A brief history of river ecosystem function, part 2: serial discontinuity to the flood pulse

In Part 1 of this brief history I talked about how ideas of zones in rivers – mainly related to fish abundance and distribution – were succeeded by those of the river continuum, emphasizing a more longitudinal, continuous movement of material, energy and species downstream.  The River Continuum Concept, as it was known, sparked enormous interest and a lot of activity thereafter. But rivers come in all shapes and sizes and one size definitely does not fit all.  Firstly, many rivers (most large ones in the world) are regulated to greater and lesser extents.  So, people started to ask how regulation might affect river functioning.  And then, those who worked in large, lowland rivers with extensive floodplains, questioned the generality of the RCC, and pondered on alternative sources of carbon in rivers and pathways of matter and energy.

The serial discontinuity concept (SDC), proposed by James Ward and Jack Stanford (Ward and Stanford 1983), took the idea of the river continuum and asked what would happen to the patterns and processes, as described in the RCC, if an instream dam or weir (those actually in the river channel, blocking the flow) was placed somewhere in the system. It contends that dams disconnect sections of the river upstream and downstream and displace resource gradients downstream to varying extents. In effect, the dam shifts everything downstream. The SDC does not say much about fish, but does make predictions about the nature of energy and materials that can be translated to fish relatively easily. This concept has been widely cited, but hypotheses coming from it, not well tested, which is somewhat surprising, given how common dams are in rivers. There is, however, general agreement that large instream dams (those actually in the river channel, blocking the flow) do have an influence on longitudinal patterns in fish assemblages. For example, Arajo et al. (2009) found that fish assemblages were affected more by damming and less by season in a large tropical Brazilian river; An and Choi (2003) recorded major changes in fish guild structure following the construction of a dam during a long-term study in Korea; and Reyjol et al. (2001) showed that in unregulated sections of a river in France, temperature determined the transition from the salmonid-dominated region to the cyprinid-dominated region, but that this changed with regulation and the presence of dams. So, the SDC certainly has merit but doesn’t seem to excite people as much as perhaps it should.

The next big idea was the flood pulse concept (FPC), proposed in 1989 by Wolfgang Junk, Peter Bayley and Richard Sparks, working in German and US rivers. It arose from a dissatisfaction with the RCC, based on observations largely derived from tropical floodplain rivers (Junk et al. 1989; Junk and Bayley 2008), although it has been more recently extended to temperate systems (Tockner et al. 2000) and to lakes (Wantzen et al. 2008) as well. The FPC emphasizes the floodplain as an important source of material and energy, inundation of the floodplain by a flood pulse as the catalyst for mobilising that material and energy; and movement of that material and energy from the floodplain into the main channel as the process that fuels food webs in floodplain rivers. The emphasis, therefore, is more on lateral connectivity than a longitudinal continuum. The flood pulse is termed a ‘batch process’, rather than a continuous process – occurring in discrete time periods. The FPC was the first real river model to put up front the significance of a conceptual framework for fish. It emphasized the importance of the floodplain for fish breeding and as a nursery habitat, while also relating fish production in the main channel to nutrients draining back from the floodplain as the flood receded. The main channel, according to the FPC was used only temporarily for migration, spawning, refuge during droughts or freezing and for hibernation. Many examples exist of fish whose life histories or peaks in feeding coincide with predictable flood pulses (e.g. Goulding 1980), Welcomme 1985). Indeed, the timing and duration of flooding has been shown to influence population dynamics (Finger and Stewart 1987; Stassen et al. 2009), growth of species associated with the aquatic/terrestrial transition zone (Gutreuter et al. 1999; Glemet and Rodriguez 2007) and/or production of young (Feyrer et al. 2006; Tonkin et al. 2008; King et al. 2009) in some species of riverine fish. For flatter, low-gradient rivers, it appears that the FPC can predict the source of carbon in food webs (Hoeinghaus et al. 2007).

The flood recruitment model (FRM) developed by John Harris and Peter Gehrke ( NSW Fisheries) for Australian systems, developed the FPC as it related to the recruitment of fish in Australia’s Murray-Darling Basin, arguing that flooding cued some species to spawn and perhaps use the floodplain, whereas others benefited through production of zooplankton derived from the floodplain, but which is washed into the main river channel (Harris and Gehrke 1994). Benefits derived from the flood pulse may be less obvious for some fishes, however. For example, species that normally living on floodplains or only occupying the edges of large rivers may be able to move among floodplain habitats during flooding, contributing to their reproductive success or overall survival (Tonkin et al. 2008). It is apparent, however, that the coupling of temperature and flooding are critical for floodplain use, which is often not the case in temperate systems (King et al. 2003).

These concerns about the coupling or otherwise of the key factors that influence use of the floodplain by fish, especially for breeding purposes, made some scientists question the generality of the FPC and FRM for some river systems. The development of other ideas, especially those related to production within the main channel of rivers, will be the focus of Part 3 of this history of river ecosystem ideas.

References

An KG and Choi SS (2003) An assessment of aquatic ecosystem health in a temperate watershed using the index of biological integrity. Journal of Environmental Science and Health – Part A Toxic/Hazardous Substances and Environmental Engineering 38, 1115-1130. Araújo FG, Pinto BCT and Teixeira TP (2009) Longitudinal patterns of fish assemblages in a large tropical river in southeastern Brazil: Evaluating environmental influences and some concepts in river ecology. Hydrobiologia 618, 89-107. Feyrer F, Sommer T and Harrell W (2006) Managing floodplain inundation for native fish: Production dynamics of age-0 splittail (Pogonichthys macrolepidotus) in California’s Yolo Bypass. Hydrobiologia 573, 213-226. Finger TR and Stewart EM (1987) Response of fishes to flooding regime in lowland hardwood wetlands. In ‘Community and evolutionary ecology of North American stream fishes.’ (Eds WJ Matthews and DC Heins) pp. 86-92. University of Oklahoma Press, Norman. Glemet H and Rodriguez MA (2007) Short-term growth (RNA/DNA ratio) of yellow perch (Perca flavescens) in relation to environmental influences and spatio-temporal variation in a shallow fluvial lake. Canadian Journal of Fisheries and Aquatic Sciences 64, 1646-1655. Goulding M (1980) ‘The fishes and the forest. Explorations in Amazonian natural history.’ University of California Press, Berkeley. Gutreuter S, Bartels AD, Irons K and Sandheinrich MB (1999) Evaluation of the flood-pulse concept based on statistical models of growth of selected fishes of the Upper Mississippi River system. Canadian Journal of Fisheries and Aquatic Sciences 56, 2282-2291. Harris JH and Gehrke PC (1994) Development of predictive models linking fish population recruitment with streamflow. Proceedings of the Australian Society for Fish Biology Workshop. In ‘Population Dynamics for Fisheries Management.’ Ed. DA Hancock) pp. 195-199. Bureau of Rural Resources Proceedings, Canberra. Hoeinghaus DJ, Winemiller KO and Agostinho AA (2007) Landscape-scale hydrologic characteristics differentiate patterns of carbon flow in large-river food webs. Ecosystems 10, 1019-1033. Junk WJ and Bayley PB (2008) The scope of the flood pulse concept regarding riverine fish and fisheries, given geographic and man-made differences among systems. In ‘Reconciling Fisheries with Conservation, Vols I and Ii. Vol. 49.’ (Eds J Nielsen, JJ Dodson, K Friedland, TR Hamon, J Musick and E Verspoor) pp. 1907-1923. Junk WJ, Bayley PB and R.E. S (1989) The flood pulse concept in river-floodplain systems. Can. Spec. Publ. Fish. Aquat. Sci. 106, 110-127. King AJ, Humphries P and Lake PS (2003) Fish recruitment on floodplains: The roles of patterns of flooding and life history characteristics. Canadian Journal of Fisheries and Aquatic Sciences 60, 773-786. King AJ, Tonkin Z and Mahoney J (2009) Environmental flow enhances native fish spawning and recruitment in the Murray River, Australia. River Research and Applications 25, 1205-1218. Reyjol Y, Lim P, Dauba F, Baran P and Belaud A (2001) Role of temperature and flow regulation on the Salmoniform-Cypriniform transition. Archiv fur Hydrobiologie 152, 567-582. Stassen MJM, van de Ven MWPM, van der Heide T, Hiza MAG, van Der Velde G and Smolders AJP (2009) Population dynamics of the migratory fish Prochilodus lineatus in a neotropical river: The relationships with river discharge, flood pulse, El Nino and fluvial megafan behaviour. Neotropical Ichthyology 8, 113-122. Tockner K, Malard F and Ward JV (2000) An extension of the flood pulse concept. Hydrological Processes 14, 2861-2883. Tonkin Z, King AJ and Mahoney J (2008) Effects of flooding on recruitment and dispersal of the Southern Pygmy Perch (Nannoperca australis) at a Murray River floodplain wetland. Ecological Management and Restoration 9, 196-201. Wantzen KM, Junk WJ and Rothhaupt KO (2008) An extension of the floodpulse concept (FPC) for lakes. Hydrobiologia 613, 151-170. Ward JV and Stanford JA (1983) The serial discontinuity concept of lotic ecosystems. Dynamics of lotic ecosystems (book) ed: T.D. Fontane & S.M.Bartell, 29-42.

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