SPHEROIDAL CARBONACEOUS PARTICLES IN A VIRGINIA MILL POND PROVIDE A RECORD OF LOCAL AND REGIONAL COAL COMBUSTION

Spheroidal carbonaceous particles (SCP), a constituent of coal fly ash, are a sensitive indicator of local and regional coal combustion archived in lake sediments. Their unique morphology and chemical composition cannot be attributed to any naturally occurring substance on Earth. SCP accumulation has also been correlated with heavy metals in sediments, including Fe, Ti, Pb, and As. We reconstructed SCP accumulation in a former mill pond in Williamsburg, VA, Lake Matoaka. The particles first appeared in Lake Matoaka in c.1750 and steadily increased from 15-300 SCP/gDM peaking in 1780. SCP concentration were constant at ~100-200 SCP/gDM from c.1800-1860, increased abruptly from 500 SCP/gDM in 1860 to >8,000 SCP/gDM in 1950. Recent accumulation rates have decreased in response to emission restricting legislation in 1970 but continue to accumulate ~1000 SCP/gDM in surface sediments. Overall, we find a bimodal distribution with peaks c. 1780 and c. 1950. Grain size analysis shows a statistically significant difference in grains from the two peaks indicating different fly ash provenance. We believe that our study is the first to identify SCPs in sediments prior to the early 1800s, making this record unique. We also find that trends in SCP accumulation mirror major historical events including prominent socio-political changes, military conflicts, and economic depressions.