Nitrogen Isotopes of Maize & Pumpkin from a Nineteenth-Century New York Farmstead: Insights Into Fertilization & Nutrient Pollution

Van Schaick Island, located at the confluence of the Mohawk and Hudson Rivers in Cohoes, New York, is historically significant as a site of early Euro-colonial land use.  The island served as the homestead of the Van Schaick family from 1674 until the 1830s.  Van Schaick Mansion, built in the 1750s, was used as military headquarters and served as the New York State capital during the American Revolution.  During the 1830s to 1852, as the Van Schaick family shrank, the island and mansion were occupied by tenants, who continued to farm on the island.  Archaeological surveys conducted at the mansion since 2016 by the New York State Museum aimed to explore the spatial dynamics of the Van Schaick family's enslavement of African Americans on the property.  One excavation uncovered a 19th-century midden for food waste disposal.  The midden was initially protected by a shed and later by a floor added in the 1850s for extra safeguarding.  The waterlogged conditions potentially facilitated the preservation of materials, revealing highly-preserved non-carbonized archaeobotanicals of over 41 different taxa.  This study focuses on historical farming practices, particularly fertilizer use by the tenants at Van Schaick Mansion.  By analyzing these archaeobotanical remains dating to the onset of industrial agriculture, we aim to understand past fertilization methods and develop a baseline to track temporal changes in NY.  Archaeology offers insights into farming practices before large-scale agriculture arose and threatened environmental and public health with nutrient pollution.  Our analysis of nitrogen stable isotopes (δ¹⁵N) from modern and archaeobotanical maize and pumpkin/squash specimens revealed that half of the Van Schaick crops slightly exceeded the unfertilized baseline, +1.6 ± 1.0 ‰ (herbivore bone collagen minus trophic enrichment), suggesting minimal or no fertilization.  Their δ¹⁵N signatures resemble expected values from mineral and atmospheric sources.  Analysis of modern pumpkin seeds showed consistency of δ¹⁵N values amongst seeds from different pumpkins growing on the same plant. However, values differed by more than 2 ‰  when compared with seeds from other plants grown in the same field. These data show the importance of understanding the natural variability when interpreting isotope values from limited samples.