The River Continuum Concept (RCC) is a model for classifying and describing flowing water, in addition to the classification of individual sections of waters after the occurrence of indicator organisms. The theory is based on the concept of dynamic equilibrium in which streamforms balance between physical parameters, such as width, depth, velocity, and sediment load, also taking into account biological factors. It offers an introduction to map out biological communities and also an explanation for their sequence in individual sections of water. This allows the structure of the river to be more predictable as to the biological properties of the water. The concept was first developed in 1980 by Robin L. Vannote, with fellow researchers at Stroud Water Research Center.
Background of RCC The River Continuum Concept is based on the idea that a watercourse is an open ecosystem that is in constant interaction with the bank, and moving from source to mouth, constantly changing. Basis for this change in the overall system is due to the gradual change of physical environmental conditions such as the width, depth, water, flow characteristics, temperature, and the complexity of the water. According to Vannote's hypothesis, which is based on the physical geomorphological theory, structural and functional characteristics of stream communities are selected to conform to the most probable position or mean state of the physical system. As a river changes from headwaters to the lower reaches, there will be a change in the relationship between the production and consumption (respiration) of the material (P/R ratio). The four scientists who collaborated with Dr. Vannote were Drs. G.Wayne Minshall (Idaho State University), Kenneth W. Cummins (Michigan State University), James R. Sedell (Oregon State University), and Colbert E. Cushing (Battelle-Pacific Northwest Laboratory). The group studied stream and river ecosystems in their respective geographical areas to support or disprove tenets of their original theory. The research resulted in the publication of 33 scientific papers (see attachment to Bibliography). The original 1980 paper received the John Martin Award from the Association for the Sciences of Limnology and Oceanography (formerly the American Society of Limnology and Oceanography) that recognizes papers still relevant ten years after their publication. Subsequent research related to the RCC by these scientists has resulted in several more scientific papers that amplify parts of the original RCC.
Living communities and food types The continuous differences of properties within the river are dependent primarily on the specific composition of the organisms in different sections of the water. Throughout the continuum of the river, the proportion of the four major food types; shredders, collectors, grazers (scrapers) and predators changes. With the exception of the predators, all these organisms feed directly from plant material (saprobes).
Shredders Shredders are organisms that feed off of coarse particulate organic material (CPOM) such as small sections of leaves. They ingest the organic matter along with volunteer organisms (fungi, microorganisms) attached to the source. The preferred size of the CPOM is about one millimeter, therefore shredders must break it up into a finer particulate. In the process of shredding, much of the now finer organic matter is left in the system, making its way further downstream. Some common shredders of North American waters include scuds (Amphipoda), aquatic sowbugs (Isopoda), cranefly larvae (Tipulidae), some caddisfly larvae (Trichoptera, Integripalpia), and some stonefly larvae (Plecoptera), whereas Atyid shrimp (Atyidae) fulfill the same role in tropical environments.
Collectors Collector organisms are designated by their use of traps or other adaptive features to filter and catch organic matter. The preferred particle size for collectors lies between 0.5 and 50 micrometers (UPOM = Ultrafine particulate organic matter and FPOM = fine particulate organic matter). This group includes some caddisflies (Trichoptera, Annulipalpia), fly larvae (Chironomidae and Simuliidae), nematodes, and many other animal groups.
Grazers The grazers (scrapers) feed off of periphyton that accumulates on larger structures such as stones, wood or large aquatic plants. These include snails, caddisflies (Glossosoma genus), and other organisms. Because of the structure of organic matter at different sections in a river, the make up and frequency of these groups in a community vary. In the upper reaches of a river, shredders and collectors make up a large percentage of total macroinvertebrates due to the excess presence of coarse plant matter. In the midreaches of a stream or river, where more light is available, there is an increase in the proportion of grazers due to the presence of periphyton. Shredders only make up a small percentage of the total invertebrates due to the lack of coarse organic matter making its way downstream. In the lower reaches, organic matter has been shredded completely to the level of FPOM or UPOM (Ultra-fine Particulate Organic Matter). Due to the increase in fine particulate organic matter, collectors are the most abundant in the lower reaches, feeding off organic matter and surface films. The proportion of predators in all sections remains largely constant and only changes in species composition. The reason for the even distribution is that predators are not dependent on the size of the organic matter but on the availability of prey animals in the area. Atypical changes in the composition of these groups of organisms within a watercourse, such as an increased number of choppers in a major river area (mid to lower reach) or a lack of these organisms in the upper reaches, suggest a possible disturbance.
Division of the riverine The River Continuum Concept assigns different sections of a river into three rough classifications. These classifications apply to all river waters, from small streams to medium-sized and large rivers and lakes.
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