Amorphous Aluminum Hydroxide Control on Sulfate and Phosphate in Sediment-Solution Systems     

Tomas Navratil  Jan Rohovec  Aria Amirbahman  Stephen A. Norton  Ivan J. Fernandez 《Water, air, and soil pollution》2009,201(1-4):87-98

We experimentally determined the adsorption characteristics of natural, freshly precipitated Al(OH)₃ for SO₄ and PO₄. The fresh Al precipitate occurred in stream sediment of Jachymov Stream (Czech Republic). The Al-rich sediment strongly adsorbed added PO₄ prior to acidification experiment; this sorbed PO₄ was released only after substantial dissolution of the sediment, at pH?<?3.67. Sorption of P by Al(OH)₃ appears to be an important control on dissolved PO₄ concentration in surface waters, unless there is a large excess of PO₄. Acidification of the sediment-solution system caused protonation of the sediment surface, thereby increasing the adsorption capacity for SO₄. Maximum SO₄ adsorption occurred at pH 4.2, below which dissolution of the sediment offset the increasing anion adsorption capacity, and formation of AISO₄ ⁺ inhibited the increasing SO₄ adsorption capacity. This research demonstrates that there are important pH thresholds for anion adsorption in freshwaters below which dissolution of the Al(OH)₃ substrate reduces total capacity for anion adsorption. In freshwaters, with sufficient concentrations of suspended Al(OH)₃, or in Al(OH)₃-rich sediment, PO₄ mobility will be severely restricted. Suspended Al(OH)₃ in acidified surface waters cannot strongly influence SO₄ concentrations because of the considerably higher total SO₄ concentrations compared to the available surface area.  相似文献   

Litterfall Mercury in Two Forested Watersheds at Acadia National Park, Maine, USA     

Katherine D. Sheehan  Ivan J. Fernandez  J. Stephen Kahl  Aria Amirbahman 《Water, air, and soil pollution》2006,170(1-4):249-265

Litterfall can be an important flux of mercury (Hg) to soils in forested landscapes, yet typically the only available data to evaluate Hg deposition is from precipitation Hg monitoring. Litterfall was collected at 39 sampling sites in two small research watersheds, in 2003 and 2004, and analyzed for total Hg. Four vegetation classes were designated in this study as hardwoods, softwoods, mixed and scrub. The mean litter Hg concentration in softwoods (58.8 ± 3.3 ng Hg g^?1 was significantly greater than in mixed (41.7 ± 2.8 ng Hg g^?1 and scrub (40.6 ± 2.7 ng Hg g^?1, and significantly lower than in hardwoods (31.6 ± 2.6 ng Hg g^?1. In contrast, the mean weighted litter Hg flux was not significantly different among vegetation classes. The lack of a significant difference in litter Hg flux between hardwoods and softwoods was attributable to the large autumnal hardwood litter Hg flux being balanced by the higher softwood litter Hg concentrations, along with the higher chronic litterfall flux throughout the winter and spring in softwoods. The estimated annual deposition of Hg via litterfall in Hadlock Brook watershed (10.1 μg m^?2 and Cadillac Brook watershed (10.0 μg m^?2 was greater than precipitation Hg deposition and similar to or greater than the magnitude of Hg deposition via throughfall. These results demonstrate that litterfall Hg flux to forested landscapes can be at least as important as precipitation Hg inputs.  相似文献   

The Effect of Fire on Mercury Cycling in the Soils of Forested Watersheds: Acadia National Park,Maine, U.S.A.     

Amirbahman  Aria  Ruck  Philip L.  Fernandez  Ivan J.  Haines  Terry A.  Kahl  Jeffery S. 《Water, air, and soil pollution》2004,152(1-4):315-331

This study compares mercury (Hg) and methylmercury (MeHg) distribution in the soils of two forested stream watersheds at Acadia National Park, Maine, U.S.A. Cadillac Brook watershed, which burned in 1947, has thin soils and predominantly deciduous vegetation. It was compared to the unburned Hadlock Brook watershed, with thicker soil and predominantly coniferous vegetation. Soils in both watersheds were primarily well drained. The fire had a significant impact on the Cadillac watershed, by raising the soil pH, altering the vegetation, and reducing carbon and Hg pools. Total Hg content was significantly higher (P > 0.05) in Hadlock soils (0.18 kg Hg ha^-1) compared to Cadillac soils (0.13 kg Hg ha^-1). Hadlock O horizon had an average Hg concentration of 134±48 ng Hg g^-1 dry weight, compared to 103±23 ng Hg g^-1 dry weight in Cadillac O horizon. Soil pH was significantly higher in all soil horizons at Cadillac compared to Hadlock soils. This difference was especially significant in the O horizon, where Cadillac soils had an average pH of 3.41±0.22 compared to Hadlock soils with an average pH of 2.99±0.13.To study the mobilization potential of Hg in the O horizons of the two watersheds, batch adsorption experiments were conducted, and the results were modeled using surface complexation modeling. The results of Hg adsorption experiments indicated that the dissolved Hg concentration was controlled by the dissolved organic carbon (DOC) concentration. The adsorption isotherms suggest that Hg is more mobile in the O horizon of the unburned Hadlock watershed because of higher solubility of organic carbon resulting in higher DOC concentrations in that watershed.Methylmercury concentrations, however, were consistently higher in the burned Cadillac O horizon (0.20±0.13 ng Hg g^-1 dry weight) than in the unburned Hadlock O horizon (0.07±0.07 ng Hg g^-1 dry weight). Similarly, Cadillac soils possessed a higher MeHg content (0.30 g MeHg ha^-1) than Hadlock soils (0.16 g MeHg ha^-1). The higher MeHg concentrations in Cadillac soils may reflect generally faster rates of microbial metabolism due to more rapid nutrient cycling and higher soil pH in the deciduous forest. In this research, we have shown that the amount of MeHg is not a function of the total pool of Hg in the watershed. Indeed, MeHg was inversely proportional to total Hg, suggesting that landscape factors such as soil pH, vegetation type, or land use history (e.g., fire) may be the determining factors for susceptibility to high Hg in biota.  相似文献