Cyanobacteria are widely distributed in marine, freshwater and terrestrial habitats. Some cyanobacterial genera can convert di-nitrogen gas (N2) to bioavailable ammonium, i.e. perform nitrogen (N) fixation, and are therefore of profound significance for N cycling. N fixation by summer blooms of cyanobacteria is one of the largest sources of new N for the Baltic Sea. This thesis investigated N fixation by cyanobacteria in the Baltic Sea and explored the fate of fixed N at different spatial and temporal scales. In Paper I, we measured cell-specific N fixation by Aphanizomenon sp. at 10 ºC, early in the season. Fixation rates were high and comparable to those in late summer, indicating that Aphanizomenon sp. is an important contributor to N fixation already in its early growth season. In Paper II, we studied fixation and release of N by Aphanizomenon sp. and found that about half of the fixed N was rapidly released and transferred to other species, including autotrophic and heterotrophic bacteria, diatoms and copepods. In Paper III, we followed the development of a cyanobacterial bloom and related changes in dissolved and particulate N pools in the upper mixed surface layer. The bloom-associated total N (TN) increase was mainly due to higher particulate organic N (PON) concentrations, but also to increases in dissolved organic nitrogen (DON). About half the PON-increase could be explained by the sum of N-fixing cyanobacteria, other phytoplankton (&gt;2µm) and zooplankton, indicating that production was stimulated by the N fixation. In Paper IV, we used a growth model based on measured photosynthesis–irradiance relationships to explore the production potential of Aphanizomenon sp. The model included data on irradiance, biomass, temperature and light attenuation (1999–2013). Until the bloom peak, the modelled production matched the measured biomass, indicating low production losses. Over the whole season, the modelled production could explain a substantial part of the summer TN increase, assuming that plausible losses (such as grazing or cell lysis) are retained within the upper mixed layer. Complementing the other data, we also investigated the nutrient content (Paper I) and varying cell width (Paper IV) of Aphanizomenon sp. By a combination of approaches, this thesis has contributed new information on cyanobacterial N fixation rates, the transfer of fixed N to other organisms in the food web and shown the potential for fixed N to stimulate summer primary and secondary production in the Baltic Sea. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.</p>

Made available in DSpace on 2017-07-25T19:29:43Z (GMT). No. of bitstreams: 1 Ademir Oliveira Ferreira.pdf: 1294842 bytes, checksum: 8d7036f6aefa0cf3c549b0c63029e109 (MD5) Previous issue date: 2009-07-13 / Decrease in soil organic carbon (SOC) content of the surface layer into deeper layers indicates the occurrence of the stratification in the profile due to continuous C addition of crop residues enriching the soil surface layer. The objective of this study was: in Chapter 3 the relationship of stratification (RE) of C of the soil organic matter (SOM) pools can be an indicator of C sequestration in no-tillage soils? In the chapter 4 the tensile strength of aggregates is affected by the C content of Pedosequence of Latosol with medium and clay texture? in Chapter 5 which is the C balance and the amount of crop residue needed to maintain a stable C balance in a Latosol with a medium and clay texture? The experimental design was a completely randomized 2x2x2 factorial with 12 treatments. Treatments consisted of: a) an Oxisol (Red Latosol) with medium and clayey texture, b) two soil sampling periods (T1 and T2) with one year interval between them, and c) two soil sampling depths (0-5 and 5-20 cm). The soil attributes assessed were: the separation of water stable aggregates classes (19-8, 8-4, 4-2, 2-1, 1-0,5 and 05-0,25 mm), particulate organic carbon (POC), total particulate nitrogen (TPN) in the aggregate classes. Also was determined total organic carbon (TOC) and total nitrogen (NT) in the whole sample and in the aggregates sizes classes and tensile strength of aggregates. The relationship of stratification was calculated by dividing the TOC and TN values of 0-5 cm layer by the values of the same attributes of 5-20 cm layer. The C sequestration rate and the stratification ratio changes were calculated by the difference between the T2 values minus T1. The tensile strength was measured in soil aggregates and assessed in 1920 aggregates for each sampling time. Also TOC and NT content were measured in aggregates. The aggregates greater than 8 mm represented more than 70 of the total mass in both the clay and in sandy soil. The relationship of stratification ratio (0-5:5-20 cm) of SOC, TN, POC and TPN soil indicated the improvement of the surface layer. A significant linear relationship between the SR and C sequestration rate in both textural classes showed an increase in C sequestration and was more evident in LV with medium texture. The increase in TOC content resulted in decreased tensile strength (TS) of the aggregates and was more evident in the 0-5 cm layer. The TS showed inverse relationship with the soil density and was higher in the LV medium texture. The rate of sequestration of C was 0.86 for the LV with medium texture and 0.76 Mg ha-1 for the clay texture and to maintain the stable balance of C is required an input of 8.6 Mg ha-1 of crop residues. The results presented confirm the hypothesis of SR to be a sensitive indicator for the rate of carbon sequestration in no-tillage soil. Key-words: Carbon stock, Carbon balance, Carbon sequestration, Soil management systems, particulate organic carbon, particulate nitrogen. / A redução no conteúdo de carbono (C) da camada superficial em direção as camadas mais profundas do solo indica a formação da estratificação no perfil devido à adição contínua de C pelos resíduos orgânicos resultando no enriquecendo a camada superficial do solo. O objetivo deste trabalho foi avaliar os seguintes assuntos: a) a relação de estratificação (RE) de C dos compartimentos da matéria orgânica do solo (MOS) pode ser um indicador do seqüestro de C no sistema plantio direto. b) a resistência tênsil dos gregados pode ser afetada pelo conteúdo de C em Pedossequencia de Latossolo com textura média e argilosa. c) o balanço de C e a quantidade de resíduos culturais necessária para manter o equilíbrio estável de C em um Latossolo com textura média e argilosa. O delineamento experimental foi um fatorial 2x2x2 inteiramente casualizado com 12 tratamentos. Os tratamentos constituíram-se de: a) um Latossolo Vermelho com textura média e argilosa, duas épocas de amostragem do solo (E1 e E2) com um ano de intervalo entre si e duas profundidades de amostragem (0-5 e 5-20 cm). Os atributos avaliados foram: a separação das classes de agregados do tamisamento úmido (19-8, 8-4, 4-2, 2-1, 1-0,5 e 05-0,25 mm), o carbono orgânico particulado (COP), o nitrogênio total particulado (NTP) nas classes de agregado, o C orgânico total (COT) e o nitrogênio total (NT) na amostra integral e nas classes de agregados e a resistência tênsil dos agregados. A relação de estratificação (RE) foi calculada dividindo-se o valor de COT e NT da camada de 0-5 cm pelo valor na camada 5-20 cm. A taxa de seqüestro de C e a variação da relação de estratificação foram calculadas através da diferença (D) entre os valores da E2 menos o da E1. A resistência tênsil (RT) do solo foi avaliada em 1920 agregados de cada época de coleta, determinando-se, também o conteúdo de COT e NT. A classe de agregado > 8 mm representou mais de 70% da massa dos agregados tanto na textura argilosa como na arenosa. Da mesma forma, o conteúdo de COT e NT foram maiores na classe de agregado > do que 4 mm comparado as demais classes nas duas classes texturais. A relação de estratificação 5:5-20 cm) de COT, NT, COP e NTP do solo indicou a melhoria da qualidade do solo da camada superficial. A relação linear e significativa entre o DRE com a taxa de seqüestro de carbono nas duas classes texturais mostrou o aumento no seqüestro de C e foi mais evidente no LV com textura média. O incremento do conteúdo de COT resultou na diminuição da resistência tênsil (RT) dos agregados e foi mais evidente na camada de 0-5 cm. A RT apresentou relação inversa com a densidade do solo e foi superior no LV textura média. A taxa de seqüestro de C foi de 0,86 para o LV textura média e 0,76 Mg ha-1 para o textura argilosa e para manter o equilíbrio estável de C é necessário o aporte de 8,6 Mg ha-1 de resíduos culturais. Os resultados apresentados confirmaram a hipótese da RE ser um indicador sensível para a taxa de seqüestro de carbono no solo em um sistema sob plantio direto consolidado.

L'eau des fleuves, des rivières, des lacs et des réservoirs ne représente que 0,26 % des 2,5 % (35 millions de km3) d'eau douce disponibles à l’état liquide sur Terre, or sa qualité et quantité ont fortement diminué ces dernières années. Sa dégradation a des conséquences sur l'agriculture, la santé, l'environnement et l'économie des territoires et est aujourd'hui au centre des préoccupations sociétales. Les objectifs de la présente thèse sont pour trois fleuves localisés dans le Bouclier des Guyanes, au nord de l'Amérique du Sud (le Maroni, l'Oyapock, l'Orénoque): (i) d'utiliser et d'adapter des outils novateurs de télédétection pour suivre et quantifier, sur du long terme, leurs charges sédimentaires en suspension, (ii) d'évaluer l'existence de tendances spatio-temporelles, ainsi que de ruptures dans les chroniques de données, (iii) de quantifier la part organique et minérale de ces charges, (iv) d'apprécier le rôle des facteurs naturels (débits et précipitations) et anthropiques (surfaces urbaines, agricoles et minières) sur les tendances observées et enfin, (v) de discuter de seuils de charges pour le suivi de la qualité de l'eau. Les résultats ont montré qu'il est possible de suivre les concentrations de matières en suspension, pour les fleuves Orénoque et Maroni avec une erreur relative de 32 et 25% respectivement. Sur la période 2000-2016, des tendances spatio-temporelles régulières ont été observées pour l'Orénoque, alors qu'elles sont en augmentation pour le Maroni avec une rupture en 2009 et en diminution pour l'Oyapock depuis 2008 (données in situ). Un lien fort avec l'augmentation de la déforestation pour les surfaces minières et les précipitations est observé pour le Maroni alors que pour l'Oyapock les tendances sont liées aux débits.Pour les deux années d'études (2014-2016), les charges minérales ont représenté la plus forte fraction des particules transportées dans les eaux du Maroni au Saut Hermina (en moyenne 93 %) et de l'Oyapock au Saut Maripa (en moyenne 82 %) avec une grande variabilité selon les mois de la teneur en carbone dans les matières transportées et pour les deux fleuves. Enfin, les rapports C/N et C/Chl-a ont dévoilé des matières organiques d'origine principalement endogène avec une forte biomasse chlorophyllienne surtout durant les basses eaux. / The water of rivers, lakes and reservoirs represents only 0.26 % of the 2.5 % (35 million of km3) of fresh water available on the liquid state on Earth, but its quality and quantity strongly decreased these last years. Her degradation has consequences on the farming, the health, the environment and the economy of territories and is now in the center of the societal concerns. The objectives of the present thesis are for three rivers located in the Guiana Shield, in the North of South America (the Maroni, the Oyapock, the Orinoco): i) to use and to adapt innovative tools of remote detection to follow and quantify, on the long term, their sedimentary loads, ii) to estimate the existence of spatiotemporal trends, as well as breaks in the chronicles of data, iii) to quantify the organic and mineral part of these loads, iv) to appreciate the role of the natural (discharge and precipitation) and the anthropological factors (urban, agricultural and mining surfaces) on the observed trends and finally, v) to discuss thresholds of concentrations for the quality monitoring of the river water.The results showed that it is possible to follow the concentrations of suspension materials, for rivers Maroni and Orinoco with a relative error of 25 and 32 % respectively. Over the period 2000-2016, regular spatiotemporal trends were observed for the Orinoco, while they are increasing for Maroni with a break in 2009 and in decrease for the Oyapock since 2008 (in situ data). A strong link with the increase of the deforestation for the mining surfaces and the precipitation is observed for the Maroni catchment while for the Oyapock the trend is explained by the specific water discharge.For two years of studies (2014-2016), the mineral loads represented the strongest fraction of particles transported in the Maroni River at Saut Hermina (on average 93 %) and in the Oyapock River at Saut Maripa (on average 82 %) with a high variability according to the months of the content in carbon in the transported materials and for both rivers. Finally, report C/N and C/Chl-a revealed organic matters of mainly endogenous origin with a strong chlorophyll biomass and especially during the low water period.