The application of sediment fingerprinting to floodplain and lake sediment cores: assumptions and uncertainties evaluated through case studies in the Nene Basin, UK

Purpose: Fine sediment has been shown to be a major cause of the degradation of lakes and rivers and, as a result, research has been directed towards the understanding of fine sediment dynamics and the minimisation of sediment inputs. The use of tracers within a sediment fingerprinting framework has become a heavily used technique to investigate the sources of fine sediment pressures. When combined with the use of historically deposited sediment, the technique provides the opportunity to reconstruct past changes to the environment. However, alterations to tracer signatures during sediment transport and storage are a major potential source of uncertainty associated with tracer use. At present, few studies have quantified the uncertainties associated with tracer use. Materials and methods: This paper investigated uncertainty by determining the differences between sediment provenance predictions obtained using lithogenic radionuclide, geochemical and mineral magnetic signatures when fingerprinting lake and floodplain sedimentary deposits. It also investigated the potential causes of the observed differences. Results and discussion: A reservoir core was fingerprinted with the least uncertainty, with tracer group predictions ∼28 % apart and a consistent down-core trend in changing sediment provenance produced. When fingerprinting an on-line lake core and four floodplain cores, differences between tracer group predictions were as large as 100 %; the down-core trends in changing sediment provenance were also different. The differences between tracer group predictions could be attributed to the organic matter content and particle size of the sediment. There was also evidence of the in-growth of bacterially derived magnetite and chemical dissolution affecting the preservation of tracer signatures. Simple data corrections for sediment organic matter content and particle size did not result in significantly greater agreement between the predictions of the different tracer groups. Likewise, the inclusions of weightings for tracer discriminatory efficiency and within-source variability had minimal effects on the fingerprinting results. Conclusions: This paper highlights the importance of tracer selection and the consideration of recognising tracer non-conservatism when using lake and floodplain sediment deposits to reconstruct anthropogenic changes to the environment and changing sediment dynamics. It was recommended that future research focus on the assessment of uncertainty using the artificial mixing of sediment source samples, the limitation of the fingerprinting to narrow particle size fractions and the development of specific particle size and organic matter correction factors for each tracer

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

An analysis of potential controls on long-term 137Cs accumulation in the sediments of UK lakes

137 Cs has been utilised extensively to investigate catchment sediment dynamics. Its activity can be indicative of sediment derived from surface sources, and its inventory in deposited sediments reflects local fallout, radioactive decay, sediment accumulation and sediment source. Lakes represent ideal depositional environments for the reconstruction of historical sediment dynamics. In the UK, depth profiles and inventories of 137 Cs in lake cores have been investigated in a large number of catchments, but no study has synthesised all of these data to identify national spatial trends. The aim of this study was therefore to determine what can be learnt from 137 Cs inventories and profiles from UK lakes. Analysis revealed that local reference fallout, the rate of linear sediment accumulation (cm year −1 ) and the lake area:catchment area ratio, are the most important factors that control lake 137 Cs inventories. Delivery of mobile 137 Cs to the lake shortly after fallout, dissolved in runoff, or associated with mobilised sediment in transit from the source to the lake, is also likely a major control on inventories, especially on down-core profiles and peak activities. It is possible that dissolved 137 Cs inputs remain important controls on activities in recently deposited sediments, as they are often higher than potential contributing catchment sediment sources. It is also likely that finer particle-size distributions in lake-bed sediments, compared with source materials, increase both activities and inventories. Uncertainties are associated with patterns of sediment deposition on the lake bed and the estimation of local reference fallout, and lakes with low catchment-derived 137 Cs inputs potentially have a comparable or lower inventory than calculated from the estimated reference fallout. Lakes with multiple inlet tributaries and poor mixing of inflows, or an irregular bed shape divided by ridges and depressions, are also likely to display considerable variability in sediment-associated 137 Cs deposition. Despite these uncertainties, 137 Cs depth profiles provide valuable information on sediment sources and dynamics when interpreted carefully in the context of other UK lakes, and in relation to the corresponding catchment and lake characteristics. Several distinctive down-core profiles and inventories reported here yielded valuable insights into catchment sediment dynamics