Lake sediments record the flux of materials (nutrients, pollutants, particulates) through a lake system both qualitatively, as changes in the composition of geochemical and biological tracers, as well as quantitatively, through changes in their rate of burial. Burial rates provide a direct link to contemporary (neo-) limnological studies as well as management efforts aimed at load reductions, but are difficult to reconstruct accurately from single cores owing to the spatial and temporal variability of sediment deposition in most lakes. The accurate determination of whole-lake burial rates from analysis of multiple cores, though requiring more effort per lake, can help resolve such problems and improve our understanding of sediment heterogeneity at multiple scales. Partial solutions to these problems also include focusing corrections based on 210Pb flux, co-evaluation of concentration profiles, trend analysis using multiple lakes, and trend replication based on a small number of cores from the same lake. Recent multi-core studies demonstrate that no single core site faithfully records the whole-lake time-resolved input of materials, but that as few as five well-placed cores can provide a reliable record of whole-lake sediment flux for morphometrically simple basins. Lake-wide sediment fluxes can be coupled with reconstructed outflow losses to calculate historical changes in watershed and atmospheric loading of nutrients, metals, and other constituents. The ability of paleolimnology to accurately assess the sedimentary flux and extend the period of reference into the distant past represents an important contribution to the understanding of biogeochemical processes and their response to human and natural disturbance.
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Acknowledgments This review is dedicated to the scientific career of our friend and colleague, Rick Battarbee, whose research, mentoring, and leadership have so greatly advanced the field of paleolimnology. Funding for the work at Lochnagar was partially supported by the Department for Environment, Food and Rural Affairs (then DETR) and the EU MOLAR project (contract No. ENV4-CT95-0007). The other work on Scottish lake metals was funded as part of Eurolimpacs (Integrated Project to evaluate the Impacts of Global Change on European Freshwater Ecosystems) (Project No. GOCE-CT-2003-505540). Work on lakes Pepin and St. Croix of the upper Mississippi River was supported by the Minnesota Pollution Control Agency, the Metropolitan Council Environmental Services, and the US National Park Service.
- Atmospheric deposition
- Multiple cores
- Sediment focusing
- Trace metals