Deicing salt inputs affected soil chemistry and microbial respiration

Background/Question/Methods

Roadside ecosystems are exposed to multiple environmental pollutants from automobiles as well as road construction and maintenance. Two common pollutants are deicing salt and inorganic nitrogen (N). The consequences of these pollutant inputs on ecosystem structure and function, however, are less known. We conducted a roadside deposition experiment in Binghamton, New York, in a site adjacent the interstate highway 81 from 2010 to 2011.  Two parallel transects were set, one next to the highway (0-m transect), another 50 meters away (50-m transect); in each transect, 6 replicate sets of plots, containing control, salt, and nitrate plots, were established to evaluate both the long-term roadside impact (0-m vs. 50-m) and the short-term experimental effect. Plots were sprayed once every two weeks from May to October, in the amount of 857.22 g NaCl and 31.46 g NaNO₃ m^-2 yr^-1. Soils were collected in both July and November of 2011 and separated into 0-5 cm and 5-15 cm sections, which were analyzed separately. 

Results/Conclusions

In July, extractable NH₄-N and NO₃-N in 0-5 cm soils were 2.44-8.63 and 1.26-4.81 mg/kg respectively; there was no treatment effect on either NH₄-N or NO₃-N. Salt treatment significantly raised soil conductivity, from 256±180 to 3034±298 μS in the 0-m transect and from 146±50 to 2688±377 μS in the 50-m transect. Soil pH was higher in the 0-m transect (7.36±0.05) than the 50-m transect (6.24±0.52). In November, salt plot conductivities were lower than July (695±218 and 744±156 μS for the 0-m and 50-m, respectively) but were still significantly higher than the control plots. N mineralization and nitrification exhibited no treatment effect in July or November. Net N mineralization rates in July were 0.28-0.87 mg/kg/d in the 0-5 cm soils, higher than those in November (0.19-0.40 mg/kg/d). Salt treatment significantly reduced microbial soil respiration in July and November; CO₂ emissions were reduced by 10-20% in the 0-m transect soils and by 25-60% in the 50-m transect soils. Soil moisture was higher in the 0-m transect than the 50-m transect and lower in July than November; organic matter content was similar among plots. Our study suggested that roadside pollutants can alter both soil chemistry and microbial processes in roadside ecosystems.