Dam builders and their works: Beaver influences on the structure and function of river corridor hydrology, geomorphology, biogeochemistry and ecosystems

Beavers (Castor fiber, Castor canadensis) are one of the most influential mammalian ecosystem engineers, heavily modifying river corridor hydrology, geomorphology, nutrient cycling, and ecosystems. As an agent of disturbance, they achieve this first and foremost through dam construction, which impounds flow and increases the extent of open water, and from which all other landscape and ecosystem impacts follow. After a long period of local and regional eradication, beaver populations have been recovering and expanding throughout Europe and North America, as well as an introduced species in South America, prompting a need to comprehensively review the current state of knowledge on how beavers influence the structure and function of river corridors. Here, we synthesize the overall impacts on hydrology, geomorphology, biogeochemistry, and aquatic and terrestrial ecosystems. Our key findings are that a complex of beaver dams can increase surface and subsurface water storage, modify the reach scale partitioning of water budgets, allow site specific flood attenuation, alter low flow hydrology, increase evaporation, increase water and nutrient residence times, increase geomorphic heterogeneity, delay sediment transport, increase carbon, nutrient and sediment storage, expand the extent of anaerobic conditions and interfaces, increase the downstream export of dissolved organic carbon and ammonium, decrease the downstream export of nitrate, increase lotic to lentic habitat transitions and aquatic primary production, induce ‘reverse’ succession in riparian vegetation assemblages, and increase habitat complexity and biodiversity on reach scales. We then examine the key feedbacks and overlaps between these changes caused by beavers, where the decrease in longitudinal hydrologic connectivity create ponds and wetlands, transitions between lentic to lotic ecosystems, increase vertical hydraulic exchange gradients, and biogeochemical cycling per unit stream length, while increased lateral connectivity will determine the extent of open water area and wetland and littoral zone habitats, and induce changes in aquatic and terrestrial ecosystem assemblages. However, the extent of these impacts depends firstly on the hydro-geomorphic landscape context, which determines the extent of floodplain inundation, a key driver of subsequent changes to hydrologic, geomorphic, biogeochemical, and ecosystem dynamics. Secondly, it depends on the length of time beavers can sustain disturbance at a given site, which is constrained by top down (e.g. predation) and bottom up (e.g. competition) feedbacks, and ultimately determines the pathways of river corridor landscape and ecosystem succession following beaver abandonment. This outsized influence of beavers on river corridor processes and feedbacks is also fundamentally distinct from what occurs in their absence. Current river management and restoration practices are therefore open to re-examination in order to account for the impacts of beavers, both positive and negative, such that they can potentially accommodate and enhance the ecosystem engineering services they provide. It is hoped that our synthesis and holistic framework for evaluating beaver impacts can be used in this endeavor by river scientists and managers into the future as beaver populations continue to expand in both numbers and range

Natürlicher und anthropogen veränderter Sedimentfluss in der Vergangenheit im Mittelgebirge Spessart

The Late Quaternary surface processes of a steep gully system in Central Europe occur mainly as multiple gully erosion and sedimentation cycles. These cycles depend largely on the relation between sediment supply and sediment transport capacity. The gully thalweg was aggraded during the Younger Dryas as a result of high sediment supply from the slopes and a diminished transport capacity in the channel instigated by a reduction in vegetation during this time. For the majority of the Holocene time period phases of headward gully incision are the dominant process, which occurs as a result of internal hydrological and geomorphic thresholds under well vegetated conditions. During this time sediment was also deposited on the gully fan. The onset of intense human agricultural activity during medieval times led to large scale slope erosion due to vegetation removal and subsequent thalweg re-aggradation. In comparison with the natural hillslope sediment flux during the Younger Dryas, erosion from human driven slope instability was found to be at least ~2.3 time more efficient. More specifically, it is clear that different land-use techniques on the catchments slopes, as reconstructed from the analysis of soil charcoal analysis, are the dominant control on overall hillslope erosion rates. The lowest erosion rate was found in an area where only small agricultural fields were maintained. The recovery of most of the catchment vegetation in the last ~ 500 years has re-stabilised the slopes and modified the internal threshold of sediment supply/sediment transport capacity, such that the gully has begun a new incision phase. Hence, sediment is again transported from the thalweg into the gully fan and floodplain of the adjacent trunk stream. The quantification of sediment fluxes reveals that the most recent and continuing phase of sediment export is also the most geomorphically significant for the trunk stream, since it is the only time in the last ~15 000 years that a large percentage of the thalweg erosion budget is able to be incorporated into the alluvium of trunk streams. Because the gully system itself has a large storage capacity, sediment delivery from small headwater catchments to trunk streams generally does not occur until vegetation has re-stabilised the slopes, and allows the sediment transport capacity to increase. The recent changes to high sediment delivery to the floodplain and adjacent stream is a possible explanation for the observed floodplain aggradation of trunk streams and the resulting changes to the rivers regime. However, it is also suggested that valley bottom damming for various purposes throughout this time is also a major factor controlling this large change in the rivers behaviour, and the investigation of this direct human impact on the river landscapes of central Europe is a critical avenue of further research.Mehrere Erosions- und Sedimentationszyklen haben die spätquartären Oberflächenprozesse in einem Einzugsgebiet eines Gullys in der Mittelgebirgsregion von Mitteleuropa geprägt. Diese Zyklen sind im Wesentlichen vom Quotienten zwischen Sedimentzufuhr und Sedimenttransportkapazität abhängig. Der Thalweg fungierte während der Jüngeren Dryas als Folge der hohen Sedimentzufuhr von den Hängen als Sedimentfalle, da keine schützende Vegetationsdecke die Hänge mehr bedeckte. Während des weitaus größten Teils des Holozäns war das Einzugsgebiet bewaldet und die Hänge daher stabil. Daraus ergab sich eine hohe Erosions- und Transportkapazität des Oberflächenabfluss im Thalweg und die daraus folgende Rückverlagerung des Gully-Kopfes, was widerum eine Ablagerung von Sedimenten im Bereich des Schwemmfächers zur Folge hatte. Der Beginn intensiver ackerbaulicher Tätigkeiten im Mittelalter führte durch die großflächige Bewirtschaftung der Hänge zu Hangerosion und zu einem erneuten Anwachsen der Thalwegsedimente. Die Menge des im Mittelalter erodierten Hangmaterials überstieg den der Jüngeren Dryas um den Faktor 2.3. Detaillierte Analysen von Hangsedimenten und den darin enthaltenen Holzkohlen zeigt, dass verschiedene Formen der Landnutzung unterschiedlich hohe Erosionsraten verursachten, mit dem geringsten Hangabtrag in den Bereichen, in denen kleine Feldgrößen vorherrschten. Die Wiederbewaldung des größten Teils des Einzugsgebiets vor ca. 500 Jahren stabilisierte die Hänge und führte zu einer erneuten Einschneidungsphase des Gullies, was erneuten Sedimenttransport zum Schwemmfächer und in den Vorfluter und dessen Aue zur Folge hatte. Die Quantifizierung und Bilanzierung des Sedimentflusses zeigt, dass dies die einzige Phase in den letzten ~ 15000 Jahren war, die den Transport einer geomorpholgisch relevanten Menge von Sedimenten in den Vorfluter verursachte, welche vom Fluss aufgenommen und in die Auelehme eingearbeitet wurden. Dies ist ein möglicher Grund für das beobachtete Anwachsen der Auelehme, aber auch Talverbauungen wie Mühlwehre spielten vermutlich eine große Rolle. Die Erforschung dieses direkten Einflusses des Menschen auf die Flusslandschaften ist ein Forschungsprojekt, das aus der hier vorliegenden Arbeit hervorgehen kann

Three major steps toward the conservation of freshwater and riparian biodiversity

J.M. and J.H. thank Stiftelsen Längmanska kulturfonden for funding travel to the conference. As.L. and K.R. thank the Estonian Research Council (grant 1121) for financial support, and A.M. acknowledges the Leverhulme Trust (RPG-2019-402). H.H. was supported by the European Union Horizon 2020 Research and Innovation Programme under the Marie Sklodowska-Curie Actions (grant agreement 860800): RIBES (river flow regulation, fish behaviour, and status), and V.A. acknowledges the support from the Leibniz Competition project Freshwater Megafauna Futures. E.J. received support through the National Laboratory for Health Security (RRF-2.3.1-21-2022-00006), Centre for Ecological Research, Budapest, Hungary, and thanks Z. Molnár for support.Freshwater ecosystems and their bordering wetlands and riparian zones are vital for human society and biological diversity. Yet, they are among the most degraded ecosystems, where sharp declines in biodiversity are driven by human activities, such as hydropower development, agriculture, forestry, and fisheries. Because freshwater ecosystems are characterized by strongly reciprocal linkages with surrounding landscapes, human activities that encroach on or degrade riparian zones ultimately lead to declines in freshwater–riparian ecosystem functioning. We synthesized results of a symposium on freshwater, riparian, and wetland processes and interactions and analyzed some of the major problems associated with improving freshwater and riparian research and management. Three distinct barriers are the lack of involvement of local people in conservation research and management, absence of adequate measurement of biodiversity in freshwater and riparian ecosystems, and separate legislation and policy on riparian and freshwater management. Based on our findings, we argue that freshwater and riparian research and conservation efforts should be integrated more explicitly. Best practices for overcoming the 3 major barriers to improved conservation include more and sustainable use of traditional and other forms of local ecological knowledge, choosing appropriate metrics for ecological research and monitoring of restoration efforts, and mirroring the close links between riparian and freshwater ecosystems in legislation and policy. Integrating these 3 angles in conservation science and practice will provide substantial benefits in addressing the freshwater biodiversity crisis.Peer reviewe

Ubiquitous LEA29Y Expression Blocks T Cell Co-Stimulation but Permits Sexual Reproduction in Genetically Modified Pigs

We have successfully established and characterized a genetically modified pig line with ubiquitous expression of LEA29Y, a human CTLA4-Ig derivate. LEA29Y binds human B7.1/CD80 and B7.2/CD86 with high affinity and is thus a potent inhibitor of T cell co-stimulation via this pathway. We have characterized the expression pattern and the biological function of the transgene as well as its impact on the porcine immune system and have evaluated the potential of these transgenic pigs to propagate via assisted breeding methods. The analysis of LEA29Y expression in serum and multiple organs of CAG-LEA transgenic pigs revealed that these animals produce a biologically active transgenic product at a considerable level. They present with an immune system affected by transgene expression, but can be maintained until sexual maturity and propagated by assisted reproduction techniques. Based on previous experience with pancreatic islets expressing LEA29Y, tissues from CAG-LEA29Y transgenic pigs should be protected against rejection by human T cells. Furthermore, their immune-compromised phenotype makes CAG-LEA29Y transgenic pigs an interesting large animal model for testing human cell therapies and will provide an important tool for further clarifying the LEA29Y mode of action

FRI0192 A SYSTEMATIC LITERATURE REVIEW TO INFORM THE 2019 UPDATE OF THE EULAR RECOMMENDATIONS FOR THE TREATMENT OF SYSTEMIC LUPUS ERYTHEMATOSUS

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