PEAT BAY: AN ARCHIVE OF LATE HOLOCENE CHANGES AND ANTHROPOGENIC IMPACTS AT THE SAVANNAH RIVER SITE, SOUTH CAROLINA

Wetland peat deposits can be excellent archives of past changes in the ecological conditions under which they formed. These changes can be identified by changes with depth in the botanical and mineralogical components of the peat, as well as changes in organic petrography (degree of humification, framework to matrix ratio, palynofacies analysis, macropore/micropore ratios, etc.). These changes may result from natural processes (plant successions, climate cycling, etc.) or anthropogenic events (land-clearing, drainage disruptions, etc.). Peat deposits can also sequester a wide variety of natural and human-derived trace elements introduced from the air or ground water. Thirteen cores were collected from Peat Bay, a wetland located at the Savannah River Site (a facility constructed during the 1950's to produce materials used in fabrication of nuclear weapons). Samples were processed at 2-cm increments for micropetrographic, palynologic, and chemical (ICP-MS) analyses. A previous radiocarbon date of 4000 ybp was available for the base this deposit.

Petrographic and palynologic analyses demonstrated the complexity of the layering and rapidity of past ecosystem changes at this site throughout its history. Several changes in organic petrography (increases in humification, fungal remains, siliceous lag layers, and decreases in palynomorph stain acceptance), as well as changes in types and percentages of palynomorphs, were interpreted as being most likely related to recent anthropogenic activities. Combined Cs-137/Pb-210 dating indicated that some of the most significant of these changes occurred in the early 1950’s, coinciding with the beginning of construction of the Savannah River Site. Other changes dating in the mid-1980’s coincided with the damming of Steel Creek to produce L-Lake, a reactor cooling reservoir located up-gradient from the study area. In general, trace element concentrations related to weapons research tended to correlate with petrographic composition and proximity to L-Lake rather than time-lines, suggesting compositional controls over sequestration of these elements.