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| Titel |
Impact of mine wastewaters on greenhouse gas emissions from northern peatlands used for mine water treatment |
| VerfasserIn |
Katharina Palmer, Anna-Kaisa Ronkanen, Björn Klöve, Jenna Hynynen, Marja Maljanen |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250112260
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| Publikation (Nr.) |
 EGU/EGU2015-12410.pdf |
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| Zusammenfassung |
| The amount of wastewaters generated during mining operations is increasing along with the
increasing number of operation mines, which poses great challenges for mine water
management and purification. Mine wastewaters contain high concentrations of nitrogen
compounds such as nitrate (NO3-) and ammonium (NH4+) originating from remnant
explosives as well as sulfate (SO42-) originating from the oxidation of sulfidic ores. At a
mine site in Finnish Lapland, two natural peatlands have been used for cost-effective passive
wastewater treatment. One peatland have been used for the treatment of drainage waters (TP
1), while the other has been used for the treatment of process-based wastewaters (TP
4).
In this study, the impact of mine water derived nitrogen compounds as well as SO42-
on the emission of the potent greenhouse gases methane (CH4) and nitrous oxide
(N2O) from those treatment peatlands was investigated. Contaminant concentrations
in the input and output waters of the treatment peatlands were monitored which
allowed for the calculation of contaminant-specific retention efficiencies. Treatment
peatlands showed generally good retention efficiencies for metals and metalloids
(e.g. nickel, arsenic, antimony, up to 98% reduction in concentration) with rather
low input-concentrations (i.e., in the μg/l-range). On the other hand, retention of
contaminants with high input-concentrations (i.e., in mg/l-range) such as NO3-,
NH4+ and SO42- was much lower (4-41%, 30-60% and -42-30%, respectively),
indicating the limited capability of the treatment peatlands to cope with such high input
concentrations.
NO3- and NH4+ concentrations were determined in surface and pore water from TP 4 in
July 2013 as well as in surface water from TP 1 and TP 4 in October 2013. Up to 720 μM
NO3- and up to 600 μM NH4+ were detected in surface water of TP 4 in July 2013. NO3-
and NH4+ concentrations in surface waters were highest near the mine wastewater
distribution ditch and decreased with increasing distances from the ditch. NO3-
concentrations were lower in pore water than in surface water, and the peak in NO3-
concentration shifted further away from the distribution ditch with increasing depth. On the
contrary, NH4+ concentrations were generally higher in pore water than in surface
water, and peak concentrations increased with increasing depth. Highest NH4+
concentrations were detected in 30 to 60 cm depth near the outlet at the south end of TP
4.
Fluxes of the greenhouse gases CH4 and N2O from 4 sampling points (2 from TP 4, 1
from TP 1, 1 from reference area) were measured on 7 different occasions 2013 and 2014.
CH4 emissions were in the same range as measured in other northern pristine peatlands in the
reference area, which is not influenced by mine wastewaters. Treatment peatlands showed
only very minor CH4 emissions or even CH4 uptake. On the other hand, treatment peatlands
showed high N2O emissions, which were in the same range as N2O emissions observed from
northern peat soils used for agriculture. Highest emissions were generally observed near the
wastewater distribution ditch of TP 4. N2O emissions from the reference area were negligible
or even negative. NO3-, NH4+ and SO42- concentrations were determined from
surface waters from each sampling point and sampling occasion. N2O emissions were
positively correlated with NO3- concentrations, indicating denitrification-derived N2O
production in treatment peatlands. On the other hand, CH4 emissions were negatively
correlated with SO42- and NO3- concentrations, indicating that the presence of
alternative electron acceptors in large amounts suppresses CH4 production in treatment
peatlands.
In conclusion, the study revealed that (i) treatment peatlands receive high loads of NO3-,
NH4+ and SO42- which are not well retained in the peatlands, (ii) mine wastewaters
positively and negatively affect N2O and CH4 emissions, respectively, (iii) N2O emissions
are positively correlated with NO3- concentrations, and (iv) CH4 emissions are negatively
correlated with NO3- and SO42- concentrations. This study thus illustrates the pronounced
impacts of mine wastewaters on processes involved in greenhouse gas turnover in peatlands
ecosystems. |
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