Paleolimnology of Lakes in Central New England

• Investigators: David Foster, Donna Francis
• Contact: David Foster
• Start date: 2000 BP
• End date: present
• Location: Central New England
• Latitude: +42.55 to +42.85
• Longitude: -72.45 to -71.97
• Elevation:
• Taxa: Chironomidae
• Keywords: disturbance, forest clearance, human impact, land-use change, paleolimnology
• Release date: 2003
• EML version: knb-lter-hfr.28.2
• Revisions:
• Abstract:

  Paleolimnological studies of three small watersheds in central New England were undertaken to determine the influence of deforestation and agriculture on lake systems, as well as the response of the lakes to agricultural abandonment and reforestation, or the cessation of disturbance. Sites were chosen to represent a range of past land-use activities, while keeping other site factors constant. The study was designed to complement the historical and paleoecological studies of the central Massachusetts area of Fuller et al. (1998) and Foster et al. (1998). Changes in terrestrial vegetation were documented using the pollen record from each lake, and changes in aquatic systems were documented through fossil chironomid assemblages (Chironomidae: Diptera) and sediment chemistry. Dated cores were analyzed for pollen, fossil chironomids, percent organic matter, carbon and nitrogen, and sedimentation changes. Increased sedimentation rates occurred in all lakes during the settlement period, and small increases in productivity changes resulted from the increased runoff. Productivity changes, as indicated by organic material, C:N ratios, and chironomid assemblages, are more pronounced in North Round and Wickett Ponds than in Pecker Pond, even though agricultural activity was most intense at Pecker Pond. North Round and Wickett Ponds are more shallow than Pecker, and were more affected by sediment and nutrient inputs from the watershed. North Round Pond was the least impacted site, with only minimal logging and no agriculture, but still significant changes occurred during the settlement period. The sedimentation rates and productivity continue to be higher than pre-settlement levels, indicating that the systems have not returned to pre-disturbance states. This is similar to the response of forest vegetation studied by Fuller et al. (1998) in the Central Massachusetts study. The low intensity agricultural practices of the 19th Century and small watershed sizes contributed to the fact that the response of these lakes was minimal.

• Methods:

  Sediment analyses

  % organic carbon was determined by standard loss-on-ignition at 550°C {Dean 1974 #1320}. Total carbon and nitrogen were determined for 5-6 mg dry subsamples wit a Fisons 1500 n/C CHN Analyzer. Average recovery of a known standard (atropine) was 99% for both nitrogen and carbon. Particle size was analyzed on 1 g subsamples previously treated with 30% h2O2 to remove organic material. Analysis was done with a Coulter LS 200 laser-diffraction particle-size analyzer employing fluid module software and a Fraunhofer optical model.

  Pollen analysis

  Sediment preparation for pollen analysis followed standard procedures . At least 500 arboreal pollen grains were counted for each level. Pollen percentages were based on a pollen sum of all terrestrial pollen grains and spores. The timing of European settlement in the cores was assessed from changes in pollen representing open vegetation, including a decline in tree pollen and an increase in herbaceous pollen, especially ragweed (Ambrosia), sorrel (Rumex) and grass (Poaceae).

  210Pb dating

  Activity of 210Pb in sediment samples was determined by the alpha activity of its daughter product 210Po after samples were prepared using the method D.R. Engstrom (personal communication). 210Pb inventory was counted on an Ortec Alpha Spectrometer 576A. Ages and sediment accumulation rates were calculated with a CRS (constant rate of supply) point transformation model {Binford 1990 #1350}{Binford, Kahl, et al. 1993 #1340}.

  Radiocarbon dating

  Bulk sediment samples (4-5 g) were analyzed at Beta Analytic, Miami, Florida, for 14C dates. The resulting determinations were converted to calendar years with the program Calib version 3.0 based on a combination of marine coral and bidecadal tree-ring data sets {Stuiver and Reimer 1993 #1410}. Age models were derived from radiocarbon dates of lake sediments along with 210Pb dates for each site. Linear interpolations were made between 14C dates. An age of 250 years was chosen for the settlement horizons based on historical information.

  Charcoal analysis

  Microscopic charcoal was tallied for each core by the point-intercept method. Eucalyptus pollen suspension of known volume and concentration was added to each sample during preparation, and eucalyptus pollen grains were counted simultaneously with charcoal to estimate charcoal-pollen ratios.

• Use:

  This dataset is released to the public and may be freely downloaded. Please keep the designated Contact person informed of any plans to use the dataset. Consultation or collaboration with the original investigators is strongly encouraged. Publications and data products that make use of the dataset must include proper acknowledgement. For more information on LTER Network data access and use policies, please see: http://www.lternet.edu/data/netpolicy.html.

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