Géochimie et distribution de métaux à l'intérieur de carottes de sédiment prises du lac Saint-Louis (fleuve Saint-Laurent) et datées par radioactivité

La distribution de la grosseur des particules, la composition géochimique et la concentration en métaux (Cu, Cr, Pb, Co, V, Ni, Hg et Zn) furent déterminés dans des carottes datées (à l'aide de matériel radioactif) provenant du lac Saint-Louis et du fleuve Saint-Laurent. Environ 20 cm de sédiments fins se sont accumulés durant les 30 dernières années à deux endroits situés à proximité du centre du lac. Par contre, une couche de sédiment de 20 cm d'épaisseur s'est déposée pendant les cinq dernières années à deux différents endroits de la partie sud du lac. Les profils de concentration des éléments majeurs et de la plupart des métaux présents dans les carottes de sédiment indiquent un apport continu de matériel de nature géochimique semblable aux aires d'échantillonnage. Une distribution uniforme de la grosseur des particules à l'intérieur du profil de sédiment montre que ces aires constituent des zones de dépôt pour des particules de propriétés hydrodynamiques semblables que transportent les eaux du fleuve. Les profils de concentration du mercure (Hg) et du zinc (Zn) dans les sédiments sont significatifs d'une charge provenant d'une source locale située sur le lac Saint-Louis. Les concentrations en métaux mesurées dans les sédiments du lac Saint-Louis dépendent du tri des particules, du transport et du dépôt des particules de la fraction limoneuse (taille comprise entre 2 µg et 63 µg) qui peuvent contenir de plus faibles concentrations en métaux comparativement aux particules de grosseur comparable à l'argile (taille < 2 µg) qui caractérisent les bassins de dépôt du lac Ontario.Particle size distribution, geochemical composition and concentrations of metals (Cu, Cr, Pb, Co, V, Ni, Hg and Zn) were determined in radiodated cores collected from Lake St. Louis, St. Lawrence River, Quebec, Canada, to assess the significance of the lake as a sink of contaminants transported through the St. Lawrence River. The cores were collected at four stations in the depositional areas identified by earlier surveys of Lake St. Louis. Stations Nos. 3 and 9 were located in the northern part of the lake, and stations 17 and 21 along the southern shore. A modified Kajak-Brinkhurst curer was used to collect the sediment cores. The concentrations of major elements and metals were determined by X-ray fluorescence spectrometry. The concentrations of Hg and inorganic C were determined by cold vapour atomic absorption spectrometry and Leco carbon analyzer, respectively. The total Pb-210 and Ra-226 levels in one centimeter sediment core sections were measured by low-energy gamma-ray spectrometry for calculation of sediment age. The effects of mixing on sediment age has been estimated.About 20 cm of fine grained sediment accumulated during the past 30 years at two sites near the centre of the lake. However, a 20 cm thick sediment layer was deposited over the past five years at two different areas in the southern part of the lake. Calculated sedimentation rate for surface sediments were 207, 296, 1837, and 2912 mg cm-2 y-1 for stations 3, 9, 17, and 21, respectively. The concentration profiles of ten major elements (Si, Al, Fe, Ca, Mg, Na, K, Ti, P, and Mn), organic and inorganic C and most of the investigated metals were similar and consistent in the sediment profiles at all stations, and indicated a continuous input of geochemically similar material at the sampling sites.A uniform particle size distribution within the sediment profile showed that these areas are settling zones for particles of similar hydrodynamic properties transported by the St. Lawrence River. The concentration profiles of Hg in the cures indicated e continuous input of Hg along the southern shore of the lake. The concentration profile of Hg in the core from the northern part of the lake had a similar pattern to that from Lake St. Clair and Lake Ontario, showing a decrease of Hg in the surficial sediments. This decrease corresponds to implemented contrat of Hg losses by industry in Canada and the USA over the past 15 years. The concentration profiles of Hg and Zn in the sediments indicated an input from local sources along Lake St. Louis.The concentrations of Cr, V and Co in sediments in the depositional zones were similar to both background and surficial sediment concentrations in depositional basins of Lake Ontario. The concentrations of Cu, Ni and Pb were lower than those in surficial sediments in Lake Ontario depositional basins. Observed concentrations of investigated metals in Lake St. Louis sediments were ascribed to the particle sorting, transport and deposition of silt-size (2 to 63 µm grain size) particles which may contain smaller concentrations of metals than clay-size (< 2 µm grain size) particles in the depositional basins of Lake Ontario. It was concluded that Lake St. Louis provides only a temporal storage for metals associated with clay-size sediment particles which may eventually become resuspended and moved downstream

Geochemistry and Organic Contaminants in the Sediments of Great Slave Lake, Northwest Territories, Canada

A study was carried out in the summer of 1987 to determine the geochemistry and distribution of trace elements, PCBs and 16 other chlorinated hydrocarbons in sediments from selected areas in Great Slave Lake, Northwest Territories, Canada. Sediment cores were collected at three sampling stations in the west basin of the lake on a transect from the Slave River delta to the outlet of the Mackenzie River. The geotechnical composition of the sediments showed the deposition of similar material at all sampling stations. Sediment dating indicated a very high sedimentation rate (46.6 g/cm&sup2;/year) at a 110 m water depth in the vicinity of the Slave River delta and mixing of bottom sediments at the southwestern part of the lake. The concentrations of trace elements (Cu, Ni, Co, Cr, V, Pb and Zn) were uniform in all sediment profiles. However, surficial sediments were enriched by arsenic, Canadian standard CLB-1 containing 51 PCB congeners was used in the determination of PCBs in the sediment. Thirty-three PCB congeners were detected and their concentrations determined in selected sections of sediment cores. The most abundant congeners were 15 and 18, 44, 49, 52 and 101 (IUPAC numbering) with maximum concentrations 3.52, 2.68, 2.44, 6.20 and 2.44, 6.20 and 2.13 ng/g respectively. The concentration pattern of PCBs in Great Slave Lake sediments indicated considerably greater quantities of lower than higher chlorinated biphenyls. Several congeners, particularly those having 7-10 chlorine atoms, were determined in concentrations smaller than 0.20 ng/g only at one sediment depth. Hexachlorobutadiene, 1, 2, 3, 4-tetrachlorobenzene, pentachlorobenzene, alpha-HCH, hexachlorobenzene, pentachloroanisol and alpha-chlordane were present at all stations at different sediment depths. Maximum concentrations of the 16 chlorinated hydrocarbons analyzed in Great Slave Lake sediments were between 0.08 and 1.04 ng/g. The concentrations of PCBs and other chlorinated hydrocarbons were about two orders of magnitude lower than those in Lake Ontario sediments.Key words: Great Slave Lake, sediments, geochemistry, PCBs, chlorinated hydrocarbonsR&Eacute;SUM&Eacute;. Au cours de l&rsquo;&eacute;t&eacute; de 1987, on a proc&eacute;d&eacute; &agrave; une &eacute;tude pour d&eacute;terminer la geochimie et la r&eacute;partition des oligo-&eacute;l&eacute;ments, des BPC et de 16 autres hydrocarbures chlorts dans des sediments provenant de zones s&eacute;lectionn&eacute;es du Grand Lac de l&rsquo;Esclave dans les Territoires du Nord-Ouest auCanada. On a pr&eacute;lev&eacute; des carottes de s&eacute;diments &agrave; trois postes d&rsquo;&eacute;chantillonnage dans le bassin ouest du lac le long d&rsquo;un axe allant du delta de la rivi&egrave;re Slave &agrave; l&rsquo;embouchure du fleuve Mackenzie. La composition g&eacute;ochimique des sediments a r&eacute;v&eacute;l&eacute; un d&eacute;p&ocirc;t de mat&eacute;riau similaire &agrave; tous les postes d&rsquo;&eacute;chantillonnage. La datation des s&eacute;diments a montr&eacute; un fort taux de sedimentation (46,6 g.cm-* par an) h 110 m sous l&rsquo;eau, dans la zone du delta de la Slave, et un m&eacute;lange des s&eacute;diments de fond dans la partie sud-ouest du lac. Les concentrations d&rsquo;oligo-&eacute;l&eacute;ments (Cu, Ni, Co, Cr, V, Pb, et Zn) &eacute;taient uniformes dans tous les profils de s&eacute;diments. Les s&eacute;diments de surface cependant contenaient en plus de l&rsquo;arsenic. On a utilis&eacute; des CLB-1 canadiens normalists contenant 51 cong&eacute;n&egrave;res de BPC pour d&eacute;terminer+les BPC dans les s&eacute;diments. On a d&eacute;tect&eacute; 33 congtntres de BPC et d&eacute;termin&eacute; leurs concentrations dans des sections choisies des carottes de suiments. Les cong&eacute;n&egrave;res les plus abondants &eacute;taient les num&eacute;ros 15 et 18,44,49,52et 101 (num&eacute;rotation de I&rsquo;IUPAC) avec des concentrations maximales respectives de 3.52, 2.68, 2,44,6,20 et 2,13 ng.g-l. Le sch&eacute;ma de concentration des BPC dans les sediments du Grand Lac de l&rsquo;Esclave r&eacute;v&eacute;l&eacute; des quantit&eacute;s considerablement plus importantes de biphenyles peu chlor&eacute;s parrapport aux biph&egrave;nyles tr&eacute;s chlor&eacute;s. On a trouv&eacute; plusieurs cong&eacute;n&egrave;res, en particulier ceux ayant de 7 &agrave; 10 atomes de chlore, en concentrations inf&eacute;rieures &agrave; 0,20 ng.g&rdquo; &agrave; seulement une certaine profondeur de s&eacute;diments. On a trouv&eacute; de l&rsquo;hexachlorobutadi&egrave;ne, du t&eacute;trachlorobenz&egrave;ne-1,2,3,4, du pentachlorobenz&egrave;ne, du H.C.H.-A, de l&rsquo;hexachlorobenz&egrave;ne, du pentachloroanisole et du chlordane-A &agrave; tous les postes &agrave; diff&eacute;rentes profondeurs de s&eacute;diments. Les concentrations maximales des 16 hydrocarbures chlor&eacute;s analysts dans les sediments du Grand Lac de l&rsquo;Esclave se situaient entre 0,08 et 1,04 ng.g&rdquo;. Les concentrations de BPC et d&rsquo;autres hydrocarbures chlor&eacute;s &eacute;taient d&rsquo;environ deux ordres de grandeur inf&eacute;rieures &agrave; celles contenues dans les s&eacute;diments du lac Ontario.Mots cl&eacute;s: Grand Lac de l&rsquo;Esclave, s&eacute;diments, g&eacute;ochimie, BPC, hydrocarbures chlor&eacute;

Trace metal distribution in the bed, bank and suspended sediment of the Ravensbourne River and its implication for sediment monitoring in an urban river

Purpose This study aims to identify a suitable sediment compartment for sediment quality monitoring by: (a) studying the concentration of trace metals (Cd, Cu, Ni, Pb and Zn) in the bed, bank and suspended sediment compartments of the Ravensbourne River to establish any differences in trace metal concentrations with compartment; (b) determining the influence of sediment particle size fractions ( 0.05) in the concentrations of metals between the suspended sediment and the < 63 μm bed sediment fraction, but there was a significant difference (p < 0.05) between the suspended sediment and the < 63 μm bank sediment fraction. There were also significant differences between the concentrations of metals in the < 63 μm and the 63 μm–2 mm fractions. Generally, the Ravensbourne River did not comply with the draft UK sediment quality guidelines for the metals analysed. Conclusions This study shows the importance of identifying a suitable sediment compartment to sample for compliance with sediment quality standards. The bed and suspended sediments are the most widely used sediment compartments for sediment monitoring, but collecting sufficient mass of the < 63 μm sediment fraction for monitoring presents a challenge for urban gravel bed rivers like the Ravensbourne River. It seems appropriate to establish individual monitoring regimes for different rivers

Imperium Nord

Storia della filosofia medievale nell'area germanica nel XIII secolo (in particolare Alberto il Grande e Dietrich di Freiberg