The algal flora of certain gravel pits in the Thames Valley

Abstract

The phytoplankton and, to a limited extent, the attached algae of four gravel pits in the Thames Valley were investigated. The pits are in two pairs, one old and the other recently excavated. In all gravel dredging has been in progress and the water of each could be clearly divided into that fairly frequently disturbed by gravel grab and that which was not so disturbed. The distribution of the algae in general and the seasonal variation for certain algae or groups of algae were considered and attempts were made to correlate these with the physical and chemical features of the environment. The maximum of an alga was not always simultaneous in all the pits. Certain algae favoured the new pits and others the old ones, but many appeared to be indifferent. Similarly, while some of the algae tended to favour the disturbed or the undisturbed water of a pit, many did not appear to be affected by disturbance and were apparently equally distributed over the pit. An attempt has been made to compare the phytoplankton of the Thames in the neighbourhood of the pits with that of the pit which is in permanent communication with the river. While, except for six species found only in the river, the species list is the same, an alga did not always occur in the river and pit samples simultaneously.