Nutrient removal from helophytes used in bioengineerings in streams receiving effluents of wastewater treatment plants

Abstract

Many bioengineering techniques for stream restoration involve the use of helophytes to reduce soil erosion and increase stream channel stabilization. However, helophytes can also play a relevant functional role by enhancing the capacity of in-stream nutrient uptake and removal. Therefore, the use of bioengineering techniques, especially downstream of the inputs from wastewater treatment plants (WWTP) may help alleviate the excesses dissolved inorganic nitrogen (DIN) and dissolved organic carbon (DOC) from these point sources. In this study, we tested the effect of helophytes on net DOC and DIN removal from subsurface stream water in the Urban River Lab facility, a set of artificial flumes filled with gravels and receiving inputs from a WWTP effluent. The experimental setting included 3 unvegetated flumes and 9 vegetated flumes with 3 species of helophytes commonly used in stream restoration (3 replicates per species). Unvegetated flumes showed a low capacity to reduce both DIN and DOC concentration, whereas flumes with helophytes showed a remarkable removal capacity along the subsurface flowpaths. These results suggest that the use of helophytes in river restoration can contribute to regulate stream water chemistry, especially in relation to solutes that are biologically important, such as carbon and nitrogen.