James Rouiller

Evidence of titanium mobility in soil profiles, Manaus, central Amazonia

Titanium minerals are classically considered to be very resistant to weathering in soils. Consequently, variations of titanium concentrations within the soils were used to estimate rates of weathering of parent material. Mobility of Ti was studied in an Amazonian ferralsol using a large set of techniques. Chemical and mineralogical studies of Ti distribution in the soil profile showed that weathering of Ti minerals follows the mineral sequence: ilmenite, pseudorutile, rutile and anatase. This weathering leads to absolute Ti losses on the profile scale. Mineral bags were located at different depths within the top soil, and removed after 6, 12, 18 months in the soil. In all bags the presence of newly generated anatase was recorded after the exposure periods, showing the rapidity of the processes. The vegetation recycles a significant quantity of Ti, increasing Ti mobility in soils. These results indicate that Ti can be mobile under certain conditions and thus should not always be used to estimate weathering rates.

Macroinvertebrate community loss as a result of headwater stream acidification in the Vosges Mountains (N-E France).

The relationships between water chemistry and aquatic macroinvertebrate communities of 41 headwater streams were studied in the Vosges Mountains (N-E of France) in an attempt to assess the impact of acidification on macroinvertebrate diversity. The taxa richness of macroinvertebrates decreased drastically in headwater streams which were characterized by low pH, low calcium and high aluminum content. All taxonomic groups were affected, but Molluscans, Crustaceans and Ephemeroptera disappeared totally from strongly acidified streams. Simple indices based on taxa richness such as the coefficient of community loss may provide accurate tools to quickly assess the impact of acidification on macroinvertebrate communities. Despite the reduction of atmospheric SO2 emissions, acidification of freshwater in the Vosges Mountains continues to affect streams which were believed in the past to constitute refuge biotopes for numerous species. Consequently, acidification represents a real threat for numerous invertebrates. This study arises the question of the evolution in the future of headwater stream ecosystems. Urgent decisions and interventions are required to preserve non-acidified streams and to restore impacted ecosystems while awaiting spontaneous recovery.

Oxide weathering and trace metal release by bacterial reduction in a New Caledonia Ferralsol

Bacterial reduction of Fe- and Mn-oxides was studied in a surfacehorizon of a New-Caledonian Ferralsol in batch experiments. Twotreatments were imposed containing different sources of organicmatter (soil organic matter with or without glucose addition) tolink organic matter biodegradation with reduction process. Theconcomitant solubilization of Ni and Co was also studied. Resultsshowed that anaerobic Fe- and Mn-reducing bacterial activity wasresponsible for Fe- and Mn-oxide solubilization by anaerobicrespiration or fermentation. When C was more available, oxidereduction was enhanced. Mn-oxide appeared as the major reduciblephase and metal source rather than goethite. Co and Ni weresolubilized with Fe and Mn but their amounts in solutiondecreased at the end of experiment. The bioavailability of heavymetals in this soil was increased by biological reduction but waslimited by adsorption or precipitation phenomena.

Validation of an operational procedure for aluminium speciation in soil solutions and surface waters

Abstract Based on various methods, this paper proposes an optimized procedure to assess Al speciation in soil and surface waters. A 5-s flash extraction of some Al inorganic species by 8-hydroxyquinoline is proposed to replace the widely used rapid extraction (15 s) procedure. All species of Al relevant to natural waters were for extractibility under the recommended conditions. The speciation of this pool may be computed by equilibrium modelling. The Al-F species were not extracted and must be computed separately by equilibrium modelling without too many uncertainties. They cannot be determined using the free F-selective electrode method, because of interferences with other ions that are too strong. The polymeric and colloidal Al species are derived from the unrecovered Al in ion chromatography using a Dionex CS-3 cationic analytical column, for which the dimeric AlSi species extracted during the 8-hydroxyquinoline extraction step must be added. Organic Al was considered as being the amount of Al not accounted for by these combined procedures. An example of speciation is given with respect to some spring waters from the Vosges mountains in France. Often less than one-third of Al was found as toxic species, which identifies the need of such determinations to assess Al toxicity in acidified ecosystems. Among the non-toxic species, the AlSi complexes were found to sometimes reach up to 50% of the total Al, which emphasizes the great influence of silica on Al toxicity in surface waters.

Occurrence of non-monomeric species of aluminium in undersaturated soil and surface waters: consequences for the determination of mineral saturation indices

The occurrence of a polymeric and/or colloidal Al pool was demonstrated on an experimental basis in various natural acid soil solutions and stream waters, even in the pH range 3.3–4. A number of these waters were found to be undersaturated with respect to various relevant mineral phases (amorphous Al(OH)3 and AIPO4, gibbsite, boehmite, variscite, imogolite, kaolinite, halloysite, jurbanite, basaluminite and alunite). Non-monomeric Al species should not occur in undersaturated aqueous systems in equilibrium; therefore the polymeric/colloidal Al pool observed in these undersaturated waters cannot be in equilibrium with monomeric Al. As a consequence, the traditional determination of saturation indices (S!) by model equilibrium calculation using total concentrations of every element is considered to be unreliable, and any valid procedure should involve the determination of monomeric species (or a part of them) by analytical speciation.

Soil solutions and surface water analysis in two contrasted watersheds impacted by acid deposition, Vosges mountains, N.E. France: interpretation in terms of Al impact and nutrient imbalance

Two acid watersheds in the Vosges mountains (N.E. France), one with a podzol, the other with an acid brown soil, were monitored by analysing soil solutions and two related springs for total chemistry and Al speciation. High concentrations of inorganic Al did not occur in the podzol upper horizons but were evident in the corresponding spring, together with low concentrations of Ca. In the acid brown soil area, high concentrations of inorganic Al occurred in the leaching water draining the upper soil horizons, but not in the undrained water nor in the spring, the latter exhibiting rather high Ca content. In both watersheds, needle yellowing in conifers could be observed and might be ascribed to Mg deficiency rather than to Al toxicity.

Evidence for the redissolution of soil spodic horizons under the influence of acid deposition in the Vosges mountains (north-eastern France)

Abstract The speciation of soluble Al present in leaching waters was studied in an acid watershed with podzolic soils from the upper soil horizons to two spring waters. The main pattern of soil water circulation during high rainfall events was found to be vertical leaching through the upper soil eluvial horizons, then lateral flowing within the upper part of the deep spodic horizons. Between the bottom of the eluvial horizons and the spring waters, organic Al disappeared, wheteas new inorganic monomeric Al species appeared. The latter were ascribed to the redissolution of the amorphous Al previously accumulated within the soil spodic horizons rather than to the dissociation of pre-existing F-bound Al or organic Al species. Atmospheric pollution-derived acidity was involved in this process, rather than soil-derived acidity. As such horizons contain high amounts of potentially toxic Al and trace metals in readily mobilizable forms, such a redissolution constitutes a true chemical time bomb for the future.

Nitrification and nitrate uptake: leaching balance in a declined forest ecosystem in eastern France.

Nitrate uptake and leaching were measured during one year in a declined fir forest on the Vosges highlands (eastern France), in order to investigate whether excess nitrification could be responsible for a deleterious acidification of the ecosystem. Nitrate uptake by the vegetation was active mainly from spring to early fall, and then reached about 66 kg N ha-1. No significant leaching loss occurred during the growth period of the vegetation. Significant nitrate leaching occurred in winter (about 17 kg N ha-1). During fall and winter the nitrification rate was of the same magnitude as values reported for other ecosystems, and, thus, was not considered to be abnormaly strong. No abnormal temporal discoupling of nitrate production and nitrate uptake occurred in the ecosystem, and forest decline must therefore have some other cause.

Importance of the Nitrogen and Sulfur Cycles in the Proton Budget in a Declining Fir Forest and its Relation to Aluminium Toxicity

In a fir stand showing symptoms of forest decline from Eastern France, the net H+ budget was strongly inflluenced by the net NO3- production/uptake/leaching balance. Aluminium toxicity was mainly related to seasonal variations of the NO3- fluxes and corresponding proton budget.

Aluminum Speciation, Toxicity and Transfer from Soils to Surface Waters in Two Contrasting Watersheds Exposed to Acid Deposition in the Vosges Mountains (Northeastern France)

Despite considerable research in the past decades, acid deposition remains a serious environmental problem for many areas in the northern hemisphere, particularly in the northeast United States (Driscoll and Van Dreason, 1993; David and Lawrence, 1996) and Central and Northern Europe (Ulrich et al., 1980; Nilsson et al., 1983; Rosseland and Henriksen, 1990; Matzner and Prenzel, 1992; DeVries et al., 1995), including the north-east of France in the Vosges mountains (Probst et al., 1990; Boudot et ai, 1994a). Acid inputs may have negative impacts on the chemistry and the biological quality of soils and surface waters, particularly through the appearance of soluble inorganic Al species (some of them being toxic to plants and aquatic communities), nutrient imbalance and low pH. Both forest decline and freshwater impoverishment may be related to acidification processes and its related nutrient imbalance as well as the occurrence of soluble Al (Baker and Schofield, 1982; Boudot et al, 1994a).