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Ecological Effects of Road De-Icing Salt on Adirondack Forests and Headwater Streams

Tiwari, Athena, Rachlin, Joseph W.
Northeastern naturalist 2018 v.25 no.3 pp. 460-478
Abies balsamea, Ephemeroptera, Plecoptera, Trichoptera, chlorides, environmental impact, forests, nutrients, nymphs, regression analysis, roads, runoff, streams, trees, Adirondacks
We collected water samples from upstream and downstream sites over 3 years on 18 study streams in the Adirondacks, NY, and conducted analysis via ANOVA for the presence of road-salt runoff, as measured by chloride ion content. Streams crossed by state roads received more road-salt runoff than streams crossed by county roads, as shown by higher mean chloride loads across different sampling years (P ≤ 0.01). The chloride load in streams was not reliably higher downstream from a road as opposed to upstream from a road for either state or county roads but varied in different sampling years (P < 0.001–P > 0.05). We collected a total of 1259 nymphs of Ephemeroptera, Plecoptera, and Trichoptera during water sampling. High levels of road-salt runoff were not associated with lower levels of Plecoptera or Trichoptera. Neither numbers of individuals nor numbers of genera of Ephemeroptera, Plecoptera, or Trichoptera collected per month showed any pattern when regressed on stream-chloride level. However, we detected no Ephemeroptera above a relatively high level of road-salt runoff (154 mg/L chloride ion). We employed the point-centered quarter method to assess forest composition on 10 transects above and below state roads. We conducted further analysis on trees in the lowest quartile of circumference in each transect as a representation of tree-species recruitment. Mean chloride-ion content of study streams, indicating adjacent forest exposure to road-salt runoff, was associated with greater recruitment of Abies balsamea (Balsam Fir), and lower Shannon–Weiner diversity. At the highest chloride levels, there was almost no recruitment of any species but Balsam Fir. Soil-cation analysis and linear regression, however, did not indicate concomitant depletion of plant nutrients, and therefore, we did not confirm the cause of the apparent relationship between higher road-salt runoff and higher Balsam Fir recruitment.