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Door klimaatverandering verandert het afvoerregime van onze grote rivieren. Hoogwaters worden hoger en frequenter, laagwaters lager en langduriger. Hoe we daarop reageren hangt af van hoe we klimaatverandering zien: als opgave, of als kans om onvolkomenheden aan te pakken. In dit artikel presenteren we aanzetten voor een meer geo-ecologisch gefundeerde inrichting, of – naar McHarg – voor design with nature.Climate change is expected to significantly influence the discharge regime of the Rhine and Meuse rivers. Floods may increase in magnitude and occur more frequently; low discharges are likely to become even smaller and last longer. How to respond to those changes? Can all river functions be fulfilled into the future and which interventions are then needed to keep the country safe and the rivers navigable? The answer to these questions depends on whether climate change is primarily considered as a challenge, or rather as an opportunity to, at the same time, redress a few deficiencies and detrimental geo-ecological developments that are being provoked by how we straightjacketed our floodplains and engineered our rivers in behalf of navigation but negatively impact biodiversity. We propose a more geo-ecologically grounded approach to our rivers’ spatial design and management – inspired by McHarg’s design with nature –, which encompasses making available much more room for safe flood discharge and reduced hydrodynamics for ecosystem development in the floodplains, as well as more nature-based river training to allow for morphological developments and natural rejuvenation.

Door klimaatverandering verandert het afvoerregime van onze grote rivieren. Hoogwaters worden hoger en frequenter, laagwaters lager en langduriger. Hoe we daarop reageren hangt af van hoe we klimaatverandering zien: als opgave, of als kans om onvolkomenheden aan te pakken. In dit artikel presenteren we aanzetten voor een meer geo-ecologisch gefundeerde inrichting, of – naar McHarg – voor design with nature.Climate change is expected to significantly influence the discharge regime of the Rhine and Meuse rivers. Floods may increase in magnitude and occur more frequently; low discharges are likely to become even smaller and last longer. How to respond to those changes? Can all river functions be fulfilled into the future and which interventions are then needed to keep the country safe and the rivers navigable? The answer to these questions depends on whether climate change is primarily considered as a challenge, or rather as an opportunity to, at the same time, redress a few deficiencies and detrimental geo-ecological developments that are being provoked by how we straightjacketed our floodplains and engineered our rivers in behalf of navigation but negatively impact biodiversity. We propose a more geo-ecologically grounded approach to our rivers’ spatial design and management – inspired by McHarg’s design with nature –, which encompasses making available much more room for safe flood discharge and reduced hydrodynamics for ecosystem development in the floodplains, as well as more nature-based river training to allow for morphological developments and natural rejuvenation.

The Integration of Metz Port and Hinterland into the River Traffic on Mosel and Rhine at the End of the Middle Ages. The city of Metz, located at the confluence of the Mosel and Seille rivers, was during the Middle Ages an important river port, despite its distance from the sea. This paper shows how Metz port and hinterland were integrated into the river traffic on the Mosel and Rhine rivers at the end of the Middle Ages. River trade study shows that Metz is at the heart of various flows, both in nature and spatial dimension. In addition to the urban and periurban traffic flows, regional flows and also more distant ones involving in particular the Rhine valley, are to be considered. They mostly concerned foodstuffs, building materials and firewood. Rivermen from Metz, called nautoniers or waudexours, were deeply involved in this river traffic. River trades were highly influenced by river flow conditions and hydraulic works, but also by a fluctuating political and economic context., Située à la confluence de la Moselle et de la Seille, la ville de Metz est à l’époque médiévale un port fluvial important, bien qu’éloigné de la mer. Il s’agit ici d’envisager l’intégration du port messin et de son arrière-pays au trafic fluvial mosello-rhénan à la fin du Moyen Âge. L’étude des échanges fluviaux montre que Metz est au coeur de flux variés, tant par leur dimension spatiale que par leur nature. Aux flux locaux, concernant le trafic urbain et périurbain, s’ajoutent des flux régionaux, mais aussi des flux plus lointains, impliquant notamment la vallée du Rhin. Ils portent pour l’essentiel sur des denrées alimentaires, des matériaux de construction, du bois de chauffage. Sans en avoir le monopole, des bateliers messins plus ou moins spécialisés, qualifiés de nautoniers et de waudexours, occupent une place importante dans ces échanges. Par ailleurs, le trafic fluvial est dépendant des conditions de navigation et des aménagements hydrauliques, mais aussi d’un contexte économique et politique fluctuant., Integratie van de haven van Metz en haar achterland in het scheepvaartverkeer op de Moezel en de Rijn aan het eind van de middeleeuwen. In de middeleeuwen vormt de stad Metz, die aan de samenvloeiing van Moezel en Seille ligt, een belangrijke binnenhaven, weliswaar ver van de zee verwijderd. De bedoeling bestaat erin de integratie van de haven van Metz en haar achterland, in het scheepvaartverkeer op de Moezel en de Rijn, aan het eind van de middeleeuwen, te bekijken. Uit de studie van rivierhandel blijkt dat Metz centraal staat in allerlei goederenvervoer, ongeacht de aard ervan of de afstand. Naast lokale handelsstromen, die te maken hebben met stedelijk en randstedelijk verkeer, komen nog regionale maar ook verdere handelsstromen aan bod, waarbij onder meer het Rijndal betrokken is. Die betreffen vooral voedingswaren, bouwmaterialen, brandhout. Zonder echter het monopolie erop te hebben, spelen min of meer gespecialiseerde binnenschippers van Metz (de zogenaamde nautoniers en waudexours) een belangrijke rol in dat handelsverkeer. De binnenvaart is overigens afhankelijk van de scheepvaart-en hydraulische omstandigheden, maar ook van een economisch en politiek wisselvallig klimaat., Ferber Frédéric. L’intégration du port de Metz et de son arrière-pays au trafic fluvial mosello-rhénan à la fin du Moyen Âge. In: Revue belge de philologie et d'histoire, tome 94, fasc. 4, 2016. Histoire médiévale, moderne et contemporaine – Meddeleeuwse, Moderne en Hedendaagse Geschiedenis. pp. 945-958.

Probability estimates of the future change of extreme precipitation events are usually based on a limited number of available Global Climate Model (GCM) or Regional Climate Model (RCM) simulations. Since floods are related to heavy precipitation events, this restricts the assessment of flood risks. In this study a relatively simple method has been developed to get a better picture of the range of changes in extreme precipitation events. Five bias corrected RCM simulations of the 1971–2100 climate for a single greenhouse gas emission scenario (A1B SRES) were available for the Rhine basin. To increase the size of this five-member RCM ensemble, 13 additional GCM simulations were analysed. The climate responses of the GCMs are used to modify an observed (1961–1995) precipitation/temperature time series with an advanced delta change approach. Changes in the temporal means and variability are taken into account. Time series resampling was applied to extend 35-yr GCM and RCM time-slices to 3000-yr series to estimate extreme precipitation with return periods up to 1000 yr. It is found that the range of future change of extreme precipitation across the five-member RCM ensemble is similar to results from the 13-member GCM ensemble. For the RCM ensemble, the time series modification procedure also resulted in a similar climate response compared to the signal deduced from the direct model simulations. The changes from the individual RCM simulations, however, systematically differ from those of the driving GCMs, especially for long return periods.

De Atlantische steur (Acipenser sturio) behoort tot een ruim 200 miljoen jaar oude diergroep. Deze kraakbeenvissen overleefden de dinosauriërs. Echter, tussen 1920 en 1990 verdween de steur door toedoen van de mens uit vrijwel alle grote rivieren van West-Europa. Het is een geweldige uitdaging om deze oervis met beenplaten en vier snorharen voor uitsterven te behoeden

Dit rapport is de Engelse vertaling van rapport 734301034

Restanten van humane geneesmiddelen komen voornamelijk via gezuiverd rioolwater in het oppervlaktewater terecht. Aangezien oppervlaktewater wordt gebruikt voor de drinkwaterproductie, is het van belang dat dit water zo min mogelijk verontreinigingen bevat. Daarom is met een rekenmodel onderzocht in hoeverre de waterkwaliteit bij de innamepunten voor de drinkwaterproductie wordt beïnvloed door restanten uit Nederlands rioolwater, dan wel door de aanvoer uit het buitenland via de Rijn en de Maas. Het onderzoek is uitgevoerd door het RIVM samen met kennisinstituut Deltares en richt zich op vier geneesmiddelen. Deze middelen worden door de drinkwaterbedrijven als probleemstoffen beschouwd. Er bestaan nog geen wettelijke normen voor. Het gaat om metformine, een medicijn tegen diabetes type 2, carbamazepine, een anti-epilepticum, metoprolol, een bloeddrukverlager en amidotrizoïnezuur, een röntgencontrastmiddel. De bijdragen vanuit het buitenland en Nederland blijken sterk te verschillen per stof, per rivier en per innamepunt. Ook is de hoeveelheid water die door de rivieren wordt aangevoerd van invloed. Bij de innamepunten langs de Maas zijn zowel de buitenlandse aanvoer als emissies vanuit Nederlandse rioolwaterzuiveringsinstallaties (rwzi's) van belang voor de waterkwaliteit. Met name in droge perioden is de invloed van gezuiverd rioolwater vanuit Nederland groter. Bij de meeste innamepunten langs de Rijn is de buitenlandse aanvoer via de Rijn belangrijker, zelfs in droge perioden. Een uitzondering vormt metoprolol, waarvoor de bijdrage vanuit Nederlandse rwzi's het grootst is. Dit komt doordat dit middel in Nederland meer wordt gebruikt dan in het buitenland. Op basis van de bevindingen kan worden bepaald welke maatregelen effectief zijn om de concentraties van deze geneesmiddelen bij de innamepunten voor drinkwater te verlagen. Zowel bij de Rijn als de Maas zal de waterkwaliteit verbeteren als de emissies in het buitenland dalen. Als emissies vanuit Nederlandse rwzi's afnemen, heeft dat een groter effect bij de innamepunten langs de Maas dan langs de Rijn, vooral stroomafwaarts. De bevindingen zijn ondermeer relevant voor de strategie die de Europese Commissie momenteel ontwikkelt met betrekking tot de aanpak van waterverontreiniging door restanten van geneesmiddelen. De conclusies zijn gebaseerd op een landelijk model met daarbij passende schematisatie. Lokaal kan het beeld anders zijn, evenals bij kleinere wateren in Nederland die niet zijn meegenomen in deze studie.

Dit rapport is in het Engels verschenen met rapportnummer 734301035

The low-lying Netherlands is at risk from multiple threats of sea level rise, storm surges and extreme river discharges. Should these threats occur simultaneously, a catastrophe will be at hand. Knowledge about the likelihood of simultaneous occurance or the so-called "compound effect" of such threats is essential to provide guidance on legislation for dike heights, flood barrier design and water management in general. In this study, we explore the simultaneous threats of North Sea storm surges and extreme Rhine river discharge for the current and future climate in a large 17-member global climate model ensemble. We use a simple approach, taking proxies of North-Northwesterly winds over the North Sea and multiple-day precipitation averaged over the Rhine basin for storm surge and discharge respectively, so that a sensitivity analysis is straight forward to apply. By investigating soft extremes, we circumvent the need to extrapolate the data and thereby permit the synoptic development of selected events to be inspected. flood barrier design and water management in general. Our principle finding is that, for the current climate, the probability of extreme surge conditions following extreme 20-day precipitation sums is around 3 times higher than that estimated from treating extreme surge and discharge probabilities as independent, as previously assumed. For the future climate, the assumption of independence cannot be rejected, at least not for precipitation sums exceeding 7 days.

Political Thoughts and Change. The Border of the Rhine in Caesar’s Gallic War The Gallic War, written by Julius Caesar, is generally considered to lie at the origins of the concept of the “ Border of the Rhine”. A more critical and in-depth reading however, reveals that the description of the river varies according to the needs of narrative and the author’s political thoughts underlying it. On the other hand, the constant changes in the world or worlds which Caesar encountered in Gaul are clear demonstrations of the concepts of “ branch connection” and “ tribal zone” developed by scholars in human and social sciences., Les Commentaires sur la Guerre des Gaules, rédigés par Jules César, sont tenus généralement pour l’acte de naissance de la «frontière du Rhin » . Une lecture critique révèle pourtant que la description du fleuve est modulée en fonction des nécessités du récit et des besoins de la pensée politique qui sous-tend ce récit. D’autre part, le caractère mouvant du/ des monde(s) rencontré(s) par César en Gaule est bien mis en évidence par les concepts de «branchements » et de «zone tribale » développés par les chercheurs en sciences humaines et sociales., Politieke overwegingen en een stroom aan veranderingen. De Rijngrens in de Commentaren over de Gallische Oorlog van Caesar De oorsprong van het concept “ Rijngrens” wordt over het algemeen in het door Caesar geschreven Commentarii de Bello Gallico gesitueerd. Uit een kritische lezing van dit document blijkt echter dat de beschrijving van deze rivier varieert al naargelang van de vereisten van de vertelstijl en de politieke overwegingen van de auteur. Anderzijds vormen de continue veranderingen die Caesar in de Gallische wereld(en) observeerde, duidelijke voorbeelden van de concepten “ vertakking” en “ tribale zone”, die werden ontwikkeld door onderzoekers in de sociale en menswetenschappen., Dignef Anthony. La pensée et le mouvant. La frontière du Rhin dans les Commentaires de César. In: Revue belge de philologie et d'histoire, tome 91, fasc. 4, 2013. Histoire médiévale, moderne et contemporaine Middeleeuwse, moderne en hedendaagse geschiedenis. pp. 1123-1142.

Of Empires and Borders. The Nature of Borders from the ninth to the thirteenth century This paper deals with the perception of borders and related practices in the Frankish and Holy Roman Empire between the ninth and the thirteenth century. Adopting a diachronic approach, it analyses how spatial organisation evolved, from the ninthcentury division treaties up to the border inquiries of the thirteenth century. The frontier was transformed from a rather imprecise and oft-moving border, presented in the texts as a list of place names, to a delimitation attested by local witnesses on behalf of administrative authorities (count, duke, king, pope). And so, rivers such as the Rhine and the Meuse were reference points rather than real frontier lines. From the thirteenth century onward, frontier inquiries were launched to resolve conflicts between local agents disputing each other’s authority on border territories., Cet article traite de la perception et des pratiques de la frontière à l’échelle de l’Empire du IXe au XIIIe siècle. Adoptant une approche diachronique, il envisage l’évolution de l’organisation spatiale sur la base de traités de partages territoriaux du IXe siècle et d’enquêtes sur les frontières menées dans le courant du XIIIe siècle. On entrevoit ainsi un processus de transformation de la frontière : imprécise voire floue, réduite à des noms de lieux énumérés dans les sources, durant le Haut Moyen Âge, elle finit par s’imposer comme une véritable délimitation ; l’attestent quelques témoins émanant des autorités comtales, ducales, royales ou encore papales. Il en ressort que le Rhin et la Meuse servent de repères mais pas nécessairement de tracé frontalier. Les enquêtes sur les frontières menées à partir du XIIIe siècle ont été rendues nécessaires par des conflits locaux d’autorité en terres frontalières., Van rijken en grenzen : de aard van grenzen van de negende tot de dertiende eeuw Dit artikel bestudeert de manier waarop grenzen en de hieraan verbonden praktijken werden gepercipieerd in het Frankische en het Heilige Roomse Rijk van de negende tot de dertiende eeuw. Met behulp van een diachronische aanpak onderzoekt het hoe grenzen als instrument van ruimtelijke ordening evolueerden van de negendeeeuwse verdeelverdragen tot de grensonderzoeken van de dertiende eeuw. Het begrip ‘ grens’ veranderde van een vrij onnauwkeurige en vaak veranderlijke afbakening, die in teksten werd voorgesteld als een lijst van plaatsnamen, naar een scheidingslijn die door lokale getuigen werd bevestigd in naam van de administratieve autoriteiten (graaf, hertog, koning, paus). Bijgevolg waren rivieren zoals de Rijn en de Maas referentiepunten eerder dan echte grensmarkeringen. Vanaf de dertiende eeuw werden er grensonderzoeken gevoerd om conflicten op te lossen tussen lokale actoren die elkaar de zeggenschap over grensgebieden betwistten., Schneider Jens. D’Empires et de frontières, La pratique de la frontière du IXe au XIIIe siècle. In: Revue belge de philologie et d'histoire, tome 91, fasc. 4, 2013. Histoire médiévale, moderne et contemporaine Middeleeuwse, moderne en hedendaagse geschiedenis. pp. 1187-1209.

Door de vergrijzing zal de emissie van geneesmiddelen en röntgencontrastmiddelen naar het oppervlaktewater toenemen. De effecten van toenemende emissies op de waterkwaliteit worden versterkt bij lage rivierafvoeren, die naar verwachting steeds vaker en langduriger zullen optreden in een veranderend klimaat. In deze studie zijn prognoses gemaakt van de toekomstige concentraties van een aantal relevante organische microverontreinigingen in de Rijn en Maas in het jaar 2050. De voorspelde concentraties van diverse geneesmiddelen en röntgencontrastmiddelen in de Rijn en de Maas overschrijden de ERM-streefwaarden voor oppervlaktewater als bron van drinkwater. Sporen van enkele organische microverontreinigingen kunnen doordringen in het drinkwater.

Door de vergrijzing zal de emissie van geneesmiddelen en röntgencontrastmiddelen naar het oppervlaktewater toenemen. De effecten van toenemende emissies op de waterkwaliteit worden versterkt bij lage rivierafvoeren, die naar verwachting steeds vaker en langduriger zullen optreden in een veranderend klimaat. In deze studie zijn prognoses gemaakt van de toekomstige concentraties van een aantal relevante organische microverontreinigingen in de Rijn en Maas in het jaar 2050. De voorspelde concentraties van diverse geneesmiddelen en röntgencontrastmiddelen in de Rijn en de Maas overschrijden de ERM-streefwaarden voor oppervlaktewater als bron van drinkwater. Sporen van enkele organische microverontreinigingen kunnen doordringen in het drinkwater.

Door de vergrijzing zal de emissie van geneesmiddelen en röntgencontrastmiddelen naar het oppervlaktewater toenemen. De effecten van toenemende emissies op de waterkwaliteit worden versterkt bij lage rivierafvoeren, die naar verwachting steeds vaker en langduriger zullen optreden in een veranderend klimaat. In deze studie zijn prognoses gemaakt van de toekomstige concentraties van een aantal relevante organische microverontreinigingen in de Rijn en Maas in het jaar 2050. De voorspelde concentraties van diverse geneesmiddelen en röntgencontrastmiddelen in de Rijn en de Maas overschrijden de ERM-streefwaarden voor oppervlaktewater als bron van drinkwater. Sporen van enkele organische microverontreinigingen kunnen doordringen in het drinkwater.

Alterra onderzocht samen met Wageningen Universiteit de gevolgen van klimaat- en landgebruikverandering op lage afvoeren in de Rijn. Hiervoor maakten ze gebruik van het grond- en oppervlaktewatermodel SIMGRO. Uit het onderzoek komt naar voren dat extreme klimaatscenario’s in 2050 zullen leiden tot aanzienlijk lagere afvoeren in de Rijn en bovendien een toename in de duur. Verder blijkt dat veranderingen in het landgebruik een veel kleiner effect hebben op lage afvoeren dan veranderingen in het klimaat. Hierdoor kunnen lagere afvoeren door klimaatverandering moeilijk opgevangen worden met alleen aanpassingen in het landgebruik

In many climate impact studies hydrological models are forced with meteorological data without an attempt to assess the quality of these data. The objective of this study was to compare downscaled ERA15 (ECMWF-reanalysis data) precipitation and temperature with observed precipitation and temperature and apply a bias correction to these forcing variables. Precipitation is corrected by fitting it to the mean and coefficient of variation (CV) of the observations. Temperature is corrected by fitting it to the mean and standard deviation of the observations. It appears that the uncorrected ERA15 is too warm and too wet for most of the Rhine basin. The bias correction leads to satisfactory results, precipitation and temperature differences decreased significantly, although there are a few years for which the correction of precipitation is less satisfying. Corrections were largest during summer for both precipitation and temperature. For precipitation alone large corrections were applied during September and October as well. Besides the statistics the correction method was intended to correct for, it is also found to improve the correlations for the fraction of wet days and lag-1 autocorrelations between ERA15 and the observations. For the validation period temperature is corrected very well, but for precipitation the RMSE of the daily difference between modeled and observed precipitation has increased for the corrected situation. When taking random years for calibration, and the remaining years for validation, the spread in the mean bias error (MBE) becomes larger for the corrected precipitation during validation, but the overal average MBE has decreased.

In Nederland staan toepassingen met SIMGRO synoniem voor complex, gedetailleerd, veel gegevens benodigd etc. Het zijn toepassingen voor een klein gebied (zoals Hupselsebeek), of redelijk groot voor Nederlandse begrippen (zoals noordwest Drentse beken). De laatste 5 jaar waren er toepassingen op geheel andere schaal, voor stroomgebieden in Brazilië, Litouwen en Argentinië. Door het gebruik van digitale gegevens en de ArcView gebruikersinterface AlterrAqua zijn zulke toepassingen goed te realiseren en geeft het de modelmaker de mogelijkheid om met de (soms beperkt) beschikbare gegevens een zo goed mogelijk model op te zetten

Recentelijk heeft veel onderzoek plaatsgevonden om de invloed van klimaatverandering te kwantificeren. Dit kan op verschillende manieren gebeuren, bijvoorbeeld kan er op basis van gemeten data een extreme-waardenverdeling worden geëxtrapoleerd. Een dergelijke aanpak heeft als nadeel dat de aanpak gebaseerd is op statistische kenmerken van het huidige klimaat, terwijl die juist waarschijnlijk veranderen. Een andere mogelijkheid is daarom het doorberekenen van klimaatscenario's zoals die worden gegenereerd met klimaatmodellen. Het landoppervlaktemodel dat in deze studie is gebruikt, namelijk het Variable Infiltration Capacity (VIC) model maakt gebruik van statistische parameters voor de invloed van verzadigde bodems. Het gebied betreft de substroomgebieden van Ruhr, Lahn, Mosel, Main en Neckar

One of the most endangered fish species worldwide is the European sturgeon Acipenser sturio. The River Rhine was home to an important sturgeon population that went locally extinct in the first half of the 20th century. In recent decades, many improvements of the ecological quality of the Rhine have taken place. Because the last remaining wild population of European sturgeon in the Gironde basin is very small and at considerable distance, it appears unlikely that rapid recolonization will take place if the Rhine is suitable again. That is why Stichting ARK, World Wildlife Fund (WWF) and the Dutch Anglers Association (Sportvisserij Nederland) have started a trajectory with the eventual reintroduction of the European sturgeon in the Rhine basin as the ultimate goal.

In 2014 zijn in het kader van het monitoringsprogramma "Monitoring contaminanten ten behoeve van de Nederlandse sportvisserij" 17 zoetwaterlocaties in Nederland bemonsterd. Van de gevangen rode alen zijn mengmonsters samengesteld voor de lengteklassen 30-40 cm en >45 cm en geanalyseerd op de aanwezigheid van dioxines, dioxineachtige- en nietdioxineachtige PCB's. De gevonden gehaltes sluiten goed aan bij de resultaten van 2013. Mengmonsters van kleine alen zijn onderzocht op 12 locaties en in 3 gevallen werden één of meerdere normen overschreden. De mengmonsters van grotere alen (>45 cm) voldeden op 9 van de onderzochte locaties niet aan één of meerdere normen. Naast aal uit de gesloten gebieden betrof dat ook aal uit het open gebied Amsterdam-Rijnkanaal bij Diemen. Per 1-1- 2015 behoort het Amsterdam-Rijnkanaal ook tot de gesloten gebieden. Anderzijds waren er ook locaties binnen de gesloten gebieden waar de mengmonsters aal wel voldeden aan de normen. Dit betrof beide locaties van het Volkerak.

In 2014 zijn in het kader van het monitoringsprogramma "Monitoring contaminanten ten behoeve van de Nederlandse sportvisserij" 17 zoetwaterlocaties in Nederland bemonsterd. Van de gevangen rode alen zijn mengmonsters samengesteld voor de lengteklassen 30-40 cm en >45 cm en geanalyseerd op de aanwezigheid van dioxines, dioxineachtige- en nietdioxineachtige PCB's. De gevonden gehaltes sluiten goed aan bij de resultaten van 2013. Mengmonsters van kleine alen zijn onderzocht op 12 locaties en in 3 gevallen werden één of meerdere normen overschreden. De mengmonsters van grotere alen (>45 cm) voldeden op 9 van de onderzochte locaties niet aan één of meerdere normen. Naast aal uit de gesloten gebieden betrof dat ook aal uit het open gebied Amsterdam-Rijnkanaal bij Diemen. Per 1-1- 2015 behoort het Amsterdam-Rijnkanaal ook tot de gesloten gebieden. Anderzijds waren er ook locaties binnen de gesloten gebieden waar de mengmonsters aal wel voldeden aan de normen. Dit betrof beide locaties van het Volkerak.

One of the most endangered fish species worldwide is the European sturgeon Acipenser sturio. The River Rhine was home to an important sturgeon population that went locally extinct in the first half of the 20th century. In recent decades, many improvements of the ecological quality of the Rhine have taken place. Because the last remaining wild population of European sturgeon in the Gironde basin is very small and at considerable distance, it appears unlikely that rapid recolonization will take place if the Rhine is suitable again. That is why Stichting ARK, World Wildlife Fund (WWF) and the Dutch Anglers Association (Sportvisserij Nederland) have started a trajectory with the eventual reintroduction of the European sturgeon in the Rhine basin as the ultimate goal.

Future changes in extreme multi-day precipitation will influence the probability of floods in the river Rhine basin. In this paper the spread of the changes projected by climate models at the end of this century (2081–2100) is studied for a 17-member ensemble of a single Global Climate Model (GCM) and results from the Coupled Model Intercomparison Project Phase 3 (CMIP3) ensemble. All climate models were driven by the IPCC SRES A1B emission scenario. An analysis of variance model is formulated to disentangle the contributions from systematic differences between GCMs and internal climate variability. Both the changes in the mean and characteristics of extremes are considered. To estimate variances due to internal climate variability a bootstrap method was used. The changes from the GCM simulations were linked to the local scale using an advanced non-linear delta change approach. This approach uses climate responses of the GCM to transform the daily precipitation of 134 sub-basins of the river Rhine. The transformed precipitation series was used as input for the hydrological Hydrologiska Byrans Vattenbalansavdelning model to simulate future river discharges. Internal climate variability accounts for about 30 % of the total variance in the projected climate trends of average winter precipitation in the CMIP3 ensemble and explains a larger fraction of the total variance in the projected climate trends of extreme precipitation in the winter half-year. There is a good correspondence between the direction and spread of the changes in the return levels of extreme river discharges and extreme 10-day precipitation over the Rhine basin. This suggests that also for extreme discharges a large fraction of the total variance can be attributed to internal climate variability.

De Atlantische steur (Acipenser sturio) behoort tot een ruim 200 miljoen jaar oude diergroep. Deze kraakbeenvissen overleefden de dinosauriërs. Echter, tussen 1920 en 1990 verdween de steur door toedoen van de mens uit vrijwel alle grote rivieren van West-Europa. Het is een geweldige uitdaging om deze oervis met beenplaten en vier snorharen voor uitsterven te behoeden

Recovery of the fish community of the river Rhine focussed mainly on the return of migratory species, in particular the Atlantic Salmon, Salmo salear, and to alesser extent on rheophilic fish species.

The aim of the present study was to analyse the causes for the absence and persistence of chironomids in sediments with a complex pollution history. Observations on the benthic community composition in floodplain lake sediments of the River Rhine, differing in contaminant level and food quality, were combined with laboratory and in situ bioassays, using the midge Chironomus riparius as a model species. The positive relation between food quality and the diversity of the communities indicated that food quality is an important factor regulating benthic community composition, overriding the potential effects of contaminants. Nevertheless, in sediments with high contaminant levels, high densities of species classified as 'pollution-tolerant', such as Chironomus sp., were observed. The laboratory bioassays verified that the contaminant concentrations in these sediments had no direct effect on survival and growth of C. riparius, although higher contaminant concentrations in the sediment resulted in a higher incidence of mentum deformities. Also, the high growth rate of C. riparius in the in situ enclosures in two of the most contaminated sediments indicated chemical stress and mentum deformities did not exclude rapid growth. This observation agrees with the abundance of the resident pollution-tolerant chironomids of the Chironomus plumosus group. In addition, the in situ bioassay pointed out that predation on chironomids added to the field enclosures was significant and is also an important factor in regulating the abundance of chironomids. In sediments with the highest food quality and low levels of contaminants the opportunistic chironomids may have been outcompeted by benthic invertebrate taxa that are not able to persist at more contaminated sites. It is concluded that tolerance of opportunistic chironomids, such as Chironomus sp., combined with their rapid rate of development, enables them to persist in contaminated sediments that are organically enriched avoiding competition with other invertebrates

In recent years, interest has grown in restoring floodplain function of regulated rivers. Successful rehabilitation of riparian systems requires knowledge of how regulation of river flow affects biodiversity and ecosystem function. The effects of changes in the river's low water-level regime on aquatic ecosystems in floodplains has received little attention so far. The aquatic vegetation of 215 floodplain lakes along the Lower Rhine (the Netherlands) was analysed in relation to lake characteristics and lake water-level fluctuations in 1999–2000. Vegetation composition was related to lake morphology and age, cattle access to the shoreline, the amount of time the river was in flood, and lake sediment area exposed at low water level (drawdown). Surprisingly, vegetation composition was correlated more strongly with lake age and occurrence of drawdown than the amount of time the river was in flood1. In recent years, interest has grown in restoring floodplain function of regulated rivers. Successful rehabilitation of riparian systems requires knowledge of how regulation of river flow affects biodiversity and ecosystem function. The effects of changes in the river's low water-level regime on aquatic ecosystems in floodplains has received little attention so far. 2. The aquatic vegetation of 215 floodplain lakes along the Lower Rhine (the Netherlands) was analysed in relation to lake characteristics and lake water-level fluctuations in 1999-2000. 3. Vegetation composition was related to lake morphology and age, cattle access to the shoreline, the amount of time the river was in flood, and lake sediment area exposed at low water level (drawdown). Surprisingly, vegetation composition was correlated more strongly with lake age and occurrence of drawdown than the amount of time the river was in flood. 4. In older lakes, water-level fluctuations are reduced due to an accumulation of clay and silt that 'seals' sediment, preventing drawdown during periods of low river levels. Our results suggest that this clay sealing process is a major driving force for aquatic vegetation succession in floodplain lakes along the Lower Rhine, as succession drives from desiccation-tolerant species (e.g. Chara spp.) in young lakes to desiccation-sensitive species (e.g. Nuphar lutea) in old lakes. 5. Water levels were stable in lakes along a river branch that was impounded below mean flow only. Here, the original low water-level regime has been replaced by an artificial regime with higher water levels than would be expected naturally. Consequently, in these lakes drawdown was rare or absent, and the aquatic macrophyte vegetation was characterized by low species richness and frequent dominance by the invasive species Elodea nuttallii. 6. Synthesis and applications. Our results show that stabilization of river water levels during low flow may negatively affect vegetation composition and succession in floodplain lakes adjacent to these rivers. A management scheme including incidental temporary lowering of the river water level, which results in drawdown of floodplain lakes, would enhance the ecological status of those rivers with stabilized water levels during low flow.

The characteristic ecology of floodplain lakes is in part due to their relatively strong water-level fluctuations. We analyzed the factors determining water-level fluctuations in 100 floodplain lakes (during non-flooded conditions) in the active floodplains of the Lower Rhine in the Netherlands. Furthermore, we explored the relationship between water-level fluctuations and macrophyte species richness, and analyzed the suitability of artificially created lakes for macrophyte vegetation. During non-flooded conditions along the Rhine, lake water-level fluctuations are largely driven by groundwater connection to the river. Hence, water-level fluctuations are largest in lakes close to the main channel in strongly fluctuating sectors of the river and smallest in isolated lakes. Additionally, water-level fluctuations are usually small in old lakes, mainly due to reduced groundwater hydraulic conductivity resulting from accumulated clay and silt on the bottom. Species richness of floating-leaved and emergent macrophytes was reduced at both small and large water-level fluctuations, whereas species richness of submerged macrophytes was reduced at small water-level fluctuations only. In addition, species richness of submerged macrophytes was higher in lakes that experienced drawdown, whereas no similar pattern was detected for floating-leaved and emergent macrophytes. The decline in amplitude of lake water-level with lake age implies that the number of hydrologically dynamic lakes will decrease over time. Therefore, we suggest that excavation of new lakes is essential to conserve the successional sequence of floodplain water bodies including conditions of high biodiversity. Shallow, moderately isolated, lakes with occasional bottom exposure have the highest potential for creating macrophyte-rich floodplain lakes along large lowland rivers. The water-level regime of such lakes can in part be designed, through choice of the location along the river, the distance away from the river and the depth profile of the lake. [KEYWORDS: connectivity ; river ecology ; river restoration ; species riches]

Dit artikel geeft een voorbeeld om faalkansen in watersystemen te bepalen via de stochastenmethode. De mechanismen, die leiden tot falen van het systeem zijn: neerslaghoeveelheid en -intensiteit, beschikbare berging in bodem en oppervlaktewater en de waterstand van de rivier de Lek. Alle mogelijke combinaties zijn doorberekend met SIMGRO. De modeluitkomsten zijn vervolgens gebruikt om een faalkansenkaart te construeren. Deze kaart is getoets aan de werknormen voor het huidige klimaat, het middenscenario 2050 en het maximumscenario 2050

Most floodplain sediments of the rivers Rhine and Meuse in The Netherlands are moderately polluted with trace metals, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and other chemicals. The effects of these sediment-bound contaminants on the productivity of benthic macroinvertebrates are unclear. Sixteen locations along a pollution gradient were investigated in creeks in the Biesbosch floodplain area. Sediment samples were analyzed for bulk sediment characteristics and contaminants (total and bioavailable concentrations of trace metals, PAHs, and PCBs). Exclosures were used to study the effect of predation by fish and birds on macroinvertebrates. Macroinvertebrates were sampled and identified to species level, and production was estimated from biomass increases inside the exclosures during a 1-mo interval in springMost floodplain sediments of the rivers Rhine and Meuse in The Netherlands are moderately polluted with trace metals, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and other chemicals. The effects of these sediment-bound contaminants on the productivity of benthic macroinvertebrates are unclear. Sixteen locations along a pollution gradient were investigated in creeks in the Biesbosch floodplain area. Sediment samples were analyzed for bulk sediment characteristics and contaminants (total and bioavailable concentrations of trace metals, PAHs, and PCBs). Exclosures were used to study the effect of predation by fish and birds on macroinvertebrates. Macroinvertebrates were sampled and identified to species level, and production was estimated from biomass increases inside the exclosures during a 1-mo interval in spring. Benthic macroinvertebrate species richness was negatively affected by sediment contamination. Production of oligochaetes and chironomids was not correlated with levels of contamination, but production of gastropods was negatively correlated with contamination. Environmental variables that reflected food availability (seston and sediment organic C) were positively correlated with contamination. Predation significantly reduced invertebrate biomass, but the effects of predation and sediment contamination were not correlated with each other. Our study suggested that the moderate levels of contamination affected the structure but not the productivity of the benthic macroinvertebrate community, probably because of the counteracting effects of contamination and associated surplus of food.

In vitro bioassays are valuable tools for screening environmental samples for the presence of bioactive (e.g., endocrine-disrupting) compounds. They can be used to direct chemical analysis of active compounds in toxicity identification and evaluation (TIE) approaches. In the present study, five in vitro bioassays were used to profile toxic potencies in sediments, with emphasis on endocrine disruption. Nonpolar total and acid-treated stable extracts of sediments from 15 locations in the Rhine Meuse estuary area in The Netherlands were assessed. Dioxin-like and estrogenic activities (using dioxin-responsive chemical-activated luciferase gene expression [DR-CALUX] and estrogen-responsive chemical-activated luciferase gene expression [ER-CALUX] assays) as well as genotoxicity (UMU test) and nonspecific toxic potency (Vibrio fischeri assay) were observed in sediment extracts. For the first time, to our knowledge, in vitro displacement of thyroid hormone thyroxine (T4) from the thyroid hormone transport protein thransthyretin by sediment extracts was observed, indicating the presence of compounds potentially able to disrupt T4 plasma transport processes. Antiestrogenic activity was also observed in sediment. The present study showed the occurrence of endocrine-disrupting potencies in sediments from the Dutch delta and the suitability of the ER- and DR-CALUX bioassays to direct endocrine-disruption TIE studies.

1. We sampled a set of 93 lakes situated in the floodplains of the lower River Rhine in search for morphometric and other factors that explain their variation in clarity. 2. Lakes with a drop in summer water level were less turbid at the time of sampling, mainly because of a lower concentration of inorganic suspended solids (ISS). 3. We also found that older lakes were more turbid than younger lakes and that this was largely because of an increase in phytoplankton. 4. Water clarity was positively related to lake depth and the presence of vegetation. 5. Model calculations indicated that the underwater light climate was strongly affected by chlorophyll and ISS, the latter being the dominant factor affecting Secchi depth. Dissolved organic carbon (DOC) was less important. 6. The high concentration of ISS suggests that intensive resuspension occurs in most of the lakes. Using a simple wave model, and assuming that vegetation protects sediments against resuspension, we could eliminate wind resuspension as an important process in 90% of the lakes, leaving resuspension by benthivorous fish as probably the most important factor determining transparency. 7. Chlorophyll a concentration showed a strong positive correlation to ISS concentration, suggesting that resuspension may also have a positive effect on phytoplankton biomass in these lakes. 8. In conclusion, in-lake processes, rather than river dynamics, seem to be driving the turbidity of floodplain lakes along the lower River Rhine.

The suitability of rehabilitated floodplains along the lower River Rhine for rheophilic cyprinids was assessed by investigating the spatial distribution of 0-group fish among, and within, three newly created secondary channels, an oxbow lake reconnected at its downstream end and several existing groyne fields. Fish were sampled during April through September 1997-1999 with seine nets and trawls and, for each sample, the habitat (physical environment) was characterized (flow, depth, substrate and inundated terrestrial vegetation). The new water bodies provide more suitable habitats for 0-group fish than the groyne fields. Their beneficial value differs, however, between reproductive guilds and depends on the morphological and hydrological conditions. Total fish density increased along a gradient of decreasing water flow whereas the proportion of rheophilic species (Barbus barbus, Gobio gobio, Leuciscus idus and Aspius aspius) decreased. Flow velocity and water depth were the most important factors determining habitat utilization. Rheophilic fish were spatially separated from eurytopic fish (e.g. Abramis brama, Rutilus rutilus and Stizostedion lucioperca). During flood events, inundated terrestrial vegetation was an important habitat for the larvae of all species. To enhance the riverine fish community, floodplain water bodies should have complex shorelines, and a high variability of flow velocities. Their slopes should be moderate to maximize the probability of terrestrial vegetation getting inundated during spring and summer. Future management of similar floodplains should focus on more diverse and accessible aquatic habitats to increase overall fish species diversity, since different types of water body clearly have complementary values

1. We analysed the vegetation structure of 215 lakes in the flood plain of the river Lower Rhine in relation to environmental variables related to hydrological connectivity, lake morphometry, lake age and land use on adjacent land. 2. The frequency distribution of the cover of submerged macrophytes was not normal, implying that submerged macrophytes in any one lake were either scarce or abundant. 3. We observed clear water lakes with submerged macrophyte dominance over a wide range of total P concentration (0.020-0.40 mg total P L-1). 4. Multiple logistic regression indicated that the probability of dominance by submerged macrophytes decreased markedly with the surface area, depth and age of the lakes. The surface area effect occurred independently of the depth. Further, there was a negative relationship between submerged macrophyte dominance and the long-term annual duration of inundation by the river. 5. Nymphaeid cover showed a distinct optimum with respect to mean lake depth, being almost absent in lakes shallower than 0.5 m. In contrast to what was found for submerged plants, the probability of occurrence of nymphaeids increased with lake age. 6. The probability of helophyte occurrence increased with lake age, and decreased with the presence of trees, cattle grazing, surface area, use of manure and mean lake depth. 7. In all cases the critical level of one factor (e.g. mean lake depth) depended on other factors (e.g. surface area or age of lake). Thus, in the present study, small lakes tended to remain dominated by submerged macrophytes up to a greater depth than large lakes, and helophytes colonised smaller lakes in an earlier phase. 8. The effect of inundation by the river was modest. This could be because most of our lakes are rarely inundated during the growing season and experience only moderate current velocities while flooded. 9. The results have practical implications for future management of flood plains for conservation purposes. In new water bodies, macrophyte domination will be promoted if many small shallow lakes, rather than few large deep ones, are excavated.

Investigations have shown that visible-near-infrared (VNIR) spectroscopy can accurately determine soil properties under laboratory conditions. In situ assessment of soil properties is of great benefit for several applications, as spectra can be acquired fast and almost continuously. The present study used partial least squares (PLS) regression to establish a relationship between soil reflectance spectra measured under field conditions and the organic matter and clay content of the soil. Spectra were acquired with a fieldspectrometer in a recently reconstructed floodplain along the river Rhine in The Netherlands. Several spectral pre-processing methods were employed to improve the performance and robustness of the models. Results indicate that, under varying surface conditions, field spectroscopy in combination with multivariate calibration does result in a qualitative relation for organic matter (R2=0.45) and clay content (R2=0.43) while under laboratory conditions more accurate results are obtained (R2=0.69 and 0.92, respectively). Soil moisture and vegetation cover had a negative influence on the prediction capabilities for both soil properties. Although the performance of the spectra measured in situ is not as accurate as physical analysis, the accuracy obtained is useful for rapid soil characterisation and remote sensing applications.

In order to identify the cause of toxicity in sediments and suspended matter, a large number of samples with different degrees of contamination was taken at various locations in The Netherlands. Standard acute bioassays were carried out with the bacterium Vibrio fischeri, the rotifer Brachionus calyciflorus and the anostracan Thamnocephalus platyurus. Chronic standard tests were performed using the water flea Daphnia magna and larvae of the midge Chironomus riparius. Some novel bioassays were performed as well. Most toxic effects observed in standard bioassays with sediments from polluted sediments (class 3 and 4 on a scale of 0¿4 according to the Dutch criteria) could be partly explained by toxic concentrations of known persistent priority pollutants, mainly heavy metals and occasionally polycyclic aromatic hydrocarbons. In some of the samples, ammonia toxicity was a confounding factor during testing. Suspended matter from the Meuse river at Eijsden, which may be considered as `new' sediment (pollution class 2), was moderately to highly toxic in almost all bioassays. This could have been associated with a combination of heavy metals, PAHs and ammonia. At two locations from the Lake IJssel area with no apparent persistent pollution, moderate and strong effects were nonetheless observed in invertebrate tests. This might have been due to agricultural run-off of pesticides, which are not routinely measured in sediments. A few effects on V. fischeri in canals and a small stream could not be explained with standard chemical analysis, but seemed associated with the outlets of sewage water treatment plants and industrial effluents. Additional chemical analysis of pore water samples from five selected sediments yielded more identified substances such as phtalates, decanes, cosanes and fragrances, but it was estimated that their contribution to the effects observed on V. fischeri, D. magna and C. riparius was negligible.

The paper reviews the past, present and future of eight anadromous fish species inhabiting the Lower Rhine (The Netherlands), viz. -sturgeon (Acipenser sturio), whitefish and houting (Coregonus lavaretus, C. oxyrinchus), smelt (Osmerus eperlanus), allis and twaite shad (Alosa alosa, A. fallax), sea trout (Salmo trutta) and salmon (Salmo salar). All species are under threat or became extinct (e.g. sturgeon, allis shad). It is not possible to single out a specific factor for the decline or disappearance. A combination of factors is responsible, as the degradation of the spawning and nursery areas, river correction for shipping, building of sluices and hydropower dams, extraction of sand and gravel and river pollution. The likelihood that a species will return via natural recovery, or restocking is assessed. The return of the sturgeon is unlikely. Present observations of sturgeon can be attributed to releases of unwanted sturgeon hybrids. A natural stock of coregonids in Dutch waters seems not feasible any more due to irreversible habitat degradation. Present day catches originate from German releases. The anadromous smelt, heavily reduced in numbers, still inhabits some of our waters, the non-migratory smelt is still very common. The allis shad is extinct and unlikely to recover. The species never spawned in the Dutch part of the Rhine. Twaite shad, declining in numbers, are still observed in the lower reaches of Rhine and Meuse. Sea trout is presumably still present in the same varying numbers as before. Spawning in our waters has not been documented. The salmon, once fished in large numbers, is now the subject of restocking programmes in Germany. Observations of individuals can partly be attributed to these programmes but also to straying salmon. Restocking programmes should be considerably improved before noticeable success is to be met.

1. Most temperate rivers are heavily regulated and characterised by incised channels, aggradated floodplains and modified hydroperiods. As a consequence, former extensive aquatic/terrestrial transition zones lack most of their basic ecological functions. 2. Along large rivers in Europe and North America, various floodplain restoration or rehabilitation projects have been planned or realised in recent years. However, restoration ecology is still in its infancy and the literature pertinent to river restoration is rather fragmented. (Semi-) aquatic components of floodplains, including secondary channels, disconnected and temporary waters as well as marshes, have received little attention, despite their significant contribution to biological diversity. 3. Many rehabilitation projects were planned or realised without prior knowledge of their potential for success or failure, although, these projects greatly contributed to our present understanding of river-floodplain systems. 4. River rehabilitation benefits from a consideration of river ecosystem concepts in quantitative terms, comparison with reference conditions, historical or others, and the establishment of interdisciplinary partnerships. 5. We present examples from two large European rivers, the Danube and the Rhine, in which the role of aquatic connectivity has been extensively studied. The Danube delta with its diversity of floodplain lakes across an immense transversal gradient (up to 10 km) serves as a reference system for restoration projects along lowland sections of large rivers such as the Rhine in the Netherlands.

To clarify the function of Lake IJsselmeer for salmonids, catch data collected throughout the year between 1995 and 1999 were related to various possible migratory strategies known for these species

The main aim of this thesis is to analyse the climate change uncertainties that are important to take into account for long term water management and to explore the communication of these uncertainties. The study design combines natural and social scientific theories and methods and consists of three different elements: 1) an assessment of the dominant uncertainty for changes in mean and extreme precipitation over the Rhine basin; 2) an assessment of the impact of the main uncertainties on changes in flood risk and associated damage in the Rhine basin and 3) an exploration of the use of simulation gaming to communicate about climate change uncertainties to water managers.

In het kader van de Monitoring chemische stoffen in Zoetwatermosselen is in 2013 wederom een actieve biologische monitoring (ABM) uitgevoerd in een aantal zoete Rijkswateren. In dit rapport worden de analyseresultaten van het monotoringprogramma 2013 gerapporteerd. De volgende vijf locaties zijn in 2013 bemonsterd: - Haringvliet – Haringvlietsluis - Hollands Diep – Bovensluis - Volkerak – Steenbergen - Bijlandsch kanaal (Rijn) – ponton Lobith - Nieuwe Waterweg - Maassluis

The main aim of this thesis is to analyse the climate change uncertainties that are important to take into account for long term water management and to explore the communication of these uncertainties. The study design combines natural and social scientific theories and methods and consists of three different elements: 1) an assessment of the dominant uncertainty for changes in mean and extreme precipitation over the Rhine basin; 2) an assessment of the impact of the main uncertainties on changes in flood risk and associated damage in the Rhine basin and 3) an exploration of the use of simulation gaming to communicate about climate change uncertainties to water managers.

In het kader van de Monitoring chemische stoffen in Zoetwatermosselen is in 2013 wederom een actieve biologische monitoring (ABM) uitgevoerd in een aantal zoete Rijkswateren. In dit rapport worden de analyseresultaten van het monotoringprogramma 2013 gerapporteerd. De volgende vijf locaties zijn in 2013 bemonsterd: - Haringvliet – Haringvlietsluis - Hollands Diep – Bovensluis - Volkerak – Steenbergen - Bijlandsch kanaal (Rijn) – ponton Lobith - Nieuwe Waterweg - Maassluis

It is often assumed that bioassays are better descriptors of sediment toxicity than toxicant concentrations and that ecological factors are more important than toxicants in structuring macroinvertebrate communities. In the period 1992 to 1995, data were collected in the enclosed Rhine-Meuse delta, The Netherlands, on macroinvertebrates, sediment toxicity, sediment contaminant concentrations, and ecological factors. The effect of various groups of pollutants (polycyclic aromatic hydrocarbons, trace metals, oil, polychlorinated biphenyls) and of ecological variables on the structure of the macroinvertebrate community were quantified. Ecological factors explained 17.3% of the macroinvertebrate variation, while contaminants explained 13.8%. Another 14.7% was explained by the covariation between ecological variables and contaminants. Polycyclic aromatic hydrocarbons explained a larger part of the variation than trace metals. The contributions of oil and polychlorinated biphenyls were small but significant. Elevated contaminant concentrations were significantly associated with differences in the macroinvertebrate food web structure. The response in bioassays (Vibrio fischeri, Daphnia magna, Chironomus riparius) was susceptible to certain contaminants but also to certain ecological factors. There was a weak correlation between in situ species composition and bioassays; 1.9% of in situ macroinvertebrate variation was explained by the bioassay responses. This seems to contradict the validity of using bioassays for a system-oriented risk assessment. Possible reasons for this discrepancy might be the manipulations of the sediment before the test and a higher pollutant tolerance of the in situ macroinvertebrates. Thus, macroinvertebrate field surveys and laboratory bioassays yield different types of information on ecotoxicological effects, and both are recommended in sediment risk assessment procedures.

Owing to river regulations in the past and intensive farming, the ecological value of the floodplains of the River Rhine in The Netherlands has decreased dramatically. One way to restore riverine biotopes is to create permanently flowing channels in the floodplain. Along the River Waal, the main branch of the Lower River Rhine, two such secondary channels have been created since 1994. A post-project monitoring programme of 5 years was set up, which included hydrological, morphological and ecological parameters. This article focuses on the monitoring of aquatic macrophytes, aquatic macroinvertebrates, fish and wading-birds. The results show that man-made, excavated secondary channels function as a biotope for riverine species including the more demanding rheophilic species. The demands for shipping and protection against flooding on the River Waal cause constraints on secondary channels. Despite these constraints there is still enough space for hydromorphological processes to create new habitats in secondary channel 1, near Opijnen. The space for hydromorphological processes is less in secondary channel 2, near Beneden-Leeuwen. The density and the number of (rheophilic) species are for a large part influenced by the water level and frequent inundation caused by the high hydrological connectivity. Man-made secondary channels seem to provide suitable habitat that is currently lacking for a broad range of rheophilic macroinvertebrate and fish species in the Lower River Rhine in The Netherlands. Owing to the lack of suitable habitats for rheophilic macroinvertebrate and fish species before the creation of the secondary channels, the importance of longitudinal and transversal migration could be illustrated by the drift of macroinvertebrates during floods and the seasonal migration of Age-() and Age-1 + fish species.