SOIL PROFILES IN BIOSWALE: IMPLICATIONS ON SOIL DEVELOPMENT AND BIOSWALE MANAGEMENT

In New York City, thousands of engineered green infrastructure sites (GI, mainly bioswales) have been built as a nature-based strategy to capture stormwater runoff, reduce the combined sewer overflow and thereby helps improve the health of local waterways. Since these GIs were built, soils in these systems have gone through unique development processes, perhaps expedited by constant flooding and dry cycles, as well as a number of anthropogenic factors. The development of soil profiles in these green infrastructure systems, has rarely been studied if at all, could control the long term sustainability and their ecological functions. The objective of the study is to understand the general characteristics of the existing soil profiles, and to understand the effects of GI design parameters on the rate and process of soil development. Four sites in Brooklyn of New York City, established between 2010-2011, are studied. The sites include three right-of-way bioswales (ROWB) and one vegetative swale (VS), each with different watershed ratio (watershed area: GI footprint) but very similar engineered soil mix installed at the beginning. The depth of soils varies from 2 to 5 feet, depending on the GI design. Because excavation for pits were not permitted, soils profiles were described in the field based on auger samples. Bulk samples from different horizons were collected for the characterization of a suite of physical and chemical properties in the lab. These include soil moisture content, texture, pH, organic matter content, total C and total N, metals, as well as black carbon. Preliminary results show interesting horizonation of these parameters, indicating the movement and redistribution of particles and chemical constituents, as well as other biogeochemical processes that led to the addition or loss of materials. These processes have important implications in water infiltration rates and thus the effectiveness for stormwater capture and storage, fate and transport of nutrients and contaminants. The results will also inform better design and maintenance requirements of such systems.