findings for vulnerability reduction, human adaptation to environmental change, and Amazonian cultural ecology are discussed. / Les populations pauvres des regions rurales des pays en développement sontconsidérées comme étant particulièrement vulnérables. Les recherches passées ontdémontré que les membres de ces populations tendent à vivre dans des environnements àrisques et font face à de plus grands défis parce qu'exclus du filet de sécurité socialeformel et parce que possédant comparativement moins de biens mobiliers et immobiliers.Aujourd'hui, de beaucoup s'inquiètent de la contribution de ces risques, en particulier desriques environnementaux, à perpétuer la pauvreté et du danger qu'ils posent pour lemaintient des modes de vie. Malgré ces inquiétudes, notre compéhension desimplications des risques environnementaux pour les modes de vie ruraux demeure faible.Cette dissertation explore le mode de vie paysan en période de changementsenvironnementaux. Il s'agit d'une étude de la réponse des paysans du moyen Ucayali auxrapides changements dans la dynamique du fleuve. L'Ucayali est un affluent majeur dufleuve Amazone, au Pérou.

This thesis examines geomorphic processes that impact thermal stratification within floodplain lakes. Previously, thermal stratification was not thought prevalent in these numerous small water bodies, despite being found in small reservoirs. Thermal stratification leads to long term anoxia in the bottom waters and the release of metals and nutrients from the sediments. This can result in water quality problems such as algal blooms (including potentially toxic cyanobacteria), loss of fish habitat and deterioration of wetland habitat. Four floodplain lakes of the Macdonald River Valley NSW were profiled and tested over 3?? years to assess to what extent, under what conditions, and with what chemical and physical effects, they thermally stratified and destratified. The morphometry, bed facies, vegetation, hydrology and local weather patterns for each lake were also investigated. Physical and chemical analyses found elevated nutrients in all four lakes and higher concentrations of total phosphorous and total nitrogen in the bottom waters. These results were not dependant on stable thermal stratification and long-term anoxia in the bottom waters. Inflow samples had much higher concentrations of nutrients than the lake samples, so the catchment is the likely source. Samples were analysed for phytoplankton and significant populations of potentially toxic cyanobacteria were present. Stratification depended upon whether the lake was "sheltered" from wind stirring or from incident radiation, either topographically by steep slopes surrounding the lakes, or by submerged and emergent vegetation. Aquatic vegetation limits the amount of transfer of turbulent kinetic energy from wind shear and the amount of incident radiation received. At one lake, sheltered areas reached temperatures much higher than less sheltered areas. Topographic sheltering can make a difference of up to three degrees Celsius across the lake surface. Destratification depended on wind speed, wind direction and orientation of the lake to the dominant wind direction. An extension to the classification of fluvial lakes (from Timms 1992) is presented, with further subdivisions to describe the lakes as "sheltered" or "open" and the type of sheltering (vegetation or topography) present.

Spatial planning in the flood area of the river Dědina Abstract The delimitation of new development areas in flood area of river is one of the steps leading to the increase of flood risk. The aim of this master thesis is to find out whether and for what reasons is the delimitation of new development areas happening in territories which are at risk of flooding. At the same time, the thesis also focuses on the role of the mayor, especially his competencies related to the management of flood risks, arising from his function. Theoretical part is based on discussion about the development of cooperation between society and natural environment and also concept of Flood Risk Management, especially in relation of the flood risk with the process of urban planning and also with the organization of public administration. The analysis of spatial plans of the 5 municipalities, or more precisely 14 local districts, located on the Dědina river in Hradec Králové region uses the borders of floodplain defined by T. G. Masaryk Water Reasearch Institute and spatial plans of analysed municipalities. The results correspond to created graphical outputs and following research of textual parts of the spatial plans. Specific additional informations were obtained during structured interviews with five mayors of the studied...