Sediment yield variability in Spain: a quantitative and semiqualitative analysis using reservoir sedimentation rates

An existing dataset of area-specific sediment yield (SSY) for 60 catchments in Spain that was retrieved from sediment deposition rates in reservoirs [Avendaño Salas, C., Sanz Montero, E., Rayán, C., Gómez Montaña, 1997. Sediment yield at Spanish reservoirs and its relationship with the drainage basin area. In: Proceedings of the 19th Symposium of Large Dams, Florence, 1997. ICOLD (International Committee on Large Dams), pp. 863–874] reveals that catchment area alone explains only 17% of the variability in SSY. In this study, an attempt to explain the remaining variability in SSY was made using a quantitative and a semiqualitative approach for 22 catchments. During a field survey, the 22 selected catchments were characterised by topography, vegetation cover, lithology, shape and the presence of gullies in the broad vicinity of the reservoir. This information was used to develop a factorial scoring index model that provides a fairly accurate and reliable prediction of SSY. A classical multiple regression model using climatic, topographic and land use properties derived from regional datasets could not explain as much variance as the qualitative index model, nor did it appear to be as reliable. The same conclusion could be drawn when using the CORINE soil erosion risk map of southern Europe. The low prediction capability of the multiple regression models and the CORINE soil erosion risk map could be attributed mainly to the fact that these methods do not incorporate gully erosion and that the land cover data are not a good representation of soil cover. Both variables have been shown to be of great importance during the field surveys. Future assessments of SSY could be quickly and efficiently made using the proposed factorial scoring index model. In comparison with other models, which demand more data, the index model offers an alternative prediction tool.     

Die Reaktion Phlogopit + Calcit + Quarz = Tremolit + Kalifeldspat + H2O + C2O

Hydrothermal experiments with mixtures of synthetic minerals have shown the reversibility of the reaction 5 phlogopite + 6 calcite + 24 quartz = 3 tremolite + 5 K-feldspar + 2 H₂O + 6 CO₂. In an isobaric T – diagram the equilibrium curve reaches a maximum at = 0,75. The P, T-values for this maximum are: 2 kb-523°; 4 kb-585°; 6 kb-625°; P±5%, T±10° C. These results give a first approximation of the P, T conditions responsible for a similar mineral reaction which has been recorded from natural metamorphic assemblages.

---

---

Herrn Prof. H. G. F. Winkler danke ich für anregende Diskussionen, desgleichen Herrn Dr. D. Puhan für wichtige Hinweise und Mitteilung seiner exp. Daten. Herrn Prof. V. Trommsdorff und Herrn P. H. Thompson bin ich für petrographische Angaben zu Dank verpflichtet. Der Aufbau der Hydrothermalanlage und die Finanzierung der laufenden Untersuchungen wurde aus den Mitteln des Fonds zur Förderung der wissenschaftlichen Forschung ermöglicht. Für diese Unterstützung gilt daher mein besonderer Dank.     

Heavy metal contamination of a Greenland fjord system by mine wastes

Since 1973, about 500,000 tons/yr of metal-rich particulate tailings from a lead/zinc flotation mill have been discharged through a submarine outfall into a two fjord system on the west coast of Greenland. Differential solubilization of particulate metals by seawater, seasonal water mixing, and sill exchange tailings dispersal processes have resulted in high, but seasonally variable Zn, Cd, and Pb contamination of the water, and suspended particulate matter (SPM).Chemical partition of the SPM shows that most (85-99 percent) of the Pb, but relatively low proportions of Zn (14-26 percent) and Cd (10–20 percent) are weakly bound to the SPM. Such particulate metal characteristics allow the real time effects of tailings discharges and dispersal on the system to be traced even in the sediments where tailings accumulation is very slow (0.1 cm/yr).Fjord seaweeds and blue mussels also contain varying amounts of Zn, Pb, and Cd depending on the metal and their location relative to the tailings outfall and apparently responded almost instantly to the metal contamination, as did the water and SPM. High Pb concentrations in the fjord mussels most likely derive from the preferential uptake of available particulate Pb, whereas the seaweeds appear to derive most of their heavy metal concentrations from the dissolved phase. The evidence from this and other sites as well as from experimental work, indicates that any discharge of Pb-bearing particles into the marine environment either directly as mine wastes or indirectly as from natural runoff from current and former lead mining sites results in immediate lead contamination of the in situ mussel population.     

Qualitative and quantitative applications of LiDAR imagery in fluvial geomorphology

The potential for geomorphological mapping and quantitative calculations of light detection and ranging (LiDAR) data within fluvial geomorphology was studied for two river catchments within Belgium (Dijle and Amblève), which differ in physical settings and floodplain morphology. Two commercial, of‐the‐shelf LiDAR datasets with different specifications (horizontal resolution and vertical accuracy) were available for parts of the floodplains of both catchments. Real‐time kinematic (RTK) Global Positioning System (GPS) data were used as ground truth for error calculations. Qualitative analysis of LiDAR data allowed the identification of former channel patterns, levees, colluvial hillslope and fan deposits. These results were confirmed by field data, topographic surveys and historical maps. The pixel resolution proved to be an important factor in the identification of small landforms: only features with a width equal to or larger than LiDAR resolution can be detected. This poses limits on the usability of regionally available LiDAR data, which often have a horizontal resolution of several metres. The LiDAR data were also used in a quantitative analysis of channel dynamics. In the study area, the width of the Dijle River channel increased 3 m on average between 1969 and 2003. A sediment budget of channel processes for the period 1969–2003 indicated a total river bank erosion of 16·1 10³ m³ and a total within channel deposition of 7·1 10³ m³, resulting in a net river erosion of 9·0 10³ m³ or c. 0·4 Mg year^?1 per metre river length. Sequential LiDAR data can in theory be used to calculate vertical sedimentation rates, as long as there is control on the error of the reference levels used. Copyright © 2008 John Wiley and Sons, Ltd.     

Impact of the Atlantic Warm Pool on precipitation and temperature in Florida during North Atlantic cold spells

Recurrent phases of increased pine at Lake Tulane, Florida have previously been related to strong stadials terminated by so-called Heinrich events. The climatic significance of these pine phases has been interpreted in different ways. Using a pollen?Cclimate inference model, we quantified the climate changes and consistently found that mean summer precipitation (P _JJA) increased (0.5?C0.9?mm/day) and mean November temperature increased (2.0?C3.0°C) during pine phases coeval with Heinrich events and the Younger Dryas. Marine sea surface temperature records indicate that potential sources for these moisture and heat anomalies are in the Gulf of Mexico and the western tropical Atlantic. We explain this low latitude warming by an increased Loop Current facilitated by persistence of the Atlantic Warm Pool during summer. This hypothesis is supported by a climate model sensitivity analysis. A positive heat anomaly in the Gulf of Mexico and equatorial Atlantic best approximates the pollen-inferred climate reconstructions from Lake Tulane during the (stadials around) Heinrich events and the Younger Dryas.     

长江入海泥沙的交换和输移过程——兼论泥质区的“泥库”效应

采用粒度谱的计算方法分析高浊度河口混合环境下悬浮泥沙和表层沉积物的交换过程,研究悬浮泥沙在河口—陆架系统的输移和归宿问题。分析表明:(1)大约有47%的悬浮泥沙沉积在长江口拦门沙海域及水下三角洲前缘,超过50%的悬浮泥沙摆脱河口的"束缚"进入杭州湾以及向南沿浙闽海岸输运,122.5°～123°E是长江悬浮泥沙向东扩散的重要界限。本文提供的粒度谱计算方法可适用于多种潮汐环境的泥沙输运和沉积的定量计算。(2)长江口悬浮泥沙与表层沉积物高交换区(交换率>0.6)主要分布在南槽口外的泥质区和杭州湾附近海域,其中长江口外泥质区的交换率高达0.9以上,说明该区域悬浮泥沙大量参与供沙和造床过程。在10～100年尺度上,长江口南槽口外的泥质区和杭州湾存在着一个显著的沉积中心,其泥沙交换速率可高达2～3cm/a以上。(3)由于受沿岸流和台湾暖流的影响,从长江口输出的大部分悬浮泥沙首先沉积在长江口南槽口外的泥质区,随后在潮流的作用下向长江口、杭州湾和沿海岸向南输运,泥质区充当了长江口系统泥沙输运和入海泥沙向南输送的"泥库"。长江口泥质区既是长江入海泥沙向口外输送的泥沙"汇",也是涨潮输入长江河口和杭州湾、浙闽沿岸泥质带的泥沙"源"。(4)由于长江口外余流向南槽口外汇聚,南槽口外含沙量较高,而且长江口水下三角洲前缘潮滩仍处于缓慢淤涨状态,上述水动力和地貌的综合分析证实了长江口外泥质区的"泥库"效应。在长江入海泥沙减少的背景下,"泥库"对河口地貌发育的贡献明显;随着流域减沙的不可逆转,口门附近的"泥库"将发挥愈来愈重要的向河口系统供沙的功能。     

Sediment‐budget modelling of multi‐sourced basin fills: application to recent deposits of the western Adriatic mud wedge (Italy)

We analysed modern mass‐accumulation patterns on the western Adriatic mud wedge (Italy), an elongated belt of shelf mud formed by coalesced prodeltas of the Adige, Po, and Apennine rivers, as part of an integrated strategy aimed at producing a quantitative sediment budget model for muddy continental shelves sourced by multiple compositionally distinct fluvial systems. Sediment provenance and source‐specific accumulation rates of surface sediments were quantified by combining results of grain‐size analysis and geochemical analysis of specific size fractions with bulk mass accumulation rates. Statistical classification algorithms adapted to compositional data were used to partition the total (geochemical) variation of sediment properties into size‐related and provenance‐specific factors. We identified geochemically distinct fluvial end‐member sediment types in two different grain‐size fractions, which were grouped into sediments derived from the Apennine rivers, and sediments derived from the Po and Adige rivers. Compositional fingerprints (end‐member compositions) of each source area were estimated by taking into account relative rates of fluvial sediment supply from rivers as predicted by numerical modelling. The end members allow us to explain geochemical compositional variation of mud‐wedge surface sediments in terms of provenance and size‐selective dispersal, and map mass accumulation rates of sediments from individual source areas (grain size<63 μm), as well as bulk sand accumulation rates (grain size>63 μm) across the western Adriatic mud wedge. The source‐specific rates of fine‐grained sediment supply derived from geostatistical estimates of mass‐accumulation rates were used to calibrate the numerical model of sediment supply to present‐day conditions.     

The sensitized photo-oxidation of n-pentadecane as a model for abiotic decomposition of aliphatic hydrocarbons in seawater

n-Pentadecane was photo-oxidized, as a surface film, on purified natural seawater under simulated environmental conditions with anthraquinone as sensitizer. Initial attack by hydrogen abstraction from carbon atoms within the chain is followed by reaction of the alkyl radicals thus generated with molecular oxygen. The stable reaction products identified by GC-MS strongly suggest that alkoxy radicals produced by cleavage of the peroxide bond are key intermediates in the decomposition of the original alkane. The alkoxy radicals stabilize themselves either as ketones by reaction with molecular oxygen which is transformed into HO₂ or, if μ-hydrogen atoms are available, by cyclic electron rearrangements similar to a Norrish type II photo-decomposition. The products of the electron rearrangements are 1-alkenes and daughter alkoxy radicals. The latter either yield methyl ketones and HO₂ radicals upon reaction with molecular oxygen or undergo further decomposition as long as γ-hydrogen atoms are available. The generation of acetone and HO₂ radicals, inferred by the proposed reaction mechanism as products of many such degradation sequences, offers a plausible explanation for their occurrence in seawater in addition to those already advanced.