Variation in Nutrient and Metal Retention in Bioretention Systems with Mycorrhizae-Inoculated Soil

摘要

Although bioretention systems are very effective at reducing peak flows and improving water quality, recent studies have shown that nutrients and metals can leach from the bioretention soil and cause degradation of receiving waters in bioretention systems with an underdrain. Mycorrhizae, particularly endomycorrhizae which enhances the root system of plants, may increase nutrient and metals uptake in bioretention systems. To evaluate whether mycorrhizae improve nutrient uptake, column studies were conducted with mycorrhizae-inoculated soil, a proprietary soil inoculated with mycorrhizae and bacteria, and bioretention soil (as a control). Ten tests were conducted with stormwater, and influent and effluent were analyzed for total phosphorus, phosphate, total nitrogen, nitrate, ammonia, copper, and zinc. Results indicate the plant root network was more extensive in soils inoculated with mycorrhizae and initially reduced nutrient and metals leaching, but this trend reversed halfway through testing when leaching from the inoculated columns became higher than the control. Variation in results were not as pronounced in the proprietary soil, which consistently retained total phosphorus and phosphate, but leached nitrogen. Other factors such as soil type, presence of other soil microbial populations, and wetting/drying cycles may have a larger impact on nutrient uptake than presence of mycorrhizal fungi.