CHARCOAL-RICH MOUNDS in LITCHFIELD COUNTY CT RECORD WIDESPREAD HILLSLOPE DISTURBANCE in the IRON CORRIDOR from MID 18Th to EARLY 20Th CENTURIES
Total Page:16
File Type:pdf, Size:1020Kb
CHARCOAL-RICH MOUNDS IN LITCHFIELD COUNTY CT RECORD WIDESPREAD HILLSLOPE DISTURBANCE IN THE IRON CORRIDOR FROM MID 18th TO EARLY 20th CENTURIES by Mary E. Ignatiadis Professor David P. Dethier, Advisor A thesis Submitted in partial fulfillment of the requirements for the Degree of Bachelor of Arts With Honors in Geosciences Williams College Williamstown, Massachusetts May 19, 2016 i ABSTRACT ACKNOWLEDGEMENTS TABLE OF CONTENTS ABSTRACT……………………………………………………….…………….……...….i ACKNOWLEDGEMENTS…………………………………………………....………….ii LIST OF FIGURES………………………………………….…………..……….…...…...v LIST OF TABLES…………………………..…….……………………………….……...x LIST OF EQUATIONS………..………….……………………………….………….….xi LIST OF APPENDICES…………………………………………………………........…xii INTRODUCTION………………………………………………………………...……….1 European settlement altered regional sediment budgets…………………….….....3 The origins of charcoaling in northwestern Connecticut………………………......5 Charcoaling as a control on sediment transport and soil formation....……….…..8 Potential effects of charcoaling activity on sedimentation in the Housatonic River Valley. ……………………………………………………………………………………………10 The study of charcoaling mounds in Europe and the U.S……………………………..…12 SETTING…………………………………………………………………..………….…14 Topography……………………………………………………..…………….….14 Bedrock geology……………………………………………………………...…..14 Quaternary geology…………………………………………………………...…17 Climate and vegetation…………………………………………….……….........18 Study Areas………………………………………………………………......…..18 METHODS……………………………………………………………………………….21 Field observations and sampling....……..………..………………...………….…21 Sample analysis………………………………………………………....………..23 Moisture content and organic content……………………………..……..23 Grain size………………………………………………………………...24 Carbon to nitrogen ratios………………………………………………...25 Modeling RCMs from field measurements…………………………………...…..25 Volume of disturbed sediment…………………………………………...28 Diffusion from field measurements…………………………...…..……..29 Modeling RCMs using LiDAR analysis in a GIS environment………………......30 Calculating diffusion within a GIS environment………………………………...32 Statistical analysis………………………...……………………………………..33 RESULTS……………………………………………………………..…………………34 Field observation and sampling of soil profiles………………………………....34 ii Soil profiles………………………………………………………………34 Sample analysis…………………………………………………………………..37 Texture…………………………………………………………….……..37 Organic matter content……………………………………………….…..38 Carbon to nitrogen ratios………………………………………………...39 Mound dimensions……………………………………………………………….40 Measurements in ArcGIS………………………………………………………...44 Volume and diffusion of mound sediments……………………………………….45 Volume……………………………………………...……………………45 Diffusion…………………………………………………………………47 Regressions of surface area, volume, and ∆CM with slope.......................49 DISCUSSION………………………...……………………………………...…………..51 Impact of mound construction on carbon cycling in northwestern Connecticut...52 Long-term impact of mound building on carbon storage………………………..57 Impact of mound construction on sediment transport…………………………...58 Contemporary sediment transport on mounds……………………………...……62 The broader impacts of Connecticut’s charcoaling industry………….......….…62 REFERENCES……………………………………………………………....……..…....64 APPENDICES…………………………………………………………………………...72 Appendix A…………………………………………………………………………........72 Appendix B…………………………..………………………………………………..…74 Appendix C………………………………………………………………………………81 Appendix D………………………………………………………………………………98 iii ABSTRACT Charcoaling mounds constructed in northwestern Connecticut from the mid-18th to early 20th centuries fueled the region’s iron industry and continue to impact the landscape today. The total number (20,500) and high concentration of mounds (40-80 mounds km-2) in Litchfield County suggests that they are important markers for the onset of the Anthropocene in this area, but the mounds have not been studied previously. We sampled soil profiles and made field and GIS-based measurements from four study areas that indicated the hillslope mounds represent a discrete pulse of downslope sediment transport and carbon sequestration. Mound sediment volumes averaged ~65 m3 and had been moved downslope 0.65-1.08 m by charcoaling activity. Dislocation of hillslope sediment for mound construction increased the average rate of sediment transport in our study 2 – 4 x 10-6 m2 yr-1, such that the impact of charcoaling activity on sediment transport was comparable to other biogeomorphic processes over the ~150 year lifetime of the industry, but insignificant on a 10 ky scale. In contrast to sediment storage, the impact of charcoaling activity on soil C storage is significant on a 10 ky scale. Mounds store refractory C in the form of charcoal up to 80 cm below the surface, 60 cm below most C storage in soil profiles from adjacent hillslopes. Charcoaling mounds are efficient long-term C reservoirs, but offset only a small fraction of the ~two million tonnes of eCO2 emitted by charcoaling activity over the lifetime of the industry. iv ACKNOWLEDGEMENTS I would like to thank David Dethier for his mentorship, extreme patience, and support during the writing of this thesis, and for encouraging me to do a thesis long before I believed that I was capable of one. I am also grateful to my field advisors, Will Ouimet and Michael Hren, and my second reader, Bud Wobus, for their advice and support this year, and to Jay Racela of the Williams Center for Environmental Studies, who made both his lab and extensive knowledge available for this project. My fellow thesis students at Williams and in the Keck Geology Consortium helped me to collect data and maintain my sanity; Sally Donovan (Carleton College) and Caroline Atwood (Williams College) merit special mention. Thank you also to the friends who volunteered to help with my lab work this summer. The Keck Geology Consortium, the Clare Boothe Luce Program of the Henry Luce Foundation, and the National Science Foundation funded my research and made this thesis possible. v LIST OF FIGURES Figure 1 Outline of southern New England (Gordon, 2000). Litchfield County, Connecticut is identified as the Salisbury District, named after the site of the first iron mine. Approximately one third of the Housatonic River watershed is within the county (Tiner, 2013). ...................................................................................................................... 2 Figure 2 “View of Cream Hill, late 19th century, Cornwall, CT” (Cornwall (CT) Historical Society). By the late 1800’s, 80% of forests in southern New England had been cleared at least once (Foster and Aber, 2004). .................................................................... 2 Figure 3 Relict charcoaling mounds (RCMs; green dots) identified from LiDAR of Litchfield County, CT. Figure from Ouimet (2015). .......................................................... 4 Figure 4 A collier packs sediment onto a charcoaling mound (Studley, 1981). ................. 7 Figure 5 Wood stack perched on a hillslope in Cornwall, CT, ready to be covered in sediment and burned (Cornwall (CT) Historical Society). ................................................. 7 Figure 6. A relict charcoaling mound (RCM) is identified by its flat surface, a steep back wall (outlined in yellow) that extends laterally as a ditch (also in yellow), and the relatively steep ledge (white) from the front rim to the downhill slope. Photos courtesy of Will Ouimet. ....................................................................................................................... 8 Figure 7 An east-west cross-section of northern Litchfield County from the Bedrock Geologic Map of Connecticut (Rodgers, 1985). Basement rocks are labeled Yg, Taconic allochthons are labeled Єm, meta-sediments are labeled Єs, and the Walloomsac formation is labeled Ow. There is no vertical exaggeration. Complete unit descriptions are in Appendix B. ............................................................................................................ 16 Figure 8 Calibrated 14C age estimates of ice margin positions and dates (from Ridge, 2015). Dates are based on the radiocarbon dating of lake-bottom sediments and on varve chronology. ....................................................................................................................... 17 Figure 9. State map of Connecticut showing our field locations (black stars) in Litchfield County (northwestern Connecticut) and Windham County (northeastern Connecticut). 19 Figure 10 A sketch illustrating field measurements of a relict charcoal mound and generalized cross-section. We measured the vertical distance from the base of the mound to its current surface using a TruePulse360 Rangefinder while standing just downhill of the mound. The original hillslope (red) extends from the top of the back cut to the base of the mound.......................................................................................................................... 22 vi Figure 11 (A) Plan view sketch of a relict charcoaling mound (RCM) showing mound length (LM; green) and platform width (WM; blue) as measured in the field. The mound is bounded by a berm or cut into the hillslope. Ditches along the sides of the mounds meet at the base of the mound and form small channels. (B) Plan view hillshade of an RCM has been annotated to show LM, WM, the back cut, and the ditches that characterize this microtopographic feature. RCMs are identifiable from LiDAR because of the contrast in the steepness of the back cut and ledge with the flat mound surface and ditch. ............... 23 Figure 12. Mound construction