Another type is bioretention structures, which are typically pits backfilled with soil, mulch and vegetation used to retain runoff for infiltration through the filter bed components, with reliance on biological and biochemical reactions within the soil matrix and around the root zones of the plants. A review of on-farm wetlands in the United Kingdom (UK) and Ireland (Newman etal., Agricultural wetlands, however, require careful planning and maintenance in order to perform their optimum design function over a prolonged period of time.