Proton and Aluminum Binding Properties of Organic Acids in Surface Waters of the Northeastern U.S.

A variety of mathematical estimators have been used to quantify the degree of protonation of naturally occurring organic acids. These estimators range from monoprotic, diprotic, and triprotic analog models to the discrete and continuous (Gaussian) distributions of a single proton binding-dissociation. Natural water samples from two long-term monitoring programs in the northeastern U.S. were used to quantify proton- and aluminum-binding properties of naturally occurring organic matter. Water chemistry observations were clustered into 0.05 pH intervals (over 3.75–7.35 pH range) and fit to a triprotic analog model. The model optimization indicates that about 5% of dissolved organic carbon participates in ion binding, and organic acids are composed of both strong and weak acids (i.e., p<i>K</i>_a1 = 2.54, p<i>K</i>_a2 = 6.19, and p<i>K</i>_a3 = 7.52 for Adirondack samples). Binding between organic acids and aluminum can substantially influence the acid behavior of dissolved organic matter and the availability of the toxic form of aluminum (i.e., inorganic monomeric aluminum)

Deposition of Mercury in Forests along a Montane Elevation Gradient

Atmospheric mercury (Hg) deposition varies along elevation gradients and is influenced by both orographic and biological factors. We quantified total Hg deposition over a 2 year period at 24 forest sites at Whiteface Mountain, NY, USA, that ranged from 450 to 1450 m above sea level and covered three distinct forest types: deciduous/hardwood forest (14.1 μg/m²-yr), spruce/fir forest (33.8 μg/m²-yr), and stunted growth alpine/fir forest (44.0 μg/m²-yr). Atmospheric Hg deposition increased with elevation, with the dominant deposition pathways shifting from litterfall in low-elevation hardwoods to throughfall in midelevation spruce/fir to cloudwater in high-elevation alpine forest. Soil Hg concentrations (ranging from 69 to 416 ng/g for the Oi/Oe and 72 to 598 ng/g for the Oa horizons) were correlated with total Hg deposition, but the weakness of the correlations suggests that additional factors such as climate and tree species also contribute to soil Hg accumulation. Meteorological conditions influenced Hg deposition pathways, as cloudwater Hg diminished in 2010 (dry conditions) compared to 2009 (wet conditions). However, the dry conditions in 2010 led to increased Hg dry deposition and subsequent significant increases in throughfall Hg fluxes compared to 2009. These findings suggest that elevation, forest characteristics, and meteorological conditions are all important drivers of atmospheric Hg deposition to montane forests

Sampling locations in this study (circles) and monitoring stations (triangles) in northeastern USA.

<p>The base map shows the sum of dry and wet Hg deposition modeled by Yu et al. (2014).</p

Concentrations of Hg in foliage of dominant species at four sites in the northeastern USA.

<p>Tree species included American beech (BE), yellow birch (YB), red maple (RM), sugar maple (SM), red spruce (RS), white ash (WA), white pine (WP) and balsam fir (BF). Error bars represent the SE of Hg concentrations of three composited samples.</p

Concentrations of Hg in bole wood of dominant species at four sites in the northeastern USA.

<p>Tree species included American beech (BE), yellow birch (YB), red maple (RM), sugar maple (SM), red spruce (RS), white ash (WA), white pine (WP) and balsam fir (BF). Error bars represent the SE of Hg concentrations of three composited samples.</p

Appendix A. Quality control metrics for mercury and nitrogen analyses.

Quality control metrics for mercury and nitrogen analyses

Biomass and Hg content of foliage, bark and bole wood in hardwood and conifer stands in this study and three published studies.

<p>Biomass and Hg content of foliage, bark and bole wood in hardwood and conifer stands in this study and three published studies.</p

Concentrations of Hg in bark of dominant species at four sites in the northeastern USA.

<p>Tree species included American beech (BE), yellow birch (YB), red maple (RM), sugar maple (SM), red spruce (RS), white ash (WA), white pine (WP) and balsam fir (BF). Error bars represents the SE of Hg concentrations of three composited samples.</p

Four sites in the northeastern USA were used in this study.

<p>Four sites in the northeastern USA were used in this study.</p

Modeling and Mapping of Atmospheric Mercury Deposition in Adirondack Park, New York

<div><p>The Adirondacks of New York State, USA is a region that is sensitive to atmospheric mercury (Hg) deposition. In this study, we estimated atmospheric Hg deposition to the Adirondacks using a new scheme that combined numerical modeling and limited experimental data. The majority of the land cover in the Adirondacks is forested with 47% of the total area deciduous, 20% coniferous and 10% mixed. We used litterfall plus throughfall deposition as the total atmospheric Hg deposition to coniferous and deciduous forests during the leaf-on period, and wet Hg deposition plus modeled atmospheric dry Hg deposition as the total Hg deposition to the deciduous forest during the leaf-off period and for the non-forested areas year-around. To estimate atmospheric dry Hg deposition we used the Big Leaf model. The average atmospheric Hg deposition to the Adirondacks was estimated as 17.4 g m yr with a range of −3.7–46.0 g m yr. Atmospheric Hg dry deposition (370 kg yr) was found to be more important than wet deposition (210 kg yr) to the entire Adirondacks (2.4 million ha). The spatial pattern showed a large variation in atmospheric Hg deposition with scattered areas in the eastern Adirondacks having total Hg deposition greater than 30 <i>μ</i>g m⁻² yr⁻¹, while the southwestern and the northern areas received Hg deposition ranging from 25–30 <i>μ</i>g m⁻² yr⁻¹.</p> </div