The impact of bioengineering techniques for riverbank protection on ecosystem services of riparian zones

Rivers and floodplains are hotspots of biodiversity and provide an exceptional number of ecological functions. However, they are negatively affected by human impact worldwide. The need for restoration is high, but its realization is often hampered by antagonistic human interests. Replacing artificial riverbank protection with bioengineering techniques can be a first and straightforward step to restore riparian ecosystems. However, bioengineering still plays a marginal role in river management. We aim to introduce new arguments for bioengineering along riverbanks by applying the ecosystem service approach. We focus on major regulating services usually provided by floodplains. Denitrification and phosphorous retention were estimated by applying proxy-based models. Carbon sequestration within vegetation was calculated using biomass equations. Our study clearly indicates an increase of ecosystem services by bioengineering measures compared to conventionally fixed riverbanks. The dismantling of riprap removes up to 30 times more nitrogen and 20 times more phosphorous from the river load. Additional slope lowering increases both values up to 50-fold. The carbon storage capacity is four times higher in reed beds and 30 times higher in willow-brush mattresses. Our results show that bioengineering techniques for riverbank protection can be a feasible tool to support general efforts towards enhancing the self-purification of rivers and contribute to mitigating climate change, especially if conducted on a larger scale.