Rewilding and the water cycle

Rewilding is a radical approach to landscape conservation that has the potential to help mitigate flood risk and low flow stresses, but this remains largely unexplored. Here, we illustrate the nature of hydrological changes that rewilding can be expected to deliver through reducing or ceasing land management, natural vegetation regeneration, species (re)introductions, and changes to river networks. This includes major changes to above- and below-ground vegetation structure (and hence interception, evapotranspiration, infiltration, and hydraulic roughness), soil hydrological properties, and the biophysical structure of river channels. The novel, complex, uncertain, and longer-term nature of rewilding-driven change generates some key challenges, and rewilding is currently relatively constrained in geographical extent. Significant changes to the water cycle that benefit people and nature are possible but there is an urgent need for improved understanding and prediction of rewilding trajectories and their hydrological effects, generation of the knowledge and tools to facilitate stakeholder engagement, and an extension of the geography of rewilding opportunities. This article is categorized under: Science of Water > Hydrological Processes Science of Water > Water Extremes Water and Life > Conservation, Management, and Awareness

BPS black holes, the Hesse potential, and the topological string

The Hesse potential is constructed for a class of four-dimensional N=2 supersymmetric effective actions with S- and T-duality by performing the relevant Legendre transform by iteration. It is a function of fields that transform under duality according to an arithmetic subgroup of the classical dualities reflecting the monodromies of the underlying string compactification. These transformations are not subject to corrections, unlike the transformations of the fields that appear in the effective action which are affected by the presence of higher-derivative couplings. The class of actions that are considered includes those of the FHSV and the STU model. We also consider heterotic N=4 supersymmetric compactifications. The Hesse potential, which is equal to the free energy function for BPS black holes, is manifestly duality invariant. Generically it can be expanded in terms of powers of the modulus that represents the inverse topological string coupling constant, $g_s$, and its complex conjugate. The terms depending holomorphically on $g_s$ are expected to correspond to the topological string partition function and this expectation is explicitly verified in two cases. Terms proportional to mixed powers of $g_s$ and $\bar g_s$ are in principle present.Comment: 28 pages, LaTeX, added comment

Combined stable-isotope and fatty-acid analyses demonstrate that large wood increases the autochthonous trophic base of a macroinvertebrate assemblage

This research was carried out within the Erasmus Mundus Doctorate Program SMART (http://www.riverscience.eu) funded by the Education, Audiovisual and Culture Executive Agency (EACEA) of the European commission

Wood mitigates the effect of hydropeaking scour on periphyton biomass and nutritional quality in semi-natural flume simulations

The daily fluctuating discharge from hydroelectric power plants, known as hydropeaking, has been shown to cause catastrophic drift in aquatic insect communities and limit secondary production, but relatively little attention has been given to its effects on periphyton, an important food resource for consumers. We simulated daily 5-h hydropeaking events over the course of 5 days in spring and summer in an open air, experimental flume system fed by a pristine 2nd order stream in the Italian Alps. We hypothesized that hydropeaking would suppress periphyton biomass and especially nutritional quality (i.e., fatty acid content). Hydropeaking resulted in decreased periphyton Chl-a and AFDM on tiles, but there was no corresponding loss on wood. Hydropeaking did not alter periphyton elemental nutrient stoichiometry but led to a disproportionate loss of periphyton fatty acid content on both substrates. Ordination of overall fatty acid profiles indicated different periphyton fatty acid profiles by substrate and a shift from physiologically important highly-unsaturated fatty acids to non-essential saturated fatty acids after hydropeaking. These results suggest that hydropeaking may have the potential to depress primary biomass and nutritional quality in downstream ecosystems, and that availability of wood substrate may mitigate part, but not all, of this effect. Since food nutritional quality, especially fatty acid content, has been suggested to be a limiting resource on production in aquatic systems, this may generate an indirect and potentially overlooked limiting effect on aquatic consumers in hydropeaking-impacted alpine rivers

The role of rewilding in mitigating hydrological extremes: State of the evidence

Landscape rewilding has the potential to help mitigate hydrological extremes by allowing natural processes to function. Our systematic review assessed the evidence base for rewilding-driven mitigation of high and low flows. The review uncovers a lack of research directly addressing rewilding, but highlights research in analogue contexts which can, with caution, indicate the nature of change. There is a lack of before-after studies that enable deeper examination of temporal trajectories and legacy effects, and a lack of research on the scrub and shrubland habitats common in rewilding projects. Over twice as much evidence is available for high flows compared to low flows, and fewer than one third of studies address high and low flows simultaneously, limiting our understanding of co-benefits and contrasting effects. Flow magnitude variables are better represented within the literature than flow timing variables, and there is greater emphasis on modeling for high flows, and on direct measurement for low flows. Most high flow studies report a mitigating effect, but with variability in the magnitude of effect, and some exceptions. The nature of change for low flows is more complex and suggests a higher potential for increased low flow risks associated with certain trajectories but is based on a very narrow evidence base. We recommend that future research aims to: capture effects on both high and low flow extremes for a given type of change; analyze both magnitude and timing characteristics of flow extremes; and examine temporal trajectories (before and after data) ideally using a full before-after-control-impact design. This article is categorized under: Human Water > Value of Water Science of Water > Hydrological Processes Science of Water > Water Extremes Water and Life > Conservation, Management, and Awareness

Trends in the use of large wood in UK river restoration projects: insights from the National River Restoration Inventory

Large Wood (LW) is increasingly employed in river restoration to promote physical habitat heterogeneity and ecological diversity. To explore how LW has been used in restoration schemes across the United Kingdom in recent decades, we analysed data on 912 LW projects archived in the UK’s National River Restoration Inventory (NRRI). The number of LW schemes has continued to increase following the earliest records in the 1990s, largely tracking overall trends in river restorations. LW projects have been predominantly located in lowland, rural streams, although there has been a notable cluster in and around London. LW projects have mainly revolved around the desire to deliver hydromorphological improvements and specifically the creation of fish habitat. Most schemes used LW in simple deflector forms despite the growing scientific evidence of the benefits of using structurally complex LW. Post project monitoring has been limited and mostly restricted to photographic records. This type of database analysis can provide important insights and help guide future restoration practice

The impact of pre-restoration land-use and disturbance on sediment structure, hydrology and the sediment geochemical environment in restored saltmarshes

Saltmarshes are being lost or degraded as a result of human activity resulting in loss of critical ecosystem services including the provision of wild species diversity, water quality regulation and flood regulation. To compensate, saltmarshes are being restored or re-created, usually driven by legislative requirements for increased habitat diversity, flood regulation and sustainable coastal defense. Yet, there is increasing evidence that restoration may not deliver anticipated ecosystem services; this is frequently attributed to poor drainage and sediment anoxia. However, physical sediment characteristics, hydrology and the sediment geochemical environment are rarely examined in restoration schemes, despite such factors being critical for plant succession. This study presents the novel integration of 3D-computed X-ray microtomography to quantify sediment structure and porosity, with water level and geochemical data to understand the impact of pre-restoration land use and disturbance on the structure and functioning of restored saltmarshes. The study combines a broad-scale investigation of physical sediment characteristics in nine de-embanked saltmarshes across SE England, with an intensive study at one site examining water levels, sediment structure and the sediment geochemical environment. De-embankment does not restore the hydrological regime, or the physical/chemical framework in the saltmarshes and evidence of disturbance includes a reduction in microporosity, pore connectivity and water storage capacity, a lack of connectivity between the sub-surface environment and overlying floodwaters, and impeded sub-surface water flow and drainage. This has significant consequences for the sediment geochemical environment. This disturbance is evident for at least two decades following restoration and is likely to be irreversible. It has important implications for plant establishment in particular, ecosystem services including flood regulation, nutrient cycling and wild species diversity and for future restoration design