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The flood pulse concept explains how the periodic inundation and drought (flood pulse) control the lateral exchange of water, nutrients and organisms between the main river channel (or lake) and the connected floodplain. The annual flood pulse is the most important aspect and the most biologically productive feature of a
river
A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of w ...
's
ecosystem
An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...
.
[Thorp, J. H., & Delong, M. D. (1994). The Riverine Productivity Model: An Heuristic View of Carbon Sources and Organic Processing in Large River Ecosystems. Oikos , 305-308] describing the movement, distribution and quality of water in
river ecosystems and the dynamic interaction in the transition zone between water and land (aquatic/terrestrial transition zones - ATTZ). It contrasts with previous
ecological theories
Theoretical ecology is the scientific discipline devoted to the study of ecological systems using theoretical methods such as simple conceptual models, mathematical models, computational simulations, and advanced data analysis. Effective models im ...
which considered
floods to be catastrophic events.
Background
River floodplain systems consist of an area surrounding a river that is periodically flooded by the overflow of the river as well as by precipitation, called the aquatic/terrestrial transition zone (ATTZ). The ATTZ is the area covered by water only during the flooding.
[Johnson, Barry L., William B. Richardson, and Teresa J. Naimo. 1995. Past, Present, and Future Concepts in Large River Ecology. p. 134-141. In BioScience, Vol. 45.] This flooding in turn creates unique habitat that is essential to the survival of many different species.
[Junk, W.J., P.B. Bayley, and R.E. Sparks. 1989. The flood pulse concept in river-floodplain systems. p. 110-127. In D.P. Dodge d.Proceedings of the International Large River Symposium. Can. Spec. Publ. Fish. Aquat. Sci. 106.] The flood pulse concept is unique because it incorporates the outlying rivers and streams which add a lateral aspect to previous concepts, e.g. the River Continuum Concept (RCC) that failed in explain processes that happen in big rivers and their floodplains. From this lateral perspective, rivers can be seen as a collection of width-based water systems.
[
Flooding consists of multiple stages. First, at the start of the flooding, nutrients rush in from the area where the flood begins. During flood periods, the most important element is called the moving ]littoral
The littoral zone or nearshore is the part of a sea, lake, or river that is close to the shore. In coastal ecology, the littoral zone includes the intertidal zone extending from the high water mark (which is rarely inundated), to coastal a ...
. As flooding begins and water levels increase nutrients that have been mineralized in the dry phase are suspended with sediments in the flood waters and main river. The moving littoral consists of the water from the shoreline to a few meters deep in the river. This pulse of water is the primary driver of high productivity and decomposition rates as it moves nutrients in and out of the system and is good breeding ground for many species of estuarial organisms.[ At this point in time production rates exceed decomposition rates. As water levels stabilize, decomposition rates outpace production rates, frequently contributing to ]dissolved oxygen
Oxygen saturation (symbol SO2) is a relative measure of the concentration of oxygen that is dissolved or carried in a given medium as a proportion of the maximal concentration that can be dissolved in that medium at the given temperature. It ca ...
deficiency. When the water starts receding, the moving littoral reverses, concentrating nutrients and contributing to phytoplankton growth.
Living communities and flood types
The flood pulse helps maintain genetic and species diversity in the floodplain ecosystem, and it brings in oxygen to help fauna and decomposition. The flood pulse also increases yields by increasing the surface area of water and showers the land with river biota. Flood plain systems also serve as migration routes, hibernation spots, and spawning
Spawn is the eggs and sperm released or deposited into water by aquatic animals. As a verb, ''to spawn'' refers to the process of releasing the eggs and sperm, and the act of both sexes is called spawning. Most aquatic animals, except for aquat ...
locations for many species.[ For the ]red-bellied piranha
The red-bellied piranha, also known as the red piranha (''Pygocentrus nattereri''), is a Type (biology), type of piranha native to South America, found in the Amazon basin, Amazon, Paraguay River, Paraguay, Paraná River, Paraná and Essequibo Ri ...
, their two annual reproductive seasons are dependent on the flooding pulse. However, the flood pulse has the potential to overpower some species; when flood pulses occur at unusual times or last for too long, terrestrial vegetation can be overwhelmed.[ Furthermore, the receding of the flood at the end of the flood pulse can lead to oxygen deficiency.
]
Human impact
River floodplain systems can be both natural and man-made; the latter occur when dams
A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use ...
and levees
A levee (), dike (American English), dyke (Commonwealth English), embankment, floodbank, or stop bank is a structure that is usually earthen and that often runs parallel to the course of a river in its floodplain or along low-lying coastli ...
create a flood plain.[ Humans have had several effects on the flood pulse. Through ecosystem alterations such as dams, debris removal, channelization, levees, navigation, irrigation, contamination, logging, fire suppression, species introduction, and agricultural runoff, humans have contributed to the destruction of wetlands and the extinction of species. Biota relies on the flood plain for food supply, spawning and shelter, and flood pulses that are too quick or slow interrupt this. This can have devastating effects on riparian ecosystems.][
]
Criticisms and alternative concepts
The flood pulse concept is one of three primary models describing large river ecosystem
River ecosystems are flowing waters that drain the landscape, and include the biotic (living) interactions amongst plants, animals and micro-organisms, as well as abiotic (nonliving) physical and chemical interactions of its many parts.Angelier ...
s. The others include the river continuum concept (RCC) and the serial discontinuity concept.[ Related theories include the nutrient spiraling concept.] Many theorists have criticized the flood pulse concept and believe that other concepts could help explain the phenomena that occur in large rivers. Some say that the flood pulse concept is inadequate because it only applies to temperate
In geography, the temperate climates of Earth occur in the middle latitudes (23.5° to 66.5° N/S of Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ranges throughout ...
and tropical
The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in
the Southern Hemisphere at S. The tropics are also referred to ...
systems.[ The flood pulse concept involves many assumptions; many theorists object to the concept on the basis of these assumptions. The flood pulse concept assumes that all systems are either hierarchical or linear, that physical features control biological structures, and that there is ]dynamic equilibrium
In chemistry, a dynamic equilibrium exists once a reversible reaction occurs. Substances transition between the reactants and products at equal rates, meaning there is no net change. Reactants and products are formed at such a rate that the co ...
between the biological and the physical rhythms.[ Because of their criticisms of the flood pulse concept, some theorists prefer the river continuum concept. However, Junk et al. argue that the river continuum concept is not sufficient because it is based on research done on small temperate streams and has mistakenly been applied to all water systems; furthermore, the river continuum concept does not explain habitats that fluctuate between lotic and ]lentic
A lake ecosystem or lacustrine ecosystem includes biotic (living) plants, animals and micro-organisms, as well as abiotic (non-living) physical and chemical interactions. Lake ecosystems are a prime example of lentic ecosystems (''lentic'' re ...
states, whereas the flood pulse concept adequately covers these systems.[
]
References
{{Rivers, streams and springs
Ecological theories
Rivers
Flood