摘要：Reactive barriers, such as denitrifying bioreactors, have been identified as a clean-up option for nutrient-laden agriculture runoff. Here we tested a 20 m long, 3.75 m wide and 2.2 m deep woodchip bioreactor receiving tile drainage water from a 5.2 ha field site, aiming at testing the hydraulic functioning of a dual-inlet system and quantifying its impact on nutrient loads (nitrogen, reactive phosphorus, organic carbon) in a region with a drainage season taking place in the hydrological winter (November to April). The hydraulic conditions in the dual-inlet bioreactor system developed differently than expected; asymmetric flow rates led to long average hydraulic retention times and a highly dispersed residence time distribution, which was revealed by a bromide tracer test. With a nitrate load reduction of 51 to 90% over three drainage seasons, the woodchip bioreactor proved at the same time to be very effective under the winter conditions of northeastern Germany. The bioreactor turned from an orthophosphate source in the first year of operation into an orthophosphate sink in the second and third year, which was not expected because of anoxic conditions (favorable for denitrification) prevailing within the woodchips. Besides an efficient nutrient retention, the woodchip bioreactor contributed to the total organic carbon load of receiving waters, which impairs the overall positive role of bioreactors within intensively agriculturally used landscapes. We consider this promising low-maintenance biotechnology particularly suitable for single drainage pipes with high discharge and high nitrate concentrations.
