Claudio Cardoso Marinho

Synergy of Fresh and Accumulated Organic Matter to Bacterial Growth

The main goal of this research was to evaluate whether the mixture of fresh labile dissolved organic matter (DOM) and accumulated refractory DOM influences bacterial production, respiration, and growth efficiency (BGE) in aquatic ecosystems. Bacterial batch cultures were set up using DOM leached from aquatic macrophytes as the fresh DOM pool and DOM accumulated from a tropical humic lagoon. Two sets of experiments were performed and bacterial growth was followed in cultures composed of each carbon substrate (first experiment) and by carbon substrates combined (second experiment), with and without the addition of nitrogen and phosphorus. In both experiments, bacterial production, respiration, and BGE were always higher in cultures with N and P additions, indicating a consistent inorganic nutrient limitation. Bacterial production, respiration, and BGE were higher in cultures set up with leachate DOM than in cultures set up with humic DOM, indicating that the quality of the organic matter pool influenced the bacterial growth. Bacterial production and respiration were higher in the mixture of substrates (second experiment) than expected by bacterial production and respiration in single substrate cultures (first experiment). We suggest that the differences in the concentration of some compounds between DOM sources, the co-metabolism on carbon compound decomposition, and the higher diversity of molecules possibly support a greater bacterial diversity which might explain the higher bacterial growth observed. Finally, our results indicate that the mixture of fresh labile and accumulated refractory DOM that naturally occurs in aquatic ecosystems could accelerate the bacterial growth and bacterial DOM removal.

Temporal coherence among tropical coastal lagoons: a search for patterns and mechanisms.

Temporal coherence (i.e., the degree of synchronicity of a given variable among ecological units within a predefined space) has been shown for several limnological features among temperate lakes, allowing predictions about the structure and function of ecosystems. However, there is little evidence of temporal coherence among tropical aquatic systems, where the climatic variability among seasons is less pronounced. Here, we used data from long-term monitoring of physical, chemical and biological variables to test the degree of temporal coherence among 18 tropical coastal lagoons. The water temperature and chlorophyll-a concentration had the highest and lowest temporal coherence among the lagoons, respectively, whereas the salinity and water colour had intermediate temporal coherence. The regional climactic factors were the main factors responsible for the coherence patterns in the water temperature and water colour, whereas the landscape position and morphometric characteristics explained much of the variation of the salinity and water colour among the lagoons. These results indicate that both local (lagoon morphometry) and regional (precipitation, air temperature) factors regulate the physical and chemical conditions of coastal lagoons by adjusting the terrestrial and marine subsidies at a landscape-scale. On the other hand, the chlorophyll-a concentration appears to be primarily regulated by specific local conditions resulting in a weak temporal coherence among the ecosystems. We concluded that temporal coherence in tropical ecosystems is possible, at least for some environmental features, and should be evaluated for other tropical ecosystems. Our results also reinforce that aquatic ecosystems should be studied more broadly to accomplish a full understanding of their structure and function.

Methane concentration in water column and in pore water of a coastal lagoon (Cabiúnas lagoon, Macaé, RJ, Brazil)

ABSTRACT The aim of this study was to evaluate methane concentration in water column and pore water at limnetic and littoral regions of a coastal lagoon. At the littoral region samples were taken from three monospecific macrophytes stands (Typha domingensis , Eleocharis interstincta and Potamogeton stenostachys ). The methane concentration in the pore water at the littoral region was higher than the concentration found at the limnetic region in each fraction of the sediment. The higher methane concentration in the superficial fraction of the sediment (0-2 cm) was shown at the P. stenostachys stand (3.7 mM). It was the only significantly different (p 0.05). It could be concluded that there was a high influence of aquatic macrophytes on the pore water methane concentration. Key words : Methane, water column, sediment, aquatic macrophytes, coastal lagoons

Mercury methylation in sediments of a Brazilian mangrove under different vegetation covers and salinities

The presence and formation of methylmercury (MMHg), a highly toxic form of Hg, in mangrove ecosystems is poorly studied. Therefore the aim of this study was to evaluate mercury methylation potentials in sediment, litter and root samples (Avicennia shaueriana and Spartina alterniflora) from different regions of a mangrove ecosystem, as well as the influence of salinity on methylation. Sediment was sampled under different depths and in mangrove regions with different plant covers and salinities. All samples were incubated with (203)Hg and MM(203)Hg was extracted and measured by liquid scintillation. MMHg was formed in all samples and sites tested including plant roots and litter. Higher Hg methylation was found in the superficial fraction of sediments (0.47-7.82%). Infralittoral sandy sediment had low MMHg formation (0.44-1.61%). Sediment under Rhizophora mangle had lower MMHg formation (0.018-2.23%) than under A. shaueriana (0.2-4.63%) and Laguncularia racemosa (0.08-7.82). MMHg formation in sediment tended to increase with salinity but the differences were not significant. Therefore, MMHg formation occurs in different sites of mangrove ecosystems and may be an important threat that requires further study.

Magnitude and variability of methane production and concentration in tropical coastal lagoons sediments

OBJETIVO: Areas alagadas costeiras sao zonas potenciais para producao de metano (CH4). O presente estudo tem como objetivo avaliar a variacao espacial da producao e concentracao de CH4 em dez lagoas costeiras tropicais, a influencia de macrofitas aquaticas na concentracao de CH4 no sedimento e como a magnitude dessas taxas de producao potencial de CH4 e em comparacao com outros ecossistemas. METODOS: Os sedimentos foram amostrados em dez lagoas costeiras, com um ponto na regiao limnetica e outro ponto nos bancos de macrofita aquatica, quando estas estavam presentes na regiao litorânea. Nos medimos a producao de CH4 como uma taxa potencial e a concentracao de CH4 foi diretamente medida das amostras de sedimento. RESULTADOS: As maiores taxas de producao potencial de CH4 (PPM) foram encontradas em lagoas alcalinas e hipersalinas. Contudo, Cabiunas, que e uma lagoa de agua doce densamente colonizada por macrofitas aquaticas tambem exibiu alta taxa de PPM. Nos tambem observamos que a concentracao de CH4 do sedimento na regiao litorânea foi mais alta que na regiao limnetica em todas as lagoas investigadas, exceto Paulista, que apresentou o padrao oposto. As taxas de producao de CH4 observadas nessas lagoas estudadas foram baixas comparadas com outros ecossistemas aquaticos. CONCLUSAO: Nossos resultados sugerem que os sedimentos de lagoas salinas sao importantes sitios produtores de CH4, e em geral, macrofitas aquaticas tem uma influencia positiva na metanogenese, o que foi evidente baseado nas concentracoes de CH4 presentes nos sedimentos dessas lagoas. Estudos adicionais deveriam focar nos processos subjacentes aos padroes do CH4 observados nas lagoas costeiras tropicais, especialmente preocupando-se com o acoplamento entre producao e concentracao de CH4.

Dynamics of dissolved organic carbon from aerobic and anaerobic decomposition of Typha domingensis Pers. and Eleocharis interstincta (Vahl) Roem. & Schult. in a tropical coastal lagoon

OBJETIVO: O objetivo deste estudo foi avaliar o estagio inicial de decomposicao de duas macrofitas aquaticas (Typha domingensis e Eleocharis interstincta) em condicoes aerobias e anaerobias; METODOS: As amostras de macrofitas aquaticas e agua foram coletadas na lagoa Cabiunas, Rio de Janeiro, Brasil. No experimento 1 câmaras de mineralizacao foram preparadas com fragmentos vegetais frescos e agua da lagoa para cada condicao (aerobia e anaerobia). A formacao de DOC e de CO2 e o consumo de O2 foram medidos durante 30 dias. No experimento 2 câmaras de mineralizacao foram preparadas com lixiviados de macrofitas aquaticas e glicose em cada condicao experimental (aerobia e anaerobia). A formacao de CO2 e o consumo de O2 foram medidos durante 1 dia; RESULTADOS: No experimento 1 as concentracoes de COD na decomposicao de T. domingensis foram maiores. Apesar disso, a formacao de CO2 foi mais eficiente na decomposicao de E. interstincta. O consumo de oxigenio aumentou no comeco da decomposicao dos detritos e tenderam a estabilizar no final. Os valores de O/C aumentaram no inicio da decomposicao e diminuiram em seguida. No experimento 2, a decomposicao aerobia apresentou maior formacao de CO2 em todos os recursos. O lixiviado de E. interstincta apresentou maior concentracao de CO2 do que o de T. domingensis em ambas as condicoes; CONCLUSAO: Os resultados mostraram que a decomposicao aerobia inicial e maior em T. domingensis. O consumo de oxigenio varia de acordo com as alteracoes quimicas dos detritos. A formacao de CO2 na decomposicao de T. domingensis e E. interstincta e irrelevante na Lagoa Cabiunas. A baixa liberacao de DOC dos detritos indicam que a mineralizacao da materia orgânica particulada e a principal via de decomposicao de T. domingensis e E. interstincta.

The role played by aquatic macrophytes regarding CO2 balance in a tropical coastal lagoon (Cabiúnas Lagoon, Macaé, RJ)

AIM: Carbon dioxide (CO2) is an important atmospheric trace gas that is involved in both the biological carbon cycle and global warming. Inland waters - mainly lakes - contribute to C cycling and have been considered a large source of atmospheric CO2. However, scientific studies usually neglect lake morphometry and the presence of aquatic macrophytes in littoral zones, which have a great potential for CO2 absorption and for C storage. This study aimed to evaluate the importance of the littoral region on the CO2 balance in the Cabiunas Lagoon, while also considering the contribution of the limnetic region and of Typha domingensis and Eichhornia azurea, prominent species in the area. METHODS: CO2 flux was estimated by a linear integration of CO2 concentrations measured in the internal atmospheric of a single-component static closed chambers at the studied sites. The distribution of macrophyte stands throughout lagoon surface was taken into account to evaluate the effects of macrophytes on CO2 supersaturation. Other factors were also measured throughout the sampling process to evaluate their relationship with CO2 flux data by means of Akaike model selection criterion. The area covered by aquatic macrophytes at the Cabiunas lagoon was estimated by profiles and transects. RESULTS AND DISCUSSION: CO2 flux through the water surface ranged from - 7.39 to 17.56 mgCO2m - 2h - 1. An emission pattern predominated, suggesting that water columns are CO2 supersaturated at all sampling sites. Rates were similar among all the sampling sites, suggesting that aquatic macrophytes do not influence CO2 saturation in the water column at Cabiunas lagoon. On the other hand, CO2 fluxes from macrophyte tissues showed a clear assimilation pattern. Influxes were higher in T. domingensis ( - 229.1 ± 320.9 mg CO2.m - 2.h - 1) than in E. azurea stands ( - 43.8 ± 39.5 mg CO2.m - 2.h - 1). Once these macrophytes covered a considerable area of the lagoon and CO2 absorption strongly overwhelmed the emission processes, then we were able to extrapolate data from the total estimated area of the evaluated sites (75% of the Cabiunas lagoon), which resulted in a net influx of 46.6 mg CO2.m - 2.h - 1. The strong Typha domingensis contribution to CO2 absorption and other C cycling processes indicate that it is one of the most important species to Carbon cycling in the studied ecosystem. Thus, it is worth considering C cycling in lake littoral zones as a key process when estimating C balance in shallow aquatic ecosystems.

Potential Methane Production Associated with Aquatic Macrophytes Detritus in a Tropical Coastal Lagoon

Anaerobic decomposition of aquatic macrophytes in the sediment of wetlands is a key source of methane to the atmosphere. An experiment was conducted in order to evaluate the potential methane production (PMP) in the sediment colonized by three species of aquatic macrophytes and in the limnetic region of a tropical coastal lagoon. The incubations were prepared and maintained (70 days) at 25.0 °C, and the PMP was measured by gas chromatography. The initial concentrations of dissolved organic carbon (DOC), carbohydrates and methane in the sediment were also measured. The sediment colonized by emergent aquatic macrophytes showed higher PMP due to the higher amounts of carbohydrates. On the other hand, PMP was lower in the limnetic region, which showed lower amounts of carbohydrates. The carbon found in the limnetic region is mainly originated from the refractory detritus of aquatic macrophytes that reaches the central region of the lagoon, with lower carbohydrate content. These results indicate that detritus quality, which means highest concentration of carbohydrates in the DOC, was the main controlling factor of methanogenesis.

Floating Aquatic Macrophytes Decrease the Methane Concentration in the Water Column of a Tropical Coastal Lagoon: Implications for Methane Oxidation and Emission

ABSTRACT In wetlands, the knowledge accumulated on the role of aquatic plants in the methane cycle focused on emergent macrophytes, to the detriment of other typologies. Herein, we evaluated whether the free-floating macrophyte Salvinia auriculata Aubl. and the floating-leaved macrophyte Eichhornia azurea (Sw.) Kunth. decrease the water column methane concentrations compared to a plant-free surface. We prepared microcosms by inserting an individual of S. auriculata or of E. azurea into chambers filled with lagoon water previously bubbled with CH 4 . Another set of chambers was incubated only with the prepared water, representing the plant-free surface. Half of the chambers were kept in the dark and half in sunlight to simulate a diel cycle. We observed greater loss of CH 4 , higher O 2 uptake and lower CO 2 outflow in the plants treatments. The decrease in methane concentrations in the E. azurea treatments was 93.5% in the light and 77.2% in the dark. In the S. auriculata

Gerenciamento de resíduos químicos em um laboratório de ensino e pesquisa: a experiência do Laboratório de Limnologia da UFRJ

This work describes the waste management system developed at the Laboratory of Limnology of Federal University of Rio de Janeiro. The initial challenge was to identify and treat a great variety of wastes generated in the analytical procedures performed in the laboratory. Since many of the students and researchers are not chemists, an intensive training was performed during the establishment of the management system. After three years, there was a deep change of attitude of the professionals involved. The present experience may be useful for other laboratories with a profile similar to the one under study.