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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

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    Aspects of atmospheric turbulence related to scintillometry
    Braam, M. - \ 2014
    Wageningen University. Promotor(en): Bert Holtslag, co-promotor(en): F. Beyrich; Arnold Moene. - Wageningen : Wageningen University - ISBN 9789461739384 - 151
    turbulentie - meteorologie - atmosfeer - scintillometrie - meteorologische waarnemingen - methodologie - turbulence - meteorology - atmosphere - scintillometry - meteorological observations - methodology

    Aspects of atmospheric turbulence related to scintillometry

    Atmospheric turbulence is the main vertical transport mechanism in the atmospheric boundary layer. The surface fluxes related to this turbulent transport are the sensible () and latent heat fluxes (). The area-averaged values of and are of interest to evaluate mesoscale numerical weather models and in water budget studies. Natural landscapes are often heterogeneous, i.e. and differ among fields.

    The fluxes can be obtained with a scintillometer system, which consists of an electromagnetic beam transmitter at one end of a propagation path and a receiver at the other end. The intensity of the electromagnetic signal at the receiver varies due to fluctuations in the refractive index of air () caused by turbulence along the path. From the magnitude of these fluctuations the structure parameter of temperature () and of humidity () can be derived. Finally, and are used to determine path-averaged and via Monin-Obukhov similarity theory (MOST). The advantage of scintillometry is that the obtained fluxes are path-averaged, which makes scintillometry a more suitable method for obtaining area-averaged fluxes over natural landscapes than traditional point measurements. However, the disadvantage is that the fluxes are not directly measured. Therefore in this thesis four questions are answered related to the applicability of MOST and to the behaviour of structure parameters over heterogeneous surfaces. The latter is important because MOST assumes homogeneous surface conditions. For our studies we used meteorological data measured at three sites (Cabauw; the Netherlands, CASES-99 experiment; Leon; Kansas; USA, LITFASS-2009 and LITFASS-2010 experiments; Lindenberg; Germany) under unstable conditions (day-time).

    MOST is restricted to the part of the atmosphere close to the surface: the atmospheric surface layer (ASL). The depth of the ASL is not constant during the day, and is relatively shallow during the morning. At those moments, the scintillometer observation level can be located outside the ASL, which can question the validity of MOST. Therefore, we proposed and compared two variations in MOST (MOST using local fluxes and MOST using surface fluxes). We found that during the afternoon when both concepts have to be valid, the values of are comparable. During the morning, the data do not unequivocally support one of the two concepts: MOSTl shows the correct temporal behaviour in, but underestimates by a factor of ten.

    The universal function that links the surface fluxes with the structure parameter in MOST needs to be determined empirically. In literature a great variety of these function can be found. Therefore, we investigate to what extent the expression for this function depends on the specific regression approaches, stability range and observation level. First, we found that applying various regression approaches has an impact on the expression. This means that studies always should specify their regression approach, when presenting new functions. We advise to use an orthogonal distance regression method, applied to the logarithmic transformation of both dimensionless groups, and weighted such that unreliable data points have a smaller influence on the fit. Second, we found that the observation height and the stability range have an impact on the coefficients too. This implies that variations found in literature may result from variations in the height and stability ranges among the datasets. Furthermore, application of a given expression on a dataset measured at a different height or within a different stability range has to be done with care.

    In order to investigate whether variations in and along a scintillometer path or aircraft flight leg are within the range of local variability, or could be attributed to surface heterogeneity, we analysed the amount of local variability in the structure parameters at different heights and under different stability regimes. We found that the variability is determined by stability and by the size of the averaging window over which the structure parameters are calculated. If instability increases, differences in structure parameters between upward motions and downward motions increase. If the averaging window size increases, the variance of the logarithmic structure parameters decreases. A rough estimation of this decrease is made by fitting a simple linear regression between this variances and the averaging window size. From this we found that for various stability classes both the offset and slope (in absolute sense) decrease with increasing instability. The offset and slope can be used to quantify the local variability, which in turn can give an indication if variations in the structure parameters along a scintillometer or flight path might be attributed to surface heterogeneity.

    Finally, our last study is an elaboration of the study of Beyrich et al. (2012). They compared obtained with the unmanned meteorological mini aerial vehicle (M2AV) with obtained with the large-aperture scintillometer (LAS) for five flights on one single day during LITFASS-2009 experiment. We investigated if the systematically larger values of the M2AV as observed by them, can be found for other days, and if these differences could be reduced or explained through a more elaborate processing of the data of both instruments. We concluded that the difference can be found for other days during LITFASS-2009 and LITFASS-2010 as well. obtained from the M2AV data is larger, which is not improved by the more elaborate data analysis. Moreover, an exact synchronization of the LAS data with the time intervals of the M2AV data does not eliminate the discrepancy between both datasets.

    All in all, this thesis defines better the borders of MOST and shows the behaviour of the structure parameters in the atmospheric surface layer.

    Beyrich F, Bange J, Hartogensis OK, Raasch S, Braam M, van Dinther D, Gräf D, van Kesteren B, van den Kroonenberg AC, Maronga B, Martin S, Moene AF (2012) Towards a validation of scintillometer measurements: The LITFASS-2009 experiment. Boundary-Layer Meteorol 144:83-112

    The Effect of a New Calibration Procedure on the Measurement Accuracy of Scintec's Displaced-Beam Laser Scintillometer
    Kesteren, A.J.H. van; Hartogensis, O.K. ; Kroonenberg, A.C. van den - \ 2014
    Boundary-Layer Meteorology 151 (2014)2. - ISSN 0006-8314 - p. 257 - 271.
    atmospheric surface-layer - stable boundary-layer - optical scintillation - inner scale - structure parameter - flux measurements - refractive-index - sensible heat - turbulence - spectrum
    We describe a new calibration procedure included in the production process of Scintec’s displaced-beam laser scintillometers (SLS-20/40) and its effect on their measurement accuracy. The calibration procedure determines the factual displacement distances of the laser beams at the receiver and transmitter units, instead of assuming a prescribed displacement distance of 2.70 mm. For this study, four scintillometers operated by Wageningen University and the German Meteorological Service were calibrated by Scintec and their data re-analyzed. The results show that significant discrepancies may exist between the factual and the prescribed displacement distances. Generally, the factual displacement is about 0.1 mm smaller than 2.70 mm, but extremes varied between 0.04 and 0.24 mm. Correspondingly, using non-calibrated scintillometers may result in biases as large as 20 % in the estimates of the inner-scale length, l0, the structure parameter of the refractive index, Cn2, and the friction velocity, u*. The bias in the sensible heat flux was negligible, because biases in Cn2 and u* cancel. Hence, the discrepancies explain much of the long observed underestimations of u * determined by these scintillometers. Furthermore, the calibration improves the mutual agreement between the scintillometers for l 0 , but especially for Cn2. Finally, it is noted that the measurement specifications of the scintillometer do not expire and hence the results of the calibration can be applied retroactively
    An Attempt to Validate Scintillometer Measurements: The LITFASS-2009 Experiment
    Beyrich, F. ; Bange, J. ; Hartogensis, O.K. ; Raasch, S. ; Braam, M. ; Dinther, D. van; Gräf, D. ; Martin, S. ; Kroonenberg, A.C. van den; Moene, A.F. ; Kesteren, A.J.H. van; Maronga, B. - \ 2012
    In: Proceedings of the 20th Symposium on Boundary Layers and Turbulence/18th Conference on Air-Sea Interaction, American Meteorological Society, 09-13 July 2012, Boston, MA). - American Meteorological Society - p. 13B.6 - 13B.6.
    The turbulent exchange of heat and water vapour are essential land surface – atmosphere interaction processes in the local, regional and global energy and water cycles. Scintillometry can be considered as the only technique presently available for the quasi-operational experimental determination of area-averaged turbulent fluxes at a horizontal scale of a few kilometres needed to validate the fluxes simulated by regional atmospheric models or derived from satellite images. It has thus been increasingly used over the last decade. The scintillometer principle is based on the quantitative evaluation of intensity fluctuations of electromagnetic radiation propagating across the turbulent atmosphere over distances up to several kilometres. Although the successful application seems to justify the broad use of this technique, a number of assumptions in the scintillometer data processing and interpretation still call for a thorough evaluation of the scintillometer principle, in particular over heterogeneous terrain. These open issues include the spatial variability and corresponding aggregation rules for structure parameters, the structure parameter vertical profiles, and the temperature-humidity correlation. Moreover, a validation of the path-averaged structure parameters of temperature and humidity derived from scintillometer data by independent measurements is still missing. To answer these questions, the LITFASS-2009 field experiment has been performed in July 2009 around the Meteorological Observatory Lindenberg – Richard-Aßmann-Observatory of the German Meteorological Service (DWD). It combined tower-based in-situ turbulence measurements, field-scale laser scintillometers, long-range optical large-aperture scintillometers, and airborne turbulence measurements using an autonomous unmanned aircraft. Questions studied included the effect of tower vibrations on scintillometer measurements, the determination of the spatial (horizontal and vertical) and temporal variability of structure parameters (underlying the scintillometer principle), and the validation of scintillometer measurements over moderately heterogeneous terrain by airborne measurements. The paper will present exemplary results from LITFASS-2009. Suggestions will be derived for a continuation of this type of studies.
    Towards a Validation of Scintillometer Measurements: The LITFASS-2009 Experiment
    Beyrich, F. ; Bange, J. ; Hartogensis, O.K. ; Raasch, S. ; Braam, M. ; Dinther, D. van; Gräf, D. ; Kesteren, A.J.H. van; Kroonenberg, A.C. van den; Maronga, B. ; Martin, S. ; Moene, A.F. - \ 2012
    Boundary-Layer Meteorology 144 (2012)1. - ISSN 0006-8314 - p. 83 - 112.
    large-aperture scintillometer - heterogeneous land-surface - convective boundary-layer - sensible heat-flux - temperature-humidity correlation - structure-function parameters - eddy-covariance measurements - flevoland field experiment - index-structure parameter
    Scintillometry has been increasingly used over the last decade for the experimental determination of area-averaged turbulent fluxes at a horizontal scale of a few kilometres. Nevertheless, a number of assumptions in the scintillometer data processing and interpretation still call for a thorough evaluation, in particular over heterogeneous terrain. Moreover, a validation of the path-averaged structure parameters derived from scintillometer data (and forming the basis for the flux calculations) by independent measurements is still missing. To achieve this, the LITFASS-2009 field campaign has been performed around the Meteorological Observatory Lindenberg – Richard-Aßmann-Observatory of the German Meteorological Service (DWD) in July 2009. The experiment combined tower-based in-situ turbulence measurements, field-scale laser scintillometers, long-range optical (large-aperture) and microwave scintillometers, and airborne turbulence measurements using an automatically operating unmanned aircraft. The paper describes the project design and strategy, and discusses first results. Daytime near-surface values of the temperature structure parameter, CT2C2T, over different types of farmland differ by more than one order of magnitude in their dependence on the type and status of the vegetation. Considerable spatial variability in CT2C2T was also found along the flight legs at heights between 50 and 100 m. However, it appeared difficult to separate the effects of heterogeneity from the temporal variability of the turbulence fields. Aircraft measurements and scintillometer data agreed in magnitude with respect to the temporal variation of the path-averaged CT2C2T values during the diurnal cycle. The decrease of CT2C2T with height found from the scintillometer measurements close to the surface and at 43 m under daytime convective conditions corresponds to free-convection scaling, whereas the aircraft measurements at 54 and 83 m suggest a different behaviour.
    Voorkomen van beschermde vissoorten t.b.v. het windpark IJsselmeerdijk
    Deerenberg, C.M. ; Boois, I.J. de - \ 2011
    IJmuiden : IMARES (Rapport / Wageningen IMARES UR C136/11) - 15
    vissen - beschermde soorten - landgebruiksplanning - windenergie - ijsselmeer - monitoring - fishes - protected species - land use planning - wind power - lake ijssel - monitoring
    Nuon onderzoekt de mogelijkheden om de bestaande windparken Harry van den Kroonenberg, Irene Vorrink en Jaap Rodenburg te saneren en deze te vervangen door een nieuw windpark en daarmee invulling te geven aan de beleidsregel 'Windmolens 2008' van de provincie Flevoland. In het kader van verzamelen van informatie over de ecologische situatie in het gebied van de windparken, heeft Nuon IMARES gevraagd informatie te leveren over het voorkomen van beschermde vissoorten in het gebied rond de windparken. Vanwege de Flora- en Faunawet (waar onder regelingen uit de Natuurbeschermingswet 1998) moet de aan- of afwezigheid van strikt beschermde soorten in het plangebied onderzocht worden, om te kunnen beoordelen of realisatie overtreding van beschermingsbepalingen kan inhouden. Het voorliggende rapport beperkt zich tot de beschermde vissoorten. Het zoekgebied betreft ruwweg het gebied dat wordt begrensd door de IJsselmeerdijk, de Flevocentrale, de Vaargeul Amsterdam-Lemmer en de Ketelbrug
    Late-Holocene evolution of the Mahakam delta, East Kalimantan, Indonesia
    Storms, J.E.A. ; Hoogendoorn, R.M. ; Dam, R.A.C. ; Hoitink, A.J.F. ; Kroonenberg, S.B. - \ 2005
    Sedimentary Geology 180 (2005)3-4. - ISSN 0037-0738 - p. 149 - 166.
    brahmaputra river system - ganges-brahmaputra - sediment transport - subaqueous delta - shelf - ocean - quaternary - record
    The late-Holocene Mahakam delta, located along the tropical eastern shore of Kalimantan, Indonesia, is considered to be a textbook example of a mixed tide-fluvial dominated delta system. The delta prograded about 60 km during the past 5000 years, which led to the development of a distinct network of distributary and tidal channels. Wave action is low due the limited fetch in the narrow strait of Makassar. Mahakam River discharge is about a quarter of the Mississippi River discharge and is characterized by absence of flood surges. Therefore, natural levees, crevasse splays and avulsions are absent in the delta plain. For the past four decennia, both modern and ancient Mahakam delta deposits have been studied in detail in order to better understand subsurface Miocene and Tertiary Mahakam deposits, which host large volumes of hydrocarbons. This study focuses on the dynamics and stratal patterns of delta plain, delta-front platform deposits and suspended sediments. Due to the predominance of semi-diurnal tides and the associated flow reversals, depositional patterns are highly variable which has resulted in the formation of characteristic sand-mud couplets. The distribution of the sand-mud couplets found in this study differs from previously proposed conceptual models. They are limited to the fluvial domain and form in the distributary channels (lateral channel bar) or at the fluvial dominated delta-front platform, which flanks the mouth bar deposits in offshore direction. The sand-mud couplets which formed as delta-front platform and lateral channel bar deposits are similar and can only be identified based on their 14C age. The sand content decreases significantly towards the tidal dominated areas due to limitation in transport capacity. Turbidity measurements taken in front of the river mouth also show rapid settlement of river plume sediments. Some 22 new AMS 14C dates show that late Holocene sea level history resembles the eustatic sea level curve giving a first approximation of the Late Holocene sea level history for East Kalimantan. The dates suggest that the progradational delta system evolved under conditions of slowly rising sea level, which compares well to the eustatic sea level curve. In addition, calculated averaged deposition rates of the sand-mud couplets indicate that deposition is driven by the spring-neap tide cycles instead of the daily tidal cycle
    The suitability of dated travertines as a record of fluvial incision: allier (France) floodplain dynamics during the late Quaternary
    Veldkamp, A. ; Kroonenberg, S.B. ; Heijnis, H. ; Berg van Saparoea, R.M. van den - \ 2004
    Quaternaire 15 (2004)1-2. - ISSN 1142-2904 - p. 159 - 165.
    Small-scale stratigraphy in a large ramp delta: recent and Holocene sedimentation in de the Volga delta, Caspian Sea
    Overeem, I. ; Kroonenberg, S.B. ; Veldkamp, A. ; Groenesteijn, K. ; Rusakov, G.V. ; Svitoch, A.A. - \ 2003
    Sedimentary Geology 159 (2003). - ISSN 0037-0738 - p. 133 - 157.
    mississippi river delta - saskatchewan river - okavango fan - level rise - sequence stratigraphy - cumberland marshes - lacustrine deltas - 1870s avulsion - evolution - canada
    The Volga delta differs from all other major deltas in the world by its extremely gentle onshore and offshore gradient (similar to 5 cm/km) and by being affected by the rapid sea-level changes of the Caspian Sea, at rates up to a hundred times the global sea-level rise. This paper reports (1) the morphological and facies development of part of the lower delta during the last full sea-level cycle between 1929 and 1995, as monitored using remote sensing and field mapping, and (2) the Holocene development of the delta from outcrop data and augered transects. During a sea-level fall of 3 m between 1929 and 1977, rapid progradation of levees, composed of fine sand, took place along over 800 distributary channels along the delta front. Smaller distributaries became filled with clay and organics. During the 3-m sea-level rise from 1977 to 1995, aggradation occurred, leading to deposition of silt and clay on the levees and minor filling of the flood basins. Sedimentation rates as established with Cs-137 dating are up to 2-5 cm/year. Total thickness of Holocene deposits in the lower delta plain is 4-10 m. A coarsening-upwards sequence in the Damchik sandpit shows freshening-upwards mollusc assemblages dated around 1000 BP, and has been attributed to the Derbent regression at that time. Four transects with a total of 79 augerings down to 7 m depth show rapid lateral facies changes of: (a) lagoonal clays deposited in the palaeo relief between the dunes, (b) channel sands, (c) levee sands and silts, (d) laminated overbank and interdistributary bay deposits, (e) mouthbar deposits and (f) prodelta clays. Holocene depositional patterns are unrelated to the present drainage network, though the spatial variability is similar to that of the present highly segmented network. Seven C-14 datings give a range of 6000-800 BP, and several phases of progradation seem to be present, but the lateral variability is too large and the age data too limited to make a solid correlation with known Holocene sea-level fluctuations. The Volga delta differs essentially from the classic river-dominated Mississippi delta because the offshore gradient is so gentle that no marine reworking takes place at the outlets, and the friction-controlled bifurcation continues basinward until a very fine maze of distributary outlets is produced. The Volga Holocene sequences more resemble those of the Atchafalaya and Saskatchewan lacustrine deltas. However, they differ from them in not being subsystems of a larger delta but the main depositional facies of the delta as a whole. Moreover, the recent Volga delta development shows that progradation is related to forced regression, not to avulsion triggered by base-level rise and/or subsidence. Thus, the Volga delta provides an excellent example of the impact of high-frequency sea-level changes on a ramp margin-type fluvio-deltaic system. (C) 2002 Elsevier Science B.V. All rights reserved.
    Modelling Holocene stratigraphy and depocentre migration of the Volga delta due to Caspian Sea-level change
    Overeem, I. ; Veldkamp, A. ; Tebbens, L. ; Kroonenberg, S.B. - \ 2003
    Sedimentary Geology 159 (2003). - ISSN 0037-0738 - p. 159 - 175.
    sequence stratigraphy - longitudinal-profile - sediment discharge - river - climate - ocean - environment - responses - dynamics - russia
    The Volga system is sensitive to allogenic control due to its low on- and offshore gradient (similar to 5 cm/km). In sequence stratigraphy, little attention has been paid to the effects of sea-level change in these ramp-margin fluvio-deltaic settings. The high-frequency sea-level changes of the Caspian basin have considerable amplitude (up to 18 m) over the Holocene time-span, which is usually considered as the lower boundary of fifth-order cycles. A process-response model, AQUATELLUS, has been used to investigate fluvio-deltaic response to sea-level fluctuation. Calibration of the model with measured data over the last century, comprising a full 3-m sea-level cycle, showed plausible progradation and sedimentation rates. The numerical modelling showed that sea-level changes forced the Holocene Volga delta to migrate similar to 200 km over the Caspian plain, leaving only thin laterally extensive deposits. The frequent depocentre shifts add a whole new perspective to the ongoing discussion about the impact of sea-level changes along the longitudinal profile. The periods during which significant deposition occurred coincide with the times that migration distances were relatively low. Thicker progradational wedges have been deposited at these time intervals, at similar to 9000-8000, similar to 7400-6700, similar to 5200-3700 and similar to 2400-900 years BP. C-14 dated deposits in the lower delta plain area corroborate the model output. Remarkably, this is both in highstand and lowstand conditions. The low gradient makes wave effects insignificant and tides are nonexistent, so that the fluvial deposits are hardly reworked and no shoreface facies or maximum flooding surface develop. The Volga delta response indicates that sequence-stratigraphic concepts are not scale-independent in low-gradient settings and that short-term high-frequency sea-level changes have a far-reaching impact on the stratigraphy. (C) 2002 Elsevier Science B.V. All rights reserved.
    Natural compositional variation of the river Meuse (Maas) suspended load: a 13 ka bulk geochemical record from the upper Kreftenheye and Betuwe Formations in northern Limburg
    Tebbens, L.A. ; Veldkamp, A. ; Kroonenberg, S.B. - \ 2000
    Netherlands journal of geosciences 79 (2000)4. - ISSN 0016-7746 - p. 391 - 409.
    geologie - geochemie - sediment - maas - limburg - geology - geochemistry - sediment - river meuse - limburg
    Unambiguously pristine and largely unpolluted sediments from the Late Weichselian and Holocene infillings of the Meuse residual channels in northern Limburg (the Netherlands) have been sampled to determine the natural compositional variation of the river’s suspended load. Bulk geochemical and granulometric analyses demonstrate that about 70␘f the variation can be ascribed to hydrodynamic mineral sorting. Clay- and fine silt-sized phyllosilicates are the most important deterministic features, hosting the bulk of Al2O3, TiO2, K2O, MgO and trace element variability (notably Ba, Cr, Ga, Rb and V). Quartz is abundant in the fine and coarse sand fractions. Na2O and the Zr-Nb-Nd-Y quartet relate to albitic feldspars and heavy minerals, respectively, in the coarse silt fraction. The granulometry should therefore be quantified if geochemical baseline data for a particular geological unit or region are drawn up and for the evaluation of potentially polluted sediments. Although provenance has not changed, the composition of Meuse sediments cannot be considered constant over a time frame of 1000-10,000 years, due to climatic change.Weathering of phyllosilicates in both interstadial and interglacial soil environments and changing relative source-area contributions alter the detrital clay-mineral supply to raise the Al2O3 and lower the K2O and MgO contents in Holocene Meuse sediments. Early diagenetic siderite and vivianite formation in gyttjas causes relative accumulations of Fe2O3, MnO, P2O5, Co, Ni and notably Zn above the phyllosilicate background values. These accumulations are natural and show that sediments with elevated trace metal contents are not necessarily polluted.Very early atmospheric pollution in relation to ore mining and smelting activities in the Roman era, however, probably caused elevated Pb contents in Subatlantic humic clays and peat samples, long before the historic pollution of the Industrial Revolution started. The Al2O3, Fe2O3 and CaO contents are used to predict the trace-element values as a function of sample granulometry, siderite/vivianite and lime content, respectively. As such, they can provide a sound basis for environmental researchers to determine baseline values of heavy metals in bulk samples of fine-grained fluvial sediments.
    Fluvial incision and channel downcutting as a response to Late-glacial and Early Holocene climate change: the lower reach of the river Meuse (Maas), The Netherlands
    Tebbens, L.A. ; Veldkamp, A. ; Westerhoff, W. ; Kroonenberg, S.B. - \ 1999
    Journal of Quaternary Science 14 (1999)1. - ISSN 0267-8179 - p. 59 - 75.
    klimaatverandering - rivieren - stroomvlakten - holoceen - maas - climatic change - rivers - floodplains - holocene - river meuse
    Late quaternary evolution of the Meuse fluvial system and its sediment composition : a reconstruction based on bulk sample geochemistry and forward modelling
    Tebbens, L.A. - \ 1999
    Agricultural University. Promotor(en): S.B. Kroonenberg; A. Veldkamp. - S.l. : Tebbens - ISBN 9789058080639 - 155
    klimaatverandering - sedimentatie - geochemie - sediment - rivieren - nederland - maas - climatic change - sedimentation - geochemistry - sediment - rivers - netherlands - river meuse

    All fluvial systems ultimately drain into alluvial basins, where the weathering products of their upstream drainage areas accumulate over a time-span varying from 10 0to 10 6years. Most silted-up alluvial basins are low-gradient deltas that are densely populated, because their high fertility maintains a high agricultural potential. Global warming due to increased concentrations of greenhouse gases in the Earth's atmosphere will very likely affect the quantity and quality of both water discharges and fine-grained sediment fluxes to these alluvial basins. The long-term interplay between tectonics, climate and sea level determines the frequency, the timing, the allocation and magnitude of erosional and depositional events in fluvial systems. Erosional or depositional events are the direct consequence of changes in the quantity of discharge and sediment fluxes and thus will influence the sediment composition too. Therefore, a thorough fundamental study of the response of fluvial systems to climatic change is indispensable to understand the natural erosional and depositional dynamics and to assess possible future changes in the bulk geochemical composition of sedimentary sequences. In this respect, the expression of past climate changes in the composition of fluvial sedimentary records may serve to predict future fluvial response to climate change: the past as a key to the future.

    This thesis presents the research results for a case study of the River Meuse that combines geomorphological, bulk geochemical and forward modelling techniques. The study focuses on the impact of climate change on the natural composition of clastic river sediments, in casu variations in the bulk geochemical composition of fine-grained residual channel infillings on a temporal scale of 10 3-10 5years. The main topic was split up into two main parts, each dealing with individual queries. Part I addresses the first goal of the research, namely to determine which fluvial sediments are likely to register a palaeoclimatic signal, where these sediments are found and how the climatic signal is expressed in these sediments. Earlier work directed the focus towards fine-grained sediments, because the clay and fine-silt size fractions are the most likely candidates to register evidence of changing weathering and transport pathways. Chapter 2, 3 and 4 describe the results of geomorphological fieldwork and subsequent laboratory analyses by zooming in on fine-grained deposits in the Meuse lower reach, which date to the 15-0 ka BP time-frame.

    Chapter 2 describes the general geological setting of the study area that forms part of the Meuse lower reach in North Limburg (southern Netherlands). The response of the River Meuse to Late Glacial climate change was reconstructed to provide insight into the origin and age of the residual channels and their infillings. Ice-cores drilled within the framework of the Greenland Ice Core Project (GRIP) indicate frequent, profound and abrupt climatic change over the last 250,000 years Before Present (250-ka BP) in the North Atlantic region and Northwest Europe. The Late Glacial part of the GRIP ice-core demonstrated that mean annual temperature rose dramatically at the beginning of the Late Glacial (14.5-ka BP; 5-°C) and in the Early Holocene (10.2-ka BP; 7-°C). Quantitative climate reconstructions based on palynological and coleopteran data for the upstream Ardennes (where the major part of the River Meuse discharge and sediment load originates) and in the Netherlands corroborated these temperature rises. The Ardennes data also indicated a fourfold increase in mean annual precipitation. The rain-fed River Meuse is very sensitive to temperature and precipitation changes and accordingly responded by lowering its Late-glacial floodplain: glacially aggraded deposits were incised and several previously active channels were abandoned and turned into low-energy depositional environments. Subsequent flooding events left their traces in the form of a discontinuous clayey and silty sedimentary record within the residual channels. Periods of sediment by-pass led to gyttja and peat accumulation. This offered excellent opportunities to date the residual channels and the intercalated clastic sediments, because the organic material has been formed amply within the dateable 14C-range.

    Extensive conventional 14C-dating of strongly organic gyttja and peat intervals in the residual channels permitted the reconstruction of two Late-glacial phases of rapid vertical channel downcutting, preceding lateral river valley degradation. The first phase dated between13.3 and 12.5-ka BP (Early Bølling) and the second one between10.2 and 9.8-ka BP (Early Preboreal). The onset of channel downcutting lagged the climatic amelioration in the Ardennes some 500-1300 years, depending on initial landscape conditions. This suggests a major influence of interstadial and interglacial vegetation growth on landscape fixation and stabilisation and soil development, resulting in a decrease of the sediment supply relative to simultaneously increasing river discharges and hence channel downcutting. Following the downcutting phases, meandering river patterns suggest low-energy river dynamics during the Late-glacial Interstadial (Late Bølling, Allerød) and the Late Preboreal. Simultaneously, increasing landscape stability contributed to a gradual fining of the sediments. Renewed climatic deterioration around 11.3-ka 14C BP (Late Allerød) and during the severe Younger Dryas cooling event (10.8-10.2 ka BP) caused a short return to high-energetic braided river conditions. All in all, the results of Chapter 2 show that the Late-glacial geological setting of the Meuse lower reach in North Limburg provided the ideal environment for deposition and preservation of fine-grained clastic sediments.

    Chapter 3 zooms in on a set of640 samples taken from non-polluted, largely unconsolidated, fine-grained residual channel infillings deposited in the Meuse lower reach. The <2000-µm fractions have been analysed for their granulometry (determined with a Laser Grainsizer), bulk geochemistry (using X-Ray Fluorescence Spectroscopy, XRFS) and part of the samples for their clay geochemistry and clay mineralogy (X-Ray Diffraction, XRD). The natural compositional variation in these fine-grained sediments was quantified using multivariate statistical analyses. This enabled distinguishing the palaeoclimatic signal from variation that is not directly related to climate, like post-depositional overprinting effects. Hydrodynamic sorting of minerals in different size fractions explained over 70% of the variation in sediment composition. Phyllosilicates in the clay and fine-silt size fractions hosted the major part of the major constituents Al 2 O 3 , TiO 2 , K 2 O, MgO and the trace elements Ba, Co, Ce, Cr, Ga, La, Nd, Ni, Pb, Rb, V and Zn. Early-diagenetic formation of siderite and vivianite in the strongly organic and clayey anoxic gyttja environment appeared to cause relative natural accumulations of Fe 2 O 3 , MnO, P 2 O 5 , Co, Ni and notably Zn above the phyllosilicate background values. High lime contents caused elevated contents of CaO and Sr, while Na 2 O and Zr, Nb, Y and Nd were more or less strongly related to the occurrence of albitic feldspars and heavy minerals respectively in the coarse silt fraction. Only 13 samples out of 636 showed strong anomalies or accumulations of the trace elements Pb, Zn, Ni and Co, which in high concentrations can pose a potential threat to the environment. This confirmed the assumption that most samples did not suffer from post-depositional anthropogenic pollution. However, bio-accumulation and very early atmospheric pollution due to small-scale ore-mining and smelting in the Roman era might explain the elevated Pb-contents found in Subatlantic clays.

    Chapter 4 deals with the same set of samples and confirms theoretical considerations that the composition of fine-grained clastic sediments does not remain constant over a period of 10 3-10 4years. The 14C-dating of frequent-occurring organic intervals and additional palynological information enabled time labelling of samples taken from intercalated clastic layers. Bivariate scatterplots showed that the Pleniglacial, Late Glacial and Holocene sample groups differ considerably in their clay contents and in their contents of several main and trace constituents. Firstly, Holocene samples were found to have significantly higher clay contents, suggesting higher clay mineral supply. Secondly, Holocene samples contained more Al 2 O 3 and less K 2 O, MgO and TiO 2 relative to Pleniglacial and Late-glacial specimens within a comparable granulometrical range.

    The typically clay-related trace elements Ba, Cr, Rb and V showed similar chronological differentiation as for the main constituents, namely lower Holocene values relative to Al 2 O 3 . However, these trace elements have higher ratios in Holocene samples relative to K 2 O and MgO, owing to relative depletion of the latter constituents. Detailed clay mineralogical analysis of separated clay fractions and clay mineral weathering literature strongly suggested that this systematic shift in sediment composition could be ascribed to both an absolute and relative increase of the smectite and vermiculite contents and interstratifications of these minerals with illite in Late-glacial Interstadial and Holocene sediments. Because overprinting effects owing to post-depositional soil formation and anthropogenic effects could be excluded, the changes in detrital clay mineralogy have been interpreted as a systematic sedimentary palaeoclimatic signal.

    Climatic amelioration and increasing landscape stability during prolonged interstadials and interglacials increased the weathering intensity (rate) of phyllosilicates and lengthened weathering duration. Widespread soil formation on Palaeozoic metapelitic rocks in the Ardennes low mountain range as well as on loess deposits has most likely caused the clays were progressively depleted of the main constituents K 2 O, MgO and TiO 2 relative to Al 2 O 3 and Ba, Cr, Ga, Rb and V (Chapter 4). The resulting higher supply of the typically pedogenetic high-Al, low-K and low-Mg smectites and vermiculites ultimately constituted a palaeoclimatic signal in the clay and fine silt size fractions of Meuse sediments. Several early diagenetic post-depositional processes favour the formation of authigenic minerals in the gyttja-redox environment (siderite and vivianite). They exclude the use of the following major and minor constituents for reconstructing long-term detrital compositional changes: Fe 2 O 3 , MnO and P 2 O 5 . In the same manner, variations in heavy mineral and lime content exclude the use of Nb, Y, Zr and the CaO-Sr pair respectively.

    Part II encompasses the second subgoal of the research, namely to answer the questions why the sediments one is interested in have been laid down there in the first place, how they relate to long-term and large-scale fluvial dynamics and how sediment compositional changes relate to internal fluvial dynamics. Sediment composition is namely directly related to the sediment flux, which itself depends on the evolution of the fluvial system. Therefore, the long-term river dynamics had to be quantified at the spatial scale of the whole drainage basin to account for other factors than climate and to get a grip on long-term compositional changes. A forward modelling study in Chapter 5 serves to understand the 15-0 ka BP lower reach results of Chapter 2-4 within its fluvio-systematic context. This context concerns the influence of external forcing on the long-term evolution of the Meuse longitudinal profile on the spatial scale of the whole drainage basin. Chapter 6 attempts to give a finishing touch by combining sediment flux calculations with bulk geochemical data to provide insight in the long-term evolution of fluvial sediment composition.

    Chapter 5 contains the interpretations concerning long-term fluvial dynamics resulting from sediment flux calculations in a well-calibrated semi 3-D forward modelling study. The longitudinal profile development of the River Meuse was simulated in response to changes in the external forcing variables tectonics, climate and sea level for the time-span 250-0 ka BP. The modelling results showed that a scenario of climate-controlled discharge and hillslope sediment supply (interstadial or interglacial increasing discharges and simultaneously decreasing hillslope sediment supply) is able to reproduce a phase of river valley degradation at the start of interglacial periods. The incisional phase is identical to the observed phase of Late-glacial incision in the Meuse lower reach, which set the favourable conditions for preservation of fine-grained sediments in the resulting residual channels (Ch. 2). This suggests that the followed forward modelling approach adequately simulates the long-term evolution of the Meuse fluvial system.

    The Profile Evolution Map visualises the long-term evolution of sediment fluxes and demonstrates the timing and allocation of erosional and depositional phases along the longitudinal profile. The downstream positions of sections along the longitudinal profile strongly determine how they respond to time-equivalent changes in the external forcing variables. The fact that the upstream and downstream sections appeared to mutually influence each other clearly indicated complex-response in the fluvial system. Tectonic uplift and climate change could be demonstrated to dominate fluvial response in the North French and Ardennes upper and middle reaches. Here, the model predicts erosional phases to be most pronounced during prolonged interstadials and interglacials, leading to climate-controlled river valley incision and degradation of the longitudinal profile. On the other hand, continuing tectonic subsidence within the Roer Valley Graben and the southern North Sea Basin and eustatic sea-level changes dominated the response in the lowermost reaches. Here, continuous deposition takes place, interrupted by an incisional phase at the beginning of interglacials. The subsequent rising Eemian and Holocene sea levels caused increased sediment aggradation, leading to gradient backfilling. This process generated a depositional wedge that protruded progressively upstream and shifted the terrace intersection land-inward over some 100-150 km.

    In Chapter 6 , the bulk geochemical data of various upstream Ardennes tributary catchments have been coupled to the sediment supply arising from climate-controlled hillslope processes and from internal valley-erosion. The integration of bulk geochemical data with calculated sediment fluxes originating from the forward modelling study allowed simulating the effects of changes in the external forcing variables on sediment composition in the fluvial system. The Geochemical Evolution Map visualises the long-term evolution of sediment composition along the longitudinal profile. We modelled a scenario of changing weathering duration, namely alternating glacial weathering-limited (short weathering duration) and interglacial transport-limited sediment supply (long weathering duration. This scenario performed well in simulating the timing and direction of changes in the long-term sediment composition. Furthermore, the simulated changes in sediment composition were of the same order of magnitude as the measured changes recorded in the fine-grained sediments of the Meuse lower reach. However, a discrepancy with absolute values indicated that the direct effects of increased weathering intensity could not be excluded, especially in prolonged interstadial or interglacial periods with transport-limited sediment supply. Furthermore, circumstantial evidence indicated that loess influxes might play an important role as well, but these have yet to be quantified.

    Holocene development of the lower Volga delta
    Kroonenberg, S.B. ; Overeem, I. ; Groenesteijn, K. ; Veldkamp, A. ; Rusakov, G.V. - \ 1999
    In: Present state, research and conservation of the nature complexes in the Astrakkan bioshere reserve and rising Caspian sealevel and increasing anthropogenic pressure: Seminar 80 years Astrakkan bioshere reserve, Astrakkan, 23-28 August 1999. - [S.l.] : [s.n.], 1999 - p. 117 - 118.
    The impact of climate change on the bulk and clay geochemistry of fluvial residual channel infillings: the Late Weichselian and Early Holocene River Meuse sediments (The Netherlands).
    Tebbens, L.A. ; Veldkamp, A. ; Kroonenberg, S.B. - \ 1998
    Journal of Quaternary Science 13 (1998). - ISSN 0267-8179 - p. 345 - 356.
    Geochemical characterization of subsurface sediments in the Netherlands
    Huisman, D.J. - \ 1998
    Agricultural University. Promotor(en): S.B. Kroonenberg; G.T. Klaver; A. Veldkamp. - S.l. : Huisman - ISBN 9789054858614 - 175
    geochemie - verwering - bodemvorming - landschap - klimaat - overstromingen - klimaatverandering - paleoklimatologie - Nederland - geochemistry - weathering - soil formation - landscape - climate - floods - climatic change - palaeoclimatology - Netherlands

    Traditionally, the Netherlands' subsurface is mainly used to obtain good quality drinking and industrial waters from the different aquifers. Due to the lack of space on the surface, increasing environmental problems and demand for energy, the subsurface will be used increasingly for other activities, including large underground infrastructural projects, underground storage of waste and greenhousegasses and underground storage capacity for the energy sector.

    In order to evaluate the effects of the underground activities, detailed knowledge about the subsurface sediments is required. The geochemical composition of the subsurface sediments and the associated mineralogy forms an important part of the information needed to make decisions where and under what restrictions the different activities in the subsurface can best be planned. This thesis is a result of the GEOBON-project, which was started in order to meet this information need. The project studied the chemical composition of subsurface sediments by sampling and analyzing cores that were made by the Geological Survey of the Netherlands as is described concisely in Chapter 2.

    Chapter 3 present results from two study areas, Brabant and Limburg, which show how sediment source, sorting processes, depositional environment, grain size, weathering and syn- and post-sedimentary diagenesis affects the geochemical composition of Miocene, Pliocene and Lower Pleistocene sediments in the Southern Netherlands:

    Chapter 3.1 contains the results of a sediment geochemical study that was performed in unconsolidated Upper Cenozoic sediments from the South of the Netherlands. Glauconite-rich sediments (Breda Formation) show anomalously high K contents and low Ba/K ratios. Major shifts in sediment composition as a result of changes in the Rijn system and shifts between Rijn and Schelde provenance as known from heavy-mineral studies are recorded in changes in the grain size dependent variations between Al, Na and K: Pleistocene Rijn sediments (Tegelen Formation) show higher Na contents than Pliocene Rijn sediments (Oosterhout and Kiezeloöliet Formations) and Schelde-derived material (Kedichem Formation), probably as a result of larger contents of sodic plagioclase. Schelde-derived sediments show low K/Al ratios as result of a smectite-dominated clay mineralogy and low contents of micas, whereas Rijn-derived sediments have high K/Al ratios which reflect an illite-kaolinite dominated clay mineralogy and higher contents of muscovite.

    The presence of siderite causes high Fe-contents in the Tegelen formation in the east of the study area. Increased Mg contents in the siderite-bearing sections from the Tegelen formation and in parts of the Oosterhout and Kiezeloöliet Formation are probably caused by the presence of minor amounts of dolomite. Localized high (pyrite-) S-concentrations are not only found in the marine-estuarine Oosterhout and Tegelen Formations but also in the fluviatile Kiezeloöliet and Kedichem Formations, which indicates at least minor marine transgressions during their deposition.

    Chapter 3.2 studies the change from a stable to an unstable heavy mineralogy in the composition of Rijn-derived sediments at the Pliocene-Pleistocene transition. This change has previously been attributed to a decrease in weathering intensity due to climatic cooling, and to a change in the Rijn sediment provenance from local to Alpine-derived. We studied the geochemistry of several sections with Pliocene and Early Pleistocene Rijn deposits, and one section (BTAB) in more detail using clay mineralogical and micromorphological techniques to study the exact nature and the cause of this change, and associated changes in sedimentary setting. We found a general increase in Na 2 O- contents at the local to Alpine provenance shift, which can be attributed to the Alpine source supplying fresh, sodic plagioclase-rich material instead of the local, strongly weathered sediments. There is a general trend of increasing K 2 O/Al 2 O 3 from the Pliocene to the Early Pleistocene that can be attributed to a similar decrease in degree of weathering.

    However, this trend is disturbed by the loss of K from clay minerals during post-depositional in situ weathering in organic-rich layers. In the Upper Pliocene BTAB section, we found a clear transition from kaolinite and high TiO 2 /Al 2 O 3 -ratios to smectite-rich material with lower TiO 2 /Al 2 O 3 that coincides with the local to Alpine provenance shift. However, Early Pleistocene sediments have TiO 2 /Al 2 O 3 -ratios that are similar to the ones before the transition so this effect is not consistent. Local high TiO 2 -anomalies, caused by preferential sorting and concentration of especially rutile in placer-like deposits occur in most Pliocene sections, but they are absent in the Upper Pliocene and Lower Pleistocene Alpine-derived deposits. Overall, the detrital geochemical variation in these deposits are primarily controlled by the source of the sediment, and hence the large-scale tectonic setting, whereas climatic control is limited.

    The Pliocene organic-rich layers were originally formed in a fresh-water fluviatile environment. Nevertheless they show high concentrations of S due the presence of abundant pyrite as a result of inundation by saline water during short-termed flooding events like spring tides or storm floods, after or alternating with one or more desiccation phases.

    Chapter 4 focuses on the effects of specific diagenetic geochemical processes that cause enrichments or depletions of certain chemical elements:

    Chapter 4.1 describes the formation of siderite (FeCO 3 ), which is often used as an indicator for the depositional environment of sediments, as it can only be formed under restricted geochemical conditions. By doing so, the possibility that siderite was formed later, under altered circumstances is often neglected. In this study, siderite in Early and Late Pleistocene deposits is investigated to establish whether it was formed syndepositional, or postdepositional under different circumstances. Within the Early Pleistocene Tegelen Formation, siderite is found as coatings around detrital dolomite grains, together with partially dissolved detrital calcite grains. Siderite also occurs as single nodules and homogeneously mixed through the groundmass. Siderite precipitation at the expense of calcite is proposed, which is likely to be an actual process as the current groundwater composition agrees well with the thermodynamics necessary for this process. Siderite formation in Late Pleistocene river fens is syndepositional and associated to both calcite and vivianite.

    A comparison between these two settings shows that siderite may be an indicator for the environment during deposition, but the presence of siderite in sediments may also be the result of interaction with groundwater under diagenetically altered circumstances.

    In chapter 4.2, we focus on the effects of multiple cycles of interchanging of fresh and saline water and oxic and reduced diagenetic environments that occur during the formation of low-gradient deltas of large river systems, driven by the glacial- to interglacial climatic cycle. Because of the reactivity of organic matter, the geochemical characteristics of organic-rich sediments can be strongly affected by these changing diagenetic environments.

    In the geochemical/sedimentary record of the Pliocene and Early Pleistocene Rijn-Maas delta, organic-rich layers display anomalous enrichments of trace elements, heavy metals and rare earth elements (REE). During marine highstands, high groundwater levels cause Fe-hydroxides to become reduced, thus releasing Fe and associated trace elements into the groundwater. At the same time, transgressions of saline water over organic surface layers and saline groundwater intrusions cause the formation of pyrite and other sulfides that may contain elevated levels of As and Mo and, depending on the Fe-source, Co, Ni, Pb and Zn. Associated with the pyrite-forming reduced environment, Y, REE, Cr, V and U are immobilized and accumulate. During lowstands, lower groundwater levels cause part of the sulfides to oxidize, except for that are present in the organic layers, where they are protected from oxidation. Fe-oxides form, and trace elements like As, Co, Ni, Pb, Zn, Y and REE are incorporated, only to form a source for Fe and trace elements during the next reduced phase.

    Chapter 5 describes the natural variation in heavy metal contents of subsurface sediments in the Southern Netherlands. The detrital heavy metal contents of these sediments show linear correlations with Al as a result of their joint occurrence in phyllosilicates. Anomalous enrichments occur as a result of the presence of glauconite (As, Cr, Ni, Pb, Zn), pyrite (As) or Fe-oxides (As, Ba, Ni, Zn), due to the interaction of organic-rich subsurface material with groundwater (Co, Ni, Zn) or as a result of anthropogenic pollution in topsoils (Cu, Pb, Zn). The contents of Al, Fe, K and S are well suited to determine background values, and to identify the cause for anomalous accumulations of heavy metals.

    Chapter 6 describes the result of a geochemical mapping campaign in an Early Pleistocene fluviatile formation (Kedichem) in the Netherlands. This is the first step towards a nation-wide geochemical database that can be used to meet the demand for information about the composition of subsurface sediments. We first determined the spatial extension and thickness of the sediment body. Subsequently, we used Fuzzy clustering techniques on approximately 2000 heavy-mineral counts from the NITG-TNO database to map the spatial extension of the Schelde, Rijn and Baltic sediment provenances within the formation.

    Geochemical data was collected during a sampling campaign in which about 600 samples from the Kedichem formation were analyzed. We used factor analysis to determine the major factors that determine the geochemical composition. These factors include clay content, presence of carbonates, pyrites and Fe,Mn-hydroxides, sodic plagioclase and zircon, and organic-matter-related diagenetic processes. We tested which lithological data from the NITG-TNO boring database is correlated the geochemical composition and therefore can be used to make a geochemical prediction model. We found that the classes Sand, Clay + Gyttja and Peat are significantly different and therefore can be used to predict the contents of Si, Ti, Al, Fe, Mn, Mg, Ca, Cr, Cu, Pb, V, Zn, Ba, Ga, Nb, Rb, Sr and Y. For the elements As, Ni, U and S, the classes Organic-poor Clay, Sand+Peat, Gyttja+Organic-rich Clay are significantly different. For Na and K, a division can be made in to Mica-rich Clay, Mica-poor Clay, Mica-rich Sand, Mica-poor Sand and Peat + Gyttja. By classifying the lithological data from the NITG-TNO core description, we made a geochemical model to predict the geochemical composition in the Kedichem formation

    We visualized this model by calculating and interpolating the average composition of 5 m horizontal slices of the Kedichem formation. The model performance is fairly good, although it has a tendency to underestimate extreme values.

    The results of our study demonstrate that geochemical characterization of sediments can be performed by doing a large number of low-cost XRF analyses, supported with a limited amount of XRD-, ICP-MS, SEM and micromorphological analyses. The geochemical variation can be determined and the speciation and hence the reactivity and conditionally availability of harmful elements can be deduced. The geochemical methods employed in this study can not only be used to study sedimentation history and stratigraphy, but they can also yield important information about the composition and reactivity of subsurface sediments which can be used for ground water quality management and evaluation of underground activities.

    Dilution of riverine heavy metal input concentrations by suspension of sediments and algal growth in the IJsselmeer.
    Winkels, H.J. ; Blom, G. ; Kroonenberg, S.B. ; Lijklema, L. - \ 1998
    Water Research 32 (1998). - ISSN 0043-1354 - p. 2931 - 2940.
    zware metalen - besmetting - sediment - transport - algen - waterverontreiniging - waterkwaliteit - rivieren - meren - nederland - waterbodems - ijsselmeer - heavy metals - contamination - sediment - transport - algae - water pollution - water quality - rivers - lakes - netherlands - water bottoms - lake ijssel
    This study evaluates the effects of sediment erosion and primary production on the temporal and spatial variability of heavy metals concentration in settling solids in the lakes IJsselmeer and Ketelmeer. Settling solids were sampled fortnightly using sediment traps at two sites in the IJsselmeer and contents of clay, organic matter, calcium carbonate, six heavy metals and 13C and 18O values were measured. Wind speed and direction, suspended solids, organic matter, chlorophyll, phaeophytin and oxygen concentrations were measured in the water compartment, as was pH, temperature and Secchi depth. Regression and multivariate analyses were used to evaluate the relationships within the data set. Principal components analysis and stepwise multiple regression show that the variation in the heavy metals concentration in settling solids is related to the windspeed and clay content, both variables that are related to erosion of sediments; and to pH, chlorophyll and CaCO3, which are related to algal growth in the lake. This supports the hypothesis that the spatial gradient in the heavy metals concentrations in deposited solids in the IJsselmeer is the result of dilution of contaminated sediments due to erosion of older, less contaminated sediments and primary production related to algal growth
    Element partioning in sediment, soil and vegetation in an alluvial terrace chronosequence, Limange rift valley, France: a landscape geochemical study.
    Korobova, E.M. ; Veldkamp, A. ; Ketner, P. ; Kroonenberg, S.B. - \ 1997
    Catena 31 (1997). - ISSN 0341-8162 - p. 91 - 117.
    The wandering of the Volga delta: a response to rapid Caspian sea-level change.
    Kroonenberg, S.B. ; Rusakov, G.V. ; Svitoch, A.A. - \ 1997
    Sedimentary Geology 107 (1997). - ISSN 0037-0738 - p. 189 - 209.
    A geological interpretation of heavy metal concentrations in soils and sediments in the southern Netherlands.
    Huisman, D.J. ; Vermeulen, F.J.H. ; Baker, J. ; Veldkamp, A. ; Kroonenberg, S.B. ; Klaver, G.Th. - \ 1997
    Journal of Geochemical Exploration 59 (1997). - ISSN 0375-6742 - p. 163 - 174.
    Contaminant variability in a sedimentation area of the river Rhine = Variabiliteit van verontreinigingen in een sedimentatiegebied van de Rijn
    Winkels, H.J. - \ 1997
    Agricultural University. Promotor(en): S.B. Kroonenberg; L. Lijklema. - Lelystad : Directoraat Generaal Rijkswaterstaat, Directie IJsselmeergebied - ISBN 9789036912105 - 161
    rivieren - waterlopen - kanalen - geologische sedimentatie - oppervlaktewater - waterverontreiniging - waterkwaliteit - stroomgebieden - drainage - milieueffect - schade - polycyclische koolwaterstoffen - aromatische koolwaterstoffen - binnenwateren - rijn - waterbodems - rivers - streams - canals - geological sedimentation - surface water - water pollution - water quality - watersheds - drainage - environmental impact - damage - polycyclic hydrocarbons - aromatic hydrocarbons - inland waters - river rhine - water bottoms

    Aquatic sediments in sedimentation zones of major rivers are in general sinks for pollutants. The sedimentation zone Ketelmeer/IJsselmeer is an important sink for contaminants of the river Rhine (i.e. river IJssel). Recent and historical pollution interact here. Redistribution of suspended solids and erosion of deposited sediment in the shallow Dutch lakes (due to wave action) are likely to change contamination levels of sediments in these lakes, which is the subject of this thesis. The aim of this research was to study and explain the variability of contaminants in the sedimentation area Ketelmeer/IJsselmeer in order to predict the fate of the contaminants in the future. For this purpose a number of methodologies and models were developed and/or adapted.

    Chapter 2 describes the collection and analysis of sediment cores, top-layer sediments and geologically different layers in Lake Ketelmeer. Sediment cores were sectioned into thin slices and the year of deposition of each layer was determined using radio-chemical analyses. The contaminant concentrations were plotted versus the year of deposition of each sediment layer to (re-)construct the history of contamination. Similar vertical changes in contaminant concentrations were found as in a number of sediment cores sampled in sandpits in Lake Ketelmeer. Further, differences in concentration between the top-layer sediments and the degree of contamination in the entire recent IJsselmeer deposits (IJm-deposits) of Lake Ketelmeer were found. The older Zuiderzee deposits (Zu-deposits) underlying the IJm-deposits have low background values for heavy metals, PAHs and PCBs. This indicates that downward transport of these contaminants with infiltrating water is negligible in this lake. The concentrations of metals and PAHs in the sediment cores reflect, without any serious alterations, the historical input of the past five decades. The pollution history is characterized by, in the early 1940s, low concentrations of metals and already elevated levels of PAHs; a possible reduction of these contaminants during the Second World War and attaining, their highest levels between 1955 and 1970. Rather low levels occur in recently deposited sediments, some of which are the lowest ever observed over the last five decades (Pb, As, and all studied PAHs). Almost all chlorinated compounds showed a certain decline in concentration in anaerobic sediments as compared to samples of the top-layer collected in 1972 and stored in the laboratory, which still reflect the original pollution input. For several PCBs this decline proved to be significant; it may have been caused by microbial dechlorination reactions in the anaerobic sediment. Consequently, the concentration profiles of the chlorinated compounds do not reflect the original pollution history directly. Despite the attenuation of concentration, peaks in PCB concentration profiles were still observed. The following trends in concentrations of PCBs can be currently observed in Lake Ketelmeer sediment:
    - Almost all PCBs studied had rather low concentrations in the early 1940s.
    - The highest levels of PCBs occurred between 1960 and 1975.
    - Recently deposited sediments also have elevated levels of PCBs as compared to the levels in layers from the early 1940s.
    Overall, recently deposited material is far less-polluted than sediment deposited in the 1960s and 1970s. These findings prove that in this lake older, highly polluted sediments are buried under a younger, less- polluted layer. However, at some locations, such as in dredged parts or erosive zones, the highly polluted layers may remain uncovered, so aquatic organisms may still be exposed to highly polluted sediments from the 1960s and 1970s through the benthic food chain.

    In Chapter 3 attention is focused on the distribution and geochronology of the sediments of Lakes Ketelmeer and IJsselmeer The concentrations of metals, PCBs, PAHs and various sediment characteristics were determined in 77 samples of the surface sediments and one 3 in core of both lakes. Absolute concentrations of these pollutants were normalized for sediment composition (e.g. clay fraction and organic matter contents). In Lake IJsselmeer the youngest geological layer (IJm-deposit) is mainly found in deep sedimentation areas (25%). This deposit is severely polluted in Lake Ketelmeer (Chapter 2). Concentrations of all polluting compounds in the IJm-deposit of Lake Ketelmeer proved to be 1.6 - 9 times higher than in Lake IJsselmeer Concentrations in the same deposit in Lake IJsselmeer were 2 - 4 times higher than those in the older sandy sediments of the lake. Concentrations of heavy metals, As and PCBs initially increase with depth, but then decrease to lower or even background levels. This corresponds with the inputs of the river IJssel). during the past five decades. As the distance from the river mouth (i.e. Lake Ketelmeer) to Lake IJsselmeer increases, there is a decrease in the degree of pollution in this (IJm-deposit) The hypothesis is developed that primary production (with related calcite formation) and mixing with eroded sediment from elswhere in Lake IJsselmeer are together responsible for this dilution.

    Chapter 4 describes the core sampling and analysis for two similar sedimentation zones of two major river deltas. Uniformly soft anoxic sediments in the Volga and Danube deltas were collected, using satellite images, which reflect the concentration of suspended solids. Cesium-isotope dating and measurement of the concentration profiles of heavy metals and PAHs, which reflect (without serious alterations) the historic pollution input into these rivers, were used in the comparison. The contents of the 7 PCBs investigated and of cadmium were below the detection limits for all sediment samples in the Volga and Danube deltas. Low, more or less constant concentrations of arsenic, copper, zinc and all studied PAHs were observed in sediments of the last five decades in the Volga river. Nickel concentrations in Volga delta sediments were rather high, and recently deposited sediments seemed to show slightly increasing levels for zinc, chromium and arsenic. The pollution history of the Danube is characterized by low concentrations of metals but elevated PAH levels in the early 1940s; increasing levels of metals and PAHs between 1950 and 1987; and decreasing levels in more recently deposited sediments. When comparing the concentrations of heavy metals, PAHs and PCBs in the aquatic sediments of the rivers Rhine, Danube and Volga deltas for the past five decades it is evident that the Volga delta was, and still is, the cleanest of the three. A combination of natural (background) inputs, industrial inputs and man made technical changes in the river systems (like the building of storage lakes) can explain most differences in the historical contaminant profiles of the three deltas. Nowadays the concentrations of heavy metals (except copper and nickel), PAHs and PCBs in sediments of the river Rhine are still higher than in the other two rivers, but the sediment loading rate for heavy metals (except cadmium and zinc) of the Danube is higher than for the other two rivers.

    In Chapter 5 the geostatistical sampling approach chosen for Lake Ketelmeer is explained. When monitoring contaminants and related sediment characteristics in an aquatic environment, their spatial variability needs to be taken into account. The sampling strategy covered short-distance variability (65 m) and long-distance variability (500 m) of the investigated variables. In Lake Ketelmeer we chose three sub-areas. The distances between sampling points takes into account the size of each sub-area. With this approach the number of sampling points needed to monitor trends of contaminants in sediments can be minimized, taking into account the necessary accuracy. The choice of sampling strategy for monitoring sub-areas, characterised by either water depth, sedimentation/erosion behaviour or sediment type, will result in different sampling spacings. For example, in Lake Ketelmeer the optimal sampling distance for monitoring Benzo(A)pyrene (BAP) in the central part of the lake was larger than near the harbour and shore, where gradiënts in water depth are steeper. Thus, when designing a dredging programme to remove seriously contaminated sediments, the identification of sub-areas is essential to ensure the adequate dredging of the sediments. If spatial variability is not taken into account for dredging contaminated layers, seriously contaminated spots may be overlooked or rather clean sediments may be dredged needless. Thorough (although expensive) spatial investigations of the contaminated layer before dredging starts, identifying critical sub-areas, is therefore recommended. Practical, cost-effective, geostatistical methods allow an efficient use of limited financial resources for monitoring aquatic sediments.

    Another important process affecting sediment concentration profiles is consolidation. Chapter 6 deals with this physical process of settling of suspended solids and the loss of water after deposition. Consolidation in principle can be described by mathematical models, but because of local circumstances in the Lake IJsselmeer area an empirical approach seemed more reliable. Five representative cores of the (IJm- deposit) were taken from deep zones of the lakes. Periodic water depth surveys at these locations over the last sixty years provided information on the net sedimentation rate and total thickness of the (IJm-deposit) at known time intervals. To calculate a time-equivalent of the depth scale, correction factors for sediment consolidation were needed. These factors were based on a simplification of the various stages of compression (i.e. 0%, 30% and 45%). A factor n , which represents changes of water content of the sediment as a dependent variable of clay content, was derived for each layer, making it possible to determine the initial, uncompressed thickness of each layer by an inverse calculation procedure. Hence, a fairly reliable time-scale for depth could be reconstructed. This time-scale was compared with radio-isotope-dated layers and the results showed close consistency.

    Annual variability of contaminants in the IJsselmeer area is described in Chapter 7. Measurements of the concentrations of six heavy metals in suspended solids, discharged by the river IJssel). and settling solids at two locations in Lake IJsselmeer showed a typical spatial gradient. The heavy metals concentrations decreased with increasing distance from the river IJssel). inlet. This spatial gradient corresponds with gradients observed in the bottom sediment (Chapter 3). Measurements in sediment cores from Lake Ketelmeer, i.e. the river mouth, and the central part of Lake IJsselmeer showed that the heavy metals concentration in sediments, deposited during the same periods, is 2 to 3 times higher in Lake Ketelmeer than in Lake IJsselmeer The concentration gradient in the settling solids is still significant when changes in the clay and organic matter content are accounted for by using normalized metal concentrations. A rough sediment mass balance for heavy metals, based on river input data and observed sedimentation fluxes, indicates that the total internal sedimentation fluxes of heavy metals in Lake IJsselmeer far exceed the external aereal loading by the river. Due to the complexity of the relationships between the measured variables, the heavy metal concentrations and variables related to primary production and erosion, single correlation analysis did not reveal clear relations and processes that could explain this dilution. Principal component analysis and stepwise multiple regression however showed that the variation in the heavy metals concentration in settling solids is related to wind velocity and clay content, both of which are related to resuspension/erosion of sediments; or alternatively, to pH, chlorophyll and CaCO 3 , which are in turn related to algal growth in the lake. Resuspension/erosion-related variables are the dominant factors explaining the variation in heavy metals concentration in the southern part of Lake IJsselmeer whereas algal-growth-related variables explain most of the variation in the metal concentrations in settling solids in the central part of the lake. In this central part, where algal concentrations are high, the negative relation between the concentration of most of the heavy metals in settling solids and the chlorophyll and organic matter concentration in the water compartment justifies the conclusion that dilution of contaminated suspended solids by primary production is active there. In the southern part of the lake, the heavy metals concentration is positively related to wind velocity and clay content. This indicates that resuspension of recent deposits contributes to the metal concentrations of the water compartment. The gradual increase in the δ 13C value with distance from the river IJssel). mouth (passing from the southern to the central part of Lake IJsselmeer shows that the freshwater sediments are mixed with eroded Zu deposits from within the lake, which were originally saline. It can be concluded, therefore, that the decrease in the heavy metals concentrations in suspended and bottom sediments in Lake IJsselmeer is the result of dilution of contaminated sediments due to erosion of old sediments and of primary production related to algal growth.

    In Chapter 8 the specific knowledge reported in all previous chapters on sediment contamination, dilution, transport and processes like consolidation and primary production occurring in this area, is integrated in a modeling framework. The sediment distribution processes and the related contaminant dilution of previous decades has been reconstructed. This exercise was the basis for prediction of the future sediment composition and contamination resulting from the expected changes in the contaminant load of the river IJssel). The adapted model STRESS-2d gives a reconstruction of resuspension, erosion, sedimentation and horizontal sediment transport processes, resulting in a good simulation of total-suspended-solids concentration and of the sediment fluxes. This model was nested into the more aggregated model DIASPORA, which simulates changes in morphology (net sedimentation fluxes) quite well. It also accounted for the effects of biogenic calcite production and the consolidation of sediment layers. The decrease of the lead concentration in sedimentation areas in Lake IJsselmeer reflects the reduced suspended input from the river IJssel). but this is dominated by the effects of internal redistribution of sediments in the area. The modelling results support the above mentioned conclusion of Chapter 7. Simulation of sediment fluxes and future contamination by lead are simulated for a constant sediment input and a 50% reduction of lead input from the river IJssel). Modelling results show a steady decrease of the lead concentration in sedimentation zones of Lake IJsselmeer and a purification effect in these zones due to the dredging of sediments in Lake Ketelmeer.

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