Abstract:Forms and quantities of organic carbon (C) fluxes at the soil surface, and organic C exports from four small (1-2 ha) headwater catchments were quantified and contrasted in the seasonally dry southern Amazon for 1 year to compare C fluxes within the terrestrial ecosystem with exports to the aquatic ecosystem. At the soil surface, the flux of litterfall C was 43 times greater than the dissolved organic carbon (DOC) flux in throughfall, with the highest rates of C deposition during the dry season. The form and timing of organic C was reversed for watershed exports, where DOC comprised 59% of the annual total organic C export, and exports were greatest during the 4-month rainy season (63% of total annual exports). Fine particulate organic carbon (FPOC) in streamwater was a substantially larger flux than coarse particulate organic carbon (CPOC), representing 37 and 4% of total annual organic C exports, respectively. Particulate organic C exports exhibited substantial seasonal variability, with FPOC and CPOC mobilized primarily in the rainy season and strongly connected to storm events. Storm flow comprised 6% of total streamflow for the year studied, and 10% of streamflow during the rainy season. In the rainy season, over 90% of FPOC exports were transported by storm flow, while only 32% of DOC exports were exported by storm flow during this period. Streamwater DOC concentrations were found to increase linearly with increasing terrestrial litterfall during the dry season (r 2 D 0Ð92, p < 0Ð001), indicating that in-stream processing of allochthonous litterfall is an important source of DOC during the dry season.

Over two hundred samples were collected in tropical headwater forested catchments in the lowland Amazon basin near Juruena, Mato Grosso Brazil. These were analyzed for fluorescence characteristics and DOC concentrations, and represented a range of terrestrial hydrologic flowpaths and firstorder streams during baseflow and stormflow conditions. The fluorescence index (FI) of McKnight et al. (2001) was found to have a significant relationship with DOC concentrations for stream water at baseflow conditions, but FI values within individual terrestrial flowpaths and stormflow varied little for the range of DOC concentrations observed. FI values were seen to increase for increasing residence time of water within the terrestrial ecosystem, while DOC concentration decreased for increasing hydrologic residence time. The FI of terrestrial flow paths indicated that DOC became increasingly characterized by microbially derived carbon for flow paths with longer residence times, on the order through fall and overland flow \ percolating soil water \ groundwater. Base flow samples of stream water had a mean FI value of 1.78, compared with 1.51 and 1.44 for through fall and overland flow, respectively, and 1.65 for percolating soil water. The FI values for stream water at base flow were also seen to vary seasonally, and were inversely proportional to DOC concentrations over time.

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RESUMO A família Onagraceae possui cerca de 650 espécies distribuídas nas regiões subtropicais e temperadas. O gênero Ludwigia ocorre em todo o Brasil, estando associado a regiões alagadas, entretanto há uma baixa densidade de estudo sobre as espécies do gênero Ludwigia para o Estado de Mato Grosso. O Córrego São José, localizado no município de Tangará da Serra, apresenta as margens degradadas pela ação do uso na agropecuária e piscicultura. Desta forma há falta de conhecimento da vegetação natural. O presente estudo tem como objetivo caracterizar as espécies de Ludwigia L. presente em quatro represas do Córrego São José. As coletas foram realizadas em agosto de 2014 e março de 2015. As amostras foram coletadas aleatoriamente ao entorno das represas, e herborizadas e identificadas. O resultado deste trabalho foi o registro de três espécies de Ludwigia: Ludwigia nervosa, L. elegans e L. tomentosa. A Ludwigia nervosa apresentou a maior abundancia (14 indivíduos) e ocorreu nas quatro represas. Enquanto as outras duas espécies, L. elegans e L. tomentosa apresentaram três indivíduos cada. A primeira apareceu nas represas 1 e 3 e a segunda apareceu nas represas 2,3 e 4. PALAVRAS-CHAVE: corpos d"água, Macrófitas, plantas aquáticas.