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Nilsson, L. & Widerlund, A. (2018). Modelling tool for predicting and simulating nitrogen concentrations in cold-climate mining ponds. Ecological Modelling, 380, 40-52
Open this publication in new window or tab >>Modelling tool for predicting and simulating nitrogen concentrations in cold-climate mining ponds
2018 (English)In: Ecological Modelling, ISSN 0304-3800, E-ISSN 1872-7026, Vol. 380, p. 40-52Article in journal (Refereed) Published
Abstract [en]

A nitrogen model was developed with the aim to trace nitrogen cycling in a cold climate-mining pond at the Aitik copper mine in northern Sweden. The model contains 10 state variables and 19 nitrogen cycling reactions. The model also includes sediment and physical properties of the pond, such as evaporation, freezing and thawing. The model was written in Mathworks MATLAB and was calibrated and validated using environmental monitoring data for the clarification pond at the Aitik mine. The data used comprised monthly values of nitrogen speciation, phosphorous and water flow. The model accurately predicts ammonium (r2 = 0.84) and nitrate (r2 = 0.82) concentrations in a time series from February 2012–August 2014. The model did not accurately predict nitrate concentrations (r2 = 0.11), presumably due to high oxygen concentration in the pond water that prevented denitrification in the water column. The transport of organic material to the sediment was also limiting denitrification in the sediment. When allowing denitrification in the water column as well as increasing the rate of transport of organic material to the sediment the nitrate prediction capacity increased to a satisfactory level (r2 = 0.54). A sensitivity analysis for the system showed that the most sensitive reactions for the water column were oxic mineralisation as well as the nitrification rate.

Place, publisher, year, edition, pages
Elsevier, 2018
National Category
Geochemistry
Research subject
Applied Geochemistry
Identifiers
urn:nbn:se:ltu:diva-68688 (URN)10.1016/j.ecolmodel.2018.04.006 (DOI)000434750500005 ()2-s2.0-85046670027 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-05-09 (andbra)

Available from: 2018-05-09 Created: 2018-05-09 Last updated: 2018-10-25Bibliographically approved
Nilsson, L. (2018). Nitrogen-cycling tracing methods: Case studies at cold-climate mine sites in northern Sweden. (Doctoral dissertation). Luleå: Luleå University of Technology
Open this publication in new window or tab >>Nitrogen-cycling tracing methods: Case studies at cold-climate mine sites in northern Sweden
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Spårningsmetoder för kvävecykeln : fältstudier vid gruvor i norra Sverige
Abstract [en]

High nitrogen effluents from mine sites is an environmental issue which has received relatively little attention historically. In recent years a number of studies have showed the environmental effects of high nitrogen discharge to natural water bodies, which include local eutrophication, high risk of acute reducing conditions and changed species composition in the receiving waters. Apart from the direct environmental effects of high nitrogen discharge some forms of nitrogen can be directly toxic- ammonia and nitric gas for instance, and some can be indirectly toxic, for instance nitrate which causes methemoglobinemia in infants if ingested.

This thesis shows how the developed nitrogen tracing methods can be applied in complex water transport systems such as in a mining environment. Two main study sites were used in this thesis, the LKAB iron mine at Kiruna and the Aitik copper mine at Gallivare operated by Boliden Mineral AB. The nitrogen tracing methods used in this study are stable isotope analysis, combined nitrogen and oxygen isotope analysis, source partitioning using linear combination of sources, numerical analysis using kinetic nitrogen reaction rates, numerical model verification using stable nitrogen isotopes, and Bayesian statistical models to estimate nitrogen concentrations. The study also demonstrates an experimental method of reducing nitrogen concentrations in the mining pond at the LKAB Kiruna site. The nitrogen reducing method was tested in a small scale mesocosm experiment at the Kiruna site in northern Sweden, where a nitrogen reduction rate of around 0.25 - 0.5% total nitrate per day could be achieved.

The nitrogen treatment method consists of fertilising the pond system with small amounts of bioavailable phosphorus. Phosphorus is generally the limiting factor for primary production and in the studied mining systems which have high nitrogen concentrations the phosphorus is assimilated into organic matter almost immediately after fertilisation. The phosphorus is assimilated into phytoplankton (algae) which then settles and is used as a carbon source during anaerobic decomposition (denitrification). The denitrification reaction reduces nitrate into nitrogen gas. This would reduce the nitrogen release from mine sites significantly, since nitrate is the dominant form of nitrogen at the two studied mine sites.

Concluding the thesis is a 2.5D model which couples a numerical kinetic nitrogen model with a hydrodynamic model. The hydrodynamic model was the Shallow Water Equations (SWE) model that incorporates wind turbulence, inlets, and outlets as source terms for the water velocities. The two models are coupled via velocity, where the nitrogen model couples via chemical mixing and fluxes are calculated from the water velocities in each model cell.

The results of this thesis suggests that nitrogen release from the the Kiruna clarification pond could be reduced significantly via the use of phosphorus fertilisation. This is due to an increased denitrification rate in the pond, and the fact that much of the discharge water from the pond system is recirculated back into the mineral processing plants. The recirculation essentially means that the nitrate in the mine water will have quite a long retention time before being passed out the receiving waters.

Although the presented nitrate reduction approach showed promising reduction rates, the potential risk of eutrophication in the receiving waters is high, as the discharge water will contain high levels of nitrogen and potentially also phosphorus. The transport pathways and possible natural attenuation of phosphorus must be thoroughly investigated before the presented nitrate reduction method can be implemented at full scale in mine ponds.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2018
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Geochemistry
Research subject
Applied Geochemistry
Identifiers
urn:nbn:se:ltu:diva-71342 (URN)978-91-7790-246-1 (ISBN)978-91-7790-247-8 (ISBN)
Public defence
2018-12-14, E632, Luleå University of Technology, Luleå, 10:00 (English)
Opponent
Supervisors
Available from: 2018-10-26 Created: 2018-10-25 Last updated: 2019-01-07Bibliographically approved
Nilsson, L. & Widerlund, A. (2017). Tracing nitrogen cycling in mining waters using stable nitrogen isotope analysis. Applied Geochemistry, 84, 41-51
Open this publication in new window or tab >>Tracing nitrogen cycling in mining waters using stable nitrogen isotope analysis
2017 (English)In: Applied Geochemistry, ISSN 0883-2927, E-ISSN 1872-9134, Vol. 84, p. 41-51Article in journal (Refereed) Published
Abstract [en]

We show how we used stable nitrogen and oxygen isotopes in ammonium and nitrate to identify and quantify nitrogen transformation and nitrogen sources at the LKAB mining site in northern Sweden. Stable nitrogen isotope analysis worked as an excellent tool for tracing nitrogen cycling in rapidly moving process waters. The isotope analysis was performed on the mining process waters at seven different key points along the water flow and we identified nitrification, ammonia volatilisation, and ammonium adsorption as nitrogen transformation processes. The source of nitrogen is historically explained as undetonated ammonium-nitrate based explosives. We used nitrate nitrogen and oxygen isotopes to quantify four nitrogen sources in the accumulated water in the mine as well as three sources in an above ground process water reservoir. The nitrate isotope data showed that most of the nitrate (70–80%) in the accumulated water underground originated from a sampling point located close to the surface and only a minor fraction (5–20%) originated directly from undetonated explosives (direct dissolution of NH4NO3 and nitrification of NH4). Nitrate from natural groundwater formed roughly 12% of mine water nitrate. In the above ground process water reservoir isotope data indicated another source of nitrogen coming from undetonated explosives.

Place, publisher, year, edition, pages
Elsevier, 2017
National Category
Geochemistry
Research subject
Applied Geochemistry
Identifiers
urn:nbn:se:ltu:diva-63724 (URN)10.1016/j.apgeochem.2017.05.025 (DOI)000410673400004 ()2-s2.0-85020263429 (Scopus ID)
Note

Validerad;2017;Nivå 2;2017-06-14 (rokbeg)

Available from: 2017-06-05 Created: 2017-06-05 Last updated: 2018-10-25Bibliographically approved
Nilsson, L. (2016). Nitrogen Cycling at Cold Climate Mine Sites in Northen Sweden. (Licentiate dissertation). Luleå: Luleå tekniska universitet
Open this publication in new window or tab >>Nitrogen Cycling at Cold Climate Mine Sites in Northen Sweden
2016 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

High nitrogen discharge from mining sites has been an environmental issue that has been closely studied in the recent years. The environmental effects of high nitrogen discharge are mainly eutrophication, but can also lead to changed species composition and algae blooms. Nitrogen is a highly abundant element and is the most abundant element in the atmosphere, where 78% by volume is present as dinitrogen (N2 ). Nitrogen is present in reduced form in all organic life as ammonium (NH4 + ). Nitrogen is also present in reduced form as nitrate (NO3 - ) or nitrite (NO2 - ) in most aquatic systems. 

Both nitrate and ammonium is contributing to eutrophication problems worldwide and ammonia (NH3 ) is direct toxic in high concentration to certain sensitive aquatic species. Nitrate in high concentration is also direct toxic, both to humans but also to aquatic biota. 

To trace and quantify different nitrogen transforming processes, their sources and their sinks is called tracing nitrogen cycling and is important due to the environmental effect of nitrogen. Nitrogen is available in many different species and oxidation states which all have their respective geochemistry. This thesis focuses on tracing the complex nitrogen cycle in two different cold climate mining systems in northern Sweden using two different methods. The two studied systems are:

The LKAB underground iron ore mine in Kiruna

Boliden Minerals AB open pit copper ore mine Aitik outside Gällivare 

Two different approaches were used to trace the nitrogen cycling. The LKAB Kiruna mine was investigated using stable nitrogen isotopes. The isotope analysis showed high capability to trace nitrogen cycling, both quantative and qualitative. We also showed the origin of the isotope signals which gives indication to the different sources of nitrogen in the mine. The presented study shows presence of nitrification, ammonium volatilization and ammonium adsorption to waste rock to occur in the water transport system. 

The nitrogen cycling in the Boliden Aitik mine was investigated using a nitrogen model which we developed as part of this thesis. The model is based on Yakushevs Redox Layer model (ROLM). The model contains the state variables ammonium, nitrate, nitrite, plankton, phosphate, dead organic material (both particulate and dissolved) as well as oxygen. The nitrogen concentrations in the Boliden Aitik mine was modeled for the clarification pond and showed, in general, low biological activity. The biological mediated reactions such as nitrification, denitrification, phytoplankton growth and grazing were low in relation to natural lake systems

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2016. p. 20
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
Keywords
Nitrogen Mining Cycling nutrients Isotopes Nitrogen-model modelling numerical-modelling Isotope-tracing Tracing Isotope geochemistry
National Category
Geochemistry
Research subject
Applied Geology
Identifiers
urn:nbn:se:ltu:diva-59661 (URN)978-91-7583-707-9 (ISBN)978-91-7583-708-6 (ISBN)
Presentation
2016-12-06, F341, Luleå Tekniska Universitet, Luleå, 13:00 (English)
Opponent
Supervisors
Funder
VINNOVA, 150 157
Available from: 2016-10-11 Created: 2016-10-11 Last updated: 2017-11-24Bibliographically approved
Nilsson, L. A mesocosm study of nitrogen transforming processes in mine waters: Isotopic verification of a biogeochemical model. Biogeochemistry
Open this publication in new window or tab >>A mesocosm study of nitrogen transforming processes in mine waters: Isotopic verification of a biogeochemical model
(English)In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515XArticle in journal (Refereed) Submitted
National Category
Geochemistry
Identifiers
urn:nbn:se:ltu:diva-71338 (URN)
Available from: 2018-10-25 Created: 2018-10-25 Last updated: 2018-10-25
Nilsson, L. & Widerlund, A.Modelling nitrate removal using an experimental treatment method in a hypothetical cold-climate mining pond.
Open this publication in new window or tab >>Modelling nitrate removal using an experimental treatment method in a hypothetical cold-climate mining pond
(English)Manuscript (preprint) (Other academic)
National Category
Geochemistry
Identifiers
urn:nbn:se:ltu:diva-71341 (URN)
Available from: 2018-10-25 Created: 2018-10-25 Last updated: 2018-10-25
Nilsson, L. & Widerlund, A.Phosphorus controlled nitrate reduction in a cold-climate mining pond – a mesocosm study.
Open this publication in new window or tab >>Phosphorus controlled nitrate reduction in a cold-climate mining pond – a mesocosm study
(English)Manuscript (preprint) (Other academic)
National Category
Geochemistry
Identifiers
urn:nbn:se:ltu:diva-71340 (URN)
Available from: 2018-10-25 Created: 2018-10-25 Last updated: 2018-10-25
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-2720-6442

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