ELEMENTAL CORE SCANNING USED TO IDENTIFY ANTHROPOGENIC AND PEAT LAYERS AT A FUTURE WETLAND RESTORATION SITE

Foothills Preserve is a wetland restoration site on a retired cranberry farm in Plymouth, Massachusetts. As part of a larger project, “Achieving Wetland: Metrics and Methods,” this work aims to determine metrics to measure success of wetland restoration sites. Collectively, we have gathered pre-restoration soil, vegetation, hydrology, water and soil chemistry data, and environmental conditions, which will all be re-assessed post-restoration. The purpose of this portion of this study is to examine what is happening in the subsurface and how elemental compositions of different soil types from the original wetland and subsequent cranberry farming will impact water and soil chemistry of the restored wetland, as well as the functioning of the wetland itself. In order to examine this, soil cores were taken from the pre-restoration site and one was scanned with an x-ray fluorescence machine. The elemental data from this scan was then plotted versus soil depth and compared with images of the core to determine correlations between element abundance and soil type. The data showed high abundances of Si, K and Os in the sand laid down during farming, and high abundances of Ti in the original peat. Ba was present in the sand and agricultural soil from farming, but not in the original wetland peat, and was therefore used to demarcate the transition from the original peat to the agricultural soil and sand. Pb was present in higher amounts in the sand and agricultural soil but not in the original peat, which could indicate residual pesticides. From this analysis, it is possible to determine where the original wetland peat ends and where the agricultural soils and sand begin, as Si, K, Os and Ti are all indicators of specific soil types. Demarcating the different soil types provides an image of how thick the anthropogenic aquifer, consisting of the agricultural soil and sand, is above the original peat. This image is useful for the restoration process because it allows decisions to be made about whether the agricultural soils and sand can be removed or if they need to be incorporated into the new wetland. The elemental composition of this anthropogenic aquifer is also important in determining whether these soils can be removed from the site and can also help predict when there will be troublesome runoff from water coming into contact with these agricultural soils. Subsequent filling of the wetland with water could mobilize soil nutrients and impact wildlife, so a thorough characterization of the subsurface can help guide restoration work on site.