Thesis advisor: Noah P. Snyder / Land cover and climate changes, attributed to natural and anthropogenic forcings, cause deviations in geomorphic processes that act to deliver sediment from watersheds to lakes. In New England, contradictory evidence exists as to the influence of deforestation associated with EuroAmerican settlement and major flood events on watershed erosion rates over the past ~250 years. Through combining sediment core analysis from Ossipee Lake, New Hampshire with geomorphic analysis of the Ossipee Lake watershed, this study quantifies Holocene through Anthropocene watershed erosion rates, and assesses variations in rates in relation to short-term historic events such as major storm events or deforestation, and long-term variations related to natural climate variability and post-glacial landscape evolution. An 8.63 m core was collected and spans the entire period from deglaciation to present. Bulk composition and age-depth modeling, utilizing both short-lived radioisotopes and radiocarbon dating, are used to quantify changes in deposition and inferred erosion rates over time. Additional insight on sedimentary processes is provided by measurements of magnetic susceptibility and bulk geochemistry. Lake-sediment data suggests clastic sediment mass accumulation rates vary between 0.0032 to 0.5870 g/cm2/yr, with deposits of increased terrestrially derived sediment focused between ~8500 to 7800, ~6500 to 2500, and 1600 cal yr BP to present. Geomorphic analysis is used to identify regions within the watershed that act to deliver sediment to Ossipee Lake. Potential sources of sediment supply include loose, unconsolidated proglacial deposits near Ossipee Lake that transition to primarily till in upland areas. Calculated bed shear stress along rivers highlights areas in the watershed capable of transporting sediment and areas that can serve as traps thus limiting sediment delivery to Ossipee Lake. / Thesis (MS) — Boston College, 2019. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

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Coastal lakes, lagoons, and wetlands often provide excellent records of environmental change related to both marine and terrestrial processes. Although coastal paleoenvironments in the Caribbean have been a subject of increasing interest, long-term environmental reconstructions from lakes on the Atlantic side of the Caribbean islands are lacking. Laguna Limon is a freshwater lake in the El Seibo province of northeastern Dominican Republic. We collected a 315-cm sediment core from the center of the lake to examine lake evolution using loss-on-ignition and foraminiferal analysis. Loss-on-ignition results indicated the presence of a low-energy lagoon in the lake's present location between about 4700 and 1400 cal yr BP. During this period a foraminiferal assemblage dominated by the brackish-water Ammonia parkinsoniana but also containing relatively-abundant normal-marine salinity taxa (e.g., Quinqueloculina spp., Archaias angulatus, and Trochulina rosea) gradually was replaced by a low-diversity assemblage dominated by Ammonia tepida and Ammonia parkinsoniana, indicating a gradual decline in salinity due to the lagoon's growing isolation from the Atlantic Ocean. By 1400 cal. Yr. BP, the lake had become a shallow wetland, indicated by sediments with a high organic content. At 1200 cal. Yr. BP the lake flooded with freshwater, as it remains today. This study provides context for ongoing research into the environmental and human history of the Laguna Limon area. / Master of Science

Lake deposits are widespread throughout the Phanerozoic rock record and have long intrigued geologists and paleobiologists in search of natural resources or fossil biota. Low-energy lacustrine depositional environments, characterized by relatively rapid sediment influx rates and shallow zones of bioturbation, likewise produce highly-resolved archives of climate and ecosystems evolution. This dissertation describes four studies that use lake sediments for Quaternary environmental analysis. In East Africa, many decades of prior study provided the critical framework necessary for in-depth paleoenvironmental research at Lake Tanganyika (3° - 9°S). Seismic stratigraphic analysis integrated with radiocarbon-dated sediment cores from the Kalya horst and platform document a dramatic lake level lowstand prior to ~106 ka and a minor, short-lived regression during the Last Glacial Maximum (32 - 14 ka). Paleobathymetric maps reveal that Lake Tanganyika remains a large, connected water body even during episodes of extreme drought, which has implications for local and regional fauna. Over shorter timescales, geochronological, taphonomic and sedimentological analyses of shell beds around Kigoma (central Lake Tanganyika) document three distinct facies-types that are time-averaged over the latest Holocene. Lake level fluctuations associated with the termination of the Little Ice Age (~ 16th century CE) and subsequent encrustation played a key role in shell bed formation and persistence along high-energy littoral platforms, which has implications for structuring specialized communities of benthic fauna. In central South America (18° - 22°S), we studied the limnogeology of small lakes in the Puna and the Pantanal. Analyses of these sites were undertaken to: 1) ascertain how the lakes act as depositional basins; 2) assess sedimentation rates; and 3) construct limnogeological databases to guide future interpretations of ancient sediment cores. At Laguna de los Pozuelos (Argentine Puna), linear sedimentation rates approach 0.14 cm*y⁻¹ in the playa-lake center, and litho- and organo-facies development are dominantly controlled by basin hydrology, climate and biological feedbacks (both nutrient cycling and bioturbation) from waterbirds. At Lagoas Gaíva, Mandioré and Vermelha (Brazilian Pantanal), short-lived radioisotopes indicate uninterrupted depositional rates of 0.11 - 0.24 cm*y⁻¹, and hydrochemical and depositional patterns respond sensitively to changes in the seasonal flooding cycle of the Upper Paraguay River.

Shallow lakes in Muskoka-Haliburton have been largely ignored in previous limnological and paleolimnological studies, as many are considered to be less desirable for cottage development and other cultural activities. Nonetheless, shallow lakes offer important habitat for many animals. 30 oligo- and mesotrophic, shallow lakes were chosen for a paleolimnological study to assess the impacts of multiple stressors on cladoceran invertebrates. Fossil cladoceran remains preserved in the sediment samples of the study lakes were used to evaluate the nature and magnitude of any changes in assemblages from both modern and pre-industrial times. Relationships between present-day assemblages and key environmental variables were investigated using redundancy analysis, which identified that lake area (p<0.01) and Secchi depth (p<0.05) were significant predictors of assemblage composition in the shallow lakes. Secchi depth was not correlated to water clarity measures, as it usually is, but rather to macrophyte abundance. The modern-day assemblages were compared to the pre-industrial assemblages using the snapshot “top-bottom” paleolimnological approach. The top and bottom assemblages were compared using an ANOSIM which was not significant (p=0.2), confirming that modern assemblages were similar to pre-industrial assemblages in shallow lakes. Full core analysis from three shallow lakes also showed only subtle changes in littoral assemblage composition through time, further supporting results from the top/bottom study. The changes recorded were mainly in the pelagic taxa, with the littoral taxa relatively very stable through time. These small, shallow lakes were then compared and combined with a deep lake set from the same region. The results show some striking differences between shallow and deep lakes. For example, pelagic taxa appear to be driving changes within assemblages across a depth gradient, with most of the changes in the deeper lakes. Water chemistry has an increasingly important role in structuring cladoceran assemblage as lakes become deeper, although lake morphometry does play an important role in defining cladoceran assemblages in all the study lakes. Cladoceran assemblages in shallow lakes appear to be more stable than deeper lakes, despite being exposed to the same regional stressors, such as acidification, calcium decline, and climate change. / Thesis (Master, Biology) -- Queen's University, 2012-12-31 13:41:52.662

The freshwater ecosystems in the western Canadian Arctic are threatened by multiple and interacting stressors, as high-latitude regions are undergoing rapid change resulting from climate warming and other human-related activities. However, due to the paucity or absence of monitoring data, little is known about long-term changes in lake ecosystems. This thesis addresses this knowledge gap by using paleolimnological techniques to assess the responses of freshwater ecosystems in the Mackenzie Delta region to three major stressors predicted to become increasingly important, namely impacts from accelerated permafrost thaw, marine storm surges, and hydrocarbon exploration. Using a paired-lake design, six reference lakes were compared to six lakes impacted by retrogressive thaw slumps, an important form of thermokarst in this region. While all of the study lakes have undergone ecologically significant biological changes over the last ~200 years as a result of warming, lakes impacted by thaw slumps have changed more due to the cumulative effects of warming and heightened permafrost thaw. In addition to warming, the outer Mackenzie Delta is a low-lying landscape that is susceptible to inundation by marine storm surges from the Beaufort Sea. A large storm event in 1999 flooded >10,000 hectares of the outer delta. My paleolimnological data show that this marine intrusion resulted in diatom assemblage changes in flooded lakes on a landscape-scale that were unprecedented in the recent past, suggesting recent warming, and associated sea-ice decreases, are making this region more susceptible to storm-surge damage. Finally, lakes impacted by sumps used to dispose of the drilling by-products of hydrocarbon exploration exhibit distinct water chemistry, and are particularly elevated in potassium and chloride, which form a major component of some drilling fluids. Related to this, a discernible change in cladoceran assemblages coeval with the time of sump construction suggest that sump failure has resulted in biological changes in affected lakes. Collectively, this research shows that the ecosystems of the western Canadian Arctic are under threat from multiple stressors that have resulted in changes to the chemistry and biology of the freshwater resources of this region. / Thesis (Ph.D, Biology) -- Queen's University, 2013-04-17 09:30:14.671

Climate change and anthropogenic activities have been known to change the rate of productivity and physical characteristics of temperate lakes. This paleolimnologcial study examines the effect of recent climate change and watershed land-usage activities in nine lakes in the North Frontenac/Addington Highlands region of Ontario, and aims to predict future lake changes based on recent trends. Despite this region being identified as an area highly susceptible to the effects of climate change, no scientific studies have examined the effects of these changes on lakes of the region. Lake sediment analysis for chlorophyll-a concentration, and organic carbon and nitrogen deposition indicate that production has increased in the majority of study lakes in the approximate past century. Water column sampling for dissolved oxygen concentration, temperature, conductivity, and turbidity found the majority of lakes to be thermally stratified and hypoxic in the bottom waters during the ice-covered and ice-free seasons. Climate records also indicate mean annual air temperatures have been increasing since the early 20th century. It was concluded that climate change is increasing production in the lakes of the North Frontenac/Addington Highlands region, and that future increases may increase the zone of hypoxia within the study lakes, or cause anoxia in the lakes. Additionally, it was also found that individual watershed land-usage events (i.e. logging, road construction) affected some of the study lakes, and possibly amplified the increase in production found in some. These findings assist in developing future lake mitigation methods, and preventing future increases in productivity. / Thesis (Master, Geography) -- Queen's University, 2013-09-26 08:41:44.182

Sediment accumulated on a lakebed archives information about past climate and changes in the regional environment. Previous studies (Burgess, 2007; Koff, 2011; Palmer, 2012) in the Northeast Arm of Lake Champlain, specifically Missisquoi Bay and Saint Albans Bay, showed a period (~9,400 - 8,600 yBP) of elevated organic matter deposition in both bays, indicating a productive event that pre-dated any possible anthropogenic influence. However, the record was abruptly cut off and any documentation representing the span of time leading up to this event was not found. The elevated organic matter levels were explained as being the result of a warm, dry environment that reduced lake level and promoted productivity within the bay. A new goal was formulated to lengthen the Holocene record for Missisquoi Bay (MSB) and Saint Albans Bay (SAB) in order to compare paleorecords and capture the span of time leading up to this highly productive event, possibly related to the Champlain Sea/Lake Champlain Transition (~10,000 yBP). One sediment core was taken from each bay as close to the original coordinates as the sediment cores obtained in previous studies (Koff, 2011; Palmer, 2012). The sediment cores were processed in the lab and sediment samples were tested for water content (WC), %C, %N, C:N, and diatom content. Each bay's sediment record consisted of a distinct marker representing lowest water level, separating a Champlain Sea unit at the bottom and an overlying Lake Champlain unit. A warming climate coupled with low lake level during this time may be the cause of the increase of productivity (%C) associated with the markers in both bays. Between ~8,600 - 9,400 yBP, a distinct marker represented evidence of a wetland in Saint Albans Bay before the onset of Lake Champlain. Diatom content in the wetland sediments indicated a generally shallow oligotrophic and alkaline body of water that shifted back and forth from brackish to freshwater. The record shows the wetland was eventually drowned as water level continued to rise, slowly transitioning into the Lake Champlain unit. Proxy results showed that internal processes within the lake continued to change in response to climatic and environmental drivers until present day conditions were reached. At ~9,400 yBP in Missisquoi Bay, there is an erosional unconformity between the Champlain Sea and Lake Champlain units, which corresponds to the low water levels also inferred from the SAB record during that time. After this unconformity, %C results show production within MSB fluctuated, similar to SAB, in response to changing climate and water levels until the present-day conditions of Lake Champlain were established. In sum, MSB and SAB each contain evidence of an ancient shoreline marker in different forms. Both markers indicate that lowest water levels occurred ~9,400 yBP and that lake level has risen ~7 - 8.5 meters since that time. The rise in lake level is associated with the transition into Lake Champlain. This Champlain Sea/Lake Champlain Transition lasted from ~9,400 yBP until ~8,600 yBP. Therefore, the oldest Lake sediment in the Northeast Arm of Lake Champlain is only 8,600 yBP.

Detailed analysis of the physical, chemical, pollen and diatom stratigraphy of sediment cores from Bull Run Lake, Oregon reveals that the lake has been subject to repeated episodes of disruption by volcanic ash fall, fire and other disturbance over the past 4300 years. With the exception of fire, these disruptions have not resulted in long term changes in the watershed or in the characteristics of Bull Run Lake. A major fire in the watershed about 750 years ago altered the vegetation. Since that time the forest has been returning to its former condition.

Thesis (M. Sc.)--York University, 2007. Graduate Programme in Biology. / Typescript. Includes bibliographical references (leaves 83-99). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004 & res_dat=xri:pqdiss & rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation & rft_dat=xri:pqdiss:MR31989.