Integrating the effects of nutrient and DOC loading on lakes over millennial timescales

Background/Question/Methods

One of the enduring themes in paleolimnology is the long-term trophic development of lakes – as a consequence of natural or anthropogenic changes in material export from the terrestrial catchment. While we’ve become reasonably proficient in using lake-sediment records to reconstruct material fluxes (nutrients, major ions, sediment) associated with human disturbance, progress on the effects of natural forcing (climate, fire, vegetation and soil development) is more limited largely because of the comparative subtlety of the signals and the complexity of the catchment processes involved. And trophic reconstruction itself has been a particularly elusive grail, owing to the fact that we have no reliable proxy for total ecosystem productivity and because heterotrophic and autotrophic production cannot at present be de-convolved in the sediment record.

Results/Conclusions

This presentation will review concepts of lake productivity from a paleo- and neo-limnological perspective along with efforts to reconstruct trophic change and its linkages to the transfer of both organic carbon and nutrients from the terrestrial system. Nutrient export, particularly that associated with human activities, has received the greatest attention in paleolimnological studies, owing to its obvious effects on autotrophic productivity. However, organic carbon subsidies, which reflect long-term-catchment vegetation succession and soil process, have equally profound effects on biological structure and trophic interactions in aquatic systems. This talk will thus consider the contrasting trajectories and drivers of heterotrophic and autotrophic production in the context of postglacial landscape development, land-use disturbance, and climate change.