Acknowledgments
[22] We thank Martin Tromp for his technical assistance, which made possible several of the field trials. We thank the EPFL, the Swiss National Science Foundation (grants 109566 and 107910), the Oregon Experiment Station, the US National Science Foundation (grant 0447415-EAR), and Masaryk University for their financial support of this work. The work in Luxembourg was supported by Water Research Centre-Deft and the Municipality of Ettelbruck. We gratefully acknowledge the insights and suggestions of Michael Gooseff and the anonymous reviewer. These comments significantly enhanced the presentation of this work.