Phosphorus mass-balance studies of Dingle Marsh, Idaho indicated that the marsh was an annual net sink for total suspended sol ids and all forms of phosphorus under consideration: total phosphorus, particulate phosphorus, total dissolved phosphorus, dissolved organic phosphorus, and orthophosphate phosphorus. During some months, however, more phosphorus was exported from the marsh than entered. Phosphorus mass-balance dynamics were compared between night and day. Total suspended solids and particulate phosphorus dynamics were controlled by sedimentation of particulate material, a physical process, and were unaffected by light conditions. Dissolved organic and ortho-phosphorus were affected by light conditions indicating, at least indirectly, that biological processes were affecting dissolved phosphorus dynamics. These phosphorus fractions were occasionally released in large amounts by the marsh at night. An in situ enclosure experiment was performed to determine major sites of phosphorus uptake/release. A twentyfour-hour rate of particulate phosphorus decrease in the enclosures could be predicted (r2=0.89) by knowing the initial concentration of total suspended solids. On a twentyfour-hour basis, periphyton, detritus, and live bulrushes tended to remove more dissolved organic phosphorus from the water than they added to it while plankton and sediments added dissolved organic phosphorus to the water. Orthophosphates were removed from the water by plankton, detritus, and periphyton with plankton dominating the changes. Live bulrushes or sediments within the bulrush system tended to be a source for orthophosphates. The open water ecosystem was a greater net source for dissolved organic phosphorus than the bulrush system. The open water system was a greater net sink, however, for orthophosphates, than was the bulrush community.

Fundação Instituto de Pesquisas Econômicas / The pressure on the natural resources has being shown more intense in the last decades, increasing degradation of air, soil and water around the world. Among the substances related to the environmental impacts that containing phosphate is one of great importance, being original from industrial discharges, domestic uses, and agricultural. The last one contributes mainly through the excessive application of phosphate fertilizers. The soil use out of its capacity generates great amount of sediments that goes to rivers, lakes and seas. When that sediment carries with it great content of phosphorus, it can unchain the eutrophication process, that is characterized by the increase of nutrients in the aquatic system, leading to the decrease in the amount of dissolved oxygen in the water, what causes the death of several species. The present work was divided in two studies that aimed to determine the relationship of phosphorus from sediments dynamics in the process of water contamination in function of soil management and vegetable cover in a small watershed at city of Agudo Rio Grande do Sul State, Brazil. Were collected samples in three periods with different predominant soil uses. The sediment concentration was obtained by drying at 105ºC. The phosphorus dessorption was made by extraction with anion exchange resin on special recipients that allow control the redox conditions. Also, was realized the chemical fractionation of phosphorus from different sites of watershed. The concentration of suspended sediments on water curses is related with characteristics of rain and soil use, and the submission of the sediments to oxygen poor atmosphere favored the phosphorus dessorption. The bioavailable phosphorus and potential bioavailable phosphorus desorbed from sediments were incremented by antropic action. The phosphorus chemical fractionation is a good index of human action on aquatic source, being possible to determine the sediments origin from sub-basins under different antropization degrees. / A pressão sobre os recursos naturais vem mostrando-se mais intensa nas últimas décadas, gerando degradação do ar, do solo e da água em todo o mundo. Dentre as substâncias relacionadas aos impactos ambientais aquelas contendo fosfatos são de grande importância, sendo originário de descargas industriais, domésticas, e agrícola. Esta última contribui principalmente através da aplicação excessiva de fertilizantes fosfatados e resíduos enriquecidos. O uso do solo fora da sua capacidade gera grande quantidade de sedimentos que vão para rios, lagos e mares. Quando esse sedimento carrega consigo alto teor de fósforo, pode desencadear o processo de eutrofização, que se caracteriza pelo aumento de nutrientes no sistema aquático, levando a diminuição na quantidade de oxigênio na água, o que causa a morte de várias espécies. Dessa forma, o presente trabalho foi dividido em dois estudos que objetivaram determinar a relação da dinâmica do fósforo dos sedimentos no processo de contaminação hidrográfica em função do manejo do solo e da cobertura vegetal da pequena bacia hidrográfica rural no município de Agudo RS. Foram coletadas amostras em três épocas com diferentes usos predominantes do solo. A concentração de sedimento foi obtida por secagem a 105ºC. A dessorção de fósforo foi realizada através da extração com resina trocadora de ânions em recipientes especiais que permitiram controlar as condições redox. Também, foi realizado o fracionamento químico do fósforo do sedimento oriundo de diferentes locais da pequena bacia. A concentração de sedimento em suspensão nos cursos de água está relacionada com as características da chuva e com o uso do solo, e a submissão dos sedimentos em ambiente pobre em oxigênio favoreceu a dessorção do fósforo. Os teores de fósforo particulado biodisponível e de fósforo particulado potencialmente biodisponível dessorvidos de sedimentos são incrementados pela ação antrópica. O fracionamento químico do fósforo é um bom indicador da ação humana sobre os mananciais aquáticos, sendo possível discriminar a origem dos sedimentos das sub-bacias com diferentes graus de antropização.

Many agricultural fields that have received long-term applications of P often contain levels of P exceeding those required for optimal crop production. Knowledge of the effect of the P remaining in the soil (residual effect) is of great importance for fertilization management. In order to characterize P forms in soils, a wide variety of methods have been proposed. The use of dialysis membrane tubes filled with hydrous ferric oxide (DMT-HFO) has recently been reported as an effective way to characterize P desorption over a long-term in laboratoty studies. However, there is little information on the relationship between kinetics of P release using this new method and plant P uptake. This method consist of a procedure of shaking a sample for a long period of time there by exploiting the whole volume of the soil which is in contrast to the actual plant mode of uptake. This method has also practical limitations in employing it for a routine soil analysis, as it is very expensive and time consuming. The objectives of this study were (i) to study the changes in labile, non-labile and residual P using successive P desorption by DMT-HFO followed by a subsequent fractionation method (combined method) (ii) to assess how the information gained from P desorption kinetic data relates to plant growth at green house and field trials (iii) to investigate the effect of varying shaking time on DMT-HFO extractable P and (iv) to propose a short cut approach to the combined method. The release kinetics of the plots from long term fertilizer trials at the University of Pretoria and Ermelo were studied. P desorption kinetics were described relatively well by a two-component first-order model (R2 = 0.947, 0.918,&0.993 for NPK, MNK,&MNPK treatments respectively). The relative contributions of both the labile pool (SPA) and the less labile pool (SPB) to the total P extracted increased with increased P supply levels. Significant correlations were observed between the rate coefficients and maize grain yield for both soil types. The correlation between the cumulative P extracted and maize yield (r = 0.997**) however was highly significant for Ermelo soils. This method was also used to determine the changes in the different P pools and to relate these P fractions with maize yield. Highly significant correlations were observed between maize grain yield and the different P fractions including total P. In both soil types the contribution of both the labile and non-labile inorganic P fractions in replenishing the solution Pi was significant where as the contributions from the organic fractions were limited. The C/HCl-Pi is the fraction that decreased most in both cases as well. Investigation was carried out to evaluate the effect of varying shaking periods on the extractable DMT-HFO-Pi for UP soils of varying P levels. Four shaking options were applied. Significant difference was observed for the treatment of high P application. Shaking option 2 seemed relatively better than the others since it showed the strongest correlation. Thus for soils with high releasing kinetics and high total P content, provided that the P release from the soil is a rate limiting step, reducing the length of shaking time could shorten the duration one needs to complete the experiment with out influencing the predicting capacity of the methodology. The other objective of this thesis was also to present a short cut method alternative to the combined fractionation method. Comparison of the sum of DMT-HFO-Pi, NaHCO3-Pi, NaOH-Pi, D/HCl-Pi and C/HCl-Pi extracted by a conventional step-by-step method with the sum of DMT-HFO-Pi and a single C/HCl-Pi extraction as a short cut approach for all extraction periods resulted in strong and significant correlations. The C/HCl-Pi fraction extracted by both methods was correlated with maize grain yield and it was found to be highly significant. This study revealed that this short cut approach could be a simplified and economically viable option to study the P dynamics of soils especially for soils where the P pool acting as a source in replenishing the labile portion of P is already identified. The method employed here therefore could act as an analytical tool to approximate successive cropping experiments carried out under green house or field condition. However, data from a wider range of soils is needed to evaluate the universality of this method. More work is also required in relating desorption indices of this method with yield parameters especially at field level. / Thesis (PhD)--University of Pretoria, 2009. / Plant Production and Soil Science / PhD / unrestricted

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L'activitat humana és una de les majors causes d'elevades concentracions de nutrients i substàncies tòxiques en els ecosistemes fluvials. Entre la gran varietat de factors que alteren aquests ecosistemes, l'eutrofització i la contaminació per metalls pesants són dos dels principals problemes ambientals en països desenvolupats. Els biofilms fluvials (també anomenats comunitats perifítiques) representen una eina valuosa per avaluar els efectes dels contaminants (ex. nutrients i metalls) en els ecosistemes aquàtics. Aquest treball pretén investigar el destí i els efectes del Cu en els ecosistemes fluvials centrant-se en les comunitats perifítiques. Diferents metodologies han estat desenvolupades i/o adaptades per investigar específicament la dinàmica del Cu, la seva toxicitat i bioacumulació en comunitats perifítiques naturals, i la interacció entre l'eutrofització i la toxicitat del Cu en aquests ecosistemes. / Human activity is one of the major causes of elevated concentrations of nutrients and toxic substances in fluvial ecosystems. Among the many ecosystem stressors, eutrophication and metal pollution are two of the major environmental problems in many developed countries. Fluvial biofilms (periphyton communities) are a useful tool for monitoring the effects of pollutants (e.g. nutrients and metals) into aquatic ecosytems. The present study aims to investigate the fate and effects of Cu in fluvial ecosystems focusing on periphyton communities. Different methodologies have been developed and/or adapted to specifically investigate the dynamics of Cu, its toxicity and bioaccumulation on natural periphyton communities, and the interaction between eutrophication and Cu toxicity in these ecosystems.