THE PHYTOPLANKTON OF SOME GRAVEL-PIT LAKES IN SPAIN

The phytoplankton communities of thirteen adjacent gravel-pit lakes in the lower Jarama river watershed (Madrid, Spain), were studied during spring mixing and summer stratification. If different seasons, the ph ytoplankton responded to different environmental factors. During sprin g, the abundance of SRP (soluble reactive phosphorus) and existence of a certain thermal stability resulted in the development of a greater biomass in some lakes. During summer, however, excessively high temper atures adversely affected the communities of the warmer lakes. At the species level, the responses were diverse; ordination techniques enabl ed us to group them.Some similarities were observed in phytoplankton c omposition between lakes, possibly due to local dispersion between adj acent lakes (frequented by abundant waterfowl).