Fe and Al oxides distribution in some ultisols and inceptisols of southeastern Nigeria in relation to soil total phosphorus

Ten highly weathered soils in southeastern Nigeria were sampled from their typical A and B horizons for analyses. The objectives were to determine the different forms of Fe and Al oxides in the soils and relating their occurrence to phosphate availability and retention in the soils. The soils are deep and often physically degraded but are well drained and coarse in the particle size distribution. They are mostly dominated by kaolinite in their mineralogy with very high values of SiO₂. The soils are acidic with low soil organic carbon (SOC) contents. The elements in the exchange complex are also low thus reflecting in the low CEC of the soil. Available phosphorus (P) in the soils are generally low while total P ranged from 157 to 982 mg kg⁻¹ with an overall average of 422 mg kg⁻¹. Total Fe in the soil is highest and their order represented as follows: Fe_t > Fe_d > Fe_ox ≥ Fe_p. The pyrophosphate extractable Fe was always higher in the top soil than in the subsoil and was attributed to the fact that these forms of Fe are associated with organic matter which is more abundant in topsoil than in subsoil. Like in Fe forms, the order of Al occurrence could generally be presented as; Al_t > Al_d > Al_ox > Al_p. More Fe and Al oxides in the soils are strongly crystalline while a small quantity is poorly crystalline Fe forms. The amorphous forms of both Fe and Al are very low in the soils when compared with the crystalline forms. The oxides that show very strong affinity to total P are Fe_d–Fe_ox, Fe_d, Al_d, Fe_t, Fe_ox and Al_ox/Al_d. To overcome this problem of P retention in the soil, we recommend constant liming of these soils to neutralize them, application of organic matter and of high dosage of phosphate fertilizer to the soils.     

Transport and sediment–water partitioning of trace metals in acid mine drainage: an example from the abandoned Kwangyang Au–Ag mine area, South Korea

Transport and sediment–water partitioning of trace metals (Cr, Co, Fe, Pb, Cu, Ni, Zn, Cd) in acid mine drainage were studied in two creeks in the Kwangyang Au–Ag mine area, southern part of Korea. Chemical analysis of stream waters and the weak acid (0.1 N HCl) extraction, strong acid (HF–HNO₃–HClO₄) extraction, and sequential extraction of stream sediments were performed. Heavy metal pollution of sediments was higher in Chonam-ri creek than in Sagok-ri creek, because there is a larger source of base metal sulfides in the ores and waste dump upstream of Chonam-ri creek. The sediment–water distribution coefficients (K _d) for metals in both creeks were dependent on the water pH and decreased in the order Pb ≈ Al > Cu > Mn > Zn > Co > Ni ≈ Cd. K _d values for Al, Cu and Zn were very sensitive to changes in pH. The results of sequential extraction indicated that among non-residual fractions, Fe–Mn oxides are most important for retaining trace metals in the sediments. Therefore, the precipitation of Fe(–Mn) oxides due to pH increase in downstream sites plays an important role in regulating the concentrations of dissolved trace metals in both creeks. For Al, Co, Cu, Mn, Pb and Zn, the metal concentrations determined by 0.1 N HCl extraction (Korean Standard Method for Soil Pollution) were almost identical to the cumulative concentrations determined for the first three weakly-bound fractions (exchangeable + bound to carbonates + bound to Fe–Mn oxides) in the sequential extraction procedure. This suggests that 0.1 N HCl extraction can be effectively used to assess the environmentally available and/or bioavailable forms of trace metals in natural stream sediments.     

Phosphate sorption desorption characteristics of some ferruginous soils of tropical region in Eastern India

Phosphate sorption and desorption experiments were conducted with four ferruginous soils (alfisols) of Eastern India, in view of the low native phosphate concentrations in tropical Indian soils. From the P-isotherm curve, standard P requirement (SPR) of the soils was determined. Phosphate sorption data were fitted to both Langmuir and Freundlich equations and mean sorption maximum values obtained for the different soil series were in the decreasing order as Matimahal > Anandapur > Mrigindih > Kashipur. The fraction of added P sorbed followed the same trend as SPR, P sorption maximum (P_max), phosphate affinity constant (K), maximum phosphate buffering capacity (MPBC), Freundlich constant K′ and phosphate desorption values. Phosphate sorption maximum was significantly correlated with MPBC, Freundlich 1/n, SPR, clay and different forms of Fe and Al. The value of K (bonding energy) was significantly correlated with MPBC, Freundlich K′ and pyrophosphate extractable Fe and Al. The MPBC was significantly correlated with Freundlich K′, Freundlich constant 1/n, clay, oxalate and dithionite extractable, amorphous and crystalline form of Fe and Al. Freundlich K′ was significantly correlated with Freundlich 1/n, pH_water, clay, dithionite extractable and crystalline form of Fe and Al. The results suggested that the soils having higher amount of extractable and reactive Fe and Al shared higher P sorbtion capacity and such soils may need higher levels of P application     

Evaluation of elemental enrichments in surface sediments off southwestern Taiwan

Surface slices of 20 sediment cores, off southwestern Taiwan, and bed sediment of River Kaoping were measured for major and trace elements (Al, As, Ca, Cd, Cl, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Pb, S, Si, Ti, V, and Zn) to evaluate the geochemical processes responsible for their distribution, including elemental contamination. Major element/Al ratio and mean grain size indicate quartz-dominated, coarse grained sediments that likely derived from sedimentary rocks of Taiwan and upper crust of Yangtze Craton. Bi-plot of SiO₂ versus Fe₂O₃^T suggests the possible iron enrichment in sediments of slag dumping sites. Highest concentrations of Cr, Mn, P, S, and Zn found in sediments of dumping sites support this. Correlation analysis shows dual associations, detrital and organic carbon, for Cr, P, S, and V with the latter association typical for sediments in dumping sites. Normalization of trace elements to Al indicates high enrichment factors (>2) for As, Cd, Pb, and Zn, revealing contamination. Factor analysis extracted four geochemical associations with the principal factor accounted for 25.1% of the total variance and identifies the combined effects of dumped iron and steel slag-induced C–S–Fe relationship owing to authigenic precipitation of Fe–Mn oxyhydroxides and/or metal sulfides, and organic matter complexation of Fe, Mn, Ca, Cr, P, and V. Factors 2, 3, and 4 reveal detrital association (Ti, Al, Ni, Pb, Cu, and V), effect of sea salt (Cl, Mg, Na, and K) and anthropogenic component (As and Zn)-carbonate link, respectively, in the investigated sediments.     

Seasonal variations of phosphorus species in sediment from the middle Adriatic Sea

Phosphorus (P) species concentrations in 0–2 cm surface sediment layer were investigated monthly from November 2001 to December 2002 at the bay, channel and open sea stations in the middle Adriatic. Modified SEDEX method was used for inorganic phosphorus species determination [P in biogenic (P-FD), authigenic (P-AUT), detrital apatite (P-DET) and P adsorbed on to iron oxides and hydroxides (P–Fe)], and organic phosphorus (P-ORG). P-FD, P-AUT and P-DET concentration ranges (1.5–5.4, 0–2.7 and 0.4–3.4 μmol g⁻¹, respectively) were similar at all stations, and showed no obvious common trend of seasonal changes. P–Fe ranged from 1.9 to 11.9 μmol g⁻¹ with the highest values at bay station and higher seasonal oscillations than other inorganic P forms. P-ORG ranged from 0.3 to 18.7 μmol g⁻¹ with higher concentrations at stations of fine-sized sediments and showed increased concentrations in warm part of the year at all stations. Correlation between concentrations of P–Fe in the surface sediment layer and orthophosphate sediment-water interface concentration gradients at bay and channel stations indicated to P–Fe importance in the orthophosphate benthic flux. For the bay station, linkage between sediment P-ORG and chlorophyll a concentrations, primary production and microzooplankton abundance was established, indicating a 1 month delay of sediment response to production fluctuations in the water column.     

Interstitial water – sediment geochemistry of N, P and Fe and its response to overlying waters of tropical estuaries: a case from the southwest coast of India

 The concentrations of N, P and Fe in surface sediments and interstitial and overlying (bottom and surface) waters of the Ashtamudi estuary located in the southwest coast of India are reported along with the various chemical species of N (NO₂–N, NO₃–N, NH₃–N and total N) and P (organic P, inorganic P and total P) in interstitial and overlying waters and discussed in terms of the physico-chemical environment of the system. The interstitial water exhibits higher salinity values compared to bottom and surface waters, indicating the coupled effects of salt-wedge phenomena and gravitational convection of more saline-denser marine water downward through surface sediments. N, P and Fe as well as their chemical forms are enriched in the interstitial water compared to bottom and surface waters. However, the dissolved oxygen (DO) shows an opposite trend. The marked enrichment of NH₃–N in the interstitial water and its marginal presence in bottom and surface waters, together with the substantial decrease in the DO concentrations of bottom water and consequent increase in the concentrations of NO₂–N and NO₃–N in interstitial and bottom waters, points to the nitrification process operating in the sediment-water interface of the Ashtamudi estuary. The enrichment of total N, P and Fe in the interstitial water compared to the overlying counterparts and the positive correlation of sediment N, P and Fe with mud contents as well as organic carbon indicate that these elements are liberated during the early diagenetic decomposition of organic matter trapped in estuarine muds. Received: 5 Oktober 1998 · Accepted: 9 February 1999     

Ammonium release characteristics of the sediments from the shallow lakes in the middle and lower reaches of Yangtze River region,China

Ammonium release from sediments has significant effects on the water quality in eutrophic lakes. In this study, the ammonium release kinetics and adsorption–desorption processes were investigated in 13 sediments of 6 shallow lakes from the middle and lower reaches of Yangtze River region, China. The results show that First Order Model best described the ammonium release process, the maximal release capacity had a strong correlation with organic matter (OM), cationic exchange capacity (CEC), total nitrogen (TN) and total phosphorus (TP). But it only had a weak correlation with Fe, Ca and Al. The ammonium release capacity in more polluted sediments was higher than that in less polluted sediments. The average release rate within 0–5 min was the highest among the experimental period, the amount released within 0–5 min accounted for approximately 50–70% of the total release capacity. The ammonium release rate had a significant and positive correlation with OM. But it did not have a strong correlation with TN, TP, Fe, Ca and Al. The ammonium potential release capacity (obtained when the water/sediment ratio was about 2,500) had strong and positive relation with OM and maximal release capacity, and it may provide useful information for the sediment release risk assessment. Henry Model best described the ammonium sorption isotherms, and ammonium adsorption–desorption equilibrium concentration can be considered as the ammonium release threshold to assess the release risk in the sediments.     

Neoarchean high-pressure margarite–phengitic muscovite–chlorite corona mantled corundum in quartz-free high-Mg,Al phlogopite–chlorite schists from the Bundelkhand craton,north central India

In quartz-free Fe, Na-poor and high-Mg, Al schists from the Bundelkhand craton in north central India, corundum porphyroblasts in finely interleaved phlogopite–chlorite aggregates with rare clinozoisite are mantled by fine-grained (<3 μm) intergrowths of outer collars (>200 μm wide) of phengitic-muscovite and chlorite (phlogopite + corundum + H₂O → phengitic-muscovite + chlorite), and <100 μm wide inner collars of margarite–muscovite (corundum + clinozoisite + phengitic muscovite → margarite + muscovite + H₂O). Wide-beam electron probe microanalyses indicate Mg in the bi-layered corona increases from corundum outwards, with a complementary decrease in Al and K. Si and Ca increase and then decrease to matrix values. The sharp chemical gradients across the highly structured bi-layered corona are inferred to suggest that the corona-forming reactions were promoted by local grain-boundary-controlled thermodynamic instability as opposed to element transport by advective diffusion. The P–T convergence of KMASH reactions and NCKMASH pseudosection phase relations computed using micro-domain compositions indicate the chlorite–phengitic muscovite outer collar formed at 18–20 kbar and ca. 630°C. The NCKMASH margarite–muscovite inner collar yielded lower metamorphic P–T conditions of 11 ± 3 kbar, ca. 630°C. U–Th–Pb chemical dating of metamorphic monazite and LA-ICPMS U–Pb isotope dating of re-equilibrated zircon yield ca. 2.78 Ga ages, which are interpreted to date corona formation and Neoarchean high-P metamorphism in the Bundelkhand craton, hitherto unknown in the Indian Precambrian. (220)     

Sources of deep groundwater salinity in the southwestern zone of Bangladesh

Twenty groundwater samples were collected from two different areas in Satkhira Sadar Upazila to identify the source of salinity in deep groundwater aquifer. Most of the analyzed groundwater is of Na–Cl–HCO₃ type water. The trends of anion and cation are Cl⁻ > HCO₃ ⁻ > NO₃ ⁻ > SO₄ ²⁻ and Na⁺ > Ca²⁺ > Mg²⁺ > K⁺, respectively. Groundwater chemistry in the study area is mainly governed by rock dissolution and ion exchange. The dissolved minerals in groundwater mainly come from silicate weathering. The salinity of groundwater samples varies from ~1 to ~5%, and its source is possibly the paleo-brackish water which may be entrapped during past geologic periods.     

International viewpoint and news

The Daliao river system in China has been seriously affected by long-term intensive industrial, urban and agricultural activities. The objectives of this study were to determine the total phosphorus (TP) content and forms of phosphate in the sediments and investigate geochemical relationships between P forms and sediment mineral phases. Twenty-seven samples of surface sediments were collected and analyzed for P and major elements. Chemical forms of phosphate in the sediments were measured by sequential selective extraction method. Results indicate that TP in the sediments of the Daliao river system averaged 703 mg kg⁻¹, in the range from 206 to 1,342 mg kg⁻¹. The sediments in the tributaries and near cities contained high TP, due to discharge of municipal and industrial effluents. The distribution of phosphate in the various mineral phases followed the order: Ca-P > RES-P > RS-P > Fe-P > Al-P > S/L-P for the Hun river and Taizi river, and Ca-P > Fe-P > RES-P > RS-P > Al-P > S/L-P for the Daliao river. Fe and Ca contents in the sediments were positively correlated to Fe associated P (Fe-P and RS-P) and Ca-P, respectively. In addition, sediment organic matter, Fe and Ca contents were positively correlated to TP in the sediments. However, Al content was not correlated to Al-P or TP in the sediments. Generally, the sediments contaminated by effluents and in tidal zone contained more bioavailable P. Possible release of P from these sediments to overlying water might pose potential risk on estuarine eutrophication.     

Mobility of Al, Co, Cr, Cu, Fe, Mn, Ni and V in sulphide-bearing fine-grained sediments exposed to atmospheric O2: an experimental study

 The major aim was to increase our knowledge on the behaviour of Al, Co, Cr, Cu, Fe, Mn, Ni and V in sulphide-bearing fine-grained sediments exposed to atmospheric oxygen. Samples of this type of sediment collected in a previous investigation at eight sites in western Finland were digested in HClO₄-HNO₃-HCl-HF at 200  °C and in HCl:HNO₃:H₂O at 95  °C (aqua regia), and subjected to extractions with ammonium acetate and hydrogen peroxide. Metals and S in the leachates were determined with ICP-AES. The results of the chemical analyses are compared with previously reported experimental data. The concentrations of Al and Fe in the sulphide-bearing fine-grained sediments are about 7% and 5%, respectively. Of the trace metals studied, Mn is most abundant followed in decreasing order by V>Cr>Ni>Cu>Co. On oxidation of the sediments, high proportions of Co, Mn and Ni, intermediate proportions of Cu but low proportions of Fe, Al, Cr and V are released. The extent of the release of a metal on oxidation is controlled either by (1) the level to which the pH of the sediments drops on oxidation (Al, Cu, Cr, V), (2) the amount of the metal associated with easily reduced phases (metal sulphides) in the sediments (Ni, Co) or (3) the sum of the amount associated with reduced phases and adsorbed on soil compounds (Mn). No control of the release of Fe on oxidation of the sediments was identified. Based on the results of the study it is argued that artificial drainage and the subsequent oxidation of sulphide-bearing sediments will result in extensive leaching of Co, Mn and Ni, moderate leaching of Cu and limited leaching of Cr and V into drainages. The major elements, Fe and Al, have the potential to be mobilised and leached in large amounts, though the proportions mobilised/leached will remain low. It is suggested that the identification of sulphide-bearing sediments with a high potential of metal release should be based on determination of metals in easily mobilised reduced compounds (dissolved e.g. in H₂O₂) and of the level to which the pH of the sediments drops on oxidation. Received: 16 October 1997 · Accepted: 9 March 1998     

Mercury enrichments in core sediments in Hugli–Matla–Bidyadhari estuarine complex,north-eastern part of the Bay of Bengal and their ecotoxicological significance

Mercury concentrations (Hg_T) in fine-grained fraction (<63 μm) of core sediments of the Hugli–Matla–Bidyadhari estuarine complex, India were analyzed. Results revealed a wide range of spatial variations (<4–93 ng g⁻¹ dry weight) with a definite enhancement level at the lower stretch of the estuarine complex infested with mangrove plants, which might act as a sink to Hg_T. An elevated concentration of Hg was encountered in surface/subsurface layer of the core in majority of the cases resulting from physical, biogenic and postdepositional diagenetic processes that remobilized and resuspended the metal from deeper sediments. A strong positive correlation was observed between the Hg and clay fraction content of the sediments, while the correlations of Hg with Al, Fe and Mn were poor. Based on the index of geoaccumulation (I _geo) and effects range-low (ER-L) value, it is considered that the sediments are less polluted and thus there is less chance of ecotoxicological risk to organisms living in sediments.     

Metal fluxes to the sediments of the Moulay Bousselham lagoon,Morocco

The metal content in surface sediments (0–2 cm, 26 samples), in a sediment core (120, 1 cm slices), taken from Moulay Bousselham (Morocco) was investigated. Concentrations of Al, Fe, Mn, Pb, Zn, Cu, Ni, Cr, Cd, As, and Hg were evaluated in surface and cored sediments of Moulay Bousselham lagoon. Significantly high concentrations in μg g⁻¹ dw of Pb (31.7–6.2), Zn (758.9–167), Cu (310.7–22), Ni (96–10.5), Cr (113–18.9), Cd (0.84–0.02), As (1–0.1), and Hg (0.61–0.02) were found in sediment samples from Moulay Bousselham lagoon. Calculated enrichment factors [EF_Me = (Me/Al)_sample/(Me/Al)_background], using Al as a normalizer, and correlation matrices showed that metal pollution in Merja Zerga of Moulay Bousselham lagoon was the product of anthropogenic sources, while the metal content in Merja Kehla was of natural origins. The results suggest that a major change in the sedimentary regime of the lagoon, associated with internal trapping and re-distribution of heavy metal, has been occurring in the past few decades. The cause would appear to be the construction of a Nador Canal at the lagoon. Probable effects concentrations (PEC) were often exceeded for heavy metals in the lagoon sediments, especially for Zn, Cu, Ni, and Cr, and four stations, stations MZ-11, MZ-12, MZ-13, MZ-14, MZ-16, and MZ-17, had multiple metals at presumptively toxic levels. These comparisons suggest that sediment metal levels in the river are clearly high and probably pose an environmental risk at some stations. The levels of most of the metals were not greatly enriched, a consideration that is of the utmost importance when contamination issues are at stake. Metal concentrations found in Moulay Bousselham lagoon were comparable to aquatic systems classified as contaminated from other regions of the world.     

<Superscript>210</Superscript>Pb-derived Sedimentation Rates and C<Subscript>org</Subscript> Fluxes in Soledad Lagoon (Cispatá Lagoon System,NW Caribbean Coast of Colombia)

With the aim of evaluating temporal changes in sedimentation and organic carbon (C_org) supplied over the last ~100 years, a sediment core was collected at Soledad Lagoon, a costal ecosystem surrounded by mangroves, located in the Cispatá Estuary (Caribbean coast of Colombia). The core sediments were characterized by low concentrations of calcium carbonate (0.2–2.9%), organic matter (3–8%), total nitrogen (0.11–0.38%), and total phosphorus (0.19–0.65 mg g⁻¹). Fe and Al concentrations ranged from 4% to 5%, and Mn from 356 to 1,047 μg g⁻¹. The ²¹⁰Pb-derived sediment and mass accumulation rates were 1.54 ± 0.18 mm year⁻¹ and 0.08 ± 0.01 g cm⁻² year⁻¹, respectively. The sediment core did not provide evidence of human impact, such as enhancement of primary production or nutrient enrichment, which may result from recent land uses changes or climate change. The C_org fluxes estimated for Soledad Lagoon core lay in the higher side of carbon fluxes to coastal ecosystems (314–409 g m⁻² year⁻¹) and the relatively high C_org preservation observed (~45%) indicate that these lagoon sediments has been a net and efficient sink of C_org during the last century, which corroborate the importance of mangrove areas as important sites for carbon burial and therefore, long-term sequestration of C_org.     

Concentration levels of some inorganic contaminants in streams and sediments in areas of pyrometallurgical and hydrometallurgical activities at the Obuasi gold mine,Ghana

This study assessed the levels of selected inorganic contaminants in streams and stream sediments in the effluent areas relating to the pyrometallurgical and hydrometallurgical treatment of gold ores in the Obuasi gold mine, Ghana. Water and stream sediment samples were taken from specific locations during the consecutive rainy and dry seasons, and concentrations of phosphate (PO₄ ³⁻), nitrate (NO₃ ⁻), chloride (Cl⁻), sulphate (SO₄ ²⁻), sodium (Na⁺), potassium (K⁺), calcium (Ca²⁺), magnesium (Mg²⁺), arsenic (As), copper (Cu), iron (Fe), zinc (Zn) and lead (Pb), were determined. Alkalinity, pH, temperature and specific electrical conductivity were also measured. In the water samples, the average pH range for both the seasons is 6.9–7.4, most anions and metals have relatively higher concentrations in the wet season than in the dry season at both the metallurgical sites. Trace metals concentrations were comparatively low (<0.01–5.00 mg/l), higher in the dry season at the pyrometallurgical sites. Irrespective of seasons, SO₄ ²⁻ (0.80–949.50 mg/l) and PO₄ ³⁻ (<0.01–6.30 mg/l) were pronounced at the pyrometallurgical sites, while NO₃ ⁻ (0.01–98.45 mg/l) and Cl⁻ (1.88-49.05 mg/l) were higher at the hydrometallurgical sites. In water samples, Ca²⁺ and SO₄ ²⁺ were the dominant cation and anion, respectively. In the stream sediments, except pH, NO₃ ⁻, Cl⁻, Na⁺ and Mg²⁺, all other parameter values were relatively higher at the hydrometallurgical areas. The average concentrations of Ca²⁺, Mg²⁺, As and Fe are remarkably high at both metallurgical sites (3,217–46,026 mg/kg). Overall, the level of parameters in the water samples are pronounced at pyrometallurgical sites, whereas the levels in sediments are higher at the hydrometallurgical sites.     

Influence of extractable soil manganese on oxidation capacity of different soils in Korea

We examined the relationship between soil oxidation capacity and extractable soil manganese, iron oxides, and other soil properties. The Korean soils examined in this study exhibited low to medium Cr oxidation capacities, oxidizing 0.00–0.47 mmol/kg, except for TG-4 soils, which had the highest capacity for oxidizing added Cr(III) [>1.01 mmol/kg of oxidized Cr(VI)]. TG and US soils, with high Mn contents, had relatively high oxidation capacities. The Mn amounts extracted by dithionite-citrate-bicarbonate (DCB) (Mn^d), NH₂OH·HCl (Mn^h), and hydroquinone (Mn^r) were generally very similar, except for the YS1 soils, and were well correlated. Only small proportions of either total Mn or DCB-extractable Mn were extracted by NH₂OH·HCl and hydroquinone in the YS1 soils, suggesting inclusion of NH₂OH·HCl and hydroquinone-resistant Mn oxides, because these extractants are weaker reductants than DCB. No Cr oxidation test results were closely related to total Mn concentrations, but Mn^d, Mn^h, and Mn^r showed a relatively high correlation with the Cr tests (r = 0.655–0.851; P < 0.01). The concentrations of Mn^d and Mn^h were better correlated with the Cr oxidation tests than was the Mn^r concentration, suggesting that the oxidation capacity of our soil samples can be better explained by Mn^d and Mn^h than by Mn^r. The first component in principal components analysis indicated that extractable soil Mn was a main factor controlling net Cr oxidation in the soils. Total soil Mn, Fe oxides, and the clay fraction are crucial for predicting the mobility of pollutants and heavy metals in soils. The second principal component indicated that the presence of Fe oxides in soils had a significant relationship with the clay fraction and total Mn oxide, and was also related to heavy-metal concentrations (Zn, Cd, and Cu, but not Pb).     

Environmental pollution impact on water and sediments of Kumaun lakes, Lesser Himalaya, India: a comparative study

A study of the water and sediment chemistry of the Nainital, Bhimtal, Naukuchiyatal and Sattal Lakes of Kumaun, has shown that the water of these lakes are alkaline and that electrical conductivity, total dissolved solid and bicarbonate HCO ₃ ⁻ are much higher in Nainital than in the other three lakes. The weathering of limestone lithology and anthropogenic pollution, the latter due to the very high density of population in the Nainital valley, are the primary sources of enhanced parameters. The low pH of Nainital Lake water is due to low photosynthesis and enhanced respiration, increasing CO₂ in the water and the consequent enhancement of Ca²⁺ and HCO ₃ ⁻ . The dissolved oxygen in Nainital Lake is less compared to other lakes, indicating anoxic conditions developing at the mud–water interface at depth. The PO ₄ ³⁻ content in Nainital is higher (124 μg/l), showing an increasing trend over time leading to eutrophic conditions. The trace metals (Cu, Co, Zn, Ni, Mn, and Sr) are present in greater amounts in the water of Nainital Lake than in the other three lakes, though Fe and Cr are high in Bhimtal and Fe in Naukuchiyatal. The higher abundance is derived from the leaching of Fe–Mg from metavolcanic and metabasic rocks. Most of the heavy metals (Cr, Ni, Cu, Mn, Fe, Sr, and Zn) significantly enrich the suspended sediments of the lakes compared to the bed sediments which due to their adsorption on finer particles and owing to multiple hydroxide coating and organic content, except for Fe, which is enriched in the bed sediments. The high rate of sedimentation, 11.5 mm/year in Nainital, compared to Bhimtal with 4.70 mm/year, Naukuchiyatal with 3.72 mm/year, and Sattal with 2.99 mm/year, has resulted in shorter residence time, poor sorting of grains, and lesser adsorption of heavy metals, leading consequently, their depletion in the bed sediments of Nainital Lake.     

Photoreduction of Fe(III) in the Acidic Mine Pit Lake of San Telmo (Iberian Pyrite Belt): Field and Experimental Work

Light-induced reduction of dissolved and particulate Fe(III) has been observed to occur in the surface waters of the acidic mine pit lake of San Telmo (143,600 m², pH 2.8, Fe_total = 2.72 mM). This photochemical production of Fe(II) is directly related to the intensity of solar radiation and competes with biologically catalyzed reactions (i.e., bacterial re-oxidation of Fe(II)) and physical processes (including ionic diffusion, advection, and convection, which tend to homogenize the epilimnetic concentration of Fe(II) at every moment). Therefore, diel cycles of Fe(II) concentration are observed at the lake surface, with minimum values of 10–20 μM Fe(II) (0.35–0.70% Fe_total) at the sunrise and sunset, and maximum values of 90 μM Fe(II) (3.2% Fe_total) at midday in August 2005. Field and experimental work conducted in San Telmo and other pit lakes of the Iberian Pyrite Belt (IPB) (pH 2.3–3.1, Fe_total = 0.34–17 mM) indicate that the kinetics of the photoreductive reaction is zero-order and is independent of the Fe(III) concentration, but highly dependent on the intensity of solar radiation and temperature. Experimental work conducted with natural Fe(III) minerals (schwertmannite, goethite, and lepidocrocite) suggests that dissolved organic matter is an important factor contributing to the photochemical production of Fe(II). The wavelengths involved in the photoreduction of Fe(III) include not only the spectrum of UV-A radiation (315–400 nm), but also part of the photosynthetically active radiation (PAR, 400–700 nm). This finding is of prime importance for the understanding of the photoreduction processes in the pit lakes of the IPB, because the photo-reactive depth is not limited to the penetration depth of UV-A radiation (upper 1–10 cm of the water column depending on the TDS content), but it is approximately equal to the penetration depth of PAR (e.g., first 4–6 m of the water column in San Telmo on July 2007); thus, increasing the importance of photochemical processes in the hydro(bio)geochemistry of pit lakes.     

Double carbonate breakdown reactions at high pressures: an experimental study in the system CaO–MgO–FeO–MnO–CO2

The pressure–temperature conditions of the reactions of the double carbonates CaM(CO₃)₂, where M = Mg (dolomite), Fe (ankerite) and Mn (kutnohorite), to MCO₃ plus CaCO₃ (aragonite) have been investigated at 5–8 GPa, 600–1,100°C, using multi-anvil apparatus. The reaction dolomite = magnesite + aragonite is in good agreement with the results of Sato and Katsura (Earth Planet Sci 184:529–534, 2001), but in poor agreement with the results of Luth (Contrib Mineral Petrol 141:222–232, 2001). The dolomite is partially disordered at 620°C, and fully disordered at 1,100°C. All ankerite and kutnohorite samples, including the synthetic starting materials, are disordered. The P–T slopes of the three reactions increase in the order M = Mg, Fe, Mn. The shallower slope for the reaction involving magnesite is due partly to its having a higher compressibility than expected from unit-cell volume considerations. At low pressures there is a preference for partitioning into the double carbonate of Mg > Fe > Mn. At high pressures the partitioning preference is reversed. Using the measured reaction positions, the P–T conditions at which dolomite solid solutions will break down on increasing P and T in subduction zones can be estimated.     

Geochemistry of sulphate-bearing water of Akra Kaur Dam,Gwadar, Balochistan,Pakistan and its assessment for drinking and irrigation purposes

This paper is an attempt to study the geochemistry of Akra Kaur Dam (AKD) water, north of Gwadar city, southern Balochistan. Representative water samples were collected from AKD reservoir to assess the suitability of water for drinking and agriculture purposes. The major ionic composition is suggestive for freshwater. The average ionic composition demonstrate SO₄ > Ca > Na > Cl > HCO₃ > Mg > K. The plots on Piper diagram reflected Ca–Mg–SO₄ type of water facies. High Ca/SO₄ and Ca/Mg ratios revealed that the water has influence of gypsum dissolution. The negative ratio of chloro-alkaline indices indicated reverse exchange between Ca and Mg in water occurred with Na and K in rocks. The pH, electrical conductivity, total dissolved salts, Ca, Mg, Na, K, HCO₃, Cl and SO₄ concentrations in the dam water were below the permissible limit, however, Na and SO₄ were above the desirable limit, set by the World Health Organization. Important parameters such as residue sodium carbonate, sodium percent, sodium adsorption ratio, permeability index, magnesium content and Kelley’s ratio were calculated to evaluate the suitability of water for irrigation purpose. The result were compared with standard permissible limits and found satisfactory. The health and agriculture hazards of sulphate-bearing water were also discussed.