A peatland is defined as any ecosystem with a waterlogged substrate and at least 30 cm of peat (Kivinen and Pakarinen 1981). Once peat has accumulated to this depth the availability of essential nutrients falls sharply. Plant species are no longer rooted in mineral soil, and they must absorb all their mineral nutrients from within a waterlogged, anoxic, peat mass. Nutrients, however, are continualLy locked up within the peat, because the low levels of oxygen inhibit microbial activity and nutrient cycling. The supply of nutrients is therefore determined by transport processes that carry nutrients in from the (1) atmosphere, (2) adjacent mineraL uplands, or (3) underlying mineral soil. These processes are strongly modified within a peatland by the physical properties of the peat and the active properties of the peat and the active sequestering of ions by the living plants. The accumulation of peat therefore creates a uniquely integrated system in which there is a delicate balance between physical and biotic processes.