River Continuum Concept
The River Continuum Concept is a model for classification and description of rivers that after the occurrence of indicator organisms also uses the geomorphology in addition to the classification of individual river sections. In limnology model descriptions and classification models are like this used to describe the condition of a water body and to judge. It offers more than the usual introduction to its pure classification of communities addition, an explanation of their sequence in the course of the water, as well as more predictable and actually observable biological characteristics of the water body. Developed the concept of 1980 by an American research group led by Robin L. Vannote.
Background
The River Continuum Concept is based on the idea after a flowing water is considered as an open ecosystem that is in constant interaction with the bank and changed constantly over the course of the source to the mouth. The basis for this change in the overall system, a gradual change of physical environment conditions such as the width, the depth, the amount of water, the flow characteristics, the temperature and the complexity of the water. According to the hypothesis that living things are adapted to such a continuous system and in turn form a continuum in which the communities over extended flow ranges with the physical conditions are consistent and an equilibrium between producers of organic material ( primarily plants) and consumers sets thereof. Along the river course there is a change in the relationship between the production and consumption ( respiration ) of the material.
Communities and food types
The continuous changes in the properties within the watercourse require above all a specific composition of the organisms in the different sections of the watercourse. Important is the share of the four major food types that are referred to as shredders, collectors, grazers or Grazer and robbers. With the exception of the robbers, all of these organisms feed directly from plant material and decompose this result. They are called Saprobier.
The shredders are organisms that shred coarse organic material such as leaves into pieces. They use material of size greater than one millimeter ( Grobpartikuläres material CPOM = coarse particulate organic matter ) and its volunteers ( fungi, microorganisms) as a food, but at the same time leave back much material. Typical shredder Central European waters are amphipods, isopods, several mayfly and stonefly larvae.
As a collector organisms are referred to that are by traps or other collective structures able to fish suspended solids from the water stream or record from the sediment, from which they feed. The particle sizes lie between 0.5 and 50 micrometers ( Ultrafeinpartikuläres organic material UPOM = ultrafine particulate organic matter, to fine particulate material, FPOM = fine particulate organic matter ). This group includes the larvae of black flies, many midge larvae, nematodes and many other animal groups.
The grazers graze the nursery of larger structures from the water, such as stones, pieces of wood or larger aquatic plants. These resources include the snails that Lidmückenlarven and also many midge larvae.
Robbers are finally organisms that feed on other animals, including about the dragonfly larvae and various beetles.
Due to the change of the existing organic material change in the river course, the shares of these groups in the communities. In the upper reaches of the river and region, there is due to the coarse plant materials a preponderance of shredders and also to collectors, grazers represent a small share of. In the middle reaches, the proportion of grazers and especially the collector, while the shredder to decline significantly and eventually disappear completely. In the lower reaches there are almost only particulate material whereby the collectors make up the majority. The proportion of predators remains largely constant in all sections and only changes in species composition, as they are not dependent 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 stream, such as an increased number of shredders in larger flow areas or the absence of these animals in the upper reaches suggest, in a malfunction.
The classification of the watercourse
The classification of the watercourse by the River Continuum Concept allows a crude classification into three sections, which is applicable to all rivers. Accordingly, let small bodies of water as streams over medium rivers and large rivers delineate.
The creek area is very narrow and lined mostly in the upper reaches of a strong riparian vegetation. This prevents the penetration of sunlight and thus the production of organic matter by photosynthesis in the water, but at the same time, it provides large amounts of plant material that falls into the river ( allochthonous organic material ). In this section, therefore outweighs the respiration compared to the production and the ratio of P: R < 1 Here living things play a big role crush the most coarse vegetable matter, as well as organisms that collect and use crushed material. In addition, grazers and predators. This area also is the largest diversity of organic material to be expected. Be completely eliminated here, however, only small particles, larger and heavier degradable components drift downstream.
In the further course of the water, the significance of the bank takes as a supplier of organic material from growing and production within the body of water is important ( autochthonous organic material ). The ratio of production to respiration is greater and amounts to P: R> 1 The proportion of shredders decreases accordingly, because the plant material is present here in the form of algae. Greater the proportion of collectors and also the grazers, the robber share remains unchanged.
In the last section lies in the river in front of a lot of particulate material also find more production rather than by photosynthesis, which is limited by opacifying particulates on the uppermost portion of the water. Here again outweighs the respiration, and the ratio is again P: R < 1 The community is in this river areas almost exclusively from collectors as well as a continued unchanged proportion of robbers.
The continuum
The continuous changes over the course of the water body can be assigned to different factors. As described above, the flow starts with an initially very much influenced by external system in which mainly organic material is consumed. After which it goes into a system with a strong in-house production of organic material, which varies depending on the daily period of sunlight. The last area may be little dependent on the outside, but still very strongly influenced by degradation processes. In a continuous system without disturbances, such as inflows, this development can be seen in all river systems, with variations (especially the temperature) are possible due to seasonal rhythm of environmental factors. The particle size of the organic material as well as its diversity also take in the course of the river is shrinking.
Resources and stability of the system
A major point of the concept makes the consideration of resource utilization of the organic material and the energy contained in the flowing waters. At each point in the flow energy is introduced in the form of organic material, it is used, stored and partially passed on to downstream location points. The existing energy also represents the limiting factor of the system and the system aims this as efficiently as possible and without loss to use. Free resources allow new species to establish themselves in the community, so that they will be used in the model again quickly. This principle is not only important for the ecosystem flow but applies to any other system alike. Here, however, it plays a larger role because unused resources are lost at one point by the constant further transport. According to the River Continuum Concept is postulated to reflect that in a river there is a constant strong pressure for optimum use of resources and a temporally uniform continuous use.
The temporal aspect of this continuity can be seen especially on the diurnal rhythm and the seasonal periodicity. During the day, the communities change primarily due to the increased grazing pressure on the day ( fish hunt mainly optical) and the changes of abiotic factors such as temperature and light. The largest diurnal variation of the factors in the middle reaches is noted here also the widest range of different animal species exist ( species diversity ), which can utilize the different conditions optimal.
Because of the, by this uniform use of resources, existing Constance a very high stability of the system noise and jitter is due. Irregularities in the use be compensated accordingly very quickly and it arises relatively soon after a new equilibrium. There is no ecological development of the system (succession ) and changes in the system are only from the outside by geological changes such as a change in the catchment area, change in the organic inputs or geological Earthmoving possible. Even after these changes, however, it comes back to a steady state and an altered, but optimally functioning river system.
Development and application of the concept
The first presentation of the comprehensive concept place in 1980 under a two-day congress of the Stroud Water Research Center held its director Robin Vannote was. It was the result of several years of study, which was paid for by the Rockefeller Foundation. The publication of the hypothesis was performed in the same year under the title "The River Continuum Concept" in the journal Canadian Journal of Fisheries and Aquatic Sciences. The concept built on the work of another American limnologists as Ruth Patrick, who has proven to the ecosystem aspect of the watercourse, and Luna Leopold, who dealt with the physical changes of the water. The essential complement to the working group of Vannote was the completion and explanation of the communities in this system. Vannote himself described the initial situation as follows:
( German: "At that time most people analyzed a square meter of water to death." )
The research was always so only small portions of the waters, and they were only very rarely considered in its entirety as watercourses.
After its publication, the River Continuum Concept quickly found acceptance among experts and became the favored model for the description of biological communities in rivers. Here it solved the classical division of the waters in Fish regions, which was developed by Robert Lauterborn 1916-1918 on the basis of the communities in the Rhine, and the division into the habitats Krenal, Rhithral and potamal by Joachim Illies in his publication " attempt at a general biocoenotic Outline of rivers "(1961 ) from. Both concepts have the disadvantage that they are always described only zones of the water and no consideration of the system allowed in its entirety, as allowed by the River Continuum Concept.
In practice, the River Continuum Concept is today mainly used for the ecological assessment of rivers and their disorders. Thus, the species composition can be determined and compared with the ideal case by the River Continuum Concept for an investigation of the biological communities in a river. Above all, an overweight or lack of feeding types can provide information on any existing disorder.
Problems, limitations and modifications
Although the River Continuum Concept has encountered widespread acceptance, it is limited in its applicability. It describes a model and an optimal smoothly varying river without disturbances and irregularities. Not included are about inflows, blockages by dams or lakes or irregular events such as flooding the shore.
In order to detect these irregularities in the model, the River Continuum Concept was developed and varied by different authors. Thus developed, for example, JV Ward and JA Stanford, 1983, the Serial Discontinuity Concept, in which they integrated the effects of geomorphic disturbances such as those mentioned congestion and inflows. The same authors presented the Hyporheic Corridor Concept before 1993, in which the vertical ( in depth ) and lateral was also connected ( from shore to shore ) structural complexity with the continuum of the river. The Flood Pulse Concept, developed by WJ Junk et al. In 1989 and further modified by PB Bayley in 1990 and K. Tockner et al. 2000 finally brought an even, that a great part of nutrients and organic material comes from the sediment and flooded parts of the landscape in the river. In particular, the productivity of very large rivers with large flood plains describes the developed in 1994 by JH Thorp and MD Delong Riverine Productivity Model ( RPM).