This thesis resulted in the development of robust chironomid-based transfer-functions for February mean air temperature and the concentration of total nitrogen (TN) in lake-water. The New Zealand transfer-functions for both variables compare favourably with chironomid-based transfer-functions for equivalent variables from elsewhere in the world, and diatom-based transfer-functions for nutrients and lake production from New Zealand. The application of the temperature and TN transfer-functions provided insight into New Zealand climate conditions during the last glacial and served as validation for the reconstructions. Chironomid-based Temperature reconstructions from lake silts preserved in the banks of Lyndon Stream indicate a maximum cooling of ca 4 ℃ between 26.6 and 24.5 ka BP, which is consistent with estimates based on beetles and plant macrofossils. A cooling of 4 ℃ is insufficient to explain the lack of canopy tree pollen in many New Zealand pollen records at this time. Other environmental parameters additional to temperature may have limited the expansion forest cover. The chironomid-based TN reconstructions infer a trend of rapidly deteriorating water-quality in a small doline in north-west Nelson, in the South Island of New Zealand following deforestation immediately surrounding the lake ca. 1970 AD. The overall trend and timing of eutrophication inferred from the chironomids was consistent with other biological proxies and actual observations of changes in lake water quality. The chironomid-based transfer-functions provide a valuable new tool for the study of longterm climate variability and improving our understanding of the response of aquatic ecosystems to long-term natural and human induced environmental change in New Zealand lakes. I have identified some possibilities for future research which should improve the performance of these transfer-functions. The improvement of the chironomid taxonomy and the expansion of the training set should be the highest priorities.

Diatom analyses were carried out on sediment cores collected from two low-lying, closed-drainage basins (PAD 9 - 58??46. 46?N, 111??19. 48?W; PAD 12 - 58??57. 29?, 111??19. 74?) in the Peace sector of the Peace-Athabasca Delta (PAD), Alberta, Canada, to provide >1000 year long records of hydro-ecological change. Results from diatom analyses were compared with macrofossil and stable isotope records from the same cores and assessed within the framework of an Athabasca River headwater climate record inferred from isotope dendroclimate data. Results from PAD 9 and PAD 12 sediment cores indicated closed-drainage conditions during the Medieval Warm Period (MWP) and the post-Little Ice Age and high water conditions during the Little Ice Age (LIA). High water levels at PAD 9 and PAD 12 reflected high water conditions on Lake Athabasca and the Rivi??re des Rochers or possibly the Peace River during the LIA (~AD 1600-1900). High water conditions were also observed at low-lying sites in the central and southern regions of the PAD (PAD 31 and PAD 37), and corresponded with evidence of high streamflows on the North Saskatchewan River. In contrast, desiccation evident at PAD 5, a site largely isolated from river influence, reflected atmospherically dry conditions during the LIA. Consistent with changes observed at PAD 5, sediment records at PAD 15, an oxbow lake off the Revillion Coup??, demonstrated low flood frequency during the early to mid-1700s. Increased water levels evident at low-lying sites located in proximity to the central open-drainage network of lakes and rivers were likely due to higher flows on the Athabasca River and potentially on the Peace River. High flows on rivers of the PAD may be attributed to snowmelt-dominated runoff during the LIA relative to the rainfall-dominated runoff during MWP (prior to ~AD 1600) and the post-LIA period (~AD 1900 to present).

The Sierra Nevada snowpack is vital to the water supply of California, the world’s sixth largest economy. Though tree ring and instrumental records show the dramatic influence of environmental change on California’s hydroclimate over the last millennium, few proxy archives assess winter precipitation variability farther back in time. Here, we use diatoms from a ~3,200 yr. old sediment core to reconstruct the paleolimnology of June Lake, a hydrologically closed glacial lake in the eastern Sierra Nevada. We test the hypothesis that limnologic and climatic changes control diatom assemblages at June Lake. Fossil diatom assemblages from June Lake sediments chiefly consist of the planktic genera Stephanodiscus and Lindavia; their relative abundances in sediments are controlled by lake response to changes in the length of the winter season. We establish a Lindavia:Stephanodiscus index to infer winter length; our results indicate three periods where winter seasons are longer than average: ~3.2-2.9 ka, ~2.2-1.7 ka, and ~0.6 ka-0.05 ka. Over the last ~100 yrs., June Lake has experienced stronger water column stratification and an expansion of the available benthic diatom habitat, indicating significantly warmer winters and lower lake levels. It is possible that this change is the result of anthropogenic climate warming.

Sediment accumulated in lakes stores valuable information about past environments and paleoclimatological conditions. Cores previously obtained from Saint Albans Bay, located in the Northeast Arm of Lake Champlain, VT record the transition from the Champlain Sea to Lake Champlain. Belrose (2015) documented the presence of a peat horizon separating the sediments of the Champlain Sea from those of Lake Champlain. Initially, this layer was thought to comprise the transition from the marine environment of the Champlain Sea to a freshwater wetland. However, based on the results from this study, the transition between marine and freshwater conditions is thought to be represented by an erosional unconformity, indicative of a lowstand at the end of the Champlain Sea period. For this study, five additional cores were collected from Saint Albans Bay along a transect following the long axis of the bay moving into progressively deeper water. These cores better constrain the spatial extent, thickness and age variability of the peat layer within the bay and allow us to better understand the environmental conditions that preceded the period of peat deposition. In each of the cores there is evidence of sediment reworking in the uppermost Champlain Sea sediments, indicated by the presence of coarse-grained sediment, which is suggestive of a lowstand at the end of the Champlain Sea period before the inception of Lake Champlain. This coarse-grained layer is immediately overlain by a thick peat horizon. The widespread occurrence of the peat layer points to a large wetland that occupied the entire inner portion of Saint Albans Bay, and lake level ~ 9 m lower than at present during the Early Holocene. Based on radiocarbon dating, this paleo-wetland existed in Saint Albans Bay from ~ 9,600-8,400 yr BP. The development of this wetland complex is time transgressive, reflecting rapidly increasing lake level during the Early Holocene. This hypothesis is supported by the basal peat radiocarbon dates, as well as by the composition of plant macrofossils recovered from the peat horizons. The shift from peat deposition to fine-grained, low organic content lacustrine sedimentation is believed to have occurred at ~8.6-8.4 ka and is likely the result of continued isostatically driven lake level rise coupled with a changing climate. Although it was not its primary focus, this study also seeks to address the variations in sediment composition in the Lake Champlain sections of the cores. Evidence from the Lake Champlain record in Saint Albans Bay indicates that there were notable fluctuations in sedimentation, which were likely linked to both climatic variations and a change in the morphology of the bay. The rebound in productivity from ~8-5 ka is likely the result of warmer conditions during the Hypsithermal period. An increase in terrigenous sedimentation during this same time suggests a change in the morphology of the bay in which the Mill River delta migrated towards the inner bay. Initially, the cooler conditions of the Neoglacial are reflected in Saint Albans Bay by a decrease in organic matter content from ~5-3 ka. During the latter part of the Neoglacial (~3-1 ka), increases in organic matter content and detrital input point to enhanced productivity in response to increased precipitation and runoff from the watershed. The most recently deposited sediments in Saint Albans Bay bear out the legacy of anthropogenic nutrient enrichment of the bay in the form of increased algal productivity.

Abstract not available

Using paleolimnological techniques, I have studied surface-water acidification and the effects of liming in Swedish lakes on a decadal to millennial time-scale. The overall objective was to contribute to the discussion on the fulfilment of goals within the Swedish liming program. One of the main goals of this program is to restore lakes to natural or nearly natural conditions, i.e. to a reference condition as termed in the EU Water Framework Directive. In this context, a key issue is to define reference conditions. This is a central theme of my thesis, as lake sediments offer a unique way to study past lake conditions. Past lake-water acidity of 12 reference lakes in the Swedish liming program (ISELAW) was determined using diatom analysis of sediment cores. Pollen, lead, and flyash from coal/oil combustion were used as indicators of impact from land use and atmospheric pollution. A general trend in these lakes is an initial decline in pH after lake formation due to natural soil processes, which was then followed by rather low pH values (pH 5.3-6.5). In six of the lakes pH increased as a result of expansion of agriculture (burning, forest grazing) 2000 to 1000 years ago. Local mining and long-range airborne pollution have also impacted the lakes since medieval time. These results show that the conditions of the study lakes were not natural prior to industrialization and recent (20th century) acidification. The ISELAW lakes were selected on the basis of representing typical limed lakes, and they have been limed and monitored since at least the 1980s. A comparison of chemical/biological monitoring data and the paleolimnological data gives somewhat diverging results. Most of the monitoring data suggest that the lakes were subjected to acidification during the 20th century, but the paleolimnological data can only identify clear evidence of acidification in five of the 12 lakes, hence, all lakes were probably not recently acidified. According to conclusions from monitoring the lakes have recovered following liming. The paleolimnological data give a more complex picture and three different responses have been identified: 1) a return to a diatom composition found in the lake one hundred to several thousand years ago; 2) very small shifts in the diatom composition; or 3) a diatom composition previously not found in the lake. The latter response raised the question whether liming can cause an unnatural diatom community. A comparison of diatoms in surface sediment samples of 31 limed lakes with pre-industrial reference samples from 291 lakes showed that liming does not create an unnatural diatom composition. These results illustrate that the goals for liming were not reached in all of the limed lakes, and that paleolimnology can play an important role for assessments of acidification and liming. The comparative study also highlights the importance of designing monitoring programs that can produce reliable and long data series. Given the results of the paleolimnological investigations, it is obvious that we cannot assume that the 19th century represented a natural or near natural state, and thus is a realistic reference conditions. Natural long-term lake development and previous land-use impacts need to be considered in defining reference conditions. Neither can we disregard the fact that humans always will impact nature. Although paleolimnological studies are time consuming, I believe that they could be simplified to the extent that paleolimnology could become a routine method for environmental management.

Water chemistry and bioindicators (diatoms and invertebrates) were examined for freshwater lakes, ponds and streams in two regions within Sirmilik National Park, northern Baffin Island, Nunavut. Significant differences were recorded between the water chemistry and diatom and invertebrate assemblages of the two regions. Modern diatom assemblages were explained mainly by specific conductivity, ORP, pH, temperature, elevation and distance from the coast. Paleolimnological techniques were applied to a sediment core from Lake BY14 on Bylot Island. Fossil diatom assemblages indicate increases in nutrients and temperature since 1935 AD. The diatom biostratigraphy does not show as large an increase in diversity and production since the middle 20th century as has been noted elsewhere, and this may be a reflection of the more nutrient-rich status of the lake relative to other Arctic lakes.

Water chemistry and bioindicators (diatoms and invertebrates) were examined for freshwater lakes, ponds and streams in two regions within Sirmilik National Park, northern Baffin Island, Nunavut. Significant differences were recorded between the water chemistry and diatom and invertebrate assemblages of the two regions. Modern diatom assemblages were explained mainly by specific conductivity, ORP, pH, temperature, elevation and distance from the coast. Paleolimnological techniques were applied to a sediment core from Lake BY14 on Bylot Island. Fossil diatom assemblages indicate increases in nutrients and temperature since 1935 AD. The diatom biostratigraphy does not show as large an increase in diversity and production since the middle 20th century as has been noted elsewhere, and this may be a reflection of the more nutrient-rich status of the lake relative to other Arctic lakes.

In the current study, sub-fossil Cladocera collected from the surface sediment of 44 shallow lakes spanning over five latitudes from north to south of Turkey using snap-shot methodology revealed strong impact of salinity on cladoceran community structure. To see the whole picture, sediment cores collected from six of the lakes and long-term monitoring data from two of the lakes were also investigated. Contemporary cladocerans and sub-fossil assemblages were compared to reveal that their responses to salinity changes were highly similar. This lead us to use sub-fossil cladocerans and salinity data from water column together while generating the calibration data set using ordination techniques. Salinity transfer function models were developed utilising weighted averaging techniques. The developed salinity transfer function was applied to cladocera assemblages from dated sediment cores. Hindcasting of the salinity inference model was performed using monitoring data and the reconstructed salinities from two central Anatolian lakes and reflected good linear correlation with the known lake salinity history. This thesis has confirmed that sub-fossil Cladocera is a valuable indicator of historical salinity change and marker for the monitoring of lakes. For the first time, the lake environmental variables and sub-fossil cladoceran species composition from the surface sediments of Turkish shallow lakes were studied and a salinity transfer function was developed to elucidate past salinity change. The approach of the current study has been proven to be reliable while interpreting past salinity conditions. Since monitoring programmes are scarce in Turkey, paleolimnological analyses would be beneficial especially when defining effective restoration strategies.

Barbados is the easternmost island in the Caribbean region, and is uniquely situated between the Atlantic Ocean and Caribbean Sea. Being an isolated island with a karstified aquifer providing the majority of the nation’s water resources, Barbados has found itself in water scarce situations in recent years. In order to better understand natural shifts in groundwater recharge (which is determined by shifts in precipitation), longer records of precipitation are needed than are available from modern measurements. This study presents a paleoclimate reconstruction for the late Holocene on Barbados using stable and radiogenic isotope ratios in speleothem lamina as proxies. In addition, it introduces the use of novel mineralogical analyses using Raman spectroscopy and large chamber-scanning electron microscopy to supplement the oxygen isotope record. For the past 1,500 years, the speleothem record indicates average δ18O values near -4.1 0/00, maximum δ18O values around -3.2 0/00 that coincide with the Little Ice Age climate event, while minimum δ18O values around -5.3 0/00 occur during the Medieval Climate Anomaly. Raman spectral analysis shows a recent period of increased Mg substitution, which potentially represents anthropogenic changes to the island’s epikarst aquifer caused by European settlement and sugar cane cultivation on Barbados. Electron imaging revealed chemically distinct layers of detritus within the stalagmite sample, facilitating precise sampling for U-series dating while also providing some information on the nature of weathering on the island. Additionally, time series analysis of the isotope record indicates multidecadal and multicentennial periodicities that conform well to that of the Atlantic Multidecadal Oscillation exerting influence on rainfall variability at the decadal scale, and the Intertropical Convergance Zone modulating rainfall at the multicentennial scale. Collectively, these data provide a climate reconstruction for the island of Barbados that is useful for better understanding change in cyclic precipitation patterns, as well as non-destructive methods for speleothem analysis that complement the isotopic study, while allowing sample preservation.