Experimental simulation of fate in rivers: a mesocosm for studies with radiolabelled substances
An artificial stream mesocosm is described which was installed to simulate fate and effects of pesticides in relevant stream compartments. The combined approach of a fate effect study will only be useful, if a detailed risk assessment is considered necessary. For pesticides with insecticidal, adsorptive or persistent properties, a simulation of a stream ecosystem is recommended. The presented system has sufficient size and complexity for self-preservation of the inherent populations except the period of oviposition of aquatic insects. It is filled with natural sediment from a nearby unloaded small stream which can also serve as control system. Investigations of fate and effects of the test substance(s) are possible in different distances from the loading area, at sites with different current velocity and in different microhabitats. The system is also suited for the investigation of water leaching through the river bed. It is part of the institute's outdoor field simulation facilities for studies with radiolabelled substances and therefore completely built in stainless steel. The circular stream trough has a length of about 35 in, a width of 0.6 m and a depth of 0.35 m. An extended segment and two inlets with aquatic lysimeters diversify current velocity. Current is generated by electrically-driven paddles. Two tanks are used for water supply and to collect water overflow. They will also be integrated in a concept of an initial once-through course which will be constructed for the simulation of a spot loading. Weaknesses and improvements of the system as well as validation studies are mentioned.