Science and Restoration- Background Reading
Vannote et al. (1980): The river continuum concept.
Abstract: From headwaters to mouth, the physical variables within a river system present a continuous gradient of physical conditions. This gradient should elicit a series of responses within the constituent populations resulting in a continuum of biotic adjustments and consistent patterns of loading, transport, utilization, and storage of organic matter along the length of a river. Based on the energy equilibrium theory of fluvial geomorphologists, we hypothesize thatthe structural and functional characteristics of stream communities are adapted to conform to the most probable position or mean state of the physical system. We reason that producer and consumer communities characteristic of a given river reach become established in harmony with the dynamic physical conditions of the channel. In natural stream systems, biological communities can be characterized as forming a temporal continuum of synchronized species replacements. This continuous replacement functions to distribute the utilization of energy inputs over time. Thus, the biological system moves towards a balance between a tendency for efficient use of energy inputs through resource partitioning (food, substrate, etc.) and an opposing tendency for a uniform rate of energy processing throughout the year. We theorize that biological communities developed in natural streams assume processing strategies involving minimum energy loss. Downstream communities are fashioned to capitalize on upstreamprocessing inefficiencies. Both the upstream inefficiency (leakage) and the downstream adjustmentsseem predictable. We propose that this River Continuum Concept provides a frameworkfor integrating predictable and observable biological features of lotic systems. Implicationsof the concept in the areas of structure, function, and stability of riverine ecosystems are discussed.
Minshall et al. (1985): Developments in stream ecosystem theory.
Abstract: Four significant areas of thought, (I) the holistic approach, (2) the linkage between streams and their terrestrial setting, (3) material cycling in open systems, and (4) biotic interactions and integration of community ecology principles, have provided a basis for the further development of stream ecosystem theory. The River Continuum Concept (RCC) represents a synthesis of these ideas. Suggestions are made for clarifying, expanding, and refining the RCC to encompass broader spatial and temporal scales. Factors important in this regard include climate and geology, tributaries, location-specific lithology and geomorphology,and long-term changes imposed by man. It appears that most riverine ecosystems can be accommodated within this expanded conceptual framework and that the RCC continues to represent a useful paradigm for understanding and comparing the ecology of streams and rivers.
Gasith and Resh (1999): Streams in Mediterranean-climate regions: abiotic influences and biotic responses to predictable seasonal events.
Abstract Streams in mediterranean-climate regions (areas surrounding the Mediterranean Sea, parts of western North America, parts of west and south Australia,southwestern South Africa and parts of central Chile) are physically, chemically, and biologically shaped by sequential, predictable, seasonal events of flooding and drying over an annual cycle. Correspondingly, aquatic communities undergo a yearly cycle whereby abiotic (environmental) controls that dominate during floods are reduced when the discharge declines, which is also a time when biotic controls (e.g. predation, competition)can become important. As the dry season progresses, habitat conditions become harsher; environmental pressures may again become the more important regulators of stream populations and community structure. In contrast to the synchronous input of autumn litter fall in forested temperate streams, riparian input to mediterranean-type streams is more protracted, with fall and possibly spring peaks occurring in streams in the Northern Hemisphere and a summer peak existing in their Southern Hemisphere counterparts. We present 25 testable hypotheses that relate to the influence of the stream hydrograph on faunal richness, abundance, and diversity; species coexistence;seasonal changes in the relative importance of abiotic and biotic controls on the biotic structure; riparian inputs and the relative importance of heterotrophy compared to autotrophy; and the impact of human activities on these seasonally water-stressed streams. Population increases in mediterranean-climate regions (particularly in fertile regions) result in an intensification of the competition for water among different users; consequently, water abstraction, flow regulation, increased salinity, and pollution severely limit the ability of the streams to survive as sustainable, self-regulated systems.
Kondolf et al. (2012): Restoring mediterranean-climate rivers.
Abstract:Mediterranean-climate rivers (med-rivers)have highly variable flow regimes, with large, periodic floods shaping the (often-braided) channels, which is different from stable humid-climate rivers, whose form may be dominated by the 1.5-year flood. There isa fundamental challenge in attempting to ‘‘restore’’such variable, ever-changing, dynamic river systems,and the most effective restoration strategy is to set aside a channel migration zone within which the river can flood, erode, deposit, and migrate, without conflicting with human uses. An apparent cultural preference for stable channels has resulted in attempts to build idealized meandering channels, but these arelikely to wash out during large, episodic floods typical of med-rivers. Med-rivers are more extensively dammed than their humid-climate counterparts, so downstream reaches are commonly deprived of high flows, which carry sediments, modify channel morphology, and maintain habitat complexity. Restoration of the entire pre-dam hydrograph without losing the benefits of the dam is impossible, but restoration ofspecific components of the natural hydrograph (tow hich native species are adapted) can restore some ecosystem components (such as native fish species) in med-rivers.
Bonada and Resh (2013): Mediterranean-climate streams and rivers: geographically separated but ecologically comparable river systems.
Abstract:Streams and rivers in mediterranean-climate regions (med-rivers in med-regions) are ecologically unique, with flow regimes reflecting precipitation patterns. Although timing of drying and flooding is predictable, seasonal and annual intensity of these events is not. Sequential flooding and drying, coupled with anthropogenic influences make these med-rivers among the most stressed riverine habitat worldwide.Med-rivers are hotspots for biodiversity in all med regions.Species in med-rivers require different, often opposing adaptive mechanisms to survive drought andflood conditions or recover from them. Thus, metacommunities undergo seasonal differences, reflecting cycles of river fragmentation and connectivity, whichalso affect ecosystem functioning. River conservation and management is challenging, and trade-offs between environmental and human uses are complex,especially under future climate change scenarios. This overview of a Special Issue on med-rivers synthesizes information presented in 21 articles covering the five med-regions worldwide: Mediterranean Basin, coastal California, central Chile, Cape region of South Africa,and southwest and southern Australia. Research programs to increase basic knowledge in less-developed med-regions should be prioritized to achieve increased abilities to better manage med-rivers.
Kiffney et al. (2014): Linking resource availability and habitat structure to stream organisms: an experimental and observational approach.
Abstract.An experiment and a mark-recapture field study of juvenile coho salmon (Oncorhynchus kisutch) were conducted to identify controls of key energy flow chains in river food webs. In the small-scale experiment, we investigated the individual and interactive effects of physical habitat structure (PHS) as small wood and resource availability (tissue of adult Chinook salmon, O. tshawytscha) on nutrients, algae,invertebrates, and fish predators including juvenile coho. In the field, we quantified the effects of natural variation in prey availability (invertebrate drift biomass), PHS (wood), and local fish density on summer growth of juvenile coho across multiple stream reaches. Adding salmon tissue to experimental channels resulted in strong bottom-up effects on select invertebrates including increased population biomass of chironomids and baetids, the numerically dominant invertebrates, and faster growth of juvenile coho. We link the enhanced growth of coho to chironomid productivity: for instance, adult chironomid flux was 4.33higher and coho consumption of these animals 33 higher in salmon-subsidized channels. PHS in experimental channels was associated with reduced algal biomass, potentially in response to increased invertebrate consumption, and invertebrate flux or export. The field study revealed coho growth was negatively related to PHS and total fish density and positively related to Diptera drift biomass; however,the effects of fish density and drift biomass on coho growth were relatively weak. The field study also indicated that prey resource availability and coho growth were associated with differences in canopy cover,with prey biomass and coho growth 2–4 times higher in reaches receiving more sunlight. As in the experiment,coho in natural stream reaches predominantly fed on adult chironomids and other Diptera, indicating that these taxa and life-stages are a key link between the benthic food web and mobile vertebrate predators. Our study showed that bottom-up processes initiated by salmon subsidies and possibly light flux determined key trophic interactions in the Cedar River food web. Moreover, we speculate that PHS may modify some of these interactions indirectly through its effects on the movement of organisms through the environment.
Roni et al. (2015): Wood placement in river restoration: fact, fiction, and future directions. (link to pdf)
Abstract: Despite decades of research on wood in rivers, the addition of wood as a river restoration technique remains controversial. We reviewed the literature on natural and placed wood to shed light on areas of continued debate. Research on river ecology demonstrates that large woody debris has always been a natural part of most rivers systems. Although a few studies have reported high structural failure rates (>50%) of placed instream wood structures, most studies have shown relatively low failure rates (<20%) and that placed wood remains stable for several years, though long-term evaluations of placed wood are rare.The vast majority of studies on wood placement have reported improvements in physical habitat (e.g., increased pool frequency,cover, habitat diversity). Studies that have not reported improvements in physical habitat often found that watershed processes(e.g., sediment, hydrology, water quality) had not been addressed. Finally, most evaluations of fish response to wood placement have shown positive responses for salmonids, though few studies have looked at long-term watershed-scale responses or studies wide range of species.