15 research outputs found
Recommended from our members
Biogeochemical characterization of suspended particulate matter in the Columbia River estuary
In order to understand what controls the composition of suspended particulate material (SPM) in estuarine turbidity maxima (ETM), a set of SPM samples collected in the Columbia River and estuary (northwestern USA) during 3 seasons (fall 1990, summer 1991, spring 1992) was analyzed for detrital mineral (Min), total organic matter [OM, as 2 x particulate organic carbon (POC)], biogenic silica (BSi), chlorophyll a, δ¹³C, and lignin. In most samples, Min, OM and BSi collectively accounted for 100% of total SPM mass, although their relative importance changed seasonally. The ETM was a trap for organic matter during all 3 seasons, which can explain the intense microbial activity and microcrustacean grazing observed previously. The organic matter was particularly rich in chlorophyll a in late spring to early summer. The source of this seasonal enrichment was mainly riverine phytoplankton. The organic matter contribution to ETM from the ocean was minor compared to the river, but apparently not negligible. Despite large seasonal variations in chlorophyll content, the δ¹³C of POC concentrated in ETM remained nearly constant between -26 and -25.5%. Vascular plant debris, as depicted by lignin phenol content, always comprised a minor fraction of the organic matter in ETM, although ETM had higher lignin levels than the OM of surrounding waters. Intertidal mudflats are if not an additional source of organic matter at least an important site for transforming riverine organic matter that is ultimately concentrated in ETM.Keywords: Suspended particulate material (SPM),
Lignin,
Particulate organic carbon (POC),
Columbia River estuary,
Aluminum,
Estuarine turbidity maxima (ETM),
Mudflats,
Chlorophyll,
ManganeseArticle appears in Marine Ecology Progress Series and is copyrighted by Inter Research
Severidade da mancha-de-alternária em cultivares de girassol na região do Cerrado do Distrito Federal Severity of alternaria in sunflower crop in the Cerrado region of Federal District, Brazil
Avaliou-se a severidade da mancha-de-alternária (Alternaria helianthi) em cinco genótipos de girassol (Helianthus annuus L.), em duas densidades populacionais e duas épocas de semeadura. Os experimentos foram conduzidos no campo experimental da Embrapa-Centro de Pesquisa Agropecuária dos Cerrados, em Planaltina, DF, no ano agrícola de 1998/1999, num Latossolo areno-argiloso. O delineamento experimental utilizado foi o de blocos ao acaso, num esquema fatorial de 5 x 2, com três repetições. A porcentagem de plantas com sintomas da mancha foi estimada por meio de observações semanais, empregandose notas de 0 a 5 nos terços inferior, médio e superior da planta. A população de plantas não influenciou na incidência de alternária. Todas as cultivares estudadas foram suscetíveis à doença. As condições climáticas transcorridas em cada época de semeadura modificaram a severidade da doença.<br>Severity of alternaria leaf spot was evaluated in five genotypes of sunflower as a result of two densities of population and two sowing dates. The experiments were conducted in the Embrapa-Centro de Pesquisa Agropecuária dos Cerrados experimental field, at Planaltina, DF, Brazil, on the crop season of 1998/1999 on an Oxisol soil. The experimental design was in randomized blocks in a 5 x 2 factorial with three replicates. The percentage of infected plants was estimated based on weekly observations considering scores from 0 to 5 in lower, middle and upper parts of the plant. The occurrence of alternaria was not influenced by density of population of 42,000 or 49,000 plants/ha. All cultivars were susceptible to the disease. The climatic conditions for each sowing date changed the disease severity