The difficulty of determining the fate of radionuclides in aquatic systems is complicated by chemical and biological differences within the system and by the variety and scope of the circulatory mechanisms. In oceans the sheer immensity of the water volume usually makes observation superficial or fragmentary. Rivers present great differences in flow, and lakes vary in internal dynamics. Above all, an ocean, a river, or a lake is an area of constant physical and biological motion and change. In the ocean the surface waters form a theater of kaleidoscopic, and frequently violent, action. The presence of man-made radioactivity in water has made it possible to follow the disposition of nutrients and wastes in the restless aquatic ecosystem.
Biological Uptake
In a water environment the minerals necessary to life are held in solution or lie in bottom sediments. They become available to animal life after being absorbed by plants, both large floating or rooted plants and tiny floating ones called phytoplankton; because the phytoplankton are found everywhere in the sea, they play a larger role. The phytoplankton concentrate minerals and become food for filter-feeding fish and other creatures, including the smaller zooplankton,[14] which, in turn, are food for other organisms. Thus the minerals enter extremely complex food chains. The cycles of nutrition are completed when fish and plants die and decomposition again makes the minerals available to the phytoplankton.
ENVIRONMENTAL RESEARCH
RAIN FOREST. A giant fan pulls air through a plastic-enclosed portion of a Puerto Rico rain forest to study the metabolism rate of trees.
HARDWOOD FOREST. Technicians preparing to tag Tennessee trees with a solution containing a radioactive cesium isotope in the start of a 10-year project. Scientists will study movement of the radioactivity into insects and their predators.
FRESHWATER. Aquatic biologists emptying plankton traps to study concentrations of radioactivity in microscopic organisms in the Columbia River downstream from the Hanford atomic plant in Washington State.