GEOCHEMICAL MECHANISMS CONTROLLING THE SPATIAL DISTRIBUTION OF NEAR-ROADWAY POLLUTANTS IN AN URBAN ECOSYSTEM

Roadways are a substantial contributor of nonpoint-source pollution to urban ecosystems. In order to better quantify the impact of this pollutant source, it is important to understand how the pollutants are transported to and sequestered within roadside sediments. In order to examine how near roadway environmental variables such as deicing salts, pH, and distance affect horizontal and vertical retention of pollutants; sediment cores were collected at 0, 10, 30, and 90m from interstate 81 as it passes through the Binghamton, NY urban corridor. The samples were partitioned into 0-5, 5-15, and 15-30cm intervals before undergoing a modified Tessier sequential extraction which separates elements into the exchangeable, carbonate bound, Fe and Mn oxide bound, organic bound, and residual fractions. Multi-elemental analysis was performed on the extracts using ICP techniques.

The total concentration of Ca, Cu, Pb, Sr, and Zn were between 1.4 and 2 times higher in the nearest roadway sites than in the more distant locations. These five elements reversed from being more concentrated in surface sediments (0-5cm) and depleted in deep sediments (15-30 cm) near the roadway (0 and 10m) to being depleted in surface sediments and concentrated in deep sediments (30 and 90m) further from the roadway. The Tessier fraction in which pollutants were stored varied with distance from the roadway. These patterns seem to be associated with the measured decrease in sediment pH from >8 to <6 with distance from the roadway and its resultant effect on metal mobility. The elevated pH near the roadway is causing pollutants such as Pb and Zn to be stored in the carbonate fraction, whereas the lower pH away from the road limits the formation of this carbonate rich zone. This higher pH and associated sequestration mechanisms adjacent to the road is providing a means to increase the pollutant storage capacity of near-roadway sediments in urban ecosystems.