Professor, University of Maryland
As (sub)urban growth continues to consume undeveloped land, stormwater runoff from impervious surfaces grows in importance as a contributor to water resources degradation. Bioretention (a soil/vegetation management practice) has been promoted as a “low impact” stormwater management practices to mitigate impacts of impervious surfaces. Fundamental, applied, and monitoring research has been completed demonstrating the performance of bioretention technologies.
Bioretention will moderate flow rates and reduce surface discharge volumes, concurrently reducing pollutant mass discharge. Understanding the unit treatment processes in bioretention allow characterization of water quality performance. Suspended solids (and bacteria) can be very effectively removed and treated via filtration mechanisms. Various adsorption processes play a large role in bioretention performance. Heavy metals and hydrocarbons are adsorbed strongly on organic and inorganic fractions of the media. Accumulations of these pollutants will occur at the surface (and near inlets) of these facilities, creating ownership challenges, but facilitating maintenance and cleanup.
Phosphorus and nitrogen species are problematic. Neither is very effectively removed via bioretention, yet nutrients are the key pollutants for many of our critical water bodies. Novel modifications to bioretention can enhance the efficacy of bioretention facilities for P and N removal. For P, this entails increasing the level of amorphous aluminum and iron in the media. N removal may be enhanced via the use of adsorbing media amendments, with a submerged anoxic zone to promote denitrification in the bioretention media depths.
Allen P. Davis is Professor and Charles A. Irish Sr. Chair in Civil Engineering in the Department of Civil and Environmental Engineering at the University of Maryland. He earned his BS, MCE and PhD degrees all from the University of Delaware. For over two decades, he has been investigating sources and treatment of pollutants in urban storm water runoff with a focus on nature-based practices, particularly bioretention. In 2010 he was awarded the A. James Clark School of Engineering Faculty Outstanding Research Award recognizing exceptionally influential research accomplishments related to urban storm water quality, its management, and the concept of Low Impact Development. He is author or co-author of over 120 peer-reviewed journal articles and a text on Stormwater Management for Smart Growth. From 2001 to 2010, he was Director of the Maryland Water Resources Research Center. He was Associate Editor for Chemosphere, Science for Environmental Technology (2004-2010), having been an Editorial Board Member since 1999. From 2003 to 2012 he was Chair of the AEESP Government Affairs Committee and was a member of the AEESP Board of Directors in 2012/2013. He is currently Editor-in-Chief of the new ASCE Journal of Sustainable Water in the Built Environment. He is a Licensed Professional Engineer in Maryland, Fellow of the American Society of Civil Engineers, Fellow of the ASCE Environmental and Water Resources Institute, and a Diplomate, Water Resources Engineer.
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