Christer Pontér

Geochemistry of manganese in the Kalix River, northern Sweden

Dissolved and suspended Mn in the Kalix River, northern Sweden, were measured weekly over a period of eighteen months. During the same period four lakes in the Kalix catchment were sampled at their outlets and in vertical profiles within the lakes, together with a stream draining a series of mires with shallow lakes. Snow melting in mid-May increased the dissolved Mn concentration in the river tenfold, compared with a concentration of 5 μg L−1 during the winter discharge (January to April). We suggest that the increase was caused by Mn-rich mire water mixing with melting snow and being transported to the river. Large concentrations of dissolved Mn built up in the hypolimnion of the lakes studied during the icecovered period. Break-up of the ice and spring-overturn in June increased the dissolved Mn concentration tenfold in lake discharge and a concomitant peak in the dissolved Mn concentration was observed in the river. Lake-derived Mn was the dominant source for Mn in the river during this time. Suspended Mn in the river was hosted mainly in detrital particles during flood in May. In mid-June, non-detrital suspended Mn started to accumulate and reached a maximum in late July and early August. The MnAl ratio was 25 times higher during this period than during flood in May, suggesting the precipitation of an Mn-oxyhydroxide phase. The precipitation of the non-detrital Mn-rich phase was correlated in time with increased temperature, increased pH and increased concentration of suspended biogenic particles. The precipitation of dissolved Mn was biologically mediated. Sedimentation and mineralisation of the non-detrital Mn phase in river and lake sediments resulted in a steady increase of the dissolved Mn concentration in the river water during autumn.

Temporal variations in dissolved and suspended iron and manganese in the Kalix River, northern Sweden☆

Abstract Particulate and dissolved Fe and Mn were measured once a week from May to September 1982 in the Kalix River, north Sweden. During winter baseflow the dissolved Fe concentration was 450 μg l−1. Early snow-melt discharge increased the concentration slightly but during springflood maximum the concentration decreased to a minimum value of 60 μg l−1 in mid-July. Particulate matter in the Kalix River is dominated by Fe which ranges between 14% and 38% of the ashed suspended load, ∼ 70–80% of the total Fe load being retained by 0.45-μm filters. Approximately 10% of particulate Fe can be accounted for by a detrital phase. The particulate Fe/Al ratio showed a mean value of 6.5 which is more than ten times the ratio in mean world river. Particulate Fe showed a peak during early snowmelt and decreased during maximum discharge similar to dissolved Fe. Dissolved Mn concentrations ranged from 1.1 to 53.4 μm l−1 with a mean value of 11.2 ± 12.4 μg l−1, whereas particulate Mn ranged from 3.1 ti 18.2 μg l−1, with a mean concentration of 10.6 ± 4.9 μg l−1. During May and June most Mn was transported in the dissolved phase whereas in July and August the particulate fraction dominated. There was a drastic increase in non-detrital particulate Mn with a concomitant decrease in the dissolved fraction in early July with peak values in mid-July and early August. The decrease in dissolved Mn and increase of particulate Mn is probably the consequence of two processes, namely addition of non-detrital particulate Mn to the river, possibly from lakes, and transformation of dissolved Mn to a particulate phase within the river. A combination of increased pH, temperature and particulate Mn triggered the precipitation of dissolved Mn, although the significance of each factor can not be evaluated from this study.

Iron and manganese layering in recent sediments in the Gulf of Bothnia

Abstract The oxidized surface layer of recent soft sediments in the Gulf of Bothnia, northern part of the Baltic Sea, has been investigated. Distinct stratification of Fe and Mn is observed, with up to five different horizons in well-developed profiles. These layered top sediments, although not previously noticed, occur extensively in the Gulf of Bothnia. There is a close association of Mn and Ni, Ba, Zn and Cu, whereas P, Ca and Sr are associated with Fe. High dissolved Fe and Mn contents coupled with a strong redox gradient are recorded in the interstitial waters. Formation of these layers is linked to varying redox conditions. Fe and Mn tend to be dissolved under reducing conditions, to migrate upwards and to reprecipitate as oxyhydroxides along favourable redox horizons. Reaching oxidizing conditions Fe precipitates prior to Mn, and is always found below the Mnrich strata. The character of the oxidized zone is quite different in the two sub-basins of the Gulf of Bothnia. Mn-rich horizons together with spherical Mn-rich nodules are frequently found in the Bothnian Bay, while in the Bothnian Sea mostly Fe-rich layers are present together with abundant Fe-rich flat concretions. This difference is interpreted as being due to a lower redox level in the Bothnian Sea.

Validation of a field filtration technique for characterization of suspended particulate matter from freshwater : Part I. Major elements

Abstract A field filtration method for the concentration and separation of suspended particulate matter (SPM) from freshwater systems for subsequent determination of major elements (Si, Al, Ca, Fe, Mn, Mg, Na, K, P, Ti and S) is validated with respect to precision and bias. The validation comprises the whole procedure including filtration, sample digestion and instrumental analysis. The method includes two digestion procedures (microwave acid digestion and alkali fusion) in combination with inductively coupled plasma atomic emission spectrometry (ICP–AES). Total concentrations of the elements have been determined in suspended particulate matter from lake and river water with low levels of suspended solids ( −1 DW), and a wide range of element concentrations. The precision of the method including filtration, digestion and instrumental determination ranges between 10 and 14% RSD for most elements on a dry weight basis. Non-detectable concentrations of some elements are reported due to small differences between blank filter levels and the amounts of elements present on the filters after sampling. The calculated sums of main inorganic components, expressed as oxides, ranges between 94.0 and 98.0% ash weight. The method limits of detection range between 3 and 100 μg, as estimated from the blank filter samples. These detection limits are 3–1000 times higher compared to the corresponding instrumental (ICP–AES) limits of detection. A better knowledge of the mechanisms of filter clogging in sampling of suspended matter is important in order to extend the applicability of the method. For the sample types investigated in this study, the amount of inorganic material in the suspended particulate matter (SPM) seems to be the most important factor controlling the maximum volume of filterable water, and Fe is presumably the most important clogging regulating parameter in the group of elements included in the inorganic matter. A critical evaluation of the indirect method of calculating concentrations in SPM as the difference between unfiltered-digested and filtered subsamples is also included.

Selective removal of trace elements from the Baltic by suspended matter

Suspended matter was collected at 30 stations in the Baltic and Kattegatt, at the thermocline and at the bottom, and analysed for Na, Ca, Mg, Si, Ti, Al, Fe, Mn, Ba, Sr, Ni and V. The composition of the suspended matter varies considerably, but can be described as a mixture of: (1) 12–25% terrigenous detritus with much Si, Al, Ti and Fe; (2) 75–88% biological matter with much Ni, V and Ba; and (3) some Mn-oxyhydroxide. The annual efflux of water from the Baltic is about 460 km3, with a suspended load in the Baltic straits of ∼1.2–3.6 mg ash material l−1 These values imply that much Si, Ti, Al, Fe, Sr, Ni and V and particularly much Ba and Mn are lost from the Baltic in the suspended load. The average suspended matter is richer in Mn(5×), Ba(2.5×), Sr(4×) and V(1.8×) than permanently depositing Baltic sediments. These constituents are relatively enriched in pelagic deposits, i.e. it is likely that much Mn, Ba and V in deep-sea sediments derive from the continents via suspended transport. This conclusion is supported by the similarity between suspended matter and average Atlantic pelagic sediment.

Rare earth abundance patterns in ferromanganese concretions from the Gulf of Bothnia and the Barents Sea

Abstract Ferromanganese concretions from the Svalbard shelf in the Barents Sea show slightly convex shale-normalized REE patterns with no Eu anomalies. Concretions from the Gulf of Bothnia, northern part of the Baltic Sea, exhibit an enrichment of light REE and negative Eu anomalies. This difference is interpreted as a consequence of different conveyor mechanisms of the REE to the sediment. It is suggested that dissolving biogenic debris contributes to the convex pattern obtained in the Barents Sea, whereas an inorganic suspended fraction with scavenged REE is the main carrier in the Gulf of Bothnia. During oxic diagenesis in the sediment, the scavenged REE are set free into the porewater and contribute to the distribution pattern in concretions found in the Gulf of Bothnia. Small Mn-rich spheroidal concretions are enriched two to five times in REE compared to average shale, whereas Mn-poor flat concretions are low in REE. Specific surface area of the concretion and the depth of burial in the oxidized surface sediment are two factors that strongly affect the enrichment of the REE. Weak Ce anomalies are present in the analysed concretions and a redox level dependence is seen.

Non-detrital Si concentrations as an estimate of diatom concentrations in lake sediments and suspended material

Abstract This paper evaluates a method, based on normalization with Al, to estimate the concentration of diatoms in suspended and deposited sediments. Provided that Al exists primarily in the detrital phase, one can calculate the fraction of non-detrital Si (i.e. biogenic Si). Suspended matter and sediment in two lakes in northern Sweden have been analyzed. Results from the normalization method are compared with microscope count data. The results from the two methods differ somewhat. Partly dissolved diatom frustules may explain part of this discrepancy. These remnants can hardly be recognized as diatoms. Therefore, they are not counted during the microscopic analysis, although they contribute to the concentration of biogenic Si. Another factor is the differences in Si content among different types of diatoms. We show that the calculated concentrations of non-detrital Si are good estimates of the diatom concentrations. By using normalization as a tool, reasonable estimates of the stocks of biogenic Si can be obtained rapidly. Using these estimates as a guide, sites where considerable changes in diatom productivity and/or dissolution rates have occurred can be identified.

Origin of iron-manganese-rich suspended matter in the Landsort Deep, NW Baltic Sea

Abstract Water sampling was undertaken in 1982 in the Landsort Deep, NW Baltic Sea, at eight depth levels. In the 0–150 m interval oxidizing conditions prevailed, with suspended phases being particularly rich in Fe (with a maximum at 150 m), Mn and Ba (with maxima at 100 m). The anoxic zone below 150 m showed high concentrations of dissolved Fe and particularly dissolved Mn which were much higher than in the Black Sea, for instance. This is probably due to the migratory behavior of the redoxcline in the Landsort Deep. The metal-rich suspended matter probably arises when dissolved Fe and Mn from the anoxic zone precipitate as hydroxyoxides at the redoxcline; lateral transport of such suspended matter may explain the large-scale selective loss of Mn and Ba from the Baltic basin.

Environmental monitoring with river suspended matter: case study in the River Dalälven, central Sweden

Abstract Heavy metal concentrations are presented for suspended sediment from the River Dalalven, central Sweden. The river is contaminated by acid mine drainage and data from the most polluted tributary, Garpenbergsan, are also presented. Element/Al ratios in the suspended phase showed that K, Mg and Ti were mainly hosted in detrital particles together with a large fraction of Si. Between 50 and 60% of the load of Fe, Ca and Na were in non-detrital form. Less than 10% of the total load of suspended Mn and P were in a detrital form. The sediment in the River Dalalven is polluted by As, Cr, Cu, Hg, Ni, Pb and Zn. These elements, except Pb, showed an even stronger enrichment in the suspended phase. This indicated that between one third and one half of the suspended load was recirculated to the water column during sedimentation. Arsenic, Cr, Cu, Hg, Ni, Pb and Zn showed linear correlations with non-detrital Fe, close to the inflow of the polluted stream Garpenbergsan. Deposition of non-detrital Fe, Na, Cr, Cu and Ni in the sedimentation basins close to the river mouth reduced the suspended discharge of these elements to the Baltic Sea. However, the basins acted as sources for non-detrital suspended As, Hg, Pb and Zn during the studied period. The calculated net export, in a non-detrital form, for these elements was 141, 3.7,1100 and 7000 kg, respectively, as measured between May and October.