in sediments from coastal areas of the northwestern Baltic Proper in sediments from coastal areas of the northwestern Tracing environmental change and human impact as recorded
Te eutrophication of the Baltic Sea due to increased anthropogenic nutrient loads during the 20th century is well documented and studied. However, in the Baltic Sea drainage area, humans have afected the environment longer than the environmental monitoring can provide data for. Sediment records from lakes and seas can provide fundamental data on the environmental conditions before ecosystems were impacted by humans and give the range of natural variation.
Tis thesis presents diatom and geochemistry stratigraphies from fve sediment records along the southeast coast of Sweden, northwestern Baltic Proper. Tese records cover time periods of 500 years to more than 2000 years. Te diatom stratigraphies and geochemical proxies allow for reconstruction of environmental histories at these sites. Te outcomes of this thesis highlight the importance of a longer time perspective than the environmental monitoring can provide.
Lena Norbäck Ivarsson carries out research within the feld of environmental science with a focus on understanding past and present ecosystem responses to environmental changes. She holds a M.Sc. in biology from Stockholm University and this is her PhD thesis. LENA NORBÄCK IVARSSONLENA NORBÄCK
Environmental Science, Environmental Studies, School of Natural Sciences, Technology and Environmental Studies & the Baltic and East European Graduate School, S dert rn University. Tracing environmental change and human impact ISBN 978-91-89109-29-2 (print) / 978-91-89109-30-8 (digital) | S dert rn University | [email protected] as recorded in sediments from coastal areas of the northwestern Baltic Proper Lena Norbäck Ivarsson
SDD SÖDERTÖRN DOCTORAL DISSERTATIONS 178
Tracing environmental change and human impact as recorded in sediments from coastal areas of the northwestern Baltic Proper Lena Norbäck Ivarsson
S dert rns h gskola Subject: Environmental Science Research Area: Environmental Studies School of Natural Sciences, Technology and Environmental Studies & the Baltic and East European Graduate School
S dert rns h gskola (S dert rn University) The Library SE-141 89 Huddinge
www.sh.se/publications
© Lena Norbäck Ivarsson
Cover image: Lena Norbäck Ivarsson, Epiphytic diatoms growing on Cladophora sp. Cover layout: Jonathan Robson Graphic form: Per Lindblom & Jonathan Robson
Printed by Elanders, Stockholm 2020
S dert rn Doctoral Dissertations 178 ISSN 1652–7399 ISBN 978-91-89109-29-2 (print) ISBN 978-91-89109-30-8 (digital) Till Berta, Aina och Birgitta
Abstract The eutrophication of the Baltic Sea due to increased anthropogenic nutrient loads during the 20th century is well documented and studied. However, in the Baltic Sea drainage area, humans have affected the environment longer than the environmental monitoring can provide data for. Sediment records from lakes and seas can provide fundamental data on the environmental conditions before ecosystems were impacted by humans and give the range of natural variation. This thesis presents diatom and geochemistry stratigraphies from five sediment records along the southeast coast of Sweden, northwestern Baltic Proper. These records cover time periods of 500 years to more than 2,000 years. The diatom strati- graphies and geochemical proxies allow for reconstruction of environmental histories at these sites. Overall, the results show that the environmental changes that have occurred in the coastal zone in recent centuries are unprecedented over the last two millennia. The records from the coastal zone show only minor variations in the diatom stratigraphies and nitrogen stable isotope signals through history until recent centuries. The results show no evidence of increased runoff of nutrients from land during medieval times. Temperature anomalies since 500 CE have had little or no significant effect on the diatom assemblages from the coastal sites, while increased nutrient input from land has had a significant effect. Anthropogenic nutrient runoff has affected the diatom assemblages most markedly during the 20th century. The results show a time lag of the onset of eutrophication of approximately 100 years between the coast and open Baltic Sea, highlighting how the coastal zone acts as a buffer for the open Baltic Sea. The timing for the onset of eutrophication in these coastal areas is site-specific. For several sites, reference conditions prevailed more than 200 years ago. Water trans- parency at this time allowed for extensive distribution of benthic diatom habitats, such as macrophytes. The years of maximum nutrient load to the Baltic Sea during the 1970s–1980s is recorded in the diatom stratigraphies, especially with regard to the concentration of diatom valves in the sediments. There has been a recovery in diatom absolute abundance since maximum pollution years. However, there is no indication of a recovery in diatom species composition in the investigated coastal sites, and these sites are thus far from reaching a “good environmental status” according to the EU Water Framework Directive. The outcomes of this thesis highlight the importance of a longer time perspective than the environmental monitoring can provide.
Keywords: Baltic Sea, paleoecology, diatom stratigraphy, stable nitrogen isotopes, hy- poxia, nutrient discharge, eutrophication, Medieval Climate Anomaly, Little Ice Age
Svensk sammanfattning Överg dningen av Östersj n under 1900-talet är väldokumenterad och har bland annat resulterat i sämre siktdjup, att cyanobakterieblomningar har blivit mer omfat- tande och vanligare, utbredd syrebrist i bottenvatten, och en f rändrad artsamman- sättning av många organismgrupper. Systematiskt provtagna mätdata från milj - vervakningen finns bara tillgänglig från 1960–70-talet och därmed vet vi väldigt lite om Östersj ns ekosystem f re människans storskaliga påverkan. Sedimentkärnor från sj ar och hav fungerar som ett historiskt arkiv som under årtusenden lagrat informa- tion om dåtidens ekosystem. I denna avhandling används bevarade subfossila kiselalger och geokemi f r att spåra milj f rändringar längs svenska sydostkusten de senaste tvåtusen åren. Resultat presenteras från fem sedimentkärnor från Östersj kusten, från Stockholms skärgård i norr till Gåsfjärden i s der, längs en sträcka på ca 250 km. Alla stratigrafier tyder på stabila f rhållanden i dessa kustområden under yngre järnålder (500 f re vår tideräkning – 1050 efter vår tideräkning (evt)) och medeltid (1050–1500 evt), fram till 1700-talet. Varken f rändringar i klimat eller markanvänd- ning har påverkat dessa kustområden i någon st rre utsträckning tills f r några hundra år sedan. Det finns inga tecken på effekter av mänsklig aktivitet som exempelvis jordbruk fram till mer nutida f rändringar. Alla unders kningsplatser har påverkats av verg dning under de senaste århundradena. Den exakta starten f r kad närings- tillf rsel skiljer sig något mellan platserna. De f rsta tecknen på verg dning är från slutet av 1700-talet, och i b rjan av 1800-talet är artsammansättningen av kiselalger redan f rändrad. Storskaliga f rändringar i markanvändning skedde under 1800- talet och fortsatte in på 1900-talet. Våtmarker och sj ar dikades ut, jordbruk med ängar och traditionell träda av jordbruksmark fasades ut till f rmån f r vallodling, till det kom konstg dsel i slutet av 1800-talet. Växande städer, industrier och reningsverk är punktkällor som i varierande grad har påverkat dessa kustområden. De f rsta teck- nen på verg dning syns ca 100 år tidigare vid kusten än i ppna Östersj n, vilket belyser kustzonens roll som näringsfilter. I ppna Östersj n har både klimatet och näringstillf rsel från land påverkat artsammansättningen av kiselalger de senaste 2 000 åren. I kustområdet däremot har de direkta effekterna av klimatet spelat en mindre roll, och artsammansättningen av kiselalger har främst varit påverkad av näringstillf rsel från land. Överg dningen har resulterat i kad pelagisk primärproduktion och därmed lägre siktdjup, vilket har begränsat utbredningen av bottenlevande arter. I Östersj n finns inga opåverkade områden kvar, och därmed inga referensområ- den f r att definiera referensvärden enligt EUs vattendirektiv. Resultaten som pre- senteras i denna avhandling visar att i flera av de unders kta kustområdena rådde ett milj tillstånd opåverkat av mänsklig aktivitet f r mer än 200 år sedan. Maximal tillf rsel av näring till Östersj n skedde under 1960–70-talet, vilket avspeglar sig i koncentrationen av kiselalger i sedimenten, något som kan användas som en proxy f r primärproduktion. Lägre koncentrationer av kiselalger i sedimenten de senaste årtiondena indikerar en bättre vattenkvalité. Däremot syns ännu ingen f rbättring i artsammansättning av kisel-
alger som indikerar en tillbakagång till referensvärden. Inte heller syns tecken på någon f rbättring vad gäller siktdjup i unders kningsområdena.
Contents
List of papers...... 13 Abbreviations and definitions ...... 15 Introduction...... 17 Thesis objectives ...... 21 Background ...... 23 Holocene history of the Baltic Sea ...... 23 The present Baltic Sea ...... 24 Effects of climate on the Baltic Sea ecosystem ...... 25 Climate during the Holocene ...... 26 Records of early human impact in lakes ...... 27 Agrarian history in southern Sweden during the last millennium ...... 28 Description of study sites ...... 31 Kanholmsfjärden...... 32 Ådfjärden ...... 32 Himmerfjärden...... 33 Bråviken...... 33 Gåsfjärden ...... 34 The western Gotland Basin ...... 35 Material and Methods ...... 37 Field work...... 37 Chronologies...... 39 Radiocarbon dating ...... 39 Lead dating ...... 40 Markers: cesium and mercury ...... 40 Correlation of cores and age-depth modeling ...... 41 Diatoms as a proxy for environmental change ...... 41 Lab procedure – diatom analysis ...... 42 Geochemical proxies ...... 43 Lab procedure – geochemical analyses ...... 44 Data processing and statistical analyses ...... 44 Results – summary of papers ...... 47 Interpretation and Discussion ...... 51 Signs of eutrophication in the coastal zone during the last centuries ...... 51 Diatom life-form ...... 55 Diatom species composition...... 55 Diatom species richness ...... 57
Diatom absolute abundance ...... 57 Stable isotope δ15N...... 57 Causes for eutrophication in the coastal zone ...... 58 Tracing human impact and climate change during medieval times ...... 61 Climate or nutrients as drivers of paleoecological trends in the Baltic Sea since 500 CE ...... 62 Implications for the environment ...... 65
Conclusions...... 67 References...... 69 Tack...... 81
Paper I ...... 95 Paper II ...... 113 Paper III...... 137 Paper IV ...... 153
List of papers
This thesis is based on the following papers referred to in the text by the Roman numerals (I-IV):
Paper I: Norbäck Ivarsson, L., Andrén, T., Moros, M., Andersen, T. J., L nn, M., and Andrén, E. (2019). Baltic Sea Coastal Eutrophication in a Thousand Year Perspective. Frontiers in Environmental Science 7. doi:10.3389/fenvs.2019.00088. Paper II: Norbäck Ivarsson, L., Andrén, T., Moros, M., J. Andersen, T. and Andrén, E. Signs of early eutrophication in the Stockholm outer archipelago as evident in a 500-year-long sediment record. (Manuscript) Paper III: Ning, W., Nielsen, A. B., Norbäck Ivarsson, L., Jilbert, T., Åkesson, C. M., Slomp, C. P., Andrén, E., Brostr m, A. and Filipsson, H. L. (2018). Anthropogenic and climatic impacts on a coastal environment in the Baltic Sea over the last 1000 years. Anthropocene 21, 66–79. doi:10.1016/j.ancene.2018.02.003. Paper IV: Norbäck Ivarsson, L., L nn, M., Andrén, T. and Andrén, E. Exploring paleoecological trends since 500 CE; a comparison between coastal and open Baltic Proper. (Manuscript)
Contributions of the author to the different manuscripts Paper I: Study design, performed field work and lab work (subsampling, prepared samples for dating, geochemical analyses and diatom analysis, performed the diatom analysis), interpreted the results, wrote the manuscript. Paper II: Study design, performed field work and lab work (subsampling, prepared samples for dating, geochemical analyses and diatom analysis, performed the diatom analysis), interpreted the results, wrote the manuscript. Paper III: Contributed with the diatom analysis and the interpretations of these results. I wrote the parts on this in the methods, results and discussion. I also contributed to the overall interpretations of results and writing of the manuscript. Paper IV: Study design, performed field work and lab work for the coastal sites. I am involved in computing the statistical analyses and interpreting the results, and I wrote the manuscript.
Related paper not included in this thesis Andrén, E., van Wirdum, F., Norbäck Ivarsson, L., L nn, M., Moros, M., Andrén, T., 2020. Medieval versus recent environmental conditions in the Baltic Proper, what was different a thousand years ago? Palaeogeography, Palaeoclimatology, Palaeoecology 555, 109878. https://doi.org/10.1016/j.palaeo.2020.109878
13
Abbreviations and definitions
BCE Before Common Era CCA Constrained Correspondence Analysis CE Common Era DCA Detrended Correspondence Analysis LIA Little Ice Age (1400–1700 CE, Mann et al. 2009) MCA Medieval Climate Anomaly (950–1250 CE, Mann et al. 2009) MoWP Modern Warm Period (from 1850 CE, Harland et al. 2013) MSFD Marine Strategy Framework Directive RDA Redundancy Analysis WFD Water Framework Directive Cal. yr BP Calendar years Before Present (present defined as 1950 CE)
Anoxia ≤0 ml/l O2, H2S present
Hypoxia ≤2 ml/l O2
15
Introduction
The eutrophication of the Baltic Sea due to increased anthropogenic nutrient loads during the 20th century is well documented and studied (HELCOM, 2009). Con- sequences of this nutrient enrichment and increased production of organic material include decreased water transparency, more intense cyanobacterial blooms, wide- spread sea bottom hypoxia and altered species composition for several organism groups (Elmgren, 2001). Since the 1950s, hypoxia has also increased in the Baltic Sea coastal zones (Conley et al., 2011; Persson and Jonsson, 2000). Some of the recorded changes resulting from present eutrophication are not new phenomena for the Baltic Sea. Pigment analyses in sediments have shown cyano- bacteria blooms to be natural reoccurring features of the open Baltic Sea, since marine water started to enter the Baltic Sea Proper some 8000 years ago (Bianchi et al., 2000; Funkey et al., 2014). Since no major fauna can live in a hypoxic environment, the sediments are not bioturbated, and thus sediments deposited during oxygen dep- letion may exhibit laminae (Jonsson et al., 1990; Persson and Jonsson, 2000; Zillén et al., 2008). A compilation of laminated sediment sequences used as proxy for hypoxia show evidence of three time periods with extensive areal distribution of hypoxia in the open Baltic Sea; 8000–4000 cal. yr BP, 2000–800 cal. yr BP and from 1800 CE to present (Zillén et al., 2008). The European Union Water Framework Directive (WFD) was adopted in 2000 CE and concerns groundwater and surface waters, including transitional and coastal waters. The main objective of the WFD is for all waters in the EU to reach good or high ecological status. A key concept for determining ecological status under the WFD is reference conditions. Reference conditions are defined in the WFD as: “… a description of the biological quality elements that exist, or would exist, at high status, that is, with no, or very minor disturbance from human activities” (Anonymous, 2000). In the case of the Baltic Sea, there are no existing undisturbed sites (reference sites) to use (Andersen et al., 2011), and thus historical data, models and expert judgement are used to determine reference conditions (European Commission, 2003). Systematic environmental monitoring of the Baltic Sea in Sweden started in some sites in the 1960s, and has been continuously developed and expanded (SMHI, 2019). Yet humans have affected the environment in the Baltic Sea longer than this (Gustafsson et al., 2012). In addition, instrumental records of climate variables, such as temperature, only span the last few centuries. This is not enough of a time span to capture the natural variability in the environment. Sediment records from lakes and seas can provide fundamental data on the environmental conditions before eco- systems were impacted by humans and on the range of natural variation. Further, significant information about the speed and direction of ecosystem changes is gained
17 TRACING ENVIRONMENTAL CHANGE AND HUMAN IMPACT if a historical point of view is considered (Saunders and Taffs, 2009; Willis and Birks, 2006). There is a need to improve our understanding of the natural variability of the Baltic Sea and its response to climate, as well as human-induced, forcing. A long-term perspective concerning how environmental changes affect the marine system will provide us with a deeper knowledge of possible future scenarios, highly important for the management of the Baltic Sea (Kotilainen et al., 2014). The hypoxic event that occurred 2000–800 cal. yr BP coincides with a climatic warm event named the Medieval Climate Anomaly (MCA), as well as with the Roman Warm Period, and has been suggested to have been caused by an increase in human population and large-scale changes in land use in the drainage area at this time (Zillén and Conley, 2010). Around the turn of the last millennium, a series of technological innovations, including the iron plow, promoted an expansion of agricultural land (Myrdal, 1999). The favorable climate conditions during the MCA, with temperatures similar to those of today, also enabled a demographic expansion (Ljungqvist et al., 2012; Myrdal and Morell, 2011). It has additionally been suggested (Kabel et al., 2012) that the warmer climate during this time caused intensified cyanobacterial blooms (cyanobacteria are favored by warm and calm waters), resulting in hypoxia. The following oxygenation of the bottom waters in the open Baltic Sea has been explained by the onset of the Little Ice Age (LIA), and the colder sea surface temperatures during this time that would suppress cyanobacteria blooms (Kabel et al., 2012). However, it has also been suggested that this oxygenation event was due to an infectious disease, the so-called Black Death, that decreased the population by half around 1350–1450 CE (Zillén and Conley, 2010). Sediment cores from the open Baltic Sea have been studied on several occasions with the aim of tracing environmental history (e.g. Andrén et al. 2000a; b; Bianchi et al. 2000). Studies from the coastal zone of the Baltic Proper include two studies from the Archipelago Sea that show an onset of eutrophication in the early 1900s (Jokinen et al., 2018; Tuovinen et al., 2010). In the Gulf of Finland, Weckstr m (2006) reports the onset of eutrophication at around 1900 CE in two urban sites, and later (1940s– 1980s) in more rural sites. Andrén (1999) reports the onset of eutrophication at circa 1900 CE in the Oder estuary, at the Polish/German border. Except for Jokinen et al. (2018), these studies only cover a time frame of the last century/centuries. Studies of long-term trends in the coastal zone are lacking. If we want to understand human impact on the Baltic Sea through history, more focus should be placed on studying the long-term perspective in coastal sites. It is reasonable to assume that a land-based human activity will affect the coastal areas first, before the effects are recorded in the sediments from the open Baltic Sea. In this thesis, sediment records from five coastal sites in the northwestern Baltic Proper are presented. These sediment cores have recorded environmental changes during the last millennia, and they have been analyzed with respect to paleoecology (diatom relative and absolute abundance), and geochemical parameters. The records from the coastal zone are further compared to a record from the open Baltic Proper
18 INTRODUCTION
(Andrén et al., 2020). In order to accurately assess ecosystem responses of the Baltic Sea in a future climate scenario, it is of high importance to increase our under- standing of ecosystem responses in history. Paleoecology has the potential to fill this gap in knowledge (Andersen et al., 2004).
19
Thesis objectives
The overall objectives of this PhD thesis are 1) to put the present severe environ- mental situation in the Baltic Sea, in terms of excess nutrient loads and climate change, in a thousand-year perspective, and 2) to contribute to an improved under- standing of the natural variability at coastal sites along the southeastern coast of Sweden. The specific objectives of this PhD thesis are to:
• investigate and date long-term environmental changes in the coastal areas of northwestern Baltic Proper. • identify the onset of anthropogenic environmental change, and how this is registered in sediment records from these coastal sites. • produce a scientific base for inferring reference conditions at these sites. • compare sediment records from the open Baltic Sea and the coastal zone, to explore if there is a synchronicity in interpreted environmental changes between these areas. • assess the relative importance of human activities versus climate variability in causing environmental change in coastal ecosystems of the Baltic Sea over the last millennia.
21
Background
Holocene history of the Baltic Sea The Baltic Sea has a short but very dynamic history driven by glacio-isostatic land uplift and eustatic sea level changes. The last deglaciation of the Baltic basin started roughly 20,000 cal. yr BP resulting in an ice lake forming in front of the melting ice sheet around 16,000 cal. yr BP, the Baltic Ice Lake (Andrén et al., 2011). This lake was initially dammed 10 meters above sea level and was drained two times when the melting ice sheet retreated from the northern tip of mount Billingen, situated between Lake Vänern and Lake Vättern (Bj rck, 2008; Andrén et al., 2011). The first time was during the end of Aller d, roughly 13,000 cal. yr BP (Muschitiello et al., 2015). This event was followed by the colder Younger Dryas when the ice sheet re-advanced and the lake was again dammed. The final drainage of the Baltic Ice Lake took place about 11,700 cal. yr BP. This was a dramatic event, with drainage occurring over the course of 1-2 years and resulting in the lake being lowered 25 meters down to the level of the world oceans (Jakobsson et al., 2007). The next phase is called the Yoldia Sea. The melting of the ice sheet provided a constant feed of freshwater to the basin and it was only during a short cooling of the climate that marine water could enter from the North Sea (lasting max. 350 years) (Andrén et al., 2007). The Yoldia Sea lasted only about 1000 years and ended when its inlet through middle Sweden was closed due to the isostatic rebound, around 10,700 cal. yr BP. A freshwater lake was formed, the Ancylus Lake. This lake had an early outlet westward through middle Sweden, but the isostatic rebound came to close this outlet and the lake level started to rise. Eventually the lake found a new outlet in the southern Baltic basin through a complex river system through Denmark with river channels, levées, and lakes (Bennike et al., 2004; Bj rck et al., 2008; Andrén et al., 2011). The ongoing melting of both the Scandinavian and the Laurentian ice sheets caused a sea-level rise of the world oceans and when this sea-level rise caught up with the isostatic land uplift in the south of Scandinavia marine water could enter through the Danish sounds, approximately 9800 cal. yr BP (Andrén et al., 2000b; Andrén et al., 2011; Berglund et al., 2005). The following brackish phase, Littorina Sea, shows a peak in salinity around 6000–5000 cal. yr BP, coinciding with the Holocene Thermal Maximum (Gustafsson and Westman, 2002; Seppä et al., 2009; Willumsen et al., 2013). Because of the isostatic land uplift in the area and a simultaneous lowering of the global sea level, the Danish sounds became gradually shallower. The inflow of marine water decreased, eventually leading to a Baltic Sea with conditions more like today (Andrén et al., 2000a, 2011; Berglund et al., 2005).
23 TRACING ENVIRONMENTAL CHANGE AND HUMAN IMPACT
The present Baltic Sea The Baltic Sea is a semi-enclosed brackish water basin, the second largest in the world after the Black Sea (Leppäranta and Myrberg, 2009). This inland sea has a constant inflow of freshwater from rivers. Intrusions of salt water from the North Sea occur irregularly through the Danish Straits and Öresund and feed the Baltic Sea with saline water. Due to this, there is a salinity gradient in the Baltic Sea, ranging from 0-4 in the northern parts, to about 15 in the Belt Sea (Leppäranta and Myrberg, 2009). There is also a vertical salinity gradient with a permanent halocline forming at around 40- 80 meters depth in the Baltic Proper. The halocline prevents mixing between the upper, more fresh water, and the lower, more saline water. The average depth of the Baltic Sea is about 54 meters with a maximum depth of 459 meters in the Landsort Deep (Leppäranta and Myrberg, 2009). Since the Baltic Sea is a geologically young sea, there are only a few macro- organisms truly adapted to the brackish water conditions. Instead, most organisms are either marine or limnic, living on the edge of what they can tolerate in terms of salinity. Because of this, the Baltic Sea is characterized by poor macro-species richness and biodiversity and the ecosystem is therefore sensitive to changes in the environment (Elmgren and Hill, 1997). The primary production is dominated by diatoms and dinoflagellates in the spring and cyanobacteria blooms during warm summer months (Klais et al., 2011). The spring bloom in the Baltic Proper is nitrogen limited, while the summer blooms of cyanobacteria are limited by the availability of phosphorous (Granéli et al., 1990). Following the decay of the cyanobacteria blooms, diatoms and dinoflagellates dominate during the autumn (Andersson et al., 2017). During recent decades, the growing season of phytoplankton has been extended with more than 100 days in the southwestern Baltic Sea. Further, the biomass produced during autumn months has increased significantly (Wasmund et al. 2019). The Baltic Sea has a large catchment area, with about 85 million inhabitants in 14 countries. There is severe pressure on this ecosystem due to human activities. Increased anthropogenic nutrient loads from e.g. sewage treatment plants, industries, and diffuse sources such as agriculture and burning of fossil fuels during the twentieth century, have led to a number of problems (Elmgren, 2001; Gustafsson et al., 2012). For example, increased primary production leads to more decomposition and consumption of oxygen. The oxygen depletion has severe effects on marine ecosys- tems, for example by killing benthic fauna and altering biogeochemical cycles (Diaz and Rosenberg, 2008). Approximately 18% of the deep water in the Baltic Proper, including the Gulf of Finland and the Gulf of Riga, is today hypoxic (≤2 ml/l O2) and approx. 8% is anoxic (≤0 ml/l O2) with H2S present (Hansson and Andersson, 2014). The Baltic Sea has shown a rapid increase of hypoxic sediments since the 1940s and the hypoxic area now covers about 80,000 km2, corresponding to about two times the size of Denmark (Carstensen et al., 2014a; Hansson and Andersson, 2014; Jonsson et al., 1990). Hypoxia is a globally increasing problem, not only in Europe but also, for
24 BACKGROUND example, along the east coast of North America, but the Baltic Sea constitutes one of the largest so-called dead zones in the world (Diaz and Rosenberg, 2008). In an anoxic sediment, phosphorous cannot be retained and buried together with iron but is instead released back to the water masses. Increased phosphorous levels stimulate the growth of nitrogen-fixating cyanobacteria during the warm summer months. The cyanobacteria supply the sea with nitrogen (Karlson et al., 2015) and when they decompose, oxygen is consumed and phosphorous is released from the sediment (Carstensen et al., 2014b). A feedback loop is thus created, which sustains the eutrophic and hypoxic states of the Baltic Sea (Conley et al., 2002, 2009; Kemp et al., 2005). Since no organisms except for bacteria and archaea can live in an anoxic environment with H2S present, the sediment is not being bioturbated. Laminated sediments can therefore be used as a proxy for anoxic conditions (Jonsson et al., 1990). Although human impact has caused eutrophication of the Baltic Sea, both hypoxia and cyanobacteria blooms are natural features of the Baltic Sea and have been present periodically during the last 8000 years (Bianchi et al., 2000).
Effects of climate on the Baltic Sea ecosystem Climate in the Baltic Sea region is to a large extent controlled by atmospheric con- ditions and is thus affected by both the global climate as well as regional circulation patterns. The weather conditions in the Baltic Sea region are highly variable due to its location in the extra-tropics of the northern hemisphere. In general, westerly winds predominate in this region. The large-scale circulation patterns in the Baltic Sea are influenced by the North Atlantic Oscillation (NAO) (The BACC II Author Team, 2015). During a positive phase of NAO, the westerly airflow is strengthened, which brings warm wet winters to northern Europe, while during a negative NAO, westerly airflows are weaker, and this brings colder and drier winters to northern Europe (Hurrell et al., 2003). The NAO shows seasonal and interannual variability, and pro- longed periods of negative or positive phases are recorded. Wind conditions in the Baltic Sea region shows some connection to the NAO, with more calmer periods during negative NAO phases and more storminess during positive phases of NAO. Precipitation in the Baltic Sea region varies greatly between regions and seasons, and no clear trend has been observed during the last century. A clear increasing trend in air temperature has been observed in the Baltic Sea region since 1871 CE. In the area investigated in this thesis, this increasing trend is of a magnitude of 0.08 ˚C per decade, which is greater than the average global increase of 0.06 ˚C between 1861– 2005 CE (The BACC II Author Team, 2015; IPCC 2007). The trends are positive for all seasons, and the temperature increase has also increased the duration of the growing season (The BACC II Author Team, 2015). The climate warming in recent centuries has led to changes in the catchment and in the Baltic Sea itself. No clear trend in the overall river runoff to the Baltic Sea has been detected. However, a decreasing trend has been observed for the southern catch-
25 TRACING ENVIRONMENTAL CHANGE AND HUMAN IMPACT ments and rivers over the last century. A reduction of ice cover and earlier ice breakup has been recorded for rivers in the drainage area. In addition, the duration of annual snow cover has become significantly shorter in western Scandinavia over the last century (The BACC II Author Team, 2015). When it comes to climate effects on the Baltic Sea itself, water temperature and sea ice respond quickly to higher air temperatures. There is a clear warming trend in sea surface temperature over the last century, with the greatest increase observed in summer months (Gustafsson et al., 2012; Mackenzie and Schiedek, 2007). The extent and duration of sea ice is associated with NAO, with more ice during negative ice phases, and less ice during positive phases (The BACC II Author Team, 2015). Salinity in the Baltic Sea is mainly governed by two factors: net precipitation and river discharge, and water exchange with the North Sea. The so-called major Baltic inflows of marine water through the Danish straits occur sporadically, usually during the winter and spring months and thus bring saline, but also cold and oxygen-rich water into the Baltic Sea (Mohrholz et al., 2015). However, in recent decades, several inflows have occurred during the summer, which brings water that is saline, but warm and low in oxygen content. No trend has been detected during the last century of salinity measurements (The BACC II Author Team, 2015). However, a reconstruction of annual mean salinities since 1500 CE indicates that the salinity has slowly increased by 0.5 salinity units since 1500 CE, peaking in the mid-eighteenth century (Hansson and Gustafsson, 2011). When it comes to wave activity and storm surges, no sig- nificant change has been recorded in the last century. The change in mean sea level in the Baltic Sea results from the combined effects of post-glacial isostatic rebound of the continental crust, global sea level rise and thermal expansion of water. It is not clear how climate change during the last century has affected the sea level in the Baltic Sea, but the rise is probably in pace with the global sea level rise, approx. 1.5 mm per year (The BACC II Author Team, 2015). Results from models predicting a 2-4˚C warming by 2100 CE indicate that ecosystem changes in the Baltic Proper will include e.g. increased primary production, larger cyanobacteria blooms and lower oxygen concentrations in bottom waters (Andersson et al., 2015).
Climate during the Holocene Historical changes in climate are reconstructed using proxies from ice cores as well as lake and ocean sediments (e.g. oxygen isotopes, pollen and insects), tree ring widths and densities and, during the historical time frame, written records on e.g. weather extremes. Climate oscillations during the Holocene are driven by astro- nomical conditions, solar activity, volcanic eruptions, concentration of greenhouse gases in the atmosphere, changes in albedo of the sea and changes in the vegetation on land (The BACC II Author Team, 2015). Summer solar insolation peaked approx. 7000–6000 years ago, and during the Holocene Thermal Maximum (approx. 8000– 4000 cal. yr BP), the temperature in the Baltic Sea region was approximately 1-3.5 °C
26 BACKGROUND warmer than today. As already mentioned, this was a time period with higher salinity in the Baltic Sea (The BACC II Author Team, 2015). Due to a decreasing trend in summer solar insolation, the climate has become more unstable and a general cooling trend is recorded the last approx. 4000–5000 years (The BACC II Author Team, 2015). The climate during the last 2,000 years has fluctuated a lot, with general warmer temperatures in the Northern Hemisphere approx. 0-300 CE (the Roman Warm Period), and colder temperatures approx. 300- 800 CE (the Dark Age Cold Period) (Ljungqvist, 2010). The climate during the last millennium has been roughly divided into three periods: Medieval Climate Anomaly (MCA), Little Ice Age (LIA) and Modern Warm Period (MoWP). There are regional differences in the intensity and exact timing of these climatic periods (Ljungqvist et al., 2012). Throughout this thesis, the definitions in Mann et al. (2009) are used, which means MCA=950-1250 CE, and LIA=1400-1700 CE. MoWP is defined as after 1850 CE (Harland et al., 2013). Proxy data show evidence for higher sea surface temperature and more intense cyanobacterial blooms during MCA (Funkey et al., 2014; Kabel et al., 2012). This could conceivably be explained by warm and dry conditions (Luoto and Nevalainen, 2018). Changes in the input of freshwater has shown to be an important factor in governing salinity changes over the last 8500 years (Gustafsson and Westman, 2002). However, reconstructing precipitation is not as straightforward as temperature re- constructions (The BACC II Author Team, 2015). In a modeling study by Schimanke et al. (2012), fresher conditions during MCA due to wetter conditions were recon- structed. Uncertainties in reconstructing past environmental conditions and eco- system responses in the Baltic Sea are tightly coupled with uncertainties in future climate scenarios. Understanding the past is key to understanding the present, and essential to being able to predict the future.
Records of early human impact in lakes Humans have affected landscapes substantially on local scales for millennia, mostly by disturbing vegetation cover by deforestation (Roberts et al., 2018). The earliest signs of landscape disturbance (in pollen records from lakes) are recorded approx. 9000-6000 years before common era (BCE) in America, Oceanica, Asia, Africa and Europe (Dubois et al., 2018). The very first signs of eutrophication of lakes are recor- ded approx. 6000–3000 years BCE in Europe and America (Dubois et al., 2018). In the drainage area for the Baltic Sea, the first signs of landscape disturbance are re- corded approx. 5000 years BCE in Finland, approx. 3800 years BCE in Estonia, approx. 2500 years BCE in Latvia, approx. 1000 years BCE in Poland and as early as approx. 6000 years BCE in northern Germany (Dubois et al., 2018). While the very first signs of eutrophication of lakes do sometimes occur simultaneously with vege- tation disturbance (for example in Germany and Estonia), they are often recorded much later. The first signs of eutrophication in lakes are recorded in Finland approx.
27 TRACING ENVIRONMENTAL CHANGE AND HUMAN IMPACT
2500 years BCE, in Latvia during the 13th century CE, and in Poland circa 1000 CE (Dubois et al., 2018). In a study from Denmark, early landscape disturbance was re- corded as early as approx. 4000 BCE, but the lake remained undisturbed until the major deforestation occurred from approx. 500 BCE. Eutrophication of this lake was further intensified during medieval times, about 1050–1500 CE (Bradshaw et al., 2005). In Sweden, signs of human activities have been registered in pollen records from approx. 3600 BCE in the southernmost part of Sweden, with signs of agriculture from approx. 2600 BCE (Åkesson et al., 2015). Closer to the area of interest in this thesis, land use changes have been interpreted from pollen stratigraphies circa 800 CE, with a simultaneous response in the diatom assemblages of these lakes (Risberg et al., 1994; Karlsson and Risberg 2006). In southwestern Sweden, the first signs of landscape disturbance are recorded approx. 300 BCE, simultaneous with an increased pH of the lake, attributed to these changes in land use (Renberg et al., 1990). In northern Sweden, continuous agriculture is recorded from the 13th century and the lake res- ponse is simultaneous with dramatic changes in the diatom assemblages (Anderson et al., 1995). Lake Mälaren has been culturally eutrophicated since the isolation of the lake circa 1200 CE, as inferred from a diatom-based Total Phosphorous reconstruc- tion (Renberg et al., 2001). This makes it impossible to define reference conditions according to the WFD. This is also highlighted in Willén, (2001), where it is suggested to instead define an acceptable deviation from an assumed pristine state.
Agrarian history in southern Sweden during the last millennium Around a thousand years ago, a series of technological innovations, including the iron plow, promoted an expansion of agricultural land (Myrdal, 1999). The favorable climate conditions during the MCA, with temperatures similar to today, also enabled a demographic expansion (Ljungqvist et al., 2012; Myrdal and Morell, 2011). It is difficult to estimate changes in population this far back in time, but between 1000 and 1300 CE the numbers of households in Mälardalen, an area around Lake Mälaren, at least doubled (Myrdal, 1999). In 1350 CE, Sweden was hit by the plague. Several more outbreaks took place during the following century, decimating the population in Sweden by half (Myrdal and Morell, 2011). This strongly altered the land use, especially in more remote areas, where peripheral farms were abandoned in favor of more fertile lands. These changes in demography are recorded in pollen diagrams from the highlands of Småland, a wooded area in the south of Sweden (Lagerås, 2016). However, the more fertile plains were not usually abandoned, at least not for long. They were instead taken over by people migrating in search of land for agriculture (Myrdal and Morell, 2011). Following the medieval agrarian crisis, there was an increase in the population and by circa 1600 CE it had reached the same level as before the plague (Myrdal and Morell, 2011). During this time when both the population and the standard of living increased, the climate became colder (Schimanke et al., 2012). This might seem
28 BACKGROUND contradictory, but except for the northernmost parts of Scandinavia, it was not the temperature, but the amount of precipitation that was of greatest importance for the size of the harvest (Charpentier Ljungqvist, 2015). Unfortunately, our knowledge of the changes in precipitation is not as extensive as that of changes in temperature. Model simulations show wetter conditions (compared to the mean annual preci- pitation from 800 to 1900 CE) during the MCA, and more dry conditions during the 14th and 15th centuries, i.e. at the beginning of LIA (Ljungqvist et al., 2016). However, other studies have reconstructed dry conditions during MCA (Helama et al., 2009; Luoto and Nevalainen, 2018). Early landscape disturbances and changes in agricultural practices have had an effect locally in lakes (Dubois et al., 2018). However, the question remains as to whether coastal seas have also been affected for such a long time. It has been suggested that major changes in the open Baltic Sea ecosystem during medieval times were caused by human activities on land (Åkesson et al., 2015; Schimanke et al., 2012; Zillén and Conley, 2010). In this thesis, the long-term effect on coastal areas of the Baltic Sea is traced using diatom stratigraphy and geochemical proxies.
29
Description of study sites
The study area for this thesis is the northwestern part of the Baltic Proper, which means the Western Gotland Sea and southeastern coast of Sweden (Figure 1, Table 1). The coast of southeastern Sweden consists mostly of rocky archipelago coastline. This area is still influenced by the last glaciation and the isostatic rebound of the area is approx. 2-4 mm/year (Harff and Meyer, 2011). The coastal sites in this study are located along a 250-km stretch of the southeast coast of Sweden (Figure 1). In most winters, all coastal sites in this study have about 90-150 days with sea ice. During summer months, all sites experience stratification due to the development of a thermocline. All sites are considered sheltered according to the classification system of wave exposure in the WFD (VISS, 2019).
Figure 1. Map showing the Baltic Sea and its drainage area (shaded in grey), and the study area with the five sampling sites along the Swedish coast, and the sampling site in the western Gotland Basin. Number 1 is Lake Mälaren, number 2 is Stockholm, number 3 is S dertälje and number 4 is Norrk ping.
31 TRACING ENVIRONMENTAL CHANGE AND HUMAN IMPACT
Kanholmsfjärden Kanholmsfjärden is a large and deep basin located in the outer parts of the Stockholm archipelago, with a surface area of approx. 35 km2 and mean and maximum water depths of 52 and 104 m, respectively (SMHI, 2019). The basin is separated from the open Baltic Proper by a rosary of islands. Salinity in surface waters is 4.3-5.5, while the deep-water salinity is 6.5-6.7 (SMHI, 2019). The stratification of the water masses prevents mixing of bottom and surface waters and the deep waters are more or less permanently hypoxic (SMHI, 2019). The islands surrounding Kanholmsfjärden to the north, east and south are very sparsely populated. The larger islands to the west are peri-urban and connected to the mainland by roads. A small sewage treatment plant is located in the southwestern part of Kanholmsfjärden, which is dimensioned for approx. 6000 people (Värmd kommun, 2019). Kanholmsfjärden is located in the outer part of the Stockholm archipelago, and the drainage area of the basin itself is restricted to surrounding islands. However, this site is influenced by the outward-flowing freshwater from Lake Mälaren passing through Stockholm. This drainage area is large, approx. 20,140 km2, and consists of 21% agricultural land and 65% wooded areas (SMHI, 2020). Further, treated sewage water from approx. 1.5 million people has its outlet in Stockholm. Environmental monitoring has been performed through recipient controls along the main fairway to Stockholm, passing through Kanholmsfjärden, in the Stockholm archipelago since 1968 CE. This was later extended to many other sites in the Stockholm archipelago. This has resulted in a relatively long time series of monitoring data being available for Kanholmsfjärden. However, since 2015, Kanholmsfjärden has no longer been a part of the recipient controls. Kanholmsfjärden is today, due to its low biovolume of phytoplankton, classified as having a moderate ecological status while the chemical status is classified as bad (VISS, 2019).
Ådfjärden Ådfjärden is located in the southern part of the Stockholm archipelago, approx. 30 km south of Stockholm, and approx. 60 km southwest of Kanholmsfjärden. This water basin has an area of approx. 5 km2, a maximum water depth of 30 m, and thresholds in the north and south are 12 m and 19 m, respectively. About 10 km of archipelago separates this site from the open Baltic Sea. Salinity in the larger area of Horsfjärden, of which Ådfjärden is a part, is 5.1-5.7 in surface waters and 5.6-5.9 in bottom waters (SMHI, 2019). Ådfjärden is not an administrative area in the environ- mental monitoring and therefore the information about this water basin is sparse. The drainage area for Ådfjärden is the smallest of all sites in this study, 158 km2, of which 72% is wooded areas and 14% agricultural land (SMHI, 2020). There are no large urban areas within the drainage area nor in the fairway through Ådfjärden, which means it is relatively unaffected by boat traffic. Ådfjärden is today classified as
32 DESCRIPTION OF STUDY SITES having a moderate ecological status and is thus affected by eutrophication (VISS, 2019).
Himmerfjärden Himmerfjärden is an estuary with a surface area of approx. 31 km2, located on the other side from Ådfärden of the peninsula S dert rn, approx. 40 km south of Stockholm. The bathymetry of Himmerfjärden is steep since the estuary is the result of a tectonically induced fault in the bedrock. Threshold depth at the inlet is approx. 15 m, and the mean and maximum water depths are 15 and 45 m, respectively. Salinity in Himmerfjärden is 5.2-5.9 in surface waters and 5.6-6.2 in bottom waters (SMHI, 2019). The drainage area of Himmerfjärden is 432 km2, and consists of 62% wooded area and 20% agricultural land (SMHI, 2020). The city of S dertälje, with around 100,000 residents, is located upstream from Himmerfjärden. Several indus- tries were established in S dertälje in the 19th century, and these expanded and be- came more numerous in the early 20th century. This enabled population growth in S dertälje and surrounding areas, especially during the 1940s (Nordstr m, 1968). Lake Mälaren has its main outlet in Stockholm, but when the water level is exceptionally high, it is also drained through a lock in S dertälje, into the Himmer- fjärden estuary (Elmgren and Larsson, 1997). The lock opened in 1819, and was re- built in 1924 (Nordstr m, 1968). Prior to the opening of the lock, Lake Mälaren had been isolated from the Baltic Sea since around 1200 CE (Price et al., 2018). According to the Swedish Maritime Administration, 2700 commercial ships and 9000 leisure boats pass through Himmerfjärden, in and out of Lake Mälaren, every year. In 1974, a sewage treatment plant opened with around 90,000 people connected, using the Himmerfjärden estuary as recipient. Since its opening, there have been several full-scale experiments with nutrient discharge in the bay, and the water quality in Himmerfjärden has been closely studied by recipient control environmental monitoring, with respect to e.g. nutrient levels, redox conditions of bottom waters and phytoplankton biomass (Elmgren and Larsson, 1997; Savage et al., 2002). Today the sewage treatment plant serves around 314,000 people and most of the wastewater from the southern suburbs of Stockholm ends up here (Winnfors, 2019). Himmer- fjärden is at present affected by eutrophication and is classified as having a moderate ecological status (VISS, 2019).
Bråviken Bråviken is a long, approx. 50 km, and narrow bay with a surface area of 130 km2. This bay is large but is divided into smaller administrative areas. The sampling site is located in the inner part of Bråviken, where the mean and maximum depths are 9 and 39 m, respectively. The bay is separated from the open Baltic Sea by thresholds of approx. 16 m. Salinity in surface waters fluctuates a lot with seasons, from 1.1 to 5.6, while the salinity of bottom waters is more stable at 6.2-6.9 (SMHI, 2019). The Motala
33 TRACING ENVIRONMENTAL CHANGE AND HUMAN IMPACT
Str m river drains into Bråviken through Norrk ping. The drainage area for inner Bråviken is large, approx. 12,724 km2, with 22% agricultural land and 67% wooded areas (SMHI, 2020). The southern part of Bråviken is flat and very shallow (<5m), with extensive distribution of green algae and seaweeds. The northern shore of Bråviken consists of a fault, which also constitutes the rim of the drainage area. The shoreline on this side is steep and the terrestrial vegetation is dominated by coni- ferous forest. The city of Norrk ping (approx. 140,000 residents), for which Bråviken is reci- pient, is located in the inner, southern part of Bråviken. Norrk ping has a long history of industries, starting with iron and weapon manufacturing in the 17th century. The metal industry declined during the 18th century due to widespread peace in the region, while the textile and paper industries were on the rise (Gejvall-Seger, 1978). These two industries dominated the area during the 19th century, with several paper mills located in Norrk ping and surrounding areas (Sjunnesson and Wahlberg, 2003). Norrk ping has continued to be an important industrial city during the 20th century. According to the Swedish Maritime Administration, 2800 commercial ships pass through Bråviken, to the harbor in Norrk ping, every year. Today, the ecological status of the outer part of Bråviken is moderate, while the inner parts are considered to have a poor ecological status (VISS, 2019), and hence are heavily affected by eutrophication.
Gåsfjärden Gåsfjärden (surface area 21 km2) is the southernmost site included in this thesis, located some 130 km south of Bråviken. The drainage area (1404 km2) is dominated by 84% wooded areas, and only 10% of the land is used for agriculture (SMHI, 2020). Mean and maximum water depths are 10 and 51 m, respectively. This basin is connected to the open sea through a narrow (<500 m) and shallow (approx. 7 m) sill, and there is an archipelago between this site and the open sea. Salinity in surface waters is 4-6.5, and in bottom waters 6.9-7.1 (SMHI, 2019). Hypoxic bottom waters typically occur from August to October. Two rivers, Marstr mmen and Botorpsstr mmen, drain into Gåsfjärden. A closed mine, Solstad Gruva, is located in the inner part of Gåsfjärden. This copper mine was active from 1630 CE until it closed in 1920 CE (Hermansson, 1966; S derhielm and Sundblad, 1996). However, there are indications of even earlier copper mining (Hermansson, 1966). Also in the inner parts of Gåsfjärden, in the village Blankaholm, a saw mill opened in 1886 CE. It expanded in the early 1900s and was in its time the largest saw mill in southern Sweden. This industry closed in 1979 CE. The ecological status of Gåsfjärden is today classified as poor (VISS, 2019).
34 DESCRIPTION OF STUDY SITES
The western Gotland Basin The western Gotland Basin is delimited by the Gotska Sand Sill at 100 m water depth in the northeast and the Hoburg-Midsj Banks at 40 m depth in the south (Leppäranta and Myrberg, 2009). It has a mean depth of 71 m but also contains the deepest location in the entire Baltic Sea, the 459-meter Landsort Deep. The surface water salinity ranges between 6.3 and 7.7 and below the permanent halocline situated at 60-80 m, the salinity is 8.7-10.3 (Leppäranta and Myrberg, 2009). A thermocline develops in the summer, creating a warmer 10-20 m surface layer. The water renewal time for the Gotland Basin is 28-34 years and in the bottom waters of the western Gotland Basin, over 36 years (Meier, 2007).
35 Table 1. Characterization of the water bodies in this thesis
Max Mean Surface Volume Threshold Surface Deep Wave Exchange Days Stratification depth depth area (km2) (km3) depths (m) salinity water exposure of water with ice (m) (m) salinity
Kanholmsfjärden 1041 521 351 1.81 N/A 4.3-5.51 6.5-6.71 Sheltered2 >40 days2 90-1502 Thermocline during summer2
Horsfjärden (larger 511, 303 N/A 621 0.871 N/A 5.1-5.71 5.6-5.91 Sheltered2 >40 days2 90-1502 Thermocline administrative area during summer2 including Ådfjärden)
Ådfjärden 303 N/A ~5 N/A 12 & 193 N/A N/A N/A N/A N/A N/A
Himmerfjärden 451 151 311 0.451 153 5.2-5.91 5.6-6.21 Sheltered2 >40 days2 90-1502 Thermocline during summer2
Inner Bråviken 391 91 571 0.511 163 1.1-5.91 6.2-6.91 Sheltered2 >10-39 90-1502 Thermocline (including days2 during summer2 Pampusfjärden)
Bråviken (entire) 491 N/A ~1203 ~1.151 163 N/A N/A N/A N/A N/A N/A
Gåsfjärden 511 101 21.21 0.221 73 4-6.51 6.9-7.11 Sheltered2 >40 days2 90-1502 Thermocline during summer2
w. Gotland Basin 4594 714 342324 24184 100 NE, 40 6.3-7.74 8.7-10.34 N/A N/A N/A Permanently S4 stratified
References: 1) SMHI “Vattenwebben” (salinity sampled every month during the years 2004–2018), and SMHI “Tabell ver havsområden” 2) VISS, 2019 3) Information from nautical charts 4) Leppäranta and Myrberg, 2009.
32 Material and Methods
Field work Sediment coring was conducted in 2011 from R/V Ocean Surveyor, in 2012 from R/V Skagerak, in 2014 from M/S Fyrbyggaren and in 2017 from R/V Maria S. Merian (Table 2). Slightly different equipment and techniques were used during the different cruises. However, the main methodology was to sample one long sediment core from each site and one complementary short core, to also retrieve the topmost soft and unconsolidated sediments. The following describes sediment coring during the 2012 and 2014 cruises: The long cores from each site were retrieved by a 3- or 5-meter-long piston corer (PC) using 20 to 30 kg of lead weights and a freefall of 0.5 meters. PVC liners with an inner diameter 4.6 cm were used. After retrieval, the cores were cut into sections 1 m (respective 1.25 m) long, sealed with end caps, marked and stored cold for later analyses in the laboratory. To recover the topmost sediments, a short, 1 m long, gravity corer (GC) with an inner diameter of 8 cm was used. The GCs were sliced onboard into 1 cm slices, marked and stored in plastic Ziploc bags. During the 2014 cruise, a second short core was collected and pushed out on deck, where it was documented by photography. All sediment core sections were stored in the cold room before opening. In the laboratory, the piston core liner sections were opened by cut- ting them lengthwise. One half of the core was placed into a core tray for visual in- spection and documentation, both through a written core description and by photo- graphy. The other half of each core section was used for sub-sampling for radiocarbon dating, diatom stratigraphy and geochemistry. In Gåsfjärden, the complementary short core was sampled with a Gemini corer. The long core was opened and documented on board. Otherwise the methods were the same as those described above. For the western Gotland Basin, different gravity core devices were used to retrieve a continuous sediment record. A short multicorer was used to ensure sampling of the uppermost soft sediments. The sediment cores were kept in a cold room and trans- ported to a lab in The Leibniz Institute for Baltic Sea Research in Warnem nde, Germany for opening and sub-sampling. The cores were opened lengthwise, scanned in a multi-sensor core logger and subsampled for radiocarbon, chemical and paleoeco- logical analyses.
37 Table 2. Sediment cores used in this PhD thesis.
Site Core label Date Ship Equipment Water Core Lat Long Results presented depth (m) length (m) in Kanholmsfjärden UPP5B June 2014 M/S Fyrbyggaren Piston corer 101 ~3 N59˚20.414' E18˚47.138' Papers II and IV Kanholmsfjärden UPP5C June 2014 M/S Fyrbyggaren Gravity corer 101 0.68 N59˚20.414' E18˚47.138' Papers II and IV Ådfjärden UPP6A June 2014 M/S Fyrbyggaren Piston corer 28 ~3 N59˚00.573' E18˚02.282' Papers I and IV Ådfjärden UPP6D June 2014 M/S Fyrbyggaren Gravity corer 28 0.72 N59˚00.570' E18˚02.289' Papers I and IV Himmerfjärden PC1208 June 2012 R/V Skagerak Piston corer 44.1 5 N58˚59.616' E17˚43.295' Papers I and IV Himmerfjärden GC1219 June 2012 R/V Skagerak Gravity corer 45 0.77 N58˚59.629' E17˚43.291' Papers I and IV Bråviken PC1205 June 2012 R/V Skagerak Piston corer 24 4.5 N58˚38.832' E16˚23.664' Papers I and IV Bråviken GC1212 June 2012 R/V Skagerak Gravity corer 23.9 0.70 N58˚38.834' E16˚23.636' Papers I and IV Gåsfjärden VG31L August 2011 R/V Ocean Piston corer 31 5.78 56˚34'23''N 16˚31'26''E Papers III and IV Surveyor Gåsfjärden VG31D August 2011 R/V Ocean Gemini corer 31 0.52 56˚34'23''N 16˚31'26''E Papers III and IV Surveyor w. Gotland Basin MSM62-1-60- March 2017 R/V Maria S. Gravity corer 218 7.94 N57˚58.64' E17˚57.37' Paper IV SL Merian w. Gotland Basin MSM62-1-60-2- March 2017 R/V Maria S. Gravity corer 203 0.42 N57˚58.74' E17˚57.56' Paper IV MUC Merian
35 MATERIAL AND METHODS
Chronologies In order to correctly interpret results from sediment archives, and to be able to compare results to other published records and timings of climatic or historical events, it is highly important to establish reliable chronologies. Age models have been constructed using a combination of different radiometric methods. The youngest sediments, <100 years, are dated by lead-210 (210Pb) and the older by radiocarbon (14C). In addition, cesium-137 (137Cs), and mercury (Hg) have been used as markers. Finding suitable coring sites in the dynamic coastal zone of the Baltic Sea is a chal- lenge and having an interest in the long-term perspective adds to these challenges. Several requirements must be met for a sediment core to function as an archive for environmental history. The first preconditions are of course that the cored site has experienced a continuous accumulation during the timespan of interest. Secondly, the two cores, taken with two different types of coring equipment, must be correlated into one splice sequence. Due to difficulties associated with dating the bulk sediment, it is also necessary to find material (macrofossils) for radiocarbon dating. The results from the different dating techniques are then used in the construction of an age-depth model, which must give reasonable accumulation rates. At the start of this project, five additional coastal sites were cored but it was not possible to construct reliable age-depth models for these. Further, the initial idea was to use laminated sequences as a proxy for hypoxic bottom waters, something that had proven to be quite straightforward in the open Baltic Sea (e.g. Zillén et al., 2008). Laminated sequences were in most cores present only in the topmost part, but further down, reflecting medieval times, the presence of diffusely laminated sediments and sulfide banding made the interpretations uncertain.
Radiocarbon dating 14C has a half-life of about 5700 years and is used to date organic material approx. 40,000 years old (Libby et al., 1949). Since the 14C/12C ratio in the atmosphere has varied through history, the 14C ages provided by the dating laboratory need to be calibrated to calendar years BP. This calibration is based on information from e.g. tree rings, laminated sediments and ice cores, which have recorded the atmospheric composition of the 14C/12C ratio through time (Reimer et al., 2013). Since we have all this information, calibrating a terrestrial macrofossil is fairly easy, and this is the preferred material to date with radiocarbon. However, in an aquatic system this is not always possible, and therefore aquatic material, e.g. algae remnants or clams have also been dated. Due to the slow circulation of the world oceans, the marine carbon has an apparent older age, the so-called reservoir age. The reservoir age of the world oceans is termed R. In the brackish system of the Baltic Sea it gets even more complicated. In this system, there is a deviation from the global R, a ΔR. The question of how large the ΔR is in the Baltic Sea has been addressed on several occasions (e.g.
39 TRACING ENVIRONMENTAL CHANGE AND HUMAN IMPACT
Andrén et al., 2000a; 2000b; Hedenstr m and Possnert, 2001; Lougheed et al., 2013; 2012). The chronology for Gåsfjärden is based only on terrestrial macrofossils. However, for the other coastal sites, the chronologies are based on a combination of terrestrial and aquatic macrofossils. A sieve with a 250 μm mesh size was used and the sediment was sieved in 1 cm intervals. The macrofossils found were examined in a stereo microscope when needed and they were determined as accurately as possible. Some of them could be deter- mined to species or genus level (for example, seeds of Betula sp. or shell of Macoma baltica), while others could be assigned to be either terrestrial or aquatic. Some plant remnants could not be specified to be either terrestrial or aquatic. The macrofossils were dried in an oven at 40° C before sending them off for dating by radiocarbon accelerator mass spectrometry (AMS) at the Radiocarbon Dating Laboratory, Lund University, Sweden and at Beta Analytical, USA. In the core from western Gotland Basin, no macrofossils were found, and instead sediment bulk samples, sent to Poznań Radiocarbon Laboratory, Poland, were used for radiocarbon dating.
Lead dating 210Pb has a half-life of 22 years and can be used to date sediments approx. 100 years back (Appleby, 2008). Gamma Dating Center, Institute of Geography, University of Copenhagen analyzed the short gravity cores from Kanholmsfjärden, Ådfjärden, Himmerfjärden and Bråviken for the activity of 210Pb using a Canberra ultralow- background Ge-well-detector. For the Gåsfjärden core, 210Pb dating was performed at the Department of Geology, Lund University. The method of 210Pb dating was not applied to the core from western Gotland Basin.
Markers: cesium and mercury The cesium isotope 137Cs is a marker for the radioactive fallout from the nuclear accident of Chernobyl in 1986, and an earlier increase can be used as a marker for the nuclear weapons testing dated to circa 1960 CE. All six sediment records included in this thesis have been analyzed with respect to 137Cs. For Kanholmsfjärden, Ådfjärden, Himmerfjärden, Bråviken and western Gotland Basin, the measurements were car- ried out at the Leibniz Institute for Baltic Sea Research Warnem nde (IOW) and Gamma Dating Center, Institute of Geography, University of Copenhagen using Canberra detectors. For Gåsfjärden, these measurements were carried out at the Department of Geology, Lund University. Elemental mercury, Hg can be used as a marker for human impact (Leipe et al., 2013). Mercury measurements were performed on the sediment cores from Kan- holmsfjärden, Ådfjärden, Himmerfjärden and Bråviken at the Leibniz Institute for Baltic Sea Research (IOW). A DMA-80 analyzer from MLS Company was used and the results were calibrated against CRM (BCR) 142R certified reference material and SRM 2709 soil standard using five concentration steps covering a range from 5 to 500 ng Hg.
40 MATERIAL AND METHODS
Correlation of cores and age-depth modeling For each site, one long and one short core have been correlated and a splice sediment sequence constructed. For Kanholmsfjärden, Ådfjärden, Himmerfjärden and Brå- viken, correlations of long and short cores are based on the matching of the mercury and the 137Cs profiles (Moros et al., 2017). For the Gåsfjärden record, correlation of the long and short cores is based on Corg concentrations. Terrestrial macrofossil samples have been calibrated using the IntCal13 cali- bration dataset. Aquatic macrofossils have been calibrated using a custom-built calibration curve with a ΔR of -135 ± 40 to compensate for the regional offset from the Marine13 calibration dataset (Reimer et al., 2013). The chosen ΔR is a mean based on the values for ΔR for clams, both suspension and deposit feeders, from three sites relatively close to the study sites as reported in the Marine Reservoir Correction Database (http://calib.org/marine/), Map Numbers 1710, 1717 and 1718 (Lougheed et al., 2013). The bulk sediment samples from western Gotland Basin have been calibrated using a mixed calibration curve consisting of 30% IntCal 13 and 70% Marine13, i.e. assuming that 30% of the carbon is of terrestrial origin and 70% of marine origin. Further discussion on reasoning behind the use of this mixing ratio can be found in Andrén et al. (2020). The other age-depth modeling parameters remained the same as for the coastal sites. For Kanholmsfjärden, Ådfjärden, Him- merfjärden, Bråviken and the western Gotland Basin, the age-depth models have been obtained using the software CLAM version 2.2 (Blaauw, 2010). For Gåsfjärden, the age-depth model was obtained using the software OxCal v4.1.7 (Ramsey, 2008). All ages in the following refer to calibrated ages in years CE. Following the publication of Paper I, the stratigraphies were analyzed in higher resolution with respect to diatoms. For the Ådfjärden record, it became obvious that the correlation of long-short core was less convincing. In Paper I, we estimated that 34 cm was lost in the top of the long core. This has been changed to 53 cm based on the diatom stratigraphy and a new age-depth model was produced. This has changed the interpretation of this stratigraphy with respect to the onset of eutrophication (>100 years earlier in Paper IV than in Paper I). Considering the uncertainties of various aspects in dating and age-depth modeling, it is a strength of this study that it includes results from several records.
Diatoms as a proxy for environmental change Diatoms are single-celled algae that can be found in almost every aquatic habitat. The diatom cell wall is impregnated with silica (SiO2) and these walls are called frustules. Frustules are made up of two halves, valves, which fit together, resembling the structure of a petri dish with lid (Round et al., 1990). There are a number of reasons to work with diatoms. They are found in virtually all aquatic environments and often at high abundances and species diversity. The species composition of diatoms is very sensitive to changes in the environment, for example pH in lakes, salinity, tempe-
41 TRACING ENVIRONMENTAL CHANGE AND HUMAN IMPACT rature (as ice algae or sensitive to changed stratification), water depth and nutrient availability. Because of the silica walls of the diatom cells, they are preserved in accumulated sediments. All these factors combined are what make the diatoms excellent paleoenvironmental indicators (Smol and Stoermer, 2010). Diatoms can live either as plankton or attached to a substrate. How the life-form of diatoms can be used as a proxy for water quality is further elaborated in the Interpretation and Discussion section. Diatom species composition is presented as relative abundances in the diatom diagrams. Vegetative cells of Skeletonema and Chaetoceros spp. were counted when possible but left out from the base sum of diatom relative abundance because of mass blooms in some levels and possible fluctuating preservation due to their very thin frustules. Due to difficulties with species delimitations and possible hybridization, Diatoma spp. were merged. For the time frame covered by this thesis, diatom preservation was not a limiting factor. Based on visual inspection of diatom frustules during analysis, the preservation of diatom valves was considered sufficient in all analyzed samples. However, in some cases a poorer preservation with substantial dissolution of valves was noticed downcore. This would have been a problem in several sites if the focus would have been on a longer time perspective than 2000 years. Even though dissolution was not a problem, broken valves has been a challenge. The counting of diatom valves was consequently carried out according to the method described by Schrader and Gersonde (1978), so the results should not be affected by the number of broken valves. However, in some samples it was difficult to assign specimen to species level, and they are therefore merged into genus and presented as e.g. Epithemia and Mastogloia spp. All identified diatom species are listed in Supplementary table 1. Chaetoceros spp. is one of the most abundant and diverse marine planktonic diatom genera in the world oceans (Malviya et al., 2016). The lightly silicified frus- tules of the vegetative cells are rarely preserved in sediments, but their heavily silicified resting spores can be found. They form under unfavorable conditions; nitrogen deficiency after a bloom event in particular has been reported to be a crucial factor in forming resting spores for some Chaetoceros species (Oku and Kamatani, 1997). All Chaetoceros spp. resting spores were counted but left out from the base sum of diatom counts. The concentration (absolute abundance presented as number of valves per gram dry sediment) of Chaetoceros spp. resting spores is presented in each diatom relative abundance diagram.
Lab procedure – diatom analysis
To clean the diatom valves and make permanent slides a quantity of approx. 0.1 g freeze-dried sediment was weighed and left overnight in 30% H2O2 and a couple of drops of 10% HCl to remove carbonates. The next day, the samples were put on a hotplate to oxidize organic matter until reaction had occurred and the samples had
42 MATERIAL AND METHODS calmed down. The beakers were filled with de-ionized water. They were left overnight and were then rinsed several times over the following days using decantation (settling time 1 cm/hour) to get rid of clay particles. Diluted ammonium (0.5 ml of 25% NH3 per l water) was added to dissolve aggregates of particles and to keep the clay in suspension. After the last rinse, 1 ml of a microsphere stock solution with a con- centration of 5.5603 x 106 microspheres/ml was added (Battarbee, 1986). The samples were then pipetted onto coverslips (#1 thickness) and left overnight to settle and dry. The following day, permanent slides were prepared using Naphrax™ as mounting media. Diatoms were analyzed under a light microscope using differential inter- ference contrast and magnification x1000 with oil immersion. A minimum of 300 diatom valves were counted at each level. Floras used for identification include Cleve- Euler (1955, 1953a, 1953b, 1952, 1951), Krammer and Lange-Bertalot (1991a, 1991b, 1988, 1986), Snoeijs (1993), Snoeijs and Balashova (1998), Snoeijs and Kasperovičienė (1996), Snoeijs and Potapova (1995), Snoeijs and Vilbaste (1994) and Witkowski et al. (2000). Absolute abundance (concentration) of diatom valves was calculated as:
𝑚𝑖𝑐𝑟𝑜𝑠𝑝ℎ𝑒𝑟𝑒𝑠 𝑖𝑛𝑡𝑟𝑜𝑑𝑢𝑐𝑒𝑑 × 𝑑𝑖𝑎𝑡𝑜𝑚𝑠 𝑐𝑜𝑢𝑛𝑡𝑒𝑑 𝑚𝑖𝑐𝑟𝑜𝑠𝑝ℎ𝑒𝑟𝑒𝑠 𝑐𝑜𝑢𝑛𝑡𝑒𝑑
For the samples from Gåsfjärden, absolute abundance was not measured.
Geochemical proxies
Geochemical proxies in this thesis include total organic carbon content (Corg), total nitrogen content (TN), and stable isotopes of nitrogen (δ15N) and carbon (δ13C). In the Baltic Sea, stable nitrogen isotope (δ15N) values at the sediment surface are generally higher in coastal areas (5-13‰) than in the open Baltic Sea (3-5%) (Voss et al., 2005; 2000). The cause for the elevated values in coastal areas is suggested to be anthropogenic nitrogen delivered by rivers and diffuse runoff (Voss et al., 2005). An increased δ15N signal has been interpreted as a result of eutrophication in different areas of the Baltic Sea (Ellegaard et al., 2006; Jokinen et al., 2018; Savage et al., 2010; Struck et al., 2000). Due to the differences in carbon sources for phytoplankton and land plants, they produce organic matter with different stable carbon isotope (δ13C) values. Marine phytoplankton produce organic matter with δ13C values of -18‰ to -22‰, while land plants show values of -25‰ to -28‰ (Kandasamy and Nagender Nath, 2016). However, in a coastal and brackish system where the primary producers are a mixture of marine and freshwater algae, the interpretation of δ13C becomes more complicated. According to Lamb et al. (2006), δ13C values of land plants and freshwater algae overlap, with land plants displaying values of -21‰ to -32‰, and freshwater algae - 26‰ to -30‰. The C/N ratio can then aid in interpreting the sources of organic matter. Since terrestrial plants consist to a high degree of nitrogen-poor cellulose and
43 TRACING ENVIRONMENTAL CHANGE AND HUMAN IMPACT lignin, the C/N ratios are usually >12. In algae, the C/N ratios are <10. However, Lamb et al. (2006) also point out that even with the help of C/N ratio, it can be difficult to distinguish the sources of organic material in coastal areas with high algal production.
Lab procedure – geochemical analyses 13 For the analyses of organic carbon (Corg), nitrogen (N) and stable isotopes δ C and δ15N, all samples were run twice to detect carbonates in the sediment. However, no carbonates were detected in any of the samples. A quantity of 7-8 mg of freeze-dried, grinded and homogenized sediment was put in tin and silver capsules. The tin capsules were immediately sealed. In the silver capsules, approx. 100 μl of 2M HCl was added to remove carbonates, and the samples were dried overnight at 60° C. The silver capsules were then sealed the next day. The samples were analyzed in a Finnigan DeltaV advantage mass spectrometer connected to a CarloErba NC2500 elemental analyzer through a ConfloIV open split interface. The carbon and nitrogen isotope measurements were normalized to the Vienna PeeDee Belemnite and atmospheric N according to (‰) = [(Rsample - Rstandard) / Rstandard] x 1000. Accuracy of the Corg and N measurements was 0.01%, and the precision was +-0.09% and +-0.02% for Corg and N, respectively. Precision in measurements of the stable isotopes δ13C and δ15N was +-0.15‰, and the accuracy was 0.04‰ and 0.05‰ for δ13C and δ15N, respectively. The δ13C values were corrected for the depletion in atmospheric δ13C since 1840 CE due to fossil-fuel burning, the so-called “Suess effect” (Keeling, 1979). The 13 equation from Verburg (2007) was used to calculate the modeled δ Catm for a given 13 year, which was then subtracted from the modeled δ Catm for the year 1840 CE. This 13 13 time-dependent depletion of δ Catm was then added to the measured δ Corg of the samples. The geochemical analyses were carried out at the Stable Isotope Lab, Department of Geological Sciences at Stockholm University and at the Department of Biology, Lund University.
Data processing and statistical analyses The diatom results were assembled and cluster analyses were performed using CONISS in the software Tilia 2.1.1 (Grimm, 1987). To detect trends and com- positional changes in the diatom dataset over time, Detrended Correspondence Analyses (DCA) have been performed using the rioja and vegan packages in R (Jug- gins, 2017; Oksanen et al., 2019). Species richness has been calculated using rare- faction analysis in the vegan package (Birks and Line, 1992). In Paper III, we assessed which effect different forcing factors may have had on the biogeochemistry and diatom composition in Gåsfjärden. For this purpose, Redundancy Analyses, also a constrained ordination method, were performed using CANOCO (ter Braak and Šmilauer, 2002). As potential forcing factors, three
44 MATERIAL AND METHODS explanatory variables were selected: 1. Percentage land cover from the REVEALS reconstruction (Sugita, 2007) from Lake Storsj n, 2. A sea surface temperature si- mulation for the Baltic Sea region (Schimanke et al., 2012), and 3. A sea surface temperature reconstruction for the North Atlantic (Sejrup et al., 2010). In Paper IV, the following statistical methods were applied: Detrended Corres- pondence Analysis (DCA) and Constrained Correspondence Analysis (CCA) were performed using the software R version 3.6.1, and the packages rioja and vegan (Juggins, 2017; Oksanen et al., 2019). DCA does not allow significance testing so to test if the total diatom assemblage changed over time, between sites, and if the change over time was different between sites, a CCA was constructed with both site and time and the interaction between site and time as constrains. Significance tests were conducted with the permutation-based ANOVA included in package vegan using the “by terms” setting, which means that the terms were tested in order and the effect of the ones tested were removed when testing the next term. When comparing DCAs from different assemblages, the position (negative or positive) of samples cannot be directly compared between analyses. The interesting information is the amount of change in position, so in the figure, DCA scores from some analyses are sign-reversed to make results more easy to compare. The levels of δ15N measurements were dated to different years in each core and, to be able to use them in comparisons between cores, they were smoothed in GAM models (library mgcv, Wood, 2017) and the predicted values for the years needed were extracted. Pearson’s product-moment correlations between the δ15N data from Bråviken, Ådfjärden, Himmerfjärden and Kanholmsfjärden and modelled total nitrogen (TN) from Gustafsson et al. (2012) were calculated. The results supported the idea that δ15N can be used as a proxy for altered nutrient input. We therefore proceeded with CCA’s for each site using δ15N and the temperature anomaly from Moberg et al. (2005) as constraining variables. This dataset is a reconstruction of temperature anomalies from the Northern Hemisphere annual mean temperature 1961-90 average based on a combination of low-resolution proxies (lake and ocean sediments) and tree-ring data, which is a high-resolution proxy. The reconstruction covers a timespan of almost 2000 years and the dataset consists of yearly temperature anomalies from year 1 to 1979 CE.
45
Results – summary of papers
The results of this thesis are presented as a summary of the four included papers:
Paper I: Baltic Sea Coastal Eutrophication in a Thousand Year Perspective In this paper, we present records from three sites along the Swedish eastern coast: Bråviken, Himmerfjärden and Ådfjärden. These have been studied with respect to lithologies, geochemistry, and diatom assemblages to trace and date early human impact with an emphasis on nutrient discharge from land. In Bråviken, the first signs of eutrophication are recorded circa 1800 CE. This is reflected in the increase in δ15N and in changes in the diatom species composition. In Himmerfjärden, the earliest sign of eutrophication is the increase in δ15N, starting circa 1800 CE. The eutro- phication signals in Himmerfjärden get more pronounced from circa 1900 CE, with a decrease in diatom species richness, and from circa 1950 CE, an increase in pelagic- to-benthic (P/B) ratio is recorded. In Ådfjärden, the eutrophication signals are recorded from circa 1900 CE. The increasing trend in the P/B ratios starts around 1900 CE in Bråviken and Ådfjärden, and around 1950 CE in Himmerfjärden. Although their detailed history differs, the results show similar general patterns for all three sites. We concluded that the recorded environmental changes during the last centuries are unique in a thousand-year perspective.
Paper II: Signs of early eutrophication in the Stockholm outer archipelago as evident in a 500-year-long sediment record In this study, we present a sediment record from Kanholmsfjärden in the Stockholm outer archipelago covering the last 500 years. The pelagic-to-benthic ratio of diatom taxa and species richness captures the major reduction in water transparency that occurred around 1910 CE. However, the DCA axis 1 reflects the compositional changes of the entire diatom assemblage and when looking at this, earlier changes from as early as circa 1835 CE are evident. This is illustrated by a slight decrease in many benthic and epiphytic taxa, as well as changes in the relative abundance of some pelagic taxa, for example the relative abundance of Pauliella taeniata, Cyclotella choctawhatcheeana and Diatoma spp. complex increases and Thalassiosira baltica decreases. The stable nitrogen isotope δ15N shows an increasing trend from circa 1880 CE. Altogether, the proxies used in this study point to major deterioration in the water quality of Kanholmsfjärden from circa 1910 CE, and earlier indications of eutrophication from around the 1830s, suggesting that reference conditions occurred almost 200 years ago.
47 TRACING ENVIRONMENTAL CHANGE AND HUMAN IMPACT
Paper III: Anthropogenic and climatic impacts on a coastal environment in the Baltic Sea over the last 1000 years This multiproxy study uses sedimentary records covering the last 1000 years obtained from one coastal site (Gåsfjärden) as well as a pollen record from nearby Lake Storsj n. We investigated the links between a pollen-based land cover reconstruction from Lake Storsj n and paleoenvironmental variables from Gåsfjärden itself, including diatom assemblages, organic carbon (C) and nitrogen (N) contents, stable isotopes of C and N, and biogenic silica contents. The Lake Storsj n record shows that regional land use was characterized by small-scale agricultural activity between 900 and 1400 CE, which slightly intensified between 1400 and 1800 CE. Substantial expansion of cropland was observed between 1800 and 1950 CE, before afforestation between 1950 and 2010 CE. From the Gåsfjärden record, prior to 1800 CE, relatively minor changes in the diatom and geochemical proxies were found. Increased P/B ratios after circa 1900 CE indicate a decreased water transparency, and Cyclotella choctawhatcheeana and Thalassiosira levanderi have increased since the 1940s. The onset of cultural eutrophication in Gåsfjärden can be traced to the 1800s and intensified land use is identified as the main driver. Anthropogenic activities in the 20th century have caused unprecedented ecosystem changes in the coastal inlet, as reflected in the diatom composition and geochemical proxies.
Paper IV: Exploring paleoecological trends since 500 CE: a comparison between coastal and open Baltic Proper This paper is a synthesis of the results from all coastal sites, which we further compare to a record from the western Gotland Basin (Andrén et al., 2020). Using ordination techniques, we explore patterns in diatom species composition and temporal changes in the stratigraphies. The results show that the diatom species composition of western Gotland Basin is different from the coastal sites, and it is becoming even more different with time. The species compositions of the coastal sites are changing with time in a different direction than western Gotland Basin. Of the coastal sites, Kan- holmsfjärden, Ådfjärden and Himmerfjärden have similar diatom species composition. Bråviken and Gåsfjärden differ, both from each other and from the other coastal sites. This suggests a heterogeneity along the Swedish southeast coast, showing that site- specific conditions (i.e. geographical preconditions such as salinity, bathymetry and availability of substrates, land use in the drainage area and closeness to a point source, e.g. sewage treatment plant) are important for the diatom species composition. We record no or very minor changes during medieval times in the coastal diatom stratigraphies. Consequently, we conclude that registered changes in the open Baltic Sea (as recorded in, for example, the lithology, carbon content and diatom species composition and absolute abundance) are attributed to climatic events and to a lesser extent to changes in land use. In the coastal records, we register early changes in the diatom assemblages suggesting changes in the environment in the 1800s (1700s in Ådfjärden). This is later followed in the first half of the 20th century by a sharp decline
48 RESULTS – SUMMARY OF PAPERS in benthic taxa suggesting a decrease in macrophytes and habitat loss for benthic diatoms, which we interpret as a decrease in water transparency and a dramatic deter- ioration in water quality due to eutrophication. In the record from western Gotland Basin, major compositional changes in the diatom stratigraphy are recorded from circa 1940. A time lag of recorded changes of approx. 100 years due to eutrophication from the coast to the open Baltic Sea is evident.
49
Interpretation and Discussion
The diatom stratigraphies and geochemical proxies used in this thesis allow us to trace environmental changes in coastal areas along the southeast coast of Sweden. Four of these records provide a long-term perspective, from before year 0 CE in Åd- fjärden, circa 350 CE in Himmerfjärden, circa 500 CE in Bråviken and circa 900 CE in Gåsfjärden. The stratigraphy from Kanholmsfjärden provides a detailed record of how the Stockholm outer archipelago has been impacted by changes in land use and population density since the 16th century. The diatom and geochemical stratigraphies suggest very stable conditions in these sites until recent centuries. There are no indications that climate has had a major effect on these coastal ecosystems during MCA and LIA, and this has led me to the conclusion that the recorded changes during recent centuries can be attributed to eutrophication.
Signs of eutrophication in the coastal zone during the last centuries The results from sediment records in five coastal sites included in this thesis display five parameters attributed to eutrophication. Two of these are based on the relative abundance of diatom taxa (diatom life-form and diatom species composition). The third parameter is diatom species richness, estimated using rarefaction analysis. The absolute abundance of diatoms in the sediment is the fourth parameter based on the diatom data. The fifth parameter, independent of the diatom data, is the signal of stable nitrogen isotope δ15N in the sediment. These five parameters are plotted by site in Figures 2-6 (for Gåsfjärden, only diatom life-form, species composition and species richness are shown in Figure 6).
51 TRACING ENVIRONMENTAL CHANGE AND HUMAN IMPACT
Figure 2. Kanholmsfjärden summary figure showing: The first axis of a detrended correspondence analysis (DCA axis 1), which summarizes compositional changes in the diatom assemblage. % benthic taxa: a decrease in the relative abundance is interpreted as a deterioration of water quality. Diatom concentration (number of valves per gram dry weight sediment): elevated values in diatom concentration in the sediment are recorded as a response to elevated nutrient levels in the water. Assessed species richness: a decreased species richness is a common response to eutrophication. Stable nitrogen isotope, δ15N: an increased δ15N signal is interpreted as a signal of more anthro- pogenic nitrogen runoff from land. Dashed lines indicate the onset and aggravation of anthro- pogenic eutrophication.
52 INTERPRETATION AND DISCUSSION
Figure 3. Ådfjärden summary figure. For details, see legend to Figure 2.
Figure 4. Himmerfjärden summary figure. For details, see legend to Figure 2.
53 TRACING ENVIRONMENTAL CHANGE AND HUMAN IMPACT
Figure 5. Bråviken summary figure. For details, see legend to Figure 2.
Figure 6. Gåsfjärden summary figure showing DCA axis 1, % benthic taxa and species richness. For details, see legend to Figure 2.
54 INTERPRETATION AND DISCUSSION
Diatom life-form Benthic taxa live associated with or attached to different substrates, e.g. macroalgae, rocks, sediment or sand grains. A decreased water transparency, caused for example by increased pelagic production due to eutrophication, will impair the availability of suitable habitats for benthic diatoms in two ways. First, there is a direct effect of de- creased light availability since (most) diatoms are dependent on enough light to maintain photosynthesis. Secondly, there is an indirect effect since reduced light availability will negatively affect the distribution of macroalgae, which are the sub- strate epiphytes grow on. Decreased water transparency leads to a decreased distri- bution of macroalgae and seaweeds (Kautsky et al., 1986). All coastal diatom assemb- lages in this study record a decrease in benthic taxa during the last centuries, with varying exact timing. The earliest changes in life-form are registered in Ådfjärden and Himmerfjärden in the 18th century (Figure 3 and 4). A second decrease in percentages of benthic taxa is registered in Ådfjärden from circa 1900 CE. In Himmerfjärden, a more pronounced decrease in benthic taxa is registered from circa 1950, and again when the sewage treatment plant opened in the 1970s. In Kanholmsfjärden and Bråviken, a sharp decrease in the relative abundance of benthic taxa is recorded circa 1900 CE (Figure 2 and 5). A decrease in benthic taxa is also registered in Gåsfjärden in the first half of the 20th century, albeit at a lower magnitude (Figure 6). The shift in diatom life-form is interpreted as a response to reduction in water transparency and a dramatic deterioration in the water quality during this time. Similar patterns with decreases in benthic and epiphytic taxa in relation to eutro- phication have been seen in several diatom records from coastal areas of the Baltic Sea, e.g. in the Oder estuary in the southern Baltic Proper (Andrén, 1999), the Gulf of Finland (Weckstr m, 2006), the Swedish coast in the Bothnian Sea (Andrén et al., 2016), and on the Danish coasts of Kattegat (Clarke et al., 2006; Ellegaard et al., 2006).
Diatom species composition To summarize major compositional changes in the diatom assemblages, the first axis of a DCA is plotted in Figures 2-6 (for detailed diatom diagrams, see Paper I (Figures 5-7), Paper II (Figure 5) and III (Figure 4)). To a large extent, the DCA curves reflect the changes in life-form discussed above. However, there are some exceptions: The record from Kanholmsfjärden shows pronounced eutrophication since circa 1900 CE, as illustrated by the decline in benthic taxa. However, the diatom assemb- lage reveals even earlier signs of environmental change from around the 1830s. This is recorded as changes in the relative abundance of some pelagic taxa, for example the relative abundance of Pauliella taeniata, Cyclotella choctawhatcheeana and Diatoma spp. complex increases and Thalassiosira baltica decreases. Bråviken shows a similar trend as that of Kanholmsfjärden, with a decline in benthic taxa from around 1900 CE. Also in this site, the DCA axis 1 curve captures earlier changes in the first half of the 1800s. This is mostly caused by changes in the pelagic taxa, namely an increase in
55 TRACING ENVIRONMENTAL CHANGE AND HUMAN IMPACT
Diatoma spp. and a simultaneous decrease in Aulacoseira spp. In the Gåsfjärden record, the first axis of the DCA captures early changes in the diatom assemblage around the mid-1800s, when e.g. Cyclotella choctawhatcheeana and Thalassiosira baltica increase. These changes in diatom species composition are a response to changes in the environments, and in the above described cases, these are interpreted as early signs of increased nutrient availability in these coastal sites. Interpreting the ecology of taxa has not always been straightforward. For example, Pauliella taeniata is a species occurring with high relative abundances in all coastal records except for Gåsfjärden. This is a pennate diatom that lives in and on sea ice and constitutes a substantial part of the spring bloom in the Baltic Sea, especially in years with a long-lasting sea ice cover (Hajdu et al., 1997). Even so, the lowest relative abundances of this species were found to coincide with the coldest period of LIA in several of the sites. In the Gulf of Finland, this species was found to be more abundant with lower levels of nitrogen, and was even suggested to be a potential indicator of water quality (Weckstr m and Juggins, 2006). However, in this study the sites with lower nitrogen levels were also deeper. M ller‐Haeckel (1985) studied the phyto- plankton composition over the course of a year in the Bothnian Bay, and concludes that P. taeniata is adapted to cold waters but also to the low light availability under the sea ice (together with e.g. Melosira arctica, Thalassiosira baltica and Fragilariopsis cylindrus). Water transparency has dramatically decreased due to eutrophication in the Baltic Sea at least during the last century (Fleming-Lehtinen and Laamanen, 2012; Sandén and Håkansson, 1996), but this trend probably started even earlier, as indicated by the decrease in benthic taxa from the early 1800s presented in this thesis. The competitive advantage of P. taeniata to low light availability could conceivably explain the low relative abundances during LIA and the somewhat surprising increase towards present day, considering modern warming. In a review paper, R hland et al. (2015) summarize how climate change has affected diatom assemblages in lakes in arctic and temperate regions. Changes in thermal stratification and vertical mixing due to warming often lead to a decrease in heavy and fast-sinking Aulacoseira spp. and an increase in relative abundance of small, fast-growing and planktonic cyclotelloid taxa. R hland et al. (2015) suggest that small cyclotelloid taxa are insensitive to changes in nitrogen availability and that recent changes in many lakes with a shift to a more cyclotelloid-dominated diatom flora are related to climate warming. These results are not translatable to a brackish, heavily polluted system like the Baltic Sea where, for example, Cyclotella spp. respond to eutrophication (e.g. Andrén et al., 1999; Tuovinen et al., 2010; Weckstr m and Juggins, 2006; Papers I, II and III in this thesis). In arctic lakes or in other regions with a minimum of other anthropogenic influences, it is straightforward to track responses to climate warming (R hland et al., 2015). In a complex system like the Baltic Sea with high human impact and multiple stressors, it is more difficult to determine which changes in the ecosystems are attributed to which external factor.
56 INTERPRETATION AND DISCUSSION
Diatom species richness Diatom species richness has been assessed using rarefaction analysis to account for differences in number of valves counted in each sample. A decrease in species rich- ness has previously been identified as a response to eutrophication (Andrén et al., 2016; Weckstr m, 2006). This is closely linked to the changes in diatom life-form and the loss in benthic habitats (Weckstr m et al., 2007). The records from Bråviken, Himmerfjärden, Ådfjärden, Kanholmsfjärden and Gåsfjärden all show a similar trend with a decrease in species richness, often simultaneously with the shift in diatom life- form. This occurs circa 1900 in Kanholmsfjärden, Ådfjärden and Gåsfjärden, and circa 1950 in Bråviken. In Himmerfjärden, a first decrease in species richness is registered already at the end of the 18th century, and a second decrease circa 1950 CE (Figures 2-6).
Diatom absolute abundance The concentration of diatom valves in the sediment is dependent on several different factors, including the numbers of diatoms produced in the water body, the efficiency with which diatoms are transported to the sediment, the extent to which diatoms are dissolved either in the water column or in the sediment, and the rate of sediment accumulation. Interpreting diatom concentration is therefore not straightforward (Battarbee et al., 2001). However, considering these difficulties, high concentrations of diatoms in the sediment can be interpreted as high (diatom) primary productivity periods (Snoeijs and Weckstr m, 2010). The trend in absolute abundance of diatoms is most clear in Kanholmsfjärden and Himmerfjärden (Figure 2 and 4). The Him- merfjärden record shows higher concentrations of diatoms after 1950 CE, and the opening of the sewage water treatment plant in the 1970s is evident. In Kanholms- fjärden, a slight increase is recorded from circa 1840, and the maximum values are recorded during the 1960s–1980s. In Ådfjärden, an increasing trend in the concen- tration of diatoms is recorded as early as in the 18th century, with the maximum values recorded in the 1940s–1970s (Figure 3). In Bråviken, the concentration of diatom values fluctuates a lot, but generally higher values are recorded after circa 1800 CE (Figure 5). There are no indications in the data that the explanations for these trends would be changes in accumulation rates or dissolution, and these events are therefore interpreted as high diatom productivity periods. This interpretation is further suppor- ted by the fact that the maximum values in many cases coincide with the maximum discharges of nutrients to the Baltic Sea at this time (Gustafsson et al., 2012).
Stable isotope δ15N Elevated values of stable isotope δ15N in coastal sediments seem to be closely related to the degree of impact from agriculture or point sources such as industries or sewage treatment plants, and an increased δ15N signal has been interpreted as a result of eutrophication in different areas of the Baltic Sea (Ellegaard et al., 2006; Jokinen et
57 TRACING ENVIRONMENTAL CHANGE AND HUMAN IMPACT al., 2018; Savage et al., 2010; Struck et al., 2000). Stable isotope δ15N has been measured in all coastal sites (Figures 2-5 and Figure 5 in Paper III). All sites show stable values until an increasing trend starts. In Kanholmsfjärden, increased values are recorded from circa 1900 CE. At this site, δ15N was only measured until circa 1980 CE, and later changes in the isotope signal are therefore not captured. In Ådfjärden and Himmerfjärden, the start of the increasing trend is recorded as early as in the 18th century. In Himmerfjärden, the increasing trend becomes more pronounced around 1800 CE. A first increase in this signal is also recorded in Bråviken around 1800 CE, a signal that gets more pronounced from circa 1850 CE. If we look at the absolute values, Himmerfjärden and Bråviken show an increase towards values more than 6‰, while in the Ådfjärden and Kanholmsfjärden records, values never exceed 5‰ and 4‰, respectively. In Gåsfjärden, an increasing trend is recorded since circa 1800 and reaches values of approx. 4‰ (see Figure 5 in Paper III). According to the δ15N signal, Kanholmsfjärden, Ådfjärden and Gåsfjärden are to a lesser degree than Him- merfjärden and Bråviken impacted by anthropogenic nitrogen. This makes sense since both Himmerfjärden and Bråviken have been, and still are, affected by point sources as a sewage treatment plant and industries (as well as by the relative short distance between the city of Norrk ping and the sampling site in Bråviken). The five parameters described above are all interpreted as responses to elevated levels of nutrients reaching the coastal zone. Changes in these coastal ecosystems did not occur exactly at the same time and are not always registered in a specific order. The results highlight the strength of the multiproxy approach.
Causes for eutrophication in the coastal zone Since the end of the 18th century, several major changes in land use and agricultural practices have occurred in Europe. There are two parts of this so-called “agrarian revolution,” and they occurred simultaneously in some places and were separated by hundreds of years in others (Emanuelsson, 2009). The first part of the agrarian revolution reached southern Sweden circa 1820, when farms started to reorganize, and the old fallow system was abandoned. The reliance in traditional meadows and pastures was reduced and instead a cropping system was introduced involving root vegetables and seeded grassland. This development of agricultural practices was also closely coupled with technological improvements, e.g. the seed drill (Emanuelsson, 2009). The second part of the agrarian revolution was the introduction of artificial fertilizers. The use of artificial fertilizers was quite widespread by 1900 in Sweden, although in small quantities. More extensive use and truly widespread use of artificial fertilizers started after World War II (Emanuelsson, 2009; SCB 1995). Lakes in fertile plains were before the 19th century considered an asset, as they were important for the harvest of Equisetum and Carex spp. (used as winter fodder for animals), and they contributed with fish and bird eggs during springtime (Emanuels- son, 2009). From the early 1800s, there was a fast-growing population in Sweden, and
58 INTERPRETATION AND DISCUSSION this led to a demand to expand the areas of arable lands. This search for arable land prompted an increased interest in draining wetlands and lakes. In Sweden, large-scale draining started in the first decades of the 19th century and was most intense in southern Sweden in the 1880s–1930s (SMHI, 1995). Lakes and wetlands have several important functions in the landscape, besides being the habitat for many animals and plants. They have an equalizing, or smoothing effect on the water flow in an area; when a lake is drained, water flow downstream will be faster and more intense than before the draining. Draining also leads to increased erosion, which leads to increased supply of nutrients to downstream waters. Further, wetlands serve as a filter as nitrogen is caught in the peat and through denitrification converted to nitrogen gas. Both nitrogen and phosphorous are further taken up by vegetation and therefore also “caught” in the wetlands. Consequently, draining of lakes and wetlands leads to increased leakage of nutrients, especially nitrogen, to downstream waters (SMHI, 1995). These changes in agricultural practices and land use are to a large extent con- nected, e.g. large areas of peatland were drained and plowed around 1900 in northern Europe. This land was very poor in phosphorous and potassium, and artificial fer- tilizers were necessary to be able to use this land for agriculture (Emanuelsson, 2009). In addition, the 1800s were also the start of a rapid increase in production forest in the investigated drainage areas. Forestry accounted for roughly 50% of the draining projects in Sweden during the 20th century (Naturvårdsverket, 2020). To summarize, the area of arable lands, seeded grasslands and production forest have shown a rapid increase since 1800 CE. This at the expense of wetlands, natural forest, meadows and pastures (Emanuelsson, 2009). As described, these large-scale changes were tightly coupled and to a large extent occurred simultaneously. The fast- growing population in Sweden since 1800 also resulted in larger cities, more industries, untreated sewage and later sewage treatment plants, etc. Adding to this is also the atmospheric deposition of especially nitrogen, which has substantially increased during the 20th century due to fossil-fuel burning (nitrogen dioxide) and agriculture (ammonia) (Gustafsson et al., 2012) The point sources have to various degrees affected the investigated sites, while the atmospheric deposition has most likely affected the sites at a similar magnitude. We can only speculate as to which of these variables have been most important in setting preconditions in our studied coastal sites. It has been estimated that the draining of lakes and wetlands is a factor of the same importance as input of fertilizers in affecting the net losses of nitrogen to the surrounding seas from arable land (Hoffmann et al., 2000). In the drainage area for Bråviken and Kanholmsfjärden, about 200 and 140 lakes, respectively, were modified (SMHI, 1995). In Mälardalen, the larger drainage area for Lake Mälaren and the Stockholm archipelago, only one-tenth of the original area of wetlands is still present today (Naturvårdsverket, 2020). The retention of nutrients in the landscape was severely altered by this large-scale perturbation of the landscape and it is likely that this had a major effect on the amount of nutrients that reached the investigated sites. However, the changes in the ecosystem and deterioration of the water quality
59 TRACING ENVIRONMENTAL CHANGE AND HUMAN IMPACT that has occurred in the sites is most likely a consequence of the combined effect of all these alterations in the drainage areas. The truly widespread use of industrial fertilizers occurred after World War II and this is also when the development and expansion of sewage water treatment plants started (SCB, 1995; L cke, 2019). This has affected the investigated sites and the years of maximum loads to the Baltic Sea can be seen in the diatom stratigraphies, especially with regard to the concentration of diatom valves in the sediments (Figures 2-5). However, the major deterioration of water quality had already occurred and the most pronounced changes in the diatom assemblages occurred as early as in the 18th century in Ådfjärden and Himmerfjärden, and around 1900 CE in Kanholmsfjärden, Bråviken and Gåsfjärden. These changes in diatom life-form are interpreted as an ecological tipping point in these ecosystems. A recovery in diatom absolute abundan- ce has been recorded since the maximum pollution years in the 1970s–1980s. How- ever, there is no indication of a recovery in diatom species composition in the investigated coastal sites. Even though it is not visible in the data from the coastal sites, it is possible that the warmer climate is aggravating the eutrophication and preventing a recovery to reference conditions (The BACC II Author Team, 2015). In the open Baltic Sea, signs of eutrophication, as manifested in, for example, a changed diatom species composition, enhanced cyanobacteria blooms, expanding areas of hypoxic bottom waters and an increased accumulation of TOC in the sedi- ments, have been recorded since the mid-20th century (Andrén et al., 2000a; Carsten- sen et al., 2014a; Funkey et al., 2014). This suggests a time lag of the onset of eutro- phication of about 100 years between the coast and open Baltic Sea. The Baltic Sea coastal zone is an efficient filter. It has been estimated to remove 16% of the nitrogen and 53% of the phosphorous inputs from land (Asmala et al., 2017). Further, archi- pelagos seem to be especially efficient as nutrient filters, and oxygen status is an important precondition for this (Carstensen et al., 2020; Edman et al., 2018). The results from this thesis support the effectiveness of the coastal filter and highlight how the coastal zone acts as a buffer for the open Baltic Sea.
60 INTERPRETATION AND DISCUSSION
Tracing human impact and climate change during medieval times In the open Baltic Sea, clear changes in primary productivity and oxygen status of bottom waters are recorded during medieval times. There is evidence of widespread distribution of hypoxia in the open parts of the Baltic Proper around 0–1250 CE (Funkey et al., 2014; Zillén et al., 2008), a period that includes the MCA. Further, the hypoxic sediment intervals coincide with increases in cyanobacteria pigments and enhanced accumulation of organic carbon in the sediment, suggesting large cyano- bacteria blooms and an increased primary production during this time (Andrén et al., 2000a; Bianchi et al., 2000; Funkey et al., 2014). The similarities between MCA and how present-day changes are registered in open Baltic Sea sediments have led to a debate concerning the causes of the wide- spread hypoxia during medieval times (Åkesson et al., 2015; Carstensen et al., 2014b; Kotilainen et al., 2014; Schimanke et al., 2012). The warmer climate triggering intense cyanobacteria blooms has been suggested to be the main driver for the development of bottom water hypoxia in the open Baltic Sea during MCA (Kabel et al., 2012). Early human impact with increased amounts of nutrients derived from land has also been suggested to be the cause (Zillén and Conley, 2010). This is supported by the modeling study by (Schimanke et al., 2012), who were not able to reproduce hypoxia in the open Baltic proper during MCA when nutrients remained at pristine levels. A recent study of a sediment core from the western Gotland Basin suggests higher salinity (at least 8-10, compared to the 6.3-7.7 today in this basin), stronger thermal stratification and high diatom primary production to be contributing factors for the development of hypoxia during MCA (Andrén et al., 2020). This interpretation is further supported by the results from the CCA in Paper IV, which show that temperature had a significant effect on the diatom assemblage during MCA (see Figure 4 in Paper IV). During MCA, there was an expansion in population and new agricultural tech- niques and tools were taken into use, e.g. the iron plow. It has been estimated that the population surrounding the Baltic Sea increased from around 4.6 to 9 million people (Zillén and Conley, 2010). This promoted an expansion of agricultural land. We register no or minor effects of this increased land use in the sediment records from the coastal zone and nothing indicating increased nutrient input from land during these times. Wetlands probably served as an effective filter for nutrients before reaching the sea. Benthic diatoms taxa constitute a large share in the records from the coastal zone, indicating good light conditions for benthic habitats. There are no in- dications of a higher diatom primary production at this time, nor of hypoxia in bottom waters as interpreted from the lithologies. Between the years 1350–1450 CE, about half of the population in Sweden died due to the plague. Agricultural lands in remote areas were abandoned. In lowlands, more fertile lands were never abandoned for long, but were taken over by others (Lagerås,
61 TRACING ENVIRONMENTAL CHANGE AND HUMAN IMPACT
2016). Following the medieval agrarian crisis, there was an increase in the population and by circa 1600 CE, it had reached the same level as before the plague (Myrdal and Morell, 2011). All coastal sites except for Gåsfjärden display maximum values of benthic taxa in the 17th century, during the coldest period of the LIA. These are fluctuations on a very small scale but could possibly be explained by wetter conditions during LIA (Luoto and Nevalainen, 2018). This would lead to an increased wetland cover in the landscape (as also indicated by the land-cover reconstruction in Paper III). More and larger wetlands would likely enhance the filtering capacity in the landscape and hence lead to less primary production in the coastal areas and a slightly increased water transparency. As mentioned in the background, little is known about precipitation during MCA and LIA and this interpretation remains therefore speculative. The results from the coastal areas presented in this thesis indicate very stable conditions until the onset of man-made eutrophication during recent centuries. There is nothing in these records that would indicate an increased amount of nutrients reaching the coast of the Baltic Sea during medieval times. Rather, the results support the hypothesis that the widespread hypoxia in the open Baltic Sea during MCA was caused by the warmer climate influencing thermal stratification, primary production of cyanobacteria and diatoms, as well as higher salinity and a stronger halocline. The results in this thesis are also in line with a multiproxy study from the Archipelago Sea, in which they do not find evidence for substantial anthropogenic impact during MCA (Jokinen et al., 2018). Further, the results in this thesis suggest that climate affected the ecosystem to a lesser degree in Baltic Sea coastal areas than in the open Baltic Sea during medieval times.
Climate or nutrients as drivers of paleoecological trends in the Baltic Sea since 500 CE Paper III includes a pollen-based land cover reconstruction from the nearby lake Storsj n. This dataset was used together with a temperature simulation for the Baltic Sea (Schimanke et al., 2012) and a sea surface temperature reconstruction for the North Atlantic (Sejrup et al., 2010) in a redundancy analysis to assess the effect climate and land-use change have had on the diatom assemblages and geochemical proxies since circa 1000 CE. The results show that the minor changes in the diatom assemblage from circa 1000 to circa 1750 CE are most strongly associated with the increase in grassland and decline in deciduous woodland but are also affected by variations in wetland cover and by climate variability. The expansion and following decline in grassland, the marked decrease in wetland, and the increased temperature are the major explanatory factors for the variation in diatom assemblage from 1800 CE until today. In Paper IV, we attempted to disentangle the effect of climate and nutrient loading on the diatom assemblages. In doing so, we have run constrained correspondence
62 INTERPRETATION AND DISCUSSION analyses with two constraining factors: the temperature anomaly data from Moberg et al. (2005), and the δ15N data from each sediment record. The first choice would have been to use pollen stratigraphies and land use reconstructions as proxies for changed land use (as in Paper III), but there were no published pollen records with high enough resolution and/or reliable chronologies in the area and time interval we were interested in. We therefore used the measured δ15N from each sediment record as a proxy for altered nutrient input. The analyses were further limited by the temperature dataset that ends at 1979, and we therefore cannot draw any conclusions about effects of climate warming during recent decades. The results show that temperature anomalies since 500 CE have had no significant effect on the diatom assemblages from the coastal sites. In all coastal sites, increased nutrient input from land has had a significant effect. In the western Gotland Basin, both temperature anomalies and anthropogenic nutrient input have had a significant effect on the diatom assemblage since circa 800 CE. A recent climate modelling study concludes that the present widespread hypoxia in the open Baltic Sea would not have developed during the last 150 years if nutrients had remained at pristine levels (Meier et al., 2019). The results suggest that climate has had a significant effect on the diatom species composition in the western Gotland Basin. However, temperature anomalies seem to have influenced the diatom assemblage in the western Gotland Basin mostly during medieval times, around 1000–1100 CE. In all records, anthropogenic nutrient runoff has affected the diatom assemblages most markedly during the 20th century. None of the eutrophication signals that are recorded during the last centuries are seen during medieval times in the coast (Figures 2-6). Only very minor changes in diatom assemblages and geochemistry are registered before the 18th century, likely related to changes in climate. To summarize, the changes in population, land use and agricultural practices during medieval times had no or very little effect on the coastal ecosystems studied in this thesis (Figure 7). The results indicate very stable conditions at these sites until the start of man-made eutrophication. There is nothing indicating that the widespread hypoxia during MCA in the open parts of the Baltic Sea was caused by an increased input of nutrients from land.
63 TRACING ENVIRONMENTAL CHANGE AND HUMAN IMPACT
64 INTERPRETATION AND DISCUSSION
Figure 7. Conceptual figure of land use and climate forcing, and the ecological responses in the coastal area and the open Baltic Sea during three time-slices of the last millennia (MCA, LIA and recent centuries). Panel A consists of land and coast. Data of land-use changes is from published sources (e.g. Myrdal, 1999; Zillén and Conley, 2010; Myrdal and Morell, 2011; Lagerås, 2016), while the interpretation of ecological conditions in the coastal zone is based on the diatom and geochemical data presented in this thesis. Panel B shows climate forcing and this is based on published climate reconstructions (e.g. Moberg et al., 2005; Helama et al., 2009; Mann et al., 2009; Ljungqvist, 2010; Luoto and Nevalainen, 2018). Panel C shows ecological conditions in the open Baltic Sea, as interpreted from published sources (e.g. Zillén et al., 2008; Kabel et al., 2012; Funkey et al., 2014; Wasmund et al., 2019), as well as the diatom data from western Gotland Basin included in Paper IV and presented fully in Andrén et al. (2020). SST= Sea Surface Temperature. *= maximum relative abundances of benthic taxa are recorded during the coldest period of LIA.
Implications for the environment The results in this thesis do not allow for quantification of reference conditions according to the EU WFD. However, it is possible to discuss this in a more qualitative way. The results suggest a very early onset of eutrophication in the coastal zone of the Baltic Sea, compared to data presented by e.g. Bonsdorff et al. (1997); Cederwall and Elmgren (1990); Conley et al. (2011); and Persson and Jonsson (2000). The exact timing for the onset of eutrophication in these coastal areas is site-specific. For several sites, reference conditions prevailed more than 200 years ago. Water transparency at this time allowed for extensive distribution of benthic habitats for diatoms, such as macrophytes. Species composition of diatoms was not altered, as we interpret from the long-term records in this study. When the results in this thesis are compared to similar studies conducted in coastal areas, it becomes clear that the timing of the onset of coastal eutrophication in the Baltic Sea is site-dependent. In the Gulf of Finland, Weckstr m (2006) has analyzed two cores from urban sites and three cores from more rural areas. Increases in small planktonic taxa start in the lowermost part of the two cores taken at urban sites, corresponding to circa 1800 CE. The three cores taken at rural sites show these signals to start in the 1940s, 1970s and in the 1980s. At a coastal bay in the Archi- pelago Sea, changes in the diatom assemblage, with increases in small pelagic taxa, are recorded from the first half of the 19th century (Tuovinen et al., 2010). From the coast of Estonia, signs of eutrophication are recorded from the mid-19th century (Andrén et al., 2007). Further, Andrén et al. (2016) report changes in the diatom com- position that indicate eutrophication from circa 1920 CE in a coastal bay of the Bothnian Bay, approx. 300 km north from the study sites in this thesis. From the Oder estuary, southern Baltic Proper, an onset of eutrophication is recorded at circa 1900 CE (Andrén, 1999). It should be mentioned, however, that these studies are con- ducted on sediment cores dating back only 100–200 years, and thus earlier changes are not recorded. In a study from the Archipelago Sea, Jokinen et al. (2018) provide a 1500-year record of environmental history of this site, and they report an onset of eutrophication around 1900 CE. Looking outside the Baltic Sea, Cooper and Brush (1993) report changes in diatom species composition as a result of European settle-
65 TRACING ENVIRONMENTAL CHANGE AND HUMAN IMPACT ments as early as around 1760 CE in Chesapeake Bay, USA. In general, ecological degradation in marine systems is recorded earlier in Europe and North America (~1800s) as compared with Asia (post-1900), explained by earlier industrialization in European and North American countries (Yasuhara et al., 2012). However, it should be noted that these types of studies are lacking, or at least are very scarce, from several parts of the world (e.g. Africa, Central and South America, and Southeast and West Asia), and a global comparison is therefore impossible to do. The results from this thesis suggests a delay of more than 100 years in the response in the open Baltic Proper to increased nutrient inputs from land. These results highlight how the coastal zone acts as a buffer zone for the open Baltic Sea. Further, archipelagos seem to be especially efficient as nutrient filters, and maintaining a high oxygen status is important for binding phosphorous (Carstensen et al., 2020; Edman et al., 2018). A correct and efficient management of the coastal zone is of course important for reaching good environmental status in the coastal zone itself, but this will also have effects on the situation in the open Baltic Sea. In addition to the fact that the coastal zone is functioning as a nutrient filter for the open Baltic Sea, there is a filtering capacity in the landscape, before nutrients reach the coast. This filtering capacity is mainly connected to lakes and wetlands (Hoffmann et al., 2000). The results in this thesis suggest that the large-scale draining of lakes and wetlands affected the coastal ecosystems in a very negative way. Before lakes and wetlands were drained, there was a double filter (wetland filter and coastal filter) before nutrients could reach the open Baltic Sea. Management and restoration of wetlands is most likely an important precondition for reaching the goal of “the Baltic Sea unaffected by eutrophication,” as formulated in the Baltic Sea Action Plan (HELCOM, 2007). A recovery in diatom absolute abundance has been recorded since the maximum pollution years in the 1970s–1980s. This agrees with measurements of chemical para- meters and phytoplankton that are carried out in the environmental monitoring (L cke, 2019). Recovery from hypoxia has also been reported from the inner parts of the Stockholm archipelago since the 1990s (Karlsson et al., 2010). However, in the data presented in this thesis, there is no indication of a recovery in diatom species composition in the investigated coastal sites, and these sites are thus far from reaching a “good environmental status.” The environmental monitoring of the Baltic Sea started (at best) in the 1960s. There- fore, pristine nutrient conditions, i.e. before human impact, are not known. Since the EU Water Framework Directive, Marine Strategy Framework Directive, and the Baltic Sea Action Plan take into consideration the interaction between human activities on land and their response in the water, it is crucial to deepen our understanding of this. The outcomes of this thesis highlight the importance of a longer time perspective than the environ- mental monitoring can provide. Additional methods are needed in order to determine reference conditions and the results from this thesis have shown the great potential of sediment cores, as natural archives, to fill the current knowledge gaps.
66 Conclusions
The overall objectives of this PhD thesis were to 1) put the present severe environ- mental situation in the Baltic Sea, in terms of excess nutrient loads and climate change, in a thousand-year perspective, and 2) contribute to an improved under- standing of the natural variability at coastal sites along the southeastern coast of Sweden. Environmental changes have been traced using diatom analysis and geo- chemistry proxies in five sediment records from the southeast coast of Sweden, northwestern Baltic Proper. These records cover time periods of 500 years to more than 2000 years and allow for reconstruction of environmental histories at these sites. The main findings are as follows:
• Long-term environmental change in the coastal zone of southeastern Sweden has successfully been traced using diatom stratigraphies and geo- chemical proxies. • The records from the coastal zone show no or only minor variations in diatom and geochemical stratigraphies through history until recent centuries. The results show no evidence for increased runoff of nutrients from land during medieval times. • Temperature anomalies since 500 CE have had little or no significant effect on the diatom assemblages from the coastal sites. In all coastal sites, increased nutrient input from land has had a significant effect. • In all records, anthropogenic nutrient runoff has affected the diatom assemblages most markedly during the 20th century. • Timing for the onset of eutrophication in these coastal areas is site-specific. For several sites, reference conditions prevailed more than 200 years ago. Water transparency at this time allowed for extensive distribution of benthic habitats for diatoms, such as macrophytes. • There is a delay of more than 100 years in the response in the open Baltic Proper to increased nutrient inputs from land. • The coastal zone acts as a buffer for nutrients before they reach the open Baltic Sea. • A recovery in diatom absolute abundance has been recorded since the maximum pollution years in the 1970s–1980s.
67 TRACING ENVIRONMENTAL CHANGE AND HUMAN IMPACT
• There is no indication of a recovery in diatom species composition in the investigated coastal sites, and these sites are thus far from reaching a “good environmental status.” • The environmental changes that have occurred in the coastal zone in recent centuries are unprecedented during the last two millennia.
68 References
Åkesson, C., Nielsen, A.B., Brostr m, A., Persson, T., Gaillard, M.-J., Berglund, B.E., 2015. From landscape description to quantification: A new generation of reconstructions provides new perspectives on Holocene regional landscapes of SE Sweden. The Holocene 25, 178–193. https://doi.org/10.1177/0959683614556552 Andersen, J.H., Axe, P., Backer, H., Carstensen, J., Claussen, U., Fleming-Lehtinen, V., Järvinen, M., Kaartokallio, H., Knuuttila, S., Korpinen, S., Kubiliute, A., Laamanen, M., Lysiak-Pastuszak, E., Martin, G., Murray, C., M hlenberg, F., Nausch, G., Norkko, A., Villnäs, A., 2011. Getting the measure of eutrophication in the Baltic Sea: towards improved assessment principles and methods. Biogeochemistry 106, 137–156. https://doi.org/10.1007/s10533-010-9508-4 Andersen, J.H., Conley, D.J., Hedal, S., 2004. Palaeoecology, reference conditions and classification of ecological status: the EU Water Framework Directive in practice. Marine Pollution Bulletin 49, 283–290. Anderson, N.J., Renberg, I., Segerstrom, U., 1995. Diatom Production Responses to the Development of Early Agriculture in a Boreal Forest Lake-Catchment (Kassjon, Northern Sweden). Journal of Ecology 83, 809–822. https://doi.org/10.2307/2261418 Andersson, A., Meier, H.E.M., Ripszam, M., Rowe, O., Wikner, J., Haglund, P., Eilola, K., Legrand, C., Figueroa, D., Paczkowska, J., Lindehoff, E., Tysklind, M., Elmgren, R., 2015. Projected future climate change and Baltic Sea ecosystem management. AMBIO 44, 345–356. https://doi.org/10.1007/s13280-015-0654-8 Andersson A., Tamminen T., Lehtinen S., J rgens K., Labrenz M., & Viitasalo M., 2017. The pelagic food web. In: Snoeijs-Leijonmalm P., Schubert H., Radziejewska T. (eds) Biological Oceano- graphy of the Baltic Sea. Springer, Dordrecht. doi.org/10.1007/978-94-007-0668-2_8 Andrén, E., 1999. Changes in the Composition of the Diatom Flora During the Last Century Indicate Increased Eutrophication of the Oder Estuary, South-western Baltic Sea. Estuarine, Coastal and Shelf Science 48, 665–676. https://doi.org/10.1006/ecss.1999.0480 Andrén, E., Andrén, T., Kunzendorf, H., 2000a. Holocene history of the Baltic Sea as a background for assessing records of human impact in the sediments of the Gotland Basin. The Holocene 10, 687–702. https://doi.org/10.1191/09596830094944 Andrén, E., Andrén, T., Sohlenius, G., 2000b. The Holocene history of the southwestern Baltic Sea as reflected in a sediment core from the Bornholm Basin. Boreas 29, 233–250. https://doi.org/10.1111/j.1502-3885.2000.tb00981.x Andrén, E., Clarke, A., Telford, R., Weckstr m, K., Vilbaste, S., Aigars, J., Conley, D., Johnsen, T., Juggins, S., Korhola, A., 2007. Defining reference conditions for coastal areas in the Baltic Sea, TemaNord 583. Nordic Council of Ministers, Copenhagen. Andrén, E., Telford, R.J., Jonsson, P., 2016. Reconstructing the history of eutrophication and quantifying total nitrogen reference conditions in Bothnian Sea coastal waters. Estuarine, Coastal and Shelf Science. https://doi.org/10.1016/j.ecss.2016.07.015 Andrén, E., van Wirdum, F., Norbäck Ivarsson, L., L nn, M., Moros, M., Andrén, T., 2020. Medieval versus recent environmental conditions in the Baltic Proper, what was different a thousand years ago? Palaeogeography, Palaeoclimatology, Palaeoecology 555, 109878. https://doi.org/10.1016/j.palaeo.2020.109878
69 TRACING ENVIRONMENTAL CHANGE AND HUMAN IMPACT
Andrén, T., Andrén, E, Berglund, B.E. & Yu, S.-Y., 2007: An Early Holocene offshore lake at the Blekinge coast, SE Sweden. GFF 129, 277-285. Andrén, T., Bj rck, S., Andrén, E., Conley, D., Zillén, L., Anjar, J., 2011. The Development of the Baltic Sea Basin During the Last 130 ka, in: Harff, J., Bj rck, S., Hoth, P. (Eds.), The Baltic Sea Basin. Springer Berlin Heidelberg, Berlin, Heidelberg, pp. 75–97. Anonymous, 2000. Directive 200/60/EC of the European Parliament and of the Council of 23 October 2000 establishing a framework for Community action in the field of water policy. Official Journal L 327/1. Appleby, P.G., 2008. Three decades of dating recent sediments by fallout radionuclides: a review. The Holocene 18, 83–93. https://doi.org/10.1177/0959683607085598 Asmala, E., Carstensen, J., Conley, D.J., Slomp, C.P., Stadmark, J., Voss, M., 2017. Efficiency of the coastal filter: Nitrogen and phosphorus removal in the Baltic Sea. Limnology and Oceano- graphy 62, S222–S238. https://doi.org/10.1002/lno.10644 Battarbee, R.W., 1986. Diatom analysis, in: Berglund, B.E. (Ed.), Handbook of Holocene Palaeoecology and Palaeohydrology. Johan Wiley & Sons Ltd., Chichester, pp. 527–570. Battarbee, R. W., Jones, V. J., Flower, R. J., Cameron, N. G., Bennion, H., Carvalho, L. & Juggins, S., 2001. Diatoms. In: Smol, John P., Birks, Harry John Betteley & Last, William M. (ed.) 2001. Tracking environmental change using lake sediments. Vol. 3, Terrestrial, algal, and siliceous indicators. Dordrecht: Kluwer Academic Bennike O, Jensen JB, Lemke W, Kuijpers A, Lomholt S (2004) Late- and postglacial history of the Great Belt, Denmark. Boreas 33:18–33 Berglund, B.E., Sandgren, P., Barnekow, L., Hannon, G., Jiang, H., Skog, G., Yu, S.-Y., 2005. Early Holocene history of the Baltic Sea, as reflected in coastal sediments in Blekinge, southeastern Sweden. Quaternary International, Baltic Sea Science Congress 2001 130, 111–139. https://doi.org/10.1016/j.quaint.2004.04.036 Bianchi, T.S., Engelhaupt, E., Westman, P., Andrén, T., Rolff, C., Elmgren, R., 2000. Cyanobacterial blooms in the Baltic Sea: Natural or human-induced? Limnol. Oceanogr. 45, 716–726. https://doi.org/10.4319/lo.2000.45.3.0716 Birks, H.J.B., Line, J.M., 1992. The use of Rarefaction Analysis for Estimating Palynological Richness from Quaternary Pollen-Analytical Data. The Holocene 2, 1–10. https://doi.org/10.1177/095968369200200101 Bj rck S (2008) The late Quaternary development of the Baltic Sea basin. In: The BACC Author Team (eds) Assessment of climate change for the Baltic Sea Basin. Springer, Berlin, Heidelberg Bj rck S, Andrén T, Jensen JB (2008) An attempt to resolve the partly conflicting data and ideas on the Ancylus-Litorina transition. Polish Geological Institute Special Papers 23:21–25 Blaauw, M., 2010. Methods and code for ‘classical’ age-modelling of radiocarbon sequences. Quaternary Geochronology 5, 512–518. https://doi.org/10.1016/j.quageo.2010.01.002 Bonsdorff, E., Blomqvist, E., Mattila, J., Norkko, A., 1997. Long-term changes and coastal eutrophication. Examples from the Aland Islands and the Archipelago Sea, northern Baltic Sea. Oceanolica Acta 20, 319–329. Bradshaw, E.G., Rasmussen, P., Odgaard, B.V., 2005. Mid-to late-Holocene land-use change and lake development at Dallund S0, Denmark: synthesis of multiproxy data, linking land and lake. The Holocene 15, 1152–1162. Carstensen, J., Andersen, J.H., Gustafsson, B.G., Conley, D.J., 2014a. Deoxygenation of the Baltic Sea during the last century. PNAS 111, 5628–5633. https://doi.org/10.1073/pnas.1323156111
70 REFERENCES
Carstensen, J., Conley, D.J., Almroth-Rosell, E., Asmala, E., Bonsdorff, E., Fleming-Lehtinen, V., Gustafsson, B.G., Gustafsson, C., Heiskanen, A.-S., Janas, U., Norkko, A., Slomp, C., Villnäs, A., Voss, M., Zilius, M., 2020. Factors regulating the coastal nutrient filter in the Baltic Sea. Ambio 49, 1194–1210. https://doi.org/10.1007/s13280-019-01282-y Carstensen, J., Conley, D.J., Bonsdorff, E., Gustafsson, B.G., Hietanen, S., Janas, U., Jilbert, T., Maximov, A., Norkko, A., Norkko, J., Reed, D.C., Slomp, C.P., Timmermann, K., Voss, M., 2014b. Hypoxia in the Baltic Sea: Biogeochemical Cycles, Benthic Fauna, and Management. AMBIO 43, 26–36. https://doi.org/10.1007/s13280-013-0474-7 Cederwall, H., Elmgren, R., 1990. Biological effects of eutrophication in the Baltic Sea, particularly the coastal zone. Ambio. Stockholm 19, 109–112. Charpentier Ljungqvist, F., 2015. Den långa medeltiden: de nordiska ländernas historia från folkvandringstid till reformation. Dialogo, Stockholm. Clarke, A.L., Weckstr m, K., Conley, D.J., Anderson, N.J., Adser, F., Andrén, E., de Jonge, V.N., Ellegaard, M., Juggins, S., Kauppila, P., Korhola, A., Reuss, N., Telford, R.J., Vaalgamaa, S., 2006. Long-term trends in eutrophication and nutrients in the coastal zone. Limnol. Oceanogr. 51, 385–397. https://doi.org/10.4319/lo.2006.51.1_part_2.0385 Cleve-Euler, A., 1955. Die Diatomeen von Schweden und Finnland. T. 4, Biraphideae 2, Kungl. Svenska vetenskapsakademiens handlingar, 0023-5377; 4:5:4. Almqvist & Wiksell, Stockholm. Cleve-Euler, A., 1953a. Die Diatomeen von Schweden und Finnland. T. 2, Arraphideae, Brachyraphideae, Kungl. Svenska vetenskapsakademiens handlingar, 0023-5377; 4:4:1. Alm- qvist & Wiksell, Stockholm. Cleve-Euler, A., 1953b. Die Diatomeen von Schweden und Finnland. T. 3, Monoraphideae, Biraphideae 1, Kungl. Svenska vetenskapsakademiens handlingar, 0023-5377; 4:4:5. Almqvist & Wiksell, Stockholm. Cleve-Euler, A., 1952. Die Diatomeen von Schweden und Finnland. T. 5, Schluss, Kungl. Svenska vetenskapsakademiens handlingar, 0023-5377; 4:3:3. Almqvist & Wiksell, Stockholm. Cleve-Euler, A., 1951. Die Diatomeen von Schweden und Finnland. [T. 1], Kungl. Svenska vetenskapsakademiens handlingar, 0023-5377; 4:2:1. Almqvist & Wiksell, Stockholm. Conley, D.J., Bj rck, S., Bonsdorff, E., Carstensen, J., Destouni, G., Gustafsson, B.G., Hietanen, S., Kortekaas, M., Kuosa, H., Markus Meier, H.E., M ller-Karulis, B., Nordberg, K., Norkko, A., N rnberg, G., Pitkänen, H., Rabalais, N.N., Rosenberg, R., Savchuk, O.P., Slomp, C.P., Voss, M., Wulff, F., Zillén, L., 2009. Hypoxia-Related Processes in the Baltic Sea. Environ. Sci. Technol. 43, 3412–3420. https://doi.org/10.1021/es802762a Conley, D.J., Carstensen, J., Aigars, J., Axe, P., Bonsdorff, E., Eremina, T., Haahti, B.-M., Humborg, C., Jonsson, P., Kotta, J., Lännegren, C., Larsson, U., Maximov, A., Medina, M.R., Lysiak- Pastuszak, E., Remeikaitė-Nikienė, N., Walve, J., Wilhelms, S., Zillén, L., 2011. Hypoxia Is Increasing in the Coastal Zone of the Baltic Sea. Environ. Sci. Technol. 45, 6777–6783. https://doi.org/10.1021/es201212r Conley, D.J., Humborg, C., Rahm, L., Savchuk, O.P., Wulff, F., 2002. Hypoxia in the Baltic Sea and Basin-Scale Changes in Phosphorus Biogeochemistry. Environ. Sci. Technol. 36, 5315–5320. https://doi.org/10.1021/es025763w Cooper, S.R., Brush, G.S., 1993. A 2,500-year history of anoxia and eutrophication in Chesapeake Bay. Estuaries 16, 617–626. https://doi.org/10.2307/1352799 Diaz, R.J., Rosenberg, R., 2008. Spreading Dead Zones and Consequences for Marine Ecosystems. Science 321, 926–929. https://doi.org/10.1126/science.1156401
71 TRACING ENVIRONMENTAL CHANGE AND HUMAN IMPACT
Dubois, N., Saulnier-Talbot, É., Mills, K., Gell, P., Battarbee, R., Bennion, H., Chawchai, S., Dong, X., Francus, P., Flower, R., Gomes, D.F., Gregory-Eaves, I., Humane, S., Kattel, G., Jenny, J., Langdon, P., Massaferro, J., McGowan, S., Mikomägi, A., Ngoc, N.T.M., Ratnayake, A.S., Reid, M., Rose, N., Saros, J., Schillereff, D., Tolotti, M., Valero-Garcés, B., 2018. First human impacts and responses of aquatic systems: A review of palaeolimnological records from around the world. The Anthropocene Review 5, 28–68. https://doi.org/10.1177/2053019617740365 Edman, M., Eilola, K., Almroth-Rosell, E., Meier, H.E.M., Wåhlstr m, I., Arneborg, L., 2018. Nutrient Retention in the Swedish Coastal Zone. Front. Mar. Sci. 5. https://doi.org/10.3389/fmars.2018.00415 Ellegaard, M., Clarke, A.L., Reuss, N., Drew, S., Weckstr m, K., Juggins, S., Anderson, N.J., Conley, D.J., 2006. Multi-proxy evidence of long-term changes in ecosystem structure in a Danish marine estuary, linked to increased nutrient loading. Estuarine, Coastal and Shelf Science 68, 567–578. https://doi.org/10.1016/j.ecss.2006.03.013 Elmgren, R., 2001. Understanding Human Impact on the Baltic Ecosystem: Changing Views in Recent Decades. AMBIO: A Journal of the Human Environment 30, 222–231. https://doi.org/10.1579/0044-7447-30.4.222 Elmgren, R., Hill, C., 1997. Ecosystem function at low biodiversity–the Baltic example. Marine Bio- diversity–Patterns and Processes. Cambridge University Press, New York. Elmgren, R., Larsson, U., 1997. Himmerfjärden: f rändringar i ett näringsbelastat kustekosystem i Östersj n, Rapport / Naturvårdsverket, 0282-7298; 4565. Naturvårdsverket, Stockholm. Emanuelsson, U., 2009. The rural landscapes of Europe: how man has shaped European nature. Stockholm: Formas. European commission, 2003. COMMON IMPLEMENTATION STRATEGY FOR THE WATER FRAMEWORK DIRECTIVE (2000/60/EC) Guidance Document No 5 Transitional and Coastal Waters – Typology, Reference Conditions and Classification Systems. Produced by Working Group 2.4 – COAST. Fleming-Lehtinen, V., Laamanen, M., 2012. Long-term changes in Secchi depth and the role of phytoplankton in explaining light attenuation in the Baltic Sea. Estuarine, Coastal and Shelf Science 102–103, 1–10. https://doi.org/10.1016/j.ecss.2012.02.015 Funkey, C.P., Conley, D.J., Reuss, N.S., Humborg, C., Jilbert, T., Slomp, C.P., 2014. Hypoxia Sustains Cyanobacteria Blooms in the Baltic Sea. Environ. Sci. Technol. 48, 2598–2602. https://doi.org/10.1021/es404395a Gejvall-Seger, B., 1978. Boken om Norrk ping. Natur och kultur, Stockholm. Granéli, E., Wallstr m, K., Larsson, U., Granéli, W., Elmgren, R., 1990. Nutrient Limitation of Primary Production in the Baltic Sea Area. Ambio 19, 142–151. Grimm, E.C., 1987. CONISS: a FORTRAN 77 program for stratigraphically constrained cluster analysis by the method of incremental sum of squares. Computers & Geosciences 13, 13–35. https://doi.org/10.1016/0098-3004(87)90022-7 Gustafsson, B.G., Schenk, F., Blenckner, T., Eilola, K., Meier, H.E.M., M ller-Karulis, B., Neumann, T., Ruoho-Airola, T., Savchuk, O.P., Zorita, E., 2012. Reconstructing the Development of Baltic Sea Eutrophication 1850–2006. AMBIO 41, 534–548. https://doi.org/10.1007/s13280-012-0318-x Gustafsson, B.G., Westman, P., 2002. On the causes for salinity variations in the Baltic Sea during the last 8500 years. Paleoceanography 17, 12–1. https://doi.org/10.1029/2000PA000572
72 REFERENCES
Hajdu, S., Larsson, U., Skärlund, K., 1997. Växtplankton, in: Elmgren, R., Larsson, U. (Eds.), Himmerfjärden: f rändringar i ett näringsbelastat kustekosystem i Östersj n. Naturvårds- verket, Stockholm, pp. 63–79. Hansson, D., Gustafsson, E., 2011. Salinity and hypoxia in the Baltic Sea since A.D. 1500. Journal of Geophysical Research: Oceans 116. https://doi.org/10.1029/2010JC006676 Hansson, M., Andersson, 2014. Oxygen Survey in the Baltic Sea 2014 – Extent of Anoxia and Hypoxia, 1960-2014 (No. 50), SMHI Report Oceanography. Swedish Meteorological and Hydrological Institute, G teborg, Sweden. Harff, J., Meyer, M., 2011. Coastlines of the Baltic Sea – Zones of Competition Between Geological Processes and Changing Climate: Examples from the Southern Baltic., in: Harff, J., Bj rck, S., Hoth, P. (Eds.), The Baltic Sea Basin. Springer-Verlag, Berlin Heidelberg, pp. 149–164. Harland, R., Polovodova Asteman, I., Nordberg, K., 2013. A two-millennium dinoflagellate cyst record from Gullmar Fjord, a Swedish Skagerrak sill fjord. Palaeogeography, Palaeoclimatology, Palaeoecology 392, 247–260. https://doi.org/10.1016/j.palaeo.2013.09.006 Hedenstr m, A., Possnert, G., 2001. Reservoir ages in Baltic Sea sediment—a case study of an isolation sequence from the Litorina Sea stage. Quaternary Science Reviews 20, 1779–1785. https://doi.org/10.1016/S0277-3791(01)00069-5 Helama, S., Meriläinen, J., Tuomenvirta, H., 2009. Multicentennial megadrought in northern Europe coincided with a global El Ni o–Southern Oscillation drought pattern during the Medieval Climate Anomaly. Geology 37, 175–178. https://doi.org/10.1130/G25329A.1 HELCOM, 2009. Eutrophication in the Baltic Sea- An integrated thematic assessment of the effects of nutrient enrichment in the Baltic Sea region. HELCOM, 2007. HELCOM Baltic Sea Action Plan (adopted by the HELCOM Ministerial meeting, Krakow, Poland 15th November 2007). Hermansson, W., 1966. Solstad koppargruva. Kalmar nations skriftserie 43, 18–51. Hoffmann, M., Johnsson, H., Gustafson, A., Grimvall, A., 2000. Leaching of nitrogen in Swedish agriculture – a historical perspective. Agriculture, Ecosystems & Environment 80, 277–290. https://doi.org/10.1016/S0167-8809(00)00154-7 Hurrell, J.W., Kushnir, Y., Ottersen, G., Visbeck, M., 2003. An overview of the North Atlantic oscillation. Geophysical Monograph-American Geophysical Union 134, 1–36. IPCC, 2007. Climate Change 2007. In: Solomon SD, Qin M, Manning Z Chen, M Marquis, KB Averyt, M Tignor, Miller HL (eds), The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge. Jakobsson, M., Bj rck, S., Alm, G., Andrén, T., Lindeberg, G., Svensson, N.-O., 2007. Recon- structing the Younger Dryas ice dammed lake in the Baltic Basin: Bathymetry, area and volume. Global and Planetary Change 57, 355–370. https://doi.org/10.1016/j.gloplacha.2007.01.006 Jokinen, S.A., Virtasalo, J.J., Jilbert, T., Kaiser, J., Dellwig, O., Arz, H.W., Hänninen, J., Arppe, L., Collander, M., Saarinen, T., 2018. A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20th century. Bio- geosciences 15, 3975–4001. https://doi.org/10.5194/bg-15-3975-2018 Jonsson, P., Carman, R., Wulff, F., 1990. Laminated Sediments in the Baltic: A Tool for Evaluating Nutrient Mass Balances. Ambio 19, 152–158. Juggins, S., 2017. rioja: Analysis of Quaternary Science Data.
73 TRACING ENVIRONMENTAL CHANGE AND HUMAN IMPACT
Kabel, K., Moros, M., Porsche, C., Neumann, T., Adolphi, F., Andersen, T.J., Siegel, H., Gerth, M., Leipe, T., Jansen, E., Sinninghe Damsté, J.S., 2012. Impact of climate change on the Baltic Sea ecosystem over the past 1,000 years. Nature Clim. Change 2, 871–874. https:// doi.org/10.1038/nclimate1595 Kandasamy, S., Nagender Nath, B., 2016. Perspectives on the Terrestrial Organic Matter Transport and Burial along the Land-Deep Sea Continuum: Caveats in Our Understanding of Biogeochemical Processes and Future Needs. Front. Mar. Sci. 3. https://doi.org/ 10.3389/fmars.2016.00259 Karlson, A.M.L., Duberg, J., Motwani, N.H., Hogfors, H., Klawonn, I., Ploug, H., Barthel Svedén, J., Garbaras, A., Sundelin, B., Hajdu, S., Larsson, U., Elmgren, R., Gorokhova, E., 2015. Nitrogen fixation by cyanobacteria stimulates production in Baltic food webs. AMBIO 44, 413–426. https://doi.org/10.1007/s13280-015-0660-x Karlsson, O.M., Jonsson, P.O., Lindgren, D., Malmaeus, J.M., Stehn, A., 2010. Indications of Recovery from Hypoxia in the Inner Stockholm Archipelago. AMBIO 39, 486–495. https://doi.org/10.1007/s13280-010-0079-3 Karlsson, S. and Risberg, J., 2006. Växthistoria och strandf rskjutning i området kring Fjäturen och Gullsj n, s dra Uppland. In. Johansson, Å. and Lindgren, C. (ed.), En introduktion till det arkeologiska projektet Norrortsleden, Bilaga 6, 71–125, Riksantikvarieämbetet, UV Mitt, Dokumentation av fältarbetsfasen. Kautsky, N., Kautsky, H., Kautsky, U., Waern, M., 1986. Decreased depth penetration of Fucus vesiculosus (L.) since the 1940’s indicates eutrophication of the Baltic Sea. Mar. Ecol. Prog. Ser 28, 1–8. Keeling, C.D., 1979. The Suess effect: 13 carbon-14 carbon interrelations. Environment Inter- national 2, 229–300. Kemp, W.M., Boynton, W.R., Adolf, J.E., Boesch, D.F., Boicourt, W.C., Brush, G., Cornwell, J.C., Fisher, T.R., Glibert, P.M., Hagy, J.D., others, 2005. Eutrophication of Chesapeake Bay: historical trends and ecological interactions. Marine Ecology Progress Series 303, 1–29. Klais, R., Tamminen, T., Kremp, A., Spilling, K., Olli, K., 2011. Decadal-Scale Changes of Dinoflagellates and Diatoms in the Anomalous Baltic Sea Spring Bloom. PLoS ONE 6, e21567. https://doi.org/10.1371/journal.pone.0021567 Kotilainen, A.T., Arppe, L., Dobosz, S., Jansen, E., Kabel, K., Karhu, J., Kotilainen, M.M., Kuijpers, A., Lougheed, B.C., Meier, H.E.M., Moros, M., Neumann, T., Porsche, C., Poulsen, N., Ras- mussen, P., Ribeiro, S., Risebrobakken, B., Ryabchuk, D., Schimanke, S., Snowball, I., Spiridonov, M., Virtasalo, J.J., Weckstr m, K., Witkowski, A., Zhamoida, V., 2014. Echoes from the Past: A Healthy Baltic Sea Requires More Effort. AMBIO 43, 60–68. https://doi.org/10.1007/s13280-013-0477-4 Krammer, K., Lange-Bertalot, H., 1991a. S sswasserflora von Mitteleuropa. Bd 2, Bacillariophyceae, T. 3, Centrales, Fragilariaceae, Eunotiaceae. Fischer, Stuttgart. Krammer, K., Lange-Bertalot, H., 1991b. S sswasserflora von Mitteleuropa. Bd 2, Bacillario- phyceae, T. 4, Achnanthaceae: Kritische Ergänzungen zu Navicula (Lineolatae) und Gom- phonema. Fischer, Stuttgart. Krammer, K., Lange-Bertalot, H., 1988. S sswasserflora von Mitteleuropa. Bd 2, Bacillariophyceae, T. 2, Bacillariaceae, Epithemiaceae, Surirellaceae. Fischer, Stuttgart. Krammer, K., Lange-Bertalot, H., 1986. S sswasserflora von Mitteleuropa. Bd 2, Bacillariophyceae, T. 1, Naviculaceae. Fischer, Stuttgart.
74 REFERENCES
Lagerås, P., 2016. Environment, society and the Black Death: An interdisciplinary approach to the late-medieval crisis in Sweden. Oxbow Books, Oxford. Lamb, A.L., Wilson, G.P., Leng, M.J., 2006. A review of coastal palaeoclimate and relative sea-level reconstructions using δ13C and C/N ratios in organic material. Earth-Science Reviews 75, 29– 57. https://doi.org/10.1016/j.earscirev.2005.10.003 Leipe, T., Moros, M., Kotilainen, A., Vallius, H., Kabel, K., Endler, M., Kowalski, N., 2013. Mercury in Baltic Sea sediments – Natural background and anthropogenic impact. Chemie der Erde – Geochemistry 73, 249–259. https://doi.org/10.1016/j.chemer.2013.06.005 Leppäranta, M., Myrberg, K., 2009. Physical oceanography of the Baltic Sea. Springer/Praxis Pub., Berlin. Libby, W.F., Anderson, E.C., Arnold, J.R., 1949. Age Determination by Radiocarbon Content: World-Wide Assay of Natural Radiocarbon. Science 109, 227–228. https://doi.org/ 10.1126/science.109.2827.227 Ljungqvist, F.C., 2010. A new reconstruction of temperature variability in the extra‐tropical northern hemisphere during the last two millennia. Geografiska Annaler: Series A, Physical Geography 92, 339–351. https://doi.org/10.1111/j.1468-0459.2010.00399.x Ljungqvist, F.C., Krusic, P.J., Brattstr m, G., Sundqvist, H.S., 2012. Northern Hemisphere tem- perature patterns in the last 12 centuries. Climate of the Past 8, 227–249. Ljungqvist, F.C., Krusic, P.J., Sundqvist, H.S., Zorita, E., Brattstr m, G., Frank, D., 2016. Northern Hemisphere hydroclimate variability over the past twelve centuries. Nature 532, 94–98. https://doi.org/10.1038/nature17418 Lougheed, B.C., Filipsson, H.L., Snowball, I., 2013. Large spatial variations in coastal 14C reservoir age–a case study from the Baltic Sea. Climate of the Past 9, 1015–1028. Lougheed, B.C., Snowball, I., Moros, M., Kabel, K., Muscheler, R., Virtasalo, J.J., Wacker, L., 2012. Using an independent geochronology based on palaeomagnetic secular variation (PSV) and atmospheric Pb deposition to date Baltic Sea sediments and infer 14C reservoir age. Quaternary Science Reviews 42, 43–58. https://doi.org/10.1016/j.quascirev.2012.03.013 L cke, 2019. Unders kningar i Stockholms skärgård 2018 – vattenkemi, plankton och bottenfauna. Stockholm Vatten och avfall. Luoto, T.P., Nevalainen, L., 2018. Temperature-precipitation relationship of the Common Era in northern Europe. Theor Appl Climatol 132, 933–938. https://doi.org/10.1007/s00704-017-2139-0 Mackenzie, B.R., Schiedek, D., 2007. Daily ocean monitoring since the 1860s shows record warming of northern European seas. Global Change Biology 13, 1335–1347. https://doi.org/10.1111/j.1365-2486.2007.01360.x Malviya, S., Scalco, E., Audic, S., Vincent, F., Veluchamy, A., Poulain, J., Wincker, P., Iudicone, D., Vargas, C. de, Bittner, L., Zingone, A., Bowler, C., 2016. Insights into global diatom distribution and diversity in the world’s ocean. PNAS 113, E1516–E1525. https://doi.org/ 10.1073/pnas.1509523113 Mann, M.E., Zhang, Z., Rutherford, S., Bradley, R.S., Hughes, M.K., Shindell, D., Ammann, C., Faluvegi, G., Ni, F., 2009. Global Signatures and Dynamical Origins of the Little Ice Age and Medieval Climate Anomaly. Science 326, 1256–1260. https://doi.org/10.1126/science.1177303 Meier, H.E.M., 2007. Modeling the pathways and ages of inflowing salt- and freshwater in the Baltic Sea. Estuarine, Coastal and Shelf Science, Timescale- and tracer-based methods for under-
75 TRACING ENVIRONMENTAL CHANGE AND HUMAN IMPACT
standing the results of complex marine models 74, 610–627. https://doi.org/ 10.1016/j.ecss.2007.05.019 Meier, H.E.M., Eilola, K., Almroth-Rosell, E., Schimanke, S., Kniebusch, M., H glund, A., Pem- berton, P., Liu, Y., Väli, G., Saraiva, S., 2019. Disentangling the impact of nutrient load and climate changes on Baltic Sea hypoxia and eutrophication since 1850. Clim Dyn 53, 1145–1166. https://doi.org/10.1007/s00382-018-4296-y Moberg, A., Sonechkin, D.M., Holmgren, K., Datsenko, N.M., Karlén, W., 2005. Highly variable Northern Hemisphere temperatures reconstructed from low- and high-resolution proxy data. Nature 433, 613–617. https://doi.org/10.1038/nature03265 Mohrholz, V., Naumann, M., Nausch, G., Kr ger, S., Gräwe, U., 2015. Fresh oxygen for the Baltic Sea – An exceptional saline inflow after a decade of stagnation. Journal of Marine Systems 148, 152–166. https://doi.org/10.1016/j.jmarsys.2015.03.005 Moros, M., Andersen, T.J., Schulz-Bull, D., Häusler, K., Bunke, D., Snowball, I., Kotilainen, A., Zillén, L., Jensen, J.B., Kabel, K., 2017. Towards an event stratigraphy for Baltic Sea sediments deposited since AD 1900: approaches and challenges. Boreas 46, 129–142. M ller‐Haeckel, A., 1985. Shade-adapted Algae beneath Ice and Snow in the Northern Bothnian Sea. Internationale Revue der gesamten Hydrobiologie und Hydrographie 70, 325–334. https://doi.org/10.1002/iroh.19850700303 Muschitiello, F., Pausata, F.S.R., Watson, J.E., Smittenberg, R.H., Salih, A.A.M., Brooks, S.J., Whitehouse, N.J., Karlatou-Charalampopoulou, A., Wohlfarth, B., 2015. Fennoscandian fresh- water control on Greenland hydroclimate shifts at the onset of the Younger Dryas. Nat Commun 6, 8939. https://doi.org/10.1038/ncomms9939 Myrdal, J., 1999. Det svenska jordbrukets historia. [Bd 2], Jordbruket under feodalismen: 1000–1700. Natur och kultur/LT i samarbete med Nordiska museet och Stift. Lagersberg, Stockholm. Myrdal, J., Morell, M., 2011. The agrarian history of Sweden: from 4000 BC to AD 2000. Nordic Academic Press, Lund. Nordstr m, A., 1968. S dertälje stads historia. D.1-2, Stockholm. Oksanen, J., Blanchet, F.G., Kindt, R., Legendre, P., Minchin, P.R., O’Hara, R.B., Simpson, G.L., Solymos, P., Stevens, M.H.H., Wagner, H., 2019. vegan: Community Ecology Package. Oku, O., Kamatani, A., 1997. Resting spore formation of the marine planktonic diatom Chaetoceros anastomosans induced by high salinity and nitrogen depletion. Marine Biology 127, 515–520. Persson, J., Jonsson, P., 2000. Historical Development of Laminated Sediments – an Approach to Detect Soft Sediment Ecosystem Changes in the Baltic Sea. Marine Pollution Bulletin 40, 122– 134. https://doi.org/10.1016/S0025-326X(99)00180-0 Price, T.D., Arcini, C., Gustin, I., Drenzel, L., Kalmring, S., 2018. Isotopes and human burials at Viking Age Birka and the Mälaren region, east central Sweden. Journal of Anthropological Archaeology 49, 19–38. https://doi.org/10.1016/j.jaa.2017.10.002 Ramsey, C.B., 2008. Deposition models for chronological records. Quaternary Science Reviews, INTegration of Ice-core, Marine and Terrestrial records (INTIMATE): Refining the record of the Last Glacial-Interglacial Transition 27, 42–60. https://doi.org/10.1016/j.quascirev.2007.01.019 Reimer, P.J., Bard, E., Bayliss, A., Beck, J.W., Blackwell, P.G., Bronk Ramsey, C., Buck, C.E., Cheng, H., Edwards, R.L., Friedrich, M., others, 2013. IntCal13 and Marine13 radiocarbon age calibration curves 0-50,000 years cal BP.
76 REFERENCES
Renberg, I., Battarbee, R.W., Mason, B.J., Renberg, I., Talling, J.F., 1990. A 12600 year perspective of the acidification of Lilia Oresjon, southwest Sweden. Philosophical Transactions of the Royal Society of London. B, Biological Sciences 327, 357–361. https://doi.org/10.1098/rstb.1990.0073 Renberg, I., Bindler, R., Bradshaw, E., Emteryd, O., McGowan, S., 2001. Sediment Evidence of Early Eutrophication and Heavy Metal Pollution of Lake Mälaren, Central Sweden. AMBIO: A Journal of the Human Environment 30, 496–502. https://doi.org/10.1579/0044-7447-30.8.496 Risberg, J., Karlsson, S., Bj rck, J. & Elfstrand, B., 1994. Älgpussen: ett arkiv f r strandf rskjutning, vegetationsutveckling och antropogen verksamhet i Järna, S dermanland, under de senaste 8 000 åren. Stockholm: Kvartärgeologiska institutionen Roberts, N., Fyfe, R.M., Woodbridge, J., Gaillard, M.-J., Davis, B. a. S., Kaplan, J.O., Marquer, L., Mazier, F., Nielsen, A.B., Sugita, S., Trondman, A.-K., Leydet, M., 2018. Europe’s lost forests: a pollen-based synthesis for the last 11,000 years. Scientific Reports 8, 716. https://doi.org/ 10.1038/s41598-017-18646-7 Round, F.E., Crawford, R.M., Mann, D.G., 1990. The diatoms: biology & morphology of the genera. Cambridge Univ. Press, Cambridge. R hland, K.M., Paterson, A.M., Smol, J.P., 2015. Lake diatom responses to warming: reviewing the evidence. J Paleolimnol 54, 1–35. https://doi.org/10.1007/s10933-015-9837-3 Sandén, P., Håkansson, B., 1996. Long-term trends in Secchi depth in the Baltic Sea. Limnol. Oceanogr. 41, 346–351. https://doi.org/10.4319/lo.1996.41.2.0346 Saunders, K.M., Taffs, K.H., 2009. Palaeoecology: A tool to improve the management of Australian estuaries. Journal of Environmental Management 90, 2730–2736. https://doi.org/10.1016/j.jenvman.2009.03.001 Savage, C., Elmgren, R., Larsson, U., 2002. Effects of sewage-derived nutrients on an estuarine macrobenthic community. Marine Ecology Progress Series 243, 67–82. Savage, C., Leavitt, P.R., Elmgren, R., 2010. Effects of land use, urbanization, and climate variability on coastal eutrophication in the Baltic Sea. Limnol. Oceanogr. 55, 1033–1046. https://doi.org/10.4319/lo.2010.55.3.1033 SCB, 1995. Handelsg dsel, stallg dsel och kalk i jordbruket; Kväve, fosfor, kalium och CaO i långa regionala tidsserier. Schimanke, S., Meier, H.E.M., Kjellstr m, E., Strandberg, G., Hordoir, R., 2012. The climate in the Baltic Sea region during the last millennium simulated with a regional climate model. Climate of the Past 8, 1419–1433. Schrader, H.-J., Gersonde, R., 1978. Diatoms and silico-flagellates, in: Zachariasse, W.J., Riedel, W.R., Sanfilippo, A., Schmidt, R.R., Brolsma, M.J., Schrader, H.J., Gersonde, R., Drooger, M.M., Broekman, J.A. (Eds.), Utrecht Micropaleontological Bulletins 17, Micropaleontological Coun- ting Methods and Techniques. Loonzetterij Abe, Hoogeveen, The Netherlands, pp. 127–176. Sejrup, H.P., Lehman, S.J., Haflidason, H., Noone, D., Muscheler, R., Berstad, I.M., Andrews, J.T., 2010. Response of Norwegian Sea temperature to solar forcing since 1000 A.D. J. Geophys. Res. 115, C12034. https://doi.org/10.1029/2010JC006264 Seppä, H., Bjune, A.E., Telford, R.J., Birks, H.J.B., Veski, S., 2009. Last nine-thousand years of temperature variability in Northern Europe. Clim. Past 5, 523–535. https://doi.org/ 10.5194/cp-5-523-2009 Sjunnesson, H., Wahlberg, T., 2003. Papper och massa i Österg tland: [från handpappersbruk till processindustri], Skogsindustriernas historiska utskotts skriftserie, 99-2494817-3. Skogsindus- trierna, Stockholm.
77 TRACING ENVIRONMENTAL CHANGE AND HUMAN IMPACT
SMHI, 1995. Sänkta och torrlagda sj ar. SMHI Svenskt vattenarkiv Rapport Nr 62. Smol, J.P., Stoermer, E.F., 2010. The diatoms: applications for the environmental and earth sciences. Cambridge University Press, Cambridge. Snoeijs, P., 1993. Intercalibration and distribution of diatom species in the Baltic Sea. Vol. 1. Opulus press, Uppsala. Snoeijs, P., Balashova, N., 1998. Intercalibration and distribution of diatom species in the Baltic Sea. Vol. 5. Opulus press, Uppsala. Snoeijs, P., Kasperovičienė, J., 1996. Intercalibration and distribution of diatom species in the Baltic Sea. Vol. 4. Opulus press, Uppsala. Snoeijs, P., Potapova, M., 1995. Intercalibration and distribution of diatom species in the Baltic Sea. Vol. 3. Opulus press, Uppsala. Snoeijs, P., Vilbaste, S., 1994. Intercalibration and distribution of diatom species in the Baltic Sea. Vol. 2. Opulus press, Uppsala. Snoeijs, P., Weckstr m, K., 2010. Diatoms and environmental change in large brackish-water ecosystems, in: Smol, J.P., Stoermer, E.F. (Eds.), The Diatoms: Applications for the Environ- mental and Earth Sciences. Cambridge University Press, Cambridge, pp. 287–308. Struck, U., Emeis, K.-C., Voss, M., Christiansen, C., Kunzendorf, H., 2000. Records of southern and central Baltic Sea eutrophication in δ13C and δ15N of sedimentary organic matter. Marine Geology 164, 157–171. https://doi.org/10.1016/S0025-3227(99)00135-8 Sugita, S., 2007. Theory of quantitative reconstruction of vegetation I: pollen from large sites REVEALS regional vegetation composition. The Holocene 17, 229–241. https://doi.org/ 10.1177/0959683607075837 S derhielm, J., Sundblad, K., 1996. The Solstad Cu-Co-Au mineralization and its relation to post- Svecofennian regional shear zones in southeastern Sweden. GFF 118, 47. The BACC II Author Team (Ed.), 2015. Second Assessment of Climate Change for the Baltic Sea Basin, Regional Climate Studies. Springer International Publishing, Cham. ter Braak, C.J.F., Šmilauer, P., 2002. CANOCO Reference Manual and User’s Guide to CANOCO for Windows: Software for Canonical Community Ordination Version 4.5. Microcomputer Power, Ithaca, NY. Tuovinen, N., Weckstr m, K., Virtasalo, J.J., 2010. Assessment of recent eutrophication and climate influence in the Archipelago Sea based on the subfossil diatom record. J Paleolimnol 44, 95– 108. https://doi.org/10.1007/s10933-009-9390-z Verburg, P., 2007. The need to correct for the Suess effect in the application of δ13C in sediment of autotrophic Lake Tanganyika, as a productivity proxy in the Anthropocene. J Paleolimnol 37, 591–602. https://doi.org/10.1007/s10933-006-9056-z Voss, M., Emeis, K.-C., Hille, S., Neumann, T., Dippner, J.W., 2005. Nitrogen cycle of the Baltic Sea from an isotopic perspective. Global Biogeochem. Cycles 19, GB3001. https://doi.org/10.1029/2004GB002338 Voss, M., Larsen, B., Leivuori, M., Vallius, H., 2000. Stable isotope signals of eutrophication in Baltic Sea sediments. Journal of Marine Systems 25, 287–298. https://doi.org/10.1016/S0924- 7963(00)00022-1 Wasmund, N., Nausch, G., Gerth, M., Busch, S., Burmeister, C., Hansen, R., Sadkowiak, B., 2019. Extension of the growing season of phytoplankton in the western Baltic Sea in response to climate change. Marine Ecology Progress Series 622, 1–16. https://doi.org/10.3354/meps12994
78 REFERENCES
Weckstr m, K., 2006. Assessing Recent Eutrophication in Coastal Waters of the Gulf of Finland (Baltic Sea) using Subfossil Diatoms. J Paleolimnol 35, 571–592. https://doi.org/10.1007/s10933-005-5264-1 Weckstr m, K., Juggins, S., 2006. Coastal Diatom–Environment Relationships from the Gulf of Finland, Baltic Sea. Journal of Phycology 42, 21–35. https://doi.org/10.1111/j.1529-8817.2006.00166.x Weckstr m, K., Korhola, A., Weckstr m, J., 2007. Impacts of Eutrophication on Diatom Life Forms and Species Richness in Coastal Waters of the Baltic Sea. AMBIO: A Journal of the Human Environment 36, 155–160. https://doi.org/10.1579/0044-7447(2007)36[155:IOEODL]2.0.CO;2 Willén, E., 2001. Four Decades of Research on the Swedish Large Lakes Mälaren, Hjälmaren, Vättern and Vänern: The Significance of Monitoring and Remedial Measures for a Sustainable Society. ambi 30, 458–466. https://doi.org/10.1579/0044-7447-30.8.458 Willis, K.J., Birks, H.J.B., 2006. What Is Natural? The Need for a Long-Term Perspective in Bio- diversity Conservation. Science 314, 1261–1265. https://doi.org/10.1126/science.1122667 Willumsen, P.S., Filipsson, H.L., Reinholdsson, M., Lenz, C., 2013. Surface salinity and nutrient variations during the Littorina Stage in the Får Deep, Baltic Sea. Boreas 42, 210–223. https://doi.org/10.1111/j.1502-3885.2012.00286.x Winnfors, E., 2009. – och vid Himmerfjärden ligger Syvab. Örebro: Ohlson & Winnfors Witkowski, A., Lange-Bertalot, H., Metzeltin, Ditmar., 2000. Diatom flora of marine coasts / Icono- graphia Diatomologica Volume 7. Gantner; Ruggell. Wood, S.N. (2017) Generalized Additive Models: An Introduction with R (2nd edition). Chapman and Hall/CRC. Yasuhara, M., Hunt, G., Breitburg, D., Tsujimoto, A., Katsuki, K., 2012. Human-induced marine ecological degradation: micropaleontological perspectives. Ecology and Evolution 2, 3242– 3268. https://doi.org/10.1002/ece3.425 Zillén, L., Conley, D.J., 2010. Hypoxia and cyanobacteria blooms – are they really natural features of the late Holocene history of the Baltic Sea? Biogeosciences 7, 2567–2580. https://doi.org/10.5194/bg-7-2567-2010 Zillén, L., Conley, D.J., Andrén, T., Andrén, E., Bj rck, S., 2008. Past occurrences of hypoxia in the Baltic Sea and the role of climate variability, environmental change and human impact. Earth- Science Reviews 91, 77–92. https://doi.org/10.1016/j.earscirev.2008.10.001
Webpages Naturvårdsverket, 2020. Våtmark. https://www.naturvardsverket.se/Sa-mar-miljon/ Vatten/Vatmark/ SMHI, 2019. Swedish Metrological and Hydrological Institute (2019). Swedish Metrological and Hydrological Institute (SMHI) Open Access Data (2019). Available online at: https://www.smhi.se/klimatdata/oceanografi/havsmiljodata/marinamiljoovervaknings data (access December 2, 2019). (Swedish Metrological Hydrological Institute, 2018) SMHI, 2020. Vattenwebb https://www.smhi.se/data/hydrologi/vattenwebb VISS, 2019. Vatteninformation Sverige (2019). Vatteninformation Sverige, (VISS) Open Access Data (2018). Available online at: http://viss.lansstyrelsen.se (accessed December 2, 2019). Värmd kommun, 2019. (https://www.varmdo.se 2019).
79
Tack
F rst och främst vill jag tacka mina handledare Elinor Andrén, Thomas Andrén och Mikael L nn. Elinor, tack f r att du lät mig bli en del av det här projektet. Tack f r att du så gener st har delat med dig av kunskap och material, och tack f r alla givande diskussioner. Tack f r all konstruktiv kritik, st ttning och uppmuntran. Ditt enga- gemang i forskning är så inspirerande och jag är otroligt tacksam f r att ha fått ha dig som handledare! Thomas, tack f r att du ppnade d rren till den spännande och komplexa värld som datering av Östersj sediment är. Det har varit utmanande, lärorikt, och ärligt talat riktigt kul emellanåt. Micke, tack f r statistikvägledning. Ditt lugn och tålamod är verkligen beundransvärt. Tack till mina handledare f r att era d rrar, telefoner och sinnen alltid varit ppna. Tack också f r att ni visat f rståelse när livet kommit emellan, det har underlättat väldigt mycket. Thank you Wenxin, Helena, Anna, Anne-Birgitte et al. for nice cooperation on the Gåsfjärden paper and for welcoming me to Lund. Matthias and Thorbj rn, thank you for cooperation on paper I and II. Thank you, Mona and Oscar for very valuable feed- back at my predissertation seminar. Richard, thank you for taking an interest in my project and for spending time explaining basically everything from how to set up a GitHub account to how the transfer function works. Fun fun fun. Thank you, Markus and Florian for making the climate data available. It was more complicated than I could have ever imagined! Tack till kapten och besättning på M/S Fyrbyggaren. Tack till personalen på Ask . Anders, tack f r hjälp med ytterst praktisk probleml sning. Att du bara kan trolla fram 40 mortlar eller 100 små glasburkar precis när jag desperat beh ver dem är fantastiskt. Tack Heike f r hjälp med de geokemiska analyserna. Tack Marianne f r assistans med SEM. Tack Malin f r assistans med Itrax. Tack Karin f r hjälpen med GIS-underlaget som krånglade i somras. I want to thank fellow PhD-students here at S dert rn. These years would have been much lonelier, and far less memorable without you. Thank you Falkje for being the absolute best partner in crime one could have. I am so lucky I got to share the first years of this PhD journey with you. Thank you Olena for being an awesome office mate, and for showing me nice pollen every now and then. Josefine, I am endlessly grateful for all the times you have picked me up and kept me on track during times of doubt. Thank you so much for the support, you are an amazing colleague and friend. Erika, Igne and Sophie, thank you for sharing the ups and downs of trying to finish a PhD this last year. I am cheering for you! Thank you also Tove, Christian, Mathilde, Kajsa-Stina, Linn, Elise, Juliana, Therese, Ola, Nikolina, Mohanad, Anton, Nasim, Tiina, Petter, Natasja, Sara, Natalya, Pernilla, Ralph and Martin. Thank you,
81 TRACING ENVIRONMENTAL CHANGE AND HUMAN IMPACT
Andrea, Anushree, Inger, Sara, Patrik, Kari, Maria and the rest of the seniors at the department. Being a part of the interdisciplinary working environment at S dert rn has been both fun and instructive. However, it has also been so important to meet people within my scientific field, and I am very thankful for the courses, workshops and conferences I have been able to attend. Thank you, School of Natural Sciences, Technology and Environmental Studies for providing such opportunities. Thanks to all the nice people I have met, Mike, Jonathan, Jenny, Sami, Christos, Hannah and many more. Jag vill uttrycka min tacksamhet f r betald f räldraledighet och skattefinansierad barnomsorg. Tack till f rskolan Skogslyan. Tack min familj och mina vänner. Tack Mamma och Pappa f r att ni tog med mig ut i naturen när jag var barn. Tack Magnus, Veronica, Tuva och Vidar, att vi har varandra är guld. Emma, tack f r allt kul häng och g tt snack, och tack f r att du mellan varven fått mig att tänka på annat det här senaste halvåret, det har varit väl- beh vligt. Lullis herregud tack f r de här 17 (?!) åren, och tack f r alla friskvårds- samtal. Må vi f r alltid vara varandras cykel på k pet. Olle, tack f r att du tror på min f rmåga även när jag inte g r det. Tack f r att du lyssnat, st ttat och peppat, och tack f r att du alltid har min rygg. Det är en ynnest att få dela livet med någon som blir lika exalterad som mig av slemmet som växer på stenarna i Emån (jaja, nästan i alla fall). Jon, du är det finaste jag vet, tack f r att du varje dag har påmint mig om vad som är viktigt. Till de jag gl mt pga härdsmälta i hjärnan, f rlåt och tack!
My PhD studies have been funded by the Baltic and East European Graduate School and the Foundation for Baltic and East European Studies within the project UPPBASER – Understanding Past and Present Baltic Sea Ecosystem Response – background for a sustainable future (grant 1562/3.1.1/2013).
82 Supplementary table 1. Diatom taxa found in the sediment records from Kanholmsfjärden, Ådfjär- den, Himmerfjärden, Bråviken and Gåsfjärden. Life-form B=Benthic, P=Pelagic. Salinity distribution F=Freshwater, BF=Brackish-freshwater, B=Brackish, BM=Brackish-marine according to BMB= Snoeijs (1993), Snoeijs and Balashova (1998), Snoeijs and Kasperovičienė (1996), Snoeijs and Potapova (1995), Snoeijs and Vilbaste (1994). KLB= Krammer and Lange-Bertalot (1991a, 1991b, 1988, 1986). Name Author Year Life- Life-form Salinity Reference form (specified) distribution
Achnanthes amoena Husdedt 1952 B Epilithic and B BMB epiphytic Achnanthes brevipes C.A. Agardh 1824 B Epiphytic and BM BMB epilithic Achnanthes dispar Cleve 1891 B Epipsammic B BMB
Achnanthes longipes C.A. Agardh 1824 B Epiphytic and BM BMB epilithic Achnanthidium K tzing 1844 B Epiphytic BF BMB microcephalum Achnanthes Hustedt 1933 B Epipsammic B BMB lemmermannii Achnanthes minuscula Hustedt 1945 B Epipsammic B BMB
Achnanthes oblongella Østrup 1902 B Epiphytic and F BMB epilithic Achnanthes pericava Carter 1966 B Epipsammic B BMB
Achnanthes punctulata Simonsen 1959 B Epipsammic B BMB
Achnanthes rupestoides Hohn 1961 B BMB
Achnanthidium (K tzing) Czarnecki 1994 B Epiphytic BF BMB minutissimum Actinocyclus normannii (Gregory) Hustedt 1957 P F BMB
Actinocyclus octonarius (W. Smith) Hendey 1954 P BF BMB var. crassus Actinocyclus octonarius (Brébisson) Hendey 1954 P F BMB var. tenellus Amphora coffeaeformis (C.A. Agardh) 1844 B Epiphytic, B BMB K tzing metaphytic and epipelic Amphora fogediana Krammer 1985 B Epipelic F BMB
Amphora holsatica Hustedt 1925 B Epipelic B BMB
Amphora inariens Krammer 1980 B KLB
Amphora copulata (K tzing) 1986 B Epipelic and F BMB Schoeman & R.E.M. epilithic Archibald
83 Amphora macilenta Gregory var. Typica 1895 B Epipelic B BMB Cleve Amphora ovalis (K tzing) K tzing 1844 B Epipelic and BF BMB epilithic Amphora pediculus (K tzing) Grunow 1875 B Epipelic and BF BMB in A. Schmidt et al. epilithic Amphora veneta K tzing 1844 B Epipelic BF BMB
Amphora wisei (Salah) Simonsen 1962 B Epipelic MB BMB
Aneumastus minor (Hustedt) Lange- 1993 B Epipelic BF BMB Bertalot Asterionella formosa Hassall 1850 P F BMB
Aulacoseira ambigua (Grunow) Simonsen 1979 P KLB
Aulacoseira crenulata (Ehrenberg) 1848 B KLB Thwaites Aulacoseira granulata (Ehrenberg) 1979 P KLB Simonsen Aulacoseira islandica (O. M ller) 1979 P F BMB Simonsen Aulacoseira subarctica (O. M ller) 1988 P F BMB Haworth Bacillaria paxillifera (O.F. M ller) 1951 B Epipelic and BF BMB Hendey epilithic Berkeleya rutilans (Trentepohl) 1880 B Epilithic and B BMB Grunow epiphytic Caloneis aemula (A. Schmidt) Cleve 1894 B Epipelic B BMB
Caloneis amphisbaena (Bory) Cleve 1894 B Epipelic B BMB
Caloneis hyalina Hustedt 1938 B Aerophil KLB
Caloneis bacillum (Grunow) Cleve 1894 B Epipelic F BMB
Caloneis undulata (Gregory) Krammer 1985 B KLB
Cavinula cocconeiformis (Gregory ex 1990 B Epipelic F BMB Greville) D.G. Mann & A.J. Stickle in Round et al. Cavinula (Hustedt) D.G. 1990 B Epipelic BF BMB pseudoscutiformis Mann & A.J. Stickle Cocconeis disculus (Schumann) Cleve 1882 B Epipsammic F BMB in Cleve & Jentzsch Cocconeis neothumensis Krammer 1990 B Epipsammic B BMB
Cocconeis pediculus Ehrenberg 1838 B Epiphytic BF BMB
Cocconeis placentula Ehrenberg 1838 B Epiphytic and BF BMB epilithic
84 Cocconeis scutellum Ehrenberg 1833 B Epiphytic B BMB
Cocconeis speciosa Gregory 1915 B Epiphytic BM BMB
Cocconeis (W: Smith) Okuno 1957 B Epiphytic BM BMB stauroneiformis Coscinodiscus granii Gough 1905 B B BMB
Craticula cuspidata (K tzing) D.G. 1990 B BMB Mann in Round et al. Ctenophora pulchella (Ralfs ex K tzing) 1986 B Epiphytic BF BMB Williams & Round Cyclostephanos dubius (Fricke) Round 1982 P F BMB
Cyclotella antiqua W. Smith 1853 P KLB
Cyclotella atomus Hustedt 1937 P F BMB
Cyclotella Prasad 1990 P B BMB choctawhatcheeana Cyclotella meneghiniana K tzing 1844 P BF BMB
Cyclotella ocellata Pantocsek 1901 P KLB
Cyclotella radiosa (Grunow) 1900 P F BMB Lemmermann Cyclotella rossii Håkansson 1990 P KLB
Cyclotella schumannii (Grunow) 1990 P Fossil BMB Håkansson Cyclotella stelligra Cleve & Grunow in 1882 P F BMB Van Heurck Cyclotella striata (K tzing) Grunow 1880 P KLB in Cleve & Grunow Cyclotella tripartita Håkansson 1990 P BMB
Cymbella amphioxys (K tzing) Cleve 1894 B KLB
Cymbella hebridica (Grunow in Cleve) 1894 B KLB Cleve Cymbella lanceolata (Ehrenberg) 1878 B Epiphytic and BF BMB Kirchner epilithic Cymbella pusilla Grunow in A. 1875 B Epipelic and BF BMB Schmidt et al. epilithic Denticula tenuis K tzing 1844 B Epilithic KLB
Diatoma bottnica Snoeijs in Snoeijs & 1998 B Epiphytic B BMB Potatova Diatoma moniliformis K tzing 1833 B Epiphytic B BMB
85 Diatoma tenuis C. A. Agardh 1812 P Epiphytic (?) BF BMB and pelagic Diatoma vulgaris Bory 1824 B Epiphytic BF BMB
Dickieia subinflata (Grunow) 1994 B Epipellic BM BMB D.G.Mann Diploneis didyma (Ehrenberg) 1854 B Epipelic B BMB Ehrenberg Diploneis elliptica (K tzing) Cleve 1891 B KLB
Diploneis oculata (Brébisson) Cleve 1894 B Epipelic BF BMB
Diploneis smithii (Brébisson) Cleve 1894 B Epipelic BF BMB
Diploneis stroemii Hustedt 1937 B Epipelic B BMB
Encyonema ceaspitosum K tzing 1849 B Epilithic BF BMB
Encyonema lacustre (C. A. Agardh) D. 1990 B Epilithic BF BMB G. Mann Encyonema silesiacum (Bleisch in 1990 B Epiphytic and F BMB Rabenhorst) D.G. epilithic Mann Encyonopsis (Grunow) Krammer 1997 B Epipelic and F BMB microcephala epilithic Epithemia adnata (K tzing) Brébisson 1838 B Epiphytic B BMB
Epithemia sorex K tzing 1844 B Epiphytic BF BMB
Epithemia turgida (Ehrenberg) 1844 B Epiphytic BF BMB K tzing Fallacia clepsidroides Witkowski 1994 B Epipelic BM BMB
Fallacia florinae (M ller) Witkowski 1993 B Epipelic B BMB
Fallacia litoricola (Hustedt) D.G. 1990 B Epipelic MB BMB Mann in Round et al. Fallacia pseudony (Hustedt) D.G. 1990 B Epipelic BM BMB Mann in Round et al. Fallacia pygmeae (K tzing) A.J. 1990 B Epipelic BF BMB Stickle & D.G. Mann Fragilaria crotensis Kitton 1869 P F BMB
Fragilaria capucina Desmaziéres 1825 P F BMB
Fragilaria delicatissima (W. Smith) Lange- 1980 P KLB Bertalot Fragilaria nanana Lange-Bertalot 1991 P KLB
86 Fragilaria neoproducta Lange-Bertalot 1991 KLB
Fragilaria parasitica (W. Smith) Grunow 1881 B Epiphytic F BMB in Van Heurck Fragilariopsis cylindrus (Grunow) Krieger 1954 P BF BMB in Helmcke & Krieger Frustulia rhomboides (Ehrenberg) De 1891 B KLB Toni Frustulia vulgaris (Thwaites) De Toni 1891 B KLB
Gomphonema Ehrenberg 1832 B Epiphytic KLB acuminatum Gomphonema olivaceum (Hornemann) 1838 B Epiphytic and BF BMB Brébisson epilithic Gomphonema parvulum (K tzing) K tzing 1849 B Epiphytic and BF BMB epilithic Gomphonemopsis exigua (K tzing) Medlin 1986 B Epiphytic BM BMB
Gomphonemopsis (Simonsen) Medlin 1986 B Epiphytic B BMB pseudexigua Grammatophora marina (Lyngbye) K tzing 1844 B Epiphytic BM BMB
Grammatophora Ehrenberg 1854 B Epiphytic BM BMB oceanica Gyrosigma acuminatum (K tzing) 1853 B Epipelic BF BMB Rabenhorst Hantzschia amphioxys (Ehrenberg) 1880 B KLB Grunow in Cleve & Grunow Hyalodiscus scoticus (K tzing) Grunow 1879 B Epiphytic MB BMB
Karayevia clevei (Grunow) 1999 B Epipsammic F BMB Bukhtiyarova Licomphora debilis (K tzing) Grunow 1881 B Epiphytic B BMB in Van Heurck Licomphora gracilis (K tzing) Peragallo 1901 B Epiphytic B BMB & Peragallo Martyana atomus (Hustedt) Snoeijs 1991 B Epipsammic B BMB
Martyana schulzii (Brockmann) 1991 B Epipsammic B BMB Snoeijs Mastogloia baltica Grunow in Van 1880 B Epipelic and BF BMB Heurck epilithic Mastogloia braunii Grunow 1863 B Epipelic and BF BMB epilithic Mastogloia elliptica (C.A. Agardh) Cleve 1893 B Epipelic and BF BMB epilithic Mastogloia exigua Lewis 1861 B Epipelic and BM BMB epilithic
87 Mastogloia lanceolata Thwaites in W. 1856 B Epipelic and B BMB Smith epilithic Mastogloia pumila (Cleve & M ller) 1895 B Epipelic and BF BMB Cleve epilithic Mastogloia pusilla Grunow 1878 B Epipelic and B BMB epilithic Mastogloia smithii Thwaites 1856 B Epipelic and BF BMB epilithic Mastogloia smithii var. Grunow 1878 B Epipelic and B BMB amphicephala epilithic Melosira arctica Dickie 1852 P and on sea ice B BMB
Melosira lineata (Dillwyn) C.A. 1824 B Epilithic and BF BMB Agardh epiphytic Melosira moniliformis (O.F. M ller) C.A. 1824 B Epilithic and B BMB Agardh epiphytic Melosira nummuloides C.A. Agardh 1824 Epilithic, B BMB epiphytic and pelagic Melosira undulata (Ehrenberg) 1844 P KLB K tzing Meridion circulare (Greville) C.A. 1831 B Epilithic and FB BMB Agardh epiphytic Navicula arenaria Donkin 1861 B Epipelic MB BMB
Navicula capitata var. (Grunow) R. Ross 1947 B Epipelic BF BMB hungarica Navicula cryptocephala K tzing 1844 B Epipelic F BMB
Navicula eidrigiana J.R. Carter 1979 B Epipelic BF BMB
Navicula flanatica Grunow 1860 B Epipelic B BMB
Navicula germainii Wallace 1960 B Epipelic B BMB
Navicula gregaria Donkin 1861 B Epipelic and B BMB epilithic Navicula lanceolata (C.A. Agardh) 1838 B Epilithic BF BMB Ehrenberg Navicula lesmonensis Hustedt 1957 B Epipelic F BMB
Navicula oestrupii Schulz 1926 B Epipelic B BMB
Navicula pavillardii Hustedt 1939 B Epipelic B BMB
Navicula peregrina (Ehrenberg) 1844 B Epipelic B BMB K tzing Navicula perminuta Grunow in Van 1880 B Epilithic B BMB Heurck Navicula phyllepta K tzing 1844 B Epipelic B BMB
88 Navicula radiosa K tzing 1844 B Epipelic F BMB
Navicula ramossisima (C.A. Agardh) Cleve 1895 B Epilithic BM BMB
Navicula rhyncocephala K tzing 1844 B Epipelic BF BMB
Navicula salinarum Grunow in Cleve & 1880 B Epipelic BF BMB Grunow Navicula scutelloides W. Smith in 1856 B Epipelic F BMB Gregory Navicula seminulum Grunow 1860 KLB
Navicula slevicensis Grunow in Van 1880 B Epipelic F BMB Heurck Navicula starmachioides (Witkowski & 1996 B Epipelic B BMB Lange-Bertalot) Witkowski in Metzeltin & Witkowski Navicula stroemii Hustedt 1931 B KLB
Navicula supralitoralis Aleem & Hustedt 1951 B Epipelic B BMB
Nitzschia bacillum Hustedt 1922 B Epipelic F BMB
Nitzschia elegantula Grunow in Van 1881 B Epipelic and B BMB Heurck epilithic Nitzschia dissipata (K tzing) Grunow 1862 B Epipelic F BMB
Nitzschia distans Gregory 1857 B Epipelic MB BMB
Nitzschia dubia W. Smith 1853 B Epipelic BF BMB
Nitzschia frigida Grunow in Cleve & 1880 P On ice BF BMB Grunow Nitzschia inconspicua Grunow 1862 B Epilithic BF BMB
Nitzschia lorenzia Grunow in Cleve & 1880 B Epipelic B BMB Grunow 1880 Nitzschia paleacea (Grunow) Grunow 1881 B Epilithic BF BMB in Van Heurck Nitzschia pusilla Grunow 1862 B Epipelic B BMB
Nitzschia salinicola Aleem & Hustedt 1951 B Epipelic BF BMB
Nitzschia sigmoidea (Nitzsch) W. Smith 1853 B Epipelic B BMB
Nitzschia thermaloides Hustedt 1955 B Epilithic BF BMB
Opephora guenter-grassii (Witkowski & 1993 B Witkowski Lange-Bertalot) et al. 2000 Sabbe & Vyverman
89 Opephora marina (Gregory) Petit 1888 B Epipsammic MB BMB
Opephora mutabilis Sabbe & Wyverman 1995 B Epipsammic B BMB and epiphytic Pauliella taeniata (Grunow) Round & 1997 P and on sea ice B BMB Basson Petroneis marina (Ralfs in Pritchard) 1990 B Epipelic BM BMB D.G. Mann Pinnularia apendiculata (Agardh) Cleve 1895 B Epipelic B BMB
Pinnularia borealis Ehrenberg 1843 B KLB
Pinnularia krockii (Grunow) Cleve 1895 B KLB
Pinnularia elegans (W. Smith) 1992 B Epipelic B BMB Krammer Pinnularia lundii Hustedt 1954 B Epipelic BF BMB
Placoneis clementis (Grunow) E.J. Cox 1987 B Epipelic B BMB
Placoneis gastrum (Ehrenberg) 1903 B Epipelic F BMB Mereschkowsky Placoneis placentula (Ehrenberg) 1908 B Epipelic BF BMB Heinzerling Planothidium calcar (Cleve) M.B. Ed- 2001 B Epipsammic F BMB lund in M.B. Edlund et al. Planothidium (K tzing) Round & 1996 B Epipsammic BF BMB delicatulum Bukhtiyarova and epilithic
Planothidium dispar (Cleve) Witkowski, 2000 B KLB Lange-Bertalot & Metzeltin Planothidium dubium (Grunow) Round & 1996 B Epipsammic F BMB Bukhtiyarova and epilithic Planothidium (Lange-Bertalot) 1999 B Epipsammic F BMB frequentissimum Lange-Bertalot and epilithic Planothidium oestrupii (Cleve-Euler) M.B. 2001 B Epipsammic F BMB Edlund in M.B. Edlund et al. Planothidium rostratum (Østrup) Lange- 1999 B Epipsammic F BMB Bertalot and epilithic Psammothidium bioretii (H.Germain) 1996 B Epiphytic F BMB Bukhtiyarova & Round Psammothidium rossii (Hustedt) 1996 B Epipsammic F BMB Bukhtiyarova & and epilithic Round Pseudopodosira westii Brander 1935 B, mainly BMB fossil Pseudosolenia calcar-avis (Schultze) 1986 P fossil BMB Sundstr m
90 Pseudostaurosira (Grunow) Williams 1987 B Epipsammic BF BMB brevistriata & Round Pseudostaurosira elliptica (Schumann) 2006 B Epipsammic B BMB Edlund, Morales & Spaulding Pseudostaurosira (Grunow) Sabbe & 1995 B Epipsammic B BMB perminuta Vyverman Pseudostaurosira zeilleri (Héribaud) 1987 B Epipsammic B BMB Williams & Round Pteroncola inane (Giffen) Round 1990 B Epiphytic BM BMB
Rhabdonema arcuatum (Lyngbye in 1844 B Epiphytic and BM BMB Hornemann) epilithic K tzing Rhabdonema minutum K tzing 1844 B Epiphytic and BM BMB epilithic Rhoicosphenia curvata (K tzing) Grunow 1860 B Epiphytic and B BMB epilithic Rhopalodia acuminata Krammer in Lange- 1987 B Epipelic and BM BMB Bertalot & epilithic Krammer Rhopalodia gibba (Ehrenberg) O. 1895 B Epipelic and BF BMB M ller epilithic Sellaphora pupula (K tzing) 1902 B Epipelic F BMB Mereschkowsky Skeletonema costatum (Greville) Cleve 1878 P B BMB
Skeletonema subsalsum (A. Cleve) Bethge 1928 P F BMB
Stauroneis spicula Hickie 1874 B Epilithic B BMB
Staurophora salina (W. Smith) 1903 B Epipelic F BMB Mereschkowsky Staurophora wislouchii (Poretzky & 1990 B Epipelic F BMB Anisimova) D.G. Mann in Round et al. Staurosira construens Ehrenberg 1843 B Epipsammic F BMB
Staurosira venter (Ehrenberg) Cleve 1879 B Epipsammic BF BMB & J.D. M ller Staurosirella martyi (Héribaud-Joseph) 2006 B Epipsammic F BMB E.A. Morales & K.M. Manoylov Stephanodiscus Grunow in Cleve & 1880 P BF BMB hantzschii Grunow Stephanodiscus medius Håkansson 1986 P BMB
Stephanodiscus (K tzing) Cleve & 1878 P F BMB minutulus M ller
91 Stephanodiscus parvus Stoermer & 1984 P F BMB Håkansson Stephanodiscus neoastrea Håkansson & 1986 P F BMB Hickel Surirella brebissonii Krammer & Lange- 1987 B Epipelic and BF BMB Bertalot epilithic Surirella minuta Brébisson in 1849 B Epipelic and F BMB K tzing epilithic Surirella turgida W. Smith 1853 B KLB
Synedra acus K tzing 1844 B Epiphytic F BMB
Synedra ulna (Nitzsch) Ehrenberg 1832 B Epiphytic F BMB
Tabellaria flocculosa (Roth) K tzing 1844 B Epilithic and F BMB epiphytic
Tabellaria fenestrata (Lyngbye) K tzing 1844 P F BMB
Tabularia fasciculata (C.A. Agardh) 1986 B Epiphytic BM BMB Williams & Round Tabularia tabulata (C.A. Agardh) 1992 B Epiphytic BF BMB Snoeijs Thalassionema (Grunow) Grunow 1932 P BM BMB nitzschioides ex Hustedt Thalassiosira baltica (Grunow) 1901 P BF BMB Ostenfield Thalassiosira eccentrica (Ehrenberg) Cleve 1904 P MB BMB
Thalassiosira guillardii Hasle 1978 P B BMB
Thalassiosira hyperborea (Berg) Hasle 1989 P B BMB var lacunosa Thalassiosira hyperborea (Cleve-Euler) Hasle 1989 P BF BMB var pelagica Thalassiosira lacustris (Grunow) Hasle in 1977 P F BMB Hasle & Fryxell Thalassiosira levanderi Van Goor 1924 P B BMB
Thalassiosira oestrupii (Ostenfield) Hasle 1972 P fossil BMB
Thalassiosira Makarova 1979 P B BMB proschkinae Thalassiosira weissflogii (Grunow) Fryxell & 1977 P B BMB Hasle Tryblionella apiculata Gregory 1857 B Epipelic B BMB
Tryblionella debilis Arnott ex O'Meara 1873 B KLB
Tryblionella levidensis W. Smith 1856 B Epipelic B BMB
92 Tryblionella navicularis (Brébisson) Ralfs in 1861 B Epipelic B BMB Pritchard Tryblionella punctata W. Smith 1853 B Epipelic B BMB
Tryblionella salinarum (Grunow in Cleve & 1889 B Epipelic BF BMB Grunow) Pelletan
93
S dert rn Doctoral Dissertations
1. Jolanta Aidukaite, The Emergence of the Post-Socialist Welfare State: The case of the Baltic States: Estonia, Latvia and Lithuania, 2004 2. Xavier Fraudet, Politique étrangère française en mer Baltique (1871–1914): De l’exclusion à l’affirmation, 2005 3. Piotr Wawrzeniuk, Confessional Civilising in Ukraine: The Bishop Iosyf Shumliansky and the Introduction of Reforms in the Diocese of Lviv 1668–1708, 2005 4. Andrej Kotljarchuk, In the Shadows of Poland and Russia: The Grand Duchy of Lithuania and Sweden in the European Crisis of the mid-17th Century, 2006 5. Håkan Blomqvist, Nation, ras och civilisation i svensk arbetarr relse f re nazismen, 2006 6. Karin S Lindel f, Om vi nu ska bli som Europa: K nsskapande och normalitet bland unga kvinnor i transitionens Polen, 2006 7. Andrew Stickley. On Interpersonal Violence in Russia in the Present and the Past: A Sociological Study, 2006 8. Arne Ek, Att konstruera en uppslutning kring den enda vägen: Om folkr relsers modernisering i skuggan av det Östeuropeiska systemskiftet, 2006 9. Agnes Ers, I mänsklighetens namn: En etnologisk studie av ett svenskt biståndsprojekt i Rumänien, 2006 10. Johnny Rodin, Rethinking Russian Federalism: The Politics of Intergovernmental Relations and Federal Reforms at the Turn of the Millennium, 2006 11. Kristian Petrov, Tillbaka till framtiden: Modernitet, postmodernitet och generationsidentitet i Gorbačevs glasnost’ och perestrojka, 2006 12. Sophie S derholm Werk , Patient patients? Achieving Patient Empowerment through Active Participation, Increased Knowledge and Organisation, 2008 13. Peter B tker, Leviatan i arkipelagen: Staten, f rvaltningen och samhället. Fallet Estland, 2007 14. Matilda Dahl, States under scrutiny: International organizations, transformation and the con- struction of progress, 2007 15. Margrethe B. S vik, Support, resistance and pragmatism: An examination of motivation in language policy in Kharkiv, Ukraine, 2007 16. Yulia Gradskova, Soviet People with female Bodies: Performing beauty and maternity in Soviet Russia in the mid 1930–1960s, 2007 17. Renata Ingbrant, From Her Point of View: Woman’s Anti-World in the Poetry of Anna Świrszczyńska, 2007 18. Johan Eellend, Cultivating the Rural Citizen: Modernity, Agrarianism and Citizenship in Late Tsarist Estonia, 2007 19. Petra Garberding, Musik och politik i skuggan av nazismen: Kurt Atterberg och de svensk-tyska musikrelationerna, 2007 20. Aleksei Semenenko, Hamlet the Sign: Russian Translations of Hamlet and Literary Canon Formation, 2007 21. Vytautas Petronis, Constructing Lithuania: Ethnic Mapping in the Tsarist Russia, ca. 1800–1914, 2007 22. Akvile Motiejunaite, Female employment, gender roles, and attitudes: The Baltic countries in a broader context, 2008 23. Tove Lindén, Explaining Civil Society Core Activism in Post-Soviet Latvia, 2008 24. Pelle Åberg, Translating Popular Education: Civil Society Cooperation between Sweden and Estonia, 2008 25. Anders Nordstr m, The Interactive Dynamics of Regulation: Exploring the Council of Europe’s monitoring of Ukraine, 2008 26. Fredrik Doeser, In Search of Security After the Collapse of the Soviet Union: Foreign Policy Change in Denmark, Finland and Sweden, 1988–1993, 2008 27. Zhanna Kravchenko. Family (versus) Policy: Combining Work and Care in Russia and Sweden, 2008 28. Rein J riado, Learning within and between public-private partnerships, 2008 29. Elin Boalt, Ecology and evolution of tolerance in two cruciferous species, 2008 30. Lars Forsberg, Genetic Aspects of Sexual Selection and Mate Choice in Salmonids, 2008 31. Eglė Rindzevičiūtė, Constructing Soviet Cultural Policy: Cybernetics and Governance in Lithuania after World War II, 2008 32. Joakim Philipson, The Purpose of Evolution: ‘Struggle for existence’ in the Russian-Jewish press 1860–1900, 2008 33. Sofie Bedford, Islamic activism in Azerbaijan: Repression and mobilization in a post-Soviet context, 2009 34. Tommy Larsson Segerlind, Team Entrepreneurship: A process analysis of the venture team and the venture team roles in relation to the innovation process, 2009 35. Jenny Svensson, The Regulation of Rule-Following: Imitation and Soft Regulation in the European Union, 2009 36. Stefan Hallgren, Brain Aromatase in the guppy, Poecilia reticulate: Distribution, control and role in behavior, 2009 37. Karin Ellencrona, Functional characterization of interactions between the flavivirus NS5 protein and PDZ proteins of the mammalian host, 2009 38. Makiko Kanematsu, Saga och verklighet: Barnboksproduktion i det postsovjetiska Lettland, 2009 39. Daniel Lindvall, The Limits of the European Vision in Bosnia and Herzegovina: An Analysis of the Police Reform Negotiations, 2009 40. Charlotta Hillerdal, People in Between – Ethnicity and Material Identity: A New Approach to Deconstructed Concepts, 2009 41. Jonna Bornemark, Kunskapens gräns – gränsens vetande, 2009 42. Adolphine G. Kateka, Co-Management Challenges in the Lake Victoria Fisheries: A Context Approach, 2010 43. René Le n Rosales, Vid framtidens hitersta gräns: Om pojkar och elevpositioner i en multietnisk skola, 2010 44. Simon Larsson, Intelligensaristokrater och arkivmartyrer: Normerna f r vetenskaplig skicklighet i svensk historieforskning 1900–1945, 2010 45. Håkan Lättman, Studies on spatial and temporal distributions of epiphytic lichens, 2010 46. Alia Jaensson, Pheromonal mediated behaviour and endocrine response in salmonids: The impact of cypermethrin, copper, and glyphosate, 2010 47. Michael Wigerius, Roles of mammalian Scribble in polarity signaling, virus offense and cell-fate determination, 2010 48. Anna Hedtjärn Wester, Män i kostym: Prinsar, konstnärer och tegelbärare vid sekelskiftet 1900, 2010 49. Magnus Linnarsson, Postgång på växlande villkor: Det svenska postväsendets organisation under stormaktstiden, 2010 50. Barbara Kunz, Kind words, cruise missiles and everything in between: A neoclassical realist study of the use of power resources in U.S. policies towards Poland, Ukraine and Belarus 1989–2008, 2010 51. Anders Bartonek, Philosophie im Konjunktiv: Nichtidentität als Ort der M glichkeit des Utopischen in der negativen Dialektik Theodor W. Adornos, 2010 52. Carl Cederberg, Resaying the Human: Levinas Beyond Humanism and Antihumanism, 2010 53. Johanna Ringarp, Professionens problematik: Lärarkårens kommunalisering och välfärdsstatens f rvandling, 2011 54. Sofi Gerber, Öst är Väst men Väst är bäst: Östtysk identitetsformering i det f renade Tyskland, 2011 55. Susanna Sj din Lindenskoug, Manlighetens bortre gräns: Tidelagsrättegångar i Livland åren 1685–1709, 2011 56. Dominika Polanska, The emergence of enclaves of wealth and poverty: A sociological study of residential differentiation in post-communist Poland, 2011 57. Christina Douglas, Kärlek per korrespondens: Två f rlovade par under andra hälften av 1800- talet, 2011 58. Fred Saunders, The Politics of People – Not just Mangroves and Monkeys: A study of the theory and practice of community-based management of natural resources in Zanzibar, 2011 59. Anna Rosengren, Åldrandet och språket: En språkhistorisk analys av h g ålder och åldrande i Sverige cirka 1875–1975, 2011 60. Emelie Lilliefeldt, European Party Politics and Gender: Configuring Gender-Balanced Parlia- mentary Presence, 2011 61. Ola Svenonius, Sensitising Urban Transport Security: Surveillance and Policing in Berlin, Stockholm, and Warsaw, 2011 62. Andreas Johansson, Dissenting Democrats: Nation and Democracy in the Republic of Moldova, 2011 63. Wessam Melik, Molecular characterization of the Tick-borne encephalitis virus: Environments and replication, 2012
64. Steffen Werther, SS-Vision und Grenzland-Realität: Vom Umgang dänischer und „volks- deutscher” Nationalsozialisten in S nderjylland mit der „großgermanischen“ Ideologie der SS, 2012 65. Peter Jakobsson, Öppenhetsindustrin, 2012 66. Kristin Ilves, Seaward Landward: Investigations on the archaeological source value of the landing site category in the Baltic Sea region, 2012 67. Anne Kaun, Civic Experiences and Public Connection: Media and Young People in Estonia, 2012 68. Anna Tessmann, On the Good Faith: A Fourfold Discursive Construction of Zoroastripanism in Contemporary Russia, 2012 69. Jonas Lindstr m, Dr mmen om den nya staden: Stadsf rnyelse i det postsovjetisk Riga, 2012 70. Maria Wolrath S derberg, Topos som meningsskapare: Retorikens topiska perspektiv på tänkande och lärande genom argumentation, 2012 71. Linus Andersson, Alternativ television: Former av kritik i konstnärlig TV-produktion, 2012 72. Håkan Lättman, Studies on spatial and temporal distributions of epiphytic lichens, 2012 73. Fredrik Stiernstedt, Mediearbete i mediehuset: Produktion i f rändring på MTG-radio, 2013 74. Jessica Moberg, Piety, Intimacy and Mobility: A Case Study of Charismatic Christianity in Present-day Stockholm, 2013 75. Elisabeth Hemby, Historiemåleri och bilder av vardag: Tatjana Nazarenkos konstnärskap i 1970-talets Sovjet, 2013 76. Tanya Jukkala, Suicide in Russia: A macro-sociological study, 2013 77. Maria Nyman, Resandets gränser: Svenska resenärers skildringar av Ryssland under 1700-talet, 2013 78. Beate Feldmann Eellend, Visionära planer och vardagliga praktiker: Postmilitära landskap i Östersj området, 2013 79. Emma Lind, Genetic response to pollution in sticklebacks: natural selection in the wild, 2013 80. Anne Ross Solberg, The Mahdi wears Armani: An analysis of the Harun Yahya enterprise, 2013 81. Nikolay Zakharov, Attaining Whiteness: A Sociological Study of Race and Racialization in Russia, 2013 82. Anna Kharkina, From Kinship to Global Brand: The Discourse on Culture in Nordic Cooperation after World War II, 2013 83. Florence Fr hlig, A painful legacy of World War II: Nazi forced enlistment: Alsatian/Mosellan Prisoners of war and the Soviet Prison Camp of Tambov, 2013 84. Oskar Henriksson, Genetic connectivity of fish in the Western Indian Ocean, 2013 85. Hans Geir Aasmundsen, Pentecostalism, Globalisation and Society in Contemporary Argentina, 2013 86. Anna McWilliams, An Archaeology of the Iron Curtain: Material and Metaphor, 2013 87. Anna Danielsson, On the power of informal economies and the informal economies of power: Rethinking informality, resilience and violence in Kosovo, 2014 88. Carina Guyard, Kommunikationsarbete på distans, 2014 89. Sofia Norling, Mot ”väst”: Om vetenskap, politik och transformation i Polen 1989–2011, 2014 90. Markus Huss, Motståndets akustik: Språk och (o)ljud hos Peter Weiss 1946–1960, 2014
91. Ann-Christin Randahl, Strategiska skribenter: Skrivprocesser i fysik och svenska, 2014 92. Péter Balogh, Perpetual borders: German-Polish cross-border contacts in the Szczecin area, 2014 93. Erika Lundell, F rkroppsligad fiktion och fiktionaliserade kroppar: Levande rollspel i Östersj - regionen, 2014 94. Henriette Cederl f, Alien Places in Late Soviet Science Fiction: The “Unexpected Encounters” of Arkady and Boris Strugatsky as Novels and Films, 2014 95. Niklas Eriksson, Urbanism Under Sail: An archaeology of fluit ships in early modern everyday life, 2014 96. Signe Opermann, Generational Use of News Media in Estonia: Media Access, Spatial Orien- tations and Discursive Characteristics of the News Media, 2014 97. Liudmila Voronova, Gendering in political journalism: A comparative study of Russia and Sweden, 2014 98. Ekaterina Kalinina, Mediated Post-Soviet Nostalgia, 2014 99. Anders E. B. Blomqvist, Economic Natonalizing in the Ethnic Borderlands of Hungary and Romania: Inclusion, Exclusion and Annihilation in Szatmár/Satu-Mare, 1867–1944, 2014 100. Ann-Judith Rabenschlag, V lkerfreundschaft nach Bedarf: Ausländische Arbeitskräfte in der Wahrnehmung von Staat und Bev lkerung der DDR, 2014 101. Yuliya Yurchuck, Ukrainian Nationalists and the Ukrainian Insurgent Army in Post-Soviet Ukraine, 2014 102. Hanna Sofia Rehnberg, Organisationer berättar: Narrativitet som resurs i strategisk kommuni- kation, 2014 103. Jaakko Turunen, Semiotics of Politics: Dialogicality of Parliamentary Talk, 2015 104. Iveta Jurkane-Hobein, I Imagine You Here Now: Relationship Maintenance Strategies in Long- Distance Intimate Relationships, 2015 105. Katharina Wesolowski, Maybe baby? Reproductive behaviour, fertility intentions, and family policies in post-communist countries, with a special focus on Ukraine, 2015 106. Ann af Burén, Living Simultaneity: On religion among semi-secular Swedes, 2015 107. Larissa Mickwitz, En reformerad lärare: Konstruktionen av en professionell och betygssättande lärare i skolpolitik och skolpraktik, 2015 108. Daniel Wojahn, Språkaktivism: Diskussioner om feministiska språkf rändringar i Sverige från 1960-talet till 2015, 2015 109. Hélène Edberg, Kreativt skrivande f r kritiskt tänkande: En fallstudie av studenters arbete med kritisk metareflektion, 2015 110. Kristina Volkova, Fishy Behavior: Persistent effects of early-life exposure to 17α-ethinylestradiol, 2015 111. Bj rn Sj strand, Att tänka det tekniska: En studie i Derridas teknikfilosofi, 2015 112. Håkan Forsberg, Kampen om eleverna: Gymnasiefältet och skolmarknadens framväxt i Stock- holm, 1987–2011, 2015 113. Johan Stake, Essays on quality evaluation and bidding behavior in public procurement auctions, 2015
114. Martin Gunnarson, Please Be Patient: A Cultural Phenomenological Study of Haemodialysis and Kidney Transplantation Care, 2016 115. Nasim Reyhanian Caspillo, Studies of alterations in behavior and fertility in ethinyl estradiol- exposed zebrafish and search for related biomarkers, 2016 116. Pernilla Andersson, The Responsible Business Person: Studies of Business Education for Sustain- ability, 2016 117. Kim Silow Kallenberg, Gränsland: Svensk ungdomsvård mellan vård och straff, 2016 118. Sari Vuorenpää, Literacitet genom interaction, 2016 119. Francesco Zavatti, Writing History in a Propaganda Institute: Political Power and Network Dynamics in Communist Romania, 2016 120. Cecilia Annell, Begärets politiska potential: Feministiska motståndsstrategier i Elin Wägners ‘Pennskaftet’, Gabriele Reuters ‘Aus guter Familie’, Hilma Angered-Strandbergs ‘Lydia Vik’ och Grete Meisel-Hess ‘Die Intellektuellen’, 2016 121. Marco Nase, Academics and Politics: Northern European Area Studies at Greifswald University, 1917–1992, 2016 122. Jenni Rinne, Searching for Authentic Living Through Native Faith – The Maausk movement in Estonia, 2016 123. Petra Werner, Ett medialt museum: Lärandets estetik i svensk television 1956–1969, 2016 124. Ramona Rat, Un-common Sociality: Thinking sociality with Levinas, 2016 125. Petter Thureborn, Microbial ecosystem functions along the steep oxygen gradient of the Landsort Deep, Baltic Sea, 2016 126. Kajsa-Stina Benulic, A Beef with Meat Media and audience framings of environmentally unsus- tainable production and consumption, 2016 127. Naveed Asghar, Ticks and Tick-borne Encephalitis Virus – From nature to infection, 2016 128. Linn Rabe, Participation and legitimacy: Actor involvement for nature conservation, 2017 129. Maryam Adjam, Minnesspår: Hågkomstens rum och r relse i skuggan av en flykt, 2017 130. Kim West, The Exhibitionary Complex: Exhibition, Apparatus and Media from Kulturhuset to the Centre Pompidou, 1963–1977, 2017 131. Ekaterina Tarasova, Anti-nuclear Movements in Discursive and Political Contexts: Between expert voices and local protests, 2017 132. Sanja Obrenović Johansson, Från kombifeminism till r relse: Kvinnlig serbisk organisering i f rändring, 2017 133. Michał Salamonik, In Their Majesties’ Service: The Career of Francesco De Gratta (1613–1676) as a Royal Servant and Trader in Gdańsk, 2017 134. Jenny Ingridsdotter, The Promises of the Free World: Postsocialist Experience in Argentina and the Making of Migrants, Race, and Coloniality, 2017 135. Julia Malitska, Negotiating Imperial Rule: Colonists and Marriage in the Nineteenth century Black Sea Steppe, 2017 136. Natalya Yakusheva, Parks, Policies and People: Nature Conservation Governance in Post- Socialist EU Countries, 2017
137. Martin Kellner, Selective Serotonin Re-uptake Inhibitors in the Environment: Effects of Citalopram on Fish Behaviour, 2017 138. Krystof Kasprzak, Vara – Framträdande – Värld: Fenomenets negativitet hos Martin Heidegger, Jan Patočka och Eugen Fink, 2017 139. Alberto Frigo, Life-stowing from a Digital Media Perspective: Past, Present and Future, 2017 140. Maarja Saar, The Answers You Seek Will Never Be Found at Home: Reflexivity, biographical narratives and lifestyle migration among highly-skilled Estonians, 2017 141. Anh Mai, Organizing for Efficiency: Essay on merger policies, independence of authorities, and technology diffusion, 2017 142. Gustav Strandberg, Politikens omskakning: Negativitet, samexistens och frihet i Jan Patočkas tänkande, 2017 143. Lovisa Andén, Litteratur och erfarenhet i Merleau-Pontys läsning av Proust, Valéry och Stendhal, 2017 144. Fredrik Bertilsson, Frihetstida policyskapande: Uppfostringskommissionen och de akademiska konstitutionerna 1738–1766, 2017 145. B rjeson, Natasja, Toxic Textiles – Towards responsibility in complex supply chains, 2017 146. Julia Velkova, Media Technologies in the Making – User-Driven Software and Infrastructures for computer Graphics Production, 2017 147. Karin Jonsson, Fångna i begreppen? Revolution, tid och politik i svensk socialistisk press 1917– 1924, 2017 148. Josefine Larsson, Genetic Aspects of Environmental Disturbances in Marine Ecosystems – Studies of the Blue Mussel in the Baltic Sea, 2017 149. Roman Horbyk, Mediated Europes – Discourse and Power in Ukraine, Russia and Poland during Euromaidan, 2017 150. Nadezda Petrusenko, Creating the Revolutionary Heroines: The Case of Female Terrorists of the PSR (Russia, Beginning of the 20th Century), 2017 151. Rahel Kuflu, Br der emellan: Identitetsformering i det koloniserade Eritrea, 2018 152. Karin Edberg, Energilandskap i f rändring: Inramningar av kontroversiella lokaliseringar på norra Gotland, 2018 153. Rebecka Thor, Beyond the Witness: Holocaust Representation and the Testimony of Images – Three films by Yael Hersonski, Harun Farocki, and Eyal Sivan, 2018 154. Maria L nn, Bruten vithet: Om den ryska femininitetens sinnliga och temporala villkor, 2018 155. Tove Porseryd, Endocrine Disruption in Fish: Effects of 17α-ethinylestradiol exposure on non- reproductive behavior, fertility and brain and testis transcriptome, 2018 156. Marcel Mangold, Securing the working democracy: Inventive arrangements to guarantee circulation and the emergence of democracy policy, 2018 157. Matilda Tudor, Desire Lines: Towards a Queer Digital Media Phenomenology, 2018 158. Martin Andersson, Migration i 1600-talets Sverige: Älvsborgs l sen 1613–1618, 2018 159. Johanna Pettersson, What's in a Line? Making Sovereignty through Border Policy, 2018 160. Irina Seits, Architectures of Life-Building in the Twentieth Century: Russia, Germany, Sweden, 2018 161. Alexander Stagnell, The Ambassador's Letter: On the Less Than Nothing of Diplomacy, 2019 162. Mari Zetterqvist Blokhuis, Interaction Between Rider, Horse and Equestrian Trainer – A Challenging Puzzle, 2019
163. Robin Samuelsson, Play, Culture and Learning: Studies of Second-Language and Conceptual Development in Swedish Preschools, 2019 164. Ralph Tafon, Analyzing the “Dark Side” of Marine Spatial Planning – A study of domination, empowerment and freedom (or power in, of and on planning) through theories of discourse and power, 2019 165. Ingela Visuri, Varieties of Supernatural Experience: The case of high-functioning autism, 2019 166. Mathilde Rehnlund, Getting the transport right – for what? What transport policy can tell us about the construction of sustainability, 2019 167. Oscar T rnqvist, R ster från ingenmansland: En identitetsarkeologi i ett maritimt mellanrum, 2019 168. Elise Remling, Adaptation, now? Exploring the Politics of Climate Adaptation through Post- structuralist Discourse Theory, 2019 169. Eva Karlberg, Organizing the Voice of Women: A study of the Polish and Swedish women’s movements’ adaptation to international structures, 2019 170. Maria Pr ckl, Tyngd, sväng och empatisk timing – F rskollärares kroppsliga kunskaper, 2020 171. Adrià Alcoverro, The University and the Demand for Knowledge-based Growth: The hegemonic struggle for the future of Higher Education Institutions in Finland and Estonia, 2020 172. Ingrid Forsler, Enabling media: Infrastructures, imaginaries and cultural techniques in Swedish and Estonian visual arts education, 2020 173. Johan Sehlberg, Of Affliction – The Experience of Thought in Gilles Deleuze by way of Marcel Proust, 2020 174. Renat Bekkin, People of reliable loyalty…: Muftiates and the State in Modern Russia, 2020 175. Olena Podolian, The Challenge of ‘Stateness’ in Estonia and Ukraine: The international dimen- sion a quarter of a century into independence, 2020 176. Patrick Seniuk, Encountering Depression In-Depth: An existential-phenomenological approach to selfhood, depression, and psychiatric practice, 2020 177. Vasileios Petrogiannis, European Mobility and Spatial Belongings: Greek and Latvian migrants in Sweden, 2020 178. Lena Norbäck Ivarsson, Tracing environmental change and human impact as recorded in sediments from coastal areas of the northwestern Baltic Proper, 2020
in sediments from coastal areas of the northwestern Baltic Proper in sediments from coastal areas of the northwestern Tracing environmental change and human impact as recorded
Te eutrophication of the Baltic Sea due to increased anthropogenic nutrient loads during the 20th century is well documented and studied. However, in the Baltic Sea drainage area, humans have afected the environment longer than the environmental monitoring can provide data for. Sediment records from lakes and seas can provide fundamental data on the environmental conditions before ecosystems were impacted by humans and give the range of natural variation.
Tis thesis presents diatom and geochemistry stratigraphies from fve sediment records along the southeast coast of Sweden, northwestern Baltic Proper. Tese records cover time periods of 500 years to more than 2000 years. Te diatom stratigraphies and geochemical proxies allow for reconstruction of environmental histories at these sites. Te outcomes of this thesis highlight the importance of a longer time perspective than the environmental monitoring can provide.
Lena Norbäck Ivarsson carries out research within the feld of environmental science with a focus on understanding past and present ecosystem responses to environmental changes. She holds a M.Sc. in biology from Stockholm University and this is her PhD thesis. LENA NORBÄCK IVARSSONLENA NORBÄCK
Environmental Science, Environmental Studies, School of Natural Sciences, Technology and Environmental Studies & the Baltic and East European Graduate School, S dert rn University. Tracing environmental change and human impact ISBN 978-91-89109-29-2 (print) / 978-91-89109-30-8 (digital) | S dert rn University | [email protected] as recorded in sediments from coastal areas of the northwestern Baltic Proper Lena Norbäck Ivarsson
SDD SÖDERTÖRN DOCTORAL DISSERTATIONS 178