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Lake sedimentary archives of medieval mining and smelting in Sweden: tracking environmental changes from site to landscape
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

While the environmental impact of the industrial age is massive, including climate change, pollution, microplastics and habitat loss, our influence reaches further back than many recognize. In Sweden, an early and important activity with large potential impact was the mining and smelting of iron, copper and silver ores over the last ~800 years. This occurred in a mineral rich region called Bergslagen, where thousands of smelters and forges and tens of thousands of mines produced the metal riches central to the growth of both local and national economies.

In this thesis, I and collaborators present data from >30 lakes in Bergslagen and its surroundings with the aim to identify and track both the metallurgical activities themselves and the environmental impacts associated with this early agricultural-metallurgical society. The results indicate that the metallurgical activities can be traced using multiproxy sediment analyses including charcoal particles from the blast furnace and other metallurgical activities at the sites, metals from the ores (Pb, Zn, Cu, Hg) and indicators of erosion associated with activity at the site or damming and rechanneling of streams. We show a widespread pattern of a spread of mining and smelting throughout Bergslagen from ~1250 CE, including activities at Moshyttan close to Nora, Gammalkroppa close to Filipstad, a hitherto unknown blast furnace close to Norberg, the copper mines in Falun and the mine and smelters at Gladhammar. A notable exception to this medieval pattern is evidence from Garpenberg of copper mining already from the 4thcentury BCE. This widespread, medieval expansion of metallurgy occurred during a time of few written sources, and indicates that this was a period of technological proliferation in Sweden.

The environmental effects of these activities were wide-ranging. Pollen-inferred vegetation reconstructions (using REVEALS) indicate a minor decline in forest cover (~10–15%) starting in the 12th and 13th centuries when the first metallurgical activities were established. The loss of forest accelerated from the 16th century, likely driven by the greatly increasing metal production at this time which required substantial amounts of charcoal. No site was totally deforested, however, and inferred forest cover is between 40 and 60% at all sites associated with metallurgy, indicating that the documented efforts to produce a sustainable yield of charcoal were largely successful. The remaining forests were likely substantially changed as historical documents and maps indicate an intensive short-rotation (~60 years) forestry was common in the region, and cadastral maps from the late 17th century indicate extensiveforest areas were ‘young’. The area of cultivated land and open land plants benefitted by grazing (e.g. Poaceae) also increased indicating an expanded agriculture from the 12th century and especially from the 16th century.

The expanded land use and forestry coincided with a decreasing spectrally-inferred lake-water total organic carbon (LW-TOC) in all studied lakes, in line with other studies, contributing to the notion that the current increase in LW-TOC observed in contemporary environmental monitoring has an underlying historical component. The decrease in LW-TOC indicated for the lakes was generally ~25% during the early land use and metallurgy but lowest values (~50% of background concentrations) were generally reached in the early–mid 20th century concurrent with increasing industrial acid deposition, which is an important driver of terrestrial carbon export. Many lakes also experienced an increase in pH (0.3–0.5 units) associated with the land use and metallurgy, but the effects are similar to the ‘cultural alkalization’ commonly observed in lakes outside of Bergslagen. One important exception is the lakes surrounding Falun where previous research had shown that the massive mining and smelting of sulfide ores contributed to a decrease in pH of ~0.5 in many near-by lakes prior to modern industrial acid deposition.

Taken together, the most important environmental effects of the medieval and early modern mining and metallurgy were driven by the host of supporting activities that produced charcoal and food for the mines, smelters and workers at the sites. The changes in forest composition and water quality have implications for our understanding of reference conditions and the long history of human impacts even in this small corner of Europe.

Place, publisher, year, edition, pages
Umeå: Umeå universitet , 2019. , p. 21
National Category
Environmental Sciences
Research subject
environmental science
Identifiers
URN: urn:nbn:se:umu:diva-163435ISBN: 978-91-7855-108-8 (print)OAI: oai:DiVA.org:umu-163435DiVA, id: diva2:1352737
Public defence
2019-10-11, KBE301 (Lilla hörsalen), KBC-huset, Umeå, 13:00 (English)
Opponent
Supervisors
Available from: 2019-09-20 Created: 2019-09-19 Last updated: 2019-09-19Bibliographically approved
List of papers
1. Was Moshyttan the earliest iron blast furnace in Sweden?: The sediment record as an archeological toolbox
Open this publication in new window or tab >>Was Moshyttan the earliest iron blast furnace in Sweden?: The sediment record as an archeological toolbox
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2016 (English)In: Journal of Archaeological Science: Reports, ISSN 2352-409X, E-ISSN 2001-1199, Vol. 5, p. 35-44Article in journal (Refereed) Published
Abstract [en]

Recently, archeological study of the establishment and spread of iron blast furnace technology in Sweden has suggested a phase of rapid expansion from AD 1150 to 1350, mainly in the historically important "Bergslagen" region in central Sweden. But the geographical extent and earliest development remains debated. One archeological investigation of Moshyttan, in the less studied western part of Bergslagen, suggested that it may have been established before 1150. To independently study the timing of blast furnace establishment at Moshyttan, and also the vegetation history of the area, we performed a multiproxy analysis of the sediment record from Fickeln, a small lake immediately downstream of the smelter site. We present radiocarbon dating (macrofossils and bulk sediment), pollen, charcoal particles and geochemistry. To establish a reliable age depth model, ages of the bulk samples were corrected for old carbon and the model was validated by comparison to chronological markers (immigration of Picea abies and airborne lead-pollution) in other lakes with varved or otherwise robust chronologies. Based on markedly increasing lead concentrations, decreases in the Pb-206/Pb-207 ratio towards values resembling Bergslagen ores, increasing charcoal particle counts and increases in iron and zinc concentrations, the establishment of the blast furnace is estimated to AD 1250-1300 with an age-depth model probability of 91%. This places the establishment of the blast furnace at Moshyttan within the known period of early expansion of iron blast furnaces in Sweden, rather than earlier as suggested by the earliest dates from the archeological study. The first signs of a human presence in the area can be seen in pollen associated with forest grazing from ca. 170 BC, and the first signs of cultivation appear ca. AD 1020, preceding the blast furnace by 200 years.

Place, publisher, year, edition, pages
Elsevier, 2016
Keywords
Lake sediment, Geochemistry, Pollen, Charcoal particles, Blast furnace
National Category
Archaeology
Identifiers
urn:nbn:se:umu:diva-142830 (URN)10.1016/j.jasrep.2015.10.040 (DOI)000415596200005 ()
Available from: 2017-12-12 Created: 2017-12-12 Last updated: 2019-09-19Bibliographically approved
2. Environmental footprint of small-scale, historical mining and metallurgy in the Swedish boreal forest landscape: The Moshyttan blast furnace as microcosm
Open this publication in new window or tab >>Environmental footprint of small-scale, historical mining and metallurgy in the Swedish boreal forest landscape: The Moshyttan blast furnace as microcosm
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2019 (English)In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 29, no 4, p. 578-591Article in journal (Refereed) Published
Abstract [en]

The history of mining and smelting and the associated pollution have been documented using lake sediments for decades, but the broader ecological implications are not well studied. We analyzed sediment profiles covering the past similar to 10,000 years from three lakes associated with an iron blast furnace in central Sweden, as an example of the many small-scale furnaces with historical roots in the medieval period. With a focus on long-term lake-water quality, we analyzed multiple proxies including geochemistry, pollen and charcoal, diatom composition and inferred pH, biogenic silica (bSi), visible near-infrared spectroscopy (VNIRS)-inferred lake-water total organic carbon (LW-TOC), and VNIRS-inferred sediment chlorophyll (sed-Chl). All three lakes had stable conditions during the middle Holocene (similar to 5000 BCE to 1110 CE) typical of oligo-dystrophic lakes: pH 5.4-5.6, LW-TOC 15-18 mg L-1. The most important diatom taxa include, for example, Aulacoseira scalaris, Brachysira neoexilis, and Frustulia saxonica. From similar to 1150 CE, decreases in LW-TOC, bSi, and sed-Chl in all three lakes coincide with a suite of proxies indicating disturbance associated with local, small-scale agriculture, and the more widespread use of the landscape in the past (e.g. forest grazing, charcoal production). Most important was a decline in LW-TOC by 30-50% in the three lakes prior to the 20th century. In addition, the one lake (Fickeln) downstream of the smelter and main areas of cultivation experienced a shift in diatom composition (mainly increasing Asterionella formosa) and a 0.6 pH increase coinciding with increasing cereal pollen and signs of blast furnace activity. The pH did not change in the other two lakes in response to disturbance; however, these lakes show a slight increase (0.3-0.5 pH units) because of modern liming. LW-TOC has returned to background levels in the downstream lake and remains lower in the other two.

Place, publisher, year, edition, pages
Sage Publications, 2019
Keywords
diatoms, environmental change, geochemistry, human impacts, lake-water carbon, sediment, total organic carbon
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-158734 (URN)10.1177/0959683618824741 (DOI)000463639500004 ()
Available from: 2019-05-21 Created: 2019-05-21 Last updated: 2019-09-19Bibliographically approved
3. Long-term development of clear- and brown-water acidic lakes in the Swedish boreal landscape: implications for contemporary lake-water quality
Open this publication in new window or tab >>Long-term development of clear- and brown-water acidic lakes in the Swedish boreal landscape: implications for contemporary lake-water quality
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

The recent browning of surface waters and its effects on water quality across northern latitudes continue to raise questions about the driving mechanisms and future trajectories. However, even when based on multi-decadal environmental monitoring data, assessments of contemporary trends and drivers often overlook potential underlying long-term changes in lake-water quality. Here we synthesize data from seven clear- and brown-water acidic lakes in the Swedish boreal landscape to conceptualize how natural and human-driven processes have regulated lake-water quality, measured as spectrally inferred lake-water total organic carbon (TOC) and diatom-inferred pH. From 10,000 BCE to ~500 CE, all studied lakes were browner (lake-water TOC 10–24 mg L-1) and underwent natural acidification, decreasing from pH ~7 to 4.7–5.4. From ~500 to 1850 CE, historical human land use caused lake-water TOC to decline by ~50% in all lakes and in the poorly buffered, clear-water lakes, pH to increase by >1 unit. During the 20th century, the interaction between centuries of land use and more recent industrial acid deposition resulted in unprecedentedly low lake-water TOC (3–8 mg L-1) in all lakes and severely re-duced pH in the poorly buffered lakes, whereas those surrounded by peatlands resisted these pH changes. These extreme values coincided with the onset of environmental monitoring, meaning that contempo-rary increases in lake-water TOC and pH occur within the context of past, long-term disturbances, which are therefore crucial to consider for the purposes of lake management and prediction of lake responses to future environmental disturbances, especially climate change.

National Category
Environmental Sciences
Research subject
environmental science
Identifiers
urn:nbn:se:umu:diva-163433 (URN)
Available from: 2019-09-19 Created: 2019-09-19 Last updated: 2019-09-19
4. Reshaping the landscape: mining, metallurgy and a millennium of environmental changes in south-central Sweden
Open this publication in new window or tab >>Reshaping the landscape: mining, metallurgy and a millennium of environmental changes in south-central Sweden
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Before the recognition of emerging environmental issues during the 20th century such as acid rain, mercury pollution, climate change and biodiversity loss, human activities had already significantly altered landscapes around the globe. As elsewhere in Europe, the introduction of agriculture into Sweden during the Bronze and Iron Ages led to changes in forest cover, especially in southern areas, but also more limited impacts in central and northern Sweden along river valleys and coastal areas. In central Sweden the rise and rapid spread of ore mining and metallurgy from the 12th and especially 13th century initiated a widespread reshaping of the landscape named after its mining heritage –Bergslagen (mining laws). This mineral rich 89,000 km2 region encompasses ~5000 metallurgical sites (furnaces, smelters, foundries, forges) and ~10000 mines registered in the Swedish National Antiquities Board’s database.

Analyses of >30 lake-sediment records using a combination of geochemical, diatom and pollen analyses, in combination with archaeological and historical records and toponyms, add important details to the early, poorly documented history of mining/metallurgy as well as provide insights into some of the environmental impacts across this large landscape. These impacts included damming of lakes and regulation of watercourses for waterpower, increase in erosion, emission of metals to surface waters and the atmosphere (and leaching from slag piles), decrease in forest cover and changes in water quality. The discontinuous appearance of pollen from cultivated plants (cereals) indicates some limited settlement before the 12th century, but the regular occurrence thereafter of cereal pollen together with a sharp increase in charcoal particles and geochemical evidence of mining/metallurgical activities, indicates mining/metallurgy was a driving force for settlement. Decline in forest cover was gradual from the 13th century, but was more significant from the late 16th century when iron and copper production increased exponentially. The increased demand for charcoal and increased agriculture, including an expansion of summer forest farms, contributed to a reduction in inferred forest cover to 40–80% – as compared to pre-anthropogenic (≤2000 BP) values of 84–95%. From the 16th century charcoal became the limiting resource within Bergslagen and metallurgy expanded to regions adjoining Bergslagen, contributing to a more widespread decline in forest cover also beyond the Bergslagen landscape.

In association with the increase in land-use activities and resulting changes in vegetation cover, there was a decline (20–50%) in spectrally inferred lake-water total organic carbon, which we hypothesize resulted from a decreased pool of labile soil carbon. In some lakes closely connected with blast furnaces, where the peasant-miners also lived and farmed, there was an increase in diatom-inferred lake-water pH – as observed previously in SW Sweden in association with Iron Age land use. Only in a suite of lakes in close proximity to the smelting of copper sulfide ores in the surroundings of Falun was there evidence for pre-20th century acidification.

While current rates of environmental change may be unprecedented, they build on an already modified landscape. Because pre-industrial conditions, i.e., pre-19th century, are often used as a reference level the scale of current changes may underestimate the full extent of ecosystem and environmental impacts.

National Category
Environmental Sciences
Research subject
environmental science
Identifiers
urn:nbn:se:umu:diva-163434 (URN)
Available from: 2019-09-19 Created: 2019-09-19 Last updated: 2019-09-19

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