Richmond J. Bartlett

Aluminum toxicity in forests exposed to acidic deposition: The ALBIOS results

The ALBIOS project was conducted to examine the influence of acidic deposition on aluminum transport and toxicity in forested ecosystems of eastern North America and northern Europe. Patterns of aluminum chemistry were evaluated in 14 representative watersheds exposed to different levels of sulfur deposition. Controlled studies with solution and soil culture methods were used to test interspecific differences in aluminum sensitivity for one indicator species (honeylocust - Gleditsia triacanthos L. ) and six commercial tree species (red spruce - Picea rubens Sarg., red oak - Quercus rubra L., sugar maple - Acer saccharum Marsh., American beech - Fagus grandifolia Ehrh., European beech - Fagus sylvatica, and loblolly pine - Pinus Taeda L. ). Overall, red spruce was the tree species whose growth was most sensitive to soluble aluminum, with significant biomass reductions occurring at Al concentrations of approximately 200–250 umol/L. Analyses of soil solutions from the field sites indicated that the conditions for aluminum toxicity for some species exist at some of the study areas. At these watersheds, aluminum toxicity could act as a contributing stress factor affecting forest growth.

System for categorizing soil redox status by chemical field testing

Abstract Useful interpretation of the mixed redox electrode potentials measured in soils and natural waters in partial equilibrium with atmospheric O2, is nearly impossible because most oxidized species of critically important N, S, Mn, Fe, and C are not electroactive. We propose that simple chemical tests be used in the field to group soils into the following soil redox status categories: Superoxic, Manoxic, Suboxic, Redoxic, Anoxic, and Sulfidic. These names connote status of oxidation and also indicate electron lability levels, respectively, of Very Low, Low, Medium, Medium High, High, and Very High. Tests involve qualitative measurement of tetramethylbenzidine oxidation colors, oxididation of added Cr, reduced Fe, easily reducible Fe, sulfide and other odors, and indicator pH.

Rapid field determination of nitrate in natural waters 1

Abstract Brucine, an organic reagent used for nitrate determinations, proved stable for at least one year when dissolved in methanol. This makes possible a consistently accurate and rapid method for field determinations of nitrate in clear solutions with a minimum of equipment. The method is also useful in the laboratory for determining nitrate in water or soil extracts. It is quicker and simpler than other colorimetric methods and more sensitive to low concentrations than the nitrate electrode.

Flow path studies in forested watersheds of headwater tributaries of Brush Brook, Vermont

An investigation was undertaken into how headwater tributaries of Brush Brook, Vermont, could have average pH differences of almost two units (4.75 and 6.7). Sampling along four tributaries revealed that most of one tributary, below an area of seeps, had consistently higher pH, Ca2+, Mg2+, and K+, and lower Al than other sites. Bedrock mapping showed numerous fractures in vicinity of the seeps. A portion of this tributarys watershed and a portion of an acid tributarys watershed were intensively mapped for soil depth. Sampling showed the widespread existence of dense basal till in the watershed of the acid tributary but none in that of the near-neutral stream. Lateral flow, found above the dense till, was chemically similar to that of the acid tributary and to solutions sampled from soil B horizons. There were no differences in the average pH of nonseep soils sampled from either watershed. Flow paths are hypothesized to be through the B horizons in the acid tributaries and from below the soil profile in the near-neutral tributary. The acid catchment should be more sensitive to environmental change.

Exchangeable cations and the pH-independent distribution of cation exchange capacities in Spodosols of a forested watershed

The cation exchange behavior of acid, high organic matter (OM) forest soils has been little studied. We measured cation exchange capacities (CEC) and exchangeable cations in fresh, field-moist samples from soil horizons of a forested mountain watershed in north central Vermont. CEC, measured by compulsive exchange on 148 horizon samples, ranged between 0.07 and 84.3 cmolc kg−1. Below pH 5.3, the CEC was linearly correlated with OM and was independent of pH. The amount of ‘permanent’ charge associated with the OM was about 30 cmolc kg−1. However, individual horizons exhibited pH-dependent charge behavior if the pH was adjusted during CEC measurement.

Reactive aluminum in the vermont soil test

Abstract Determination of Reactive Al by extracting a soil sample with pH 4.8 NH4 OAc (1.25 N acetate) characterizes for northern acid soils the quantity of soil acidity that must be neutralized to meet lime need and also lower the P adsorbing capacity. Extracted Al is used in conjunction with pH in 10 mM CaCl2 to calculate the lime requirement directly. First, the amount of P fertilizer needed is approximated, based on the P intensity (Available P) determined in the same NH4 OAc extract. Then the recommended amount is increased by a P‐fixation factor obtained from the Reactive Al measured, and decreased by a Reserve P factor derived from fluoride extractable P. Unlike a buffer lime requirement method, which predicts lime needed to reach a target pH, the Reactive Al test estimates the quantity of acidity that must be neutralized to prevent fixation of P fertilizer by soil Al and to release P from Al‐bound sources. Attaining a particular target pH is not the primary goal. The Reserve P test measures the am...

Apparent pH independence of charge in forest organic surface soil horizons

Conventional wisdom states that the source of negative charge in organic soil horizons is pH dependent and, therefore, acidification will decrease charge and the ability to retain nutrient cations. Using a variety of methods, we found that the native cation exchange capacity (CEC) of northeastern US forest soils varied with the amount of soil carbon (about 0.5 cmol per %C), independent of field pH. However, individual soil samples exhibited dramatic charge variability if the pH was adjusted during CEC measurement, as much as 20 cmolc kg− per pH unit change. These last two statements appear to be mutually exclusive. Extrapolating from pH-adjusted samples, the point of zero “base” cation capacity was consistently about 1.5 pH units below the native pH. We hypothesize the amount of charge is at a steady state with humification and decomposition processes. Response of soils to long-term acidification may be much different than that of short-term laboratory adjustments.

Light-induced disappearance of nitrite in the presence of iron (III).

Understanding of rapid disappearance of nitrite in natural waters and its impact on nitrogen natural cycling has remained limited. We found that NO2- disappeared rapidly in pH 3.2 aqueous Fe(III) solutions both in sunlight and in 356 nm light. Quantum yields of the NO2- loss at 356 nm were 0.049-0.14 for initial levels of 10-80 microns NO2- and 200 microns Fe(III). The NO2- loss (at 356 nm) followed apparent first-order kinetics. The rate constants were 1.3 x 10(-3) (40 microns NO2-) and 4.1 x 10(-4) s-1 (80 microns NO2-) for 100 microns Fe(III), and 2.3 x 10(-3) (40 microns NO2-) and 7.5 x 10(-4) s-1 (80 microns NO2(-1)) for 200 microns Fe(III) (t1/2 = 8.7, 27.9, 5.1, and 15.3 min, respectively). The rate constants were directly proportional to [Fe(III)]0 and inversely proportional to [NO2-]0. Agreement between the rate constants obtained experimentally and those calculated mechanistically supports the hypothesis that NO2- was oxidized to NO2 by .OH radicals from photolysis of FeOH2+ complexes, and at high [NO2-]0 (e.g., 80 microns) relative to [Fe(III)]0, hydrolysis of NO2 or N2O4 to form NO3- and NO2- could be significant. This study showed that light and Fe(III)-induced oxidation of NO2- (rate = approximately 10(-1)-10(-2) microns s-1) was more rapid than its direct photolysis (rate = approximately 10(-4) microns s-1), and the photolysis could be a significant source of .OH radicals only in cases where the Fe(III) level is much lower than the NO2- level ([Fe(III)]/[NO2-] < 1/80). This study suggests that the light and Fe(III)-induced oxidation of NO2- would be one potential important pathway responsible for the rapid transformation of NO2- in acidic surface waters, especially those affected by acid-mine drainage or volcanic activities. This study also may be of interest for modeling certain acidic atmospheric water environments.

Predicting toxicity of reactive ‘solution’ aluminium using kinetic speciation

We assayed the toxicity of Al by measuring lengths of Medicago sativa roots that formed during 3 to 5 days of equilibration of seeds with swirled solutions. Toxicity of ‘solution’ Al, as evidenced by retarded root growth, was reliably predicted by the rapidly reactive (RR) labile Al, determined using the pyrocatechol violet kinetic speciation method of Bartlett et al. (1987). Compared to the slowly reactive (SR) or the total reactive (TR) values, the RR Al results had fewer irregularities caused by colloidal Al or soluble Al strongly complexed by excess hydroxyl, organic, or phosphate ligands and were much more responsive to differences in Al reactivity that influenced root growth. The Al was not toxic when RR Al tested below 5 μM. The RR test correctly predicted colloidal (Tyndall beam positive) Al phosphate as toxic in some treatments, and in others, non-toxic. Hydroxy Al polymers, formed by the slow titration of AlCl3 with NaOH (presumably including Al13), were clearly toxic, but toxicity was less when pH was increased by added hydroxyls. When the total Al concentration was kept constant, the degree of toxicity was inversely proportional to the pH and directly proportional to the RR Al test values. The pH was not a good predictor of toxicity of hydroxy Al when the Al concentration was varied, and not a good predictor of toxicity of phosphate or citrate Al at either constant or varied Al concentration. Desorption results suggest probable toxicity of any Al species that is adsorbed onto a root under the conditions of this study. The RR Al values appeared to integrate the variables affecting reactivity of Al and produce a clean separation between toxic and not toxic.