The composition and ecology of periphyton communities in freshwaters. II. Inter-relationships between water chemistry, phytoplankton populations and periphyton populations in a shallow lake and associated experimental reservoirs (‘Lund tubes’)

Abstract

Water chemistry, phytoplankton populations and periphyton populations on Potamogeton pectinatus, have been compared in a shallow, brackish lake, Hickling Broad, and in two enclosed, 20 m diameter butyl rubber reservoirs, placed in it. The seasonal changes of periphyton on Hippuris vulgaris and Myriophyllum spicatum in the lake have also been examined. The lake has been made more eutrophic by agricultural land drainage and roosting gull populations, the tubes to a greater extent by gulls perching on their rims. The water in the tubes became persistently dominated by colonial blue-green algae, a spring diatom pulse was absent, and severe nitrogen limitation was found. Periphyton on P. pectinatus in the tubes was scanty. In the lake, however, though phytoplankton chlorophyll a levels were lower, an alternation of spring diatom and summer colonial blue-green algae was recorded. Nitrogen limitation was less severe in the lake and abundant periphyton crops, mainly of diatoms, developed on P. pectinatus and to an even greater extent on the other macrophytes. The differential development of the periphyton in the tubes and lake was related to differential nitrogen availability in these phosphorus-enriched waters, and the muted seasonality of the phytoplankton in the tubes to the absence of flushing of the water body in autumn and winter. The periphyton diatom populations were of two species groups, one apparently confined to the periphyton, the other of species shared with the plankton. These latter, Diatoma elongatum and Synedra sp underwent cell division in both the periphyton and in the plankton and appeared not to be casual introductions into either community.