River Continuum Concept
The River Continuum Concept is a model for classifying and describing rivers , which uses geomorphology as well as classifying individual water sections according to the occurrence of key organisms . In limnology , model descriptions and classification models like this one are used to describe and assess the condition of a body of water. In addition to the simple classification of communities, which was customary up to its introduction, it also provides an explanation for their sequence in the course of the water as well as other predictable and actually observable biological properties of the water. The concept was developed in 1980 by an American research group led by Robin L. Vannote .
background
The River Continuum Concept is based on the idea that a river is viewed as an open ecosystem that is in constant interaction with the bank and that changes continuously from the source to the mouth . The basis for this change in the overall system is a gradual change in physical environmental conditions such as width, depth, amount of water, flow properties , temperature and the complexity of the water. According to the hypothesis , living beings are adapted to such a continuous system and in turn form a continuum in which the communities are in harmony with the physical conditions over longer river areas and a balance is established between producers of organic material (primarily plants ) and consumers of the same. Along the course of the river, there is a change in the relationship between the production and consumption ( respiration ) of the material.
Communities and diet types
The continuous changes in the properties within the flowing water primarily result in a specific composition of the organisms in the different sections of the water. What is important is the proportion of the four important types of nutrition, which are referred to as chopper, gatherer, grazer (or "grazer") and robber. With the exception of the predators, all of these organisms feed directly on plant material and thereby decompose it. They are called saprobians .
The grinders are organisms that grind coarse organic material such as leaves into pieces. They use material with sizes over a millimeter (coarse particulate material, CPOM = coarse particulate organic matter) and its growth ( fungi , microorganisms ) as food, but at the same time leave a lot of material behind. Typical shredders in Central European waters are amphibians , water lice , various mayflies and stonefly larvae .
Organisms are referred to as collectors which, through trap or other collecting structures, are able to fish suspended matter from the water flow or to absorb it from the sediment on which they feed. The particle sizes are between 0.5 and 50 micrometers (ultrafine particulate organic material, UPOM = ultrafine particulate organic matter, to fine particulate material, FPOM = fine particulate organic matter). This group includes the black fly larvae , many mosquito larvae , roundworms and many other animal groups.
The grazers graze the growth of larger structures in the water, such as stones, pieces of wood or larger aquatic plants. These include snails , eyelid mosquito larvae and also many mosquito larvae.
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After all, predators are organisms that feed on other animals, including dragonfly larvae and various beetles .
Due to the change in the existing organic material, the proportions of these groups in the communities change in the course of the river. In the upper reaches and the brook region there is a preponderance of shredders and foragers due to the coarse plant matter, and grazers make up a small proportion. In the middle reaches the proportion of pasture-goers and especially the foragers increases, while the shredders decrease significantly and finally disappear completely. In the lower reaches there is almost only particulate material, whereby the collectors make up the largest part. The proportion of predators remains largely constant in all sections and only changes in the species composition, since these do not depend on the size of the organic material, but on the availability of prey. Atypical changes in the composition of these groups of organisms within the course of a river, such as an increased number of shredders in larger river areas or a lack of these animals in the upper reaches, suggest a disturbance.
The division of the flowing water
The division of the river according to the River Continuum Concept allows a rough classification into three sections, which is applicable to all rivers. According to this, small bodies of water can be delimited as streams from medium-sized rivers and large rivers .
The stream area is very narrow in the upper reaches and mostly lined with thick bank vegetation . This prevents the penetration of sunlight and thus the production of organic material by means of photosynthesis in the water, but at the same time it supplies large amounts of plant material that falls into the river (allochthonous organic material). In this section, respiration outweighs production and the ratio is P: R <1. Here living beings play a major role, which crush the mostly coarse plant material, as well as organisms which collect and use crushed material. There are also grazers and robbers. The greatest diversity of organic material can also be expected in this area . However, only very small particles are completely broken down here, larger and more difficult to break down components drift further downstream.
In the further course of the water, the importance of the bank as a supplier of organic material decreases and production within the water becomes more important (autochthonous organic material). The ratio of production to respiration increases and is P: R> 1. The proportion of shredders decreases accordingly, as the plant material is in the form of algae . The proportion of gatherers and grazers is increasing, the proportion of robbers remains unchanged.
In the last section there is a lot of particulate material in the river, and further production takes place through photosynthesis, which is limited to the uppermost area of the water by turbid suspended matter. Here again the respiration predominates , and the ratio is again P: R <1. The community in these river areas consists almost exclusively of gatherers and a still unchanged proportion of predators.
The continuum
The continuous changes over the stretch of the water can be proven by various factors. As described above, the flow begins with a system that is initially very strongly influenced by the outside and in which mainly organic material is consumed. Then it goes into a system with strong in-house production of organic material, which varies from day to day depending on the sunlight. The last area is little dependent on the outside, but is still very much influenced by degradation processes. In a continuous system without disturbances, e.g. from tributaries, this development can be observed in all river systems, whereby variations due to the seasonal rhythm of the environmental factors (especially the temperature) are possible. The particle size of the organic material as well as its diversity continue to decrease in the course of the river.
System resources and stability
An essential point of the concept is the consideration of the resource use of the organic material and the energy contained therein in the flowing water. At every point in the river, energy is introduced in the form of organic material, it is used, stored and partly passed on to places downstream. The available energy also represents the limiting factor of the system, and the system endeavors to use it as efficiently and loss-free as possible. Free resources allow new species to establish themselves in the community so that they can be used again quickly in the model. This principle is not only important for the “river” ecosystem, but applies equally to every other system. However, it plays a bigger role here, as unused resources are lost in one place due to the constant onward transport. According to the River Continuum Concept, it is postulated that in a river there is a constant strong compulsion to optimally use resources and to use them continuously over time.
The temporal aspect of this continuity can be seen primarily in the daily and seasonal periods. In the course of the day, the communities change mainly due to the increased feeding pressure during the day (fish mainly hunt optically) and the changes in abiotic factors such as temperature and light. The greatest daily change of the factors can be seen in the middle reaches, here there is also the largest spectrum of different animal species ( species diversity ) that can optimally use the different conditions.
Due to the constancy that exists through this even use of resources, the system is very stable in the event of disruptions and fluctuations. Irregularities in use are accordingly compensated very quickly, and a new equilibrium is established relatively soon afterwards. In addition, there is no ecological development of the system ( succession ), and changes to the system are only possible from the outside through geological changes such as a change in the catchment area, change in the organic input or geological earth movement. Even after these changes, however, there is again a steady state and a changed, but optimally functioning river system.
Development and application of the concept
The first presentation of the comprehensive concept took place in 1980 during a two-day congress of the Stroud Water Research Center , headed by Robin Vannote. It was the result of a multi-year study funded by the Rockefeller Foundation . The hypothesis was published in the same year under the title "The River Continuum Concept" in the Canadian Journal of Fisheries and Aquatic Sciences . The concept built on the work of other American limnologists, such as Ruth Patrick , who highlighted the ecosystem aspect of the running water, and Luna Leopold , who dealt with the physical changes in the water. The essential addition to the Vannote working group was the addition and explanation of the communities in this system. Vannote himself described the initial situation as follows:
- "In those days, most people studied a square meter of water to death."
(German: "Back then, most people analyzed a square meter of water to death." )
The research was therefore only ever carried out on small sections of the body of water, and these were only extremely rarely considered as running waters in their entirety.
After its publication, the River Continuum Concept quickly found acceptance among experts and became the preferred model for describing the communities in rivers. Here it solved the classic division of the waters into fish regions , which was developed by Robert Lauterborn between 1916 and 1918 on the basis of the communities in the Rhine , as well as the division into the habitats Krenal , Rhithral and Potamal by Joachim Illies in his publication “An attempt at a general biocenotic structure the flowing waters ” (1961). Both concepts had the disadvantage that they only ever described zones of the water and did not allow a consideration of the system in its entirety, as is made possible by the River Continuum Concept.
In practice, the River Continuum Concept is mainly used today for the ecological assessment of rivers and their disturbances. After examining the biocenoses in a river, the species composition can be determined and compared with the ideal case according to the River Continuum Concept. Above all, being overweight or lacking a certain diet can provide information about a possibly existing disorder.
Problems, Limits, and Modifications
Although the River Continuum Concept has met with wide acceptance, it is limited in its applicability. As a model, it describes an optimal and evenly changing river without disturbances and irregularities. This does not include, for example, inflows , congestion through dams or in lakes, or irregular events such as flooding of the bank.
In order to capture these irregularities in the model, the River Continuum Concept was expanded and varied by various authors. For example, JV Ward and JA Stanford developed the Serial Discontinuity Concept in 1983 , in which they integrated the effects of geomorphological disturbances such as the aforementioned congestion and tributaries. The same authors presented the Hyporheic Corridor Concept in 1993 , in which the vertical (in depth) and lateral (from bank to bank) structural complexity was connected to the continuum of the river. The Flood Pulse Concept , developed by WJ Junk et al. 1989 and further modified by PB Bayley 1990 and K. Tockner et al. 2000, finally brought about the fact that a large part of the nutrients and organic material comes from the sediment and flooded parts of the landscape into the river. The Riverine Productivity Model (RPM) developed by JH Thorp and MD Delong in 1994 describes the productivity of very large rivers with large floodplains .
References
- ↑ River Continuum ( Memento of October 28, 2008 in the Internet Archive )
literature
River Continuum Concept
- RL Vannote, GW Minshall, KW Cummins, JR Sedell and CE Cushing: The River Continuum Concept. (PDF; 956 kB) In: Canadian Journal of Fisheries and Aquatic Sciences. Volume 37, Ottawa 1980, No. 1, pp. 130-137. ISSN 0706-652X
- Winfried Lampert and Ulrich Sommer : Limnoecology. Georg Thieme, Stuttgart 1993, 1999. ISBN 3-13-786402-X
- DN Gordon, TA McMahon, BL Finlayson, CJ Gippel and RJ Nathan: Stream Hydrology - An Introduction for Ecologists. John Wiley & Sons, Chichester W Suss 2004. ISBN 0-470-84357-8
Advanced concepts
- JW Junk, PB Bayley and RE Sparks: The flood pulse concept in river floodplain systems. In: Canadian Special Publications of Fisheries and Aquatic Sciences. Volume 106, 1989, pp. 110-127. ISSN 0706-652X
- JV Ward and JA Stanford: The serial discontinuity concept of river ecosystems. In: TD Fontaine and SM Bartell (Eds.): Dynamics of lotic ecosystems. Science Publications, Ann Arbor Mich 1983, pp. 29-42. ISBN 0-250-40612-8
- JA Stanford and JV Ward: An ecosystem perspective of alluvial rivers, connectivity and the hyporheic corridor. In: Journal of the North American Benthological Society. Volume 12, Allen, Lawrence Kan 1993, pp. 48-60. ISSN 0887-3593
- PB Bayley: The flood pulse advantage and the restoration of river floodplain systems. In: Regulated Rivers. Research & Management. Volume 6, 1990, pp. 75-86. ISSN 0886-9375
- K. Tockner, F. Malard and JV Ward: An extension of the flood pulse concept. In: Hydrological Processes. Volume 14, Whiley, Chichester 2000, pp. 2861-2883. ISSN 0885-6087
- JH Thorp and MD Delong: The riverine productivity model: an heuristic view of carbon sources and organic processing in large river ecosystems. In: Oikos . Volume 70, Blackwell, Oxford 1994, No. 2, pp. 305-308. ISSN 0030-1299
