Field intercomparison of four methane gas analysers suitable for eddy covariance flux measurements

Eddy covariance (EC)-flux measurement technique is based on measurement of turbulent motions of air with accurate and fast measurement devices. For instance, in order to measure methane flux a fast methane gas analyser is needed which measures methane concentration at least ten times in a second in addition to a sonic anemometer, which measures the three wind components with the same sampling interval. Previously measurement of methane flux was almost impossible to carry out with EC-technique due to lack of fast enough gas analysers. However during the last decade new instruments have been developed and thus methane EC-flux measurements have become more common. Performance of four methane gas analysers suitable for eddy covariance measurements are assessed in this thesis. The assessment and comparison was performed by analysing EC-data obtained during summer 2010 (1.4.-26.10.) at Siikaneva fen. The four participating methane gas analysers are TGA-100A (Campbell Scientific Inc., USA), RMT-200 (Los Gatos Research, USA), G1301-f (Picarro Inc., USA) and Prototype-7700 (LI-COR Biosciences, USA). RMT-200 functioned most reliably throughout the measurement campaign and the corresponding methane flux data had the smallest random error. In addition, methane fluxes calculated from data obtained from G1301-f and RMT-200 agree remarkably well throughout the measurement campaign. The calculated cospectra and power spectra agree well with corresponding temperature spectra. Prototype-7700 functioned only slightly over one month in the beginning of the measurement campaign and thus its accuracy and long-term performance is difficult to assess.

The implications of laboratory Rn-222 flux measurements to the radioactivity in groundwaters: the case of a karstic limestone aquifer

Laboratory time-scale experiments were conducted on Carboniferous Limestone gravels from the Mendip Hills area, England, with the purpose of evaluating the release of Rn-222 to the water phase. The specific surface areas of the samples were 4.14 and 1.69 cm g(-1), which provided, respectively, values of 50.6 and 12.7 pCi for the released Rn. These results allowed the calculation of the emanation coefficient of this rock matrix with respect to the release of Rn, where completely different values corresponding to 23% and 6% were found, suggesting that the extent to which grain boundaries or imperfections in aggregates of micro-crystals of calcite intersect the particle surface certainly affects the Rn release. They also permitted the evaluation of models for the generation of Rn in rocks and transfer to water, in order to interpret the radioactivity due to this gas in groundwaters from the karstic aquifer of the Mendip Hills area, where the calculated activities in groundwater based on the values of 23% and 6% for the emanation coefficient were about 51 and 15 times higher than actually measured in groundwater. Therefore, the emanation coefficient in nature is considerably smaller than in the lab experiment, and another factor k (0 < k < 1) may be introduced into the equations related to the modelling, with the aim of adjusting the theoretical-practical results. (C) 1997 Elsevier B.V. Ltd. All rights reserved.

Analysis on the formation of a FRC by flux measurements and MHD simulations

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Particle flux measurements from moorings and surface sediment studies of sediment cores in the SE Pacific Ocean

Flux of siliceous plankton and taxonomic composition of diatom and silicoflagellate assemblages were determined from sediment trap samples collected in coastal upwelling-influenced waters off northern Chile (30°S, CH site) under "normal" or non-El Niño (1993-94) and El Niño conditions (1997-98). In addition, concentration of biogenic opal and siliceous plankton, and diatom and silicoflagellate assemblages preserved in surface sediments are provided for a wide area between 27° and 43°S off Chile. Regardless of the year, winter upwelling determines the maximum production pattern of siliceous microorganisms, with diatoms numerically dominating the biogenic opal flux. During the El Niño year the export is markedly lower: on an annual basis, total mass flux diminished by 60%, and diatom and silicoflagellate export by 75%. Major components of the diatom flora maintain much of their regular seasonal cycle of flux maxima and minima during both sampling periods. Neritic resting spores (RS) of Chaetoceros dominate the diatom flux, mirroring the influence of coastal-upwelled waters at the CH trap site. Occurrence of pelagic diatoms species Fragilariopsis doliolus, members of the Rhizosoleniaceae, Azpeitia spp. and Nitzschia interruptestriata, secondary components of the assemblage, reflects the intermingling of warmer waters of the Subtropical Gyre. Dictyocha messanensis dominates the silicoflagellate association almost year-around, but Distephanus pulchra delivers ca. 60% of its annual production in less than three weeks during the winter peak. The siliceous thanatocoenosis is largely dominated by diatoms, whose assemblage shows significant qualitative and quantitative variations from north to south. Between 27° and 35°S, the dominance of RS Chaetoceros, Thalassionema nitzschioides var. nitzschioides and Skeletonema costatum reflects strong export production associated with occurrence of coastal upwelling. Both highest biogenic opal content and diatom concentration at 35° and 41°-43°S coincide with highest pigment concentrations along the Chilean coast. Predominance of the diatom species Thalassiosira pacifica and T. poro-irregulata, and higher relative contribution of the silicoflagellate Distephanus speculum at 41°-43°S suggest the influence of more nutrient-rich waters and low sea surface temperatures, probably associated with the Antarctic Circumpolar Water.