Diversity, biotic and similarity indices: A review with special relevance to aquatic ecosystems

Diversity Indices, Biotic Indices and Similarity Indices are reviewed considering their ecological application, both theoretical and practical. Eighteen diversity indices in eight groups, nineteen biotic indices in ten groups and five similarity indices are examined for their applicability to biological systems, particularly aquatic ecosystems. All the diversity indices were found unsuitable except for Simpsons D, Hurlberts PIE, indices based on the theory of Runs (SCI and TU) and possibly McIntosh's M. Indices based on information theory, such as H′ and H, although the most commonly used diversity indices were unsatisfactory due to the lack of exploration of their biological relevance. The use of H′ in aquatic ecosystems is only justified until the more satisfactory indices are adequately field tested.Biotic indices are highly specialised for a particular type of water pollution, usually organic pollution. Chutter's and Chandler's biotic index appear to be most favoured. In their present form, however, such indices are necessarily limited to the geographical area in which the tolerance lists were compiled. Although many comparisons have been made between diversity indices and biotic indices, these were found to be spurious as one index reflects community structure the other the physiological response of indicator species to one type of pollution. Such comparisons have usually been justified by claiming that one index performs better when compared to the term “water quality”, which is usually left undefined.The five similarity indices examined have been used in aquatic systems. It is not clear which of these indices is best to use. The percentage similarity index (PSC) and Pinkham and Pearson's index (B) appear to be most favoured for aquatic systems, though there is a need for further research and field testing of similarity indices for water pollution.The relationship and definitions of diversity and stability are examined. Though discussion is by no means concluded on this topic it is clear that diversity does not automatically lead to either stability or instability but may be found with both. Disturbance to an ecosystem may often increase diversity provided it is of intermediate frequency, yet an ecosystem may also become more diverse without becoming less stable.The numbers of these three types of indices have become legion, as has their use. It is time that only those indices with biological relevance were used. It is hoped that work will now concentrate on the promising members of the two indices of community structure (diversity and similarity) as these are of broad applicability while biotic indices are limited to one or a few pollutants and one geographical area.     

Effects of a diesel spill on freshwater macroinvertebrates in two urban watercourses,Wiltshire, UK

The impacts of a spill of approximately 9800 L of diesel on a small stream and the River Ray (near Swindon, Wiltshire, UK) were examined using kick-net sampling of freshwater macroinvertebrate families at impacted and reference sites. Initial impacts (10 days after the spill) 50 m downstream of the spill were severe, with only 9% survival of individuals (excluding oligochaete worms) and 56% survival of invertebrate families. The percentage survival of macroinvertebrates increased progressing downstream from the spill, with no detectable impacts beyond approximately 4 km downstream. The crustacean families Asellidae and Gammaridae were particularly sensitive to the diesel spill. The recovery of the macroinvertebrate community was assessed 13.5 months after the spill. At this time, recovery was almost complete, with only minor impacts at the sites closest to the spill. The use of live laboratory sorting of samples from impacted sites provided essential information on the impacts of the diesel spill.     

The validity of the Gammarus:Asellus ratio as an index of organic pollution: abiotic and biotic influences.

In freshwaters. Gammarus spp. are more sensitive to organic pollution than Asellus spp. and the relative abundance of the two taxa has been proposed as a pollution index. We tested the validity of this by examining the relationship between the Gammarus: Asellus (G : A) ratio and (1) a suite of physico-chemical variables. (2) established biotic (average score per taxon, ASPT) and richness (species richness (S) and Ephemeroptera, Plecoptera and Trichoptera families richness (EPT family richness)) indices generated from the macroinvertebrate community. In addition, we investigated a suspected biotic interaction, predation, between Gammarus and Asellus. Both univariate and multivariate analyses showed that the G: A ratio was sometimes responsive to changes in parameters linked to organic pollution, such as BOD5 and nitrate levels. However, the G : A ratio also appeared responsive to variables not directly linked to organic pollution, such as conductivity and distance from source. There were significant positive correlations among the G : A ratio and the ASPT, S and EPT, indicating that changes in the relative abundances of Gammarus and Asellus were reflected in changes in the pollution sensitivity and richness of the wider macroinvertebrate community. A laboratory experiment revealed significant predation of Asellus aquaticus juveniles by Gammarus duebeni celticus adults, but no reciprocal predation. We propose that the G: A ratio may be useful as a crude measure of organic pollution that could supplement more complex indices in a multimetric approach to pollution monitoring or be used for monitoring individual sites, where a simple technique is required for monitoring purposes over a period of time. Also, we urge recognition of the possible role of biotic interactions among taxa used in the generation of pollution indices.     

An equivalent plasticity theory for jointed rock masses

A non-representative volume element (NRVE) approach to equivalent rock mass properties shows that the form of the elastic–plastic constitutive equations is the same for homogeneous material elements and multiple-material elements, subsequently homogenized. Thus the average stress and strain increments in an arbitrary jointed rock mass volume are related by {dσ}=([C*_ep]){dε} where σ is effective stress. The equivalent elastic-plastic properties matrix [C*_ep] is the sum of an equivalent elastic moduli matrix [C^*] and a plastic ‘correction’ matrix [C*_p, as usual. However, there are no equivalent plastic potentials Y^* or yield functions, failure criteria F^* or strengths. The equivalent elastic-plastic properties are constructed from the elastic moduli and strengths of the rock mass joints, the intact rock between and strain influence functions that relate local to overall average strains. Numerical examples that simulate laboratory-like tests on jointed rock cubes illustrate the approach.     

Heavy metal bioaccumulation and macroinvertebrate community changes in a Mediterranean stream affected by acid mine drainage and an accidental spill (Guadiamar River, SW Spain)

In the 1998 Aznalcóllar mining accident, 5 million cubic meters of toxic waste were spilled into the Guadiamar River (SW Spain). This paper describes the likely effects of metal pollution on the macroinvertebrate community in the first 15 km of the river adjacent to the mine, 2 years after the spill. The contents of Zn, Cu, Pb, As, Cd, Tl, and Sb in water, sediment, and in the caddisfly Hydropsyche were analysed, together with some physico-chemical parameters. From the results of physico-chemical and community parameters, the studied area was divided into three sections: the first section contained upstream control stations, not affected by current mining activities, and with a diverse macroinvertebrate community structure (mean number of families = 19); the second section, close to the mine, was severely polluted, with more than 50 mg l(-1) of Zn or 1.6 mg l(-1) of Cu in water, a pH of nearly 4, and a very diminished macroinvertebrate community (three families); in the last section, 6-15 km downstream from the mine, the water quality improved, metal concentrations decreased, pH reached neutrality and the macroinvertebrate community comprised eight families. We also determined metal concentrations in the larvae of Hydropsyche and found increases of 3- to 35-fold (for Cu and Cd, respectively) compared to control sites. As far as we are aware, these values are the highest concentrations so far detected in this caddisfly anywhere in the world. Different patterns of metal and pH tolerance were identified in macroinvertebrates. Most of the species were intolerant to present pollution levels and were only present in control sites. Others were tolerant to metal pollution but not to low pH and were present in the main river downstream of the mine, while a very few species managed to live in the most polluted section, with very low pH and high metal concentrations.     

Preliminary studies on the leaching of some trace metals from kitchen faucets

Preliminary studies were carried out on the leaching of copper, zinc, chromium, cadmium and lead from eight kitchen faucets by samples of raw, filtered and distributed Ottawa water, a sample of well water and deionized water containing 2 mg l⁻¹ aqueous fulvic acid. Leaching was effected by allowing the test solutions to stand in the inverted faucets for two successive 24-h periods. Concentrations of the metals found in the leachates were copper: first leaching, 0.12–28.0 mg l⁻¹, second leaching, 0.08-3.54 mg l⁻¹; zinc: first leaching, 0.13-10.25 mg l⁻¹, second leaching, 0.06-2.85 mg l⁻¹; chromium: first leaching, < 1.0 × 10⁻³ − 0.395 mg l⁻¹, second leaching, < 1.0 × 10⁻³−0.032 mg l⁻¹; cadmium: first leaching, < 0.05 × 10⁻³−0.01 mg l⁻¹, second leaching, < 0.05 × 10⁻³−4 × 10⁻³ mg l⁻¹; and lead: first leaching, < 0.2−110.0 mg l⁻¹, second leaching, < 0.2−82.0 mg l⁻¹. The faucets containing lead-soldered copper joints released high concentrations of lead, particularly in the case of leaching with the aqueous fulvic acid solution. Under the conditions of the present investigations it is indicated that in some cases the concentrations of metals leached could lead to intakes in excess of the maximum permissible limits for these metals. However, further investigations will be required to determine the possible contribution of these faucets to metal intake under normal usage.     

Heterogeneous distribution of radionuclides, barium and strontium in phosphogypsum by-product

Phosphogypsum (PG) is a high volume by-product of the phosphate fertilizer industry which is composed mainly of CaSO₄·2H₂O. Impurities in PG include F, trace elements and naturally-occurring radionuclides. Radium-226 content is sufficiently high in some PGs that it has limited PG usage in building materials and as an amendment to agricultural soils. Radium likely exists in PG as a sulfate solid solution with Ba, and possibly Sr. This study determined the distribution of ²²⁶Ra, Ba, Sr, U, Th and ²¹⁰Pb among three size fractions (fine: <20 μm; medium: 20–53 μm; coarse: >53 μm) in PGs derived from three different phosphate rock sources. All chemical species, except for Sr in PG derived from Idaho rock, were enriched in the <20-μm fraction relative to the other size fractions and relative to unfractionated PG. On average, fine fraction ²²⁶Ra and ²¹⁰Pb contents were enriched approximately sixfold over unfractionated PG. ²²⁶Ra was enriched in the fine fraction to a greater degree than were Ba or Sr, indicating that Ra behavior in PG is distinct from these other elements. The combination of (i) particle sorting during PG deposition, and (ii) non-uniform distribution of radionuclides in PG, may contribute to radionuclide heterogeneity at PG repositories.     

Runoff-related agricultural impact in relation to macroinvertebrate communities of the Lourens River, South Africa

A field study at the Lourens River, South Africa, was undertaken during the pesticide application period between November 2001 and January 2002 in order to investigate the potential relation of agricultural pollution to the aquatic macroinvertebrate fauna. The upper regions of the Lourens River were free of contamination (LR1), whereas subsequent stretches flowing through a 400-ha orchard area (LR2) received transient insecticide peaks. Continuously operating suspended-particle samplers as well as flood samplers operating during runoff events were used to measure pesticide contamination. In addition, various physicochemical and morphological parameters were examined. A survey of the macroinvertebrate communities associated with the rocky substrates was carried out every three weeks. Community indices were calculated using the South African Scoring System (SASS 5) for bioassessment of water quality in rivers. The two sites differed in pesticide pollution as well as in average turbidity levels (LR1 5.5 mg/L; LR2 64.3 mg/L), but were similar in bottom substrate composition and most other abiotic factors. At the downstream site (LR2), pesticide values of 0.05 microg/L azinphos-methyl in water as well as 49 microg/kg azinphos-methyl, 94 microg/kg chlorpyrifos and 122 microg/kg total endosulfan in suspended particles were found during runoff conditions. The macroinvertebrate communities of the two sampling sites were similar in terms of number of total individuals, but differed significantly (ANOVA) in average number of taxa (LR1 11.7, LR2 8.9). Seven out of 17 investigated taxa occurred in significantly reduced numbers or were even absent at the downstream site LR2. The community characteristics determined by SASS 5 showed a significantly less sensitive community structure at the downstream site (TS 41; ASPT 4.6), indicating continuously lower water quality compared to site LR1 (TS 80; ASPT 6.9). It is concluded that the Lourens River macroinvertebrate communities are affected by agricultural pollution, with pesticides and increased turbidity as the most important stressors.     

Responses of aquatic organisms to metal pollution in a lowland river in Flanders: a comparison of diatoms and macroinvertebrates

The role of macroinvertebrates and diatoms as indicator for metal pollution was investigated by assessing both biota along a metal gradient in the Belgian river the Dommel. Macroinvertebrates and diatoms were sampled in summer and winter and physical-chemical characteristics of the water were measured at four different sample periods and related to sediment characteristics. Although metal concentrations, except cadmium, in the water nowhere exceeded water quality standards, high metal concentrations were measured in the sediment, indicating historical contamination of the Dommel. At the sites that were situated downstream of the pollution source, high levels of conductivity and chloride were measured in the water. Redundancy Analysis (RDA) indicated pH, phosphate and zinc as the significant environmental variables explaining each respectively 7.7%, 11.6% and 22.6% of the macroinvertebrate community composition. Two clusters could be separated, with Gammarus pulex, Leptocerus interruptus, Baetis rhodani and Cloeon dipterum associated with low zinc concentrations and Tubificidae, Asellus aquaticus, Erpobdella sp. and Chironomus thummi-plumosus associated with higher zinc concentrations. Ammonium (10.6%), conductivity (16.5%), chloride (11.4%) and zinc (5.9%) turned out to be significant variables explaining the diatom community structure. Based on physical-chemical differences and species composition, three different groups could be separated. With this Tabellaria flocculosa and Fragilaria capucina var. rumpens were associated with low metal concentrations, Gomphonema parvulum and Nitzschia palea with elevated concentrations and Eolimna minima and Sellaphora seminulum with high zinc concentrations. In conclusion, the diatom community best reflected the metal gradient. With regard to water quality indices, those based on macroinvertebrates best followed the metal pollution gradient and were most strongly correlated with physical-chemical variables of water and sediment. This study indicated that to assess the effect of metal pollution in lowland rivers, the combined use of macroinvertebrates and diatoms is more appropriate than the use of both biota separately.     

Initial effects of the toxic waste spill (Aznalcóllar mine accident) on the aquatic macrofauna of the Guadalquivir Estuary

The initial effects of the toxic waste spill in April 1998 at the Aznalcóllar mine (SW Spain) on the nektonic community of the Guadalquivir Estuary were examined at three sampling sites using univariate and multivariate techniques. Since studied communities showed a considerable seasonal trend, only seasonally homogenous periods were compared to analyse effects of the spill: May-August 1997 (before spill) and May-August 1998 (after spill). Results of both techniques (two-way nested ANOVA and ANOSIM tests, P > 0.05) indicated that there was no significant difference between the nektonic community of the estuary before and after the spill (monthly number of species, abundance, biomass and similarity among samples). Conversely, an unusually high density was observed at the outer sampling site immediately after the spill for species typical of more stagnant estuarine habitats. This feature seems to indicate that the fauna in the estuarine area through which the untreated water penetrated into the main course may have been disturbed. Results also suggest that this initial sudden input of fresh water to the estuary could have enhanced the effects of an increased river flow (a drop in the salinity). Nevertheless, longer temporal series of data, especially for permanent estuarine inhabitants, are recommended before conclusions can be drawn on the effects of the toxic waste spill on estuarine communities.     

Spatial heterogeneity and diversity of vegetation at the landscape level in Inner Mongolia, China, with special reference to water resources

Inner Mongolia, China, was divided into five different areas (landscapes) based on the annual overland flow of water (AOF): <2, 2–5, 5–10, 10–50, and >50 mm. Two maps of plant communities with a 1-cm² grid and the AOF were overlaid (scale: 1 cm = 15 km). Each plant community that occurred in each 1 cm × 1 cm cell (S-cell) was recorded, and the number of occurrences of each community type was counted for groups of four neighboring S-cells (L-cell). These data were statistically analyzed using the power law for each of the five landscapes. The per L-cell community richness and diversity for dry (AOF < 2 mm) and subhumid (AOF > 50 mm) landscapes were low compared to those of the three mesic landscapes (2–50 mm AOF). Community spatial heterogeneity was low in mesic landscapes. The dry and subhumid landscapes consisted of a small number of community types and exhibited monotonous spatial change, while the mesic landscapes consisted of rich plant communities that were spatially intermingled because natural conditions, such as climatic and edaphic conditions, in the landscapes are complex and divided into small areas, and, furthermore, historical anthropogenic activities such as livestock grazing, especially in landscapes with AOFs of 2–50 mm, have divided the landscape into small fragments.     

Shaft resistance of a pile embedded in rock

A rational calculation procedure is proposed for establishing the shaft resistance of a pile embedded in rock, based upon the Hoek and Brown failure model. The state of the art of the calculation of the pile shaft resistance is analysed. Nearly all the recommendations that have appeared in the technical literature, for calculating the ultimate shear strength of a shaft embedded in rock (τ_ult) propose that τ_ult=ασ_c^k(σ_c;τ_ulten MN/m²) where the coefficient α, considered as a constant dimensional value, ranges from 0.1 to 0.8, if the unconfined compressive strength (σ_c) is expressed in MN/m². In most cases, the exponent k is 0.5.A comparison is made between the results yielded and the different empirical theories that have been put forward with respect to this shaft resistance. It can generally be stated that the results obtained with this theory are reasonable for long and deeply socketed piles (high confining pressures) but the results are on the safe side in some cases where short piles (low confining pressures) are involved.This paper is a continuation of the works developed by the same authors with piles working at the tip, socketed in rock.     

Effect of temperature and pH value on the growth-rate constants of nitrifying bacteria in the activated-sludge process

The specific growth rates of nitrifying organisms were determined under non-equilibrium conditions in laboratory-scale activated sludge plants at three temperatures and six pH values. The highest growth rate for the first stage (to nitrite) was 0.61 d⁻¹; no nitrification was observed over a 7 week period at pH 6.0 at any temperature, indicating a μ value of <0.06 d⁻¹. Fewer data were obtained for the second stage (to nitrate); in all but one of ten comparisons the specific growth rate was lower (by an average of 16%) than for the first stage. The effects of temperature and pH value were not as expected probably because of greater effects resulting from the differences in composition and strength of the sewages used.It is shown that calculations of μ from simple measurements made on full-scale plants can give an early warning of harmful changes in the aeration tank well before the concentration of ammonia in the effluent increases.     

Evaluating the input and source of faecal contamination in the cattle farming and forested regions of the Oconee watershed

Sites along Sugar Creek and the Apalachee River were monitored to compare the water quality in cattle farming regions with the forested regions of the Oconee watershed. Dissolved oxygen (6.68 mg/L) and turbidity [23.91 nephelometric turbidity units (NTU)] in Sugar Creek and the Apalachee River were similar. Overall, cattle farming sites along Sugar Creek had higher levels of NO₃^? and PO₄^?3 during the summer months. In contrast, the forested sites on the Apalachee River had elevated concentrations of inorganic nutrients only during spring rain events. The concentration of faecal bacteria was greater in the cattle farming areas compared with the level of faecal bacteria in the forested areas, and microbial source tracking with the bovine‐associated Bacteroides (BoBac) DNA marker indicated that cattle were the major source of faecal bacteria in Sugar Creek.     

pH adjustment in anaerobic digestion

In the pH range 6·0–7·5, the pH in anaerobic processes is controlled by the interaction of the carbonic system and a net strong base. The acid-base state of a digestor can be monitored by only measuring pH and CO₂ partial pressure. Shock doses of strong bases and carbonates causes temporary undersaturated CO₂ conditions and excessively high pH. Bicarbonate dosing leaves the CO₂ solubility equilibrium unchanged. In the absence of a CaCO₃ precipitation inhibiting agent. CaCO₃ solubility limits the pH, and Ca(OH)₂ dosing is unable to raise the pH significantly. Orthophosphates inhibit CaCO₃ precipitation. With [PO₄] > 1·0 × 10⁻³mole·1⁻¹. CaCO₃. precipitation is partially inhibited. Ca(OH)₂ dosing being approximately 45 per cent effective for doses up to 15000 mg 1⁻¹ as CaCO₃. At [PO₄] < 1·0 × 10⁻³moles·1⁻¹ orthophosphates eventually precipitate out during Ca(OH)₂ dosing, thus removing the inhibition mechanism: pH is then limited by the CaCO₃ solubility. Most wastes contain [PO₄] > 2·0 × 10⁻³moles·1⁻¹ making pH adjustment with Ca(OH)₂ possible to a pH of about 7·2 although the dosages will be very high. The pH changes in a process following dosing can be predicted by the graphical representation of the carbonic and net strong base systems.     

Influence sur la survie jusqu'a eclosion des embryons de carpe commune (cyprinus carpio l.) apres traitement, pendant la fecondation et le developpement precoce, par le carbendazime, un fongicide antimitotique de synthese

The toxicity of the systemic antimitotic fungicide carbendazim, a benzimidazol compound, was studied both by trout and common carp insemination, as well as on the early development of the common carp.The toxicity is several grades of magnitude higher for these stages of the vital cycle compared with the effect on the adult stages: whereas The Pesticide Manual states that for the adult Carp, an LC₁₀₀ (24 h) > 1000 mg 1⁻¹ we find, during insemination at pH 9: LC₁₀₀ (30 min) < 5 mg l⁻¹ and during insemination at pH 7: LC₁₀₀ (30 min) <2.5 min l⁻¹.During early development we find, for instance, LC₁₀₀ (30 min) < 5 mg 1⁻¹ before the end of activation and LC₁₀₀ (24 h) < 1 mg l⁻¹ before the end of epiboly.In the course of insemination, the egg is more sensitive to carbendazim at pH 7 than at pH 9: this difference may be attributed to a greater solubility of the non ionic form of the molecule in the biological membranes.The resistance of the embryo to short treatment grows at the end of activation. This may be attributed to the decrease of the shell permeability during activation.Before the end of activation, the resistance to short intoxication seems to be able to fluctuate, which perhaps corresponds to the existence of sensitive stages in the mitotic cycle.The resistance to an over 24-h exposure increases abruptly at the end of epiboly, which could correspond to a protective part played by the enveloping layer.We suggest the possibility of classifying aquatic pollutants by correlating their physiological mode of action to the resistance profile of the fish embryo.The carp egg seems to be a favourable biological model for studying the effects of aquatic pollutants.     

Bromide concentration in Swedish precipitation, surface and ground waters

The occurrence of bromide in precipitation, surface and ground waters in Sweden has been investigated (300 samples). The concentration of bromide in precipitation is 0.05–0.15 μM in the south and <0.05 μM in the north of Sweden. The concentrations of bromide and chloride are well correlated. For river water the same areal distribution pattern as for precipitation is found, but the concentrations are 2–4 times higher. The molar ratio Br/Cl is 1 × 10⁻³ which is lower than that for sea water (1.54 × 10⁻³) and, most likely, also lower than for precipitation. A detailed study of Lake Mälaren has been made. The north-eastern feeder streams, passing an area of post-glacial clay, showed unusually high bromide concentrations (0.3–3 μM) and Br/Cl quotients (2 × 10⁻³-8 × 10⁻³). No correlation between the concentrations of bromide and chloride was found. Rough calculations indicate that fertilizers and chemicals added to the fields could only contribute a minor fraction of the bromide found. Analysis of 18 ground water samples indicated increased bromide levels as compared to surface waters.     

Weathering indices and their applicability for crystalline rocks

In the recent past, several weathering indices have been proposed to characterize the extent of weathering and weatherability depending upon the nature and requirement of the study. The weathering index provides a quantitative measure of the extent of weathering of rock; hence it can provide input to the prediction models to assess the strength and deformational properties of rocks and classifications of weathered rock material. In the present study some of the important weathering indices, broadly categorized as chemical, (micro) petrographical and engineering weathering indices, are reviewed and studied experimentally for three common rocks of India, namely granite of Malanjkhand, basalt of Nagpur and quartzite of Delhi, along with results of other rocks reported by other researchers. The study reveals that none of the existing chemical weathering indices is valid for genetically different common rock types and useful for engineering purposes. However, loss on ignition (LOI) may provide an approximate estimation of altered minerals (clays and hydroxides) in tested rocks. It has also shown good correlation with petrographic indices and engineering index properties. Among the petrographic indices, crack density (ρ_cr) and unsound constituent (an input to the micropetrographic index) indices provide good correlation with engineering index properties. To quantify the extent of weathering in terms of strength degradation due to weathering in rock, an index is suggested – strength ratio (R_s) – which is the percentage of uniaxial compressive strength (σ_c) of weathered rock with respect to σ_c of fresh rock. Its significance is shown statistically through the relationships with other indices for several rock types including sedimentary and metamorphic rocks. Electronic Publication     

Long term peace river characteristics as a measure of a phosphate slime spill impact

Selected stations on the Peace River, Florida were sampled following a spill of phosphate slime (3.8 × 10⁶1) into the river in 1972. Selected chemical analyses were repeated in 1974 to determine the long-term effect of the phosphate slime spill. Constituent fluxes were calculated (kg constituent/s) for each station, and percent deviations from calculated values for successive stations were also calculated. Short term effects of the spill were identified, and differences in the significant correlations also appeared. Deviations from calculated values were associated with dilution in 1972 for phosphorus, iron, and molybdenum; in 1974, the dilution effect seemed evident only for phosphorus. The implications in terms of the phosphate slime spill and the effect on red tide blooms near the mouth of the river are considered.     

Iron and manganese oxides in Finnish ground water treatment plants

Large amounts of ochreous precipitates are formed on aeration of Fe containing Finnish ground waters during purification for drinking purposes. Sixty-four precipitates were characterized chemically and mineralogically. X-ray diffraction (XRD) indicated that the Fe-rich precipitates consist mainly of a poorly ordered ferrihydrite (5 Fe₂O₃ · 9 H₂O) which only has 2–3 of the 6 XRD lines characteristic of better ordered ferrihydrite. The surface area ranges between 325 and 433 m² g⁻¹ corresponding to a particle size of 5 nm. The ferrihydrites contain 3–7% Si strongly associated with the ferrihydrite as indicated by an i.r. absorption band at 960–975 cm⁻¹ which is associated to Fe-O-Si bonds. Si-containing ferrihydrite typically forms by rapid oxidation of ground waters with 1–23 mg 1⁻¹ Fe and 7–12 mg 1⁻¹ Si at pH 6–7. Very similar products formed in a simulation experiment in which artificial ground water with 20 mg 1⁻¹ Fe was oxidized in the presence of 12 mg 1⁻¹ Si. A1 < 4 mg 1⁻¹ Si lepidocrocite (γ-FeOOH) was formed showing that Si in the system prevents the formation of the more stable and better crystallized FeOOH forms. A transformation of 2-line ferrihydrite to better ordered ferrihydrite or goethite with time is indicated. The Mn-oxide birnessite was identified in black precipitates formed in one plant.