ISSN:
1573-5117
Keywords:
potamoplankton
;
algae
;
rotifers
;
storage zones
;
local pulseinoculates
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract The seasonal succession of the potamoplankton of the Middel Loire was studied fortnightly from June to October 1995, a period of low water flow. The increase in dissolved oxygen, suspended matter, BOD5 and chlorophyll a, associated with the decrease in nutrients downstream, are typical of eutrophic rivers. Algae were the principal components of the suspended matter flux in the river. Their density increased from the upper site of Dampierre-en-Burly to the lower site of Saint-Laurent des Eaux, with respective maxima of 68 ×106 cells l-1 and 106 × 106cells l-1. A large rotifer community developed in association with the algal growth, with densities up to 3700 ind l-1 at Dampierre-en-Burly and up to 5800 ind l-1 at Saint-Laurent des Eaux. They had a high Shannon-Weaver diversity, while grazing appeared to control the algae. As the year progressed to the warmer season, the biomass of the β and β α mesosaprobic rotifer species increased parallel with algae. The water theoretically transported potamoplankton at 0.2 ms-1 during mid-summer, which meant that the biomass of the algae doubled in minimum 17 km and that of the rotifers in 34 km. From these values and the distances between sampling stations, we deduce that inoculation points were located in areas which could be as short as a hundred meters. Not only algae, but also rotifers are capable of restoring an inoculum of organisms from place to place. Summer hydrodynamics, close to localised lentic areas, were responsible for an increase in plankton abundance in the stream. These movements had an ecotone effect at the boundary between standing and running water, creating pulses. The lower regions were progressively enriched by successive inoculates, dilution and seeding inputs, which did not prevent the growth of algae and of parthenogenetic species in the river. Such processes, which occur in years of low flow, are responsible for the large variations in plankton density observed between years.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1003127230386
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