DesJardins, Michelle J'aime2024-12-172024-12-172003https://hdl.handle.net/1828/20855Sediment cores were collected from two lakes in Kejimkujik National Park, Nova Scotia to investigate natural and anthropogenic inputs of Hg and Pb to the lakes and the reliability of the lake sediments to record depositional history. The total mass of Hg accumulated in the sediments of Big Dam West Lake (BOW) and Big Dam East Lake (BDE) since inception after the Wisconsinan Glaciation 13,000 years ago is estimated to be 14.7 and 3.4 kg, respectively. Hg profiles indicate that the average flux of Hg to the lakes for the last 20 years has been 25.0 and 13.0 μg/m2/yr for BDW and BOE, respectively, which is 3 times higher than pre-industrial background sediments. Hg profiles show that the timing of recent historical anthropogenic activities have been preserved in the Hg profiles of both lakes. However, the magnitudes of the Hg increases are asynchronous when plotted as a function of time, but not when plotted as a function of depth, thereby suggesting that post-depositional diagenetic remobilization may partially be responsible for the upcore emichments. Unlike the Hg flux profiles, which show BOW having a greater flux of Hg throughout the cores, the Pb flux profiles show that the two lakes had similar fluxes of Pb at pre-1850 depths. Above these depths, BOE shows significantly larger Pb flux rates than BOW. In the top 3 cm, BDE's Pb flux of 5.3 mg/m2/yr is 1.9 times greater than BDW's Pb flux of2.8 mg/m2/yr. This difference is believed to be the result of upward remobilization, with more Pb being remobilized in BDE. The total mass of Pb accumulated since inception is estimated to be 5305 and 1502 kg in BDW and BDE, respectively. Only the Pb increases in BDW coincide with historical increases in atmospheric Pb inputs associated with automobile emissions. Neither lake however records any significant decreases in the uppermost sediments as would be expected from the significant reductions in atmospheric Pb concentrations that have occurred since the phasing out of leaded gasoline in the 1970' s. Furthermore, profiles of Pb isotope ratios show fluctuations in the profiles that coincide with known historical events, but the anthropogenic component is always more radiogenic than expected, suggesting there is upward remobilization of Pb from deeper more radiogenic sediments in both lakes. This interpretation is further supported by concentration profiles from six cores which show that the Pb profiles align better when plotted as a function of depth rather than age. These results provide strong evidence that the Pb concentration profiles, at least in BDE, are more a function of depth, and thus diagenetic conditions, than of depositional history. Porewater data provide further evidence to support the interpretation of Pb and Hg remobilization in the sediments of BDW and BDE. Upward decreasing concentrations of both Hg and Pb measured in porewaters suggest that diffusion of Hg and Pb will predominantly occur in an upward direction. Dissolved oxygen, pH and Eh profiles show the disappearance of DO by 4 cm depth accompanied by significant changes in pH and redox between O and 6-7 cm. BDE in particular shows rapid changes in pH and redox between 5 and 7cm depth, indicating that the decay of organic matter is much more rapid in BDE than BDW, which supports the data from the sediment profiles that indicate more Pb is remobilized in BDE than BDW. Precipitation samples were collected over a one-year period to determine sources of anthropogenic heavy metal pollutants to the park using Pb isotope ratios. Pb isotope compositions indicate that anthropogenic pollution from populated and industrial regions of northeastern U.S. and southeastern Canada is being transported to Kejirnkujik National Park. In general there was a dominantly Canadian source during the fall months of 2001 and a dominantly American source during the winter and spring months of 2002. The isotopic composition of the precipitation samples range from 206Pb/2°7Pb ratios of 1.165 to 1.20, indicating U.S. contributions ranging from 30-100% or Canadian contributions ranging from 0-70%. The annual average 206Pbi2° 7Pb ratio is 1.181 and indicates that on an annual basis the U.S. contribution of Pb to Kejirnkujik National Park is 62% (or 38% Canadian). The average annual Pb isotope composition of the precipitation represents the value of the anthropogenic component that should be observed in the surface sediments. However the calculated 206Pbi2°7Pb anthropogenic component in all sediments cores is more radiogenic than would be expected, indicating that there is upward remobilization of Pb from deeper more radiogenic sediments in both lakes. Knowing the true isotopic composition of anthropogenic Pb from precipitation and that of the background sediments, a calculation is presented to quantify the magnitude of remobilized background Pb in the topmost sediment layer. Only BDE provides the necessary conditions to allow such a calculation. The amount of remobilized background Pb in the topmost sediment sample from a BDE core is estimated to be approximately 25.1 μgig, which is 51 % of the total Pb in the labile fraction of that sample.enAvailable to the World Wide WebThesis