If the soil once again becomes saturated, these seeds may sprout. Drainage does not immediately create a new soil, but it does change the processes that are currently occurring in the soil. The most significant changes in an artificially drained soil will be the increased nitrate concentration due to aeration of the soil, the increased flow of water through macropores, and the increase in dryland species. These changed can be either beneficial or harmful depending upon the circumstances. The increased nitrate is a boon for agricultural use, but it also increases the amount of nitrate that can be washed out of the soil and carried to rivers by the tile.
Agricultural runoff is a major source of nonpoint water pollution.
The increased water flow out of the soil and into the streams coupled with the loss of biota capable of a high rate of transpiration, increases the possibility of extreme flooding. But the increased drainage also allows important food crops to be grown. The reduced amount of water in pore spaces can also cause subsidence.