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Long-term development of clear- and brown-water acidic lakes in the Swedish boreal landscape: implications for contemporary lake-water quality
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.ORCID iD: 0000-0002-8208-496x
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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: urn:nbn:se:umu:diva-163433OAI: oai:DiVA.org:umu-163433DiVA, id: diva2:1352730
Available from: 2019-09-19 Created: 2019-09-19 Last updated: 2019-09-19
In thesis
1. Lake sedimentary archives of medieval mining and smelting in Sweden: tracking environmental changes from site to landscape
Open this publication in new window or tab >>Lake sedimentary archives of medieval mining and smelting in Sweden: tracking environmental changes from site to landscape
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:nbn:se:umu:diva-163435 (URN)978-91-7855-108-8 (ISBN)
Public defence
2019-10-11, KBE301 (Lilla hörsalen), KBC-huset, Umeå, 13:00 (English)
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Supervisors
Available from: 2019-09-20 Created: 2019-09-19 Last updated: 2019-09-19Bibliographically approved

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Myrstener, ErikNinnes, SofiaMeyer-Jacob, CarstenBindler, Richard

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