Macroinvertebrate Diversity Distribution and Response to Climate Change in Running Waters of Switzerland

In Switzerland, the mean annual temperature has increased by approximatively 2°C since 1864, for the most part in the last 40 years, and the temperature is expected to keep increasing. The warming of water and the changes in the flow regime are very likely to affect freshwater ecosystems. Rivers and streams of Switzerland suffer multiple anthropogenic pressures that impact their physicochemical and morphological properties. This results in a significant proportion of running waters showing a poor biological state, and climate change imposes an additional stress to biodiversity, increasing the species extinction risk. So far, no study has formally predicted (i.e. through predictive models) the potential impacts of climate change on Swiss river and stream biodiversity. Despite all the uncertainties inherent to any modelization process in ecology, this thesis aims at filling this gap using niche-based models, and at offering a countrywide insight into the running water biodiversity in the face of climate change. More generally, it informs about the main drivers of stream biodiversity of temperate mountainous regions that are impacted by human activity, and provides insights into the relative importance of the climate change threat for running water ecosystems.En Suisse, la température annuelle moyenne a augmenté d'environ 2°C depuis 1864, en grande partie au cours des 40 dernières années, et cette tendance devrait se poursuivre dans le futur. L'augmentation de la température de l'eau ainsi que les altérations des régimes hydrologiques risquent fortement d'impacter les écosystèmes d'eau douce. Les rivières suisse subissent de multiples pressions anthropiques impactant certaines de leurs propriétés physicochimiques et morphologiques. L'altération de ces propriétés provoque une diminution générale du potentiel biologique des cours d'eau, et le changement climatique représente une pression supplémentaire sur la biodiversité, augmentant ainsi le risque d'extinction des espèces. Jusqu'à présent, aucune étude n'a formellement prédit (i.e. par le biais de modèles prédictifs) les impacts potentiels du changement climatique sur la biodiversité des cours d'eau en Suisse. Malgré les incertitudes inhérentes à la modélisation écologique, cette thèse vise à combler cette lacune en utilisant des modèles basés sur le concept de niches écologiques, et à évaluer la biodiversité des eaux courantes à l'échelle nationale face au changement climatique. Plus généralement, elle informe sur les principaux moteurs de la biodiversité des cours d'eau des régions montagneuses tempérées qui sont impactées par l'activité humaine, et évalue l'importance relative de la menace du changement climatique pour les écosystèmes d'eau courante

Assessment of the aquatic macroinvertebrate communities in seven cut-off channels in the French Upper-Rhône River, ten years after the restoration works

1) A functional analysis of aquatic invertebrate assemblages was carried out to supplement a more traditional analysis of taxonomic composition in a restored floodplain of the French Upper-Rhône. The data originated from the long-term (2003-2015) monitoring of seven lateral or cut-off channels in the Belley sector. The restoration of the floodplain occurred in winter 2004-2005 and comprised an increase in the residual flow in the by-passed river and the dredging or reconnection of some floodplain channels. Both measures increased the lateral hydrological connectivity between the river and the floodplain water-bodies. 2) Taxonomic composition and three taxonomic metrics, i.e. rarefied richness, relative abundance of alien species, and Ephemeroptera, Trichoptera and Plecoptera (EPT) richness, were analyzed for up-and downstream sites of six restored and one control cut-off channels. In parallel, 11 traits divided in 59 categories were selected to analyze the trait composition. Three complementary functional diversity indices and seven metrics from Merritt et al. (2002) used as surrogates of ecosystem attributes to provide an insight into functional ecosystem processes. 3) In contrast to our expectations, neither a functional homogenization due to the overall increase of lateral connectivity nor similar patterns of changes in comparable sites were observed. This reflects a high taxonomic and functional diversity between sites. The majority of the biotic variables we assessed at the site scale fluctuated between years, and though dificult to quantify, this suggests a level of dynamism that we interpret as a positive sign in the recovery of a 'living and flowing' Rhône River, as expressed in the original aims of the restoration project. 4) The study points the need to improve our understanding of the cut-off channel functioning to optimize ecological restoration projects of large floodplain sectors. We were also faced with issues related to trait information and we suggest that direct field or laboratory measurements of the traits carried by 'actual' individuals, and linking them with the ecosystem functioning would provide more precise and meaningful functional analyses

Assessment of the stream invertebrate β‐diversity along an elevation gradient using a bidimensional null model analysis

[Formula: see text] ‐Diversity, commonly defined as the compositional variation among localities that links local diversity (α‐diversity) and regional diversity (γ‐diversity), can arise from two different ecological phenomena, namely the spatial species turnover (i.e., species replacement) and the nestedness of assemblages (i.e., species loss). However, any assessment that does not account for stochasticity in community assembly could be biased and misinform conservation management. In this study, we aimed to provide a better understanding of the overall ecological phenomena underlying stream [Formula: see text] ‐diversity along elevation gradients and to contribute to the rich debate on null model approaches to identify nonrandom patterns in the distribution of taxa. Based on presence‐absence data of 78 stream invertebrate families from 309 sites located in the Swiss Alpine region, we analyzed the effect size of nonrandom spatial distribution of stream invertebrates on the [Formula: see text] ‐diversity and its two components (i.e., turnover and nestedness). We used a modeling framework that allows exploring the complete range of existing algorithms used in null model analysis and assessing how distribution patterns vary according to an array of possible ecological assumptions. Overall, the turnover of stream invertebrates and the nestedness of assemblages were significantly lower and higher, respectively, than the ones expected by chance. This pattern increased with elevation, and the consistent trend observed along the altitudinal gradient, even in the most conservative analysis, strengthened our findings. Our study suggests that deterministic distribution of stream invertebrates in the Swiss Alpine region is significantly driven by differential dispersal capacity and environmental stress gradients. As long as the ecological assumptions for constructing the null models and their implications are acknowledged, we believe that they still represent useful tools to measure the effect size of nonrandom spatial distribution of taxa on [Formula: see text] ‐diversity

inAccessMod: An R package to automate data downloading and processing for AccessMod

inAccessMod is an R package that simplifies the process of downloading and preparing geospatial layers required for AccessMod, an official software from the World Health Organization (WHO) used to model physical accessibility to healthcare. The package makes it easy to prepare all necessary inputs by automating tasks such as data downloading, cropping, masking, projection, and resampling with easy-to-use functions. inAccessMod includes additional functions that help users modify inputs and perform complex analyses like merging sub-national travel scenarios. The package also facilitates handling of health facility data from The Health Resources and Services Availability Monitoring System (WHO/HeRAMS) (WHO, 2022), and performs specialized result assessments like ranking of health facilities based on their coverage

Improved Landsat-based snow cover mapping accuracy using a spatiotemporal NDSI and generalized linear mixed model

Snow cover extent and distribution over the years have a significant impact on hydrological, terrestrial, and climatologic processes. Snow cover mapping accuracy using remote sensing data is then particularly important. This study analyses Landsat-8 NDSI snow cover datasets over time and space using different NDSI-based approach. The objectives are (i) to investigate the relation snow-NDSI with different environmental variables, (ii) to evaluate the accuracy of the common NDSI threshold of 0.4 against in-situ snow depth measurement and (iii) to develop a method that optimises snow cover mapping accuracy and minimises snow cover detection errors of omission and commission. Landsat-8 snow cover datasets were compared to ground snow depth measurements of climate stations over Switzerland for the period 2014–2020. It was found that there is a consistent relationship between NDSI values and land cover type, elevation, seasons, and snow depth measurements. The global NDSI threshold of 0.4 may not be always optimal for the Swiss territory and tends to underestimate the snow cover extent. Best NDSI thresholds vary spatially and are generally lower than 0.4 for the three snow depth threshold tested. We therefore propose a new spatiotemporal NDSI method to maximize snow cover mapping accuracy by using a generalized linear mixed model (GLMM). This model uses three environmental variables (i.e., elevation, land cover type and seasons) and raw NDSI values and improves snow cover mapping accuracy by 24% compared to the fixed threshold of 0.4. By using this method omissions errors decrease considerably while keeping a very low value of commission errors. This method will then be integrated in the Snow Observation from Space (SOfS) algorithm used for snow detection in Switzerland

The interplay of flow processes shapes aquatic invertebrate successions in floodplain channels - A modelling applied to restoration scenarios

The high biotic diversity supported byfloodplains is ruled by the interplay of geomorphic and hydrological pro-cesses at various time scales, from dailyfluctuations to decennial successions. Because understanding such pro-cesses is a key question in river restoration, we attempted to model changes in taxonomic richness in anassemblage of 58 macroinvertebrate taxa (21 gastropoda and 37 ephemeroptera, plecoptera and trichoptera,EPT) along two successional sequences typical for former braided channels. Individual models relating the occur-rence of taxa to overflow and backflow durations were developed fromfield measurements in 19floodplainchannels of the Rhônefloodplain (France) monitored over 10 years. The models were combined to simulate di-versity changes along a progressive alluviation and disconnection sequence after the reconnection with the mainriver of a previously isolated channel. Two scenarios were considered: (i) an upstream + downstream reconnec-tion creating a lotic channel, (ii) a downstream reconnection creating a semi-lotic channel. Reconnection led to adirect increase in invertebrate richness (on average x2.5). However, taxonomical richness showed a constant de-crease asisolationprogressedand reachedanaverage of 2 for EPTand 7 for gastropodsatthe end of the scenarios.With more than 80% of the taxonomic models with an AUC equal or higher than 0.7 and slopes of linear relationsbetween observed and predicted richness of 0.75 (gastropods) and 1 (EPT), the Boosted Regression Trees (BRT)provided a goodbasis for prediction ofspeciesassemblages. These models canbeusedto quantify a priorithe sus-tainability and ecological efficiency of restoration actions and helpfloodplain restoration planning andmanagement

Thermal regime, together with lateral connectivity, control aquatic invertebrate composition in river floodplains

International audience1. Large river floodplains are dynamic environments, where alternating low and high flows are key ecological processes shaping aquatic biota. As a result of fluctuations in flow in floodplain channels, the diversity of benthic assemblages is assumed to result from the balance between surface flow connections, which are dominant during high flows, and groundwater inputs, which are dominant during low flows. However, the relative importance of these inputs in explaining aquatic invertebrate diversity has never been tested. 2. The response of aquatic invertebrates to hydrological changes of a river flood-plain was investigated in seven braided and six braided-anastomosed flood-plain channels of the French upper Rhône River that are fed by three different processes: groundwater supply (which controls the thermal inertia of the water bodies), surface slow flow connections (i.e. diffuse overbank flows; passive overflow), and surface shear stress-related connections (i.e. condensed flows; active overflow) during high flows. 3. Generalised dissimilarity models indicated that floodplain invertebrate composition had complex relationships with the three processes considered. The relative importance of the latter appeared dependent upon the morphology of the floodplain channels. In the braided channels, the effects of shear stress-related connections were more prominent than in the anastomosed ones, for which the effects of the three processes were more similar. 4. Overall, the diversity of flow connections, that is, lateral surface water connections (both shear stress-related and slow, as defined above) and vertical connection with groundwater (inferred through thermal inertia) enhanced the species turnover at the reach scale. Thermal inertia influenced invertebrate composition when, during low flow periods, surface flow connections had limited effect. 5. Our results highlighted that the role of hydrologic connectivity upon flood-plain diversity cannot be reduced to a single process. They also indicate the importance of vertical connectivity for maintaining biodiversity in floodplain habitats where surface flow connectivity is neither frequent nor constant

Impacts of climate change on aquatic insects in temperate alpine regions: Complementary modeling approaches applied to Swiss rivers

Freshwater biodiversity loss is a major concern, and global warming is already playing a significant role in species extinctions. Our main goal was to predict climate change impacts on aquatic insect species distribution and richness in Swiss running waters according to two climate change scenarios (RCP2.6 and RCP8.5), using different modeling approaches, that is, species distribution models (SDMs), stacked-SDMs (S-SDMs) and a macroecological model (MEM). We analyzed 10,808 reaches, used as spatial units for model predictions, for a total river network length of 20,610 km. Results were assessed at both the countrywide and the biogeographic regional scales. We used incidence data of 41 species of Ephemeroptera, Plecoptera and Trichoptera (EPT) from 259 sites distributed across Switzerland. We integrated a coupled model for hydrology and glacier retreat to simulate monthly time-step discharge from which we derived hydrological variables. These, along with thermal, land-cover, topographic and spatially explicit data, served as predictors for our ecological models. Predictions of occurrence probabilities and EPT richness were compared among the different regions, periods and scenarios. A Shiny web application was developed to interactively explore all the models' details, to ensure transparency and promote the sharing of information. MEM and S-SDMs approaches consistently showed that overall, climate change is likely to reduce EPT richness. Decrease could be around 10% in the least conservative scenario, depending on the region. Global warming was shown to represent a threat to species from high elevation, but in terms of species richness, running waters from lowlands and medium elevation seemed more vulnerable. Finally, our results suggested that the effects of anthropogenic activities could overweight natural factors in shaping the future of river biodiversity

SWATCH21: a project for linking eco-hydrologic processes and services to aquatic biodiversity at river and catchment levels

The objective of the SWATCH21 project is to improve our understanding of eco-hydrologic services at the catchment level, and biodiversity at the river scale. Six research questions are proposed: (i) How can we improve the access to input data for hydrological and ecological modeling? (ii) What is the role of glacier and snow in modifying the hydrological services? (iii) How can we best assess hydrologic services supplies and demands with the available data and tools? (iv) What will be the impact of the main hydrologic changes on species diversity in rivers? (v) Can we meet the targets of multi-sectorial river-related policies under different climate and landuse forecasting scenarios? (vi) How detailed do ES data and models need to be to answer relevant policy questions? The above questions are tackled through an integrated framework to access, share, process, model, and deliberate on hydrologic ecosystems services. State-of-the-art models have been selected, and will be compared and improved to model different ecosystems and their services. Initial results from a first SWAT model of Switzerland and Species Distribution Models are presented. Expected outputs from various climate and land use change scenarios include rivers' hydrology, predicted biodiversity, and the assessment of ecosystem services in terms of provisioning services (e.g. water resources), regulating services (e.g. nutrient, sediment and flood water retention), and cultural services (e.g. biodiversity, recreation). The expected outcome of the project is to improve integrated evidence-based water policy in the future through the analysis of tradeoffs and synergies between services