Aluminium speciation in the Vienne river on its upstream catchment (Limousin region, France)

The aim of this study was to investigate the speciation of aluminium in the river Vienne on its upstream catchment (Limousin region, France) over a period of seven years (May 1998-September 2004) in order to assess harmful effects on aquatic life. Two sampling points were selected: the first at 4 km from the spring (Peyrelevade), and the second one at 89 km from the spring (Royères). The aluminium speciation was computed with Mineql+ 4.5 speciation software. Organic matter and phosphorous play a major role in aluminium speciation. If we consider the free aluminium ion (Al3+) as being the only toxic form of aluminium, the concentrations of toxic forms recorded at Peyrelevade and Royères were always below the toxic values for fish. However, if the sum of the concentrations of Al3+, Al(OH)2+, Al(OH)2+ and Al(OH)4- is taken into consideration, the concentration of aluminium recorded may have adverse effects on aquatic life in the upstream catchment of the river Vienne. Al(OH)4- is the major contributor to the concentration in toxic aluminium recorded. In general, Al(OH)4- forms appears in water during the summer with water alkalinisation due to an increase in photosynthetic activities.     

Studies of silica in the oat plant

Summary Silicon in soil solutions is present entirely as monosilicic acid and soils are capable of maintaining a steady concentration in solution despite repeated withdrawals. This concentration is always below the saturation figure of 120 ppm SiO₂ and varies amongst soils of the same pH.Both ferric and aluminium oxides adsorb monosilicic acid but among oxides of similar crystallinity, aluminium oxide is more effective than ferric oxide. When added to a soil, both ferric and aluminium oxides lowered the concentration of monosilicic acid in solution. Aluminium oxide again had the greater effect and one sample lowered the concentration of monosilicic acid from 48 to 9 ppm SiO₂.In pot experiments oats were grown in a soil to which ferric and aluminium oxides had been added and also in soils differing naturally in their content of free sesquioxides. The uptake of silica by the plants can be explained simply in terms of the concentration of silica in the soil solution and the amount of water transpired. This indicates that oats take up silica passively in the transpiration stream.     

Low-pH-mediated elevations in cytosolic calcium are inhibited by aluminium: a potential mechanism for aluminium toxicity

Aluminium, the most abundant metal in the earth's crust, is highly toxic to most plant species. One of the prevailing dogmas is that aluminium exerts this effect by disrupting cellular calcium homeostasis. However, recent research gives strongly conflicting results: aluminium was shown to provoke either an increase or a decrease in cytosolic free calcium concentration ([Ca2+]c). To solve this question, we have adopted a novel approach: [Ca2+]c measurements in intact plant roots as opposed to isolated cells, and the correlative measurements of intracellular and external pH. The results obtained show that plant roots respond to low external pH by a sustained elevation in [Ca2+]c. In the presence of aluminium, this pH-mediated elevation in [Ca2+]c does not occur, therefore any potential calcium-mediated protection against low pH is likely to be irreversibly inhibited. The severity of the inhibitory effect of aluminium on [Ca2+]c depends on the concentration of external calcium, thus perhaps explaining why the effects of aluminium toxicity are ameliorated in calcium-rich soils. It seems possible that a primary toxic effect of aluminium might be to impair calcium-mediated plant defence responses against low pH.     

Thallium Behavior in Soils Polluted by Pyrite Tailings (Aznalcóllar,Spain)

Thallium content and chemical speciation was studied at 91 sites contaminated by water and tailings spilled from the settling pond of a pyrite mine into the Agrio and Guadiamar rivers in Aznalcóllar (Spain). The contamination was highly heterogeneous, with 15% of the affected area seriously contaminated, 55% moderately contaminated and 30% uncontaminated. The total Tl content in the surface horizon increased with respect to the background level, more than 4-fold in the uppermost 10 cm of the soils, and clearly decreased with depth without contaminating either the subsoil or groundwater. Most of the Tl (approximately 75%) was in non-extractable forms, either as a component of the particles in the tailings or adsorbed to crystalline oxides. The remaining Tl was held on, or occluded in, amorphous or poorly crystallized oxides. In acidic soils, the adsorption of Tl was dominated by iron oxides (Feo) and, in neutral-alkaline soils, by aluminium oxides (Alo). A relatively high amount of the Tl adsorbed by amorphous oxides in the uppermost 10 cm of the soils was extracted with acetic acid, and was presumably bio-available (mean values approximately 15% of the Tlo). The EDTA is a strong extractant of inorganic forms of aluminium and, consequently, the quantity of Tl extracted by EDTA in neutral-alkaline soil (mean values more than 10% of the total Tl) could be higher than the truly bio-available fraction. Approximately 1% of the total Tl was extracted with calcium chloride, but only in the neutral-alkaline soil was the extraction significantly related to the cation-exchange capacity and, thus, adsorbed by the negative charges of the clay and organic matter. The Tl soluble in water (< 0.1%) declined with the pH in the neutral-alkaline soils, and was unrelated to any soil property in the acid soils. Thus, the behavior of Tl is determined by climatic conditions, soils properties and time.     

Effects of aluminium on growth and nutrient uptake of Betula pendula seedlings

The response to aluminium concentrations was evaluated for birch seedlings ( Betula pendula Roth, formerly Betula verrucosa Ehrh.) by using a growth technique that provides stable internal concentrations of nutrients in plants. Aluminium was added as aluminium nitrate and aluminium chloride and pH was kept at 3.8±0.2 by adding HCl or NaOH. The seedlings were grown in two different series of nutrient treatments, either with near-optimum conditions (relative addition rate 25% day⁻¹) or with constant nutrient stress (relative addition rate 10% day⁻¹) before the aluminium addition. Growth reduction occurred at aluminium concentrations greater than 3 m M , and lethal effects at aluminium concentrations greater than 15 m M . In plants subjected to near-optimum conditions before aluminium addition, the internal nutrient concentrations decreased with increasing aluminium concentration for all macronutrients. The concentration of the macronutrients N, K and P decreased gradually with increasing aluminium concentration, while the concentration of Ca and Mg decreased fairly abruptly when aluminium concentrations exceeded 1 m M . The same tendency was observed in nutrient stressed birch seedlings, but the pattern was more scattered. Relative growth rate of the seedlings was not affected by a low Ca/Al ratio. In all treatments, the molar Ca/Al ratio in/on the roots was below 0.2 at the end of the experiments. As decrease in growth occurs only at high aluminium concentrations, there is no reason to suggest that aluminium in acid soils is growth limiting for natural birch stands.     

Aluminium tolerance in plants and the complexing role of organic acids

The aluminium cation Al(3+) is toxic to many plants at micromolar concentrations. A range of plant species has evolved mechanisms that enable them to grow on acid soils where toxic concentrations of Al(3+) can limit plant growth. Organic acids play a central role in these aluminium tolerance mechanisms. Some plants detoxify aluminium in the rhizosphere by releasing organic acids that chelate aluminium. In at least two species, wheat and maize, the transport of organic acid anions out of the root cells is mediated by aluminium-activated anion channels in the plasma membrane. Other plants, including species that accumulate aluminium in their leaves, detoxify aluminium internally by forming complexes with organic acids.     

Deschampsia cespitosa and soil acidification: general and trait‐specific responses to acid and aluminium stress in a solution experiment

Genetically based adaptation and phenotypic plasticity represent important means of coping with natural or human‐induced increases in soil acidity. In the present study, we examined the role of phenotypic plasticity in the grass Deschampsia cespitosa by testing for general and trait‐specific responses to acid and aluminium (Al) stress. We sampled tussocks (genets) from sites in southern Sweden differing in their exposure to acid deposition, and quantified the performance of each genet under low pH and high Al levels in a solution experiment using the length and biomass of both shoots and roots as response variables. In agreement with results from a previous solution experiment, the overall performance (expressed as total biomass) declined under acid and Al stress, and there was no evidence for local genetic adaptation with respect to acidity. Three Öland populations showed signs of being stimulated by high Al levels, despite originating from relatively basic soils. We observed a significant increase in root length under high Al levels and hypothesize that this response may be adaptive in the natural soil environment, allowing growing roots to “escape” patches of soil with toxic concentrations of this element. Our results for D. cespitosa indicate that phenotypic plasticity has the potential to mitigate the negative effects of soil acidity in this species.     

Populations of Myriophyllum alterniflorum L. as bioindicators of pollution in acidic to neutral rivers in the Limousin region

Myriophyllum alterniflorum D.C. (Haloragaceae) was studied in the acidic to neutral rivers Vienne and Gartempe (Limousin region, France). Two complementary levels of organisation were evaluated to determine their usefulness for pollution assessment: morphological traits of river populations, and eco-physiological responses to ammonium enrichment in indoor experiments. Inter-node length, stem diameter and leaf length were measured and their ratio calculated for 100 selected plants collected in 20 homogeneous areas. Using multidimensional analysis, their ecological significance for trophic assessment was demonstrated: stem diameter was linked to conductivity, and leaf length/stem diameter ratio to phosphates. Nitrate reductase activity was measured in three populations (upstream, median and downstream populations) after experimental enrichment with ammonium. Ammonium enrichment decreased activity starting at very low concentrations. However, inhibition levels depended on tested populations, with upstream populations being less sensitive due to natural ammonium content in water. The differences could be explained by an eco-adaptation to the trophic level of water. The relationships between the two levels of organisation are discussed. These results could help to distinguish different ecotypes using Myriophyllum alterniflorum.     

Estimating the chemical compositions of soil solutions by obtaining saturation extracts or specific 1:2 by volume extracts

The aluminium tolerance of several tree species was studied in a cloud forest in Northern Venezuela, growing on a very acid soil and rich in soluble Al. The Al-accumulator species (>1000 ppm in leaves) were compared to non-accumulator ones in relation to total Al concentration in xylem sap, pH and Al concentration in vacuoles, and rhizosphere alkalinization capacity. The Al³⁺ concentration in the soil solution and the xylem sap were also measured. The results show that in the Al-accumulator plant Richeria grandis, xylem sap is relatively rich in Al and about 35% of it is present in ionic form. In the non-accumulator plant studied (Guapira olfersiana) there is no Al detectable in xylem sap. The pH of vacuolar sap of several Al-accumulator species studied was very acidic and ranged between 2.6–4.8, but the presence of Al in vacuoles was not correlated with the acidity of the vacuolar sap. Both Al-accumulator and non accumulator plants had the capacity to reduce acidity of the rhizosphere and increased the pH of the nutrient solution by one unit within the first 24 hours. Trees growing in natural, high acidity-high Al³⁺ environment show a series of tolerance mechanisms, such as deposition of Al in vacuoles, Al chelation and rhizosphere alkalinization. These partially ameliorate the toxic effects of this element, but they probably impose a high ecological cost in terms of photosynthate allocation and growth rate.     

Effect of exchangeable aluminium on the reduction of potato scab

The severity of the incidence of the fungal disease, potato scab, varies with different soil groups at the same soil pH. At a soil pH of 5.3, potato scab is easily controlled in soils of western Hokkaido (soil group A) by simply decreasing soil pH, but in soils from eastern Hokkaido (soil group B) it is not so easily controlled. The difference appears to be due to higher levels and exchangeable aluminium in Group A.Addition of sufficient aluminium or ferrous sulfate to a group B soil decreased the incidence of potato scab in a field experiment. Higher levels of aluminium sulfate depressed crop production. It is concluded that aluminium ions control the incidence of potato scab in acid soils. It is suggested that, in soils with low exchange acidity Y1, potato scab can be controlled by adding sufficient aluminium to increase their exchange acidity Y1 to above 7–8.     

太湖流域河流水质状况对景观背景的响应

为探索流域水质对景观背景的响应,以太湖流域为研究对象,在0.5—24 km共9个尺度上运用冗余分析研究了土地利用、河网密度、降水量、地形等景观背景因子与河流水化学指标的关系。结果表明:2006—2010年太湖流域河流水质状况总体较差,但整体有逐渐改善的趋势,超标水质指标主要包括总磷(TP)、氨氮(AN)、生化需氧量(BOD)、化学需氧量(COD)和溶解氧(DO),上游地区主要表现为林区和平原水网区的差异,下游地区主要表现为河段上下游间的差异。河流水质受到多种景观背景因子的综合影响,并表现出尺度依赖性和区位差异性。AN、TP、DO在流域上游与聚落用地正相关,在下游则与耕地、河网密度正相关。COD、BOD在流域上游主要与自然湿地负相关,与人工湿地正相关,在下游则与坡度负相关,与河网密度正相关。总方差贡献率在上下游表现出一致的尺度依赖特征,均在较小(0.5—1 km)和较大(16 km)两个尺度上具有较高的解释能力。自然湿地和坡度,河网密度和耕地分别为上游、下游地区在较小和较大尺度上解释能力最高的景观因子。     

Enhancement of cr(lll) phytoaccumulation

Chromium (III) accumulation in high biomass agricultural crops, sunflower (Helianthus annum) and Indian mustard (Brassica juncea) was studied using four soils (pH 4.6 to 7.6) contaminated with different rates of CrCl₃.6H₂O in the presence of synthetic chelate and organic acids. Chromium is essential for normal glucose metabolism in humans and animals, but its contamination and recovery from soils is of environmental concern. Adding ethylenediaminetetraacetic acid (EDTA), citric acid, or oxalic acid to Cr(III)‐contaminated soils significantly increased Cr concentration in plant shoots and roots. Adding Cr(III) complexes of EDTA, citric acid, and oxalic acid to soils dramatically increased (>200‐fold) Cr concentration in shoots and roots. Plant growth was severely decreased but was dependent on soil type, chelate rate, form, and time of chelate application. Chelates and organic acids enhanced Cr(III) accumulation, but its toxic effects were not avoided. Chromium(III) complexes were as toxic to plants as Cr(VI). The phytoaccumulation and recovery of Cr(III) from soils were limited and depended on soil type.     

Effect of sulfuric acid discharge on river water chemistry in peat swamp forests in central Kalimantan,Indonesia

To estimate the range of area that is affected by sulfuric acid pollution after pyrite oxidation, the surface water chemistry of two rivers in peat swamp forests in central Kalimantan, Indonesia, was surveyed at 1.0- to 3.0-km intervals in September 2003 and 2004 (dry season) and March 2004 and 2005 (rainy season). Water discharged from canals into the main stream of the Sebangau River and the Kahayan River showed lower pH compared to the mainstream water of the rivers, implying sulfuric acid loading from the canal to the main stream of the rivers. The ratio of concentrations of sulfate ion/chloride ion, which was used as a parameter for estimating the contribution of pyritic sulfate to river water chemistry, showed that sulfuric acid loading from pyrite oxidation occurred from the river mouth up to 150 km upstream in both rivers. Water of the main stream of the rivers as well as water discharged from artificial canals into the main stream in the rainy season showed much higher acidity and a higher ratio of sulfate ion/chloride ion than that in the dry season. This result implies that the discharge of pyritic sulfate from peat swamp forests to the limnological system is much higher in the rainy (high water table) season than the dry (low water table) season. Water in the canal in the rainy season was found to be highly acidic (pH = 2.0–3.0). Pyrite oxidation after peatland development causes not only acidification of soil but also acidification of the limnological ecosystem.     

Benthic faunas of streams of low pH but contrasting water chemistry in New Zealand

Water chemistry and benthic invertebrate communities were investigated at 37 sites on acid streams originating on the Stockton-Denniston Plateau, North Westland, New Zealand. The region is characterised by high rainfall and runoff, highly acidic soils and the presence of extensive coal measures that have been mined for over 120 years. Four groups of streams were identified: naturally acid plateau streams with clear water and very low conductivity; brown water (humic) streams with pH<4 and low conductivity; coastal plains streams with higher pH and conductivity; and streams contaminated by acid mine drainage. TWINSPAN and cluster analysis also grouped streams into four groups based on presence-absence of invertebrate taxa, the groups being similar to, but not identical to those based on physico-chemical factors. Diptera (mainly Chironomidae) were represented by most species in all site groups followed by Plecoptera in plateau streams, and Trichoptera on the coastal plain and where mine drainage occurred. Species of Orthocladiinae (Chironomidae), Plecoptera and Trichoptera were found at the most contaminated sites (pH <3, conductivity >900 µS cm^–1, total reactive aluminium >25 mg 1^–1). The leptophlebiid mayfly Deleatidium was found at 32 of the 37 sites, and some species of Plecoptera, Trichoptera and Chironomidae were also widely distributed. Our findings indicate that species tolerant of low pH (i.e., <4.5) are not confined to humic waters as has been postulated, but also occur in soft, non-humic waters where concentrations of labile, non-organically bound aluminium may be elevated.     

Some effects on the growth of brown trout from exposure to aluminium at different pH levels

Yearling brown trout, Salmo trutta L., were exposed to various concentrations of inorganic aluminium (0–3.7 μM1⁻¹) over a pH range of 4.3–6.5 in a flow-through bioassay apparatus using synthetic test media. Low pH, in the absence of aluminium, produced little effect on growth or survival except at the lowest pH tested (4.3). At pH less than 5.5, concentrations of total aluminium in excess of 1 μM 1⁻¹ (27μg 1⁻¹) were found to retard growth. The effects of a given aluminium concentration were markedly reduced at pH above 5.5.
The change in aluminium toxicity with pH must be related to changes in aluminium chemistry. When growth rates are correlated with the different aluminium species, calculated using thermodynamic equilibrium constants given in the literature, it appears that the Al(OH)^{2 +} species is the most toxic, with a small contribution also coming from polymeric complexes.     

The effects of pH and calcium on the growth ofLeucaena leucocephala in an oxisol and ultisol soil

Leucaena was grown for eleven weeks in a pH and calcium amended oxisol and ultisol to determine whether poor growth in acid soils is related to calcium deficiency or low pH induced effects, such as aluminium toxicity. Soil pH was ameliorated by the addition of either CaCO₃, or SrCO₃, while CaCO₃ or Ca(NO₃)₂ were used to modify calcium supply. In both soils, CaCO₃, and SrCO₃ application resulted in an increase in pH and a reduction in exchangeable aluminium although the response of leucaena to the applied amendment varied between the two soils. In the oxisol there was little effect of increased pH on growth, but a marked response to Ca application. In the ultisol, growth was improved by increasing pH but there was no response to increased calcium. The effects of liming on these soils are discussed in relation to alternative strategies available for utilising leucaena and other tree legumes.     

Water quality and the distribution of some fishes in an area of acid sulphate soils,Kalimantan, Indonesia

The drainage from acid sulphate soils severely affects water quality, with pH values commonly around 3, and toxic concentrations of ferrous iron and aluminium. The water quality in an area of acid sulphate soils on the southern coastal plain of Kalimantan, Indonesia, was examined and an inventory of fish species was made. The ionic composition of the water can be described as a simple dilution series of the hypothetical mineral Fe(II)₄Na₈Ca₂Mg₆Al₄H₁₀(SO₄)₂₇, originating from the oxidation of pyrite and weathering products of clay minerals. The oxygen concentrations were variable, ranging from <10% to >100% saturation, without a clear relation to ionic concentrations. Fish were encountered over the entire pH range of 2.8–5.2. Although species distribution showed some correlation with water quality, the species showed widely overlapping ranges, and they are not suitable for use as indicator organisms on the present detailed scale. The most likely explanation for the poor correlation between fish distribution and water quality are seasonal and local fluctuations in quality. These presumably eliminated the more sensitive species, and only those with a high acidity tolerance were found in the area.     

Perch,Perca fluviatilis L., in Small Lakes: Relations between Population Characteristics and Lake Acidity

Perch population characteristics of small lakes were examined with a special reference to lakes which have acidified recently due to atmospheric deposition of air pollutants. The population density and biomass of perch were higher in an acid (pH 4.5) clear water lake with low aluminium concentration than in recently acidified (pH 4.3–4.7) clear water lakes with higher aluminium levels. The structure of perch population in an acid (pH 4.4) humic lake was similar to recently acidified clear water lakes. The population density and the biomass of perch were significantly higher in 6 lakes with pH>5.0 than in 6 lakes of pH<5.0 whereas the mean age and length at a given age were higher in the more acid lakes.     

Acid rain and soil

A summary of important chemical properties of soil is given and the way in which acid rain may affect these properties is discussed. Acid rain may suppress microbiological decomposition and nitrification processes, thus influencing the nutrient status of soils. It has also been found that soil organic matter is less soluble in more acid solutions. Changed nutrient availability patterns are predicted in a low pH environment and enhanced leaching of essential elements from the soil exchange complex has been observed. Increased solubility of potentially toxic elements such as aluminium may also occur from soils which have been exposed to acidified rainfall.     

Determination of the total concentration and speciation of Al(III) in tea infusions

The aluminium species in different tea infusions were investigated, by determining their stability constants and concentration. This was done for some particular samples using a simple experimental method based on the sorption of aluminium on the strongly sorbing resin Chelex 100, by a batch procedure. From the thermodynamic information obtained it is possible to calculate the concentration of the different species, and in particular that of the free metal ion, which is very important for evaluating the adsorption of aluminium on biological membranes. It was found that aluminium in the tea infusions here considered is present at high total concentration, approximately 0.1 mM, but mainly linked to strong complexes, for instance with side reaction coefficient higher than 10(5.11) at pH 3.95 in one case (tea 1). This could be the reason for the low toxicity of aluminium in tea. These strong complexes were not dissociated even in the presence of Chelex 100. In this case only a limiting value of the reaction coefficient could be evaluated. The presence of the very strong complexes was found in all the tea sample here considered. In two of the considered samples (one black and one green tea) a part of Al(III) was linked to less strong complexes, for example with a reaction coefficient 10(4.14) (tea 2, pH 4.20). The presence in the considered tea infusions of other substances able to complex aluminium was also detected, by the well known ligand titration procedure, at concentration ranging from 0.65 to 3.37 mM in three tea infusions, and at somewhat higher concentration in the case of the ready drink, which was also considered for comparison.