A tale of three cities: Mercury in urban deciduous foliage and soils across land-uses in Poughkeepsie NY, Hartford CT, and Springfield MA USA

Mercury is a global pollutant that harms human and wildlife health through chronic exposure. The role of urban forests in Hg biogeochemistry has been understudied in cities without historical mining or current coal combustion. This study aimed to quantify total Hg concentrations and pools in urban forests to determine whether adjacent land-use impacts Hg accumulation. Three cities in the northeastern United States were studied: Hartford, Connecticut; Poughkeepsie, New York; and Springfield, Massachusetts. We identified ~20 urban forests sites in a ~10 km by ~10 km grid for each city and sampled foliage and soil at each site. Foliage from Populus exhibited significantly lower Hg concentrations (15.6 ± 2.1 ng g −1 ) than mean foliar Hg concentrations (23.7 ± 0.6 ng g −1 ) but most deciduous genera had comparable concentrations. Average forest floor Hg concentrations (195 ± 21 ng g −1 ) and Hg pools (1.9 ± 0.5 mg m −2 ) were similar to previous, non-urban studies in the region. Average A horizon (182 ± 19 ng g −1 ) and B horizon (125 ± 14 ng g −1 ) Hg concentrations were double those of regional forest soils. Mineral soil Hg pools for the top 30 cm (49 ± 6 mg m −2 ) averaged two to ten times higher than rural, montane forests in the region. Soil pH, LOI, and %clay were poorly correlated with mineral soil Hg concentrations. Instead, highest foliar and soil Hg concentrations and pools were in urban forests adjacent to high and medium intensity developed areas in Springfield and Hartford. To differentiate the impact of land-uses not captured by the National Land Cover Database (NLCD) system, we implemented new land-use categories. Industrial areas had highest foliar and soil Hg concentrations and pools of any land use. Our results show increasing land-use increases Hg accumulation in urban forests.