The long, the short and the stalled: on the attributes of phytoplankton selected by physical mixing in lakes and rivers

Abstract

Paradoxically, although turbulence characterises the open water environments of planktonic organisms in lakes, rivers and seas, most species of phytoplankton are smaller than the size of the smallest eddies dissipating the energy and, so, must function in an immediate medium which is inherently viscous. Intensively mixed systems, such as wind-stirred shallow lakes, rivers and estuaries, however, constantly readjust the vertical position of suspended algae and, often, other non-living, light-absorbing particles with the effect that the light field to which the algae are subject is erratic and the received day-time light dose is aggregately depressed: cells need to photoadapt accordingly. In fluvial environments the additional constraint of rapid, horizontal, supposedly unidirectional, transport is applied, requiring the attribute of rapid processing of primary products and cell replication. Significant downstream recruitment, however, is benefitted by the presence of so-called 'dead-zones' which retain water (and suspended plankton) sufficiently to accommodate additional cell divisions.

Morpho-physiological responses of a subtropical strain of Cylindrospermopsis raciborskii (Cyanobacteria) to different light intensities

“…This is particularly relevant in Alagados reservoir, where light is a regulating factor of phytoplankton growth during late fall and winter, due to both the seasonal declining of atmospheric irradiance coupled with shortening of day length in fall and winter in South Brazil (Fernandes et al 2005a), and the mixing zone usually greater than the photic zone (unpublished data). Large overwintering populations are one reason why cyanobacteria with low specific growth rates become dominant in summer phytoplankton communities (Reynolds 1994). As reported by Dokulil (2015), the C. raciborskii population of Lake Alte Donau survived adverse periods, being able to inoculate the phytoplankton assemblage in the following spring.…”

The past and future of phytoplankton in the UK's largest lake, Lough Neagh

“…This is concerning because it suggests that even a 60% reduction of the 2008 phosphorus and nitrate loads is not enough to break its dominance in the lake. This is a phenomenon often seen in shallow, turbid, poorly flushed and nutrient rich lakes (Reynolds, 1994), where a positive feedback is established for this low-light tolerant cyanobacteria. The PROTECH model also reflects this low-light specialization in its modelling of Planktothrix, hence its continued dominance in most of the scenarios.…”

Responses of phytoplankton functional groups to the hydrologic regime in the Daning River, a tributary of Three Gorges Reservoir, China

“…As a result, the suspended particulate matter of the mainstream and tributary generated the turbid condition in the estuary and in the upstream in the Daning River, respectively. Species selectivity in the turbid kinetic habitats was likely to favor diatoms, especially those with high surface/volume ratios and which show adaptability to low light, such as species of group MP (Reynolds, 1994). This group, including Melosira and pennate diatoms, such as Navicula, Nitzschia and Stauroneis, includes all the meroplanktonic (mostly diatoms) autotrophic organisms which can adapt to frequently mixed, inorganic, turbid habitats (Bovo-Scomparin and Train, 2008;Padisák et al, 2009).…”