Pre-Columbian lead pollution from Native American galena processing and land use in the midcontinental United States

Abstract

The presence and sources of pre-Columbian (before 1492 CE) lead (Pb) pollution in the midcontinental United States were investigated using geochemical and Pb isotope analyses on sediment cores recovered from Avery Lake, a floodplain lake located directly adjacent to the Kincaid Mounds archaeological site on the lower Ohio River, Illinois. Geochemical results indicate the presence of Pb pollution during the Baumer (300 BCE to 300 CE) and Mississippian (1150–1450 CE) occupations, and since the 1800s. Pb isotope results link Mississippian Pb pollution to the processing and use of galena primarily from southeastern and/or central Missouri, and to a lesser extent the upper Mississippi River valley, with ∼1.5 t (metric tons) of galena-derived Pb deposited in Avery Lake during this time. Pb pollution during the Baumer phase, equating to ∼0.4 t of Pb, was not accompanied by a Pb isotope excursion and most likely originated from local biomass burning. These results provide new information about the environmental impacts associated with pre-Columbian Native Americans’ interaction with and utilization of their landscape and its resources. INTRODUCTION Archaeological records indicate that galena (PbS, a lead-sulfide mineral and primary lead ore) was utilized by pre-Columbian Native American populations in eastern North America for nearly 10,000 yr (Walthall, 1981). While some evidence has indicated that pre-Columbian societies generated limited lead (Pb) pollution as a biproduct of copper mining (Pompeani et al., 2013) and biomass burning (Bird et al., 2019; Pompeani et al., 2019), there has been no conclusive evidence that the extraction, trade, and use of galena specifically resulted in environmental impacts. This contrasts with other regions with long histories of Pb ore utilization, like Europe and South America, where early Pb pollution signals are widely distributed and well preserved in natural archives (e.g., Bränvall et al., 2001; Cooke et al., 2008). One explanation for this difference is that smelting was not needed to extract Pb from North American Pb ores given extensive surface exposures of high-purity galena deposits throughout the Missouri, Ohio, and upper Mississippi River basins (Walthall, 1981). There is also little indication that pre-Columbian societies developed smelting techniques prior to European contact. Instead, Pb ores like galena were either utilized in crystal form or ground into a powder. Despite this, it is unlikely that there were no environmental impacts associated with the extraction, processing, and use of galena by Native American populations prior to 1500 CE. Instead, pollution was likely expressed on a local level, which would account for the lack of widespread pre-Columbian Pb pollution in eastern North America. As a consequence, site-specific investigations are required to uncover environmental impacts associated with pre-Columbian galena use. Here we present new data from Avery Lake, a floodplain lake located directly adjacent to the Kincaid Mounds archaeological site in southern Illinois, USA (Bird et al., 2019; Butler et al., 2011). Specifically, we used geochemical and isotopic methods to quantify Pb pollution and its provenance through time. STUDY SITE AND BACKGROUND Kincaid Mounds (hereafter Kincaid) is located in southern Illinois on a portion of the lower Ohio River’s floodplain known as the Black Bottom (Fig. 1). While smaller archaeological sites have been identified across the Black Bottom, Kincaid represents a primary locus of habitation on Avery Lake’s northern shore (Muller, 1986). Archaeological evidence indicates that this site was intermittently occupied since ca. 4000 BCE, with the first evidence for intensive settlement and village construction beginning during the Early and Middle Woodland Baumer phase from 300 BCE to 300 CE (Butler and Crow, 2013; Butler and Welch, 2006; Parker and Butler, 2017). Kincaid was subsequently abandoned, or intermittently occupied by a sparse population, from ca. 350 to 650 CE (Butler and Wagner, 2012). After 650 CE, Kincaid was repopulated during the Late Woodland Lewis phase, which transitioned into the Mississippian period sometime between 1000 and 1150 CE (Pursell, 2016). The Mississippian occupation (1150–1450 CE) is the best studied at Kincaid because large earthworks, bastioned fortifications, and an extensive village were constructed during this time (Butler et al., 2011). Between 1400 and 1450 CE, Mississippians abandoned Kincaid, along with much of the central Mississippi and Ohio River valleys (Cobb and Butler, 2002; Milner and Chaplin, 2010), in what has been suggested to be a response to a severe ∼100-yrlong drought between 1350 and 1450 CE (Bird et al., 2017). Kincaid and the surrounding Black Bottom remained largely unoccupied until the 1800s, when Euro-American settlers began utilizing the region for river commerce and agriculture (Bird et al., 2019; Muller, 1986). Recently reported multi-proxy results from Avery Lake complement the archaeological perspective of Kincaid’s occupation history and reveal additional information about preColumbian land use and environmental impacts Downloaded from https://pubs.geoscienceworld.org/gsa/geology/article-pdf/4848236/g46673.pdf by guest on 31 October 2019 2 www.gsapubs.org | Volume XX | Number XX | GEOLOGY | Geological Society of America (Bird et al., 2019). For example, the most intensive pre-Columbian occupations identified in the archaeological record (the Baumer and Mississippian) were each characterized by extensive land clearance as evidenced by simultaneous lows in arboreal (tree) pollen and peaks in Ambrosia (ragweed) pollen, the latter being an indicator of landscape disturbance (Wright, 1967). Low population densities during the Baumer occupation and significantly increased population densities during the Mississippian occupation (Butler and Wagner, 2012) were additionally reflected in bulk sediment δ15N variations (Bird et al., 2019). Whereas δ15N was relatively invariant during the Baumer occupation, indicating low population densities, it abruptly increased by ∼4‰ to over 6.5‰ between 1130 and 1185 CE, suggesting that population densities reached ∼60 people/km2 (Cabana and Rasmussen, 1996). δ15N values subsequently decreased, but remained elevated until after ca. 1460 CE, which agrees with the site being abandoned between ca. 1400 and 1450 CE. Three distinct Pb concentration peaks are also apparent in the Avery Lake data during each of the major occupations in the Black Bottom, i.e., Baumer, Mississippian, and the Euro-American occupation since ca. 1800 CE (Bird et al., 2019). These Pb anomalies remained even after normalization to the conservative elements zirconium (Zr) and titanium (Ti), indicating that they represent excess Pb in the environment (Boës et al., 2011). Given their temporal association with human occupations, and that they did not occur under any other conditions, the Pb anomalies are attributed to anthropogenic pollution. Anthropogenic sources of Pb during the past ∼200 yr have been extensively investigated, with wood and coal combustion (1800s and 1900s), ore smelting (1800s to present), and the use of leaded petroleum products (1940s to the 1970s) generally implicated as the sources of modern Pb pollution (Graney et al., 1995). Here, we focus on the pre-Columbian Pb signals, as little is known about the occurrence and/or sources of early Pb pollution in North America. METHODS We selected 30 samples from Avery Lake sediment core A-14 (Bird et al., 2019) for Pb isotope analyses at the Department of Geological Sciences, University of Florida (Gainesville, Florida, USA). Samples were processed and measured in an ISO 6 clean lab equipped with ISO 4 laminar-flow hoods following Kamenov et al. (2009). About 0.05 g of sediment was weighed in acid-cleaned Teflon vials and digested with Optima-grade HF and HNO3. The sample solution was then evaporated, and the residue was dissolved in 1N Optima-grade HBr. This solution was loaded on columns packed with Dowex 1X-8 resin to separate Pb for isotope analysis. Samples were washed 3× with 1 ml of 1N HBr, and the Pb fraction was collected in 1 ml of 3N HNO3. Pb isotope compositions were determined on a Nu-Plasma multicollector–inductively coupled plasma–mass spectrometer (MC-ICP-MS), with Tl normalization. The reported Pb isotope data are relative to the following long-term values of NIST (U.S. National Institute of Standards and Technology) standard NIST 981: 206Pb/204Pb = 16.937 (± 0.004, 2σ), 207Pb/204Pb = 15.490 (± 0.004, 2σ), and 208Pb/204Pb = 36.695 (± 0.009, 2σ). The Avery Lake age model and proxy results discussed below (X-ray fluorescence [XRF], pollen, δ15N) were previously developed by Bird et al. (2019) (see the GSA Data Repository1). RESULTS AND DISCUSSION The Pb isotope results show consistent trends across all time series, with two primary features standing out. The first is a long-term baseline, which averages 19.250, 15.676, and 38.885 for 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb, respectively (Fig. 2). The second is an abrupt, positive Pb-isotope-ratio excursion toward higher values during the Mississippian period between 1150 1GSA Data Repository item 2019403, description of the methods of sample collection, Avery Lake core stratigraphy, age control, organic carbon and total nitrogen elemental abundances and isotopic composition, pollen, and X-ray fluorescence geochemistry, and the Pb pollution calculations using XRF data, is available online at http://www.geosociety.org/datarepository/2019/, or on request from [email protected]. The data from this study are archived with the U.S. National Oceanic and Atmospheric Administration (NOAA) Paleoclimatology Database, https:// www.ncdc.noaa.gov/paleo/study/27711. Southern App. Timberville Nittany Arch