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 change. 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 the Mayfly (Ephemeroptera), Odonata (damselflies) and stone fly (Plecoptera) larvae, whereas decapods (particularly Atyid shrimp) 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 fly larvae, 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.