Title

Design of Stormwater BMPs for Surface and Groundwater Protection Based on Site-Scale Soil Properties: Phase I

Creator

Kelly Kibler, University of Central FloridaFollow
Lisa Chambers, University of Central FloridaFollow
Melanie Beazley, University of Central FloridaFollow

Keywords

Soils, nutrients, stormwater BMPs, roadway runoff, Biosorption Activated Media, nitrogen, nitrate, phosphorus, microbiome, organic matter, clay

Description

Phase I of this research developed experimental methodologies to quantify and compare the rates and means of nitrogen and phosphorus transformations through diverse soil profiles. Six sites were selected for study from areas of distinct geologic history in Florida. Soils from the six sites were chosen to represent a gradient of clay and organic matter content, two constituents that were hypothesized to influence nutrient remediation potential in soils. A commercially-available engineered infiltration media, Biosorption Activated Media (BAM), was also tested for comparison. Physical, chemical and biological attributes of the six soils and BAM were fully characterized. Each soil was subjected to extensive laboratory and field testing to parametrize hydraulics and nutrient transformation rates within the soil profile, including when exposed to simulated stormwater hydrology and nutrient loads. All soils effectively removed inorganic nitrogen and retained phosphorus; however, there were notable performance differences related to soil characteristics. The data largely support project hypotheses, that clay content and organic matter content positively influence nitrogen and phosphorus remediation. However, soils containing either the highest or lowest organic matter and clay contents did not perform as well as soils that contained moderate amounts of both. BAM also decreased concentrations of nitrogen and phosphorus, though with slightly less efficiency than soils. Though the research is preliminary, results underscore that nutrient cycling potential of project site soils should be understood before soils are amended for the purpose of remediating stormwater nutrients. This Phase I study suggests that nutrient remediation potential may be predictable based on soil properties.

Abstract

Much of Earth’s nutrient cycling takes place in soils. Characteristics of soils control physical, chemical, and biological processes that determine rates of nutrient fluxes, storage, or transformation. As remediation of excess nutrients in stormwater runoff is one function of stormwater Best Management Practices (BMPs), the soil profile constitutes one of the most important factors of BMP design. Variation observed in BMP effectiveness (e.g., why one BMP design works effectively in one place and not another) can often be explained by variations in the soil profile, either through direct means or by a soil’s influence on hydraulics of stormwater flow through the vadose (unsaturated) zone. The objective of this research is to identify soil characteristics most strongly related to nutrient (nitrogen, N, and phosphorus, P) remediation within the soil profile and to apply this understanding to improve both efficiency and cost-effectiveness of stormwater BMP design.

Phase I of this project developed experimental methodologies to quantify and compare the rates and means of nitrogen and phosphorus transformations through diverse soil profiles. Six sites were selected for study from areas of distinct geologic history in Florida. Soils from the six sites were chosen to represent a gradient of clay and organic matter content, two constituents that were hypothesized to influence nutrient remediation potential. A commercially-available engineered infiltration media, Biosorption Activated Media (BAM), was also tested for comparison. Physical, chemical and biological attributes of the six soils and BAM were fully characterized across sites and with profile depth. Each soil was subjected to extensive laboratory and field testing to parameterize hydraulics and nutrient transformation rates within the soil profile, including when exposed to simulated stormwater hydrology and nutrient loads.

Soils consistently decreased concentrations of inorganic nitrogen and phosphorus from simulated runoff. Mean efficiency of nitrate (NO₃^- ) removal from soils ranged from 75%­­–90%, mean decrease of ammonium (NH₄⁺) concentration ranged from 31%–90% and mean decrease of total P concentrationranged from 65%–98%. BAM also generally decreased concentrations of N and P, though with slightly less efficiency than soils; mean reductions of NO₃^- and total Pby BAM were 60% and 21%, respectively. BAM was the only media tested that was a source of inorganic N. BAM released small amounts of NO₃^- following prolonged exposure to runoff, but increased NH₄⁺ concentrations by a mean 43%. Removal of total N varied between soils due to an experimental effect of organic N released by decomposing root matter in soil cores taken from highly vegetated areas. Nitrogen cycling (N removal and N release) were largely balanced in soils immediately after extraction from field sites. However, after being exposed to conditions similar to a stormwater infiltration basin (repeated infiltration of stormwater with a consistent external load of N), N release and N removal were no longer balanced for some soils. The directionality of the imbalance varied within the tested soils; N removal potential increased in some soils but decreased in the soils with the highest clay and highest organic matter.

Though all soils effectively removed inorganic N and retained P, there were notable performance differences related to soil characteristics. The data largely support project hypotheses, that clay content and organic matter content positively influence N and P remediation. However, soils containing either the highest or lowest organic matter and clay contents did not perform as well as soils that contained both. The best nutrient remediation performance overall was observed in two soils that both contained moderate and comparable amounts of clay and organic matter. Results of this preliminary study suggest that soils with clay content ranging from 5%–8% and organic matter content in the range of 400 g/kg–500 g/kg in the surface 10 cm and 60 g/kg–300 g/kg in 10–30 cm layers were associated with the greatest nutrient remediation potential. Furthermore, soils with pH over 7 and metal content in the range of 10² mg/kg–10³ mg/kg were observed to retain phosphorus at high levels. Importantly, though clay content was similar, the two soils had different overall grain size distributions, which suggests that the organic matter may be as important as the mineral size class when predicting the nutrient remediation potential of a soil. Engineered media, including the BAM tested in this study, do not typically contain organic matter.

Overall, results underscore that properties of project site soils should be understood before soils are amended for the purpose of nutrient remediation. While this preliminary work offers a promising direction for identifying soils that require amendment, thus justifying the material and environmental costs of soil replacement, longer term study under more natural environmental conditions is needed to predict the nutrient remediation potential of heterogeneous soils.

Date Created

Summer 8-4-2023

Semester

Summer

Type

Publication

College

College of Engineering and Computer Science

Unit

CECE

Type

article

Department

CECE

Recommended Citation

Kibler, K. M., L. G. Chambers, M. Beazley, K. Goos, C. K. Nitsch, N. Young, M. Blow, N. Cheek, K. Johnsen, A. Lacoursière, A. Patel, J. Volk, P. Espinosa-Badel, and S. G. Parker (2023). Design of Stormwater BMPs for Surface and Groundwater Protection Based on Site-Scale Soil Properties: Phase I. Final Report to the Florida Department of Transportation, BDV24-977-43.