Transmission of Atmospherically Derived Trace Elements Through an Undeveloped, Forested Maryland Watershed

Abstract

The transmission of atmospherically derived trace elements (Al, As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Se, and Zn) was evaluated in a small, undeveloped, forested watershed located in north-central Maryland. Atmospheric input was determined for wet-only and vegetative throughfall components. Annual throughfall fluxes were significantly enriched over incident precipitation for most elements, although some elements exhibited evidence of canopy release (Mn) or preferential uptake (As, Cr, and Se). Stream export was gauged based on systematic sampling under varied flow regimes. Particle loading appears to contribute significantly to watershed export (>10%) for only As, Pb, and Fe, and then only during large precipitation/runoff events. The degree of watershed transmission for each trace element was evaluated based on a comparison of total, net atmospheric input (throughfall) to stream export over an annual hydrologic cycle. This comparison indicates that the atmospheric input of some elements (Al, Cd, Ni, Zn) is effectively transmitted through the watershed, but other elements (Pb, As, Se, Fe, Cr, Cu) appear to be strongly sequestered, in the respective orders noted. Results suggest that precipitation and subsequent soil pH are the primary factors that determine the mobility of sequestered trace element phases.To further resolve primary atmospheric and secondary weathering components, the geochemical model NETPATH was applied. Results indicate that minerals dissolved include chlorite, plagioclase feldspar, epidote, and potassium feldspar; phases formed were kaolinite, pyrite, and silica. The model also indicates that weathering processes contribute negligible amounts of trace elements to stream export, indicative of the unreactive orthoquartzite bedrock lithology underlying the watershed. Thus, the stream export of trace elements primarily reflects atmospheric deposition to the local watershed.

Metal Pools, Fluxes, and Budgets in an Acidified Forested Catchment on the Precambrian Shield, Central Ontario, Canada

“…The mass budget was recalculated by doubling the bulk deposition inputs as a generous estimate of dry deposition to the forest canopy, and the same metals still exhibited release from the terrestrial compartment. Other mass balance studies for forested uplands have produced similar results: typically Cu, Pb, As, and Cr are retained; Fe, Mn, Ni, Cd, and Zn demonstrate either retention or release; and Al, Ba, and Sr are released (Lawlor and Tipping 2003;Lindberg and Turner 1988;Scudlark et al 2005).…”

“…Many metal mass budget studies are at the whole catchment scale (Dillon et al 1988; Lindberg and Turner 1988;Scudlark et al 2005;Yang et al 2002), which neglects internal processes, although some studies have investigated fluxes within the catchment or a portion of the catchment in more detail (Bergkvist 1987;Ukonmaanaho et al 2001). For metals, only a select few are typically studied, primarily Pb, Cd, Cu, Ni, and Zn, because these elements are recognized pollutants with welldocumented impacts.…”

The impact of urban expansion and agricultural legacies on trace metal accumulation in fluvial and lacustrine sediments of the lower Chesapeake Bay basin, USA

“…Unlike many industrial and agricultural sources which contribute metals to local catchments, atmospheric deposition can transport particles long distances while simultaneously acting as a confined source of contamination (Kim et al, 2000;Scudlark et al, 2005;Mason et al, 1997). Airborne contaminant sources are widely varied and range from the industrial -smelters, coal fired power generation, foundriesto the domestic -emissions from heating, corrosion of metal structures, and dust from automobile wear (Kim et al, 2000;Petti, 1989;Scudlark et al, 2005).…”

“…Airborne contaminant sources are widely varied and range from the industrial -smelters, coal fired power generation, foundriesto the domestic -emissions from heating, corrosion of metal structures, and dust from automobile wear (Kim et al, 2000;Petti, 1989;Scudlark et al, 2005). In addition to aerosol deposition, the erosion of contaminated soils and remobilization of fluvial sediments enriched in metals provide an extensive supply of trace metals to fluvial systems.…”

Trace Elements in High-Elevation Soils on Six Mountains in Maine, USA

“…Trace elements and other pollutants exist in high‐elevation forest ecosystems due to inputs from parent material, wet and dry atmospheric deposition, interception of wet cloud moisture, and bioaccumulation/cycling from the vegetation. In areas with little human influence, trace elements in soils can be attributed to inputs from bedrock parent material (Wang et al, 2009; Scudlark et al, 2005; Moyse and Fernandez, 1987), or to fallout of terrestrially derived aerosols, which are chemically similar to the soils of their origin and are commonly rich in manganese (Lee et al, 2008). Atmospheric deposition may factor more strongly as a potential input to high‐elevation soils because of orographic effects on precipitation and cloud formation and interception.…”