We all know one when we see one...
[1]More about the instream biota and their role as water quality indicators>>>
A River Ecosystem
Rivers are situated within catchments, an area of land that is drained by the river. The catchment (aka, watershed) includes the river and everything that happens within its sloped boundaries. Because a river is an open energy system, degradation of a lotic habitat can be difficult to source. The image below does a fairly good job illustrating how the effects of activities within a catchment become concentrated within a river channel, ultimately manifesting in the physical parameters of a lotic ecosystem.
A paragon, "healthy stream," is considered to be cool, well oxygenated, have sufficient canopy cover, a variety of stable heterogeneous substrates, and a diverse biotic community. But those conditions may not be "normal" for a stream course within a particular geology or at a given latitude.
[2]On Vernacular,
Regarding the relativity of data, statistics,-- my own assessment: If my tone seems overly emphatic, the gesture is admittedly somewhat compensatory for a perceived prevalence of hasty generalizations, unrepresentative samples, and baseless polemics concerning issues of character, and quality. Asserting such judgement merits an equally scrutinous exposition of the employed semantics, accounting for descriptive or prescriptive rhetorical strategies. When characterizing a river, the data's affect is founded its spatial-temporal significance, pertinently concerning the history and positioning itself within a larger trajectory of a given catchment. Because a river supports a nesting of microhabitats that inform and comprise a larger lotic ecosystem, it's imperative to locate and evaluate these elements within their respective dimensions.
Dimensions of a River
Longitudinal-- upstream and downstream; unidirectional flow of a river supports profound and predictable change in the physicochemical conditions within a river
Lateral-- land-water interfaceVertical-- air-water interfaceTemporal-- this dimension supports predictable changes in physicochemical factors and biota related to seasonal changes
*Scale-- though technically not a dimension, considering the degree of spatial and temporal heterogeneity best contextualizes the data within a highly dynamic habitat.
River Topography
Returning to a rather reductive circumscription of "river," we're more pointedly talking about water confined to a channel, the streambed over which it flows, and the channel's banksides. Rivers as part of the hydrologic cycle innervate a catchment, acting a drainage for the basin, facilitating instream nutrient and sediment transport.
Unstable bed and channel morphology results in various topographical patterns. A river's morphology is restricted by the geology of its catchment. Depending on the proximate conditions, a river may carve down through a terrace or "sidewind," naturally reestablishing its domain with each successive flooding and deposition. The image below maps the abandoned channel paths of the Mississippi.
[5]
Maturity: Age, Order, and Course
A river can be categorized by order (derived from the number of tributaries that feed into the mainstem) and by age, a complement of stream course morphology. (e.g The classic meandering pattern is characteristic of a mature, mid-order stream.)
[6]
[7]
A River's Course: Locating a Transect
A river's total expanse (or stream course) can be transected across its longitudinal dimensions. These sections and their characteristics reflect their chronological designation. The chronology is tied to the unidirectional flow of a river, begging at its source in the upper course, passing through the middle course, and finally terminating in the lower course. These stream reaches are similarly personified, the upper reaches being described as youthful, the middle reaches, mature, and the lower reaches, old. The parsimonious illustration below lists characteristics and features respective to their course.
[8]
Stream Velocity and Flow
[9]
Standing bankside, watching a stretch of river for a time, one would notice percolating patterns in the waters surface. In areas with a course streambed the water churns, turning over the surface and oxygenating the water. These areas are called riffles. In areas of high sedimentation or bends, the stream velocity tends to slow. These areas are called pools. In a meandering river, a natural pool-riffle sequence is naturally established by the variances in deposition and the substrate. A classic meandering sequence is pictured in the diagram.
The Streambed: Substratum and Substrate
The streambed (or the solid over which a volume of water flows) traverses the longitudinal and lateral dimensions of a river. As suggested in Stream Velocity and Flow, the relationship between flow and streambed composition is similarly instrumental in cultivating the substratum. The substratum is an amalgam of microhabitats comprised of organic and mineral particles that serves as the nexus for biotic interaction and energy exchange.
Streambed composition is crucial for lotic biota. Of course, a streambed's physical composition has the distinct ability to delimit oxygen in within a habitat by tempering current velocity, vegetation, and deposition; but the substratum holds equal value as real estate. The texture and total surface area is determinant in providing space, refuge, and food (directly or indirectly) for lotic biota.
A substrate, elementally speaking, is living or dead organic matter or mineral particles (Giller). These particles can be classified by size, material, or embeddeness. Embeddedness is an index of the degree to which these particles are sedimented. The illustration below cases characteristics along the spectrum (reproduced from Murdoch).
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Embeddedness and the stability of the substrate are limiting factors for instream biota.
Some predictable trends in biotic community structure and trophic composition linked to embeddedness:
*Biodiversity and abundance tend to increase with substrate stability.
*The greater the embeddedness, the more homogeneous the the substrate becomes, leading to an increase in depositional areas.
*As embeddedness increases, biotic productivity of the habitat tends to decrease.
Further exposition about the role sedimentation plays in Water Quality and Habitat Assessment>>>
Refs--
[2] http://www.chiefscientist.qld.gov.au/publications/understanding-floods/assets/floods-factors.jpg
[3] http://mindblowingscience.com/wp-content/uploads/2012/05/meandering-river.jpg
Dimensions of a River
Longitudinal-- upstream and downstream; unidirectional flow of a river supports profound and predictable change in the physicochemical conditions within a river
[3]Lateral-- land-water interfaceVertical-- air-water interfaceTemporal-- this dimension supports predictable changes in physicochemical factors and biota related to seasonal changes
*Scale-- though technically not a dimension, considering the degree of spatial and temporal heterogeneity best contextualizes the data within a highly dynamic habitat.
River Topography
[4]Returning to a rather reductive circumscription of "river," we're more pointedly talking about water confined to a channel, the streambed over which it flows, and the channel's banksides. Rivers as part of the hydrologic cycle innervate a catchment, acting a drainage for the basin, facilitating instream nutrient and sediment transport.
Unstable bed and channel morphology results in various topographical patterns. A river's morphology is restricted by the geology of its catchment. Depending on the proximate conditions, a river may carve down through a terrace or "sidewind," naturally reestablishing its domain with each successive flooding and deposition. The image below maps the abandoned channel paths of the Mississippi.
[5]Maturity: Age, Order, and Course
A river can be categorized by order (derived from the number of tributaries that feed into the mainstem) and by age, a complement of stream course morphology. (e.g The classic meandering pattern is characteristic of a mature, mid-order stream.)
[6][7]A River's Course: Locating a Transect
A river's total expanse (or stream course) can be transected across its longitudinal dimensions. These sections and their characteristics reflect their chronological designation. The chronology is tied to the unidirectional flow of a river, begging at its source in the upper course, passing through the middle course, and finally terminating in the lower course. These stream reaches are similarly personified, the upper reaches being described as youthful, the middle reaches, mature, and the lower reaches, old. The parsimonious illustration below lists characteristics and features respective to their course.
[8]Stream Velocity and Flow
[9]Standing bankside, watching a stretch of river for a time, one would notice percolating patterns in the waters surface. In areas with a course streambed the water churns, turning over the surface and oxygenating the water. These areas are called riffles. In areas of high sedimentation or bends, the stream velocity tends to slow. These areas are called pools. In a meandering river, a natural pool-riffle sequence is naturally established by the variances in deposition and the substrate. A classic meandering sequence is pictured in the diagram.
The Streambed: Substratum and Substrate
The streambed (or the solid over which a volume of water flows) traverses the longitudinal and lateral dimensions of a river. As suggested in Stream Velocity and Flow, the relationship between flow and streambed composition is similarly instrumental in cultivating the substratum. The substratum is an amalgam of microhabitats comprised of organic and mineral particles that serves as the nexus for biotic interaction and energy exchange.
Streambed composition is crucial for lotic biota. Of course, a streambed's physical composition has the distinct ability to delimit oxygen in within a habitat by tempering current velocity, vegetation, and deposition; but the substratum holds equal value as real estate. The texture and total surface area is determinant in providing space, refuge, and food (directly or indirectly) for lotic biota.
A substrate, elementally speaking, is living or dead organic matter or mineral particles (Giller). These particles can be classified by size, material, or embeddeness. Embeddedness is an index of the degree to which these particles are sedimented. The illustration below cases characteristics along the spectrum (reproduced from Murdoch).
[10]Embeddedness and the stability of the substrate are limiting factors for instream biota.
Some predictable trends in biotic community structure and trophic composition linked to embeddedness:
*Biodiversity and abundance tend to increase with substrate stability.
*The greater the embeddedness, the more homogeneous the the substrate becomes, leading to an increase in depositional areas.
*As embeddedness increases, biotic productivity of the habitat tends to decrease.
Further exposition about the role sedimentation plays in Water Quality and Habitat Assessment>>>
Refs--
Giller, Paul S., and Björn Malmqvist. The Biology of Streams and Rivers. Oxford: Oxford UP, 1998. Print.
Goldsmith, Edward, and Nicholas Hildyard. The Social and Environmental Effects of Large Dams. Camelford, Cornwall: Wadebridge Ecological Centre, 1984. Print.
Murdoch, Tom, Martha Cheo, and Kate O'Laughlin. The Streamkeeper's Field Guide: Watershed Inventory and Stream Monitoring Methods. Everett, WA: Adopt-a-Stream Foundation, 1996. Print.
Images:
[1] A river (?) http://intmstat.com/vectors/river4c.gif[2] http://www.chiefscientist.qld.gov.au/publications/understanding-floods/assets/floods-factors.jpg
[3] http://mindblowingscience.com/wp-content/uploads/2012/05/meandering-river.jpg
[4] http://mountainbeltway.files.wordpress.com/2010/06/river-channel1.jpg
[5] http://www.galaxygoo.org/blogs/simmon/fisk_mississippi_overview.JPG
[6] http://farm5.static.flickr.com/4019/4690937436_7b155be9c5.jpg
[7] http://www.kunenerak.org/_system/showThumb.aspx?file=UserFiles/Image/RiverBasin/Strahler-stream-order.gif&w=500
[8] http://worldbuildingschool.com/files/2012/08/RiverCourse.jpg
[9] http://www.ucpress.edu/img/excerpts/moj01a.jpeg
[10] Drawing reproduced from The Streamkeeper's Field Guide: Watershed Inventory and Stream Monitoring Methods
[5] http://www.galaxygoo.org/blogs/simmon/fisk_mississippi_overview.JPG
[6] http://farm5.static.flickr.com/4019/4690937436_7b155be9c5.jpg
[7] http://www.kunenerak.org/_system/showThumb.aspx?file=UserFiles/Image/RiverBasin/Strahler-stream-order.gif&w=500
[8] http://worldbuildingschool.com/files/2012/08/RiverCourse.jpg
[9] http://www.ucpress.edu/img/excerpts/moj01a.jpeg
[10] Drawing reproduced from The Streamkeeper's Field Guide: Watershed Inventory and Stream Monitoring Methods
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