Studies in Recolonization of Stream Substrates by Aquatic Organisms

The colonization of limestone gravel, limestone gravel + organic matter, and limestone gravel from a river bed was followed over time in order to compare two possible stream reclamation substrates with a control (river gravel). After nine weeks of colonization by benthic micro- and macro-organisms there were few significant differences between the river gravel control and limestone gravel and limestone gravel + organic matter, the two gravels under test. Specific differences were noted in algal composition of the epilithon, with the numbers of Cyanophyta and Chlorophyta being 50% below those on river gravel while the numbers of Bacillariophyta were considerably higher (300 to 1000%), yet the chlorophyll a concentration was approximately the same on all three gravels at 0.4 µg•cm-2. However, the similar numbers and biomass of micro-invertebrates on the three gravels suggested that the amount of energy available for higher trophic levels was equivalent. A major difference between the river gravel and the two test gravels was in the very much larger macro-invertebrate population found in the latter. It was concluded that, although limestone rubble would be a suitable substrate for river reclamation, the time for recolonization would be considerably longer than indicated in the study because of the very high levels of propagules available from the river in which the experiments were carried out.