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River-floodplain connectivity is defined as the water mediated transfer of materials and energy between a river or stream and its adjacent floodplain. It is generally accepted that restoring and/or enhancing river-floodplain connectivity can reduce the downstream flux of reactive solutes such as nitrogen (N) and phosphorus (P) and thus improve downstream water quality. However, there is little scientific literature to guide ecological engineering efforts which optimize river-floodplain connectivity for solute retention. Therefore, the aim of my dissertation research was to examine feedbacks between inundation hydrology and floodplain biogeochemistry, with an emphasis on analyzing variation experienced along the river continuum and the cumulative effects of river-floodplain connectivity at the basin scale. This was completed through four independent investigations. Field sites ranged from the Atchafalaya River Basin, the largest river-floodplain system in the continental US, to the floodplain of a recently restored headwater stream in Appalachia. We also developed a method to examine river-floodplain connectivity across large- river networks and applied that methodology to US stream network. Largely, our results highlight the role floodwater residence time distributions play in floodplain biogeochemistry. In headwater streams, residence times restrict redox dependent processes (e.g. denitrification) and downstream flushing of reactive solutes is the dominant process. However, in large-river floodplains, redox dependent processes can become solute limited because of prolonged residence times and hydrologic isolation. In these floodplains, the dominant process is often autochthonous solute accumulation. Further, results from our modeling study suggest large-river floodplains have a greater impact on downstream water quality than floodplains associated with smaller streams, even when considering cumulative effects across the entire river network. / Ph. D.

Die Verbreitung von gebietsfremden Arten in Gebiete außerhalb ihres natürlichen Verbreitungsgebietes kann zu einem Verlust der Biodiversität führen. Einst als produktionssteigerndes Mittel eingesetzt, wurden viele gebietsfremde Baumarten in Mitteleuropa und Deutschland eingeführt und verblieben dort in den Wäldern. Unter anderem wurde in den Hartholzauenwäldern der Mittelelbe in Sachsen-Anhalt die nordamerikanische Rot-Esche (Fraxinus pennsylvanica) eingebracht und sie nimmt heute rund 50 % der Fläche ein. Um die Fragen zum Einfluss der Etablierung von F. pennsylvanica auf die Vielfalt der Waldstrukturen und der Arten in der Krautschicht zu bearbeiten, wurden vergleichende Erhebungen in 20 Beständen durchgeführt, die sich hinsichtlich der Bestandsanteile von F. pennsylvanica im Oberstand unterscheiden. Die Bestände wurden hinsichtlich der Bestandsstruktur und Totholzaufkommen sowie auf kleineren Plots mit je einem Bezugsbaum (F. pennsylvanica oder Quercus robur als Referenz) das Bodenmikrobiom und Bodenvegetation sowie Naturverjüngung der Gehölze untersucht. Am deutlichsten scheint die Einflussnahme von F. pennsylvanica in Reinbeständen. Diese sind weniger stark strukturiert und weisen mehr Anfälligkeiten gegenüber Umwelteinflüssen auf. Für alle anderen Bestandsformen waren die Effekte eher gering und zum Teil konnte in Misch- oder Dominanzbeständen eine höhere Diversität als in Referenzbeständen festgestellt werden. Unabhängig von der gesetzlichen Lage zum Umgang mit Neophyten in Schutzgebieten wird F. pennsylvanica als in die Hartholzauenwälder der Mittelelbe eingegliederte Baumart eingeschätzt, die das Potenzial hat, ausfallende Arten, wie die heimische Gewöhnliche Esche (Fraxinus excelsior), zu ersetzen. / The spread of alien species in areas outside their natural range can lead to a loss of biodiversity. Once used as a tool of increasing production, many alien tree species were introduced into Central Europe and Germany and remained in the forests there. Among other, the north american Green Ash (Fraxinus pennsylvanica) was introduced into the hardwood floodplain forests of the Mittelelbe in the federal state of Saxony-Anhalt and today it occupies around 50% of the area. In order to address the questions about the influence of the establishment of F. pennsylvanica on the diversity of forest structures and species in the herbaceous layer, comparative surveys were carried out in 20 stands that differed in terms of the proportion of F. pennsylvanica in the upper stand. Investigations on stand structure and deadwood as well as, in smaller plots with a reference tree (F. pennsylvanica or Quercus robur as a reference), investigations on soil microbiome, ground vegetation and natural regeneration were examined. The influence of F. pennsylvanica appears to be clearest in pure stands. These are less structured and are more susceptible to environmental influences. For all other types of stands, the effects were rather small and, in some cases, a higher diversity was found in mixed or dominant stands than in reference stands. Regardless of the legal situation regarding the handling of neophytes in protected areas, F. pennsylvanica is considered to be a tree species integrated into the hardwood floodplain forests of the Mittelelbe, which has the potential to replace failing species such as the common ash (Fraxinus excelsior).

The Kafue Flats floodplain wetland system in southern Zambia is under increasing climate and human pressures. Firstly, drought episodes appear more prevalent in recent years in the region and secondly, two dams were built on the lower and upper ends of the wetland in 1972 and 1978, respectively, across the Kafue River which flows through the wetland. The study uses multi-temporal remote sensing to assess change in extent and vigour of green vegetation, and extent of water bodies and dry land cover on the Kafue Flats. The change detection's management value is assessed. Four normalised, co-registered digital Landsat images from 24 September 1984, 3 September 1988, 12 September 1991 and 20 September 1994 were used. The main change detection method used was comparison of classifications, supplemented by Normalised Difference Vegetation Index (NDVI) and Principal Component Analysis (PCA) change detection. Ancillary land use and environmental data were used in interpreting the change in the context of cause and effect. The results indicate inconsistent trends in the changes of most land cover classes, as a result of manipulation of the wetland by man through annual variations in the timing and magnitude of regulated flows into the wetland, as well as burning. However, the results also show spatial reduction in the wetland's dry season dense green reed-grass vegetation in upstream sections which are not affected by the water backing-up above of the lower dam. Sparse green vegetation is replacing the dense green vegetation in these upstream areas. It is inferred that this dry season degradation of the wetland threatens bird species which may use the reeds for dry season nesting. It is proposed that ground surveying and monitoring work at the micro-habitat level is necessary to ascertain the implications of the losses. It is concluded that, in spite of difficulties, multi-temporal remote sensing has a potential role in wetland change assessment on the Kafue Flats at the community level, but that it needs to be supplemented by targeted, micro-habitat level ground surveys.

The object of this work is an analysis of the influence of extreme hydrological events (floods and droughts) in terms of interaction between groundwater and surface water in the river floodplain. The aim of this thesis is also the evaluation of the hydrological regime of the upper Lužnice basin and evidence of retention potential preserved natural floodplain. The selected objectives of the work were resolved on the basis of the values of groundwater levels and surface water in the area of interest. Based on data from underground wells and a digital terrain model, it was possible to create an image of the distribution of groundwater levels in river floodplains during selected hydrological situations. Data from surface flow was obtained from several habitats in the flow direction Lužnice. This has enabled graphically illustrate individual flood waves and characterize their size, speed and transformation after the passage of a preserved natural floodplain of Lužnice river. Carried out research has been confirmed retention capacity of the floodplain, which is most significant at flow rates slightly in excess of the flow capacity of the river bed. However, extreme floods or in periods with many culminations in a relatively short time leads to reduces water retention capability of the floodplain. In...

En Afrique Sub-Saharienne, les zones humides forment d'importantes zones de pâturages pour bon nombre de pastoralistes. Le régime d'inondation de ces plaines influence leur fonc tionnement et leur productivité. Pour comprendre et maitriser ces régimes, il est donc essentiel d'évaluer l'impact de l'infrastructure hydro-électrique sur les dynamiques d'inondations en aval des barrages. Pourtant, le manque de données disponibles, l'absence de modèles validés et la forte variabilité environnementale rendent cet exercice difficile. Cette thèse contribue à quantifier l'impact du changement des ressources hydriques sur la productivité fourragère des prairies inondables dans le Delta du fleuve Tana, au Kenya. 1/ Les caractéristiques de croissance et la productivité d'une prairie inondable à Echinochloa stagnina (Retz) P. Beauv. ont été déterminées pour différents régimes de fauche, d'irrigation et conditions d'inondations. Ensuite, un modèle de croissance adapté à des Graminées en C4, tropicales et pérennes, de prairies inondables a été développé. Il constitue, à notre connaissance, le premier modèle éco-physiologique adapté à ce type de prairies. 2/ Des processus hydrologiques importants pour le fonctionnement des écosystèmes (étendue, période, durée et fréquence d'inondation) ont été caractérisés grâce à un modèle de bilan hydrologique et à l'utilisation de techniques de télédétection, et cela en dépit de la faible instrumentalisation du bassin, du peu de données topographiques et d'un fort couvert nuageux. 3/ Une analyse préliminaire de l'impact de différents scénarios d'inondations sur la production fourragère a été effectuée en utilisant des indicateurs de services écosystémiques. Cette thèse participe à l'amélioration de nos connaissances des services écosystémiques des zones humides par la construction de modèles et par l'évaluation de scénarios dans une région du monde où ce type de données est rare. / Wetlands are a vital resource for many pastoralists in Sub-Saharan Africa as they provide dry-season grazing zones. As floods are essential for wetland ecosystems, the assessment of water abstraction and hydroelectric infrastructure on downstream flooding dynamics is crucial. Yet, scarce data, environmental variability and the lack of models make this challenging. This research contributes to quantifying the influence of changing water resources on fodder pro- duction of floodplain grasslands in the Tana River Delta, Kenya. 1/ Growth characteristics of floodplain grasslands of Echinochloa stagnina (Retz) P. Beauv. for different flood and manage- ment options were determined and a quantification of their productivity achieved. This kind of data is scarce for floodplain grasslands. A plant growth model adapted to tropical floodplain conditions and perennial C4 grasses was developed, and is the first known physiologically based model for floodplain grasslands. 2/ Hydrological processes of ecological importance (flood extent, timing, duration, frequency) were characterized in a poorly gauged basin using a water-balance model combined with remote-sensing techniques, despite precise knowledge of discharge rates, topography and a high cloud cover. 3/ A preliminary analysis explored different flooding scenarios and their impact on fodder production through the use of simple ecosystem service indicators. This PhD contributes to the repertoire of wetland ecosystem ser- vices by building biophysically based simulation models and exploring possible scenarios in a region of the world and an ecosystem where these type of evaluations are rare.

Ao longo dos anos, vêm sendo desenvolvidos trabalhos comprovando a importância de áreas alagadas naturais para a manutenção e preservação da qualidade das águas e do ecossistema fluvial. Este fato, associado à importância dos sistemas rios-planícies de inundação, fazem com que sua investigação e preservação sejam consideradas prioritárias. O objetivo desta pesquisa é analisar experimentalmente fatores que influenciam hidrogramas, conforme a ecologia fluvial de áreas alagadas da microbacia do rio Jacupiranguinha localizado no Baixo Ribeira do Iguape, SP. A concretização deste objetivo iniciou-se com a definição da área de estudo, bem como sua importância para a região. Foram então instaladas cinco estações linimétricas e uma estação climatológica, e em seguida, com os dados de vazão coletados em campo, foram construídas a curva-chave da entrada da área alagada e as incertezas relativas aos seus parâmetros. A partir desses estudos e com o levantamento topográfico de toda planície de inundação, foi determinada a relação entre áreas inundáveis, vazões e cotas hidrométricas do rio. Além disso, com os dados climatológicos, vazões e vegetação superficial foi possível determinar as componentes (precipitação, escoamento superficial, evaporação e armazenamento) do balanço hídrico da micro-bacia. O monitoramento linimétrico do rio Jacupiranguinha, junto com suas séries históricas e curvas de permanência, possibilitou também o cálculo de sua vazão ecológica. Finalmente foram construídos quadros síntese-conceituais, integrando as relações entre todas as variáveis hidrológicas e limnológicas selecionadas, demonstrando assim a forte associação entre o sistema rio-áreas alagadas. / It is very important to improve our knowledge about the floodplains, which have been proved by studies, since these areas are vital to the maintenance and preservation of the quality of waters and the fluvial ecosystem. This fact, associated with the importance of the wetlands-river system, makes its investigation and preservation to be considered number one priority. The objective of this research is to analyze factors that may influence hydrographs, according to the fluvial ecology of wetlands in micro basin of Baixo Ribeira do Iguape Valley, SP. The work began with the definition of the studied field and its importance to the area. Subsequently, five hydrometric station and one meteorological station were installed, and therefore the rating curve in the entrance of floodplain was calculated along with the uncertainties related to its parameters. With these studies and with the topographic survey, it was possible to find the relation between wetlands, river stage and flow. The climatologically information, the river stage and the superficial covering vegetation are essential factors to determinate the components (precipitation, superficial flow, evaporation and the storage) of the water balance at the micro basis of Jacupiraguinha river. The hydrometric observation of the river along with historical series and the probability-duration curve make it possible to calculate the ecological flow. Finally, conceptual charts integrating the relations between hydrological and limnologicals factors were built showing the strong association with the wetlands-river system.

Obwohl es sehr detaillierte Studien zur Nährstoffretention in einzelnen Auen und Feuchtgebieten gibt, ist die Bedeutung von Auen für die Nährstoffbilanz auf Landschaftsebene wenig untersucht. Dies liegt an dem geringen Wissensstand über die wichtigsten Parameter der Nährstoffretention, nämlich die überflutete Auenfläche sowie die in die Aue strömende Nährstofffracht. Zusätzlich gibt es bislang keinen Ansatz, demzufolge beide Parameter abhängig vom Abfluss, und damit variabel für verschiedene zeitliche Einheiten, berechnet werden können. Aus diesem Grund analysiert diese Arbeit die Überflutungshäufigkeiten der Auen von drei Flüssen, Elbe, Main und Rhein. Darauf aufbauend wird eine Abhängigkeit zwischen der überfluteten Fläche und dem Abfluss empirisch abgeleitet, die auf detaillierten Berechnungen der etablierten Software Flys basieren. Ausgehend auf diesen im Folgenden generalisierten Ergebnissen werden eine letztendlich Ereignis basierte mittlere überflutete Auenfläche sowie einströmende Nährstofffracht abhängig vom jeweiligen Abfluss berechnet. Diese und weitere Geoinformationsdaten wie auch Pegel und Gütedaten finden Eingang in jährliche und monatliche empirische Retentionsmodelle. Die berechnete Nährstoffretention in den Auen ist abhängig von der hydrologischen Konnektivität der Auen und dem tatsächlichen Abfluss. Deshalb wird letztendlich das weiterentwickelte Konzept der Ereignis bezogenen Nährstoffretention angewendet und als am realistischsten in Kombination mit hydro-exponentiellen Retentionsmodellen erachtet. Für die naturnahe Elbe werden in Monaten mit Hochwässern bis zu 9% bzw. 10% Retention der transportierten TP bzw. der NO3-N Fracht berechnet. Die Übertragbarkeit dieser Ergebnisse auf eine deutschlandweite Kulisse ist durch die generalisierten Methoden geschaffen. Die vorliegende Arbeit leistet damit einen Beitrag, die Bedeutung der Auen für die Nährstoffbilanz auf Landschaftsebene abhängig von hydrologischen Gegebenheiten zu quantifizieren. / Although there are detailed studies on nutrient retention in single wetlands and floodplains, the role of riparian floodplains for nutrient retention is not investigated very well on a landscape scale, since knowledge on the most important parameters for nutrient retention, inundated floodplains and incoming load, is insufficient. Additionally, a method for describing these parameters as discharge dependent variables is missing. Therefore, the present work analyzes the flooding frequencies on floodplains of three study rivers, Elbe, Main and Rhine. The relation of inundated floodplain extent and current discharge conditions based on detailed results of the established Software Flys is deduced empirically. Based on these subsequently generalized results, finally event related average inundated floodplain extent respectively, incoming nutrient loads are calculated by considering the effects of the hydrologic conditions of each river system. Therefore, available geodata as well as data on water quality and discharge is processed and serves as input data for yearly and monthly empirical retention models. The calculated nutrient retention in floodplains varies with hydrological connectivity of the floodplain to the surface waters as well as with the current hydrologic condition of the river system. For this reason the finally developed concept of event related nutrient retention is suggested as the most realistic in combination with hydro-exponential retention models. The Elbe floodplains are the most natural, and in years with high floods nutrient retention in the floodplains contributes up to 9% respectively 10% of the monthly transported load of TP and NO3-N, which is significant. The transfer of the results to a German-wide application is possible due the generalization of the methods carried out. With the presented results the hydrology dependent role of floodplains for nutrient balances in river systems can be quantified on a landscape scale.

A Amazônia tem sido palco de inúmeras discussões acerca do papel que o meio ambiente desempenha na estruturação das sociedades humanas. Até recentemente, na maior parte das discussões sobre a natureza das limitações ambientais na Amazônia, tem sido comum a escolha de fatores limitantes únicos. Nesses debates as populações Caboclas são de extrema relevância, uma vez que constituem o segmento populacional mais numeroso na Amazônia. Frente a um cenário mundial de crescentes mudanças nos padrões nutricionais, o conhecimento mais aprofundado sobre o consumo alimentar dessas populações, ainda incipiente, é de natural relevância. Assim, este estudo apresenta a comparação dos padrões de consumo alimentar de unidades domésticas assentadas em diferentes ambientes da Amazônia: a Várzea Estuarina (Ilha de Marajó, município de Ponta de Pedras-PA), a Várzea Estacional (Ilha de Ituqui, município de Santarém-PA), e a Floresta de Terra Firme (Floresta Nacional de Caxiuanã, municípios de Melgaço e Portel-PA). O objetivo principal foi determinar e comparar os padrões de consumo alimentar das unidades domésticas, principalmente no que diz respeito às calorias e proteínas, e entender como as unidades domésticas se articulam e se distribuem em relação ao ambiente em que vivem. O método utilizado para coleta de dados foi o recordatório de 24 horas. Concluiu-se, neste trabalho que: (1) existem diferenças significativas no padrão de consumo entre os diferentes ambientes estudados; (2) os padrões encontrados para os ambientes de Várzea não são mais semelhantes entre si do que em relação à Terra Firme; (3) as unidades domésticas das comunidades da Floresta de Terra Firme não parecem apresentar menor consumo de alimentos, calorias, ou proteínas do que os demais ambientes; (4) parece haver a formação de um grande grupo composto por unidades domésticas da Várzea Estuarina e da Terra Firme, ambientes de maior diversidade de alimentos, e outro grupo constituído pelas unidades domésticas da Várzea Estacional; (5) as unidades domésticas não se distribuem conforme as bacias nas quais estão assentadas. Assim, o poder explicativo do modelo de tipologia de bacias se vê comprometido, pelo menos em se tratando de ambientes, como a grande parte dos encontrados na região Amazônica, que se encontram em posições intermediárias no gradiente ambiental, não coincidindo com os protótipos de Várzea ou Terra Firme normalmente retratados na literatura. / The Amazon has been the scene of numerous discussions about the environment´s role in the structuring of human societies. Until recently, in the majority of the discussions about the nature of the environmental constraints in the Amazon, the choice of single limiting factors has been a constant. In these discussions, the Caboclo societies are very important, since they are the most numerous segment of the Amazonian population. Faced with a scenario of increasing global changes in dietary patterns, a deeper knowledge on the food intake of these populations, still in its infancy, is of natural relevance. Thus, this study presents a comparison of food consumption patterns of households settled in different Amazonian environments: the Estuarine Floodplain (Marajo Island, muncipality of Ponta de Pedras-PA), the Seasonal Floodplain (Ituqui Island, municipality of Santarem-PA), and the Upland Forest (FLONA Caxiuana, municipalities of Melgaco and Portel-PA). The main objective was to determine and compare the food consumption patterns of households, especially with regard to calories and proteins, and to understand how the households are structured and distributed in relation to their environment. The method used to collect data was the 24-hour food-recall. The conclusions of this study were: (1) there are significant differences in consumption patterns between the different environments, (2) the patterns found in the diferent Floodplains environment don´t show greater similarity (3) the households of the communities of Upland do not appear to have a lower consumption of food, calories, or protein in comparison to other environments, (4) there seems to be the formation of a large group of households that include both the Estuarine Floodplain and the Upland Forest, environments with a wider variety of foods, and another group with the households of the Seasonal Floodplain (5) the households are not distributed according to the basin in which they are settled. Thus, the explanatory power of this model finds himself committed, at least when it comes to environments, such as the majority of those found in the Amazon region, that find themselves in intermediate positions in an environmental gradient, not matching the Floodplain or Upland prototype usually portrayed in the literature.

Der geschichtliche Prozess der Bodenbesetzung und – nutzung auf der Grundlage von Entwaldung und ungeordneter Bodenbewirtschaftung verursachte Konflikte zwischen der Zielsetzung der Umweltsanierung und der sozialwirtschaftlichen Reproduktion der auf Flächen mit hohen Umwelteinschränkungen siedelnden Landwirte. Diese Dichotomie zeigt sich derzeit in der Anwendung des Umweltrechts, insbesondere im neuen brasilianischen Waldschutzgesetz, das 1965 durch das Bundesgesetz Nr. 4.771 erlassen wurde, wenn es sich um Naturschutzgebiete (APPs) handelt, also um Landstriche entlang der Gewässer, die entsprechend geschützt und deren natürliche Vegetationsbedingungen erhalten werden müssen. Ausgehend von Elementen der Flussgeomorphologie gründet sich die von der vorliegenden Untersuchung verfolgte Diskussion auf die Hinterfragung der geometrischen Maβnahmen der Naturschutzbestimmungen durch die Vorlage einer Methodik zur Bestimmung dieser Flächen. Um zum Ergebnis zu gelangen, wird eine geschichtliche Rückbesinnung auf den Bodenbesetzungsprozess in Nordwest Rio Grande do Sul, zu der die Proben der Untersuchung gehören, sowie eine theoretische Interpretation des weltweiten Naturschutzes vorgenommen und werden die Naturschutzgebiete für Brasilien auf drei Untersuchungsebenen diskutiert: der gegebene gesetzliche Rahmen, die Verwendung dieser Flächen und der Zustand, in dem diese sich im Nordwesten von Rio Grande do Sul befinden. Die soziale Funktion des landwirtschaftlichen Betriebs wird als wichtiger Punkt dieser Diskussion betrachtet, denn von ihr ausgehend geschieht der ganze Prozess der Verantwortungsüberweisung für den Schutz oder Nichtschutz von Naturschutzgebieten. In diesem Sinne untersuchen wir auch, wie IBAMA, FEPAM und Staatsanwaltschaft sich positionieren und angesichts der gesetzten Thematik handeln. Für die vorgeschlagene Methodik bestimmten wir drei Bereiche des Flusses Santo Cristo zu Pilotflächen, für die wir die Längsdeiche und Auen als Parameter für die Bestimmungen der Naturschutzgebiete definierten. Ebenso beurteilten wir die Bodenstruktur der Region, um eine der Art der lokalen Betriebshöfe unmittelbar verbundene Deutung zu ermöglichen. Von diesen Vorzeichen ausgehend wurde eine kritische Lesart des Verhaltens dieser Flächen möglich, indem ihre derzeitige Verwendung derjenigen der gesetzlichen Anforderungen entgegengestellt wurde. Aus der vorliegenden Untersuchung ergeben sich als wesentliche Schlüsse: Eine vertiefte Untersuchung über die Naturschutzgebiete ist dringend und erforderlich, um einen neuen Gesetzesvorschlag zu erarbeiten, der effektive Fachparameter zur Bestimmung der Naturschutzgebiete festlegt und der gleichzeitig die Entwicklung von Untersuchungen anstrebt, die darauf zielen, alternative nachhaltige Nutzungsalternativen für diese Flächen vorzulegen; Beurteilung der Schutz- und Erhaltungskonzeptionen in der Absicht, dass letztere eine breite Palette von Vorteilen für die kleinen landwirtschaftlichen Betriebshöfe in dem Maβe mit sich bringen, wie die Bodenschutzmaβnahmen zum Ausgleich der Natur beitragen und in der Erzeugung dieser Betriebshöfe einen reellen Gewinn erbringen. Schlieβlich legen wir eine Reihe von Studien vor, die in der Absicht einer Vertiefung der von uns erforschten thematischen Diskussion verfolgt werden können. / O processo histórico de uso e ocupação da terra, baseado no desflorestamento e no manejo desordenado do solo, tem gerado conflitos entre os objetivos de recuperação ambiental e de reprodução socioeconômica dos agricultores assentados sobre áreas de elevadas restrições ambientais. Esta dicotomia reflete-se na atualidade através da aplicação mais efetiva da legislação ambiental, principalmente, do Código Florestal brasileiro, instituído pela Lei Federal n. 4.771 de 1965, que trata das Áreas de Preservação Permanente, APPs, que são as faixas marginais aos corpos hídricos que devem ser devidamente preservadas e mantidas com vegetação nativa. A discussão apresentada pelo presente estudo está pautada no questionamento das medidas geométricas contidas na definição das APPs nesse instrumento legal, buscando apresentar uma metodologia para a definição destas áreas a partir de elementos da geomorfologia fluvial, além daqueles relacionados com a cobertura vegetal de entorno. Para chegar aos resultados desse estudo se apresenta uma retomada histórica do processo de ocupação da Região Noroeste do Rio Grande do Sul, na qual se inserem as áreas amostrais, faz-se uma leitura teórica sobre conservação da natureza em nível mundial e discute-se as APPs em três níveis de análise para o Brasil: a) o arcabouço jurídico que está posto; b) o uso destas áreas e c) o estado da arte em que elas se apresentam no noroeste do Rio Grande do Sul. A discussão da função social da propriedade rural é vista como ponto importante desta discussão, por ser a partir dela que se dá todo o processo de responsabilização pela preservação ou não das APPs. Neste sentido, buscamos também compreender como o Ibama, a Fepam e o Ministério Público Estadual se posicionam e desenvolvem as suas atividades frente à temática colocada. Definimos como áreas piloto para a aplicação da metodologia proposta, três setores do Rio Santo Cristo, para os quais definimos os diques marginais e as planícies de inundação como parâmetros para a definição das APPs. Da mesma forma, avaliamos a estrutura fundiária da região para possibilitar uma leitura diretamente relacionada com o tipo de propriedade existente no local. A partir destas definições foi possível estabelecer uma leitura crítica das características dessas propriedades, comparando o seu uso atual com as exigências legais. Ficam como principais conclusões do presente estudo: a) que é urgente e necessário um estudo mais aprofundado sobre a questão das APPs para que seja possível apresentar uma proposta de alteração da legislação que busque parâmetros técnicos efetivos para a definição das APPs; b) que se busque igualmente o desenvolvimento de estudos que objetivem apresentar alternativas de uso sustentado para estas áreas; c) que se avaliem os conceitos de preservação e conservação com o intuito de compreender que o último traz uma grande gama de benefícios para as pequenas propriedades rurais, na medida em que as práticas conservacionistas auxiliam no equilíbrio da natureza e trazem um ganho real na produção destas propriedades. Por fim, apresentamos um conjunto de estudos que podem ser realizados com o intuito de aprofundar as discussões da temática por nós pesquisada. / The historic land grab and land usage process based on deforestation and disorderly land management caused conflicts between environmental cleanup and socioeconomic reproduction of the farmers settled on areas that underlie strict environment restrictions. This dichotomy at present gets evident in the application of the environmental legislation, particularly the new Brazilian Forest Code entitled by the federal Law No. 4.771 of 1965, when it involves permanent nature reserve (APPs), that is, marginal stripes along water corps that must be preserved with the associated original vegetation. The discussion herewith stated is based on the closer examination of the geometrical measures of the definition of the permanent nature reserves trying to present a method for the definition of theses areas out of the elements of the fluvial geomorphology. To reach the result, we make recourse to the historical land grab process in the northwestern region of Rio Grande do Sul, to which belong the areas herein studied. We make a theoretical interpretation of nature conservation at international level and discuss nature reserves at three study levels for Brazil: the given legal framework; the usage of these areas; and their conditions in northwest Rio Grande do Sul. The discussion of the social function of the farms is seen as an important aspect of this discussion because thereof happens the responsibleness for the conservation or not conservation of the preservation areas. We also study the positioning of Ibama, Fepam and prosecution in this question. We determinate three segments of the Santo Cristo river as pilot areas for the application of the proposed methodology, wherefore we defined natural levee and floodplains as patterns for the definition of nature preservation areas. We did also evaluate region’s estate to allow an understanding directly related to the kind of local property. These definitions allowed us establishing a critical understanding based on the behaviour of these areas comparing their current usage to the legal demands. The most important conclusions of this study are: 1) a deeper study of nature preservation areas urges and is necessary to allow the presentation of a new legal proposal that looks for effective technical patterns for the definition of nature reservation areas; 2) that one also tries to develop studies that try to show alternatives of sustainable usage of these areas; 3) that preservation and conservation concepts get evaluated with the intend to understand that this brings a wide scope of benefits to the small farms thus far as the conservation practices help to stabilize nature and to carry a real gain in the production of these farms. Finally we present a scope of studies that can be done with the aim of deepening the discussions of the question here studied.