TIMING OF FORMATION AND DURATION AND FREQUENCY OF OCCUPATION OF A BEAVER POND IN SOUTHWESTERN NEW HAMPSHIRE

Channel modifications of the modern Cold River, located in southwestern NH, are caused predominately by beaver damming and large scale events. Located along the river is a beaver-dammed pond occupying an abandoned meander loop. The pond is not shown on historic topographic maps, but is clearly evident on the latest 1998 map, leading to the hypothesis that the meander was abandoned during the 1936 Great New England hurricane. Channel abandonment may have been aided by a sturdy 7-ft. high and 44-ft. wide beaver dam. The frequency of occupation was estimated to be around 15 years based on young ash and forsythia growing on the dam.

Six Cores were taken with a Livingston core at the predicted location of the thalweg, allowing the cores to obtain the maximum thickness. Core 1 (BP17-LC2-Sec1) the longest core, measuring 86cm, was taken beneath the cut bank of the dammed meander, and a wood sample was obtained from the bottom of the core. Core 2 (BP17-LC4-Sec1) was 75 cm. The wood from core 1, the lowermost gyttja from core 2, and 3 samples from the remains of dead tree in the pond were sent in for radiocarbon dating. Magnetic susceptibility was taken with a point sensor at 1 cm intervals for each core and used for correlation. To determine the duration and frequency of occupation, cores were subsampled for later analysis of bulk densities and stable isotopes using a mass spectrometer.

The calibrated (2 sigma) radiocarbon dates are as follows: 7436-7524 ±33 BP for the bottom most gyttja in core 2; 137-224 ±24, 277-320 ±27, and 137-224 ±24 BP for the trees; and 554-610 ±32 years BP for the wood in core 1. The radiocarbon dates demonstrate that not only was the meander abandoned several thousand years before the 1936 hurricane, but more interestingly shows that the Cold River reached its current grade by around 7500 BP. The age variations for the wood samples suggest that over the long term, beavers periodically dammed and abandoned the meander, allowing the pond to form and dry up on a time scale of hundreds of years. The duration and frequency of occupation during the lifetime of a particular pond has yet to be determined.