Connectivity in rivers Wohl, Ellen
Progress in physical geography,
06/2017, Volume:
41, Issue:
3
Journal Article
Peer reviewed
Connectivity describes the degree to which matter and organisms can move among spatially defined units in a natural system. River connectivity is typically described in longitudinal, lateral, and ...vertical dimensions within the river corridor and the watershed and can be conceptualized as a continuum from fully connected to disconnected over diverse temporal and spatial scales. Explicit characterization of connectivity helps understanding of disparities among short-term, local rates of flux and inferred fluxes over larger scales. Connectivity also strongly influences the response of rivers to natural and human disturbances. Investigations of connectivity facilitate the recognition of processes that cross traditional disciplinary boundaries, as well as understanding of nonlinear behavior and retention within rivers. Enhancing the ability to identify, quantify, and predict the processes that create and maintain connectivity is integral to the effective management of rivers.
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Through their modifications of channels and floodplains, beavers are a premier example of ecosystem engineers. Historical and stratigraphic records suggest that hundreds of millions of beavers once ...modified small to medium rivers throughout the northern hemisphere. Where beavers actively modify the channel and floodplain with dams, ponds, and canals, their activities increase habitat abundance and diversity, biodiversity, nutrient uptake, attenuation of downstream fluxes of water and sediment, and resilience of the river corridor to disturbances. Loss of beavers through commercial trapping and habitat modification occurred simultaneously with other human modifications of uplands and river corridors. The cumulative effects of these human modifications have been to greatly reduce the ecosystem services provided by rivers. Contemporary efforts to re-introduce beavers in North America and Eurasia and to mimic the effects of beaver engineering with beaver dam analogues and Stage 0 restoration represent a good start, but fundamental questions remain about the extent of such restoration efforts needed to create and maintain significant increases in riverine functions.
Headwaters, defined here as first- and second- order streams, make up 70%-80% of the total channel length of river networks. These small streams exert a critical influence on downstream portions of ...the river network by： retaining or transmitting sediment and nutrients; providing habitat and refuge for diverse aquatic and riparian organisms; creating migration corridors; and governing connectivity at the watershed-scale. The upstream-most extent of the channel network and the longitudinal continuity and lateral extent of headwaters can be difficult to delineate, however, and people are less likely to recognize the importance of headwaters relative to other portions of a river network. Consequently, headwaters commonly lack the legal protections accorded to other portions of a river network and are more likely to be significantly altered or completely obliterated by land use.
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Published by the American Geophysical Union as part of the Water Resources Monograph Series, Volume 19. What are the forms and processes characteristic of mountain rivers and how do we know them? ...Mountain Rivers Revisited, an expanded and updated version of the earlier volume Mountain Rivers, answers these questions and more. Here is the only comprehensive synthesis of current knowledge about mountain rivers available. While continuing to focus on physical process and form in mountain rivers, the text also addresses the influences of tectonics, climate, and land use on rivers, as well as water chemistry, hyporheic exchange, and riparian and aquatic ecology. With its numerous illustrations and references, hydrologists, geomorphologists, civil and environmental engineers, ecologists, resource planners, and their students will find this book an essential resource. Ellen Wohl received her Ph.D. in geology in 1988 from the University of Arizona. Since then, she has worked primarily on mountain and bedrock rivers in diverse environments.
Fluvial geomorphology has been the largest single subdiscipline within geomorphology for many decades. Fluvial geomorphic expertise is integral to understanding and managing rivers and to developing ...strategies for sustainable development. This paper provides an overview of some of the significant advances in fluvial geomorphology between 1960 and 2010 with respect to: conceptual models; fluvial features and environments being studied; tools used by fluvial geomorphologists; geomorphic specialty groups within professional societies; journals in which fluvial geomorphic research is published; and textbooks of fluvial geomorphology. During this half century, fluvial geomorphology broadened considerably in scope, from a focus primarily on physical principles underlying process and form in lower gradient channels with limited grain size range, to a more integrative view of rivers as ecosystems with nonlinear behavior and great diversity of gradient, substrate composition, and grain size. The array of tools for making basic observations, analyzing data, and disseminating research results also expanded considerably during this period, as did the diversity of the fluvial geomorphic community.
•Between 1960 and 2010, fluvial geomorphology broadened in scope.•1960 focus on physics in lower gradient rivers with limited grain size range.•By 2010 integrative view of diverse river ecosystems with nonlinear behavior
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7.
Disconnected rivers Wohl, Ellen E
2004, 20041110, 2008, 2013-09-02
eBook, Book
This important and accessible book surveys the history and present condition of river systems across the United States, showing how human activities have impoverished our rivers and impaired the ...connections between river worlds and other ecosystems.Ellen Wohl begins by introducing the basic physical, chemical, and biological processes operating in rivers. She then addresses changes in rivers resulting from settlement and expansion, describes the growth of federal involvement in managing rivers, and examines the recent efforts to rehabilitate and conserve river ecosystems. In each chapter she focuses on a specific regional case study and describes what happens to a particular river organism-a bird, North America's largest salamander, the paddlefish, and the American alligator-when people interfere with natural processes.
To effectively manage wood in rivers, we need a better understanding of wood mobility within river networks. Here, we review primarily field-based (and some numerical) studies of wood transport. We ...distinguish small, medium, large, and great rivers based on wood piece dimensions relative to channel and flow dimensions and dominant controls on wood transport. We suggest further identification and designation of wood transport regimes as a useful way to characterize spatial-temporal network heterogeneity and to conceptualize the primary controls on wood mobility in diverse river segments. We draw analogies between wood and bedload transport, including distinguishing Eulerian and Lagrangian approaches, exploring transport capacity, and quantifying thresholds of wood mobility. We identify mobility envelopes for remobilization of wood with relation to increasing peak discharges, stream size, and dimensionless log lengths. Wood transport in natural channels exhibits high spatial and temporal variability, with discontinuities along the channel network at bankfull flow and when log lengths equal channel widths. Although median mobilization rates increase with increasing channel size, maximum mobilization rates are greatest in medium-sized channels. Most wood is transported during relatively infrequent high flows, but flows under bankfull can transport up to 30% of stored wood. We use conceptual models of dynamic equilibrium of wood in storage and of spiralling wood transport paths through drainage networks, as well as a metaphor of traffic on a road, to explore discontinuous wood movement through a river network. The primary limitations to describing wood transport are inappropriate time scales of observation and lack of sufficient data on mobility from diverse rivers. Improving models of wood flux requires better characterization of average step lengths within the lifetime travel path of a piece of wood. We suggest that future studies focus on: (i) continuous or high-frequency monitoring of wood mobility; (ii) monitoring changes in wood storage; (iii) using wood characteristics to fingerprint wood sources; (iv) quantifying volumes of wood buried within river corridors; (v) obtaining existing or new data from unconventional sources, such as citizen science initiatives, and (vi) creating online interactive data platforms to facilitate data synthesis.
•Instream wood dynamics need to be incorporated into models of river systems.•Summarizes existing transport research around flow, wood and reach characteristics•Consolidates field mobility data related to increasing channel widths and flow•Identifies disconnects between driving processes and how mobility is measured•Constrains and conceptualizes thresholds between wood dynamic regimes
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