Changes in the density of zooplankton passing through the cooling system of a power-generating plant

The densities of copepods, copepod nauplii, barnacle nauplii, and bivalve larvae were determined at the inlet and outlet of the cooling system of a large power station, which is located on a lake system with a narrow opening to the sea. The variability in plankton abundance in the cooling water was examined and a sampling technique was devised to obtain data that could be reliably compared between inlet and outlet. This technique consisted of lowering and raising a net sampler through the water column. There was no significant change in numbers of copepods after passage through the cooling system. However, significant changes were recorded for copepod nauplii and bivalve larvae (decreases), and barnacle nauplii (increase). Possible causes for these changes are discussed.