Bioretention Infrastructure to Manage the Nutrient Runoff from Coastal Cities

Although bioretentions have been proven to reduce stormwater runoff volumes and remove many pollutants, reports are variable as to the nutrient removal performance of this green infrastructure technology, pointing to the need for further investigation. In this work, the nutrient removal performance of six bioretentions in New York City (NYC)’s Bronx River Sewershed was quantified by identifying differences among dissolved nutrient concentrations in influent, infiltrate, and overflow liquid samples during 26 storms. Results indicate that the studied bioretentions are sources, rather than sinks, of nitrogen and phosphorus. Statistical analyses revealed higher levels of measured water quality indicators in the infiltrate of the bioretentions as temperature and the dry weather period before a storm increase, and lower levels of most indicators as the rainfall depth before sampling and the loading ratio of the bioretention increase. In this paper, the monitoring methods developed for evaluating the nutrient removal performance of the bioretentions are described, the data collected on bioretention nutrient removal performance is reported, and the statistical correlations between measured water quality indicators, local environmental conditions and the bioretention site properties are discussed.