"Our first research project at the Jokimaa soil research centre Soilia focused on storm water infiltration in urban soil, and specifically on how the process is affected by vegetation.
We built eight lysimeters in the Soilia area, each of which had a bottom layer imitating urban soil (mineral soil with varying grain-size) and an organic surface layer. In six of the lysimeters we planted plants resistant to both humid and arid conditions (reed canary grass, willows and purple loosestrife), while the remaining two lysimeters served as plant-free controls. The lysimeters were periodically irrigated with artificial storm water, and the water that seeped through the soil layers was analysed (for nutrients and heavy metals).
During the one-year experiment conducted at Soilia, we discovered that vegetation has a major impact on soil permeability (infiltration): Without plant life, the water flooded on top of the soil for a long time, whereas no flooding occurred in the systems that included plants. Metals and phosphorous were effectively absorbed into the soil, while nitrogen was only partially absorbed.
The research project showed that typical urban soil effectively absorbs emissions caused by traffic, preventing them from reaching surface and ground waters."
Professor | Urban Ecosystem Studies
University of Helsinki | Department of Environmental Sciences