Effect of calcareous road dust on land snails (Gastropoda: Pulmonata) and millipedes (Diplopoda) in acid forest soils of the Daniel Boone National Forest of Kentucky, USA

Abstract

This study examined the effect of calcareous road dust on land snails (Gastropoda: Pulmonata) and millipedes (Diplopoda) on forested ridge tops with naturally acidic soils. Pitfall trapping was conducted on twelve 50 m long transects perpendicular to roads that had been surfaced with limestone gravel for approximately 50 years. Sampling was carried out during 1-week periods twice per year for 3 years. Soil pH decreased from 7.0 to 4.3, and extractable-Ca from 18.3 to 0.6 cmol +/kg, with increasing distance from the road; both variables were significantly higher at the roadside than at distances of 25 and 50 m. Six genera and five identifiable species of snails, and seven orders and six identifiable families of millipedes were collected. Dry mass of snails and millipedes differed significantly ( P<0.001) with distance from the roadside, with snail dry mass about 10× and millipede dry mass about 3× higher at the roadside than at 50 m. Dry mass was positively correlated with both pH and extractable-Ca for both taxa. The taxonomic composition of the snail assemblages differed significantly between plots at roadside and at 50 m; Triodopsis albolabris Say and Mesomphix sp. were most important on roadside plots, and Zonitoides nitidus Muller and Paravitrea capsella Gould were most important on 50 m plots. The large snail species, T. albolabris, composed 69% of the total dry mass at the roadside but was absent from 50 m plots. This study shows that soil invertebrate assemblages may be altered in proximity to roads surfaced with calcareous gravel. The potential for such effects, especially in ecosystems with naturally acidic soils, should therefore be considered when designing road systems or developing forest management plans.