Charles T. Driscoll

Long-Term Effects of Acid Rain: Response and Recovery of a Forest Ecosystem

Long-term data from the Hubbard Brook Experimental Forest, New Hampshire, suggest that although changes in stream pH have been relatively small, large quantities of calcium and magnesium have been lost from the soil complex and exported by drainage water because of inputs of acid rain and declines in atmospheric deposition of base cations. As a result, the recovery of soil and streamwater chemistry in response to any decreases in acid deposition will be delayed significantly.

A procedure for the fractionation of aqueous aluminum in dilute acidic waters

Abstract A procedure was developed for the fractionation of aqueous aluminum. This procedure results in the determination of acid-soluble aluminum, non-labile monomeric aluminum and labile monomeric aluminum. Acid-soluble aluminum is thought to include colloidal aluminum and extremely non-labile organic complexes. Non-labile monomeric aluminum is thought to include monomeric alumino-organic complexes. Labile monomeric is comprised of aquo aluminum as well as inorganic complexes of aluminum. The inorganic speciation of aluminum may be calculated by using labile monomeric aluminum, pH, fluoride and sulfate data with a chemical equilibrium model. This procedure was evaluated using synthetic and natural water solutions. In natural waters, levels of labile monomeric aluminum increased exponentially with decreases in solution pH, while non-labile monomeric aluminum was strongly correlated with organic carbon concentration. Non-labile monomeric aluminum was observed to be relatively insensitive to changes in sol...

Mercury as a Global Pollutant: Sources, Pathways, and Effects

Mercury (Hg) is a global pollutant that affects human and ecosystem health. We synthesize understanding of sources, atmosphere-land-ocean Hg dynamics and health effects, and consider the implications of Hg-control policies. Primary anthropogenic Hg emissions greatly exceed natural geogenic sources, resulting in increases in Hg reservoirs and subsequent secondary Hg emissions that facilitate its global distribution. The ultimate fate of emitted Hg is primarily recalcitrant soil pools and deep ocean waters and sediments. Transfers of Hg emissions to largely unavailable reservoirs occur over the time scale of centuries, and are primarily mediated through atmospheric exchanges of wet/dry deposition and evasion from vegetation, soil organic matter and ocean surfaces. A key link between inorganic Hg inputs and exposure of humans and wildlife is the net production of methylmercury, which occurs mainly in reducing zones in freshwater, terrestrial, and coastal environments, and the subsurface ocean. Elevated human exposure to methylmercury primarily results from consumption of estuarine and marine fish. Developing fetuses are most at risk from this neurotoxin but health effects of highly exposed populations and wildlife are also a concern. Integration of Hg science with national and international policy efforts is needed to target efforts and evaluate efficacy.

Acidification and alkalinization of soils

Acidification or alkalinization of soils occurs through H+ transfer processes involving vegetation, soil solution and soil minerals. A permanent change in the acid neutralizing capacity of the inorganic soil fraction (ANC(s)),i.e. soil acidification (ΔANC<0) or soil alkalinization (ΔANC>0), results from an irreversible H+ flux. This irreversible H+ flux can be caused either by direct proton addition or depletion, by different mobility of components of the ANC(s) or by a permanent change in redox conditions. The contributions of (a) acidic atmospheric deposition, (b) nitrogen transformations, (c) deprotonation of CO2 and of organic acids and protonation of their conjugate bases, (d) assimilation of cations and anions by the vegetation, (e) weathering or reverse weathering of minerals and (f) stream output to changes in the ANC(s) are illustrated by means of H+ budgets for actual soils and watersheds.

The biogeochemistry of calcium at Hubbard Brook

AbstractA synthesis of the biogeochemistry of Ca was done during 1963–1992in reference and human-manipulated forest ecosystems of the Hubbard BrookExperimental Forest (HBEF), NH. Results showed that there has been a markeddecline in concentration and input of Ca in bulk precipitation, an overalldecline in concentration and output of Ca in stream water, and markeddepletion of Ca in soils of the HBEF since 1963. The decline in streamwaterCa was related strongly to a decline in SO

Mercury Contamination in Forest and Freshwater Ecosystems in the Northeastern United States

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Nitrogen Pollution in the Northeastern United States: Sources, Effects, and Management Options

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