Thursday 3rd of july – from 10:30 to 18:30
Session A6 : Contaminant dynamics
Contaminant storage in depositional environments induced by river engineering in the upper Seine Estuary (France)
BARROIS Jean-Marie, DEBRET Maxime, COYNEL Alexandra, JACQ Kévin, EVRARD Olivier, COPARD Yoann, LEMOINE Jean-Philippe, MOURIER Brice, WINIARSKI Thierry, FISSON Cédric, PORTET-KOLTALO Florence
France
Short abstract : The extensive engineering of the Seine estuary upstream of Rouen (France) since the 1950s to support the growth of river transport has led to a significant recalibration of the riverbed. These morphological changes have enhanced sedimentation in sheltered areas, which are known to trap contaminants from upstream anthropized watersheds. As part of the DESTOX project, five depositional environments, constructed between 1953 and 1981, and each of them storing up to 1.105 m3 of sediment, are being investigated. Ten sediment cores were collected from a mudflat embanked in 1972. Concentrations of PAHs, PCBs, alkanes, metals and 137Cs activities are being measured along one of the cores (1.62 m). PAH concentrations will be estimated on the 9 other cores using hyperspectral imaging (following the method from Jacq et al., 2024) and interpolated to assess the PAH stock at the site scale. Preliminary results show PCB concentrations of up to 3.9 ± 0.4 mg kg-1, which is 50 times higher than the average concentration measured in suspended particulate matters currently circulating in the Seine Estuary. The aim of this work is to measure the extent of contamination in sediment stocks in the upper estuary in order to better understand the potential risk associated with the remobilization of these sediments. Such remobilization could be triggered by extreme hydrological events, restoration work, sea-level rise or other processes.
Working with left-censored data: an illustration of the maximum likelihood estimation method to study the spatio-temporal trends of glyphosate and AMPA in the Seine River.
TEYSSIER Lisa, BONNEAU Jérémie, KIM Boram, TEDOLDI Damien
France
Short abstract : This work investigates the spatial and temporal trends of glyphosate and one of its main degradation products, aminomethylphosphonic acid (AMPA), at several river monitoring points within the greater Paris area (Marne and Seine Rivers, upstream and downstream of the urban areas). To handle datasets containing up to ~50% left-censored data, the maximum likelihood estimation (MLE) method was applied, thus avoiding distorting the information through common practices such as ignoring these data points or substituting them with half the reporting limit. We aimed to illustrate a practical approach to handle left-censored data in environmental studies using glyphosate and AMPA as examples. We modeled the variability of their concentrations with a lognormal distribution, and found a significant contribution of the urban areas to pollution levels in surface waters. Notably, AMPA concentrations downstream of Paris were an order of magnitude higher compared to rural sections of the Marne river. Temporal trend analyses showed a general decline in glyphosate concentrations, as well as AMPA to a lesser extent, following the “Labbé” law prohibiting the use of pesticides in urban areas. While our findings suggest an influence of the Greater Paris urban areas to pollution levels, the study of underlying processes were beyond the scope of this work. Broader, more comprehensive analyses with additional data are necessary to confirm and consolidate these results.
Evolution of suspended particulate matter quality collected by particle-traps during the deployment phase: influence on trace metal/geochemical tracer concentrations
CLAVEAU Maeva, MASSON Matthieu, FRUCHET Alexis, GRUAT Alexandra, DHERRET Lysiane, DABRIN Aymeric
France
Short abstract : In the context of regulatory monitoring of sediment contaminants, particle traps (PTs) represent an alternative method for sampling suspended particulate matter (SPM). These traps enable time-integrated collection of SPM, target the finest and most contaminant-bearing fractions, and can be easily deployed on a large spatial scale. They also provide an effective means of sampling SPM from different tributaries to identify the origin of SPM at river and stream outlets using their geochemical fingerprints. The deployment of these traps in the Rhône River, the Saône River, and one of its tributaries, the Ardières River, revealed an underestimation of the concentrations of certain trace metal elements (TME) in the SPM collected by this method. These underestimations are not systematic across all TMEs and are not correlated with the granulometric bias previously observed. These results suggest the occurrence of organic matter degradation processes within the trap, potentially releasing TMEs into the dissolved phase. This calls into question the use of TMEs as conservative tracers for sediment origin. To ensure the robustness of this method and to better understand potential degradation processes within the traps, an experimental setup was implemented to monitor changes in TME concentrations over time under controlled conditions in SPM collected using traps. During this experiment, an analytical method for determining TMEs in the residual and conservative fraction of particles was applied to assess whether it could mitigate the effects of potential degradation of particle-associated tracers in the trap. This research addresses a critical challenge in developing a robust and operational method that combines time-integrative SPM sampling with a suitable analytical approach to trace the origin of sediments across hydrosystems.
Session A7 : Questioning the trajectory of rivers to improve action
Evolution and relationship between land use and the active channel over the last half century in the Ebro basin
GARCÍA-RODRÍGUEZ Saioa, SÁENZ DE OLAZAGOITIA Ana, BALLARÍN Daniel, IBISATE Askoa, SÁNCHEZ-FABRE Miguel, ORMAETXEA Orbange, ORTIZ DE ARRI Ibai, MENTXAKA Galder, PIRCHI Valeria, GARCÍA Juan Miguel, FERRER-BOIX Carles, OLLERO Alfredo
Spain
Short abstract : The EbroHydromorph project aims to study the morphological changes of the middle Ebro river (between Logroño and La Zaida) in recent decades, and sediment transport in particular. In a first phase, a historical study of land use changes in the Ebro river basin draining to the end point of the study section is being carried out, with the aim of finding out how this has affected the hydrogeomorphological conditions of the river courses. The elaboration of the cartography of the mid-20th century has been a laborious task carried out by digitising the uses and completing it with some of the maps already drawn up previously in some areas of the studied basin. Land use cover of the mid-20th century have been reconstructed and compared with those available in the 2014 land use mapping, analysing in greater detail the modification of the active channel surfaces of the entire basin, as an indicator of the changes in flow and sediment inputs. The preliminary results show a drastic reduction of active channel surfaces, while forest, artificial and grassland areas have increased.
Urbanization and Development of an “Artificial” Floodplain: the South Platte River Through Denver, Colorado, USA
CHIN Anne, ONEILL Dani, WILSON Gretchen, BOYER Anne-Lise, BELLETI Barbara, REY Louis, PIÉGAY Hervé
United-States
Short abstract : Although floodplains are among the most species-rich ecosystems across Earth’s surface, development on floodplains has become common to meet growing human populations. Many studies have shown how urbanization on floodplains has led to drastic loss of biodiversity and other functional aspects of floodplains at global scales. Few have documented, however, the detailed transformation of floodplains over decadal periods from natural to partly artificial features on the landscape. This study follows the South Platte River floodplain north of the Denver area in Colorado (USA) through rapid urbanization since 1937. Historical and GIS analyses of maps and aerial imagery show changes in land use from agricultural to industrial, along with reductions in wetlands and riparian habitat areas. Remote sensing analysis of the growing number of gravel mining pits on the floodplain also produces a chronology of the management of mining pits as water reservoirs. Shifts in perceptions among residents of the area, revealed through text mining from local newspapers, have accompanied such changes. Results contribute toward informing planners, managers, and communities on the process of urbanizing floodplains. Findings also provide a template for comparison with other examples of urbanizing floodplains around the world.
Studying engineered rivers from the sky: benefits of oblique aerial photographs to inform the socio-environmental trajectory of the Rhône River (1910-1960)
ARNAUD Fanny, JACOB-ROUSSEAU Nicolas, FRIOUX Stéphane, BERTHIER-LAUMOND Salomé, DUNESME Samuel
France
Short abstract : Aerial photographs are commonly used to analyze temporal changes of territories. While vertical images are frequent in diachronic studies, lesser-known oblique images offer a better perception of landscape features, such as topography, vegetation and anthropogenic structures. As part of the Rhône Valley Human-Environment Observatory, a database has been built up from oblique aerial photographs of the Rhône river (1919-1961), taken from the IGN “Remonter le temps” portal. It contains some 200 oblique photographs documenting the Rhône from Lake Geneva to the Mediterranean Sea, enriched with detailed metadata and published in an interactive photo library. This work opens up numerous interdisciplinary research perspectives on the socio-environmental trajectory of the contemporary Rhône river, landscape transformations induced by major engineering works, urbanization and industrialization of the fluvial corridor, or heritage aspects and uses. This iconographic database also provides a wealth of educational material for various stakeholders.
Historical changes in the extent of the flooded area of a mountain river induced by human impacts
HAJDUKIEWICZ Hanna, HAJDUKIEWICZ Maciej, RUIZ-VILLANUEVA Virginia, RADECKI-PAWLIK Artur, ZAWIEJSKA Joanna
Poland
Short abstract : During the 20th century, many mountain rivers in Europe were subjected to intensive human impacts, which significantly altered their channel morphology. However, the influence of these changes on past river responses to floods and channel hydrodynamics remains unclear. In this study, we performed hydraulic modeling using data from archival aerial photographs to assess how human-induced changes affected hydraulic parameters of floods and channel incision between 1964 and 2012, influencing the extent of the flooded area of the Czarny Dunajec River (Polish Carpathians). Data on the vertical position of the channel were extracted (as Digital Elevation Models) from archival aerial photos from 1964 and 1983 and Airborne Laser Scanning-derived DEM from 2012. The values for water depth, flow velocity, and bed shear stress for four flood scenarios of different magnitudes, along with the critical diameter of channel sediment, increased significantly between 1964 and 1983. The flow velocity within the floodplain zone did not increase for the two largest flood scenarios, due to the expansion of riparian forests during the second half of the 20th century. The increase in flow rate was accompanied by a progressive reduction (by 44% for 34 m³/s) in the extent of flooded areas, particularly between 1964 and 1983. Between 1983 and 2012, changes in hydraulic parameters were less pronounced and the reduction in the extent of the flooded area was less significant.
Reducing the scale of analysis and promoting microgeohistory : the example of a high-risk area in the Garonne valley (Couthures-sur-Garonne, Lot et Garonne, France)
VALETTE Philippe, FARGUES Sara, LESPEZ Laurent
France
Short abstract : Analyzing territories using a microgeohistorical approach means taking a closer look. Here, we look at a high-risk area in the Garonne valley, the village of Couthures-sur-Garonne (Lot-et-Garonne) and its relationship with the river over time. The village is located on the concave part of a meander, on the left bank near Marmande. It is particularly affected by floods, which are more frequent than on the rest of the river (February 2003, December 2003, March 2006, January 2009, January 2014, December 2019, February 2021). The recurrence of this hazard, and the risk it poses to local populations, means that we need to understand the shapes, formations and processes that characterize the Garonne, in order to better understand the close relationship between the river and the people who live along its banks. Over the course of time, these interactions have been expressed through vernacular practices and defensive policies designed to protect against both erosion and flooding, demonstrating forms of adaptation to the river’s hazards.
Re-Storying Rivers through Community Engagement: The Detroit River Story Lab
PORTER David
United-States
Short abstract : The successful management of urban river systems requires cultural as well as technical expertise. This paper presents a case study of an interdisciplinary university initiative devoted to fostering stewardship of natural resources in a river city by supporting community-centered narrative infrastructure projects along the river’s shores. Over the past five years, students and faculty at the University of Michigan’s Detroit River Story Lab have helped to catalyze transformative projects in the domains of place-based education, public heritage, and community journalism that demonstrate the critical role played by narrative epistemologies in the long-term success of river restoration efforts. Topics to be covered include research methods, principles of community engagement, and strategies for integrating the natural and human sciences in riverine contexts.