Community responses to organic loading in a microcosm.

Aquatic microcosms consisted of bacteria, Chlorella, blue-green alga, ciliate protozoa, rotifer and aquatic oligochaete. Invertebrates declined to extinction when organic loading was added at a young stage, while invertebrates in the mature stage hardly became extinct after loading. Algae in the sediment, which increased as succession proceeded, contributed to the stabilization of invertebrate populations. Invertebrates in microcosms loaded at a young stage were extinct by a temporary rise of the un-ionised ammonia concentration, caused by accumulation of total ammonia (due to the small amount of algae in the sediment) and by high pH. The mature microcosm showed high stability because a large amount of algae and low pH inhibited the increase of un-ionized ammonia subsequent to loading. -from Authors