京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第22785号 / 農博第2428号 / 新制||農||1081(附属図書館) / 学位論文||R2||N5305(農学部図書室) / 京都大学大学院農学研究科地域環境科学専攻 / (主査)教授 藤原 正幸, 教授 村上 章, 教授 中村 公人 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

This thesis presents an experimental study, both in the field and laboratory to cast more light on the primary role of the river floodplains in releasing and/or removing total-P to/from the in-stream load, under high runoff and flood conditions, by investigating the soil total-P spatial and vertical deposition patterns and topsoil erodibility, along the three (3) main river sections (e.g., headwaters, transfer and deposition zones) of an agricultural watershed, such as the Turkey River (TR). In soils, phosphorus, P, primarily exists as sediment-bound and less often as dissolved. During wet hydrological years, soil erosion and surface runoff are the main P release and transport mechanisms, while during dry hydrological years, P leaches to the deeper soil levels and is transported to freshwaters through groundwater discharge. In between the upland areas and the river network, there is a buffer zone, known as floodplain that regulates the flux exchanges between these two watershed components. Floodplains play an essential role in the riverine system health by supporting important physical and biochemical processes and improving the water quality downstream. These characteristics have led to the conclusion that floodplains primarily act as sinks for P. However, floodplains are subject to erosion as well, where soil particles along with the attached P are removed from the topsoil or enter re-suspension, under high runoff and flood conditions. The study provides an insight into the soil total-P deposition patterns across the floodplains of five (5) identified field sites and couples them with topsoil erodibility to eventually address the research objectives, which can be summarized as follows: (i) investigation of the soil total-P spatial and vertical variability across the floodplains along the main river zones and development of relationships between P variability and soil physical properties (e.g., soil texture); (ii) identification and characterization of the soil total-P deposition patterns across the floodplains (e.g., short- vs. long-term P deposition areas); and (iii) comparisons of the soil total-P concentrations and critical shear stresses among the main river zones and determination of their primary function either as P sources or sinks, under high runoff and flood conditions. Following that line of thinking, this research results comprise of three (3) parts, each one addressing a specific objective. The first part of the results includes the soil texture and total-P concentration analyses of the extracted soil profiles to identify the soil total-P spatial and vertical deposition patterns across the floodplains, as well as, to investigate the total-P variability with respect to soil physical properties (e.g., soil texture). The second part of the results focuses on investigating the role of topography (e.g., flat vs. ridge vs. swale land surfaces) and flood characteristics (e.g., frequency, magnitude, duration) in soil total-P spatial and vertical deposition patterns across the river floodplains to understand the time-scale nature of the P storage. The last part of the results presents the experimentally determined topsoil critical shear stress values and erodibility rates to characterize the floodplains’ primary function, based on their location along the three (3) main river zones, either as sources or sinks for total-P, during high runoff and flood conditions. Overall, the results of this research show that (i) the total-P concentration in soils is tightly related to the fine particle content and monotonic linear relationships can be established between the two variables. In other words, the higher the fine particle content, the higher the total-P concentration in soils; (ii) a mixture of two normal distributions fit the log-transformed soil total-P concentration data of each field site considered in this study. The fitted distributions successfully capture the two peaks of the soil total-P concentration data correspond to the lower and upper floodplain terraces; (iii) the lower floodplain terraces (e.g., 2- and 5-year floodplains) are characterized by significantly lower soil fine particle percentage contributions and total-P concentrations compared to the upper floodplain terraces, at a 5% confidence level. These patterns can be attributed to the fact that the lower floodplain terraces are frequently flooded and/or under inundation compared to the upper floodplain terraces and thus part of the fine particles along with the attached P are regularly winnowed away. Therefore, the lower floodplain terraces can be considered as short-term P storage means, in between two consecutive major flood events, while the upper floodplain terraces act more as long-term P storage means; (iv) there is a longitudinal increase in the topsoil critical shear stress values, which follows the increase in the fine particle content reconfirming the principle that the more the fine particle content in soils, along with the existence of vegetation with dense, well-developed root systems, the more resistant to erosion are the soils. From a soil erodibility perspective, the floodplains along the headwaters zone can be considered as major fine sediment and total-P sources contributing to the in-stream loads, while the floodplains along the deposition zone primarily act as sinks for fine sediment and total-P. As far as the role of the floodplains along the transfer zone, they can be considered as sinks for fine sediment and total-P during low magnitude runoff and flood events (e.g., 2-; 5-; and 10-year return periods), while during higher magnitude events, they act as sources releasing fine sediment and total-P; and (v) topsoil samples characterized by dense, well-developed root systems fall approximately along a trend line that follows almost a parallel pattern with the trend line for the topsoil samples without dense and/or well-developed root systems. The existence of dense, well-developed vegetation root systems to topsoil consistently increases its critical shear stress threshold (e.g., > 1 Pa) and thus its ability to resist erosion.

Made available in DSpace on 2014-12-17T14:01:58Z (GMT). No. of bitstreams: 1 ThiagoPNM.pdf: 364395 bytes, checksum: d196df37d1feef6ed3e5d5cd9f931834 (MD5) Previous issue date: 2009-02-10 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The eutrofization is a natural process of accumulation of nutrients in aquatic?s body that it has been accelerated for the human?s actives, mainly the related with the activities of camp, industrial and the inadequate disposition of the domestic sewage. The enrichment of the aquatic?s body with nutrients, mainly the nitrogen and the phosphorus, and the consequent proliferation of algae and Cyanobacteria can commit the quality of the water for the public provisioning, for the fish farming and for other ends. The problem becomes more critical when there is a shortage of water naturally as in the semi-arid area of the Brazilian northeast. Before that problem this work had as objective evaluates the trophic state of six reservoirs of the basin of River Serid? of Rio Grande of Norte and also estimate the capacity of load of match of the reservoir and risk probabilities based on the established limits by the resolution Conama 357/05. The results demonstrate that the six reservoirs are eutrofization, with concentration of total phosphorus and cloro a in the water upster to 50 e 12 μg l-1. The results show that space homogeneity exists in the state trophic of the reservoirs, but a significant variation interanual in function of the increase of the concentrations of nutrients and decrease of the transparency of the water with the reduction of the body of water accumulated in the reservoirs.The results of the simulation risk estocastic show that the reservoirs could receive annually from 72 to 216 Kg of P, assuming a risk of 10% of increasing in more than 30 μg l-1 the annual medium concentrations of total match in the water of these reservoirs. This load could be high in until 360 kg of P a year in case the managers assume a risk of 10% of increasing in more than 50 μg l-1 the annual medium concentrations of total phosphorus in the waters of these reservoirs / A eutrofiza??o ? um processo de ac?mulo de nutrientes em ambientes aqu?ticos que tem sido acelerado pelas atividades antr?picas, principalmente as relacionadas com as atividades agropastoris, industriais e a disposi??o inadequada dos efluentes dom?sticos. O enriquecimento do ambiente aqu?tico com nutrientes, principalmente o nitrog?nio e o f?sforo, e a conseq?ente prolifera??o de algas e cianobact?rias podem comprometer a qualidade da ?gua para o abastecimento p?blico, para a piscicultura e para outros fins. O problema se torna mais cr?tico quando h? naturalmente uma escassez de ?gua como na regi?o semi-?rida do nordeste brasileiro. Diante dessa problem?tica este trabalho teve como objetivo avaliar o estado tr?fico de seis reservat?rios da bacia do Rio Serid? no Rio Grande do Norte e tamb?m mensurar a capacidade de carga de f?sforo dos reservat?rios visando o seu enquadramento segundo a resolu??o CONAMA 357/05. Os resultados demonstram que os seis reservat?rios encontram-se eutrofizados, com concentra??es de f?sforo total e clorofila a na ?gua superiores a 50 e 12 ?g l-1 respectivamente. Os resultados mostram que existe uma homogeneidade espacial, mas uma significativa varia??o interanual no estado tr?fico dos reservat?rios em fun??o das varia??es do volume de ?gua acumulado nos reservat?rios. Os resultados da simula??o estoc?stica de risco mostram que os reservat?rios com maior capacidade de carga poderiam receber anualmente at? 216 Kg de P, assumindo um risco de 10% de aumentar em mais de 30 ?g l-1 as concentra??es m?dias anuais de f?sforo total na ?gua destes reservat?rios. Esta carga poderia ser elevada em at? 360 kg de P por ano caso os gestores assumam um risco de 10% de aumentar em mais de 50 ?g l-1 as concentra??es m?dias anuais de f?sforo total nas ?guas destes reservat?rios