Increasing concerns over future anthropogenic effects on climate change as a result of increasing greenhouse gases generate concomitant efforts to better characterize recent climate in order to more accurately predict climate in the future. To this end, a multiproxy study of climate variability in western Ireland from lacustrine sediment was undertaken. The interpretation of paleoclimate records derived from lacustrine carbonate minerals is difficult without a good understanding of the mechanisms that generate variation in isotope values of modern surface waters. Variation in surface waters are ultimately incorporated into lacustrine sediment records conflated by temperature. Therefore, a study of the spatial distribution of ä¹⁸O and äD values of lake and river waters from 144 locations in Ireland has been conducted to provide insight into the behavior of lakes and rivers in Ireland, including source, recycling and loss through evapotranspiration. A 7.6 m sediment core was recovered from Lough Inchiquin that provides evidence for rapid and long-term climate change from the Late Glacial to the Holocene. This was determined using carbon and oxygen isotope analyses of lacustrine calcite as well as carbon from bulk organic sediment fractions. Several significant climate perturbations were identified in the ä¹⁸O_calcite record such as the Oldest Dryas, Younger Dryas, and the 8.2 ka cold event. A previously undescribed climate anomaly between 7,300 to 6,700 cal. yr B.P. characterized by low ä¹⁸O</span>_calcite values with high frequency variability. Variations in carbon isotopes of calcite and bulk organics from the Late Glacial to the Holocene are significant in magnitude (~12) and have similar trends that record temporal shifts in the relative contributions of carbon from the weathering of limestone versus the weathering of terrestrial organic matter. ä¹³C_calcite and ä¹³C_org suggest a rapid recovery of terrestrial vegetation following the Younger Dryas. Change in Ää¹³C_{calcite - org} documents a rapid increase in exogenous fluxes of carbon into the lake at ~9 ka.

Ensåsengruvan is a mine situated within Ljusdals municipality in central Sweden. Themine was in use from 1984 to 1991 and has since been undergoing a remediation program. Mine tailings from sulfide rich ore is a potential environmental hazard due to its tendency to cause acid waters and heavy metal leakage. Lake Ensjön is situated one kilometer from the mine area. Due to the hydrological conditions it was not expected to receive inflowing water from the mining area. A study done in 2005 showed high amounts of heavy metals in the lake. In this study water and sediments was analyzed to confirm the results from the 2005 study. Water was sampled two times during summer 2006 from the lake and adjoining streams. Sediment samples were collected with a core sampler at ten different locations within the lake. The water and sediment samples were analyzed for heavy metal content. Sub-samples from different depths in the sediment core were extracted so that conclusions on the contamination history could be drawn. The sediments were dated trough Cs-137 analyses. The depth in the profile with the highest Cs-137 content can be dated to the time of the Chernobyl fallout (1986). After dating, relevant samples were analyzed for metal content. The results show that Ensjön is contaminated by a local source. The surface sediments are high in copper, zinc, nickel and cadmium content. The content is high both compared to the samples from deeper in the sediment core and the surface sediments analyzed in the reference study done in 1980. The amounts of heavy metals are also high relative to the standards set by the Swedish Environmental Protection Agency. The water from the stream adjoining the lake from the mining area is high in content of the previously mentioned metals. The methods used, including sediment dating and metal analyses together with water analyses, has proven to be useful in investigating a suspected contamination from a point source. It can be concluded that Lake Ensjön is contaminated with water from the mine waste. No other sources in the catchment area can be the source of the enriched amounts of heavy metals. Focus should in further work be put upon finding the exact source of leakage from the mining area. / Från Enåsengruvan i Ljusdals kommun utvanns ur sulfidmalm guld, silver och koppar under åren 1984 till 1991. Avfall från sulfidmalmsgruvor medför miljöproblem genom försurning och läckage av tungmetaller. Vanligtvis täcks avfallet med jordmassor eller vatten för att förhindra påverkan på naturen. De studier som genomfördes under prospekteringen visade på att Ensjön, som är belägen inom en kilometers avstånd från gruvområdet, inte skulle påverkas av gruvan men en provtagning under 2005 visade på höga halter av tungmetaller i sjön. I denna studie har Ensjöns vattenkvalitet undersökts genom vatten och sedimentanalyser. Vattenprover i sjön och dess inlopp togs två gånger under sommaren 2006 och sedimentprover togs vid ett tillfälle på tio olika lokaler i sjön. En djupprofil av sedimenten analyserades för att föroreningshistoriken från innan gruvan togs i bruk till nutid skulle kunna kartläggas. För att datera sedimenten analyserades de med avseende på Cs-137. De högsta halterna av Cs-137 kan härledas till nedfallet från Tjernobylolyckan 1986. Efter datering valdes lämpliga prover ut för metallanalys. Resultaten visar på förhöjda halter av koppar, zink, nickel och kadmium. Halterna i ytsedimenten är höga både jämfört med de halter som återfinns på större djup i sedimentprofilen, motsvarande avsättning innan gruvdriften och vad som uppmättes i referensstudien från 1980. Halterna är även höga relativt de jämförvärden som Naturvårdsverket satt upp. Vattenanalyserna visar på att vattnet i inflödet från gruvområdet innehåller höga halter av de tidigare nämnda metallerna. Metoden med Cs-137-datering och analys med avseende på metaller av sediment har visat sig fungera väl för kartläggning av en nutida förorening från en punktkälla. Tillsammans med kompletterande vattenprover ger det en bra bild av den rådande situationen. Då resultaten visar att Ensjöns vatten är påverkat av en punktkälla och alla andra källor kan uteslutas får det anses klarlagt att sjöns vatten är påverkat av dränagevatten från gruvområdet. Fortsatta studier bör fokusera på att klarlägga den exakta källan till läckaget från gruvområdet.

The Arctic represents a huge area with poor infrastructure contributing to limited possibilities to establish monitoring and research programs. From the investigations that have been performed we know that the arctic environment is affected by anthropogenic emissions from lower latitudes, but knowledge about underlying transport processes, the arctic pollution extent and the rates of changes are limited. This is of particular concern since we are facing climate changes that will not only influence the pole-ward transport of pollutants, but also change conditions for the already accumulated pollutants in the arctic environment. In this thesis lake sediments and soil samples are used to study sub-arctic and arctic time trends and loads of PCBs, PBDE, pesticides, mercury and lead. The study sites are the area around Kangerlussuaq, located in western Greenland, and the Swedish mountains. The temporal trends for PCBs (69 congeners), PBDE (#47) and two pesticides (chlordane and hexachlorobenzene) are studied in seven surface lake sediment cores from Greenland. The concentrations of these persistent organic pollutants are one to two orders of magnitude lower compared to lake sediments from lower latitudes, but with temporal trends following emission and usage trends at lower altitudes, i.e., decreasing trends for PCBs, increasing for PBDE and no specific trends for the pesticides. A delayed deposition of the low-chlorinated PCBs compared to the high-chlorinated PCBs may support the hypothesis of ‘cold condensation’ and ‘global fractionation’ i.e., volatile compounds are fractionated during the pole-ward transport. For lead the concentration in three Greenland lake sediments is about 10 times lower than in sediments from industrial regions, but the past 200 years’ temporal trends follow emission trends in industrial regions. The mercury concentration and enrichment following the Industrial Revolution in the mid 19th century are in three lake sediments from Greenland and in twelve lake sediments from the Swedish mountains comparable with those in sediments from industrial regions; a result of the long atmospheric residence-time for mercury, making it a global pollution. Recently decreased mercury emissions in North America and Europe give declining concentrations in the sediment surfaces, especially in lakes located in the Swedish mountains. In Greenland deeper sediment cores, spanning the last 8000 years, there are substantial fluctuations in mercury concentration and stable lead isotopes (206Pb/207Pb). These fluctuations are the result of variations in deposition to the lake of aeolian material, driven by past variations in arctic climate. In surface soil the mercury concentrations and inventories from the Swedish mountains are 1.5-2 times higher than in soils from Greenland, but for both regions the concentrations are below the critical concentration set up by UN-ECE to protect the terrestrial ecosystem. No indications for mercury enrichment in colder areas, as suggested by the hypothesis of ‘cold condensation’, or in coastal areas, as suggested by the hypothesis of ‘mercury depletion events’, were observed. The highly minerogenic surface soils in sub-arctic and arctic regions have reduced capacity to store mercury, compared to boreal soils.

Varved (annually laminated) sediments are of great interest for inference of past environmental conditions, as they provide dated records with high time resolution. After deposition, the sediment varves are affected by diagenesis; i.e., chemical, physical and biological changes that occur within the sediment. An important premise when reconstructing past environmental conditions using lake sediments is that the signal of interest is preserved in the sediment. In this thesis I have used a unique collection of ten stored freeze cores of varved lake sediment from Nylandssjön in northern Sweden, collected from 1979 to 2007. The suite of cores made it possible to follow long-term (up to 27 years) changes in iron (Fe), sulfur (S), carbon (C), nitrogen (N), δ13C and δ15N in the sediment caused by processes that occur in the lake bottom as the sediment ages. The sediment geochemistry and resulting changes were followed in years for which there are surface varves in the core series. Fe and S concentrations analyzed by X-ray fluorescence spectroscopy showed no diagenetic front in the sediment and the data do not suggest a substantial vertical transport of Fe and S in the sediment. A model based on thermodynamic, limnological, and sediment data from the lake, showed that there are pe (redox) ranges within which either FeS (reduced specie) or Fe(OH)3/FeOOH oxidized species) is the only solid phase present and there are pe ranges within which the two solid phases co-exist. This supports the hypothesis that blackish and grey-brownish Fe-layers that occur in the varves were formed at the time of deposition. C and N analyzed with an elemental analyzer showed that within the first five years after deposition the C concentration of the sediment decreased by 20% and N by 30%, and after 27 yr in the sediment, there was a 23% loss of C and 35% loss of N. The C:N ratio increased with increasing age of the sediment; from ~ 10 in the surface varves to ~12 after 27 years of aging. δ13C and δ15N analyzed on a mass spectrometer showed that δ13C increased by 0.4-1.5‰ units during the first five years, after that only minor fluctuations in δ13C were recorded. Another pattern was seen for δ15N, with a gradual decrease of 0.3-0.7‰ units over the entire 27-year-period. The diagenetic changes in the stable isotope values that occur in Nylandssjön are minor, but they are of about the same magnitude as the variation in the isotopic signal in the varves deposited between 1950-2006. My results show that diagenesis does not change the visual appearance of the varves, except for varve thickness; the varves get thinner as the sediment ages. As the color of Fe in the varves likely reflects the environmental conditions at the time of deposition this creates possibilities for deciphering high-temporal-resolution information of past hypolimnetic oxygen conditions from varves. My findings on C, N, δ13C and δ15N will have implications for interpretations of paleolimnological data. The diagenetic effects should be carefully taken into consideration when C, N, δ13C and δ15N in sediment cores are used to study organic matter sources or paleoproductivity, in particular when dealing with relatively small and recent changes. In addition to the significance of diagenetic effects on sediment parameters, a comparison of the varves in Nylandssjön and the adjacent lake Koltjärnen, and the two deep basins of Nylandssjön show that subtle features in the lakes and their catchments affect the appearance of the varves, which make interpretation of varves complicated.

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The aim of this work is to test the proposed approach of algal scavenging as a driver of sediment mercury (Hg) on different time scales and to gain a better understanding of the mechanisms of Hg accumulation in lake sediments. A 3000-year sediment record from Nylandssjön in northern Sweden was analysed for this purpose, as well as a 20-year sediment record from the seasonal sediment traps of this lake. The diatom proxy biogenic silica (bSi) was determined by Fourier transform infrared spectroscopy (FTIRS) and chlorophyll-a (Chl-a) as a proxy for primary productivity by non-destructive visible near-infrared reflectance spectroscopy (VNIRS). Silica, normalised to minerogenic matter by aluminium (Si/Al) as an indirect diatom proxy and other geochemical parameters were analysed by the non-destructive method of X-ray fluorescence spectroscopy (XRF). The Hg content in the sediment was determined using the the thermal decomposition atomic absorption spectrophotometers (TD-AAS) method. Over the different time scales, organic matter (OM) is an important control factor for Hg, which in turn was strongly associated with primary productivity. Hg was normalised against OM by determining the Hg/LOI or Hg/C ratios. No positive correlation was found between the normalised Hg ratios and the proxies of primary productivity (bSi, Chl-a and Si/Al). Negative correlations between OM and minerogenic elements coinciding with human-induced erosion events and increasing Hg levels in the sediment were found. This is true, both for the long-term record in the sediment cores and the high-resolution data from the sediment traps. Furthermore, in the seasonal sediment record of the sediment traps, in-lake processes like lake turnover in spring and autumn could be linked to precipitation of iron oxyhydroxides (FeOOH) and increasing sedimentary Hg. This may be supported by the parallel sediment accumulation of other metals like nickel (Ni) and zinc (Zn) at the time of the lake turnover.

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Using a comparative spatial and temporal analysis on sediment cores from 8 lakes in the Mackenzie River Delta uplands region, NT, Canada, this study assessed how persistent organic pollutant (POP) deposition to lake sediments was affected by: (1) the presence of retrogressive thaw slumps on lake shores; and (2) changes occurring with increased autochthonous primary productivity. POPs examined included polychlorinated biphenyls (PCBs), penta- and hexachlorobenzenes (CBzs), and dichlorodiphenyltrichloroethane and metabolites (DDTs). Surface sediments of slump-affected lakes contained higher total organic carbon (TOC)-normalized POP concentrations than nearby reference lakes unaffected by thaw slumps. Inorganic sedimentation rates were positively related to contaminant concentrations, suggesting that the influx of siliciclastic material reducing organic carbon in slump-affected lake water indirectly results in higher concentrations of POPs on sedimentary organic matter. This explanation was corroborated by an inverse relationship between sedimentary POP concentrations and TOC content of the lake water. Deposition proxies of autochthonous carbon were not significantly correlated to POP fluxes of surface sediments, and historical profile fluctuations did not coincide with variation in POP deposition. Thus this study does not support the contention that algal-derived organic carbon increases the delivery of organic pollutants to sediments (the algal-scavenging hypothesis), as previously proposed for mercury. Higher POP concentrations observed in surface sediments of slump-affected lakes are best explained by simple solvent switching processes of hydrophobic contaminants onto a lower pool of available organic carbon when compared to neighbouring lakes unaffected by thaw slump development.