A Study of Hydraulic and Nutrient Retention Dynamics inVegetated and Non-Vegetated Bioretention Mesocosms

摘要

Bioretention systems are stormwater treatment devices installed to remove bothdissolved and particulate pollutants. As stormwater percolates through the bioretentionsystem, dissolved pollutants are removed from solution by chemical and biologicalprocesses. In our study, 20 bioretention mesocosms (10 with loamy sand and 10 with sandyloam, half with and half without vegetation) were used to investigate hydraulic behaviorand dissolved nutrient retention. The mesocosms were dosed with 120L to 160L syntheticstormwater comprising 0.8 mg-l~(-1) TP and 4.8 mg-l~(-1) TN over 3h to 5h. The infiltration andpercolation rates in the sand was rapid (>15 cm-h~(-1)), while rates in the loam were much less(2-3 cm-h~(-1)). Retention time in the sand was 1.5h while that in the loam was well over 10h.The effluent was collected in 150L containers. Composite samples were taken after 24h inthe sand and 48h in the loam. Average TP retention in the vegetated loam mesocosms wasover 90%, compared to 75% in non-vegetated (barren) mesocosms. TP retention in thesand was very high (average 90%), regardless of treatment. TN retention increased to 80%in the vegetated loam mesocosms from 43% in barren loam mesocosms. TN retention in thesand was less overall, with retention increasing to 41% in the vegetated loam mesocosmsfrom 26% in barren mesocosms. Increasing retention time in the sand mesocosms increasedretention of nitrogen to 61%, nearly a 50% increase in retention performance. Nutrientretention persisted even under very high nutrient loads. While the loam is initially a lesseffective media by itself, the presence of vegetation substantially improves TP and TNretention. TN retention performance is improved by increasing in retention time.