Urban streams can be an impediment to movement and land use. In the past, some streams have been engineered into underground pipes. This solves issues related to human movement, but can alter the macroinvertebrate composition. Occasionally, the process is reversed; the pipes and earth removed in a process known as daylighting. Studying stream biodiversity pre- and post- daylighting is one way to assess the impact of stream engineering.
New Zealand scientists* studied the effects of daylighting on two streams in an Aukland, NZ park. Two reaches of a stream that had been diverted into pipes were uncovered and replaced by engineered stream channels and banks for 90 meter stretches. Daylighting substantially increased the biodiversity in the stream. 44 new taxa were collected and 11 disappeared. After daylighting, more algae and less micro-organismal biofilm resources were present in the stream driving the change in species composition. Although there may be good reasons for diverting streams into underground pipes, it can be important to understand that such engineering has an effect on biodiversity.
*M.W. Neale & E.R. Moffett. Re-engineering buried urban streams: Daylighting results in rapid changes in stream invertebrate communities. Ecological Engineering 87 (2016) 175–184.