Characterization of Nutrient and Metal Leaching in Roadside Ditches Maintained with Cool and Warm Season Grasses

Alex Boger,Laurent Ahiablame

doi:10.3390/hydrology6020047

Abstract

Roadside ditches play an important role in the quantity and quality of receiving waters. Very little, however, is known about the fate and transport of nutrients and trace metals in roadside ditches, especially their leaching to shallow groundwater. This study sought to document selected water quality constituent levels in infiltrated water (i.e., leachate) in roadside ditches maintained with permanent vegetation. Leachate sampling wells were installed in four roadside ditches, and water samples were collected from the wells following major rainfall events during the years 2016 and 2017. The samples were analyzed for nutrient and metal concentrations. Results indicated that nutrient concentrations in the water samples range from 0.00600 to 0.0107 mg/L for orthophosphate (PO4–P), 0.00500 to 6.80 mg/L for nitrate (NO3–N), 0 to 0.007 mg/L for nitrite (NO2–N), and 0.0100 to 314 mg/L for chloride (Cl−). Concentrations of the metals examined varied between 0.0100 and 104 mg/L in water samples. While there was no specific pattern in both nutrient and metal concentrations when roadside ditches maintained with cool season grass were compared to those of warm season grass ditches, results suggest that grass types will likely affect differently uptake of nutrients and metals in the ditches.

Highlights

Roadside ditches are important features of the drainage network in the United States
With similar mean rainfall amounts during the study period, the average nutrient concentrations at the Trent site generally appears to be lower than nutrient concentrations at the Pierre site, except for Cl− concentrations
While the intent of the study was not to compare the two sites, it is worth noting that the Trent site is an interstate highway which receives frequent deicing salt during winter due to higher traffic volume compared to the Pierre site, a state road, with less deicing maintenance and less traffic

Summary

Introduction

Roadside ditches are important features of the drainage network in the United States. They are mostly designed to rapidly convey storm runoff downstream, reducing the risk of potential road closure as a result of flooding and water logging [1,2,3]. While roadside ditches intercept and efficiently drain runoff from adjacent roads, fields, and parking lots [5,6], they are conduits of road salts, fertilizers, pathogens, and various contaminants in runoff to streams and rivers, leading to deterioration of downstream water quality [1,2,7]. By quickly discharging runoff and related pollutants to receiving waters, roadside ditches are comparable, by analogy, to high-velocity faucets [4,8,9]

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Conclusion