Hydraulic Habitat of Plants in Streams

Abstract

Plant development in unshaded streams is reviewed within the context of a conceptual habitat model. Resource factors (incorporating light, nutrients and temperature) predominantly govern the processes of biomass gain and hydraulic factors (incorporating separate temporal and spatial scales) predominantly govern the processes of biomass loss. It is postulated that differences in hydraulic stability among streams over periods greater than a year govern whether a stream (or site) is dominated by periphyton, bryophytes or macrophytes. Hydraulic stability over periods of less than a year governs the average periphyton biomass. During steady‐state, interspate periods the effect of spatial differences in hydraulics varies depending on the stage of plant development. Periphyton and macrophyte colonization is enhanced by low velocities, and growth rate and organic matter accrual can be enhanced by moderate velocities. However, high velocities retard colonization and organic matter accrual. For mature communities, the peak biomass of periphyton and macrophytes can be negatively correlated with velocity. This is in contrast with bryophytes, which are often restricted to areas of high velocity on stable substrata. Hydraulic habitat suitability curves have yet to be developed for plant communities in streams.

Influence of slight differences in environmental conditions (light, hydrodynamics) on the structure and function of periphyton

“…In our experiments, the growth dynamics of periphyton and the change in its diversity over time matched those reported in numerous other studies (Biggs 1996;Guasch et al 1997;Hillebrand and Sommer 2000;Sekar et al 2002): the number of algal species, revealed by finger printing, indicated a loss of richness and diversity. We observed a decrease in the Shannon index, in the number of bands present per profile, and a change in species composition between the two stages of maturity.…”

“…In our experiments, the biomass, number of algal and bacterial cells, and primary production increased under all experimental conditions. Schematically, global changes in periphyton display three successive phases (Biggs 1996): a colonization phase, an exponential growth phase and an aging phase. The start of the growth phase is characterized by a low biomass and fairly high diversity.…”

“…In contrast to the algal community, the structure of the bacterial community does not seem to be determined by its maturity. In view of these findings, and despite the limited number of samples taken over time, it is possible to consider that our sampling times represent the beginning and end of the growth phase of the periphyton as defined by Biggs (1996) and other authors.…”

Ecological significance of hydrological connectivity for wetland plant communities on a dryland floodplain river, MacIntyre River, Australia

“…Conversely, subsidy (or stress) will influence abundance more than the species pool because the subsidy can only act on the available pool, but will directly contribute to recruitment success. Hydraulic disturbance is also more likely to influence abundance more than species pool because, although different taxa may be more susceptible to losses associated with hydraulic stress (Biggs 1996), it is unlikely that species would be totally lost from a wetland (Riis and Biggs 2003).…”

Changes in the spectral and chemical properties of a water mass passing through extensive macrophyte beds in a large fluvial lake (Lake Saint-Pierre, Québec, Canada)

“…Furthermore, the low current velocities in these lakes allow small particles to settle and these may then serve as substrates for the colonization of aquatic plants. Aquatic vegetation is principally limited by high current velocity and low light conditions (Barko et al, 1986;Biggs, 1996). Shallow fluvial lakes thus represent ideal environments for macrophyte development.…”