Litter selfie : a citizen science guide for photorecording macroplastic deposition along mountain rivers using a smartphone

Macroplastic pollution in mountain rivers can threaten water resources, biodiversity, and the recreational values provided by them. The first step towards evaluating and then mitigating these risks is the systematic collection of reliable and spatially uniform data on the amount and type of macroplastics deposited in different land covers occurring in a mountain river channel. To maximise the opportunity for the large-scale collection of such data using the citizen science approach, we propose in this study an illustrated step-by-step guide to sample the macroplastic deposited along mountain rivers and to record the collected information using a photo taken by smartphone and a simple online form. Our guide includes three steps: (i) the location of sampling plots across 3-4 predefined surface covers occurring in mountain rivers of temperate climate, (ii) the hand collection of macroplastic deposited in them, and (iii) the photorecording and archiving of information on macroplastics collected using a smartphone and an online form. The proposed guide can allow for the low-cost collection of data on macroplastic deposition in mountain rivers on regional and global scales. The collected data can be further analysed by environmental scientists to quantify the amount and types of macroplastic deposited and to evaluate the resulting risks. They can be also used as illustrative materials to increase the awareness of local communities about the plastic pollution problem

Quelles améliorations sont nécessaires pour garantir la qualité des eaux de nos rivières? : nouveau regard sur l'utilisation d'indices biot iques dans l'évaluation de la santé des cours d'eau

Benthic invertebrate-based indexes are commonly used as proxies for river health, especially river water quality. Scores of BMWP-PL index (a Polish equivalent of the British Biological Monitoring Working Party score system) were determined for 20 unmanaged and channelized cross-sections of the Biała River and compared with water quality and physical habitat parameters in the cross-sections. The two types of cross-sections clearly differed in the physical habitat conditions, whereas physico-chemical parameters of the river water mostly varied in the downstream direction. The number of recorded taxa ranged from 3 to 26 and the respective scores of the BMWP-PL index indicated the water to vary between high and poor quality. Since the analysed water quality was consistently high, the BMWP-PL scores were not related to physico-chemical parameters of the water but to physical habitat parameters, with the number of low-flow channels explaining the largest proportion of the variance in the index values. The lacking dependence on physico-chemical water parameters renders the BMWP-PL as indicator of the ecological integrity of rivers, related to their hydromorphological and physico-chemical characteristics, rather than of water quality

River widening in mountain and foothill areas during floods: Insights from a meta-analysis of 51 European Rivers

River widening, defined as a lateral expansion of the channel, is a critical process that maintains fluvial ecosystems and is part of the regular functioning of rivers. However, in areas with high population density, channel widening can cause damage during floods. Therefore, for effective flood risk management it is essential to identify river reaches where abrupt channel widening may occur. Despite numerous efforts to predict channel widening, most studies have been limited to single rivers and single flood events, which may not be representative of other conditions. Moreover, a multi-catchment scale approach that covers various settings and flood magnitudes has been lacking. In this study, we fill this gap by compiling a large database comprising 1564 river reaches in several mountain regions in Europe affected by floods of varying magnitudes in the last six decades. By applying a meta-analysis, we aimed to identify the types of floods responsible for more extensive widening, the river reach types where intense widening is more likely to occur, and the hydraulic and morphological variables that explain widening and can aid in predicting widening. Our analysis revealed seven groups of reaches with significantly different responses to floods regarding width ratios (i.e., the ratio between channel width after and before a flood). Among these groups, the river reaches located in the Mediterranean region and affected by extreme floods triggered by short and intense precipitation events showed significantly larger widening than other river reaches in other regions. Additionally, the meta-analysis confirmed valley confinement as a critical morphological variable that controls channel widening but showed that it is not the only controlling factor. We proposed new statistical models to identify river reaches prone to widening, estimate potential channel width after a flood, and compute upper bound width ratios. These findings can inform flood hazard evaluations and the design of mitigation measures

Exploring large wood retention and deposition in contrasting river morphologies linking numerical modelling and field observations

Large wood tends to be deposited in specific geomorphic units within rivers. Nevertheless, predicting the spatial distribution of wood deposits once wood enters a river is still difficult because of the inherent complexity of its dynamics. In addition, the lack of long‐term observations or monitored sites has usually resulted in a rather incomplete understanding of the main factors controlling wood deposition under natural conditions. In this study, the deposition of large wood was investigated in the Czarny Dunajec River, Polish Carpathians, by linking numerical modelling and field observations so as to identify the main factors influencing wood retention in rivers. Results show that wood retention capacity is higher in unmanaged multi‐thread channels than in channelized, single‐thread reaches. We also identify preferential sites for wood deposition based on the probability of deposition under different flood scenarios, and observe different deposition patterns depending on the geomorphic configuration of the study reach. In addition, results indicate that wood is not always deposited in the geomorphic units with the highest roughness, except for low‐magnitude floods. We conclude that wood deposition is controlled by flood magnitude and the elevation of flooded surfaces in relation to the low‐flow water surface. In that sense, the elevation at which wood is deposited in rivers will differ between floods of different magnitude. Therefore, together with the morphology, flood magnitude represents the most significant control on wood deposition in mountain rivers wider than the height of riparian trees

The role of flood hydrograph in the remobilization of large wood in a wide mountain river

Floods can mobilize large amounts of unconsolidated material, which also includes large wood in forested river basins. Yet, the influence of the shape and volume of flood hydrographs on wood dynamics in rivers remains poorly understood. Quantitative data on this relation are, however, critically needed to properly address management strategies and to improve the relevant understanding of wood dynamics in rivers. In this work we used a deterministic model, run in a multi-scenario mode, to simulate the transport of wood pieces fully coupled to hydrodynamics. The goal was to analyze how the transport of large wood occurs under different unsteady flood scenarios. We applied the model to two contrasting geomorphic configurations (channelized, single-thread and multi-thread reaches) in the Czarny Dunajec River in Poland, where extensive field observations of wood transport and deposition after floods of different magnitude were available to validate, interpret, and discuss model results. We show that the peak of wood transport is generally reached before the flood peak, and that the wood remobilization ratio is not always positively correlated to peak discharge. We found a positive correlation between the number of mobilized wood pieces and the duration of the rising limb. In addition, hysteresis was observed in the relationship between wood remobilization and discharge. We conclude that numerical modelling allows analysis of wood dynamics in a detail which cannot typically be achieved in field observations. Therefore, modelling improves our understanding of the process and helps disentangling the complex linkages between flood hydrographs and large wood transport dynamics in rivers