Fingerprinting historical fluvial sediment fluxes

In order to better understand the human impact on fluvial sediment dynamics at various timescales, information on the changing connectivity between the various geomorphic units in a landscape is crucial. Quantitative sediment budgets for various time periods provide a first assessment of changes in coupling between slopes and river systems. However, the application of sediment fingerprinting can yield additional spatial information on the sediment pathways. Furthermore, the fingerprint approach can also be used in cases where detailed sediment budgets are difficult to obtain. Provenance studies have been executed in various sedimentary environments, covering a wide variety of spatial and temporal scales. Here, an overview is provided of the tracer properties that can be used to distinguish between the various sediment sources in a river catchment. From this general compilation, those tracers useful to fingerprint fine-grained floodplain deposits on a historical timescale (decadal to millennial) are identified. Geochemical and mineralogical compositions, mineral magnetic signals and isotope ratios can be considered the most suitable fingerprinting properties. The impact of source area weathering, grain size selectivity of erosion and sedimentary processes and post-depositional alteration on tracer properties from source to sink are considered. Finally, a synopsis is given of the qualitative to fully quantitative approaches that can be used to discriminate the sources of fine-grained alluvial sediments. © SAGE Publications 2012.status: publishe

Towards a quantification of agricultural carrying capacity in the past: the application of a soil erosion model to estimate crop productivity

Humans have impacted their environment throughout history, especially since the introduction of widespread agriculture and the associated forest logging activities, thereby creating anthropogenic landscapes in which environmental processes are no longer in equilibrium. Under certain conditions, this has led to a drastic reduction in carrying capacity with negative feedback to the sustainability of society. Soil erosion and the resulting reduced agricultural productivity has been pushed forward as one of the contributing factors responsible for the collapse of ancient societies. Yet, quantitative data supporting these hypothesis is still lacking. Furthermore, more attention was recently given to the resilience of ancient societies against soil erosion and its negative consequences, challenging the ideas of collapse. In order to tackle these questions, local site-specific information on land use and soil erosion needs to be upscaled to entire regions or territories. A modeling approach can help to achieve this. The territory around the ancient city of Sagalassos (Taurus Mountains, SW Turkey) was selected to quantify crop productivity through space and time. In order to simulate erosion, the spatially distributed soil erosion & sediment delivery model WaTEM/SEDEM was used. Results show how land cover variations and the depletion of soil reservoir have a larger influence on the central valley sedimentation rates in comparison to climatic variability. The general amount and spatial pattern of net erosion was well reproduced by the model, although it failed to capture the more detailed field work derived sedimentary chronologies. The soil erosion model offers the opportunity to get information on soil depths in both space and time, which can be used as input for the crop productivity model. The model results from the Gravgaz catchment show how deforestation and agriculture led to the depletion of the existing soil reservoir while creating agricultural potential in the central valley’s through the accumulated sediments. Although preliminary results show that soil thickness on its own isn’t a strong predictor for crop yields, future work will include soil thickness at least as one of the factors controlling crop productivity. Promising soil properties – crop yield relations can be found in literature, but they still need to be verified for the territory of Sagalassos. Hence, present day crop yield data need to be collected to form a basis for model validation. Furthermore, soil properties of ancient soils will have changed throughout time. Therefore, the model will have to include the dynamic properties of soils over time.status: publishe

Geomorphologic coupling and decoupling in a Mediterranean mountain catchment under changing environmental conditions as evidenced by sediment fingerprinting

status: accepte

A sediment fingerprinting approach to understand the geomorphic coupling in an eastern Mediterranean mountainous river catchment

To understand the response of a river to anthropogenic disturbance, knowledge of the links between erosion, sediment deposition, and sediment export is crucial. Therefore, starting from field observations and connectivity proxies, a sediment fingerprinting approach using geochemical tracers was used to elucidate the subrecent sediment dynamics in the 264-km2 Büğdüz River catchment in SW Turkey. A topography-based connectivity index was used as a proxy for hillslope–channel coupling and stream power estimations as a proxy for the within-channel connectivity. Quantitative provenance information provides a link between potential sediment sources and the derived sediment currently stored within the fluvial system. Provenance signals from both contemporary river bed sediments (n = 144) and subrecent floodplain deposits (n=28) provide more insight into the coupling of the hillslopes to the river channel and the coupling within the river channel itself. Furthermore, comparing the provenance signal with the areal extent of potential sediment sources upstream in the form of enrichment ratios sheds light upon the variation of the erodibility of the sources and the connectivity within the catchment. Results indicate that the valley gradient exerts an important control on the spatial variability of geomorphic coupling in the Büğdüz catchment. Furthermore, different sediment sources (lithologies) show distinct sediment production rates. In addition to the observed spatial variability, coupling relations are characterized by an important seasonal variation, indicated by variable contributions of local and more distant sediment sources.status: publishe

Sensitivity of the Eastern Mediterranean geomorphic system towards environmental change during the Late Holocene: a chronological perspective

Alluvial and colluvial sediment deposition provide a vital record of environmental change during the Holocene. Firm chronological control on these archives is necessary to enable us to relate sediment dynamics to human activity and climate variability. In the Eastern Mediterranean, such relationships are hard to establish due to the lack of spatially well-distributed sediment archives with good chronological control. This scarcity is problematic with respect to regional-scale reconstructions of the temporal variation of sediment dynamics. Here, we present a radiocarbon database (n=178) of geomorphological activity collected from multiple distinct sediment archives within the territory of Sagalassos in south-western Turkey. The data were grouped according to their sedimentary facies for analysis using cumulative probability distributions (CPDs) and sedimentation rate (SR) modelling. Two small-scale colluvial valleys, where chronological information was abundant, were investigated in more detail. Results show that sedimentation chronology differs between individual, nearby cores, as it depends strongly on the local geomorphic situation. A generalizing approach combining multiple core results yields more widely valid conclusions. High sedimentation rates coincided with the initial major anthropogenic disturbance of the landscape and decreased afterwards, probably due to hillslope soil depletion. CPD and SR analysis indicates that in general colluvial sedimentation rates did not change much from 2000 BC onwards. River floodplain sedimentation, in contrast, increased markedly during the first millennium BC and during recent times, and a significant time lag in enhanced sediment deposition between the upper and lower reaches of the river valleys was observed. © 2012 John Wiley & Sons, Ltd.status: publishe

Unravelling changing sediment sources in a Mediterranean mountain catchment: a Bayesian fingerprinting approach

To determine the provenance of Holocene floodplain deposits of the Bügdüz catchment in southwest Turkey a Bayesian fingerprinting approach was used. An important requirement for any provenance study is that the potential sediment sources show sufficient spatial and compositional heterogeneity. The spatial distribution of potential sources, in this case the various lithologies present within the catchment, was mapped using field observations and ASTER and Quickbird satellite images. To distinguish the source lithologies a set of geochemical tracers was identified with the use of a Linear Discriminant Analysis. This optimum fingerprint was then used in the mixing model to determine the sediment provenance. The Bayesian mixing model uses Markov chain Monte Carlo random walks to determine the most probable source composition and mixing proportions. The uncertainty associated with the input data can be incorporated into the model through the prior probability distributions. The spread of the posterior probability distributions represents the uncertainty associated with the mixing proportion calculation. The main contrasts in provenance of the floodplain deposits reflect the spatial distribution of potential sediment sources throughout the catchment. There are, however, also important temporal variations in sediment provenance and lateral differences due to the nature of floodplain build-up. The observed spatial and temporal variability of sediment provenance gives a first indication that hill slope-channel and within-channel coupling relations are not uniform through the catchment and that different locations showed a distinct response to disturbances.status: publishe

Reconstructing changing sediment sources in a Mediterranean mountain river catchment using composite sediment fingerprinting

status: accepte

Using pollen data to distinguish between climatic and anthropogenic driven landscape change in south-western Turkey, and its implications for understanding sediment dynamics

status: publishe

Human induced soil erosion and the implications on crop yield in a small mountainous Mediterranean catchment (SW-Turkey)

Many hillslopes in the limestone dominated Taurus Mountain Range (SW Turkey) are characterized by severely depleted soils, while a significant amount of sediment is being stored in the valley bottoms. The same holds true for the 11.4 km2 endorheic Gravgaz basin in the vicinity of the Hellenistic-Roman city of Sagalassos in SW Turkey. Previous palaeo-environmental research in this basin already yielded both detailed sedimentological and palynological information on sedimentation in the valley bottom and vegetation changes that took place during the last several millennia. An adapted WATEM/SEDEM geomorphic model version was used to simulate the impact of the observed changes in vegetation cover, climate and hillslope soil properties on hillslope soil erosion and valley bottom sediment deposition over the last 4000 years. The calibrated WATEM/SEDEM model is able to reconstruct the temporal changes of sedimentation in the valley bottom reasonably well. To simulate the impact of historic soil erosion on crop productivity a simple crop yield model was coupled to the reconstructed soil thickness maps. The main outcomes are that soil erosion was mainly driven by deforestation and hence anthropogenic activity, but the resulting soil erosion did not cause a complete collapse of crop yields. On the contrary, we were able to quantify that the sediment accumulation in the lower lying valley bottoms compensated at least a part of the loss in crop yield from the hillslopes: potential crop yield value changed from 2.80 t ha− 1 a− 1 before widespread deforestation to 2.58 t ha− 1 a− 1 during Roman-Imperial times and 2.19 t ha− 1 a− 1 at present. These model approaches are tools that allow us to quantify human impact in the past, going beyond traditional qualitative descriptions, which will ultimately lead to a better understanding of human-environment interactions in the past