Northeastern Section - 49th Annual Meeting (23–25 March)

Paper No. 12
Presentation Time: 8:00 AM-12:00 PM


COLL, James M., Civil, Environmental and Architectural Engineering, University of Kansas, 116 Switch Rd, Andover, NH 03216,

After retrieving nearly 10 meters of sediment from the bottom of what was believed to be a kettle bog, a remnant of the last glacial retreat up the Baker Valley in New Hampshire, a high resolution organic content record has been established, going back more than 6000 years, with three radiocarbon dates constraining this interval. All ages are presented as calibrated years before present. Preliminary analyses of the core reveal several unexpected, high magnitude features in the organic content time series. Since the mid-Holocene, the bog has experienced a general downward trend in organic content; from roughly 35% LOI at 6000 yr. BP to 20% by 1000 yr. BP. During this period, the record of organic content oscillates sinusoidally by ±7.5 % LOI from the trend line. Organic content increases abruptly to 45-50% LOI after 1000 yr. BP, and stays at that level until ca. 400 ± 35 yr. BP. While the visual stratigraphy of the core matches changes in composition in certain places, this large spike in organic matter occurred in an otherwise unremarkable core section, and the increase to 45% LOI is represented by multiple samples. After 400 yr. BP, LOI values plunge to below 3% in the span of 2 centimeters, and remain low for another 30 cm. The texture of low LOI interval is very fine sand and is a distinctly lighter color, most likely representative of a flood event that mobilized Baker River alluvium and deposited it into the relatively deeper water of the bog pond. Although the Bog elevation is mapped at just above the 100-year flood limits on FEMA maps, the Baker River experienced many very high magnitude floods during the later 1800’s and early 1900’s. While it’s uncertain if these large floods pre-date deforestation by logging, we anticipate that information as an outcome of our research. Above the sand deposit, in the upper 50 cm of the core, LOI recovers to values of about 45%, but the core color remains lighter than before 400 yr. BP. Our uppermost radiocarbon date falls within this interval, just as organic levels increase above the sand deposit. Core water content tracks that of LOI along the entire length of the core. Research is ongoing, and we are continuing to add new data series and date analyses to this unique and unstudied portion of the Baker River Valley.