Variability in precipitation, temperature and river runoff in W Central Asia during the past ~2000yrs

The tributary rivers Amu Darya and Syr Darya contribute major amounts of water to the hydrological budget of the endorheic Aral Sea. Processes controlling the flow of water into rivers in the headwater systems in Tien Shan (Kyrgyzstan) and Pamir (Tajikistan) are therefore most relevant. Lake water mineralization is strongly dependent on river discharge and has been inferred from spectrometrically determined gypsum and other salt contents. Comparison of high-resolution mineralization data with tree ring data, other proxies for tracing temperature and snow cover in NW China, and accumulation rates in the Guliya Ice Core indicate that mineralization over the past ~2000. yrs in the Aral Sea reflects snow cover variability and glacier extent in Tien Shan and Pamir (at the NW and W edges of the Tibetan Plateau). Snow cover in W Central Asia is preferentially a winter expression controlled by temperature patterns that impact the moisture-loading capacity over N Europe and NW Asia (Clark et al., 1999). We observed that the runoff, resulting from warmer winter temperatures in W Central Asia and resulting in a reduction of snow cover, decreased between AD 100-300, AD 1150-1250, AD 1380-1450, AD 1580-1680 and during several low frequency events after AD 1800. Furthermore, we observed a negative relationship between the amount of mineralization in the Aral Sea and SW summer monsoon intensity starting with the Little Ice Age. Based on these observations, we conclude that the lake level changes during the past ~. 2000. yrs were mostly climatically controlled. Around AD 200, AD 1400 and during the late 20th century AD, human activities (namely irrigation) may also have synergistically influenced discharge dynamics in the lower river courses. © 2011 Elsevier B.V

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

Sediment source fingerprinting: benchmarking recent outputs, remaining challenges and emerging themes

Abstract: Purpose: This review of sediment source fingerprinting assesses the current state-of-the-art, remaining challenges and emerging themes. It combines inputs from international scientists either with track records in the approach or with expertise relevant to progressing the science. Methods: Web of Science and Google Scholar were used to review published papers spanning the period 2013–2019, inclusive, to confirm publication trends in quantities of papers by study area country and the types of tracers used. The most recent (2018–2019, inclusive) papers were also benchmarked using a methodological decision-tree published in 2017. Scope: Areas requiring further research and international consensus on methodological detail are reviewed, and these comprise spatial variability in tracers and corresponding sampling implications for end-members, temporal variability in tracers and sampling implications for end-members and target sediment, tracer conservation and knowledge-based pre-selection, the physico-chemical basis for source discrimination and dissemination of fingerprinting results to stakeholders. Emerging themes are also discussed: novel tracers, concentration-dependence for biomarkers, combining sediment fingerprinting and age-dating, applications to sediment-bound pollutants, incorporation of supportive spatial information to augment discrimination and modelling, aeolian sediment source fingerprinting, integration with process-based models and development of open-access software tools for data processing. Conclusions: The popularity of sediment source fingerprinting continues on an upward trend globally, but with this growth comes issues surrounding lack of standardisation and procedural diversity. Nonetheless, the last 2 years have also evidenced growing uptake of critical requirements for robust applications and this review is intended to signpost investigators, both old and new, towards these benchmarks and remaining research challenges for, and emerging options for different applications of, the fingerprinting approach

Checklist for the use of potassium concentrations in siliciclastic sediments as paleoenvironmental archives

International audienceWeathering indices quantify the release of mobile elements from source units of soils and sediments. They have been employed in geosciences for more than three decades, but their performance in sedimentary archives can still be improved by deciphering other forcing factors than climatic. From the most common alkali and alkaline earth metals included in the weathering indices, K seems to be most suitable for deciphering paleoclimate records of temperate to subtropical non-arid climates, assuming the interpretation respects the complex of controlling factors on sediment geochemistry. As a case study, normalised K concentrations in siliciclastic sediments of the Most Basin (Miocene period, central Europe) are revisited here and variations compared with modern fluvially transported solids. Existing knowledge on manifold controls of K concentrations in sediments is summarised and used to propose list of possible controlling factors, in particular Al/Si and Zr/Rb as grain-size proxies, Ti/Al as provenance proxy relevant for K concentration in parent rocks, and K/Rb as a measure for possible effects of metasomatism. The K/Al or K/Ti element ratios may be efficient in chemostratigraphic correlations in siliciclastic basins and efficient proxies for chemical weathering in the source area. The proposals in this work should stimulate future studies to overcome the underrepresentation of continental sediments in paleoclimate reconstructions

Using Sedimentary Archives to Reconstruct Pollution History and Sediment Provenance: The Ohře River, Czech Republic

In industrialised areas rivers and their floodplains are often highly polluted. The historic contamination of floodplains offers an important archive of past polluting activities and fluvial sediment dynamics. It can also present a significant threat to contemporary aquatic ecosystems and water quality resulting from the remobilisation of sediment-associated pollutants from floodplain secondary sources. Therefore, knowledge of the type and level of pollutants present and their spatial distribution in floodplains is essential for supporting measures to mitigate future impacts. Here, we outline an approach for reconstructing pollution history and extent by using floodplains as archives of historic chemical contamination coupled with geochemical and geomorphological analyses to account for variations in sediment provenance and depositional processes. The study is situated in the Ohře River(total catchment area of 5606 km2), which provides an excellent test case given its complex pollution history, heterogeneous geology and variable deposition patterns. Most severe pollution in this river system has originated from a chemical factory in Marktredwitz, Germany (mainly Hg) and uranium processing in Nejdek, the Czech Republic (mainly U); historical lead mining and modern coal combustion have also played a role. The geological/geochemical variability of the Ohře catchment re�quired extensive sampling along the river course. Variations in several major lithogenic elements, in particular Al, K, Rb, Si and Ti allowed the river course to be subdivided to geochemical river reaches using simple scatter plots (Ti against Al/Si ratio and Rb against K) or PCA; there was no need to sieve the sediment samples before analyses or perform other discrimination of sediment lithology. The geochemical river reaches reflect catchment geology and hence they exhibit distinct background functions for Cu, Pb, and Zn and varying background concentrations of U. Titanium was the best performing reference element. The Ohře River has deposited most historical pollution in former (abandoned or laterally shifting) channels rather than in overbank fine-grained materials. The former channel sediments can be recognised by a specific surface topography, vegetation cover and sediment lithology; the use of geographic information systems (evaluating historical maps, aerial photographs and DTM by LIDAR) is indispensable in the study of the depositional patterns. The narrow floodplain limited floodplain deposition, and has probably allowed particulates to travel through the channel for tens of kilometres, in the case of U pollution in 10 years. Dams constructed in the 1960s in the upper and middle river reaches have suppressed downstream transport of pollution and combined with certain channel engineering projects to prevent bank erosion are likely to have further limited the deposition of overbank fines. The study clearly shows that in the Ohře floodplain the fills of former channels are more suitable as pollution archives than the distal floodplain sediments (overbank fines outside the channel belt). The approach outlined here is applicable to reconstructions of pollution histories for any river characterised by varied catchment geochemistry and deposition in their channel belts