Phosphorus retention performance in vegetated and non-vegetated bioretention mesocosms using recycled effluent

Abstract

Phosphate removal from stormwater and wastewater is essential to prevent eutrophication of waterways. The aim of our study was to evaluate phosphorus retention in vegetated and non-vegetated (barren) bioretention mesocosms. Existing well-established bioretention mesocosms with sandy loam, loamy sand and gravel media were irrigated with 60.9 g-m-2 (609 kg-ha-1) TP from recycled effluent between August 2006 and March 2007. Initially, P retention in the barren loam and sand media approached 100%, while gravel retention was only 20%. However, after application of this load, retention by all barren media had declined substantially. In contrast, retention by vegetated treatments remained very high, with 92% of the total mass load retained in the vegetated loam, 84% in the sand,and 55% in the vegetated gravel. These results indicate that the vegetated treatments provide far more TP retention than the barren treatments. Over the 31 week period, the difference in retained loads was 15.4 g-m-2 P in the vegetated loam mesocosms, 16.9 g-m-2 P in the vegetated sand mesocosms, and 23.5 g-m-2 P in the vegetated gravel mesocosms. These removal rates substantially exceed typical phosphorus uptake rates for plants, suggesting that other plant-soil-microbe interactions are influencing phosphorus retention in the vegetated mesocosms.