Intermittent rainstorms cause pulses of nitrogen, phosphorus, and copper in leachate from compost in bioretention systems.
Bioretention systems rely on vegetation and mixtures of soil, sand, and compost to filter stormwater runoff. However, bioretention systems can also leach metals and nutrients, and compost may be a major contributor to this leaching. To safely implement bioretention systems, it is crucial to determine the composition of compost leachate. We characterized and quantified the leachate composition of compost following intermittent, simulated storm events. Columns of municipal compost were irrigated to simulate 6-month, 24-hour rain storms in the Seattle-Tacoma region. Outflow was analyzed for pH, electrical conductivity (EC), particulate concentration, surface tension, dissolved organic carbon (DOC), nitrogen, phosphorus, and copper. Results indicate a decrease of chemical concentrations over the course of individual storms and following repeated storms, but each new storm released another peak of constituents. The decrease in phosphorus, copper, and DOC concentrations with repeated storms was slower than for nitrate and EC. Nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR) showed that the DOC consisted mainly of aliphatic and aromatic components typical of fulvic and humic acids. Less than 3% of the original copper content from the compost leached out even after nine storm events. Nonetheless, copper concentrations in the leachate exceeded regulatory discharge standards. Our results show that compost can serve as a sustained source of leaching of nutrients and metals.
Department of Crop and Soil Sciences, Washington State University, Puyallup, WA 98371, Pullman, WA 99164, USA.
Jessica M
JM
Mullane
Department of Crop and Soil Sciences, Washington State University, Puyallup, WA 98371, Pullman, WA 99164, USA. Electronic address: flury@wsu.edu.
Markus
M
Flury
Department of Crop and Soil Sciences, Washington State University, Puyallup, WA 98371, Pullman, WA 99164, USA; Institute of Environmental Sciences and Engineering, School of Civil and Environmental Engineering, National University of Sciences and Technology, Sector H-12, Islamabad, Pakistan.
Hamid
H
Iqbal
Department of Crop and Soil Sciences, Washington State University, Puyallup, WA 98371, Pullman, WA 99164, USA.
Patrick M
PM
Freeze
Natural Resources Program Extension, Washington State University, Puyallup, WA 98371, USA.
Curtis
C
Hinman
Department of Crop and Soil Sciences, Washington State University, Puyallup, WA 98371, Pullman, WA 99164, USA.
Craig G
CG
Cogger
Department of Crop and Soil Sciences, Washington State University, Puyallup, WA 98371, Pullman, WA 99164, USA.
Zhenqing
Z
Shi
D003300:Copper / Q000032:analysis*; D004784:Environmental Monitoring; D009584:Nitrogen / Q000032:analysis*; D010758:Phosphorus / Q000032:analysis*; D011891:Rain; D014865:Waste Disposal, Fluid / Q000379:methods*; D014874:Water Pollutants, Chemical / Q000032:analysis*
D014874:Water Pollutants, Chemical; D010758:Phosphorus; D003300:Copper; D009584:Nitrogen
Bioretention systems; Compost; Copper; Dissolved organic carbon; Leachate; Nutrients