Dissociation Of Organic Acids Research Articles

RAIN project: Role of organic acids in moderating ph change following reduction in acid deposition

The RAIN project (Reversing Acidification In Norway) entails catchment-scale experimental manipulations to investigate the effect on water and soil chemistry of drastic changes in precipitation chemistry. At Risdalsheia in southernmost Norway wet deposition of acid is excluded from a 860-m2 headwater catchment by means of a roof and “clean” precipitation is added beneath. Four years of acid exclusion (through June 1988) have resulted in lower concentrations of the strong acid anions NO3 (from 35 to 7 ueq L-1) and SO4 (from 110 to 53 ueq L-1) in runoff. The decline in strong acid anion concentrations has been compensated partially by a decrease in concentrations of base cations (55%) and partially by an increase in alkalinity (45%). pH has increased only slightly from 4.0 to 4.1. Organic acids have become increasingly important for the pH of runoff. Runoff from the shallow organic soils contains 10 to 20 mg C L-1 total organic carbon (TOC). The concentration of organic anions (estimated from the ionic balance) has increased from about 22 ueq L-1 in 1984 to 49 ueq L-1 in 1987. This increase is due to increased dissociation of organic acids and not to change in TOC concentrations. The organic C in these acid samples apparently has a maximum charge density of about 4.5 ueq mg C-1 and pK of about 4.

Nutrient and proton budgets in four soil-vegetation systems underlain by Pleistocene alluvial deposits

Proton budgets of four soil-vegetation systems in a 3 ha woodland with acidic and calcareous soils were derived from three years of hydrochemical monitoring of rain- and canopy throughfall water, soil solutions at various depths and measurements on litterfall and tree growth. Soil water fluxes were obtained from dynamic simulation of water transport, calibrated with measured water potentials and water contents in the soil. Atmospheric input is predominantly ammonium sulphate. Only 5–20% of the annual uptake of nutrient elements from the soil is stored in wood, bark and roots of trees. Free H + inputs from the atmosphere are almost completely neutralized in the tree canopy by exchange with cations from the vegetation. The forest floor and the 0– 10 cm mineral surface layer at the acidic soil sites, however, produce free H + , mainly by nitrification, partly by organic acid dissociation. Most of this H + is neutralized at greater depth by nitrate uptake or denitrification, and by dissolution of cations from soil minerals, mainly aluminium in the acid soils. The dominant role of N transformations in the H + budget of these soil vegetation systems is clearly due the high anthropogenic inputs of ammonium sulphate. As a result, the rate of weathering of acidic soils has probably increased severalfold.

Reacidification of Two Lime Amended Soils in Western Oregon

AbstractLeaching of basic cations by winter rainfall and irrigation water and the increasing use of NH+4‐fertilizers have resulted in wide‐spread soil acidity in western Oregon. While applications of liming materials are often made in this region, the rates at which limed soils reacidify are generally not known. The objectives of this study were to: (i) quantify long‐term acidification rates of two lime‐amended soils in western Oregon, and (ii) identify soil‐plant processes which may control acidification rates. Lime applications ranging from 0 to 14 650 kg ha−1 were made on a Nekia sicl (Xeric Haplohumults, initial pH 5.0) and from 0 to 11 200 kg ha−1 on a Woodburn sil (Aquultic Argixerolls, pH 5.3) in the Willamette Valley of western Oregon in 1971 to 72. Monitoring of soil pH and levels of extractable basic cations applied in the liming materials for 11 to 12 yr permitted estimation of the rate of acidification of soils receiving different amounts of lime. Whether estimated by declines in pH or extractable basic cations, soil acidification rates increased with increasing quantities of lime initially applied. Acidification rates of unlimed Nekia soil were 0.025 pH units yr−1 and 0.17 cmol(+) Ca2+ + Mg2+ kg−1yr−1 while the unlimed Woodburn soil showed no net acidification. Maximum rates of acidification of 0.09 pH units yr−1 and 0.62 cmol(+) extractable Ca2+ + Mg2+ kg−1yr−1 on the Nekia soil and 0.08 pH units yr−1 and 0.36 cmol(+) extractable Ca2+ kg−1yr−1 on the Woodburn soil were measured on plots receiving the highest amounts of lime. Faster reacidification of soils amended with higher lime rates is explained by the pH dependence of acidifying processes such as nitrification, CO2 release via plant and microbial respiration, mineralization of organic matter and dissociation of organic acids in soil solution. Ca2+ release from mineral weathering appeared to have an important effect on soil pH and extractable Ca2+, particularly in the absence of large inputs of acidifying materials such as NH+4‐fertilizers. Accurate prediction of soil acidfication rates will require additional information concerning the pH dependence of soil acidifying processes, the quantity and composition of seasonal through drainage, and the rates of mineral weathering in soils.

Deuterium Isotope Effects on the Protolytic Dissociation of Organic Acids in Electronically Excited States

Deuterium Isotope Effects on the Protolytic Dissociation of Organic Acids in Electronically Excited States