2,599 research outputs found
Characterization of Hydraulic Habitat and Retention Characteristics Across Different Channel Types; Introducing a New Field-based Technique
No full textUnderstanding the interactions between
physical habitat and aquatic biodiversity has become a
key research objective in river management. River
research and management practitioners are increasingly
seeking new methodologies and techniques for
characterizing physical habitat heterogeneity. The
physical biotope has been widely employed as the
standard mesoscale unit in river surveys. However,
few surveys have quantified the combined physical
heterogeneity at the meso- and microscale scale via a
single technique. This paper describes a new field
methodology for assessing variations in hydraulic
habitat and retention across different channel types
(e.g. step-pool, bedrock, plane-bed and pool-riffle).
Hydraulic habitat and retention was measured by
timing 100 flow tracers across a 100-m stream length,
and recording the types of trapping structures. The
pattern of flow tracers and retention varied significantly
between channel types and structures. Rocks
(boulders and cobbles) were more important retentive
structures than eddies and snags (woody material and
vegetation). The results indicate the importance of a
diverse hydraulic environment, woody material and
channel substrate character in increasing physical
heterogeneity within a stream reach. The findings
suggest that the field methodology may be an effective
tool to assess differences in physical heterogeneity pre
and post river restoration activities
Imperialist women in Edwardian Britain : the Victoria League, 1899-1914
No full textThis thesis, based on private papers, society records, autobiographies and
memoirs, newspapers and periodicals, examines one mainly female imperialist
organisation - the Victoria League - and the women who ran it. It considers two related
questions - what made Edwardian women imperialist, and how, within the limits of
Edwardian society, could they express their imperialism? The thesis shows that several of
the League's founders and executive had visited South Africa during or shortly before
the Boer War, and that this experience, particularly for those who came into close contact
with Milner, was pivotal in stimulating them to active imperialism. The Victoria League,
founded April 1901, aimed to promote imperial unity and a British South Africa in a
variety of suitably 'womanly' ways: Boer War charities, imperial education, exporting
literature and art to the white dominions (particularly the Transvaal), welcoming colonial
visitors to Britain, arranging for the welcome of British settlers in the colonies, and
promoting social reform as an imperial issue. It worked overseas through a number of
independent Victoria Leagues in Australasia, the Imperial Order, Daughters of the Empire
in Canada, and the Guild of Loyal Women in South Africa; and at home with a number
of similar (though largely male) imperial propaganda societies. The thesis also considers
the Victoria League's attitude to race, particularly through its debate over entertaining
Indian students. It ends with a discussion of the options available to imperialist women;
and of the obstacles they faced in questions of authority (how far and in what ways a woman
could pronounce on imperial subjects) and of ideology (as expressed through the anti-suffrage
campaign). It concludes that the Victoria League, by transferring areas of
activity long acknowledged as 'feminine' to the imperial stage, redefined areas of female
competence and enlarged woman's 'separate sphere' to include the active propagation of
imperialism
An Assessment of Variants in the Professional Judgement of Geomorphologically-based Channel Types.
No full textRiver classification is a useful tool for researchers and managers wishing to organise, simplify and understand the forms and processes within freshwater systems. Many classifications require surveyors to classify reaches into specific channel types in a field environment. Channel types should be identifiable based on a field surveyor’s
judgement of channel characteristics and landscape settings; these include channel planform, valley confinement, dominant bed material, and/or instream geomorphic features (e.g. gravel bars). Accurate classification of reaches into the correct channel
type is important to ensure consistency in management strategies, and to assess the impact of engineering activities on the physical and ecological status of rivers. In this paper, we examine the variation in professional judgement of geomorphologically based channel types by scientists with different disciplinary backgrounds, and varying levels of involvement in classification systems using a photo-questionnaire. Results indicate that there can be a large level of discrepancy in typing rivers; the choice of the modal channel type for each reach varied between 25.9% and 75.1% of the respondent selections. There were also differences in the level of agreement between
earth scientists (with hydrogeomorphological or geological training), ecological scientists (with freshwater biology training) and practitioners involved in river conservation and management. A high level of experience in classification systems translates to a lower number of channel types being chosen per reach. In response to these results, the use of a photographic approach to typing needs to be fully tested and users fully trained before operational use. Furthermore, we advocate that designers of
geomorphic typologies should aim to have a representative and workable number of classes within a typology with an emphasis for rationalisation of classes rather than expansion of numbers
Ponding in Intermittent Streams: a Refuge for Lotic Taxa and a Habitat for Newly Colonising Taxa?
No full textIntermittent rivers are temporally dynamic, shifting between lotic, lentic (ponding) and dry habitat phases, yet almost all research effort has focussed on the lotic phase, with limited research attention on the lentic and dry phases. Information regarding the biological diversity of the lentic phase is vital to quantify the total aquatic biodiversity, their use as flow refugia, and the long-term conservation and management of intermittent rivers. In this study, we compared the diversity and composition of macroinvertebrates from perennial, intermittent and ponded sites in two intermittent rivers in the United Kingdom. We examined whether instream ponding provided refugia for lotic taxa and a habitat for newly colonising taxa. A total of 129 taxa (perennial - 86, intermittent - 82, ponding - 78) were recorded. Instream ponds were found to support heterogeneous communities compared to flowing sites. Twenty-two percent of taxa were recorded only from ponded sites, many of which were lentic specialists, while 38% of taxa persisted in instream ponds after flow had ceased. Results from this study highlight that instream ponds provide an important flow refuge for macroinvertebrates including rheophilic taxa, which move into instream ponds when channels become longitudinally disconnected, and makes a significant contribution to aquatic diversity in intermittent rivers, providing suitable habitat for newly colonising taxa. Aquatic diversity in intermittent rivers may have been underestimated historically, failing to acknowledge the ecological contribution of the lentic phase. Incorporating the ponding phase alongside the lotic phase will ensure the total aquatic biodiversity of intermittent rivers is quantified and effective biodiversity conservation and management strategies are employed
Are all rivers equal? The role of education in attitudes towards temporary and perennial rivers
No full text1. Temporary rivers (TRs) are prevalent, biodiverse ecosystems yet often overlooked and underprotected. This may be because inadequate understanding of their ecosystem services leaves them undervalued by society. However, evidence of negative attitudes towards TRs is scant.
2. We investigated the strength and extent of negative attitudes by surveying undergraduate students from Australia, UK, and USA on their agreement (positive attitude) or disagreement (negative attitude) with statements about the ecosystem services, moral consideration, and protection of perennial and TRs. Students were surveyed at the start and end of teaching units covering environmental topics.
3. Disagreement with statements was uncommon (17% across all statements and surveys) and attitudes towards TRs were mostly positive. However, attitudes towards perennial rivers were more positive, particularly in comparison with non‐flowing TRs and with regard to their aesthetic value and recreational amenity. There were no significant differences in attitudes towards perennial and TRs in one teaching unit in Australia, and responses were more often more positive at the end of teaching units in the UK.
4. Our study indicates education can change attitudes. The overall positive response to statements may reflect underlying environmental awareness and pre‐existing interest of participants enrolled in environmental and biology degrees, but not necessarily specific knowledge of TRs. General environmental education across the wider community could improve attitudes towards TRs, particularly when they are not flowing or in regions where they are uncommon or inconspicuous, and could support positive protection measures and innovative, inclusive management
Colonisation of terrestrial vegetation in an intermittent river:Diversity responses to seasonal drying
No full textIntermittent rivers are dynamic ecosystems that experience a predictable or unpredictable loss of surface water and are characterised by changing lotic, lentic (ponding) and dry habitats. Plant communities colonising dry channels during the desiccation stage can be diverse, abundant and differ in their tolerances to water availability and habitat conditions. This study examines the colonisation of terrestrial vegetation in two intermittent rivers in the United Kingdom, and whether terrestrial plant taxonomic richness and functional diversity increase during the dry phase. Six reaches were surveyed for terrestrial plants during the dry phase over a standard 100 m length every month from April to October 2021. We found the channel and bank taxonomic richness increased with drying duration. Functional traits of vegetation height, clonality, clonality richness and Ellenberg's value of light moisture also increased with stream desiccation. Bed sediment conditions (the proportion of sand and gravel) and the 12-month antecedent percentage of zero flow days were the key drivers of plant community composition. We believe plant propagules from the riparian zone and channel vegetation on topographic high points in the channel aided plant colonisation of the riverbed once flow ceased. Past research may have underestimated the biodiversity value of intermittent rivers by failing to include the ecological importance of plants during the dry phase. Information on plant diversity of the dry phase is important to determine the overall biodiversity of intermittent rivers for their long-term conservation and management
The ecological importance of unregulated tributaries to macroinvertebrate diversity and community composition in a regulated river
No full textIn regulated rivers, dams alter longitudinal gradients in flow regimes, geomorphology, water quality and temperature with associated impacts on aquatic biota. Unregulated tributaries can increase biodiversity in regulated environments by contributing colonists to the main channel and creating transitional habitats at a stream junction. We assessed whether unregulated tributaries influence macroinvertebrate communities in two mainstem rivers during summer low-flows. Three tributary junctions of upland cobble-gravel bed streams were surveyed in an unregulated and a regulated river in the Sierra Nevada Mountains, California, USA. We found distinct physical habitat conditions and increased macroinvertebrate abundance and diversity in unregulated tributaries on the regulated river, but macroinvertebrate diversity did not increase downstream of tributary junctions as predicted. On the unregulated river, macroinvertebrate diversity was similar in upstream, downstream and unregulated tributary sites. Our findings highlight that unregulated tributaries support high macroinvertebrate diversity and heterogeneous communities compared to the mainstem sites in a regulated river, and thus likely support ecological processes, such as spill-over predation, breeding and refugia use for mobile taxa. We suggest unregulated tributaries are an integral component of river networks, serving as valuable links in the landscape for enhancing biodiversity, and should be protected in conservation and management plans
Flow intermittence in river networks: understanding the ecohydrological diversity of aquatic–terrestrial ecosystems
No full textTemporary streams comprise dynamic mosaics of lotic, lentic and terrestrial habitats and dominate global river networks, occurring across regions with contrasting climate types. Recent advances in our ecohydrological understanding of temporary streams have focused on systems in arid, semi-arid and mediterranean climates. In this special issue, we present new temporary stream research from underrepresented regions, primarily cool, wet temperate climates but also continental central Europe and the mediterranean-climate region of South Africa. We bring together observational case studies, laboratory experiments, and field surveys spanning surface water and groundwater habitats. Papers within the special issue explore ecological responses to flow intermittence; examine biodiversity patterns of rare and endemic species at broad spatial scales; characterize diverse responses to drying events within and among populations; demonstrate the value of long-term observational data in understanding the hydrological drivers that underpin biotic responses; and present opportunities to improve temporary stream monitoring and management. Collectively, these contributions complement dryland research to advance global understanding of temporary stream ecohydrology. However, the terrestrial communities that inhabit dry channels remain a notable research gap, which we address in a review of global literature. As global change causes an increase in their extent across climate regions, we urge researchers and stakeholders to collaborate to implement recommendations that address the challenges associated with the effective management of temporary streams as aquatic–terrestrial ecosystems
Do legacy effects of deposited fine sediment influence the ecological response of drifting invertebrates to a fine sediment pulse?
No full textThe deposition of excess fine sediment and clogging of benthic substrates is recognised as a global threat to ecosystem functioning and community dynamics. Legacy effects of previous sedimentation create a habitat template on which subsequent ecological responses occur, and therefore, may have a long-lasting influence on community structure. Our experimental study examined the effects of streambed colmation (representing a legacy effect of fine sediment deposition) and a suspended fine sediment pulse on macroinvertebrate drift and community dynamics. We used 12 outdoor stream mesocosms that were split into two sections of 6.2 m in length (24 mesocosm sections in total). Each mesocosm section contained a coarse bed substrate with clear bed interstices or a fine bed substrate representing a colmated streambed. After 69 days, a fine sediment pulse with three differing fine sediment treatments was applied to the stream mesocosms. Added fine sediment influenced macroinvertebrate movements by lowering benthic density and taxonomic richness and increasing drift density, taxonomic richness, and altering drift assemblages. Our study found the highest dose of sediment addition (an estimated suspended sediment concentration of 1112 mg l caused significant differences in benthic and drift community metrics and drift assemblages compared with the control treatment (30 l of water, no added sediment). Our results indicate a rapid response in drifting macroinvertebrates after stressor application, where ecological impairment varies with the concentration of suspended sediment. Contrary to expectations, bed substrate characteristics had no effect on macroinvertebrate behavioural responses to the fine sediment pulse
Method, substrate type and sample replication affect measurements of fine sediment content in river beds
No full textExcessive fine sediment (particles <2 mm) in riverbeds negatively impacts river ecology. Riverbed fine sediment measurements are therefore critical in research, monitoring and management seeking to protect, maintain or restore riverine ecosystems. However, there is no single, widely adopted method and limited evidence‐based guidance about how to choose between numerous available field techniques to achieve accurate, repeatable and consistent results. We therefore compared the intercorrelations of six commonly employed fine sediment methods across 29 sites (constituting 667 independent observations): the original resuspension method and two alternative turbidity derivatives (turbidity tube and turbidimeter), Wolman pebble counts, McNeil sampling and visual estimations at reach and patch scales. Performance evaluation focused on issues of practical significance, including comparisons of fines content between surface and subsurface measures, local substrate composition, spatial scale of application (reach and patch) and sample replication. Most methods yielded estimates of fines that were strongly correlated with each other, but these differed depending on local substrate composition, suggesting that different methods are better applied to certain substrate types. Differences between reach fine sediment estimates were typically larger as the proportion of fine sediment increased, whilst the converse was true for patch‐scale measures. On average, surface measures do not provide reliable information about subsurface fines content. We also found that an inexpensive, rapid version of the resuspension method utilising a turbidity tube performs as well as costlier alternatives, providing a valuable means of estimating fines in most riverine environments. The spatial scale of sampling (reach or patch) and the number of replications made a significant difference to the estimates obtained using visual observations. We make pragmatic recommendations, providing a significant step forward in standardising fine sediment measurement in riverbeds. Practitioners and researchers should select methods that suit local substrate conditions, while recognising that their choices will influence the results obtained
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