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See detailAnthropogenic impact on alluvial sedimentation rates during the last millennia in the Ardennes (Belgium)
Houbrechts, Geoffrey ULg; Notebaert, Bastiaan; Petit, François ULg et al

Conference (2014, February 03)

Alluvial deposits of numerous rivers in the Ardennes have been dated by using iron slag content and 14C. On the basis of these analyses, several periods of increased sediment deposition have been ... [more ▼]

Alluvial deposits of numerous rivers in the Ardennes have been dated by using iron slag content and 14C. On the basis of these analyses, several periods of increased sediment deposition have been identified. Before the first deforestations, rivers in this region developed multiple channels in alluvial forests (anabranching rivers), which are still distinguishable in the topography of many floodplains by means of LIDAR survey. Moreover, during this period, floodplains were not well-developed and probably very humid, which explains the presence of peat layers within the alluvial sequences. In the Amblève catchment, the first increased sedimentary deposition of the Holocene occurred during the Bronze Age, probably in relation to deforestation and first cropland agriculture in the area. Archaeological data indicate Roman occupation in parts of the catchment, and Roman Period colluvium has been found at one site. Several peat layers have been dated in the Lienne catchment to around 1000 BP and probably indicate very low anthropogenic pressure. From the 11th Century onwards, there was an increase in sedimentation, coinciding with a higher concentration of charcoal in alluvial deposits. In many catchments there is an important increase in the sedimentation at the end of the 14th century, which can be related to the development of numerous iron-working sites. Analyses of slag concentration produced in these sites allow us to reconstruct the evolution of the floodplain topography in relation to the periods of blast furnaces activity. Total sedimentation in the smaller valleys since the initiation of iron industries amounts 0.5 to 1.0 m, which is in most cases about 40% of the total sediment present in the floodplains and corresponds to a mean sedimentation rate ranging between 10 and 20 cm/century. Such values are explained by former agricultural practices and woodland clearance associated with the huge demand for charcoal by the iron industry. For instance, about 20 ha of forest were cleared for the yearly consumption of a refining forge or a blast furnace and more than three hundred iron factories existed in the Ardenne Massif between the 14th and the 19th century. [less ▲]

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See detailHolocene floodplain deposition and scale effects in a typical European upland catchment : A case study from the Amblève catchment, Ardennes (Belgium)
Notebaert, Bastiaan; Verstraeten, Gert; Houbrechts, Geoffrey ULg et al

in Holocene (2013), 23(8), 1184-1197

This study quantifies Holocene alluvial sediment deposition in the Belgian Amblève catchment (1080 km2), situated in the Ardennes uplands. An extended coring data set is used for a quantitative ... [more ▼]

This study quantifies Holocene alluvial sediment deposition in the Belgian Amblève catchment (1080 km2), situated in the Ardennes uplands. An extended coring data set is used for a quantitative description and a quantification of the alluvial depositions. The floodplains fall into three main types: the upper and lower floodplains and the steep reaches. Total Holocene alluvial sediment deposition amounts to 32 Tg, or 0.029 Tg/km2. Dating of sediments using iron slag as tracer shows that on average 42% of contemporary storage was accumulated during the last 600 years. Radiocarbon dating of fluvial deposits at eight sites in the catchment confirms that the majority of the sediment is relatively recent. The increased sedimentation rates for this period are related to anthropogenic land use, possibly enhanced by climatic variations. A fluvial sediment budget was constructed for this 600 yr time period and shows that export from the catchment has about the same importance as storage in the floodplains, while lateral reworking of existing floodplain deposits only affects half the quantity of sediments. Overall, floodplain sediment storage in the Amblève catchment, comparable with other upland catchments, is of lesser importance compared with catchments dominated by loess. This can mainly be explained by lower sediment supply resulting from less intense anthropogenic land use, despite the higher sediment transport efficiency through the fluvial system. Floodplain sediment storage is scale-dependent, with initially a sharp increase in catchment area-specific sediment deposition, followed by a steady decrease with increasing catchment area. [less ▲]

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See detailFluvial architecture of Belgian river systems in contrasting environments:implications for reconstructing the sedimentation history
Notebaert, Bastiaan; Houbrechts, Geoffrey ULg; Verstraeten, G. et al

in Netherlands Journal of Geosciences - Geologie en Mijnbouw (2011), 90(1), 31-50

Accurate dating is necessary to get insight in the temporal variations in sediment deposition in floodplains. The interpretation of such dates is however dependent on the fluvial architecture of the ... [more ▼]

Accurate dating is necessary to get insight in the temporal variations in sediment deposition in floodplains. The interpretation of such dates is however dependent on the fluvial architecture of the floodplain. In this study we discuss the fluvial architecture of three contrasting Belgian catchments (Dijle, Geul and Amblève catchment) and how this influences the dating possibilities of net floodplain sediment storage. Although vertical aggradation occurred in all three floodplains during the last part of the Holocene, they differ in the importance of lateral accretion and vertical aggradation during the entire Holocene. Holocene floodplain aggradation is the dominant process in the Dijle catchment. Lateral reworking of the floodplain sediments by river meandering was limited to a part of the floodplain, resulting in stacked point bar deposits. The fluvial architecture allows identifying vertical aggradation without erosional hiatuses. Results show that trends in vertical floodplain aggradation in the Dijle catchment are mainly related to land use changes. In the other two catchments, lateral reworking was the dominant process, and channel lag and point bar deposits occur over the entire floodplain width. Here, tracers were used to date the sediment dynamics: lead from metal mining in the Geul and iron slag from ironworks in the Amblève catchment. These methods allow the identification of two or three discrete periods, but their spatial extent and variations is identified in a continuous way. The fluvial architecture and the limitation in dating with tracers hampered the identification of dominant environmental changes for sediment dynamics in both catchments. Dating methods which provide only discrete point information, like radiocarbon or OSL dating, are best suited for fluvial systems which contain continuous aggradation profiles. Spatially more continuous dating methods, e.g. through the use of tracers, allow to reconstruct past surfaces and allow to reconstruct reworked parts of the floodplain. As such they allow a better reconstruction of past sedimentation rates in systems with important lateral reworking. [less ▲]

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See detailEvolution of floodplain sedimentation during the last millennia in the Ardenne Massif (Belgium)
Houbrechts, Geoffrey ULg; Notebaert, Bastiaan; Verstraeten, Gert et al

Poster (2009, July)

In the Ardenne massif, several periods of increased sediment deposition have been identified during the last millennia. They can be correlated to increasing anthropogenic land use pressure. The majority ... [more ▼]

In the Ardenne massif, several periods of increased sediment deposition have been identified during the last millennia. They can be correlated to increasing anthropogenic land use pressure. The majority of the sediments found in floodplains were deposited in the last 4000 years, and in many cases even in the last 1000 years. In the Amblève catchment, the first increase in sediment deposition of the Holocene occurred during the Bronze Age (3200 BP), related to first deforestations and crop cultures in the area. Several organic depositions have occurred between 2700 BP and 1000 BP and probably indicate low anthropogenic pressures or more humid periods. From the 11th century onwards, there was an increase in sedimentation, and alluvial deposits contain more charcoal. A second important increase in sedimentation is observed in headwater catchments at the end of the 14th century, which can be related to the development of many iron factories. In the Ardenne massif, more than 300 iron factories existed between the 14th and the 19th century and about 20 ha of forest were cleared each year for the consumption of a refining forge or a blast furnace. Analysis of slag concentration produced in former factories and redistributed in the floodplain allows us to reconstruct the evolution of floodplains since the inception of the iron industries. The results show that not all floodplains in the Amblève catchment are equally sensitive to catchment disturbances. In the headwater stream (Chavanne river, 10-20 km²), about 80 cm of sediment has been deposited since the inception of the iron industries (towards 1540 AD). In the lower Lienne valley (100-150 km²), almost no sediment accumulation occurred in the floodplains after the beginning of iron melting (towards 1400 AD). This difference could be explained by the larger stream power of the Lienne river (100-120 W/m2 for Qb). [less ▲]

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See detailResponse of floodplain sedimentation to catchment disturbances in different environments
Notebaert, Bastiaan; Houbrechts, Geoffrey ULg; Verstraeten, Gert et al

Poster (2009)

Holocene floodplain sediments are an important environmental archive, that can be accesed for reconstructing the past landscape dynamics either qualitatively (e.g. palynology) and quantitatively (e.g ... [more ▼]

Holocene floodplain sediments are an important environmental archive, that can be accesed for reconstructing the past landscape dynamics either qualitatively (e.g. palynology) and quantitatively (e.g. sediment budgeting). In this study Holocene alluvial sediment deposition in two contrasting Belgian catchments was quantified and dated: the Lienne (148 km²) in the Ardennes massif and the Dijle (750 km2) in the loess region. These catchments experienced a comparable Holocene climatic variation, but differ in topography and geology with highest relief energy in the Lienne catchment. Land use history also differs with high land use intensities in the Dijle catchment since Roman times, but at least since the Middle Ages there were also large deforestations in the Lienne catchment. Detailed cumulative Holocene sediment deposition was assessed for each catchment using more then 1000 hand augerings. Detailed radiocarbon dating of fluvial deposits was performed in the Dijle catchment, while iron slag was used as a tracer for sediments deposited after 1350 AD in the Lienne catchment. Results show that sediment deposition is much larger in the Dijle catchment (~4.5 Mg ha-1 catchment area) then in the Lienne catchment (~0.2 Mg ha-1 catchment area). Dating results from the Dijle catchment show an increase of sediment deposition in the late Holocene, first starting in the colluvial valleys and later on prograding towards the main valleys. Variations in sedimentation rates can clearly be related to anthropogenous land use pressure, and the majority of the sediments found in colluvial and alluvial valleys were deposited in the last 4000 years, and in many cases even in the last 1000 years. Variations in sediment deposition within the catchment can partially be explained by differences in river valley physical settings (mainly valley slope), while in other cases hill slope sediment delivery (upstream erosion, connectivity between hill slopes and the river system) is the explaining factor. In the Lienne catchment, between 80 and 100% of the sediments present in the main valley were deposited before 1350AD, thus before the main period of forest clearance. On the other hand, about 50% of the Holocene sediment present in a main tributary was deposited after 1537 (local start of iron industry). This difference with the main valley can be explained by a difference in physical settings of the river (valley slope, stream power). These results show that the physical settings of river valleys determine how sensible the river systems are to catchment disturbances. Floodplain deposition is determined by an interplay of hill slope sediment delivery (hill slope erosion and connectivity) and physical settings of the valley itself (valley slope, discharge). As a result, quantification of floodplain deposition alone, cannot be used as a measure for historic soil erosion within a catchment or to determine intensity of human impact on the catchment. [less ▲]

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See detailFluctuation of sediment production during the last millennia in the Ardenne Massif (Belgium)
Houbrechts, Geoffrey ULg; Notebaert, Bastiaan; Petit, François ULg et al

Poster (2009)

In the Ardenne massif, floodplains have recorded fluctuations in the production of sediment and several periods of increased sediment deposition have been identified. Before the first deforestations ... [more ▼]

In the Ardenne massif, floodplains have recorded fluctuations in the production of sediment and several periods of increased sediment deposition have been identified. Before the first deforestations rivers developed multiple channels in alluvial forests. Floodplains were not well-developed and probably very humid, which explains the presence of peat layers within the alluvial sequences. In the Amblève catchment, the first increased sedimentary deposition of the Holocene occurred during the Bronze Age (3200 BP), in relation to deforestation and the first crop cultures in the area. An organic deposition has occurred around 2700 BP and could correspond with a period of climatic degradation. Several peat layers have also been dated to around 1000 BP and probably indicate very low anthropogenic pressure. From the 11th Century onwards, there was an increase in sedimentation and a greater concentration of charcoal is present in the alluvial deposits. In many catchments there is an important increase in the sedimentation at the end of the 14th century, which can be related to the development of many iron factories. Analyses of slag concentration produced in these former factories allow us to reconstruct the evolution of the floodplain topography since the inception of the iron industries, in relation to the periods of activity. Total sedimentation in the smaller valleys since the initiation of iron industries amounts 0.5 to 1.0 m, which is in most cases about 50% of the total sediment present in the floodplains and corresponds to a mean sedimentation rate ranging between 10 and 20 cm/century. Such values are explained by various former agricultural practices and forest clearings associated with the huge demand for charcoal by the iron industry. About 20 ha of forest were cleared for the yearly consumption of a refining forge or a blast furnace and more than three hundred iron factories existed in the Ardenne Massif between the 14th and the 19th century. [less ▲]

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