Paleolimnological Study of Willard and Russell Ponds in New Hampshire

ABSTRACT

Long-term environmental trends in Willard and Russell ponds in New Hampshire were assessed using paleolimnological techniques. Algal microfossils (diatom valves and chrysophyte scales) and pollen remains were analyzed from sediment cores representing the depositional environment of the last 200–300 years. Sediment characteristics and geochemical data were also studied to assess past limnological and watershed changes. The export of ions from the watershed has increased in both ponds and trace metal concentrations in sediments have increased over the post-industrial period. Pollen data suggest that the terrestrial vegetation in the watershed had changed in the past. Stratigraphic changes in diatom and chrysophyte taxa indicated lakewater quality changes in Willard and Russell ponds in the past. Diatom assemblages were quantified to infer past total phosphorus (TP), pH, and chloride (CI) concentrations, using diatom-based inference models that have been developed for the lakes in the northeastern USA. Past inferred TP concentrations remained relatively unchanged and both water bodies can be categorized as oligotrophic for the past 200–300 years. However, inferred pH and CI levels have changed in the study ponds. Although changes in inferred CI are most likely related to watershed disturbances, the recent decline in inferred pH is most likely due to increased acidic precipitation. The study shows the usefulness of a paleolimnological approach in determining long-term water quality monitoring trends. These long-term data would be useful in developing effective lake management and restoration plans in New Hampshire.

Key Words:

• paleolimnology
• diatoms
• chrysophytes
• metals
• New Hampshire