Using Natural Archives to Reconstruct Environmental Changes Caused by Human Activities

Abstract

The objective of this thesis was to develop new approaches and perspectives in resolving historical information from natural archives. Paleolimnology, the study of past aquatic environments using lake sediment cores, has greatly advanced our understanding of previous environments. This thesis intended to expand the range of historical information that may be used in paleolimnology and for historical reconstructions. Here I used pond sediments and a bat guano deposit as natural archives that recorded a history of events that I interpreted using a combination of chemical and biological measurements. In particular, I applied sterols and stanols as novel approaches for interpreting historical information in natural archives. First, I examined the chemical and biological composition of lake sediments to track the human occupation of Dorset and Thule people in Canada’s High Arctic. As predicted, sterols, stanols, cadmium, copper, and zinc increased in sediments deposited during known periods of human occupation owing to nutrient addition, whereas these increases were absent in reference sites. These methods were further corroborated in a study of 20th century human occupation at Resolute Bay by examining similar constituents in waterbodies that received wastewater discharge. Second, I used δ15N and δ13C to track the agricultural history of Jamaica using a 4,300-year-old bat guano deposit. I then used C/N, δ13C, and sterol and stanol ratios to detect two periods of increased frugivory relative to insectivory-based foraging. Metals normalized to titanium increased during the Industrial Revolution and 206Pb/207Pb values tracked the introduction and subsequent ban of leaded gasoline. I also examined the same chemical constituents in fresh bat guano from frugivorous, insectivorous, and sanguinivorous bats. C/N values decreased and cholestanol, cholesterol, and cholesterol/(cholesterol+sitosterol) values increased in bat guano according to trophic level. This thesis demonstrated the strength of examining several independent lines of evidence to reconstruct historical activities in both High Arctic waterbody sediments and a bat guano deposit. I showed that human activities were traceable within natural archives over several thousand years thus demonstrating that the multi-proxy approach is a powerful tool that can conduct a broad range of analyses in various natural archives.