Browsing by Author "Wharton, Geraldene"

Now showing 1 - 3 of 3
  • Thumbnail Image
    ItemOpen Access
    The current state of the use of large wood in river restoration and management
    (Wiley, 2019-03-25) Grabowski, Robert C.; Gurnell, Angela M.; Burgess‐Gamble, Lydia; England, Judy; Holland, David; Klaar, Megan J.; Morrissey, Ian; Uttley, Chris; Wharton, Geraldene
    Trees fall naturally into rivers generating flow heterogeneity, inducing geomorphological features, and creating habitats for biota. Wood is increasingly used in restoration projects and the potential of wood acting as leaky barriers to deliver natural flood management by ‘slowing the flow’ is recognised. However, wood in rivers can pose a risk to infrastructure and locally increase flood hazards. The aim of this paper is to provide an up‐to‐date summary of the benefits and risks associated with using wood to promote geomorphological processes to restore and manage rivers. This summary was developed through a workshop that brought together academics, river managers, restoration practitioners and consultants in the UK to share science and best practice on wood in rivers. A consensus was developed on four key issues: (i) hydrogeomorphological effects, (ii) current use in restoration and management, (iii) uncertainties and risks and (iv) tools and guidance required to inform process‐based restoration and management.
  • Thumbnail Image
    ItemOpen Access
    Plants face the flow in V-formation: a study of plant patch alignment in streams
    (Association for the Sciences of Limnology and Oceanography (ASLO), 2018-12-14) Cornacchia, Loreta; Folkard, Andrew; Davies, Grieg; Grabowski, Robert C.; van de Koppel, Johan; van der Wal, Daphne; Wharton, Geraldene; Puijalon, Sara; Bouma, Tjeerd J.
    Interactions between biological and physical processes, so‐called bio‐physical feedbacks, are important for landscape evolution. While these feedbacks have been quantified for isolated patches of vegetation in aquatic ecosystems, we still lack knowledge of how the location of one patch affects the occurrence of others. To test for patterns in the spatial distribution of vegetation patches in streams, we first measured the distance between Callitriche platycarpa patches using aerial images. Then, we measured the effects of varying patch separation distance on flow velocity, turbulence, and drag on plants in a field manipulation experiment. Lastly, we investigated whether these patterns of patch alignment developed over time following locations of reduced hydrodynamic forces, using 2‐yr field observations of the temporal patch dynamics of Ranunculus penicillatus in a lowland chalk stream. Our results suggest that vegetation patches in streams organize themselves in V‐like shapes to reduce drag forces, creating an optimal configuration that decreases hydrodynamic forces and may therefore encourage patch growth. Downstream patches are more frequently found at the rear and slightly overlapping the upstream patch, in locations that are partially sheltered by the established upstream vegetation while ensuring exposure to incoming flow (important for nutrient availability). Observations of macrophyte patch dynamics over time indicated that neighboring patches tend to grow in a slightly angled line, producing a spatial pattern resembling the V‐formation in migratory birds. These findings point to the general role of bio‐physical interactions in shaping how organisms align themselves spatially to aerodynamic and hydrodynamic flows at a range of scales.
  • Thumbnail Image
    ItemOpen Access
    Self-organization of river vegetation leads to emergent buffering of river flows and water levels
    (The Royal Society, 2020-07-15) Cornacchia, Loreta; Wharton, Geraldene; Davies, Grieg; Grabowski, Robert C.; Temmerman, Stijn; van der Wal, Daphne; Bouma, Tjeerd J.; van de Koppel, Johan
    Global climate change is expected to impact hydrodynamic conditions in stream ecosystems. There is limited understanding of how stream ecosystems interact and possibly adapt to novel hydrodynamic conditions. Combining mathematical modelling with field data, we demonstrate that bio-physical feedback between plant growth and flow redistribution triggers spatial self-organization of in-channel vegetation that buffers for changed hydrological conditions. The interplay of vegetation growth and hydrodynamics results in a spatial separation of the stream into densely vegetated, low-flow zones divided by unvegetated channels of higher flow velocities. This self-organization process decouples both local flow velocities and water levels from the forcing effect of changing stream discharge. Field data from two lowland, baseflow-dominated streams support model predictions and highlight two important stream-level emergent properties: vegetation controls flow conveyance in fast-flowing channels throughout the annual growth cycle, and this buffering of discharge variations maintains water depths and wetted habitat for the stream community. Our results provide important evidence of how plant-driven self-organization allows stream ecosystems to adapt to changing hydrological conditions, maintaining suitable hydrodynamic conditions to support high biodiversity