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Up to 99% of the energy available to stream communities consists of terrestrial plant detritus (leaves, needles, twigs). Aquatic hyphomycetes, a heterogeneous group of aquatic fungi, are an indispensable link in the food web between this detritus and stream invertebrates, which in turn provide the basic diet for many fish. The annual production of the fungi is similar to that of bacteria and invertebrates, but little is known about their taxonomy, biology and ecology. One of my objectives is to document the diversity of aquatic hyphomycetes in Maritime streams, both by conventional (microscope-based) and molecular (DNA-based) techniques. At the same time, I am interested in factors that control or regulate fungal numbers and productivity. A more thorough understanding of fungal ecology will allow us to evaluate the potential impact of human activities - will they result in declining fungal diversity? if so, what are the impacts on ecosystem functions performed by these fungi? Of particular interest are the effects of logging, heavy metal pollution, atmospheric nitrogen deposition and global warming. This is done by a combination of lab studies and field manipulation of Canadian streams as well as by comparisons with streams in Germany, Portugal, and India. To understand how complex patterns in nature arise from the simple events typically found in lab experiments will require computer modeling. A related interest concerns the role of fungi in wetlands, especially in salt marshes of the Bay of Fundy and in freshwater marshes dominated by cattails.