Mudanças de uso e manejo influenciam o acúmulo de carbono (C) no solo e o fluxo de gases do efeito estufa (GEE). No Brasil, sobretudo nos biomas Amazônia e Cerrado, historicamente vegetações nativas são convertidas em pastagens e agricultura emitindo consideráveis quantidades de GEE para a atmosfera. Áreas sob pastagens e agricultura vêm sendo convertidas em sistemas mais intensificados e tecnicamente mais avançados, tais como os sistemas de integração lavoura-pecuária (ILP), os quais têm a capacidade de acumular C no solo e mitigar as emissões de GEE para atmosfera. O objetivo deste estudo foi avaliar as modificações nos estoques de C do solo e nos fluxos de GEE em áreas sob mudança de uso da terra nos biomas Amazônia e Cerrado. Foram avaliadas áreas sob vegetação nativa, pastagens, sucessão de cultivos e ILP em diferentes condições edafoclimáticas. O manejo da fertilidade do solo sob pastagem afeta produção de biomassa, que por sua vez influencia o acúmulo ou perda de C. Pastagem cultivada em solo fértil acumulou 0,46 Mg de C ha-1 ano-1. Sob baixa fertilidade natural, obsrvou-se perdas de 0,15 e 1,53 Mg de C ha-1 ano-1, respectivamente para pastagem não degradada e degradada. A conversão de vegetação nativa e pastagem para agricultura, mesmo cultivada sob SPD, reduziu o estoque de C, exibindo perdas de 0,69 a 1,44 Mg ha-1 ano-1. A implantação de sistemas de ILP em áreas sob sucessão de cultivos aumentou os estoques de C no solo, com taxas varaindo de 0,82 a 2,58 Mg ha-1 ano-1. Aplicando a modelagem matemática, com o modelo Century, verificou-se as mesmas tendências de acúmulo ou perdas de C no solo. Entretanto, o modelo subestimou os estoques de C em todas as áreas avaliadas. Em Montividiu, a avalaição do fluxo de GEE em diferentes usos e manejos da terra, evidenciou maior emissão CCO2 na pastagem (10820 kg ha-1) e esta foi significativamente maior em relação à sucessão de cultivos (4987 kg ha-1) e ILP (6565 kg ha-1). Emissão de N-N2O foi maior em ILP (2,00 kg ha-1 ano-1) e menor na vegetação nativa (0,35 kg ha-1 ano-1). Os fluxos de C-CH4 resultaram em emissão de 1,67 kg ha-1 ano-1 na pastagem e em absorção nas demais áreas. Em ILP, os manejos aplicados à soqueira do algodoeiro, resultaram em diferenças nos fluxos de GEE. O manejo químico, sem perturbação do solo, reduziu a emissão de CO2, aumentou a emissão de N2O e não influenciou os fluxos de CH4. Utilizando as taxas de acúmulos de C e os fluxos de GEE obteve-se o seqüestro de C no solo. As taxas de seqüestro, expressas em C equivalente, evidenciaram perdas da ordem de 0,43 e 0,77 Mg ha-1 ano-1, respectivamente para a conversão de Cerrado para pastagem e sucessão de cultivos. Implantação de ILP em áreas sob sucessão de cultivos resultou em seqüestro de C pelo solo, independente do manejo aplicado. Manejo químico seqüestrou 1,05 Mg de C ha-1 ano-1. Manejo mecânico com o equipamento Cotton 1000 e grade aradora seqüestraram 0,58 e 0,71 Mg de C ha-1 ano-1, respectivamente. A implantação de sistemas ILP se mostrou uma excelente alternativa para acumular C no solo e mitigar as emissões de GEE para atmosfera. / Changes on land use and management influence the accumulation of carbon (C) in soil and the greenhouse gas (GHG) fluxes. In Brazil, especially in Amazonia and Cerrados biomes, the native vegetation has been historically converted in pastures and agriculture causing considerable amount of GHG emissions to the atmosphere. Recently, pastures and agricultural activities have been adopting more intensified and technically advanced land management systems, such as the integrated crop-livestock (ICL) system, which has the capacity to increase soil C accumulation and promote GHG mitigation. The objective of this study was to evaluate the alterations in soil C stock and GHG fluxes in areas under land use changes in the Amazonia and Cerrados biomes. The study focused on areas under native vegetation, pasture, crop succession and ICL under different edaphoclimatic conditions. The fertility management of soil under pasture affects the biomass production which, in turn, influences not only the soil C accumulation but also the C loss. This study showed that pasture cultivated in fertile soil presented an accumulation of 0.46 Mg of C ha-1 year-1. Under naturally low soil fertility, losses of 0.15 and 1.53 Mg of C ha-1 year -1 were observed in non-degraded and degraded pastures, respectively. Conversion of native vegetation and pasture to agriculture, even when cultivated under no-tillage, caused the reduction of C stock and showed losses from 0.69 to 1.44 Mg ha-1 year -1. The implementation of ICL systems in crop succession areas caused the increase of soil C stock with rates ranging from 0.82 to 2.58 Mg ha-1 year -1. By applying the Century model, the same tendencies in soil C accumulation and C loss were observed. However, the model underestimated the C stock in all areas under evaluation. In Montividiu, Goiás State, the evaluation of GHG fluxes from different land uses and management showed that pasture produced higher C-CO2 emissions (10829 kg ha-1 year -1) than crop succession (4987 kg ha-1 year -1) and ICL (6565 kg ha- 1 year -1). The N-N2O emission was higher from ICL (2.00 kg ha-1 year-1) and lower from native vegetation (0.35 kg ha-1 year-1). Regarding the C-CH4 emissions from pastures, the fluxes were in the order of 1.67 kg ha-1year-1 while the other areas showed sink. In ICL, the soil management applied to the cotton stalk resulted in GHG flux differences. Chemical management with no soil disturbance reduced the CO2 emissions, increased N2O emissions and showed no influence on CH4 fluxes. Carbon sequestration rates, expressed in C equivalent, showed losses in the order of 0.43 and 0.77 Mg ha-1 year-1, respectively, from the conversion of Cerrado to pasture and crop succession. The implementation of ICL in areas under crop succession resulted in C sequestration in soil, regardless the type of management applied. Chemical management produced C sequestration of 1.05 Mg ha-1 year -1. Mechanical management with Cotton 1000 equipment and full tillage produced the sequestration of 0.58 and 0.71 Mg of C ha-1 year-1, respectively. The implementation of ICL systems showed to be an excellent alternative for soil C accumulation and mitigation of GHG emission.

Climate change is one of the largest problems facing this generation. Anthropogenically caused increases of greenhouse gas emissions is a significant culprit to this problem. Although the obvious problems such as cars, industry, and urbanism garnish a significant amount of the criticism, natural sources such as wetlands are also beginning to contribute to this issue. This is becoming increasingly significant as wetlands shift from being sinks of greenhouse gases to becoming sources as various anthropogenic impacts, including global warming itself, begin to affect the health of the wetlands. The aim of this project is to look at four common types of wetlands, being tropical mangroves, temperate coastal marshes, inland meadows, and subarctic peatlands, all located in different climactic areas of the world, and by doing a meta-analysis of available data of greenhouse gas production for each wetland type, observe how differences in their greenhouse gas production may contribute or be affected by climate change and global warming. Results of the meta-analysis revealed that the most significant production of the potent greenhouse gas nitrous oxide occurs in coastal wetlands such as tropical mangroves and coastal marshes, while the greenhouse gas methane is seen to be produced most in subarctic peatlands. These contributions of wetlands to global greenhouse gas production are not as significant as other anthropogenic contributions. However, subarctic wetlands contribute to more than half of the global methane emissions, and the most important aspect of wetland greenhouse gas production is that they are producing more greenhouse gases than they would normally be sequestering, contributing more than the basic greenhouse gas production data can display. Global climate changes such as temperature increase and sea level rise could also make these levels of greenhouse gas production become worse, although measures to decrease the effects of this such as regulations on anthropogenic nitrogen input, macrophyte presence, and prevention of peat burning.

Kleine, flache Gewässer gelten als sogenannte „hotspots“ der Primärproduktion und Kohlenstoffbindung. Diese Doktorarbeit zielt darauf ab, die Primärproduktion verschiedener kleiner Gewässer zu quantifizieren sowie die Mechanismen, die den Kohlenstoffkreislauf dieser Systeme beeinflussen, zu analysieren. Der Fokus liegt dabei auf dem Einfluss globaler Veränderungen, die diese Mechanismen verändern können Im ersten Abschnitt wurde die Primärproduktion (PP) in kleinen, temporären Söllen untersucht, die sehr anfällig für Störungen sind. Ich konnte zeigen, dass die PP der Sölle im Sommer außergewöhnlich hoch ist, was hauptsächlich auf eine hohe Makrophytenproduktion zurückzuführen ist Im zweiten Teil analysiere ich die Ergebnisse eines Experiments zum Einfluss erhöhter Temperaturen auf die benthische PP kleiner Gewässer im Frühjahr. Acht Mesokosmen wurden bei normalen und um 4°C erhöhten Wassertemperaturen gemäßigter Breiten betrieben. In der ersten Hälfte des Experiments konnte ich eine erhöhte benthische PP in den erwärmten Mesokosmen feststellen, die auf direkte Temperatureffekte und indirekte Auswirkungen einer höheren Nährstoffverfügbarkeit zurückzuführen war. Anfang Juni stieg jedoch der Einfluss der Makroinvertebraten auf das Periphyton in den erwärmten Mesokosmen, so dass keine Unterschiede in der PP mehr auftraten. Schließlich, untersuche ich die Resilienz eines Sees gegenüber einem plötzlichen Eintrag gelösten organischen Kohlenstoffs (DOC) aus dem terrestrischen Umland, der zu einer starken Braunfärbung des Wassers führte. Der Fokus liegt dabei auf Veränderungen der Wasserqualität und der aquatischen PP des Sees, nachdem sich die DOC-Konzentration verfünffacht hatte. Drei Jahren nach Erreichen der maximalen DOC- und Gesamt-Phosphor im See sanken diese signifikant, lagen jedoch noch immer 1,5- bzw. 2-fach oberhalb der Ausgangskonzentrationen vor dem DOC-Eintrag. Die benthische PP zeigte eine teilweise Erholung, erreichte jedoch ebenfalls nicht die Ausgangswerte. / Small, shallow freshwater ecosystems are now considered hotspots of primary production & carbon sequestration. Yet till recently they’ve been mostly neglected. This thesis aims at explaining the underlying mechanisms affecting carbon cycling in these systems, particularly focusing on how contemporary global changes alter ecological equilibria. In the first section, using a compartmental approach, I study primary production in small, temporary ponds (kettle holes) within agricultural fields that are highly susceptible to environmental & anthropogenic disturbances. I show that summertime gross primary production (GPP) in kettle holes is exceptionally high, mostly driven by a strong macrophyte production. In winter, periphyton contributes to the majority of the systems’ GPP. High summertime deposition, correlated to GPP, and low sediment mineralization rates, signified a high potential for carbon burial. In the second experiment, I test the impact of increased temperatures on periphyton production during spring. I use eight mesocosms running at normal & +4°C temperatures. Initially, I recorded elevated periphyton GPP in the warmed treatment driven by direct temperature effects & indirect effects of higher nutrient availability. By late spring, the trend is reversed due to increased grazing pressure in the warm treatment. In the third study, I investigate a lake’s resilience to a sudden brownification event: A 5-fold increase in dissolved organic carbon (DOC) concentrations. Within three years after peak brownification, the lake DOC & total phosphorous concentrations dropped significantly but seem to have plateaued at 1.5 & 2-fold their pre-brownification levels, respectively. Consequently, benthic GPP, which had collapsed due to light limitation at peak brownification, marked only a partial recovery, while phytoplankton (& whole-lake) GPP remained higher than pre-brownification levels. Phytoplankton & periphyton exhibited an inverse response to DOC & TP concentrations.