Acidic Mining Lakes Research Articles

P retention in an acidic mining lake under the influence of flooding with river water

P retention in an acidic mining lake under the influence of flooding with river water

Photochemical Degradation of Organic Carbon in Acidic Mining Lakes

The investigated coal mining lakes of the Lusatian lignite mining district and the mid-German lignite district are geogenically acidified caused by pyrite and marcasite oxidation. All lakes are characterized by high ionic strength and extremely high concentrations of dissolved ferric iron. In oxic water layers, up to 10% of total iron is present as Fe(II). Mean concentrations of dissolved organic carbon (DOC) are extremely low in the investigated Lusa-tian lakes (<0.1 mmol/L). During summer months, DOC concentrations below the detection limit were observed in epilimnetic layers accompanied by increased concentrations of ferrous iron. It is suggested that photochemical reactions are responsible for depletion of DOC and formation of ferrous iron as it has been described for acidic soft-water lakes. The coupling of DOC degradation and ferrous iron production was verified with sunlight exposure experiments. Samples of acidic mining lakes were irradiated in quartz glass vessels. Up to 50% of DOC was transformed to CO2 after 300 min of irradiation with natural sunlight, and the light-induced production of Fe(II) was up to 450% (compared to 100% Fe(II) concentration before irradiation). As a consequence of acidification and photochemical reactions, the carbon budget of investigated mining lakes is kept low because organic carbon is finally oxidized to carbon dioxide which leaves epilimnetic water layers as a gas. Photochemischer Abbau von organisch gebundenem Kohlenstoff in sauren Bergbaurestseen Die untersuchten Bergbauseen der Braunkohlenabbaugebiete des Lausitzer Braunkohlenreviers und des mitteldeutschen Braunkohlenreviers sind durch Pyrit- und Markasitoxidation geogen versauert. Alle Seen sind durch hohe Ionenstarken und extrem hohe Konzentrationen an gelostem Eisen(III) charakterisiert. In oxischen Wasserschichten liegen bis zu 10% des Gesamteisens als Eisen(II) vor. Die Konzentrationen von gelostem organischen Kohlenstoff (DOC) sind in den untersuchten Seen der Lausitz meist extrem niedrig (< 0.1 mmol/L). Wahrend der Sommermonate liegen die DOC-Konzentrationen im Epilimnion unterhalb der Nachweisgrenze und werden von ansteigenden Konzentrationen an Eisen(II) begleitet. Es ist zu vermuten, dass photochemische Reaktionen, wie sie fur saure Weichwasserseen beschrieben wurden, fur diese Verarmung an DOC und die Bildung von Eisen(II) verantwortlich sind. Der Zusammenhang zwischen dem DOC-Abbau und der Eisen(II)-Bildung wurde mit Sonnenlicht-Experimenten bestatigt. Proben aus sauren Bergbauseen wurden in Quarzglasgefasen bestrahlt. Bis zu 50% des DOC wurde nach 300 Minuten Bestrahlung mit naturlichem Sonnenlicht zu CO2 transformiert und die Lichtinduzierte Bildung von Eisen(II) machte bis zu 450% aus (bezogen auf 100% Eisen(II)-Konzentration vor der Bestrahlung). Als Konsequenz der Versauerung und der photochemischen Reaktionen bleibt das Kohlenstoffbudget der untersuchten Bergbauseen niedrig, da der organische Kohlenstoff letztlich zu Kohlendioxid oxidiert wird, der das Epilimnion als Gas verlasst.

Seasonal succession of phytoplankton in acidic mining lakes

Seasonal succession of phytoplankton in acidic mining lakes

Organic matter preservation in the sediment of an acidic mining lake.

Sustainable management of acidic mining lakes requires knowledge on the origin and reactivity of its sedimentary organic matter. We identified different pools of organic matter (OM) in the Fe-rich sediment (up to 35 wt %) of an acidic (pH 2.8) mining lake using delta13C-signals, C/N ratios, and the markers alkanes, lignin-derived phenols, and benzenepolycarboxylic acids (BPCA). Additionally, a density fractionation was applied to each sediment layer. Three fractions, aquatic (AOM), terrestrial (TOM), and lignite-derived (LOM) organic matter, were discriminated, of which AOM comprises only a small fraction, with a minimum at the sediment bottom. The terrestrial contribution to sedimentary OM is higher than that of AOM but still low throughout the sediment core, whereas lignite-derived OM constitutes the major C-fraction, even in the upper sediment layers. The size of the carbon pools was quantified with a mass-balance approach, in which the BPCA content was utilized as an estimate for the lignite fraction in combination with the delta13C-signals of the three C fractions. The largest amount of OM was found in the heaviest (>2.4 g cm3) of the three density fractions of the two upper sediment layers, which implies strong interaction with iron hydroxides. Comparisons with C-oxidation rates revealed that besides the refractory origin of the OM, sorptive preservation by solid iron phases controls C-reactivity in the sediment and, hence, the internal neutralization capacity of the lake system.

An In-lake Reactor to Treat an Acidic Lake: the Effect of Substrate Overdosage

An “in-lake” reactor system was developed to treat acidic mining lakes. The reactor uses the microbial processes of sulfate reduction and iron reduction followed by precipitation of iron sulfides to remove acidity, sulfur, and iron from the lake water. The basic reactor design is a straw-filled tube, which was vertically installed in the water column of an enclosure in the lake. Bottom water was pumped through the reactor, and ethanol was continuously fed as substrate for the microbial processes.

Benthic photosynthesis in an acidic mining lake (pH 2.6)

Natural neutralization of acidic mining lakes is usually limited by the availability of organic carbon. We investigated whether benthic photosynthesis could contribute to primary production in an acidic mining lake (pH 2.6). The occurrence and light dependence of benthic photosynthesis in the lake was investigated using oxygen microelectrodes. Oxygen microprofiles measured in light and darkness were significantly different, indicating photosynthetic activity. The photic zone was 300 μm thick and the highest photosynthetic activity was found at the sediment surface, which was covered by a dense layer of diatoms. These algae, predominantly Eunotia spp. and Pinnularia obscura, were found to be adapted to low light intensities. The community compensation irradiance was 6.8 μE m−2 s−1, corresponding to an annual mean compensation depth of 1.8 m. These results imply that 13% of the lake area could have a net efflux of oxygen from the sediment. Even at an irradiance as low as 1.2 μE m−2 s−1, photosynthetic activity was detected. The relatively low light requirements for benthic photosynthesis in this acidic environment may be due to an efficient absorption of red light, the dominant wavelength available in this ferric iron‐rich lake. Our results suggest that benthic photosynthesis can play an important role in the biogeochemistry of acidic mining lakes.

Neutralisation of acidic mining lakes with river water

Neutralisation of acidic mining lakes with river water

CHEMICAL CHANGES IN SEDIMENT PORE-WATERS OF AN ACIDIC MINING LAKE AFTER ADDITION OF ORGANIC SUBSTRATE AND LIME FOR STIMULATING LAKE REMEDIATION

In the past five years, enclosures have beeninstalled in an acidic mining lake in Lusatia to investigate insitu remediation processes. They were treated with straw, withstraw and Carbokalk, or with Carbokalk alone, where Carbokalkis a by-product of the sugar industry (solid precipitate ofnon-sugars after lime clarification of extracted sugar beetjuice). Sediment samples were taken as cores to get informationabout the behaviour of organic and inorganic components insediment pore-water with depth. Vertical distributions of pH,soluble reactive phosphate, nitrate, ammonium, silica,aluminium, iron, manganese, calcium, magnesium, sodium,potassium, sulphate, and DOC were measured. The resultingprofiles, each consisting of 15 data points at differentdepths, were compared by cluster analysis. The similarities ofsediment cores from different treated enclosures relating toprofiles of chemical components were discussed. Increasedconcentrations of potassium and sulphate were found in pore-water after substrate treatment. The data imply dissolution ofpotassium iron sulphate hydroxide minerals (jarosite) after anincrease of pH caused by dissolution of lime and by sulphatereducing processes which were stimulated by organic substrateaddition.

Composite Biofilms grown in Acidic Mining Lakes and assessed by Electron Microscopy and Molecular Techniques

Microbial consortia of composite biofilms, grown in surface water of acidicmining lakes near Lauchhammer, Germany, were investigated. The red-brown colored lake water was acidic (pH 2.5), had high concentrations of Fe(III), Al(III), and sulphate and low concentrations of dissolved organic matter. As a result the abundance of bacteria in the lake is with 104 cells mL-1 rather low. One input of organic material into the lake are autumnal leaves from trees, growing in the lakeside area. From aliquots of unfixed birch leave biofilms the 16S rRNA genes were amplified by PCR and community fingerprints were determined by single-strand conformation polymorphism (SSCP) analysis. Specific bands within the fingerprints were extracted from SSCP gels and sequenced for the taxonomical affiliation.These results were compared with those from the second type of biofilms which were grown on sterile substrata, floating submersed in surface waters of the lakes. By excising the bands from the gel and sequencing the individual bands bacterial taxa, common to both types of biofilms, were found but also some, which were only present in one type of biofilm. Ultrathin sectioned biofilms often showed bacteria associated with electron dense particles as main inorganic constituents. Elemental microanalysis by energy dispersive X-ray analysis (EDX) revealed them to contain iron, sulfur and oxygen as main elemental fractions and electron diffraction ring pattern analysis classified them to be schwertmannite. These bacteria and their interactions with each other as well as with the inorganic minerals formed in this lake generally is of great interest, in order to use these results for bioremediation applications.

Functions of Straw for In Situ Remediation of Acidic Mining Lakes

The addition of straw in combination with ‘Carbokalk’, a by-product from the sugar-industry, was successfully used to stimulate microbial alkalinity generation in an acidic mining lake. To get detailed information about functions of straw, anenclosure experiment was carried out. Straw bundles were placedat the sediment surface of an acidic mining lake (ML 111) and thephysiochemical conditions and the microbiology of the sediment-water contact zone were studied. Straw was degraded by anaerobic microorganisms and dissolved organic carbon (DOC) leached from straw bundles. Pigmented flagellates responded to the DOC supply in the water column anda considerable amount of algal carbon was transported to the sediment. Straw addition led to microbial reduction of iron andsulfate in the sediment. Sulfate reduction was observed at a pHof 5.5. The pH, however, was not high enough to precipitate H2S completely. Thus, some H2S diffused into the watercolumn, where it was reoxidized. Straw did not create orstabilize an anoxic water body above the sediment. Microbial sulfate reduction and pyrite formation only took place in the sediment,whereas iron reduction also took place in the straw. Straw, however, altered the flow conditions above the sediment surfaceand prevented complete mixing of the profundal water. Straw didnot serve as a substratum for a reactive biofilm. We conclude that the most important function of straw for mining lake remediation is to be a long-term nutrient source for microbialalkalinity generation in the sediment.

The Application of Stable Isotopes for Assessing the Hydrological, Sulfur, and Iron Balances of Acidic Mining Lake ML 111 (Lusatia, Germany) as a Basis for Biotechnological Remediation

Stable isotope (δ18O–H2O, δ2H–H2O δ34S–SO42-) andhydrochemical data (SO42-, Fe-concentrations) have beenused to estimate the annual groundwater inflow and outflow of mining lake ML 111 and to calculate the total amount of dissolvedsulfate and iron that is carried into the lake by groundwater. The hydrological balance suggests an annual groundwater inflow of 23 700 m3 and an annual groundwater outflow of 15 700 m3. The calculation of the sulfur and iron balances yielded an annual sulfate input of 37 800 kg and an annual iron input of 7000 kg with the groundwater inflow. Furthermore it was shown that significant fluxes of these elements go into the lake sediments which results in continuous release of acidity in the lake water.

HYDROGEOLOGICAL BASIS FOR BIOTECHNOLOGICAL REMEDIATION OF THE ACIDIC MINING LAKE 'RL 111', LUSATIA (GERMANY)

The drainage basin of the acidic mining lake ‘RL 111’ was characterized by hydrogeological and geochemical models to assess its influence on a planned biotechnological remediation of the lake water and lake sediment. Ground, seepage and lake water, as well as the surrounding sediments, were examined to model the hydrodynamic processes and the geochemical developmentof the lake. The geochemical conditions seem to behave in a stable manner (steady state conditions). A reduction of the high sulphate andacid input has not been observed since the beginning of our investigations. The biotechnological remediation of the whole lake should consider a treatment of the dump sediments to improvethe quality of the inflowing groundwater, as well as to reduce erosion.

Functional groups and activities of bacteria in a highly acidic volcanic mountain stream and lake in Patagonia, Argentina.

Acidic volcanic waters are naturally occurring extreme habitats that are subject of worldwide geochemical research but have been little investigated with respect to their biology. To fill this gap, the microbial ecology of a volcanic acidic river (pH approximately equal to 0-1.6), Rio Agrio, and the recipient lake Caviahue in Patagonia, Argentina, was studied. Water and sediment samples were investigated for Fe(II), Fe(III), methane, bacterial abundances, biomass, and activities (oxygen consumption, iron oxidation and reduction). The extremely acidic river showed a strong gradient of microbial life with increasing values downstream and few signs of life near the source. Only sulfide-oxidizing and fermentative bacteria could be cultured from the upper part of Rio Agrio. However, in the lower part of the system, microbial biomass and oxygen penetration and consumption in the sediment were comparable to non-extreme aquatic habitats. To characterize similarities and differences of chemically similar natural and man-made acidic waters, our findings were compared to those from acidic mining lakes in Germany. In the lower part of the river and the lake, numbers of iron and sulfur bacteria and total biomass in sediments were comparable to those known from acidic mining lakes. Bacterial abundance in water samples was also very similar for both types of acidic water (around 10(5) mL(-1)). In contrast, Fe(II) oxidation and Fe(III) reduction potentials appeared to be lower despite higher biogenic oxygen consumption and higher photosynthetic activity at the sediment-water interface. Surprisingly, methanogenesis was detected in the presence of high sulfate concentrations in the profundal sediment of Lake Caviahue. In addition to supplementing microbiological knowledge on acidic volcanic waters, our study provides a new view of these extreme sites in the general context of aquatic habitats.

The role of organic carbon excretion by bulbous rush roots and its turnover and utilization by bacteria under iron plaques in extremely acid sediments

Bulbous rush ( Juncus bulbosus) is a pioneer species in highly acidic mining lakes (pH 2.5–3) of the Lusatian mining district in the eastern part of Germany. These areas are known to be extremely low in inorganic carbon. The objective of this work was to determine if roots of bulbous rush with iron plaque formation acquire higher concentration of carbon for photosynthesis than roots without iron plaque. Microscopic examination of the microbial component in roots with iron plaque, levels of organic exudates, stable carbon isotopes and biomass production were measured to test this hypothesis. The roots contain iron plaques surrounding a rhizobacterial community and an interstitial space with a chemical composition differing widely from lake waters and pore-water sediments. The rates of exudation release by roots without iron plaque was minute but important to an estimation of the turnovers rates of dissolved organic carbon under the plaque. This protective environment allows for bacterial rapid recycling of carbon exuded by roots back to the plant. Thus, dissolved inorganic carbon in the root-plaque interstitial space is higher than in the surrounding water and the pore-water sediments. The differences in the δ 13C and biomass production among plants with and without iron plaque suggests that iron plaque and presumably the microscale phenomena may be important in allowing bulbous rush to maintain a positive carbon balance in the low carbon environment of acidic mining lakes.

Review of Benthic Invertebrate Fauna in Extremely Acidic Environments (pH ≤ 3)

Some benthic invertebrate species are able to colonise habitats in extremely acidic waters. We compiled a list of acid-resistant benthic invertebrates from the literature and extended it by studying extremely acidic mining lakes in eastern Germany. Acid-resistant species were registered for some habitats with pH ≤ 3, such as volcanic lakes, acid strip streams, and acidic mining lakes. Twenty nine taxa were found in waters with pH below 3. Diptera comprised 48.3% of the total number of taxa, followed by Coleoptera with 10.3%, Trichoptera 10.3%, Ephemeroptera, Megaloptera, and Plecoptera each with 6.9%, and Odonata, Hirudinea, and Acari each with 3.5%. Chironomus (Diptera: Chironomidae) were the most common genus in extremely acidic environments with 9 species. In Germany, Chironomus crassimanus was found to be the most abundant species in extremely acidic mining lakes. Generally, aquatic insects were the most common group of benthic invertebrates.

Bulk Chemistry Analysis of Sediments from Acid Mine Lakes by Means of Wavelength Dispersive X-ray Fluorescence

Bulk chemistry analysis of sediments from an extremely acidic mine lake of the Lusatian lignite mining district was performed using X-ray fluorescence analysis and a wavelength dispersive spectrometer (Siemens SRS 3000). Because of pronounced changes in sample composition along the cores, we applied the fundamental parameter option for matrix correction only to the main components. The capabilities of the scattered radiation method were examinated for the trace constituents.

Redox and pH conditions in the water column and in the sediments of an acidic mining lake

Physico-chemical parameters of the acidic mining lake (ML) 111 in the Lusatian region (Germany) were determined in April and August 1997 using a multiparameter probe for the water column and punch-in pH and Eh electrodes for the sediment, respectively. Samples of the sediment profile were taken by a gravity corer. Besides determination of the physico-chemical parameters, grain size and water contents were determined after sediment slicing. Differences in the redox state of the water body, deduced from oxygen saturation between April and August, could not be inferred. However, a shift in pH to lower values was apparent. Data support the conclusion that the enhanced oxygen content was consumed for oxidation of ferrous iron to ferric iron (oxides/hydroxides) coupled with the release of protons. In the sediment, different buffer systems of iron compounds could be detected within separate zones with values below and above pH 3. At higher pH values, the redox conditions are controlled and stabilized by the presence of Fe-oxide-hydroxides and possibly Fe-sulfates.

Prediction of water chemistry in mine lakes: The minewall technique

Water chemistry in mine lakes, derived from open-pit and underground mining, has been studied for more than 30 years. The compilation of this work has led to a predictive technique named ‘Minewall’, developed for the former Canadian mine environment neutral drainage (MEND) program. Minewall includes procedures for collecting relevant data, interpreting the data, and optional computer modelling of complex scenarios. Key geochemical requirements of Minewall are unit-surface area-production rates, total reactive rock-surface area in a mine, and time-varying reaction-product retention and flushing. Data from several open-pit and underground mines are presented to illustrate the technique. For example, the measured unit-surface area rates of sulphide oxidation and zinc production from rock surfaces span approximately three orders of magnitude. At one site, the rate of physical weathering was equivalent to the rate of chemical weathering, indicating new reactive minerals would continue to be exposed through closure. Also, the case studies indicate that up to 90% of weathering products are retained on the rock surfaces each year, and are thus available for relatively fast release upon closure and flooding of a mine, potentially leading to an acidic mine lake.

A New Medium Free of Organic Carbon To Cultivate Organisms from Extremely Acidic Mining Lakes (pH 2.7)

An algal culture medium was developed which reflects the extreme chemical conditions of acidic mining lakes (pH 2.7, high concentrations of iron and sulfate) and remains stable without addition of organic carbon sources. It enables controlled experiments e.g. on the heterotrophic potential of pigmented flagellates in the laboratory. Various plankton organisms isolated from acidic lakes were successfully cultivated in this medium. The growth rates of a Chlamydomonas isolate from acidic mining lakes were assessed by measuring cell densities under pure autotrophic and heterotrophic conditions (with glucose as organic C-source) and showed values of 0.74 and 0.40, respectively. Ein neues Medium, frei von organisch gebundenem Kohlenstoff, zur Kultivierung von Organismen aus extrem sauren Tagebauseen (pH = 2.7) Es wurde ein Kulturmedium entwickelt, welches die extreme chemische Situation von sauren Tagebauseen widerspiegelt (pH = 2.7, hohe Konzentrationen an Eisen und Sulfat) und ohne Zugabe von organischen Kohlenstoffverbindungen stabil bleibt. Es ermöglicht kontrollierte Experimente z. B. über das heterotrophe Potential pigmentierter Flagellaten im Labor. Verschiedene Planktonorganismen, die aus sauren Seen isoliert wurden, konnten erfolgreich in diesem Medium kultiviert werden. Die Wachstumsraten eines isolierten Chlamydomonas-Stammes wurden über die Zelldichten unter rein autotrophen bzw. heterotrophen Bedingungen (mit Glukose als organischer C-Quelle) aufgenommen und ergaben Werte von 0.74 bzw. 0.40.

A New Medium Free of Organic Carbon To Cultivate Organisms from Extremely Acidic Mining Lakes (pH 2.7)

An algal culture medium was developed which reflects the extreme chemical conditions of acidic mining lakes (pH 2.7, high concentrations of iron and sulfate) and remains stable without addition of organic carbon sources. It enables controlled experiments e.g. on the heterotrophic potential of pigmented flagellates in the laboratory. Various plankton organisms isolated from acidic lakes were successfully cultivated in this medium. The growth rates of a Chlamydomonas isolate from acidic mining lakes were assessed by measuring cell densities under pure autotrophic and heterotrophic conditions (with glucose as organic C-source) and showed values of 0.74 and 0.40, respectively. Ein neues Medium, frei von organisch gebundenem Kohlenstoff, zur Kultivierung von Organismen aus extrem sauren Tagebauseen (pH = 2.7) Es wurde ein Kulturmedium entwickelt, welches die extreme chemische Situation von sauren Tagebauseen widerspiegelt (pH = 2.7, hohe Konzentrationen an Eisen und Sulfat) und ohne Zugabe von organischen Kohlenstoffverbindungen stabil bleibt. Es ermoglicht kontrollierte Experimente z. B. uber das heterotrophe Potential pigmentierter Flagellaten im Labor. Verschiedene Planktonorganismen, die aus sauren Seen isoliert wurden, konnten erfolgreich in diesem Medium kultiviert werden. Die Wachstumsraten eines isolierten Chlamydomonas-Stammes wurden uber die Zelldichten unter rein autotrophen bzw. heterotrophen Bedingungen (mit Glukose als organischer C-Quelle) aufgenommen und ergaben Werte von 0.74 bzw. 0.40.